design, validation and commissioning processes for metal
TRANSCRIPT
Design, validation and commissioning
processes for metal structures belonging to the
railway signaling infrastructure
Faculty of Civil and Industrial Engineering
Master Degree in Transport Systems Engineering
Course of Railway Engineering
Candidate
Fatima Chemsi
Supervisor External Supervisor
Prof. Eng. Stefano Ricci Eng. Claudio Cantatore
The present thesis was written within an internship in
Bombardier Transportation
"If I have seen further it is by standing on the shoulders of Giants."
(Isaac Newton)
My first acknowledgements go out to the professors that I have had the honor
of learning from all along this degreeโs program, who with their passion and
sincere dedication have transmitted to me valuable knowledge and above all
the continuous desire to learn.
I thank in particular Professor Stefano Ricci, the supervisor of this thesis, for
his time, dedication and support by every means possible at every step of the
writing process.
I would also like to thank the people of Bombardier Transportation;
Eng. Diego Marino for offering me the unequaled opportunity to conduct my
thesisโ internship within one of the leading companies in the world in the
railway sector.
Eng. Claudio Cantatore, my supervisor in the company, for providing me
with the help and the necessary support to complete my work.
And Eng. Alessio Spaziani, for his kindness and for always being available
to help me during this process.
I also thank Eng. Salvatore Musella and Eng. Nicolรฒ Di Domenico of Rete
Ferroviaria Italiana for the kindness with which they helped me and for
having provided me with the material I needed to write this thesis.
I write it on this page and I will not fail to tell you out loud, THANK YOU!
Thanks to my family for encouraging me through all these years, especially
my parents for their everlasting support both financially and morally. Thank
you for accompanying me with every means possible to the top of the
springboard. Thank you for making this day possible.
I thank Marta for always being there.
I thank my friends for making the difficult days a little less difficult and for
helping me overcome the obstacles more lightly and with a smile.
A heartfelt thank you to all!
Fatima Chemsi
Rome, January 21th 2019
Table of contents
Table of contents 4
List of figures: 6
List of tables: 8
CHAPTER 1: OBJECTIVES OF THE THESIS 1
CHAPTER 2: INTRODUCTION TO RAILWAY SAFETY AND SIGNALING SYSTEMS 4 2.1 Evolution of safety and line signaling systems: 10 2.2 Description of the structures supporting the signaling infrastructure: 31
2.2.1 Fiberglass poles 31 2.2.2 Signal Cantilever bridge 34 2.2.3 Signal Bridges 36
CHAPTER 3: INPUT NECESSARY FOR THE PRELIMINARY DESIGN OF THE STRUCTURES 37 3.1 Railway track Planimetry 38
3.1.1 Transition curves 39 3.1.2 Switches 43
3.2 Railway track cross sections 46 3.3 Schematic signaling plan 48
CHAPTER 4: GEOMETRIC DEFINITION OF THE STRUCTURES 52 4.1 Analysis of the schematic signaling plan 52 4.2 Analysis of the track planimetry 53 4.3 Analysis of the cross section drawings 54 4.4 Staking operations 56 4.5 Design of the structures 58
4.5.1 Choice of the type of structure to be designed 58 4.5.2 Definition of the geometric measurements of the structure: 66
4.6 Selection of structure types to be designed by the structural engineer 68
CHAPTER 5: STRUCTURAL DESIGN 71 5.1 Documentation to be supplied to the structural engineer 72
5.1.1 Geological and seismic report 72 5.1.2 Geometric characteristics of the structures 90 5.1.3 Loads to be assigned to the structures 90
5.2 Documentation supplied by the structural engineer 90 5.2.1 Technical report 90 5.2.2 Construction (or detailed) design of the structure 131 5.2.3 Maintenance plan 133
CHAPTER 6: PRODUCTION AND FACTORY ACCEPTANCE OF STEEL STRUCTURAL ELEMENTS 145
6.1 Processes for production of structural steel 145 6.1.1 Cast iron transformation process: 145 6.1.2 Steel rolling 150 6.1.3 Rolling defects: 151
6.2 Regulatory framework for the production of hot laminates for structural steel 152 6.2.1 Controls on steels (for concrete reinforcement or for metal structures): 154 6.2.2 Processing centers (or transformation centers): 156 6.2.3 Laboratory tests to be performed on structural steel rolled products: 157 6.2.4 Checks of bolted joints 164
6.3 Welding process: 165 6.3.1 Types of welding: 167 6.3.2 Welding techniques: 168 6.3.3 Regulatory framework for welding processes of structural steel elements: 169
6.4 Factory acceptance of the structure 170
CHAPTER 7: ACCEPTANCE OF THE STRUCTURE AND CONSTRUCTION OF THE PLINTH AT THE BUILDING SITE 174
7.1 Acceptance of the structure materials on-site before starting the construction 174 7.1.1 Steel 175 7.1.2 Concrete 179
7.2 Construction of the plinth on site 183 7.3 Assembling of the structure on-site: 188
7.3.1 Analysis and assessment of possible risks 189 7.3.2 Instructions for workers 190 7.3.3 Emergency procedures 192 7.3.4 Mounting of structures 192
CHAPTER 8: COMMISSIONING OF THE STRUCTURE AT THE BUILDING SITE 197 8.1 Load tests 199
CHAPTER 9: CONCLUSIONS 201
APPENDIX A: Examples of cross sections located in the Casablanca triangle 202
References 207
List of figures: Figure 1: Signal Cantilever bridge ......................................................................................................... 1 Figure 2: Signal bridge .......................................................................................................................... 1 Figure 3: Manual signal ...................................................................................................................... 10 Figure 4: Disc signal ............................................................................................................................ 14 Figure 5: Wing signal (main signal) .................................................................................................... 14 Figure 6: Wing signal (advance signal)............................................................................................... 15 Figure 7: Candlestick signal ................................................................................................................ 15 Figure 8: Fixed light signal .................................................................................................................. 17 Figure 9: Minimum visibility distance as a function of the maximum permitted speed ..................... 20 Figure 10: Line buoy ........................................................................................................................... 23 Figure 11: Monitor SCMT+RSC ........................................................................................................... 24 Figure 12: Indication authorizing maximum speeds of 300 km/h ...................................................... 24 Figure 13: Indication authorizing maximum speeds of 270 km/h ...................................................... 24 Figure 14: : Indication authorizing maximum speeds of 160 km/h .................................................... 24 Figure 15: : Indication that invites the train to stop before the first signal detected ......................... 24 Figure 16: Indication that orders the driver to travel on sight stopping before the first signal detected ............................................................................................................................................. 25 Figure 17: Control signal - lanterns .................................................................................................... 27 Figure 18: Operating light signal ........................................................................................................ 27 Figure 19: Control signals on the right side of the track .................................................................... 28 Figure 20: : Identification table for LC according to FS ....................................................................... 29 Figure 21: Diagram of automatic LC signals arrangement according to FS ....................................... 29 Figure 22: Fiberglass pole ................................................................................................................... 32 Figure 23: Standard dimensions of a 2 lights main signal in FS ......................................................... 33 Figure 24: Signal cantilever bridge installed along the Casablanca-Tangier line ............................... 34 Figure 25: Signal Cantilever bridge schematic representation .......................................................... 36 Figure 26: Signal Bridge installed along the Casablanca-Tangier line ............................................... 37 Figure 27: Example of a railway track planimetry .............................................................................. 39 Figure 28: Equilibrium of a vehicle running a curve ........................................................................... 40 Figure 29: Equilibrium of a vehicle running a curve with a cant ........................................................ 40 Figure 30: Example of the transition curves tables contained in a railway track planimetry ............ 42 Figure 31: : Representation of tangency points between planimetric elements in a railway track planimetry .......................................................................................................................................... 43 Figure 32: Switch example ................................................................................................................. 43 Figure 33: Switch schematization ....................................................................................................... 44 Figure 34: Train wheelset running on a track ..................................................................................... 45 Figure 35: Example of switch tables contained in a railway track planimetry ................................... 46 Figure 36: Schematization of the railway superstructure and characteristics measurements........... 47 Figure 37: Example of a schematic signaling plan ............................................................................. 49 Figure 38: Elements of the schematic signaling plan - schematization of the joint ........................... 49 Figure 39: Elements of the schematic signaling plan - schematization of double comunication ....... 49 Figure 40: : Elements of the schematic signaling plan - schematization of signal portals ................. 50 Figure 41: : Elements of the schematic signaling plan - schematization of signal cantilever bridges 50 Figure 42: Elements of the schematic signaling plan - schematization for reflecting signs ............... 50 Figure 43: Elements of the schematic signaling plan - schematization of signal for ending zone at limited speed ...................................................................................................................................... 50 Figure 44: : Elements of the schematic signaling plan - schematization of banalized line ................ 50 Figure 45: : Elements of the schematic signaling plan - definition of the action zone boundaries of a control post ........................................................................................................................................ 51 Figure 46: Two-dimensional schematic representation of the overhead line system indicating key elements. Dimensions indicate typical values .................................................................................... 55 Figure 47: Electric traction infrastructure .......................................................................................... 56 Figure 48: Signal portal referring to 2 tracks ..................................................................................... 60 Figure 49: Interaxis representation .................................................................................................... 60
Figure 50: vehicle's overall dimensions when cornering .................................................................... 61 Figure 51: Gabarit categories according to SNCF ............................................................................... 62 Figure 52: International gauge G1 and national gauges ................................................................... 63 Figure 53: Example of correct spacings between plinth and rail ........................................................ 64 Figure 54: Example of the installation of a signal cantilever bridge in presence of an obstacle ........ 65 Figure 55: Example of installation of 2 signal cantilever bridges instead of a simple portal due to the altitude difference between the tracks .............................................................................................. 66 Figure 56: Example of incorrect mounting of the signal cage ............................................................ 68 Figure 57: Example of correct installation of the signal cage ............................................................ 68 Figure 58: signal bridge with 2 cantilever beams ............................................................................... 69 Figure 59: ZS9 seismogenic zonation.................................................................................................. 75 Figure 60: Seismic hazard values according to OPCM 3519/2006 ..................................................... 76 Figure 57: Seismic zonation in terms of Amax for RPS2011 ............................................................... 77 Figure 58: Seismic zonation in terms of Vmax for RPS2011 ............................................................... 77 Figure 63: Coring procedure with direct circulation of fluids ............................................................. 80 Figure 64: Example of extruding the soil from the core drill .............................................................. 81 Figure 65: Example of core sample storage ....................................................................................... 81 Figure 66: Standard penetration test ................................................................................................. 82 Figure 67: Stress and deformation diagram for steel ......................................................................... 93 Figure 68: Stress and deformation diagram for concrete .................................................................. 96 Figure 69: Concrete reinforcement steel ............................................................................................ 97 Figure 70: Stress and deformation diagram for reinforcement steel ................................................. 98 Figure 71: Characteristic values of qsk actions for vertical surfaces parallel to the track ................. 107 Figure 72: Characteristic values of qsk actions for horizontal surfaces parallel to the track ............ 108 Figure 73: Characteristic values of qsk actions for vertical surfaces parallel to the track................ 108 Figure 74:Illustrations of the exposure factor ce(z) for c0=1,0, k=1,0 ............................................... 114 Figure 75: Principal system............................................................................................................... 117 Figure 76: Deformations of the principal structure with the deformation method.......................... 117 Figure 77: Form functions with higher than 1 Figure 78: Linear form functions ................... 121 Figure 79: Local reference system for the rods................................................................................. 124 Figure 80:Local reference system for the shell element ................................................................... 124 Figure 81: Design response spectrum............................................................................................... 127 Figure 82: Representation of the Winkler model for the foundation ground ................................... 129 Figure 83: Joint detail nยฐ1 of executive project drawing .................................................................. 132 Figure 84: Example of Plinth details of an executive project drawing.............................................. 132 Figure 85: Joint detail nยฐ2 of executive project drawing .................................................................. 133 Figure 86: Schematic representation for plinth subsidence ............................................................. 138 Figure 87: Example of moisture penetration .................................................................................... 139 Figure 88: Example of cracking, detachment of concrete and rust formation on reinforcement steel.......................................................................................................................................................... 140 Figure 89: Bessemer converter ......................................................................................................... 148 Figure 90: L.D converter ................................................................................................................... 149 Figure 91: Electric furnace ................................................................................................................ 149 Figure 92: Steel rolling ...................................................................................................................... 150 Figure 93: General scheme of rolling processes ............................................................................... 151 Figure 94: Rolling defects ................................................................................................................. 152 Figure 95: Sampling indications for testings according to UNI EN 10025-1 standard ..................... 159 Figure 96: Sampling indications for testings according to UNI EN 10025-1 standard ..................... 160 Figure 97: Resilience test on steel .................................................................................................... 162 Figure 98: Test specimens for resilience test (dimensions are indicated in mm) ............................. 162 Figure 99: Brinell hardness test ........................................................................................................ 163 Figure 100: Elements constituting a bolt .......................................................................................... 165 Figure 101: Excavation scheme forformworks ................................................................................. 186 Figure 102: Plinth-column coupling detail ........................................................................................ 187 Figure 103: Executive project drawing for plinth-column coupling .................................................. 187 Figure 104: Example of the introduction of anti-shrinkage expansive mortar ................................. 188 Figure 105: Example of steel dowel pins .......................................................................................... 194
Figure 106: Example of torque wrench ............................................................................................ 195
List of tables:
Table 1: Parameters for the definition of clothoids _______________________________________42 Table 2: Comparison between requested investigation and executable investigations for the structures _______________________________________________________________________78 Table 3: Soil categories accordin to the DM 17-01-2018 __________________________________87 Table 4: Topographic categories according to the DM 17-01-2018 __________________________89 Table 5: Maximum values of the topographic amplification coefficient ST ____________________89 Table 6: Exposure classes for concrete according to UNI EN 206-1 ________________________ 101
1
CHAPTER 1: OBJECTIVES OF THE THESIS
The present thesis aims to define a process covering the preliminary and
construction design phases, up to the manufacturing, construction and
commissioning of the steel structures belonging to the railway signaling
infrastructure. These structures are:
Signal cantilever bridges
Figure 1: Signal Cantilever bridge
Signal bridges (or portals)
Figure 2: Signal bridge
2
The definition of these processes aims to create a reference guideline for all
the stakeholders that will be involved in the project, defining design criteria
and parameters to be considered and evaluated during the design,
manufacturing and construction phases in order to avoid errors, delays and
therefore increases in costs.
The need to define a reference for the design and construction of these
structures derives from the lack of relevant international standards or
Country-specific railway administration regulations covering the whole
process from the preliminary design to the commissioning.
Unlike other structures for which standardized technical and dimensional
specifications exist and may vary according to local regulations, for these
structures are not present. The motivation for this lies in the variability of
working hypotheses and site conditions that have to be considered.
The project underlying the thesis, which showed the need to implement these
guidelines, is located in the Kingdom of Morocco and in particular in what is
called the Casablanca triangle, consisting of the following stations:
โข Casa Port;
โข Ain Sebaa;
โข Casablanca Voyageurs.
After a brief description of these structures, the input documents that are
provided for the design and construction of these structures will be analyzed
in order to establish which input documents must be requested at a
preliminary stage.
The description of the pre-sizing process of the structures will continue, with
the identification of the location within the railway track and the study of the
visibility of the signal.
3
The structural design of the works will require a structural engineer who will
have to realize the project of the steel works (the portals themselves) and their
foundations.
The projects defined in this way must be delivered to the factory which will
take care of the supply of certified and CE-marked steels according to the
European standards of the rolling processes and construction of the
structure. In these guidelines, in addition to the specifications on materials,
the criteria for acceptance of the structure at the factory will also be defined.
While the structure is made in the factory and then assembled on site, the
foundation is excavated and cast-in-place. Also for this, however,
requirements for acceptance of materials (concrete and steel for
reinforcement) and criteria for their realization will be defined.
Finally, the commissioning processes for the structures, with the description
of on-site verifications to be performed will be specified.
Briefly, the end goal of this thesis is to create a procedural standard to be used
in every contract that requires the design and construction of metallic
structures necessary for railway signaling, in order to allow a precise and
organized management of the process starting from the first preliminary
stages to the completion of the work.
4
CHAPTER 2: INTRODUCTION TO RAILWAY
SAFETY AND SIGNALING SYSTEMS
The railway signaling systems constitute that set of devices which are in
charge of the exchange of information between the fixed installations and the
moving vehicle with the purpose of ensuring that the train's journey takes
place under conditions of safety while ensuring high availability of the
infrastructure.
The objectives of the signaling system are many, but can be summarized in
five main points:
Allow a spacing of traffic;
Ensuring the protection of traffic at the turnouts at the station;
Manage traffic on railway tracks;
Avoid derailments due to excessive speed;
Protect level crossings.
To obtain the spacing, the line is subdivided into elementary sections, called
Block Sections, of variable length (e.g. in Italy at RFI it is generally 1350 m).
On each block section only one train can circulate at a time.
As can be seen from the definitions, security is at the basis of signaling. In
each transport system, it is possible to recognize two distinct groups of
security conditions:
โข The safety in the motion of a single train: function of the road safety
and of the vehicles constituting the train;
โข The safety in the motion of each train placed in relation to the
simultaneous circulation at the same site of other vehicles of the same
5
type or even of different types (such as road traffic at level crossings):
in this case there are a set of rules and precautions to guarantee that a
train will occupy a certain stretch of track. In fact, the track is viable
only when the route is free from other trains circulating in the same
block section and also from maneuvers. To make this possible, while
the train considered runs through the block section, the track canโt be
occupied by the contemporary motion of other trains and even
maneuvers are forbidden.
Unlike the road case, the freedom of the block section canโt be ascertained by
the train driver. In fact, this is not possible taking into account the train speed
and its corresponding long braking distances and the fact that the driver canโt
have the certainty of the freedom of the route on long distances. Therefore,
at least in the traditional systems, it is the ground personnel that manages the
traffic, to ascertain the state of freedom of the route and to inform the train
driver about it. Information is provided by means of signals whose meaning
is preventively and unequivocally established. Optical signals can also be
used together with on-board systems supporting the driver directly in
his/her cab or even replaced by other means, thanks to the new developed
technologies.
Generally, to ensure the safety conditions on the line, when a train leaving a
station must reach the next station it is necessary to follow these steps:
โข Ascertaining the freedom of the section between the two stations:
this assessment is responsibility of the train Movement Director of
the departure station;
โข Permissive disposal of a starting signal at the departure station;
6
โข Occupation of the above signal followed by the immediate return
to the stop aspect as the train passes it, in order to prevent a second
train to consider the indication of green light valid;
โข Blocking the route section;
โข Clearance the route section and making it usable for the next train.
In stations, these phases are implemented with further phases mainly due to
the presence of turnouts:
โข Route setting, arrangement of the switches according to the route
that the train must travel;
โข Switch locking, guaranteeing that the position of the switches
remains secured in the required position;
โข Check of route compatibility and assumption of certainty that
incompatible routes will not be defined at the same time;
โข Verification of freedom of the route section;
โข Permissive aspect of the signal for allowing train departure over
that route, blocking the route and the position of its switches, until
the route has been completely traveled by the train;
โข Signal occupation;
โข Route release, once it has been completely traveled.
These phases must be observed both in the case where safety is entrusted
exclusively to manual controls and operations as well as if it is entrusted to
fully automatic systems (e.g. interlocking systems).
There are fundamental concepts underlying railway signaling and safety:
Fail-Safe;
7
Redundancy;
Wired logic systems. Relays;
Programmed logic systems.
Fail-Safe refers to those systems for which any failure causes a situation of
lesser usability but equal safety, i.e. a more restrictive situation for
circulation until the trains running on the fault-affected section have come
to a complete standstill, at the limit. An example of a suitable Fail-Safe
system is the so-called cycle control. The operations of trains on a line
section are repetitive actions that follow one another according to certain
cycles. Fail-safe safety can be achieved by allowing each phase to start only
if the previous phase has had a complete and regular course: in this way
any anomaly prevents the succession of the cycle phases, thus blocking the
circulation.
On the other hand, the redundancy method, requires that, for a complex
plant, redundancy is achieved at least by doubling the conditions that must
be met in order to achieve a given operation. An example of a redundancy
method may be spatial duplication, obtained by using two or more
independent devices that must simultaneously provide matching output
signals.
In general, between fail-safe and redundancy criteria, it is preferable to
focus more on fail-safe criteria, as they allow high levels of security to be
guaranteed at a competitive cost.
The translation of these two principles has led to the introduction in the
railways of logic systems wired via relays, using this as an elementary
component through which it is possible to design and compose more and
more articulated circuits.
8
The relay is still the main component of the safety and signaling systems,
and it is precisely that elementary logic device through which increasingly
complex modules and schemes can be created.
Regarding safety and signaling systems, we refer to electric relays, which
can be used:
โข To replace a weak incoming power supply with a more
robust one;
โข To replace an incoming power supply with an output
power supply of different characteristics;
โข To multiple from a single incoming power supply to
several outgoing circuits.
Programmed logic systems are made by using electronic components and
software program processing. The use of this more flexible and easily
applicable technology, in relation to the reduction of space requirements
(e.g. for relay cabinets) and lower costs in large-scale use, has allowed the
introduction of a new way of designing and implementing safety and
signaling systems. In this case, safety-critical applications are defined, in
which fail-safe conditions are guaranteed by means of safeware
technologies, i.e. safety is entrusted to the result of processing logic
(software) and to electronic components (hardware) with safety features.
At European level, this new technology has led to the introduction of the
following standards for both electromechanical and electronic systems:
โข EN 50124, coordination of the isolation: This European
standard concerns the coordination of insulation in the
railway sector. It applies to signaling, rolling stock and
9
fixed installation equipment. These standards therefore
cover the isolation of electrical and electronic devices. One
objective of insulation coordination is to avoid oversizing
of the insulation itself.
โข EN 50126, The specification and demonstration of
reliability, availability, maintainability and safety (RAMS):
this standard defines the characteristics of availability,
reliability, maintainability and safety of the systems, as
well as the set of technical and functional requirements for
the proper implementation of a system.
โข EN 50128, Telecommunication, Signalling and Processing
Systems - Software for Railway Control and Protection
Systems: This standard focuses on the methods that need
to be used to provide software that meets basic safety
integrity requirements.
โข EN 50129, Railway applications - safe electronic systems
for signaling: this standard covers the requirements for
computerized rail signaling systems, considering safety
aspects.
โข EN 50159, Fixed installations - contact wire belonging to
railway electric traction systems: this standard applies to
the design and construction of contact wires for the
railway electric traction infrastructure, tram and metro, for
complete renewals in electrified sections or new
electrifications. The standard contains the design
requirements, the elements for testing the lines and some
components and the methods for dimensioning the
structures.
10
2.1 Evolution of safety and line signaling systems:
On the first railway lines there were no safety systems and the signals were
made by colored flags or, at night, by colored lanterns.
Figure 3: Manual signal
Generally, trains stopped at all stations and the information was
communicated directly to the drivers by the train movement director
(TMD).
The first system used by the TMDs to define when trains could leave the
station was the time-distance system: a train could only be forwarded after
a certain time had elapsed since the departure of the previous train. The
protection in the event of an anomaly with a train stopped on the line was
provided by the train staff through the exposure, at a reasonable distance,
of hand signals.
This type of system did not guarantee absolute safety and would not have
been suitable for higher speeds and greater circulation.
Subsequently, space-based distance systems were developed based on the
criterion that ensures the presence of only one train at a time between two
11
successive distance points (block sections). In single-track lines, therefore,
were defined spacer posts, i.e where trains had to wait for the TMDโs consent
to leave the stations. In the classic double track lines, on the other hand, there
could also be spacers at intermediate points of the section, where the trains
had to stop and respect the signals made with flags or lanterns.
Train spacing could be implemented by telephone communications and
according to two traffic regimes:
o โArrivedโ regime: in this regime, a train that was sent from
station A, arrived at station B, which once received the train
and verified its completeness, had to send to station A a
dispatch of โarrivedโ indicating the distinctive number of the
train. At this point from station A it was possible to send the
next train. In a system like this, it is obvious how important it
is to record at both stations the dispatch and compliance with
certain rules and controls to ensure its regularity. The system
of joint arrangements was then abandoned by FS.
o Phone block: in this type of regime, if station A must send a
train to station B, the station A must ask for a real consent also
remembering the last train already sent. Station B will give its
approval only if the previous train has arrived in it
completely. Today this system is still used in secondary lines
as a replacement for other systems.
The need to introduce fixed signals began to be felt mainly for the purpose
of being able to create a kind of access door for trains that must enter the
station. The station's protection signals were then introduced and which
could take two positions:
12
โข Closed, to indicate the prevented way to the internal exchanges at
the station;
โข Open, to allow trains to enter the station.
A set of circuits of the station apparatus also made it possible to guarantee,
by means of appropriate electrical connections, the real condition of the free
section, from the departure signal of the forwarding station, to the
protection signal of the arrival station.
As speeds increased, it became clear that it was impossible for a driver,
especially in adverse weather conditions, to obtain the distance of free
visibility in relation to the longer braking distances.
At the beginning, it was remedied admitting some overcoming of the
signal, disposed consequently to opportune distance from the protected
point. A subsequent measure was to precede the protection signal (main
signal) by another fixed, not maneuverable signal, called โadvance signalโ.
The purpose of this signal was to draw the driver's attention to the point
where he had to start reducing his speed.
The attention signal then became a real โadvance signalโ, maneuverable,
able to notify in advance the indications of principal signal. The latter took
the name of โmain signalโ and became, then, a signal which must not be
exceeded in the event of stop signal.
Between the advance signal and the main signal, the distance must be
calculated, and has to be at least equal to the braking distance
corresponding to the maximum speed allowed on the route for the specific
train in transit, then increased by a certain safety margin. This distance will
therefore be a function of the speed but also of the slope of the line.
13
In Italy, for speed conditions up to 140 km/h, the distance generally used
between warning signal and main signal is 1200 m. In some cases,
especially when it is necessary to bring the signal in a position of safe
visibility (out of curves, tunnels, etc. ...) the distance of 1200 m may be
exceeded, but within certain limits, not to require the driver to remember
for too long the previous indication.
Usually, in Italy, the protection signal is combined with the advance signal
of departure and getting thus a coupled signal that can have three different
aspects:
Impeded way (stop signal): red;
Permissive signal with warning of the next impeded way:
yellow;
Permissive signal with subsequent clearance warning: green.
The first fixed signal used essentially as a protection signal was the disc-
shaped signal. The disc signal consisted of a large table, usually circular and
red painted, able to rotate around a vertical axis, to present itself in the face
of the trains to be stopped and at the edge to the trains to which the
approval was to be granted.
14
Figure 4: Disc signal
The disc signal was in fact disrupted in 1920 and later, this signal was
replaced by the traffic light or wing signal. This signal consists of a
rectangular sail, always visible to the trains, and which can assume two
different positions: horizontal for the blocked way and inclined downwards
for signaling the free way.
Figure 5: Wing signal (main signal)
In the Italian railways type, the wing has two glasses, one red and one
green, and depending on how the wing is arranged, one in front of the
15
other, it give โimpeded wayโ with the red color and โproceedโ with the
green color.
The wing signal has been used also as an advance category signal, in this
case it is yellow and with fish tail shaped extremities. The movement of the
wing is the same as the one for the main signal. [9]
Figure 6: Wing signal (advance signal)
At a point where the line branches, it is advisable to include with the
indication of permissive and impeded way, also information enabling to
identify the road into which it is being forwarded.
Signals with overlapping wings or candlesticks were then inserted. The
wings, in this case, could be at the same height (in the case of two or more
lines with switches to be covered at 30 km/h) or different: in this case, the
upper one indicated the correct route and the lower one(s) the deviated
branch.
Figure 7: Candlestick signal
16
The wing signal, however, had two major drawbacks although less than
those related to the disc signal: to have a moving part exposed to the
weather and provide a daytime indication different from the night one.
To overcome these problems, they switched to permanently luminous
signals, which, at first, the so called color fires.
A color fire signal is a signal with several overlapping eyes in which each
eye has a light bulb and each eye has a differently colored lens.
With this system, it was possible to create multiple signals with
overlapping lights, but the presented 2 major problems:
o When a signal was taken in full by the sun's rays, it gave the
impression that all the lights were on;
o Requiring two or three eyes overlapped for each indication,
they were considerably cumbersome.
It was then completely abandoned and replaced by the moving screen light
signal.
A moving screen light signal consists of a single optical complex, with a
single filament bulb, placed in the fire of a spherical mirror. A three-aspect
signal (red, yellow and green), as it goes from yellow to green, it goes
through red for a moment. If a driver was passing through, in the last
stretch in which he saw the signal, at the very moment of this red flash, he
was obliged to carry out an emergency brake if he doubted that it was not a
switchover of a stop aspect of the signal. This situation could often arise on
lines with heavy traffic. For this reason, a moving screen signal was studied
and realized in which the central slide of the fan is yellow while green and
red are lateral.
17
The eye of the signal is mounted in the center of a large pan that, acting as a
background, improving its visibility, a purpose which is concurrently a
sunscreen (visor) that protrudes forward, covering the top of the beginning
of the light stream.
Figure 8: Fixed light signal
On FS network and others such as SNCF1, the fixed signals are located to
the left of the trains. This is due to the traditional movement of trains
running on the double track to the left.
In a double track line the signals referring to the left track are placed to the
left of the track itself and their screen is circular. Those referring to the right
track are placed to the right of it and their screen is square.
Signals shall, as a rule, be placed as close as possible to the track to which
they relate and those placed in tunnels shall not be equipped with a sail
(neither round nor square).
Specific rules must be regarded to place signals along the tracks.
Regarding departure main signal:
1 SNCF stands for โService National des Chemins de Ferโ, which is the national French railway company.
18
Departure signals shall be placed after the โnormal stop
pointโ (at stations or stops), which is defined as the point
where trains normally stop to carry out passenger or freight
related operations;
If the departure signal refers to several tracks from which
trains always depart from stops (trains may not pass without
stopping on these tracks), the signal must be placed at a
suitable point and is always round sailing;
If the departure signal refers to more than one track and trains
can pass through one of these without stopping, the signal
must be placed to the left or right of that track and, in any
case, close to it;
At stations, it is allowed that the signal that controls the
departure from a single track (not a running track) is placed to
the right of the same (square sail) and as close as possible to it;
Departure signals referring to one or more tracks from which
trains can be routed on a truncated track shall be placed
before the tip of the switch that leads to the truncated track
and at least 50 m from the bumper or the end of that track.
Specific rules for protection main signals require they shall be placed at
least 100 meters from the point that is intended to protect:
The protection main signal for stations, turning points,
crossings, etc. shall be placed at least 100 meters from the
point that is intended to protect:
The tip of the first switch encountered by the train;
19
The limit cross of the intersection or of the first switch
encountered by the train (if taken by the trailing side);
The limit picket of the shunting;
The point where the tail of the train of maximum permitted
composition can be found stopped at the station or at a
subsequent main signal.
The main signals protecting level crossings must be at least 50
meters from the crossing itself.
On electrified lines, protection main signal shall in any case be
placed before the electric traction bridges of the station contact
wire sectioning.
Under normal weather conditions, main signals and advance signals
advance signals shall be visible at 200 meters if the maximum train speed in
the section of line preceding the signal is greater than or equal to 90 km/h
and 150 meters if lower.
In cases due to the orographic layout of the line (curves, ridges etc.) which
prevent the respect of these minimum standard values, the central offices of
RFI (in particular the office called Technical Direction) may authorize
shorter distances of visibility after reducing the maximum speed of the line,
if necessary, in the section concerned (that preceding the signal). These
maximum line speed values are calculated approximately based on the
following graph in relation to the physiological reaction times of the
drivers.
This reduced visibility distance is given in a special box in a special booklet
describing the characteristics of each line called Line Booklet (FL) / Time
Booklet (FO).
20
Figure 9: Minimum visibility distance as a function of the maximum permitted speed
Advance signals shall be placed on the same side of the main signals to
which they relate.
After describing the methods used to indicate the various inputs to be given
to the driver, the track circuits are now going to be described.
This allows to define automatically the state of freedom of the route, i.e.
whether it is possible to allow a train to run on a given section of track.
In its simplest form, a track circuit is a direct current electrical circuit which,
fed from one end by means of a battery or accumulator, supplies a track
relay at the other end. Part of the circuit consists of the two rails of the
section that must be to be controlled, so that each of the two rails carries a
polarity. The track section that will be controlled is the one between two
insulated joints, which, while guaranteeing mechanical tightness, interrupt
the electrical continuity between the two adjacent rails. If a line is
electrified, the electrical continuity required as a return circuit must always
be guaranteed at least on one rail. In general, however, even for non-
electrified lines, the insulation of both rails is avoided.
0102030405060708090100110120130140150
406080100120140160180200
Max
imu
m a
llow
ed s
pee
d [
km/h
]
Minimum distance [m]
Minimum visibility distance
21
On direct current electrified lines, track circuits supplied with 50 Hz
alternating current are used.
Modern track circuits are audio-frequency (2-4 KHz) electronic circuits and
are of the digital type with frequency modulated signals. The digital
electronic track circuits are easily interfaced with computerized systems,
such as the Static Central Devices and, in Italy, are being applied on the
high speed lines.
However, in order to define the passage of the train at a certain point and to
ascertain the release of the section, it is necessary to introduce the
equipment called pedals.
This equipment is placed on a rail of the track and is operated by the wheel
of the train that passes through it.
A simple type of pedal is that one equipped with a moving part which,
when activated by the wheel flange, closes the electrical contacts.
Another type of pedal is the SILEC one, which is very popular on French
railways. This pedal has a mobile arm that can always be operated by the
wheel flange and is used only for the automatic control of the half-barriers
of level crossings and never for liberation tasks.
Another type of pedal is the one with magnetic action, which can feel the
variations that occur in a special magnetic circuit when the metal masses of
the wheels in transit pass through it.
The most used type of pedal for the purpose of evaluating the clearance of
the way is the electromechanical one. This type of pedal controls the
inflection of the rail that occurs between two crossbars when a train pass.
In order to ensure that a train does not enter a given section of track if no
previous train has left it, interlocking systems are set up.
Interlocking systems are automatic, creating track circuits that cover the
entire section or by installing axle counting pedals, located on the track in
22
and out of the block section to count the number of axles in and out of a
section.
The automatic interlocking system can be reversed and used even in the case
of a double track line to banalize the line. It may be necessary, in fact, banalize
a track to create priorities and allow fast trains to overtake slow trains, or run
in two directions on one of the two tracks while the other is out of service.
In fact, an automatic interlocking system causes the occupation of a section
when a train penetrates from the two ends.
Until now, attention has been focused on the care that a designer of a safety
system must put in building circuits and equipment such that any failure,
even if unlikely, blocks the circulation by taking the signals to impeded
way.
This precaution, however, can be in vain if the distraction of the driver or
situations of poor visibility, imply that the train passes the signal of an
impeded way and maybe even at high speeds.
Over the years, therefore, it have begun the study of systems capable of
repeating on board locomotives the indication of fixed line signals.
There are two types of on-board systems:
Point or discontinuous system (Discontinuous Digital Signal
Repetition)
Continuous systems (Continuous Signal Repetition)
In the first case, there are buoys mounted along the line at each signal,
which is capable of informing the installed equipment on board, giving it
an indication corresponding to the appearance of the signal at that time.
23
Figure 10: Line buoy
In continuous systems, on the other hand, there is always a continuous
connection between track and train via a track circuit and thus a change in
the appearance of the signal that can be made known to the driver.
Recently, among the interlocking systems that allow to protect the driver's
driving and thus prevent the train from exceeding certain limits, the Train
Running Control System is taking off. In this system, the track-side
subsystem transmits the data to the on-board subsystem in such a way as to
control the speed of the train at that point on the line. This system is of a
discontinuous type and the transmission of signals always takes place by
means of buoys placed on the track, attached to the crossbars and therefore
the reception of the signal takes place only at these points.
24
Figure 11: Monitor SCMT+RSC
According to SNCF, here is the type of information on the monitor:
Figure 12: Indication authorizing maximum speeds of 300 km/h
Figure 13: Indication authorizing maximum speeds of 270 km/h
Figure 14: : Indication authorizing maximum speeds of 160 km/h
Figure 15: : Indication that invites the train to stop before the first signal detected
25
Figure 16: Indication that orders the driver to travel on sight stopping before the first signal detected
Considering the signaling in stations, in addition to the assessment of
permissive or impeded way, there are all those commands that are added to
determine the desired route. Even in this case, the historical evolution has
passed from the mechanical remote control of the signals to the centralized
control of all the bodies in a single central apparatus that also allows all the
necessary controls.
The first traffic light signals were controlled by means of flexible
transmissions, made of steel ropes, sliding on pulleys supported by small
posts arranged along the tracks. The manoeuvre was then carried out by
means of large levers equipped with counterweights or with balanced
cranks that turned a winch on which the flexible rope could be wound and
turned.
When it was then decided to subordinate the manoeuvring of the signals
according to certain conditions, keys were used that once introduced into
the manoeuvring device allowed it to move.
Subsequently, hydrodynamic equipment was used, which allowed the
various yard bodies to manoeuvre by means of water under pressure. This
completely Italian innovation has been totally abandoned to date.
Currently, the equipment are all electrical and the maneuvers are
effectuated by means of relays and motors applied to the signals, exchanges
and bodies of the yard.
26
The evolution of modern central equipment, i.e. those cabins in which all
the command and control devices of the various bodies are centralized, has
been:
o Electric Central Apparatus with individual levers;
o Electric Central Apparatus with Itinerary Pushbuttons;
o Static Central Apparatus.
According to the "Regulations for the Circulation of Trains": manoeuvre is
defined as any movement of traction vehicles or vehicles, which normally
takes place within a place of service, except for the start of a train that has
received the order of departure and for the entry of an incoming train, up to
the point of normal stop.
In non-centralized yards, the manoeuvres were commanded by means of
station operators with hand signals, via direct agreements with the
diverters in charge of the exchange manoeuvres, under the supervision of
the TMD.
In centralized yards, instead, it is necessary to adopt special signals for the
manoeuvres that are traditionally defined as low signals.
Initially the low signals consisted of a parallelepiped box called lantern that
could be rotated by 90ยฐ around its vertical axis.
27
Figure 17: Control signal - lanterns
In more recent installations, the low signal described, which in Italian
jargon called a โmarmotโ, has been replaced by a more reliable light signal,
without any movement.
Figure 18: Operating light signal
Low signals are usually inserted to the left of the track. If they were placed
to the right of the track, they would be presented with an arrow pointing to
the track they are referring to.
28
Figure 19: Control signals on the right side of the track
Regarding level crossing signaling we have the following classification:
Level crossings with barriers operated on site;
Level crossings with remotely controlled barriers;
Level crossings with automatically operated barriers.
For level crossings operated at a distance, historically were initially used
barriers operated with a simple wire transmission that could be controlled
using manoeuvring levers; the system was then replaced by a double wire
system in which the flexible wire transmission has an entry and an exit
branch.
Like all remote systems, this system is equipped with a ringer that is
mechanically operated at least five seconds before the barriers begin to
move.
This was followed by the use of electrically operated barriers. In the event
of a power failure, even accidental, the barriers are lowered.
The level crossings are therefore equipped with electrical control boxes for
direct current barriers, which are operated with a motor like that used for
the switches.
29
Remote controlled level crossings are equipped with the following devices:
o Closing control;
o Checking the integrity of the barriers;
o Control on the freedom of the level crossing.
Level crossings regulated by FS have the following signs:
Figure 20: : Identification table for LC according to FS
Figure 21: Diagram of automatic LC signals arrangement according to FS
From the above, it can be seen that technological evolution and the growing
drive towards automation in recent decades have favored the replacement
of activities traditionally carried out by human operators with automatic
30
systems. Those systems involve the command and the control of traffic and
the unification of the same activities through central systems, generally far
from the line, which are fewer and fewer in number and under the
responsibility of a small number of operators, with responsibility for the
management of increasingly extensive areas of the railway network.
Here 3 important command and control systems are therefore introduced:
CTC systems: Centralized traffic control and command;
CCL systems: Control of Line Circulation;
SCC Systems: Command and Control Systems.
The technique of centralized traffic control originated in the United States
where a telephone operator called dispatcher could communicate the entire
route to be travelled to the drivers of the various trains and give
instructions regarding the shunting to be carried out. The system then
evolved with remote-controlled systems capable of allowing the central
operator to manoeuvre the exchanges and signals directly.
Obviously, the availability of such a system, Centralized Train Control
(CTC), reducing the work of the central operator at the same traffic
intensity, made possible to create longer line sections than those entrusted
to the dispatcher.
The introduction, then, of electronic equipment, has allowed continuous
operation and the so-called cyclical exploration of the state of controls, so
that the overall situation of all the peripheral stations is continuously
examined and renewed at the center by interventions of only a few seconds
(polling). The commands to specific remote places are made by interrupting
the polling and sending the commands themselves, after selecting the place
to be remotely controlled.
31
While a CTC system does not extend beyond 150 km, an SCC system can
control an area that extends beyond 1000 km. With this system it is possible
having, for a country, the presence of the infrastructure manager in a few
strategic centers of command and control.
Finally, in the description of the evolution of signaling systems, the
innovative European systems called ERTMS/ETCS systems should be
introduced.
The ERTMS/ETCS (European Rail Traffic Management System/European
Train Control System) standard is one of the most significant innovations
introduced into the European railway landscape and allows trains of
different nationalities to run on the basis of common information
transferred using a common language, managed with interoperable
trackside and on-board subsystems. The standard defines the way in which
signaling information is exchanged between trackside installations and
trains, identifying the transmission techniques to be used, the format and
the content of the messages. The ERTMS/ETCS system thus provides the
driver, in a standard manner, with all the information necessary for
optimum driving, continuously monitoring the effects of his actions on the
safety of the train's running and activating emergency braking in the case of
train speeds above the maximum permitted speed for safety. There are
currently different levels of implementation of the ERTMS system, level 1 is
the basic level and the next 2 provide more and more automated
technologies.
2.2 Description of the structures supporting the signaling
infrastructure:
2.2.1 Fiberglass poles
32
The fiberglass poles are used in the railway sector to support light signals
and are an excellent alternative to metal structures.
In general, this type of support consists of an armoured fibreglass pole and
one or more high pressure moulded fibreglass shelves.
The pultrusion process (pull+extrusion) is a continuous process used to
produce reinforced polymer profiles.
Figure 22: Fiberglass pole
The dimensions of main signal according to FS standards are shown in the
figure below:
33
Figure 23: Standard dimensions of a 2 lights main signal in FS
Generally, a pole of this type is equipped with the following accessories:
โข Ladder;
โข Channel parapet made of fiberglass armchairs;
โข High pressure molded fiberglass platform;
โข Kit of the relative fixing elements in stainless steel;
โข Additional parapet;
โข Tilting platform in case of three-light signal;
โข Anchorage plate of the ladder in hot-dip galvanized iron.
This structure must be positioned on a foundation plinth made of
reinforced concrete and must be anchored to this structure by means of an
anchoring plate.
34
The material used for the construction of these poles gives it excellent
performance and mechanical characteristics such as: lightness and high
mechanical characteristics and therefore resistance.
The lightness allows easy transport and installation. Furthermore, high
electrical insulation characteristics are guaranteed, in the absence of
earthing, chemical and atmospheric resistance without the need for
maintenance.
2.2.2 Signal Cantilever bridge
The station signals, both single and multiple, can be installed on cantilevered
beams or on portals depending on the spaces available in the station itself
and according to the criteria that will be defined in the following chapters.
These structures can take 2 configurations, the normal one as shown in the
figure below and with the addition of a further beam in order to cover an
additional track.
Figure 24: Signal cantilever bridge installed along the Casablanca-Tangier line
These steel structures are lattice structures made of galvanized steel and
installed on a reinforced concrete foundation.
35
These structures consist of a support that is directly anchored by means of a
plate and anchoring kit to the concrete foundation, and a beam (or 2 beams)
at the top connected to it by means of special metal carpentry.
The geometrical dimensions of the beams are very variable and the
parameters that influence their length will be described in chapter 4, as well
as the sizing criteria. The height of the pillars is defined based on the
arrangement of the elements of the electric traction infrastructure.
The dimensioning of the beam and the definition of the different profiles to
be adopted are defined by the structural designer. For example, with regard
to the metal structures installed in Morocco, metal profiles of the UPN type
have been installed and reinforcements with diagonal elements with an L-
section or other minor UPN sections have been adopted; the pitch of the
different metal modules has been fixed at 0.75m.
The constituent elements of these structures can be divided in primary (with
structural purpose) and secondary (with non-structural purpose) ones:
PRIMARY
โข Supporting column
โข Load-bearing beam
โข Plinth
SECONDARY
โข Signal cages
โข Ladders
โข Hand rail
36
Figure 25: Signal Cantilever bridge schematic representation
2.2.3 Signal Bridges
As mentioned above, station signals can be installed on cantilevered beams
or portals. The main difference between these 2 structures is obviously the
presence of an additional column that allows a longer dimension of the beam
for the laying of more signals in reference to more tracks.
The support portals for railway signaling, like the cantilevered beams, can
also take on more configuration depending on whether 1 or 2 overhangs are
added to the basic structure so as to cover additional tracks.
The installation criteria for these structures are more binding than for
cantilevered beams as the minimum safety distances from the tracks for both
plinths will have to be taken into account, but this will be discussed in
chapter 4.
37
The constituent parts of these structures are similar to those of cantilevered
beams with the addition of one (or more) steel column(s).
Figure 26: Signal Bridge installed along the Casablanca-Tangier line
38
CHAPTER 3: INPUT NECESSARY FOR THE
PRELIMINARY DESIGN OF THE STRUCTURES
This chapter defines the input documents necessary to the preliminary
design of the structures, an operation prior to the actual structural design
that is entrusted to a free-lance structural engineer certified by the state or to
a civil engineering firm.
By preliminary design, it is meant the definition of the geometric sizes of the
several structures based on their position along the railway track,
considering different aspects that will be better clarified in the next chapter.
The input documents to be provided to the contracting company in order to
proceed with the design, supply and installation of the metal support
structures for signaling are:
โข Railway track planimetry;
โข Railway track cross sections (showing electrical traction elements);
โข Signaling scheme plan.
3.1 Railway track Planimetry
The railway track planimetry represents the planimetric course of the railway
in reference to a particular height generally referring to the top of the rail (or
running plane). In this elaborate, there is information regarding the
geometric development of the whole route and of the switches.
The geometric elements of a railway route are:
โข Straight sections;
โข Circular curves;
39
โข Transition curves.
The value of the radius of the circular curves affects both the maximum
admissible speed on a line (running costs, profitability, external costs, etc.)
and the easiness (or not) of insertion of the railway in the territory
(construction and maintenance costs).
On the existing lines, speed increases can be introduced with respect to the
limits envisaged in the project, introducing geometric variations on the track
and / or accepting greater stresses on the wheel-rail contact.
The figure below represents an example of a railway track planimetry.
Figure 27: Example of a railway track planimetry
3.1.1 Transition curves
The vehicle, when running on a curve, is subjected to the centrifugal force
which causes the vehicle to roll-over, stressing the external rail of the track
and reducing the comfort for the passengers.
40
The forces acting on a vehicle running on a curve are:
โข Weight force (P);
โข Centrifugal force (FC) expressed as a function of the vehicle weight (P),
gravitational acceleration (g), square of speed (v2) and radius of the
curve (R).
๐น๐ =[(
๐๐) ๐ฃ2]
๐
Figure 28: Equilibrium of a vehicle running a curve
Figure 29: Equilibrium of a vehicle running a curve with a cant
To increase the speed, and keep the same transversal acceleration, is
generally used to create an inclination of the platform with respect to the
horizontal plane, raising the external rail with respect to the interior one, thus
improving the comfort conditions for passengers. The cant values, however,
must be limited for coexistence on the lines of trains circulating at different
speeds, in fact slow trains encountering an excess of cant, would suffer the
41
effect of the centripetal force. The maximum allowed elevation in Italy is 160
mm.
The passage between a straight section to a circular curve or between two
circular curves with different radius must always occur through a transition
curve, in order to limit the abrupt variation of the transversal acceleration
that is generated for the transition from an element to the other. The
transition curve is sized trying to keep the jerk2 as smooth as possible and
making sure that the speed of rotation of the vehicle around its axis of gravity
increases uniformly. Transition curves also have the function of making a
progressive variation of the external rail elevation during the passage from a
straight section (zero elevation) to the circular curve (maximum calculated
elevation).
There are 3 transitions curves that are adopted on railway tracks:
โข Cubical Parabola;
โข Sinusoidal transition curve;
โข Clothoid, which has the particularity of allowing the
continuous variation of the radius from an infinitely large value
(corresponding to the straight section), up to whatever radius
value. The general equation of the clothoid is:
๐ โ ๐ = ๐ด2
In the railway track planimetry there are tables with inside the calculation
parameters of each transition curve inserted in the track layout. An example
is shown in the figure below, with reference to the Moroccan line.
2 variation of the uncompensated acceleration in the time unit.
42
Figure 30: Example of the transition curves tables contained in a railway track planimetry
In this track layout, the geometrical element chosen as transition curve
between a straight line and a circular curve is the clothoid and the tables
inserted therein have the following form:
Xs Abscissa of the curve vertex
Ys Ordinate of the curve vertex
R Curve radius
A Scaling factor of the clothoid
L Length of the clothoid
T Tangent to the circular curve
dec Arc offset from the straight line
Dv Length of the curve + clothoid
Dc Length of the curve
Table 1: Parameters for the definition of clothoids
For each curve are also reported the coordinates of the tangency point
between transition curves and straight lines, the tangency point between a
transition curve and a circular curve, the midpoint of the circular arc and the
center of the curve.
43
Figure 31: : Representation of tangency points between planimetric elements in a railway track planimetry
ORP1 Tangency point straight line โ entrance transition curve
FRP1 Tangency point transition curve โ circular curve
BX Midpoint of the circular arc
FRP2 Tangency point circular curve โ exit transition curve
ORP2 Tangency point exit transition curve โ straight line
centre Center of the curve
3.1.2 Switches
Figure 32: Switch example
For the switches, in the railway track planimetry, there is a table showing the
coordinates of the 4 necessary points for its univocal definition:
PA Switch point
CA Geometric center
44
TA 1 โ TA 2 Heels of the switch
Figure 33: Switch schematization
A switch is a device that makes possible the passage of a vehicle from the
track in which it is running to another track that branches off from it.
Switches must therefore be able to assume two distinct positions: one in
which the vehicle must be able to continue on the track in which it is located,
and another in which the train can move and start running on the deviated
track.
In a switch, there are two fundamental characteristic parts:
โข A movable part, commonly called the needle frame, capable of
assuming two different positions to guarantee the continuity of
the entry track and the exit track deviated from it.
โข A fixed part, in which the march of vehicles is made possible,
on one or the other exit.
The two main parts are connected to each other by four short rails called
intermediate rails.
In order to allow the flange of a wheel to move on a route other than that
corresponding to the rail on which it is rolling (i.e. to bring the wheel onto a
different rail) it is necessary that the new rail be brought closer to the first in
order to move the wheel flange on it and thus bring the whole wheel to the
new direction.
45
Figure 34: Train wheelset running on a track
It is evident that the passage of the wheel on the new rail, approached to the
first, must be smooth and that, once the two rails are approached, the
exchange must be safe and complete. To guarantee all this, the end of the
mobile rail in order to ensure a perfect adaptation of its side to the side of the
fixed rail has a particular shape. In fact this is the reason for the characteristic
thinning of the tip of the moving intermediate rail, the so called needle.
The fixed rail part against which the needle is supported is instead called a
stock rail3.
The fixed part, that is the heart of the switch, has a width that is the function
of the deflection angle formed by the axis of the two exiting routes from the
switch.
On the railway track planimetry are reported the types of switches and their
dimensions.
3 In Italian, it is called a โcontragoโ
46
Figure 35: Example of switch tables contained in a railway track planimetry
Taking as an example the railway track planimetry of the Moroccan line in
particular referring to the station of Casa Voyageurs, in the table are shown
the coordinates of the points forming each switch.
3.2 Railway track cross sections
The railway land consists of a railway superstructure supported by a road
body.
The railway superstructure is normally composed of:
โข The rails which together with the sleepers on which they are fixed
by means of suitable attachment devices, and to the switches
constitute the track (or the armament);
โข A layer of crushed stone, called ballast, which supports the
armament.
47
Figure 36: Schematization of the railway superstructure and characteristics measurements
The railway body, on the other hand, is formed:
โข From the actual roadway built on surveys or other works of art,
whose upper part is called the road platform and also includes
complementary work such as quays, roads and access roads for the
tracks;
โข From works of art, such as surveys, viaducts, bridges, tunnels,
trench walls, which create the plano-altimetric layout of the railway
line, ensuring the necessary functionality and integration with the
territory;
โข Minor and protective works of art such as bridges, platform gutters
and guard ditches.
In the Moroccan project, the sections shown in the elaborates contain no
information about the type and height of the catenary, nor the presence of
any poles that support it. Because of the modifications carried on the tracks,
the electric traction infrastructure must necessarily have undergone some
changes in its configuration which are not deducible from the documents
provided.
48
From these cross sections documents, it is only possible to obtain information
on the geometry of the track and the position of the structures near the tracks
that could interfere with the installation of any structures necessary for the
signaling implant.
A useful information obtainable from the cross sections is the cant value of
the rails in a curve, allowing to determine the rolling plane with respect to
which the heights are defined.
Very important information for the design of the positioning of the structures
necessary for the electric traction and signaling infrastructures, in addition to
the knowledge of the position of structures outside the tracks, is the interaxis
between the tracks, which allows to know if it is possible to install these
structures between a track and another, respecting the minimum distances
of the structures from the inner edge of the rail closest to the obstacle.
The sections, therefore, are a useful tool to know the existing and project
armament that is necessary for the study and design of the signaling systems
but they are not sufficient for the drafting of the entire project. Some
examples of cross section drawing are reported in Appendix A.
3.3 Schematic signaling plan
The schematic signaling plan shows schematically, and therefore without
respect for the proportions, the topography of station tracks, turnouts and
line tracks, passenger buildings, platforms, road crossings, tunnels and the
position and the type of signals that must be present in the specific points of
the line (and that are not built or installed yet) without indications (or only
with preliminary assumptions) about the structures to be designed to
support them.
49
The positioning of the signals is strictly linked to the regulations referred to
in the drafting of the schematic plan.
In the Moroccan project, basically the French regulation was applied and
therefore according to the indications of the SNCF.
Here is an example of schematic signaling plan:
Figure 37: Example of a schematic signaling plan
The figures below show some elements in the schematic signaling plane of
the Casablanca Triangle:
Figure 38: Elements of the schematic signaling plan - schematization of the joint
Figure 39: Elements of the schematic signaling plan - schematization of double comunication
50
Figure 40: : Elements of the schematic signaling plan - schematization of signal portals
Figure 41: : Elements of the schematic signaling plan - schematization of signal cantilever bridges
Figure 42: Elements of the schematic signaling plan - schematization for reflecting signs
Figure 43: Elements of the schematic signaling plan - schematization of signal for ending zone at limited speed
Figure 44: : Elements of the schematic signaling plan - schematization of banalized line
51
Figure 45: : Elements of the schematic signaling plan - definition of the action zone boundaries of a control post
52
CHAPTER 4: GEOMETRIC DEFINITION OF THE
STRUCTURES
The definition of the geometry of the structures is a complex and important
process where the slightest mistake would lead to delays and therefore be
financially costly.
This process consists of several phases:
Analysis of the schematic signaling plan and the staking reports
giving the first information about location of signals along the tracks
Analysis of the track planimetry providing distances between tracks
at those locations
Analysis of the cross section drawings showing:
o Tracks
o Elements belonging to the electric traction infrastructure
o Any other obstacle affecting the design and the structure
location (boundary walls, bridges, tunnels etc.)
Staking operations to verify the actual feasibility on site (not all the
obstacles are shown in the above-mentioned documents)
Design of the structures
o Choice of the type of structure to be designed
o Definition of the geometric dimensions of the structure
4.1 Analysis of the schematic signaling plan
The schematic signaling plan is drawn up by experienced railway signaling
professionals based on a reference standard. For instance, in Italy, the
53
schematic plan is elaborated on the basis of the FS standards for the location
and appearance of signals (Norme per lโubicazione e lโaspetto dei segnali)
and the related circulars of 19-05-1981 and 09-01-1984. In other railway
administrations different rules are regarded.
From the signaling scheme plan are extrapolated information about the
location of the signals along the line or in the station and the type of signals
to be installed on the structures. There are only preliminary assumptions on
the type of structures (Portals, Cantilever bridges or poles) to be installed;
neither it is possible to see planimetric data of the locations where the
structures will be installed (straight section, circular curve or transition
curve), nor there is information about the distance between the tracks nor the
presence of elements of the electric traction infrastructure.
That is why staking operations are needed to get the information necessary
to the geometrical definition of the structures.
4.2 Analysis of the track planimetry
The track planimetry is a scaled top view of the tracks providing all the
planimetric data necessary to the design of metallic structures.
For the realization of the structures, the track plan represents a fundamental
input document because once the type of signals to be installed has been
deduced from the schematic plan, it is possible to deduce the planimetric
element (straight section, circular curve or transition curve) in which the
structure will be installed, leading also to initial considerations regarding the
visibility of the signals. This document also shows the distances between the
tracks allowing to make preliminary assumptions about the possibility or not
to install the plinths of the structures, as well as the presence of obstacles such
as boundary walls that represent design constraints to the construction of the
structures.
54
After the analysis of the track plan, staking operations are carried out in order
to verify the site conditions and detect other possible design constraints not
present or deductible from this document.
4.3 Analysis of the cross section drawings
A first evaluation of the positioning and the type of structure to be installed
is carried out on the basis of the cross-sections drawings provided as input
documents.
From the cross-sections are deduced information about the distance between
the tracks, the presence of obstacles, if any, that prevent the installation of the
structure at a certain location of the line and of elements belonging to the
electric traction infrastructure.
On the basis of these information, taking into account the minimum safety
distances imposed by the harmonized European standards, a first design
hypothesis can be made and which will then be confirmed or not after the
staking procedures are carried out.
It is necessary for design purposes to have the cross-sections of the railway
platform elaborated in the point where the structures will be installed in
order to have information on the differences in height between the tracks as
well as the presence and actual location of the elements belonging to the
infrastructure of electric traction.
Verifying the presence of electric traction infrastructures is essential for
compliance with the safety standards described in the EN 501101, which
requires a minimum distance of 1.12 m between the metal structures and the
tension elements.
The elements to consider in this case are 3:
55
Catenary
Contact wire
Feeder
Figure 46: Two-dimensional schematic representation of the overhead line system indicating key elements. Dimensions indicate typical values
The contact wire to which the trains are electrically connected with a sliding
system (pantograph) is powered by electrical substations. For direct current
traction, safety regulations impose a minimum distance between the contact
wire and the top of rail of 4.40 m (typical values are around 4.7 โ 4.8 m). The
contact wire should have the following characteristics:
Maintain a constant distance from the track
Present an equal yield to the passage of the pantograph
Keep the conductors along the axis of the path
For railway speeds, the inertia of the pantograph mass would not allow
immediate reaction to the inevitable changes in height of the line. Therefore,
load-bearing ropes are used and which are arranged between the supports
according to a curve, said catenary, while the contact wire (rectilinear) is
connected to said rope by means of the droppers.
56
The supporting ropes are propped up by a Teflon insulator fixed on the shelf
while shelves are fixed to the poles by tie rods. In straight sections, the poles
are spaced about 60 m from each other but the distance is smaller if the curves
are circular.
The line is arranged according to a catenary and the distance between the
rope and the contact wires at the suspension point is 1.20 m. The length of
the droppers is made so that the wires of the contact wire are horizontal. The
feeder runs along the railway line and is mounted on the catenary support
poles.
Figure 47: Electric traction infrastructure
4.4 Staking operations
Once the track planimetry has been analyzed, deducting the first information
about the presence of obstacles and the distance between the tracks, and once
the input cross sections have been analyzed, the next step are the staking
procedures.
Staking means the operation for which the conditions deduced from the
previous documents are verified on site and obtaining other information that
could not be obtained from the previous documents.
57
The cross sections are processed with a distance ranging from 25m to 30m so
the information about the elements of electric traction infrastructure are not
constant and need to be verified on site.
The purpose of staking is therefore to verify the possibility or not of installing
the structures, by checking:
The presence of electric traction elements:
o Foundation plinths of poles and portals
o Consider the minimum distance between the metal parts and the
elements under tension according to the UNI 501101 standard;
Presence of obstacles not deductible from the documents previously
analyzed;
Presence of other constraints that would not allow the installation of
structures and where excavations are not allowed, such as overpasses
or bridges.
Therefore, starting from the track plan, with the exact information on the
location of the points to be staked (kilometers and hectometres) it is possible
to perform the staking operations on site with the help of tools such as:
Total station
Satellite receivers (GPS)
Odometer
58
4.5 Design of the structures
4.5.1 Choice of the type of structure to be designed
Before proceeding with the geometric definition of the structures it is
necessary to have a cross-section of the railway platform on the points where
the structure will have to be installed.
Stakes are placed following the distance rules described in the previous
paragraph on the basis of the geometric element of the alignment in which
the stakes are placed in and in correspondence with each of these points the
cross section of the infrastructure is elaborated.
The exact positioning of the metal structures deduced from the schematic
signaling plane must also be checked and staked in order to have a cross-
section of the rail platform in the point in question, as it is highly unlikely
that between the points staked previously is also the one relative to the
position of the signal.
The project alternatives are mainly 5:
Cantilever bridge
Cantilever bridge in โTโ shape
Simple Portal (two columns)
Portal (two columns) with one or two additional arms
Portal with more than 2 columns
The choice of the type of structure to be designed depends on:
Number of tracks and their relative distance
Presence on-site of obstacles detected during staking procedures
59
Altitude difference between the tracks
The choice of the type of structure is not a standard process, but it must
consider a series of factors that must be evaluated on a case-by-case basis.
As an indication, it can be said that it starts from the evaluation of the number
of tracks to which the signals refer:
2 tracks Cantilever bridge
3 tracks Cantilever bridge in โTโ shape
3 tracks Simple or with 1-2 arm(s) Portal
3 tracks Normal or with 1-2 arm (s) Portal
Actually, it often happens that for several reasons the choice falls into a
combination of those structures in order to guarantee all the safety standards.
In the following paragraphs are reported a series of factors to consider for
choosing the most suitable type of structure.
Distance between the tracks:
The distance between the tracks is a fundamental parameter to consider
when choosing the type of structure to be designed in order to establish
whether there is sufficient space for the insertion of the plinth in reinforced
concrete.
60
Figure 48: Signal portal referring to 2 tracks
In the image above, the spacing between the 2 tracks was sufficient for the
portal installation.
The distance between two neighbor tracks can be considered sufficient when:
โข It is possible to install the column so that the safety
distance between the fixed obstacle and the
kinematic Gabarit is respected, this distance is
defined as "free margin" and is set by FS in 150 mm.
โข The excavation for the plinth can be done without
damaging the track
Figure 49: Interaxis representation
61
The structure gauge (or Gabarit) of the vehicles have been fixed for a vehicle
that is, in static conditions, centered on a straight section. When the vehicle
goes along a curve, in relation to the wheelbase, the length and the
mechanical characteristics of the vehicle, the shape of the vehicle protrudes
towards the inside of the curve in the central part i (between the axles of the
bogie) and towards the outside of the curve in the parts between the axle of
the bogie and the nearest end of the vehicle e (as shown in the figure below).
The i and e values depend on the wheelbase (p), the length (lc) and the
semi-width of the bogie (b/2) as well as the radius of curvature (R).
Figure 50: vehicle's overall dimensions when cornering
To pass from the structure gauge to the minimum obstacle profile (PMO)
determining the minimum distances at which to place the obstacles present
along the line, it must be considered a margin that also takes into account the
characteristics of suspension and rolling of vehicles, speed and radius of the
curves.
Each country has its own Gabarit standards. For example SNCF defines 2
categories of Gabarit:
โข The nominal Gabarit: independent of the rolling plan in its
measurement mode which are done in a horizontal and vertical
orthonormal coordinate system.
62
โข The limit Gabarit: which measurements are done in reference to an
orthonormal coordinate system according to the rolling plane.
Figure 51: Gabarit categories according to SNCF
The UIC (Union Internationale des Chemins de Fer) has defined common
international gauges in order to allow the circulation of vehicles on different
networks . The G1 is the international limit gauge (allowed to circulate on all
lines open to international traffic for which there are no special conditions)
to which are added the B and C for high-speed lines.
The figure shows the international limit gauge G1 and other gauges adopted
in other countries.
63
Figure 52: International gauge G1 and national gauges
While the legislation refers to the distance between the fixed obstacle (in this
case the steel column of the structure supporting the railway signals) and the
structure gauge, it does not take into account the space necessary for placing
the plinth installed in the subsoil.
The plinth cannot be built too close to the railway platform in order to avoid
damage to the railway infrastructure during the excavation for the plinth
installation. In fact, if the plinth is too close a preliminary reinforcement must
be considered to support the railway site. The distance of the plinth from the
railway platform is established by the structural engineer on the basis of the
considerations he made when designing the structure. The minimum
distance from the edge of the plinth toward the railway platform and the
64
external part of the first railhead towards the structure varies in a range of
1.5 -2.0 m.
Figure 53: Example of correct spacings between plinth and rail
The plinth develops in length, parallel to the course of the tracks, therefore
its width should be considered. The type of structure and the "order of
magnitude" of the loads applied to it, whose width varies between 2.2 and
2.9 m, should be noted as well.
The portals are more difficult to install as they demand a series of
requirements, including the presence of the free margin necessary for the
installation not of one, but of 2 plinths, always respecting the safety distances
and ensuring that there are no obstacles between the structure and the
railway platform.
Presence of on-site obstacles
For the choice of the typology of structure it is necessary to verify, with a
survey in the field, that there are no fixed obstacles (for example walls or
pickets). The staking operations are fundamental also in this case because
often there are obstacles not deductible from the documents provided
leading to the choice of a typology of structure over others that perhaps from
the documents alone was not the one that was expected to be realized. The
65
presence of obstacles influences the choice as it may happen situations where
their presence makes it necessary to adopt configurations of structures
specific to the situation.
Figure 54: Example of the installation of a signal cantilever bridge in presence of an obstacle
Altitude differences between the tracks
The difference in altitude between the different tracks is one of the most
binding parameters for the choice of the structure. Given a certain number of
tracks, in the case of a large difference in height between the different
platforms, we could resort to completely different structures.
In the example below (case with 4 total tracks), the choice fell on 2 simple
cantilever bridges rather than a portal due to the altitude difference,
resulting in higher costs for the design and the construction of the
structures.
66
Figure 55: Example of installation of 2 signal cantilever bridges instead of a simple portal due to the altitude difference between the tracks
4.5.2 Definition of the geometric measurements of the structure:
Once the typology of the structure has been chosen, the next step is to define
the geometrical measurements that will characterize it.
The dimensions to be evaluated for each structure are:
Height of the column/s
Cantilever length (for cantilever bridge or arm/arms of the portal)
Length of the beam (for portal)
The height of the column is obtained once the exact height of the overhead
catenary for the electric traction is known, keeping in mind the minimum
distance of 1.12 m imposed by the EN501101 standard between each metal
part and the active elements up to 25kV.
67
All the structures designed along the Casablanca-Tangier line have 10 m high
columns (input received by ONCF electric traction department). The total
height of the structure will be known once the beam is also definitively sized.
The length of the cantilever beams and portals depends on:
The number of tracks and their relative distance based on the point of
the line in which they will be installed.
The laying side of the structure with respect to the tracks, in fact the
length of the cantilever varies according to the presence of obstacles
or to the short distances that do not allow the installation of reinforced
concrete plinths.
The position of the signal on the cantilever beam, in fact signals must
be installed to the left with respect to the direction of travel of the train,
so if the cantilever beam is also installed from the left side, there will
be a shorter length, while if the structure is installed on the right side,
it will be longer for positioning the signal on the left side with respect
to the direction of travel, at a suitable distance from the axis of the
track. The distance between the signal axis and the track axis to which
the signal refers varies according to local regulations. With regard to
the Moroccan project (and therefore according to the ONCF4) the
distance is maintained in a range of 1.25 - 1.35 m. As it can be seen
from the previous figure in which there are 2 cantilevers bridges that
cover the same number of rails, but one positioned on the left and one
right with respect to the direction of travel, the length of the cantilever
beams are in fact respectively 8.4 m and 9.7 m.
4 ONCF stands for โOffice National des Chemins de Ferโ, which is the Moroccan national railway
company.
68
Position of the signal cage with respect to the steel beam modules.
Two factors have to be considered: The bolts for mounting the signal
cage on the beam must not conflict with the elements of the steel beam
and its position must also be such as to allow maintenance workers to
intervene. The example in the first figure is not realistic, in addition to
the image not properly scaled, there is an interference between the
bolts for mounting the cage and the vertical modules of the beam. The
second figure instead shows a realistic example of correct installation
and highlights how to comply with the above criteria it was necessary
to add another module to the steel beam, thus increasing its total
length.
Figure 56: Example of incorrect mounting of the signal cage
Figure 57: Example of correct installation of the signal cage
4.6 Selection of structure types to be designed by the structural
engineer
Once the site conditions have been studied through staking operations and
after considering the parameters listed above, it is necessary to try to group
69
all the structures designed into a small number of structure types. This will
reduce structural design costs.
In the case of the design of new implants over large areas it is not conceivable
to design a different structure for each location, in fact it is reasonable to
define "standard structure types" able to comply with the installation
requirements in several situations.
In other cases, the same metallic structure type can be associated with several
types of plinth, thus allowing its installation in several locations without
changing the design of the metallic parts. A typical case is, for the same is
the possibility to choose between two or more plinth types according to the
distances plinth-track, without starting a new structural design from scratch.
In the figures below are some examples of structures designed along the line:
Figure 58: signal bridge with 2 cantilever beams
70
Figure 59: Signal bridge with 1 cantilever beam
Figure 60: Signal cantilever bridge in T shape with an extra cantilever
71
CHAPTER 5: STRUCTURAL DESIGN
The structural design of the structures is carried out by a civil structural
engineer registered at the professional board of engineers.
For the design of the structures it is necessary to provide the following
inputs:
A geological and seismic report of the area in which the structures will
be installed
The geometric data of each structure type to be designed
o The geometric dimensions defined according to the criterions
listed in the previous chapter
o Information about the maximum length of the beams, in view
of the transport of the parts of the structure to the building site
and the galvanization plant where the structural elements will
be. For the structures manufactured and installed in Morocco,
the maximum length was set at 14m. It will then be up to the
designer to define the points where the cuts will be made based
on the points more or less stressed during the operational life
of the structure and to dimension corresponding joints.
o Information about any cuts along the handrail to allow
maintenance operations on the light panels placed behind. The
cuts must be provided because any cuts on site would
compromise the finishing of the galvanization.
The loads to be assigned to the structures (Weight of the signals, of the
luminous panels and metallic plates)
72
Any contract specific requirement about material and its finishing
(e.g. galvanization thickness and type)
Mechanical details of the objects to be installed to allow a proper
predisposition of their supports
The designer of the structure is responsible to dimension the structure by
providing all the necessary documentation for its construction:
Technical report:
o Specification of the reference standards adopted and brief
description of the project to be designed
o Specifications on the materials used
o Evaluation of the loads considered to be applied on the structure
o Calculation report
o Results and verifications
o Verification of bolted joints
o Verification of the plinth
Executive design of the structure with all the construction details
Maintenance plan
5.1 Documentation to be supplied to the structural engineer
5.1.1 Geological and seismic report
The geological and seismic report is a necessary document for the designer
engineer both for the evaluation of the type of foundation to be designed
based on the type of subsoil and the definition of the seismic response that
the structure must present.
73
This report is subdivided into:
Description of the planned structure
Seismic hazard evaluation
General geological framework
Description of the survey methodologies followed
Geological model
Seismic considerations
o Identification of the soil category of the foundation
o Topographic amplification effects
o Definition of the elastic response spectra in acceleration
5.1.1.1 Description of the planned structure
The structures in question are cantilever signal bridges and regular signal
bridges which belong to usage class IV and are classified as type 2
constructions in accordance to the Ministerial Decree DM 17-01-2018 of the
Italian legislature. They are therefore described as ordinary structures of a
limited size and average importance with a 50-year nominal life (years in
which the structure, subject to regular maintenance, maintains specific
performance levels).
According to the DM 17-01-2018, the reference period for seismic action is
evaluated based on a reference period VR that depends on the type of
construction (type 2, in our case) that equals the product of the nominal life
of the structure (VN) and the use coefficient CU.
๐๐ = ๐๐. ๐ถ๐
74
The use coefficient value is, for buildings belonging to class IV, equal to 2.
The reference life for these structures is therefore of a 100 years.
5.1.1.2 Seismic hazard evaluation:
The seismic hazard evaluation depends on the seismological characteristics
of the area such as typology, size and depth of the seismic sources as well as
the energy and frequency of the earthquakes. This evaluation estimates the
values of the parameters suitable to predict the probability of exceedance
using probabilistic methodologies for a region at a given period of time.
Those parameters include speed, acceleration, intensity as well as the spectral
ordinates describing the shaking produced by the earthquake in conditions
of rigid soil and without morphological irregularities.
The seismogenic zonation reference in Italy is the ZS9, a variation of the
previous ZS4 zonation owing to the introduction of updated data on the
geometry of the seismogenic sources.
The SZ9 zonation consists of a subdivision of the Italian territory into 36
demarcated areas on the basis of geological-structural information, tectonic
and of other characteristics of seismicity such as the spatial distribution,
frequency of earthquakes or even the maximum magnitude released.
75
Figure 59: ZS9 seismogenic zonation
Zones are identified by appointed numbers and have each different
seismogenic characteristics. The areas indicated with letters have not been
used for the evaluation of the seismic hazard.
The OPCM5 of April 28th 2006 nยฐ 3519 stating the โgeneral criteria for the
identification of seismic zones and for the formation and updating of the lists
of the same areasโ identifies and approves the general criteria and the seismic
hazard map of reference in Italy by defining 4 zones, each of which is
identified by a maximum acceleration ag and with an exceedance probability
of 10% in 50 years (referring to rigid soils).
The evaluation of the acceleration ag is carried out on the basis of studies of
seismic hazard conducted on updated data and validated methodologies and
measured on a sufficient number of points and with the estimates of
associated uncertainties.
5 OPCM = โOrdinanza del presidente del consiglio dei ministriโ
76
Figure 60: Seismic hazard values according to OPCM 3519/2006
For the assessment of seismic risk, Morocco relies on the โEarthquake-
resistant building regulations RPS2011โ decreed by the Department of
Quality and Technical Affairs of the Ministry of Housing and City Policy.
Similarly, to the Italian approach, the RPS2011 requires a subdivision of the
national territory into homogeneous seismic areas presenting approximately
the same level of seismic risk with a certain probability of occurrence.
In each zone, the values defining the seismic hazard are considered to be
constant and refer to the maximum horizontal acceleration (Amax) or velocity
(Vmax) to the ground for a probability of exceedance of 10% in 50 years. This
equals to a return period of 475, corresponding to moderate earthquakes
likely to occur several times during the nominal life of the structures.
77
The
Moroccan railway line from Casablanca to Tangier, as seen on the previous
figures, crosses zones with different seismic risks thus requiring different
assessments when designing the structures based on their location on the
Moroccan territory.
5.1.1.3 General geological framework:
This part of the technical report provides a geological description of the
territory in which the structures will be installed giving information about
the stratigraphy of the soil since each type of soil differs in its reaction and
the order in which they occur starting from the ground-level.
In addition to the stratigraphy, descriptions of the hydrogeological aspects
of the territory if near the installation sites of the structures are also included.
Figure 62: Seismic zonation in terms of Vmax for RPS2011 Figure 61: Seismic zonation in terms of Amax for RPS2011
78
5.1.1.4 Description of the adopted survey methodologies:
In Italy, the surveys required for the different types of structures depend on
regional regulations. The table x shows the investigation conducted by the
Regional Regulation 7-02-2012 for the Lazio region and the testing that can
be performed according to the type of structure.
Generic requested investigation
Investigations needed for the structures in
question
Nยฐ 1 geognostic survey Nยฐ 1 geognostic survey
Nยฐ2 penetration tests Nยฐ1 penetration tests
Nยฐ2 MASW analyses for Vs30
calculation Nยฐ2 MASW analyses for Vs30 calculation
Measure of foundamental
frequency of the terrain Unneeded test for this typology of structure
Direct seismic test Unneeded test for this typology of structure
Stability Checks
Unneeded test since the applied loads are
modest and don't alter the stability conditions
of the area
Table 2: Comparison between requested investigation and executable investigations for the structures
For the characterization of the stratigraphy, the physical-mechanical and the
seismic response of the terrain on-site tests are used such as:
Continuous coring surveys with a depth value varying from 20 to 25
meters from the ground-level with at least one equipped with a
piezometer test to measure the groundwater.
Dynamic penetration test performed to evaluate the stratigraphy and
geotechnical parameters of the soil.
79
MASW Seismic surveys for the evaluation of the equivalent mean
speed Vs30 indicating the speed of the shear waves in the first 30 m in
depth from the ground-level.
On-site geotechnical investigations are directed and checked by a geologist
certified by the State and carried out in compliance with the UNI EN/1997
regulation.
Continuous coring surveys
A geognostic survey is a survey methodology that allows the direct
inspection of the soil by perforating the ground using a drill. It is used for:
Reconstruction of the stratigraphic profile of the soil crossed.
Collection of representative samples to be submitted to subsequent
laboratory investigations
Reaching a certain depth
Coring surveys are performed by rotation and the drilling tool is composed
of a core drill (simple, double or triple) equipped at its end with a toothed
crown. The procedure starts by applying to the tool, through a battery of rods
that connects it to the surface, a simultaneous action of pushing and rotating.
The diameters used normally vary between 75 millimeters and 150
millimeters.
The drilling procedure can either be performed dry or with the introduction
of fluids.
The injection of the drilling fluid can be done on direct circulation if the fluid
falls in the internal rods or by inverse circulation (less frequent) if the fluid
80
goes down along the walls of the hole. The use of fluids significantly
increases the speed of advancement but makes the coring of soft or coarse-
grained materials more complicated.
The direct circulation scheme is represented in the following diagram (figure
61) the pump lifts the fluid out of the tank and feeds it into the central tube.
From the bottom of the hole, the fluid rises to the surface, taking away the
crushed soil that settles in the collecting tank.
Figure 63: Coring procedure with direct circulation of fluids
The main goal for continuous coring surveys is the determination of the
stratigraphy of the terrain and the extraction of soil samples for laboratory
investigations. The perforation is performed by rotation through simple,
double or triple core drill according to the nature of the soil. These
instruments minimize the disturbance of the materials and allow the
collection of representative samples (core samples).
81
Figure 64: Example of extruding the soil from the core drill
The core samples extracted from the core drill are then placed in appropriate
boxes, suitable for their conservation and on which the survey identification
number and the reference depth are indelibly marked.
Figure 65: Example of core sample storage
Penetration tests
Those surveys have been developed all over the world starting from the
studies of Mohr in the United States in 1927. Their widespread diffusion is
mainly linked to the possibility of operating directly on site providing
continuous geotechnical indications.
82
The Standard Penetration Test (SPT) consists in allowing a standardized
sampler (Raymond sampler with thick walls) to penetrate the ground under
the blows of a hammer weighting 63.5 Kg.
The hammer is dropped from a constant height of 0.75 m and the
measurements are made for three consecutive advances of 15 cm each,
counting the number of blows needed (NSPT) for each advance. The resistance
to penetration of the soil is characterized by the sum of the number of blows
for the second and the third advances (N = N2 + N3). The test is performed at
the bottom of a probing hole (possibly altering the soil as little as possible)
previously excavated by means of a coring machine for example, at the
desired depth.
Figure 66: Standard penetration test
An object of conic shape embedded in the ground by successive blows
encounters during the penetration process, a resistance directly proportional
to one of the materials. If the material is the soil, this resistance gives the
physical-mechanical characteristics of the terrain in its natural state and
therefore, for coarse-grained soils this resistance depends mainly on the
83
thickness of the granules, while on fine-grained soils it depends on its natural
water content.
Unlike the SPT test which is performed during the perforation process, the
DP (Dynamic Probing test) consists in measuring the resistance to
penetration of a metallic conical tip, connected to an extensible steel rod with
the addition of successive rods of standardized dimensions, fixed
perpendicularly to the ground by dropping the hammer of a given weight
from a constant height. The information provided by the test is continuous,
as penetration resistance measurements are performed through infixing.
The characteristics of the equipment and the execution methods have been
standardized in the International Reference Procedures elaborated by the
ISSMFE (International Society for Soil Mechanics and Foundation
Engineering) which includes four types of penetrometer on the basis of the
weight of the hammer:
DPL (light) M โค 10 kg
DPM (medium) 10 kg < M < 40 kg
DPH (heavy) 40 kg < M < 60 kg
DPSH (super heavy) M โฅ 60 kg
The count of the blows necessary for the advancement of a length of rod of
established length (NSPT) allows the use of empirical relationships that
provide the resistance of the soil to the infixing (Rd). This allows the
correlation of NDPSH to NSPT and the comparison of NDPSH (nยฐ of shots counted
to the advancement of the rod obtained with a super heavy hammer) with
the Qc obtained from the static test.
The dynamic resistance at the tip correlated to the number of blows N is
evaluated with the Dutch formula:
84
๐ ๐ท๐ =๐2. ๐ป
๐ด. ๐. (๐ + ๐)=
๐2. ๐ป. ๐
๐ด. . (๐ + ๐)
in which:
RDP = Dynamic resistance at the tip (Area A)
e = /N = piling per blow
M = blowing mass (dropping height H)
P = total mass (rods and whole system)
MASW analysis
The MASW6 method is a non-invasive investigation technique (it is in fact
not necessary to perform a drilling or excavation, limiting therefore the costs)
which identifies the speed profile of vertical shear waves (Vs) based on
surface waves measurements made through a certain number of sensors
(accelerometers or geophones) placed on the surface of the ground.
Those surveys are necessary to the:
Evaluation of the projectโs seismic action at the level of the foundation.
Evaluation of the potential risk for liquefaction of the soil occurring
on saturated soils in which the strength and stiffness of it is reduced
by earthquake shaking or other rapid loading.
Evaluation of the seismic acceleration for the calculation of slope
stability and/or retaining structures against seismic action.
6 acronym for Multi-channel Analysis of Surface Waves
85
Evaluation under seismic conditions of the load-bearing capacity
(capacity of soil to support the loads applied to the ground) and the
subsidence of road embankments, retaining structures and
foundations of buildings.
The predominant contribution to surface waves is given by Rayleigh waves
which travel at a speed depending on the stiffness of the portion of soil
involved in the propagation process of waves. In a stratified medium, the
Rayleigh waves are dispersive, i.e. waves with different wavelengths
propagate with different phase velocity and group velocity. In other words,
the apparent phase (or group) velocity of the Rayleigh waves depends on the
propagation frequency. The dispersive nature of surface waves is correlated
to the fact that high frequency waves with short wavelengths propagate in
the most superficial layers and therefore give information on the most
superficial part of the soil. In contrast, low frequency waves propagate in the
deeper layers and therefore affect the deeper layers of the soil.
The MASW method is divided into three phases:
Calculation of the phase velocity (experimental)
Calculation of the numerical phase velocity
Identification of the vertical shear waves velocity profile Vs suitably
modifying the thickness h of the soil layer, the shear speeds Vs and
compression speed Vp, the mass density ฯ of the layers covering the
soil model, the dispersion curve and the phase velocity (or dispersion
curve) corresponding to the assigned soil model.
The soil model and therefore the velocity profile of shear waves can be
identified by a manual or an automatic procedure or by a combination of the
86
two. The number of layers of the soil model, the Poisson coefficient U, and
the mass density ฯ are generally assigned and the thickness h and Vs are
variable parameters.
In the manual procedure, the user assigns different values of the velocities Vs
and thickness h attempting to bring the numerical dispersion curve closer to
the experimental dispersion curve. In the automatic procedure, the search for
the optimal speed profile is entrusted to a global or local search algorithm
that tries to minimize the error between the experimental curve and the
numerical curve (Rome 2002, Joh 1998).
Generally, when the relative error between the experimental curve and the
numerical curve is between 5% and 10%, there is a satisfactory correlation
between the two curves, the velocity profile of the shear waves Vs and
therefore the type of consequent seismic soil represents a valid solution from
an engineering point of view.
After determining the velocity profile of vertical shear waves Vs, it is possible
to calculate the equivalent velocity in the first 30m of depth Vs30 and then to
identify the seismic category of the terrain.
๐๐ 30 =30
โโ๐
๐๐ ๐
๐1
The process of classification of the subsoil through the values of Vs, in the
DM 17-01-2018 is referred to as โsimplified approachโ and is applicable only
if the soil is inscribed in one of the categories described in the table below,
otherwise, the effect of the local seismic response must be evaluated through
specific studies described in the DM.
87
Category Foundation Soil Vs
A
Rocky outcrops or very rigid soils, possibly including
surface soils with poorer mechanical properties with a
maximum thickness of the layer of 3m > 800 m/s
B
Tender rocks of very thick coarse-grained soils or very fine-
grained soils characterized by a gradual improvement of
mechanical properties with depth
360 m/s < Vs <
800 m/s
C
Deposits of medium-thick coarse-grained soils or medium-
thick fine-grained soils with substrate depths >30m
characterized by improved mechanical properties with
depth
180 m/s < Vs <
360 m/s
D
Deposits of low density coarse-grained soils or scarcely
thickened fine-grained soils with substrate depths >30m
characterized by improved mechanical properties with
depth
100 m/s < Vs <
180 m/s
E
Soils with characteristics attributable to those defined for
categories C or D and substrate depth not exceeding 30m.
100 m/s <Vs <
360 m/s
Table 3: Soil categories accordin to the DM 17-01-2018
5.1.1.5 Geological Model:
The geological model consists in the definition of the stratigraphy and of the
nominal average geotechnical parameters obtained on the basis of the
investigations carried out and explained in the previous paragraph.
The most superficial layer in the stratigraphy shows for the type of structures
in question, the railway ballast for an average depth of 0.6 meters from the
ground-level and then the other layers for a depth of about 15m.
88
For each of the layers, from the investigations carried out, the following
parameters must be deducted:
Weight per unit of volume
Weight per unit of saturated volume โ
Angle of internal friction
Effective cohesion cโ
Undrained cohesion Cu
Oedometric Modulus Ed
5.1.1.6 Seismic considerations:
The classification is carried out on the basis of the Vs30 equivalent velocity
values of share wavesโ propagation within the first 30 m of depth. For
superficial foundations, this depth refers to the laying surface of it. To define
the seismic action for the project, the DM 17-01-2018 defines the stratigraphic
profile categories of foundations.
The amplification of the seismic motion due to irregularities of the
topographic profile was considered one of the main causes of damage
concentration during several earthquakes. Topographic amplification can
occur when local conditions are represented by the irregular morphology of
the surfaces and by topographic irregularities in general. These conditions
contribute to the concentration of the seismic waves near the relief ridge
following the reflection phenomena on the land and of the interaction
between the incident wave field and the diffract wave field. If the
topographic irregularity is represented by a bedrock, a pure topographic
amplification effect occurs while in the case of reliefs replaced by non-rocky
89
materials the amplifying effect is the result of the interaction (hardly
separable) between the topographic and lithological effect.
For complex topographic conditions, it is necessary to conduct specific
analyzes of the local seismic response. For simple configurations, the
classification provided by the technical regulations of the DM 17-01-2018 can
be adopted and provides the value of the topographic amplification
coefficient ST, necessary for the studies of the elastic response spectra of
acceleration and function as well as of the location of the opera or
intervention.
Category Characteristics of the topographic surface
T1
Flat surface, slopes and reliefs with an average inclination i โค
15ยฐ
T2 Slopes with an average inclination i > 15ยฐ
T3
Reliefs with ridge width much less than at the base and
average inclination 15ยฐ โค i โค 30ยฐ
T4
Reliefs withridge width much less than at the base and
medium inclination i > 30ยฐ
Table 4: Topographic categories according to the DM 17-01-2018
Category Location of the structure or intervention ST
T1 - 1
T2 At the top of the slope 1.2
T3
At the ridge of a relief with an average inclination
> 30ยฐ 1.2
T4
At the ridge of a relief with an average inclination
โค 30ยฐ 1.4
Table 5: Maximum values of the topographic amplification coefficient ST
90
5.1.2 Geometric characteristics of the structures
The task of the structural engineer is to size the structure based on the
information received and to produce all the documentation necessary for its
realization.
The geometrical dimensions of the structure and the parameters to be
considered for their definition were discussed in the previous chapter.
5.1.3 Loads to be assigned to the structures
The loads that are communicated to the structural engineer concern the
weight in Kg of the signals that the structures will have to support.
The type of signal to be mounted on each individual structure is deduced
from the schematic signaling plan and the technical specifications of the
signals are instead supplied by the company manufacturing these signals.
In the design phase, the signal and/or specific sign for each individual
structure is not considered, but rather a combination of them is. In particular,
it is the heaviest combination in terms of weight of the signals that is
considered to size the structure.
The positioning of the signal on the structure is defined in the preliminary
phase and derives from all the considerations made in the previous chapter.
5.2 Documentation supplied by the structural engineer
5.2.1 Technical report
The technical report is a document including the preparation of the
calculations for the metallic structures and the reinforced concrete plinths,
91
considering all the preparatory aspects for the design of each construction
detail and providing all the verification systems.
5.2.1.1 Specification of the reference standards adopted
In Italy, the reference regulation for construction is the Ministerial Decree 17-
01-2018.
More generally, Europe relies on the Eurocodes covering every phase of the
structural project, particularly for the design of these structures we refer to:
Eurocode 0: Basis of structural design
EN 1990:2003 Basis of structural design
Eurocode 1: Actions on structures
EN 1991-1-1:2009 General actions - Densities, self-weight, imposed
loads for buildings.
EN 1991-1-3:2003 General actions - Snow loads
EN 1991-1-4:2005 General actions - Wind actions
EN 1991-1-5:2004 General actions - Thermal actions
EN 1991-1-6:2005 General actions - Actions during execution
EN 1991-1-7:2007 General actions - Accidental actions
Eurocode 2: Design of concrete structures
EN 1992-1-1:2004 General rules and rules for buildings
EN 1992-2:2005 Concrete bridges - Design and detailing rules
92
Eurocode 3: Design of steel structures
EN 1993-1-1:2005 General rules and rules for buildings
EN 1993-1-5:2006 General rules - Plated structural elements
EN 1993-1-10:2005 Material toughness and through-thickness
properties
EN 1993-1-11:2006 Design of structures with tension components
5.2.1.2 Specifications on the materials used
In this part of the technical report are provided the characteristics of the
materials with which the structure was conceived in order to guarantee all
safety standards and design performances.
Steel
Steel is a metal alloy composed of 98% of iron and 2% of carbon which gives
it its typical strength. The graph below shows the behavior of a steel sample
subjected to a mono-axial traction test which is the most important laboratory
test for the characterization of the type of steel and from which the
characteristic parameters for the purposes of design are deduced.
93
Figure 67: Stress and deformation diagram for steel
The graph reports on the ordinate the axial stress to which the material is
subjected while on the abscissa we find the elongation. The behavior of a
tensile steel can be divided into 4 phases:
Elastic phase: the application of a certain load determines a
proportional elongation of the sample, the diagram is rectilinear and
the deformations are elastic: after the elimination of the load, the steel
sample reacquires the initial size. This phase is governed by the law
of Hook:
๐ = ๐ธ. ๐
Where "ฯ" represents the applied load, "E" indicates the Young's
modulus (considered constant and equal to 210000 N/mm2), while "ฮต"
is the elongation (ฮต=ฮL/L).
Elasto-plastic phase: By increasing the load, the deformations are no
longer directly proportional to the applied stress in fact the diagram
slightly curves to the right. The steel sample stretches and the
elongations increase more rapidly than the increase of the load.
Permanent elongations are added to the elastic deformations and are
94
as large as the load increase. The highest point of the curve section of
the graph is called yield strength (fyk).
Strain hardening and necking: In this phase, as the load increases,
elongations also increases until reaching its maximum value and
causing an increase in resistance. The deformations in this case are
plastic and even after the removal of the applied load, it will not be
possible to return to the initial size of the sample. Once the breaking
load (ftk) has been exceeded, there is the so called necking
phenomenon which corresponds to an area reduction of the section
and that point is also stochastically coinciding with the breaking point.
After the necking phenomenon, by continuing to increase the load, the
sample breaks.
The European standard UNI EN 10025-2 describes the quality of the types of
steel commonly adopted in buildings and provides the technical
characteristics of the materials in question.
Yield strength (fyk) [N/mm2]
Breaking load (ftk) [N/mm2]
Poisson coefficient (ฮฝ)
Young's modulus or elasticity (E) [N/mm2]
Thermal expansion coefficient (ฮฑ) [m/m /ยฐC]
Bolts:
Regarding bolts, the European reference standards are the UNI EN ISO 4016:
2002, the UNI 5592: 1968.
95
Bolts are classified into resistance classes, for the Eurocode 3 the following
classes are considered: 4.6, 4.8, 5.6, 6.8, 8.8 and 10.9.
The nominal values of the breaking load and of the yield strength of the bolts
can be deduced directly and very simply from the code that characterizes the
class: each abbreviation is composed of two numbers where the first,
multiplied by 100, indicates the value of the breaking load (ftk) in N/mm2 and
the second, preceded by the point, indicates the coefficient that multiplied by
the value of the breaking load gives the yield strength (fyk) in N/mm2.
The characteristic resistance of a tensile bolt fk, N is obtained as the yield with
the variant that the multiplicative coefficient must not exceed the value of .7,
i.e for the bolts of classes 8.8 and 10.9 the characteristic tensile strength is
obtained by replacing โ.8โ and โ.9โ the value โ.7โ.
In the technical report the resistances of the adopted bolt classes must be
specified.
PLINTH IN REINFORCED CONCRETE
Concrete
Concrete is a material obtained by mixing a hydraulic binder, an inert
material and water. Portland cement is normally used as the binder, while
inert material is crushed stone from the shattering of sedimentary or
metamorphic eruptive rocks. The concrete responds well to compression,
which is why the laboratory test that is carried out to characterize it is the
compression test, while in the design phase its tensile strength is not even
considered. The diagram below shows the reaction of a concrete sample to a
monoaxial compression test.
96
Figure 68: Stress and deformation diagram for concrete
On the axis of the ordinates there is the compressive stress while on the
abscissae we can read the deformations. The diagram has a parabolic trend
up to a 0.2% deformation and then presents a perfectly plastic course up to
the tensile deformation conventionally fixed at 0.35%. A non-linear behavior
is also noted for the concrete, even for low levels of applied load. The
maximum stress level below which the behavior of the compressed concrete
can be considered linear-elastic is about 30% of the peak resistance. The peak
load corresponds to a deformation of 0.2% which is somehow independent
from the resistance of the concrete. Concrete has a softening behavior,
meaning that once the peak load is reached, the material is not able to absorb
deformations greater than the one corresponding to the peak load, except
through a reduction of the load itself.
The compression tests are performed on cylindrical specimens (fck,
determining the characteristic cylindrical resistance of the concrete) or on
cubic specimens (Rck, which indicates the characteristic cubic resistance). The
technical standards consider the following relationship between the two
characteristic resistances:
๐๐๐ = 0,83. ๐ ๐๐
97
In the technical report, the class of concrete to be used must be specified, for
example the C20/25, where "C" stands for "Concrete", "20" indicates the value
of the characteristic cylindrical resistance at 28 days (concrete setting time),
while "25" indicates the characteristic cubic resistance. In addition to the
concrete class, the following parameters must be specified:
Weight per unit of volume [kN/m3]
Poisson coefficient
Thermal expansion coefficient [m/m /ยฐC]
Reinforcement steel
Steel for reinforced concrete must be weldable and with improved adhesion,
i.e it must be designed with transversal ribs or indentations, uniformly
distributed over the entire length, suitable for increasing adherence to
concrete.
Figure 69: Concrete reinforcement steel
98
In the figure below is represented the behavior of the weldable reinforcing
steel subject to a monoaxial traction test:
Figure 70: Stress and deformation diagram for reinforcement steel
Mainly 4 phases are distinguishable:
Elastic linear phase: any deformation due to the application of a load
lower than the value of yield fy, once removed, does not leave residual
deformations. The material returns to its initial configuration.
Deformation at a constant load: considerable deformations can be
noticed by keeping the yield load fy constant.
Hardening: After the deformation ฮตh is reached, there is a partial
recovery (hardening) and the tension can grow up to the maximum
value fu.
Necking: Further deformations are noted with a decreasing of the load,
accompanied by a reduction of the section until the specimen breaks.
99
In the technical report, the characteristic qualities of the selected steel type
must be indicated according to EN 1992-1-1 regulation:
Yield strength (fyk) [N/mm2]
Breaking load (ftk) [N/mm2]
Poisson coefficient (ฮฝ)
Young's modulus or elasticity (E) [N/mm2]
Thermal expansion coefficient (ฮฑ) [m/m/ยฐC]
Exposure class and durability
The specifications on the selected materials conclude with indications
relating to the exposure class, the durability of the materials (for the concrete,
reference is made to the UNI EN 206-1 standard) and to any treatments to be
submitted to the materials such as galvanization for steels (including the
bolts).
Galvanization is an industrial process consisting in covering a metal product
with a thin and strongly adherent layer of another metal in order to protect
it from corrosion. The most frequent galvanizing process consists in coating
steel and iron products with zinc. The most common type of a galvanizing
process is the hot-dip, which is carried out by immersing the product in a
tank containing molten zinc (with small amounts of other metals), at a
temperature of approximately 450 ยฐC. After the procedure, on the surface of
the steel there is the formation of several layers consisting of almost pure zinc
(outer layer), alloys and intermetallic iron-zinc compounds of various
composition. The overall thickness depends on the type of manufactured
article, but generally it is of the order of at least 50รท100 ฮผm. The protective
mechanism of the layer that is thus formed is twofold. In addition to
100
constituting a physical barrier that slows down the corrosion and
deterioration of the steel surface, zinc acts with an electrochemical
mechanism (hence the name of galvanization given to the process): if the
coating is damaged, leaving portions of the underlying material uncovered,
the surrounding zinc acts as a sacrificial anode (cathodic protection) avoiding
oxidation (rust formation) of the iron. Before embedding, the surface of the
manufacture to be galvanized must be subjected to degreasing and pickling.
The galvanized products can withstand for years exposed to oxidizing or
aggressive environments (atmosphere, rains, soils, sea water, etc.) especially
if the protection is reinforced by the subsequent application of suitable
paints.
The durability of the concrete is its ability to last over time, resisting the
aggressive actions of the environment, chemical attacks, abrasion or any
other degradation process that involves not only the cement paste but also
reinforcement steel.
The following table shows the exposure classes for the structural concrete
basing on environmental conditions of the site according to the UNI EN 206-
1 standard.
101
Table 6: Exposure classes for concrete according to UNI EN 206-1
5.2.1.3 Evaluation of loads
There are many loads acting on the structures to be evaluated during the
design phase.
102
Thermal action:
The thermal variations that act on the structures can be classified in:
Variations that only produce displacements and deformations
Variations that produce even or only coercion states (internal
solicitations)
Considering a free body in space and subjecting it to a temperature variation
ฮT. Due to the effect of thermal variation, the body undergoes at every point
a deformation ฮตT, whose magnitude is directly proportional to the
temperature variation.
The proportionality constant, i.e the coefficient of thermal expansion is
characteristic for each material and is indicated with ฮฑ:
๐๐ก = ๐ผ. โ๐
Since the body is free to deform in any direction of space, because it is free of
constraints, the thermal variation produces only displacements and
deformations without causing any state of stress to arise within the body.
When we consider the effects of a thermal variation on a beam or on a beam
system subject to an assigned number of constraints, the effects that are
recorded vary according to the number and disposition of the constraints. In
particular, it is possible to notice:
Only deformations and displacements (as in the case of the free body)
Deformations, displacements and internal stresses
103
Internal solicitations only
The cantilever bridges and the portals are statically simple and overall
isostatic structures therefore stresses due to thermal variations can be
considered negligible in terms of influence on the stress state of the structure.
However, it is up to designer to evaluate case by case.
Structural own weight (permanent)
The loads acting on the structures are divided into permanent and variable.
The load due to the weight of the structure is a permanent load and is
evaluated on the basis of the weight per unit of volume of the materials used
(concrete and steel) as indicated in paragraph 2.1 of the Eurocode 1 or the
Ministerial Decree 17-01-2018 in Italy.
The evaluation of the weight of the metal structure and of the reinforced
concrete plinth is left to the structural modeling and design software to which
the values of the specific weights of the materials are supplied as input data.
Non-structural weight (permanent)
The permanent non-structural weight refers to all metal elements not
belonging to the supporting structure (column (s) and beam (s)), that are
mounted and which are present during the normal operation of the structure.
Those permanent gravitational actions are derived from the geometric
dimensions and the weights per unit of volume of the materials constituting
the structure.
104
For these structures, the non-structural permanent loads are spelled out in
terms of concentrated loads acting on the assembly points on the supporting
structure and their position on the structure. Here the loads to consider:
Weight on the catwalk
Weight of the climbing cage
Weight of the signal cage
Weight of the signals (signals, reflecting signs, LED illuminated
signs)
Mobile overloads
Overloads include loads related to the intended use of the structures. In this
case we consider the weight of workers equipped with tools for maintenance
in the external climbing cage and on the catwalks. The value of those loads
are assigned by the Eurocodes.
Snow actions
The load due to the snow is computable by following the calculations
reported on the Eurocodes. Here the process to follow according to the Italian
Ministerial Decree 17-01-2018:
๐๐ = ๐๐ ๐. ๐๐ . ๐ถ๐ธ . ๐ถ๐ก
where:
qsk is the reference value of the snow load on the ground and
depends on the local climate and exposure conditions, considering
105
the variability of snowfall from area to area. Adequate statistical
surveys and specific local studies take into account both the height
of the snowpack and its density. The reference value of the snow
load on the ground, for locations at less than 1500 m above sea
level, it is assumed to be not lower than that calculated on the basis
of the expressions provided by Ministerial Decree 17-01-2018 in
paragraph 3.4.2 corresponding to a return period of 50 years for
the different areas of Italy.
For altitudes higher than 1550 m above sea level, local conditions
of climate and exposure must be taken into consideration, using
snow load values no lower than those foreseen for 1500 m.
ฮผi is a coefficient depending on the shape of the roof, on its
inclination with respect to the horizontal plane and on the local
climatic conditions of the construction site. For the structures
subject of this thesis, it is permissible to consider a form coefficient
of 0.8 relative to horizontal roofs and pitches less than or equal to
30 ยฐ.
CE is the exposure coefficient, taking into account the specific
characteristics of the area in which the structure will be built, in
case of scarce information about it we assume CE = 1.
Ct is the thermal coefficient, considering the reduction of the snow
load due to its dissolution, caused by the heat loss of the
construction. This coefficient depends on the thermal insulation
properties of the material used in the roof, in the absence of specific
studies or documents it is assumed as a precautionary measure
Ct=1.
106
Aerodynamic effects caused by the transit of trains
Among the loads to be considered in the sizing phase of this type of structure
is the aerodynamic effect due to the passage of trains on the surfaces near the
tracks. This topic is reported in the FS document "Overloads for the
calculation of railway bridges - Planning instructions, 'performance and
testing' and in the EN 1991-2: 2003. The extent of the actions depends on the
following factors:
โข The square of the train speed
โข The aerodynamic shape of the train
โข The shape of the structure
โข The position of the structure and its distance from the track
Actions can be summarized by equivalent loads acting in areas close to the
head and tail of the train; these equivalent loads are considered characteristic
values of the actions.
The values of the aerodynamic actions are combined with the wind action
according to the rules reported in the above mentioned FS standard, relative
to the combinations of the actions for the ULS7. There are 3 case studies:
โข Vertical surfaces parallel to the track
โข Horizontal surfaces above the track
7 ULS is the Ultimate Limit State. The ultimate limit state is the design for the safety of a structure
and its users by limiting the stress that materials experience. In order to comply with engineering
demands for strength and stability under design loads, ULS must be fulfilled as an established
condition.
107
โข Horizontal surfaces adjacent to the track
โข Structures with multiple surfaces alongside the vertical, horizontal
or inclined track.
The last case is related to the type of structures object of this thesis which
corresponds to a combination of the first case and the third one, therefore
concerning vertical surfaces parallel to the track (figure 69) and horizontal
surfaces adjacent to the track (figure 70). From the diagrams below it is
possible to obtain the characteristic values of the actions to be included in the
load combinations to the ULSs.
Figure 71: Characteristic values of qsk actions for vertical surfaces parallel to the track
108
Figure 72: Characteristic values of qsk actions for horizontal surfaces parallel to the track
Figure 73: Characteristic values of qsk actions for vertical surfaces parallel to the track
Wind loads
The direction of the wind is generally considered horizontal, and it applies
actions on the constructions that vary in time and space, causing dynamic
effects. Below are reported the indications of the Italian legislation
concerning wind actions:
109
Basic wind velocity
The basic wind velocity (vb) is the average value over 10 minutes, at 10 m
height above the ground on a homogeneous flat terrain of exposure category
II and referred to a return period TR = 50 years.
In the absence of specific and adequate statistical surveys, vb is given by the
expression:
๐ฃ๐ = ๐ฃ๐,0. ๐๐
where:
vb,0 is the fundamental value of the basic wind velocity at sea level
and depends on the area where the construction is located.
ca is the altitude coefficient provided by the relation:
๐๐ = 1 for ๐๐ โค ๐0
๐๐ = 1 + ๐๐ (๐๐
๐0) for ๐0 < ๐๐ โค 1550 ๐
where:
๐0, ๐๐ are parameters depending on the building aite
๐๐ is the altitude above sea level of the site where the building is
located.
For altitudes higher than 1500 m above sea level, basic wind velocity values
can be derived from appropriate documentation or adequately proven
statistical surveys referring to local climate and exposure conditions. The
values used shall not be less than those forecast for 1500 m altitude.
110
Reference wind velocity
The reference wind velocity vr is the average value over 10 minutes, at 10 m
height above the ground on a homogeneous flat terrain of exposure category
II and referred to a return period TR = 50 years defined by the mathematical
relationship:
๐ฃ๐ = ๐ฃ๐ . ๐๐
where:
vb is the basic wind velocity
cr is the return coefficient, function of the project return period TR
(expressed in years).
In the absence of specific and adequate statistical surveys, the return
coefficient is provided by the following mathematical formula:
๐๐ = 0.75โ1 โ 0,2. ๐๐ [โ๐๐ (1 โ1
๐๐ )]
Unless otherwise specified, it is assumed TR = 50 years, corresponding to cr =
1. For a new construction or for the transitional phases related to
interventions on existing buildings, the return period of the action can be
reduced as specified below:
111
โข For construction phases or transitional phases with a project
duration of no more than three months, it is assumed TR 5 years;
โข For construction phases or transitional phases with a project
duration between three months and one year, it is assumed TR 10
years.
Equivalent static actions
Wind actions are constituted by pressures and depressions acting on the
normal direction with respect to the surfaces of the structures.
The action of the wind must be determined considering the most severe
combination of the pressures acting on the two faces of each element
(internally and externally).
The overall action exerted by the wind on a building is given by the result of
the actions on the individual elements. The wind direction is the one
corresponding to one of the main axes of the building plan.
Wind pressure
Wind pressure is given by the expression:
๐ = ๐๐ . ๐๐ . ๐๐. ๐๐
where:
โข qr is the reference kinetic pressure
โข ce is the exposure coefficient
โข cp is the pressure coefficient
โข cd is the dynamic coefficient
112
Tangent action of the wind
The tangent action per unit of surface parallel to the wind direction is given
by the expression:
๐๐ = ๐๐ . ๐๐ . ๐๐
where:
qr is the reference kinetic pressure
ce is the exposure coefficient
cf is the friction coefficient
Reference kinetic pressure
The reference kinetic pressure is given by the expression:
๐๐ =1
2๐๐ฃ๐
2
where:
๐ฃ๐ is the reference wind velocity
๐ is the air density assumed conventionally constant and equal to
1.25 kg/m3
Expressing ๐ in kg/m3 and ๐ฃ๐ in m/s, qr is expressed in N/m2
113
Exposure coefficient
The exposure coefficient ce depends on the height โzโ above the ground of
the considered point, on the topography of the terrain and on the exposure
category of the site where the construction is located. In the absence of
specific analyzes considering the origin direction of the wind and the actual
roughness and topography of the land surrounding the building, for heights
above the ground not greater than z = 200 m, it is given by the formula:
๐๐(๐ง) = ๐๐2๐๐ก ln (
๐ง
๐ง0) . [7 + ๐๐ก๐๐ (
๐ง
๐ง0)] for ๐ง โฅ ๐ง๐๐๐
๐๐(๐ง) = ๐๐(๐ง๐๐๐) for ๐ง < ๐ง๐๐๐
where:
kr, z0, zmin are tabulated according to the exposure category of the
construction site
ct is the topography coefficient
The exposure category is assigned according to the geographic position and
the roughness of the land. In the bands within 40 km from the coast, the
exposure category is independent of the altitude of the site.
114
The topography coefficient ct is generally set equal to 1, both for the flat areas
and for the undulating, hilly and mountain areas
In the case of buildings located at the top of hills or isolated slopes, the
topography coefficient ct can be obtained from data supported by
appropriate documentation.
Figure 74:Illustrations of the exposure factor ce(z) for c0=1,0, k=1,0
Aerodynamic coefficients
The pressure coefficient cp depends on the type and geometry of the
construction other than its orientation with respect to the wind direction.
115
The coefficient of friction cf depends on the roughness of the surface on which
the wind exerts the tangent action.
Both of these coefficients, defined aerodynamic coefficients, can be derived
from data supported by appropriate documentation or experimental wind
tunnel tests.
Dynamic coefficient
The dynamic coefficient takes into account the reductive effects associated
with the non-simultaneity of the maximum local pressures and of the
amplification effects due to the dynamic response of the structure.
It can be cautiously assumed to be equal to 1 in recurring constructions, such
as buildings with a regular shape not exceeding 80 m in height and industrial
buildings, or it can be determined by specific analyzes or by referring to data
of proven reliability.
For this type of structures wind is considered based on different directions
with respect to the structure, below the cases to be considered in the design
phase:
Wind parallel to the tracks:
o Wind on the catwalk
o Wind on the pylon
o Wind on the external cages
o Wind on the climbing cage
Wind perpendicular to the tracks:
o Wind on the catwalk
o Wind parallel to the cantilever (or to the beam for the portals)
o Wind on the pylon
116
o Wind on the external cages
o Wind on the climbing cage
5.2.1.4 Calculation report
Calculation methods
The calculation report shows the results of the calculations concerning the
verification of the working tensions of the materials and of the ground in
compliance with current regulations. There are also reported the calculation
methodologies adopted, in general:
โข For static loads: The deformation method
โข For seismic loads: The method of modal analysis or equivalent static
seismic analysis.
The method of deformations (or displacements) is a resolutive method for
hyperstatic structures and is generally the one used in automatic calculation
software.
The principal system is geometrically determined and obtained by adding
constraints until the structure has its beams perfectly constrained. The
principal system is soluble (since is formed by constrained beams) and
respects the congruence (all the real constraints have been maintained).
However, the equilibrium is not respected since to keep the knots locked, it
is necessary to apply forces and/or couples that are different from the real
ones.
117
Figure 75: Principal system
The actual system is found by applying to the principal system the actual
displacements and/or rotations (๐i ) of the nodes that have been locked.
Figure 76: Deformations of the principal structure with the deformation method
118
The real displacements and/or rotations (๐i) are obtained by imposing that in
order to obtain them are applied in the nodes of the principal system forces
and/or rotations that, added to those caused by the load, restore the external
forces and/or rotations actually acting on the nodes themselves (which are
known). All these forces and/or couples are calculated on a system that is
solvable (the principal system formed by a set of embedded beams).
Therefore, the determining equations of ๐i are equations of equilibrium. Once
calculated the ๐i, the displacements and the rotations at the extremes of all
the beams are known and therefore with the formulas of the beam embedded
with the subsidence and rotations of the known constraints we can determine
the Normal stress, bending moment and shear stress.
The method of modal analysis concerns the study of the dynamic behavior
of structures that are subjected to vibrations (such as seismic vibrations). In
structural analysis, it allows the determination of the properties and the
response of a structure, constrained or free, in autonomous dynamics or
excited by dynamic forcing stress imposed from the outside. In the case of
simple bodies, modal analysis is able to study the dynamic behavior in detail
through the evaluation of its natural frequency and its associated vibrating
modes. In the case of complex structures, they are previously schematized
through the finite elements method in order to obtain the same results
referred to the whole.
The problem of free oscillations in a system without damping can be
explained by the following relation:
๐๏ฟฝฬ๏ฟฝ + ๐พ๐ฅ = 0
admitting solutions like:
119
๐ฅ(๐ก) = ๐(๐ก)
and having in general:
๐(๐ก) = ๐ด. sin(๐๐ก + ๐)
Vectors and pulsations are found in correspondence with the eigenvalue
problem:
(๐พ โ ๐2๐)๐ = 0
If the mass and stiffness matrices are nonsingular8 there will be โnโ solutions,
otherwise if the matrix M has rank โrโ the solutions will be just โrโ. The
stiffness matrix is generally nonsingular, meaning that there are no rigid
motions, while the mass matrix can often be singular since the rotational
moments of inertia are currently neglected. From the above formulas, it is
important to deduce how the dependence on time and position are
decoupled, in the course of a main oscillation the shape of the oscillation does
not change: only the amplitude of the oscillation changes with time.
The dynamic behavior of a structure is seen as the sum of a certain number
of elementary oscillations, each of which occurs according to its own period.
Moreover, in general, the various oscillations are not in phase with each other
therefore the maximums are reached at different times. Therefore, the overall
behavior is given by the sum of all the elementary modes:
8 The concept of nonsingular matrix is for square matrix, it means that the determinant is nonzero,
and this is equivalent that the matrix has full-rank.
120
๐ฅ(๐ก) = โ ๐๐(๐ก)
(i = 1, n)
The modal analysis serves to find a certain number โmโ (m << n) of these
pendulums while not having information about the shape of the oscillation.
The free oscillation of the model (not of the structure) is obtained by
imposing all the initial conditions in order to obtain the amplitudes and
phases of each of the oscillations. As for seismic analyzes, a sort of weighted
average of all these oscillations is made, arriving at a result in terms of
displacements and deformations (Analysis with the response spectrum).
For the calculation of this type of structure, it is hypothesized that in
correspondence with the seismic planes, the floors are infinitely rigid in their
plan and that the masses, for the purposes of calculating the plan forces, are
concentrated at their altitudes
Calculation of displacements and characteristics
The calculation of displacements and characteristics is generally done
according to the finite element method. This method allows to solve the
problem of determining the state of stress and deformation in elements under
load conditions for which the analytical solution canโt be found or obtained.
The continuous, which has infinite degrees of freedom, is discretized, with a
set of elements of finite dimensions and interconnected in predefined points
(nodes).
The form functions bind the displacements at the generic point of the finished
element to the nodal displacements. For linear form function we have:
121
๐ข = ๐1 + ๐2๐ฅ + ๐3๐ฆ
๐ฃ = ๐4 + ๐5๐ฅ + ๐6๐ฆ
in which the coefficients โaโ are constant, u is the displacement and v is the
speed.
The choice of the form function influences the phase of subdivision into finite
elements. Using finite elements with linear form functions allows to model
the movements within the single finite elements through linear functions.
This process requires a very thick subdivision in correspondence of the areas
of the element in which there is expected to be a high degree of stress.
The introduction of finite elements allowing the use of form functions having
a higher degree, consent to adapt the degree of the form function to the
particular application (passing from simple interpolating polynomials to
more complex polynomials). It is the calculation program that, once having
fixed the type of subdivision into finite elements, uses functions of a suitable
degree form (in a hierarchical way, starting from polynomials of a lower
degree).
Figure 77: Form functions with higher than 1 Figure 78: Linear form functions
122
For the metallic structures studied in this thesis work there are 2 types of
elements that can be defined and used:
One-dimensional rod element (beam) joining two nodes each with 6
degrees of freedom. For precision purposes, the shear and axial
deformability of these elements are also taken into account. Moreover,
these rods are not considered flexible from node to node but have on
the initial and final part 2 infinitely rigid sections formed by the beam
part incorporated in the thickness of the column; these rigid traits
provide the knot with a real dimension.
The two-dimensional shell (quad) element that unites 4 nodes in space. Its
behavior is twofold, it works as a plate for the loads acting on the
plane and as a plate for the orthogonal loads.
After assembling the stiffness matrices of the single elements in that of the
spatial structure, the resolution is pursued by various methods, such as the
Cholesky method.
For the purpose of resolution of the structure, the X and Y displacements and
the rotations around the vertical axis Z of all the nodes lying on a rigid
declared deck are mutually constrained.
Seismic and dynamic analysis with concentrated masses
Dynamic seismic analysis is carried out through modal analysis, the search
for modes and relative frequencies is pursued by the method of iterations in
the subspace. The number of vibration modes considered must be sufficient
to ensure the excitation of more than 85% of the total mass of the structure.
Modal forces are evaluated for each direction of the earthquake and are
123
applied to each spatial node (3 forces, in the X, Y and Z directions, and 3
moments).
For the verification of the structure, it is usual to refer to the modal analysis,
therefore first the solicitations and the modal displacements are calculated
and then their effective value is computed. The equilibrium at the nodes loses
its meaning and the values of the seismic stresses are combined linearly (in
sum and in difference) with those for static loads in order to obtain the
seismic stresses in the two directions of calculation. It is necessary to define
with respect to which axis the angles of the seismic input directions are
evaluated in relation to the global reference system.
Reference systems, units of measurement and sign convention
It is important to define the reference system adopted for each individual
element:
Global reference system of the spatial structure: the reference system
consists of three Cartesian orthogonal axes (O-XYZ) where for
example the Z axis, which represents the vertical axis, can be
considered pointing upwards. The rotations are considered positive if
they agree with the vector axes.
Local reference system of the rods: the reference system, whether inclined
or not, consists of three Cartesian orthogonal axes. Generally, the Z
axis coincides with the longitudinal axis of the rod and is oriented
from the initial to the final node. The X and Y axes will be oriented
accordingly.
124
Figure 79: Local reference system for the rods
Local reference system of the shell element: the reference system of the
shell element is also constituted by three Cartesian orthogonal axes.
Generally, the X axis coincides with the direction between the first and
the second input node, the X axis lying in the shell plane and the Z
axis in the thickness direction.
Figure 80:Local reference system for the shell element
It is important to specify the units of measurement adopted for:
o Lengths
o Strength
o Time
125
o Temperature
It is also essential to define the conventions on the signs adopted. The loads
acting on the structures are of 2 types:
Loads and moments distributed along the coordinated axes
Loads and nodal couples concentrated on the nodes
Conventionally the distributed forces are considered positive if they agree
with the local reference system of the rod, the concentrated loads are positive
if their direction agrees with the global reference system.
In the calculation report must be inserted a section dedicated to the
explanation of the acronyms used in the tables of the thermal and distributed
loads on the rods, the concentrated loads, the shell thermal loads and the
loads on the shell elements. Beyond the tables that must be inserted are
related to:
Section archive:
o Angular with unequal sides
o Static characteristics of the profiles (moment of inertia, plastic
resistance module ...)
o Data for verification of the Eurocode
o Characteristics of the material
General structure data:
o Geometric dimensions
o Seismic parameters (nominal life, usage classes ...)
o Parameters of the seismic elastic spectrum to the Operability
Limit state (OLS)
126
o Parameters of the seismic elastic spectrum to the Damage
Control Limit State (DCLS)
o Parameters of the seismic elastic spectrum to the Life-Saving
Limit State (LLS)
o Parameters of the seismic elastic spectrum to the Collapse
Prevention Limit State (CPLS)
o Parameters of the steel construction system
o Safety coefficients adopted for the materials
Coordinates of the nodes
Spatial rod data
Spatial shell data
Constraints and nodal settlements
Loads distributed on the rods
Loads concentrated on the nodes (thermal, distributed and
concentrated)
Loads on the shells
Load combinations
5.2.1.5 Results and verifications
In this section of the technical report are shown all the results of the analyzes
made using the calculation software. In particular, there are:
Graph of the spectral accelerations as in the figure below, but in
which the relative trends must be reported for each single load
combination both in horizontal and vertical direction.
127
Figure 81: Design response spectrum
Table with excited frequencies and masses
Graphical representation of the vibrating modes of the
structure
โข Graphic representation of the deformed structure considering the
wind parallel to the tracks
โข Graphic representation of the deformed structure considering the
wind orthogonal to the tracks
โข Graphical representation of the deformed structure for vertical
earthquake
Graphical representation of the maximum stress state in the
absence of earthquake
Graphical representation of the stress state with vertical
earthquake
Graphical representation of the stress state with earthquake
parallel to the tracks
Graphical representation of the stress state occurring in presence
of an earthquake having direction orthogonal to the tracks
128
5.2.1.6 Verification of the plinth
This section shows the calculation results concerning the reinforcement
project, the resistance checks of the elements and the verifications related to
a foundation built on plinths.
For these structures, direct rectangular plinths are used and are generally
assumed to stay perfectly rigid as regards the calculation of the contact
pressures with the ground, which therefore have a linearly variable trend.
The soil is simulated as a reactive elastic compression surface (Winkler
model) and non-reactive tensile surface. The distribution and the extent of
the stresses on the ground is therefore a function of the resulting eccentricity
of all the efforts that discharge into the foundation, including the weight of
the plinth.
Winkler model: It is the most used model for calculating stresses in
foundation elements. The foundation soil is schematized as a bed of springs
having stiffness โkโ (Winklerโs โkโ), independent of each other;
consequently, the lowering of a spring does not involve also the lowering of
the adjacent spring. The value to be attributed to Winkler's โkโ is an
expression of the geotechnical model of the subsoil. This value is generally
defined as the ratio between the applied load and the subsidence โwโ
obtained using an appropriate calculation method and the information
obtained from geotechnical investigations.
129
Figure 82: Representation of the Winkler model for the foundation ground
The calculation of the plinth reinforcement can be performed using
simplified procedures. This is possible since the foundation plinths are
sufficiently thick to consider the plate behavior as that of four independent
brackets fixed to the base of the column.
The reinforcement of the basic grating can be obtained from the simple
bending calculation of the single brackets. Those corbels are considered
loaded by the pressure of the soil resulting from the combination of the
heaviest load.
The shear verification is therefore always carried out on the same brackets,
on a reference section distant from the column thread of a section equal to
half of the maximum height of the plinth. The satisfaction of such verification
automatically implies satisfaction of the punching9 verification.
If the length of the inspection bracket is less than 1.5 the maximum height of
the plinth, it is assumed to be sufficiently thick so as not to require any shear
verification. The verification of the base reinforcement is carried out with the
brace strut and tie scheme.
In the plinth verification section of the technical report, must be present
tables regarding:
9 Punching results from the application of a concentrated load or a reaction acting on a relatively small area of a plate or a foundation, called โloaded areaโ.
130
โข General calculation data
o Criteria for calculating the plinths
Minimum cover
Minimum percentage of reinforcement in a tensile
area
o Calculation criteria for poles
Load bearing capacity of the poles
Minimum percentage of total reinforcement
Tie factor at the top of the pole
Minimum net cover of the reinforcement concrete
brackets
o Verifications carried out using the Eurocodes method
Partial geotechnical coefficients
o Characteristics of the materials
Characteristics of the reinforced concrete
Stratigraphic characteristics
Load combinations:
o Ultimate Limit States (ULS) load combinations
o Life-saving Limit State (LLS) load combinations
o Rare load combinations to the serviceability Limit State (SLS).
o Frequent Load combinations to the serviceability Limit State
(SLS).
o Permanent load combinations to the serviceability Limit State
(SLS).
Loads on the plinths and hence on the foundation
Direct plinth verifications
o Slip check
o Serviceability limit state of the plinths
131
5.2.2 Construction (or detailed) design of the structure
Among the most important output documents provided by the structural
engineer are the construction drawings.
In Italy, according to Presidential Decree 554/99 art. 38, the drawings are
drawn up on a scale of at least twice that of the final project, or in any case
in such a way as to allow the performer a reliable interpretation and
execution of the works in all their elements.
The graphic elaborations of an executive project include:
the drawings including all the graphic drawings of the final project;
the drawings which are necessary for the execution of the works on
the basis of the results, studies and investigations carried out during
the executive design phase;
drawing of all the construction details;
drawings illustrating the detailed methods of execution;
drawings needed to define the dimensional, performance and
assembly characteristics of the prefabricated components.
The construction design of the structures, according to Presidential Decree
554/99 art. 39 must include:
the graphic drawings of the whole structure (Carpentry, profiles and
sections) on a scale of not less than 1:50;
detailed graphic works on a scale of at least 1:10.
132
Below are some details of the graphic drawings of the executive project of
the structures installed on the Moroccan line. Respectively there are 2
details on the joints and some details about the reinforced concrete plinth,
in particular about the positioning of the metal plates on the plinth for the
subsequent positioning of the columns, the details about the plates
themselves and other details.
Figure 83: Joint detail nยฐ1 of executive project drawing
Figure 84: Example of Plinth details of an executive project drawing
133
Figure 85: Joint detail nยฐ2 of executive project drawing
5.2.3 Maintenance plan
The maintenance plan of the structures is the document that serves to
forecast, plan and program the maintenance activity. The aim of the
maintenance plan is to assure the functionality and quality features of the
structures over their nominal life (as defined by the design) as well as the
efficiency and economic value of it.
The user and maintenance manuals represent the tools with which the user
relates to the property, avoiding abnormal behavior that may damage or
compromise its durability and characteristics. Those manuals are also
consulted by maintainers who will use methods that are more suitable for a
management that combines economic efficiency and durability of structure.
Manuals define the procedures for collecting and recording information as
well as the actions necessary to set up the maintenance plan and to organize
the maintenance service efficiently, both technically and economically.
The user manual sets up a method of inspection of the artifacts that identifies
on the basis of the requirements set by the designer during the drafting of the
134
project. In this manual are presented a series of faults that can affect the
durability of the structure and for which a maintenance intervention could
represent lengthening of the useful life and maintenance of the asset value.
The maintenance manual, on the other hand, represents the tool for the
subjects having the task of managing the asset to be able on planning the
activities. In fact, in this elaborate there are information based on the forecast
of the maintenance interventions whose frequency is presumed, the
indicative cost indexes and the medium and long-term implementation
strategies.
The maintenance plan is organized in relation to the art. 40 of the LLPP
regulation, in:
User manual;
Maintenance manual;
Maintenance program, organized in:
o The performance sub-program, which considers the services
provided by the structure and its parts during its life cycle.
o The control sub-program, which defines the program of checks
and controls in order to detect the performance level
(qualitative and quantitative) in the subsequent moments of the
asset's life.
o The maintenance sub-program, which reports the different
maintenance interventions in order to provide the information
for a correct conservation of the asset.
These instruments, in accordance with the UNI 10874 standard, are needed
to achieve the following objectives:
135
Technical-functional objectives:
o Establish a system for collecting "basic information" and
updating it with "return information" following the
interventions allowing through the implementation and
constant updating of the "information system", to know and
maintain correctly the building and its parts;
o Allow the identification of the most appropriate maintenance
strategies in relation to the characteristics of the structure and
to the more general property management policy;
o Instruct technical operators on inspection and maintenance
operations to be carried out, favoring the correct and efficient
execution of the interventions;
o Instruct users on the correct use of the building and its parts on
any minor maintenance operations they can perform directly;
on the correct interpretation of the indicators of a fault or
malfunction state and on the procedures for its reporting to the
competent maintenance structures;
o Define the instructions and procedures to check the quality of
the maintenance service.
Economic objectives:
o Optimizing the use of the structure and extending its life
cycle by carrying out targeted maintenance operations;
5.2.3.1 User manual
The structural components of the structure object of the project are listed with
a description, their function and their correct use.
136
The structures that are the object of this thesis are the signal cantilever
bridges and portals for railway signaling, therefore the structural units will
be:
For simple signal cantilever bridges, we have:
โข Reinforced concrete plinth
o Description: Structural element in reinforced cement
conglomerate with horizontal or sub-horizontal surface
development with surfaces in contact with the ground or
concrete slab.
o Function: Distribution of the loads of the structure on the
ground.
o Proper use: the plinth is designed to withstand the design loads
of the elevated structure. It is advisable that the laying plan in
a foundation is all at the same level.
โข Steel column
o Description: Structural element in steel with vertical or sub-
vertical linear development.
o Function: Support beams.
o Proper use: The column is designed to withstand the project
loads transmitted by the beams. The integrity and functionality
must not be compromised and a periodic check of the degree of
wear is necessary with the simultaneous recognition of any
anomalies.
โข Steel beam
o Description: Structural elements in steel with horizontal or sub-
horizontal linear development.
137
o Function: Support for railway signal cages.
o Proper use: The steel beams are designed to withstand the
project loads acting on them or transmitted by the elements
connected to them and their integrity and functionality must
not be compromised. It is necessary to periodically check the
degree of wear with the simultaneous recognition of any
anomalies.
In the case of T-shaped cantilevers bridges, there will be 2 cantilevers and
therefore 2 beams whose description, functionality and mode of use coincide.
For simple portals or with 1 or 2 cantilevers, the situation is similar since the
components are the same and therefore the mode of use and functionality are
equal to the ones referred to the cantilever bridges.
5.2.3.2 Maintenance Manual
Reinforced concrete plinth
The minimum level of performance for the reinforced concrete plinth is the
guarantee that the performance specifications indicated in the structural
design are respected.
Abnormalities found in the foundation plinths:
Subsidence: due to different causes and sometimes with
manifestations of the lowering of the foundation's laying plan.
138
Figure 86: Schematic representation for plinth subsidence
Deformations and displacements: due to external causes that alter
the normal configuration of the element.
Detachment: disaggregation and detachment of significant parts of
the material that can also occur through the expulsion of
prefabricated elements.
โข Exposure of reinforcing steel: detachment of parts of concrete
(concrete cover) and relative exposure of the steel rods to corrosion
phenomena due to the action of atmospheric agents.
โข Cracks: degradation noticeable by the formation of continuity
solutions of the material and which may involve the reciprocal
displacement of the parts.
โข Not perpendicularity of the manufacture: due to failures or events
of a different nature.
โข Moisture penetration: appearance of moisture spots due to the
absorption of water.
139
Figure 87: Example of moisture penetration
The image above shows the typical white efflorescence, consisting of sodium,
potassium, calcium and magnesium sulfates that appear on the concrete due
to moisture. The intervention methods are varied and regulated by the UNI
EN 1504 standard, include:
o Hydrophobic impregnation: treatment of concrete to obtain a
water-repellent surface
o Fluoro-carbonic impregnation: performs the same function as
hydrophobic impregnation while maintaining the breathability of
concrete.
o Impregnation: treatment of concrete aimed at reducing the
porosity of the surface and reinforcing it. Pores and capillarity are
partially or totally filled, this treatment generally produces a thin,
discontinuous film on the surface of the concrete.
o Coating: treatment aimed at obtaining a continuous protective
layer on the surface, with thickness ranging from 0.1 mm to 5.00
mm. The used binders are, for example, organic polymers, organic
polymers with cement as filler or hydraulic cement modified with
polymeric latex.
140
โข Swelling: variation of the shape of the concrete surface affecting the entire
thickness of the material. It is recognizable being given by the typical
"bubble" trend combined with the action of gravity.
Figure 88: Example of cracking, detachment of concrete and rust formation on reinforcement steel
In the image above we can see the cracking and the detachment of pieces of
concrete, in particular the total fall of the concrete cover with a consequent
exposure of the reinforcement rods which due to the action of atmospheric
agents led to the formation of rust.
Controls:
For this type of structures, the controls are set with an annual frequency
performed by specialized operators. The control procedure is visual and it is
supplemented by any non-destructive tests.
141
Steel beams and columns:
As for the reinforced concrete plinth, the beams and columns must ensure
that the performance specifications indicated in the structural design are
respected.
Abnormalities found in beams and columns in steel:
โข Bubbles or cracks: they may occur in the surface protective layer
with danger of corrosion and rust formation.
o Causes: action of atmospheric agents and environmental
factors, impacts or minimal external mechanical stresses; loss
of adhesion of the protective layer;
o Effect: exposure of the metallic element to the corrosive agents
and to the formation of rust;
o Evaluation: moderate;
o Required resources: anti-rust and / or passivating products,
paints, manual equipment, specific treatments;
o Performer: specialized company;
Corrosion or presence of rust: presence of areas corroded by rust,
extensive or localized even at joints and junction elements.
o Causes: loss of protective and/or passive layers, exposure to
atmospheric agents and environmental factors, presence of
chemical agents;
o Effect: reduction of the thicknesses of the various parts of the
element, loss of stability and resistance of the structural
element;
o Evaluation: serious
142
o Required resources: anti-rust products, passivating agents,
paints, products and/or specific treatments for rust removal,
manual equipment;
o Performer: specialized company.
โข Deformations and distortions: presence of evident and excessive
geometrical and shape variations of the structural element.
o Causes: excessive deformations and distortions occur when the
stress to which the structural element is subjected exceeds the
corresponding resistance of the material;
o Effect: loss of stability and resistance of the structural element
o Evaluation: serious;
o Required resources: new components, reinforcing elements,
provisional works;
o Performer: specialized company.
โข Local buckling: local instability phenomenon that can occur in the
metal sheets constituting a structural steel element.
o Causes: concentrated loads, changing of the load conditions;
o Effect: loss of stability and load bearing capacity of the
structural element;
o Evaluation: serious;
o Required resources: reinforcing elements, stiffeners, new
components, welding equipment in place
o Performer: specialized company
โข Tightening of jointed elements: loss of clamping force in the bolts
joining the steel elements.
o Causes: incorrect installation of jointed elements, change of
loading conditions, external causes;
143
o Effect: loss of strength of the joint and therefore loss of stability
of the structural element;
o Evaluation: serious;
o Required resources: manual equipment, special equipment,
torque wrench
o Performer: specialized company
โข Fireproof treatments: loss of protection and/or fire-retardant
coatings
o Causes: atmospheric agents and external environmental
factors, deterioration of coatings, minimal external mechanical
stresses
o Effect: loss of protection against high temperatures leading to
considerable deformations and therefore the possible collapse
of structural elements
o Evaluation: serious
o Required resources: fireproof products, manual equipment,
specific treatments
o Performer: specialized company
Controls:
For this type of structures, the controls are set with an annual frequency
performed by specialized operators. The control procedure is visual and
supplemented by any non-destructive tests.
144
5.2.3.3 Maintenance schedule
The outcome of each inspection is the subject of a specific report to be kept
together with the related technical documentation. At the end of each
inspection, the technician in charge, if necessary, indicates any maintenance
operations to be carried out and express a summary judgment on the state of
the structure.
145
CHAPTER 6: PRODUCTION AND FACTORY
ACCEPTANCE OF STEEL STRUCTURAL ELEMENTS
6.1 Processes for production of structural steel
6.1.1 Cast iron transformation process:
Steel is a metal alloy, meaning that there are dispersions of a solid into
another solid. There are:
โข Solvent: base metal (metal material present in greater quantity)
โข Solute: alloying metal (metal or non-metal material present in smaller
quantities and added to modify or improve the properties of the base
metal.)
Metals are polycrystalline solids, i.e. they are aggregates of many crystals
called grains and whose dimensions depend mainly on the cooling rate and
heat treatments. During the solidification of a liquid metal, the "crystalline
grains" are gradually formed throughout the mass.
Steel is a metal alloy, in particular it is a Fe-C alloy, in which carbon can be
present in the combined state in the form of iron carbide Fe3C (cementite), or
in pure form as graphite.
Depending on the percentage present in the alloy, ferrous materials are
classified as follows:
โข Iron, with C <0.008%
โข Steel, with C = 0.008 - 2.06%
146
โข Cast iron, with C = 2.06 - 6.67%
The physical, mechanical and technological properties of these alloys depend
essentially on the carbon content (and the undergone heat treatment). The
increase in the percentage of carbon in the alloy causes:
โข Increased tensile strength (capacity of the material withstands normal
axial traction stresses)
โข Increase in hardness (resistance to plastic deformation)
โข Increase in fusibility (property of a material to melt at certain
temperatures)
โข Decrease in resilience (ability of a material to absorb elastic
deformation energy)
โข Decreased lengthening
โข Reduction of weldability
โข Reduction of forgeability (ability of a metallic material to be plastically
deformed when hot).
Cast iron can be of 2 types:
โข Pig iron: obtained from the blast furnace and contains high
percentages of carbon (4-6%)
โข Second cast iron: obtained by re-casting, in a special oven, the cast iron,
with the addition of scrap iron and other elements. Here the types of
second cast irons:
o White cast iron: carbon is in the form of Cementite Fe3C
o Lamellar cast iron: carbon is in the form of lamellar graphite
147
o Spheroidal cast iron: carbon is in the form of spheroidal
graphite
The transformation process from cast iron to steel is called cast iron
conversion, in which the carbon content of the cast iron is reduced to obtain
the desired carbon content: decarburization of the cast iron.
In order to obtain the steel with the desired characteristics, in addition to the
reduction of the carbon content, the impurities are reduced and the
percentages of the alloying (silicon, phosphorus, sulfur, oxygen and other
gases) are modified with correction or refining operations. The
decarburization of the cast iron takes place in special ovens called
"converters", by means of a stream of compressed air that passes through the
liquid mass.
The first used converters include the Bessemer and the Thomas. Due to the
speed of the process and the presence of nitrogen (added in by the air blown)
those converters provide steel of poor quality. On the other hand, the steel
produced with the L.D converter (Linzer Dusenverfahren) or electric
furnaces is of higher quality.
Bessemer and Thomas converter
It consists of a pear-shaped receptacle, internally lined with refractory
materials and revolving around a central pivot, the difference between the
Bessemer converter and Thomas is in the type of coating: acid type in the first
(silica bricks) and basic type in the second (magnesia bricks).
The converter is loaded with liquid cast iron in a horizontal position and then
brought back to a vertical position, during this operation air under pressure
148
is introduced through holes in the bottom. The oxygen contained in the air
burns the carbon in the cast iron which gradually turns into steel.
Figure 89: Bessemer converter
L.D. Converter
The acronym L.D indicating Linzer Dusenverfahren, stands for "process with
Linz spear". A long "spear" feeds pure oxygen into the converter containing:
โข Liquid cast iron (70%)
โข Iron scrap (for 30%)
โข Lime
The exothermic reaction would bring the oven temperature to 2000 ยฐ C: this
is why ferrous scrap is introduced in fact it absorbs heat and lowers the oven
temperature to 1650 ยฐC. This converter produces high quality steels without
sulfur and little percentages of phosphorus and oxygen; they have excellent
mechanical and technological characteristics, more than 75% of the steel is in
fact manufactured with this method.
149
Figure 90: L.D converter
Electric furnace:
Commonly called โelectric arc furnaceโ since graphite electrodes are used
and after the current flows through them, they create an electric arc. The
electric arc can snap between the 2 electrodes or between the electrode and
the metallic bath creating an environment suitable for consuming excess
carbon. The high temperatures reached and the lack of chemical interference
due to combustion makes possible to produce steel with a low sulfur and
phosphorus content, as well as to treat cast iron, and is therefore suitable for
the manufacture of special steels starting from an already refined steel.
Figure 91: Electric furnace
150
6.1.2 Steel rolling
The steel produced is marketed in the form of semi-finished products
obtained through the rolling process. Rolling is carried out directly at the end
of the continuous casting of the steel coming from the furnace or on the
ingots.
Laminates are subdivided in:
โข Plates (thickness โฅ 6 mm)
โข Sheets (thickness <6 mm)
The first rolling is carried out hot in order to change the melt microstructure
into a finer and more regular grain for subsequent rolling. The purpose of the
first rolling is also to dimensionally uniform the element and to reduce its
porosity thus increasing its ductility. Small diameter rollers tend to deform
the surface more and put it in compression, while with large diameter rollers,
friction limits the deformation of the surface and the interior deforms more
and results in a compression state.
Figure 92: Steel rolling
151
After the first rolling, are produced:
โข Blooms: with a square section from which the beams of various
sections or rails will be produced.
โข Slabs: with a rectangular section and that will proceed to further
rolling procedures to produce laminates such as plates.
โข Billets: smaller, square or round to be used for subsequent drawing.
The following diagram shows the general scheme of the rolling processes:
Figure 93: General scheme of rolling processes
6.1.3 Rolling defects:
Surface and structural defects may occur during the rolling process.
152
Surface defects may derive from inclusions in the material of oxide, dirt
and/or other scales. Defects on the surface of the laminate can also occur as
result of the pre-rolling processes. In hot rolling, the oxides are removed in
advance with a torch treatment.
Structural defects, on the other hand, distort or compromise the integrity of
the laminate. Here are listed the main structural defects resulting from rolling
processes:
a) Undulations on the edge
b) Zippered cracks in the center
c) Cracks at the edge
d) Alligatoring
Figure 94: Rolling defects
6.2 Regulatory framework for the production of hot laminates for
structural steel
The standard that defines steel products by classifying them according to
shape, size, appearance and surface condition is UNI EN 10079. In addition
153
to the finished products, this standard also includes a series of "semi-
finished" products from rolling mills.
The standard that defines the technical conditions for the supply of hot-rolled
(long and flat) products for structural use is UNI EN 10025. Hot-rolled long
steel products are commonly divided on the market into 2 macro-categories:
โข Beams: profiles whose straight section resembles that of the letters H,
I, and U and whose core has a height equal to or greater than 80 mm.
โข Merchant Laminates: this category ranges between bars (flat, convex,
round, polygonal, etc. and not intended for cement reinforcement),
angles and profiles that include profiles with L, T, I, U, H section
(completely identical to the beams except for the height of the core
which is less than 80 mm).
The materials and products for structural use must be:
โข Univocally identified by the manufacturer
โข Qualified under the responsibility of the manufacturer
โข Accepted by the construction manager
For the typology of structures covered by this thesis, are used materials and
products for which European standards are available and their use on
structures is permitted only if accompanied by the:
โข Declaration of performance: describes the performance of construction
products in relation to the essential characteristics of these products, in
accordance with the harmonized technical specifications. It contains
information such as the reference of the product-type for which the
154
declaration of performance is drawn up, the system or systems of assessment
and verification of constancy of performance, the intended uses of the
construction product and the list of essential characteristics as set out in the
harmonized technical specification for the declared intended use or uses.
This declaration is drawn up according to a model in Annex III of EU
Regulation 305/2011.
โข CE marking: It is affixed only to construction products for which the
manufacturer has drawn up the declaration of performance in accordance
with EU regulation 305/2011 and is the only marking attesting the conformity
of the construction product to the performance declared in relation to the
essential characteristics in accordance with the harmonized technical
specifications in the UNI EN 1090-1: 2012 standard.
In drawing up the declaration of performance and the qualification
documentation, the manufacturer assumes responsibility for the conformity
of the construction product with the declared performances.
6.2.1 Controls on steels (for concrete reinforcement or for metal structures):
The controls that are mandatory for each structural element are:
โข Control in the production plant, to be carried out on the production
lots10
โข In processing centers
โข Acceptance on site
10 It refers to continuous production, ordered chronologically by affixing marks to the finished product. A
production batch must have homogeneous nominal values (dimensional, mechanical formation) and can be between 30 and 120 tons.
155
Each type of steel destined for structural use, therefore both beams and
reinforcing steel for concrete, must be produced by means of a permanent
control system inside the plant, having to guarantee the same level of
reliability in the conformity of the finished product, regardless of the
production process.
The quality management system during the manufacturing process must
follow the provisions of the UNI EN ISO 9001 standard and certified by a
third party body that operates according to the UNI CEI EN ISO / IEC 17021-
1 standards.
The UNI EN ISO 9001 defines the minimum requirements that the quality
management system of an organization must demonstrate to satisfy in order
to guarantee the level of quality of the product. Today this standard
represents the best known international standard applicable to any
organization, regardless of the type and the economic sector to which it
belongs. This standard promotes the adoption of a process approach in the
development, implementation and improvement of the effectiveness of a
quality management system.
The UNI CEI EN ISO / IEC 17021 standard is the international standard that
defines the requirements for organizations that provide audits and
certification of management systems in general for the quality, environment
and health and safety of workers. The purpose of this standard is to ensure
that all the interested parties that the certified management systems meet the
requirements of the reference standard, substantially serves to guarantee the
credibility of the certifications.
The regulations require that each qualified product must constantly be
recognizable as regards the qualitative characteristics and traceable to the
production plant through indelible marking from which the reference of the
156
manufacturing plant11, the plant, the type of steel and its steel is
unequivocally deductible possible weldability. These marks may be made by
different systems based on their use. Markings can be carried out with the
impression on the rolling products with hot and cold procedures. The
branding is mandatory and its application methods are regulated.
6.2.2 Processing centers (or transformation centers):
The transformation centers are defined as the external plants to the
production factories or the fixed or mobile construction site, which receives
the basic elements from the steel producer and packages the structural
elements directly usable on site, ready to be installed. These centers can
receive and work only products originally qualified accompanied by the
required documentation (CE marking and declaration of performance).
These plants must be equipped with a control system (in compliance with the
UNI EN ISO 9001 standard) of the processing in order to ensure that the
processes performed there ensure compliance with the mechanical and
geometric characteristics of the products.
The products supplied on site after the intervention of a processing center
must be accompanied by documents attesting to the origin and production
processes of the element itself.
During the production process within manufacturing centers special
attention must be paid to the roll face milling, cutting, drilling and bending
processes, as well as to the welding procedures. The technical director of the
workshop must ensure that the processes adopted do not alter the original
mechanical characteristics of the material.
11 The plant refers to a production unit, with its own plants and warehouses for the finished product.
157
The checks must concern at least 1 test every 30 t of steel of the same category
coming from the same factory, even if acquired at different times, having the
foresight to take samples from different types of products or thicknesses from
time to time.
The data obtained from the experimental tests must meet the requirements
of the harmonized European standards UNI EN 10025 for the tensile and
resilience tests, as well as the UNI EN 10210-1 and UNI EN 10219-1 standards
for the chemical-physical characteristics.
6.2.3 Laboratory tests to be performed on structural steel rolled products:
For the realization of metal structures and composite structures steel must be
used in compliance with the standards UNI EN 10025-1, UNI EN 10210-1 and
UNI EN 10219-1 and must possess the CE mark.
For the declaration of services and labeling, the methods provided for by the
European standards have to be applied and in particular it will be necessary
to provide:
โข Declaration of the geometric characteristics and properties of the
material.
โข Declaration of component performance on the basis of Eurocodes.
โข Declaration based on a specific project specification.
In the processing centers, laboratory tests must be performed on the beams
produced to verify their mechanical characteristics. The values of the yield
and breaking stress must, of course, always be lower than the table limits
present in the standards and must be checked that the manufacturing
tolerances respect the limits indicated in the applicable European standards.
158
The tests are carried out by taking samples in well-defined points of the
laminated product. The tests that must be carried out on the production lots
are:
โข Chemical analysis
โข Tensile test
โข Proof of resilience
โข Hardness test
โข Microscopy
โข Surface roughness
In the tables below the indications relating to the sampling and the type of
test according to the UNI EN 10025-1 standard.
159
Figure 95: Sampling indications for testings according to UNI EN 10025-1 standard
160
Figure 96: Sampling indications for testings according to UNI EN 10025-1 standard
6.2.3.1 Chemical analysis:
The chemical analysis is performed with an emission spectrometer which
analyzes the metal by means of an electric discharge between the sample,
previously prepared by grinding, and a tungsten or silver electrode in an
inert atmosphere chamber (argon). The excitation of the specimen generates
a beam of light that purposely dispersed by a prism hits the phototubes
161
sensitive to the various bands with different wavelengths that are generated
and at each determined wavelength corresponds an element to be analyzed.
6.2.3.2 Traction test:
The tensile test consists of subjecting a steel sample having a constant section,
with a tensile load applied along its axis. The applied load must increase
gradually until the sample is broken. From this test we obtain the stress-
deformation graph characteristic of the various types of steel (see figure 65).
From the test we get:
โข Unitary breaking load (R)
โข Unitary load of deviation from proportionality (given by the ratio
between total load to yield limit and the original section of the tube
expressed in mm2)
โข Elongation (A%)
6.2.3.3 Proof of resilience
It consists in hitting with a club of known weight, one meter from its fulcrum,
a steel sample in which a notch has been made to facilitate the breaking. With
the resilience, the toughness of the steel and the bending resistance by impact
are measured. The notch on the specimen can be in a shape of a "V" or "U".
162
Figure 97: Resilience test on steel
Figure 98: Test specimens for resilience test (dimensions are indicated in mm)
The test can be performed at room temperature at 0 ยฐ C or at a temperature
below zero ยฐ C.
The results are expressed in Joule per cm2.
6.2.3.4 Hardness test
The hardness of a material is defined as its resistance to deformation, as its
resistance to being damaged by another harder material. The hardness values
163
obtained depend on the type of test to which the specimens have been placed,
there are 3 methods:
โข Brinell hardness (Rockwell): An indenter (hard metal ball with diameter
D) is forced into the surface of a test tube and the diameter of the
impression d left on the surface after releasing the load F is measured.
Brinell hardness represents the quotient between the applied load and
the area of the spherical surface of the impression.
Figure 99: Brinell hardness test
โข Vickers hardness: A diamond penetrator having the shape of a straight
pyramid with a square base with a vertex angle between opposite
specified faces, is made to penetrate within the surface of a tube; then
the length of the diagonal of the impression left on the surface is
measured after removal of the test load, F.
6.2.3.5 Optical microscopy
Optical microscopy is a fundamental method for the structural analysis of
materials. The possibility of enlarging a section of the suitably treated
material allows to investigate the thermal history of the preparation from the
moment of its solidification in the foundry. This test gives precious and
almost always complete information about the use of the material, as it
determines the mechanical resistance, the corrosion resistance and the wear
164
of the material itself. The technique is particularly effective for the study of
heat treatment anomalies, for the evaluation of inclusions, for the
interpretation of breakages and for the evaluation of the welding and
coatings. The results of these tests must be interpreted in order to be able to
issue a diagnosis on the analyzed material. From the images are extracted
information such as the percentage of presence of the various phases
constituting the material, the distribution, the circularity and the dimensional
degree of the graphite spheroids.
6.2.3.6 Roughness
The roughness is measured using tools called roughness meters. Roughness
is a property of the surface of a body, consisting of geometric micro-
imperfections normally present on the surface or even resulting from
mechanical processing. The roughness measurement procedure consists in
recording the profile of the surface obtained along a determined
measurement line (or scan).
6.2.4 Checks of bolted joints
The connecting elements must comply with the provisions contained in the
following standards:
โข UNI EN ISO 3506-1: 2010 for screws (item "a" in the figure below)
โข UNI EN ISO 3506-2-2010 for nuts (element "b" of the figure below)
โข UNI EN ISO 3506-3: 2010 for headless screws and similar parts not subject
to tension (element "c" of the figure below)
165
Figure 100: Elements constituting a bolt
The main tests carried out in the laboratory to know the quality of the
connecting elements are:
โข Traction test on test tubes
โข Tensile test on full screw
โข Hardness test
โข Resilience on a test tube
โข Toughness of the head of screws
โข Shear test
โข Determination of the percentage elongation after rupture
โข Determination of the breaking load
โข Determination of yield strength
โข Tearing resistance
โข Check the tightening torque of the bolt
6.3 Welding process:
The welding technique allows two metal parts to be joined through the use
of heat. The localized fusion of the edges of the pieces to be joined is obtained
by the addition or not of a filler material.
The brazing procedure refers to when the base material is not melted but only
heated and the process of joining the materials is made by melting only the
filler material, having a melting temperature lower than that of the base
material.
166
A material is considered weldable when it lends itself to the realization of a
structure in which continuity is assured and that presents characteristics that
meet the required quality standards.
The welding process involves one or more types of materials, which mainly
fulfill two roles:
โข Base material: it is the material that makes up the pieces to be welded;
it can be the same for both pieces (homogeneous welding), or different
(heterogeneous). The most commonly combined metallic materials are
steel, aluminum alloys, nickel alloys and titanium alloys. The only
polymeric materials that can be welded are the thermoplastic ones.
โข Filler material: it is the material that is introduced in the form of rods,
wires or strips and deposited in the molten state between the flaps to
be joined. The filler materials are always particularly pure, so the
impurities within the molten area of a joint generally come from the
base material.
The management of the various welding and brazing procedures is based on
the choice of specific parameters for each type of process. On a general level,
in most processes it is possible to identify mainly two characteristic
parameters:
โข The specific power: represents the thermal power delivered per unit of
surface of base material, measured in W/cm2;
โข The welding speed: represents the speed of the thermal source,
measured in cm/min.
167
6.3.1 Types of welding:
At the macroscopic level, the processes that have been most developed in the
industrial field belong to the fusion welding group.
These processes use heat, generated in various ways, to merge the base
material. The most commonly used processes can be classified in the
following sub-groups:
โข Electric arc: Arc welding refers to a group of processes that exploits
the electric arc generated between two electrodes. The โarcโ can be
obtained using:
o A fusible electrode;
o A refractory electrode, that is not fusible;
In the first case, the melting electrode, supplies the filler metal. On the other
hand, when non-fusible electrodes are used at the arc temperature, the filler
material (if necessary) is supplied separately, using rods or wires. The
fundamental element to obtain an electric arc is the current. It is possible to
supply the arc both with direct current (DC) and with alternating current
(AC). The choice between DC and AC depends on the type of process used
and on the material to be welded.
The main types of electric arc welding are:
Manual Metal Arc welding (MMA)
Submerged arc welding (SAW)
168
Continuous wire under gaseous protection (MIG /
MAG)
Under gaseous protection and with an non fusible
electrode, the so called Tungsten Inert gas (TIG)
โข Resistance welding: It is a joining process without filler metal, in which the
heat required to melt the edges to be welded is provided by the resistance
opposed to the passage of an electric current through the area to be joined.
โข Oxyacetylene: Oxyacetylene welding is a process that uses, as a heat source,
the flame resulting from the combustion of acetylene (C2H2) with oxygen
(O2).
โข Concentrated energy: This group includes the processes that use energy
bundles that can concentrate very high powers on the piece, ranging from
several thousand to several million watts per square millimeter of surface.
6.3.2 Welding techniques:
The welding process can be manual, semi-automatic, automatic or robotic,
depending on the equipment and mode of execution.
โข Manual: In the manual process, the welder manually adjusts the
equipment and moves the electrode or heat source (electrode coated
and oxyacetylene welding);
โข Automatic: a device feeds the electrode or the beam generating
source, to keep it at a suitable distance from the piece and move it
169
along the welding line (submerged arc welding, with electric arc
under MIG / MAG gas protection and TIG, with concentrated energy).
โข Semi-automatic: The semi-automatic process is a middle way between
the two previous ones: a device feeds the electrode wire or delivers
the current while keeping the other parameters constant, while the
operator has the task of moving the electrode along the line welding
(electric arc processes under MIG / MAG and TIG gaseous protection).
โข Robotic: If the operation is carried out using an industrial robot or a
programmable manipulator, it is defined a robotic welding procedure.
It is mainly used for electric arc welding under MIG / MAG and TIG
gas protection and for laser welding, but also in the final assembly of
cars for the resistance union of the bodywork.
6.3.3 Regulatory framework for welding processes of structural steel elements:
For the welding of structural steel elements, reference is made to the UNI EN
ISO 4063: 2011 standard for electric arc welding, while for other types of
welding, theoretical and experimental supporting documentation must be
provided.
For each welding technique, operators must possess qualifications:
โข The welders in semi-automatic and manual processes must be
qualified according to the UNI EN ISO 9606-1-2017 standard by a third
party that can choose the manufacturer according to criteria of
competence and independence. The Italian legislation also requires in
170
addition to what is required by European legislation that welders who
perform T-joints with corner cords must be specifically qualified and
can not be qualified only by the execution of head-head joints.
โข The operators of automatic or robotic procedures must instead be
certified according to the UNI EN ISO 14732: 2013 standard.
All welding processes must instead be qualified by WPQR (qualification of
welding procedures) according to the UNI EN ISO 15614-1: 2017 standard.
The welding processes carried out must be accompanied by documentation
that certifies them in the molten area and in the thermal zone and providing
the following characteristics:
โข Ductility
โข Yield
โข Toughness12
6.4 Factory acceptance of the structure
The factory acceptance of a structure consists of a series of processes and
checks on the structures in order to ensure that what is produced by the
factory itself complies with the functional specifications of the project.
As seen in the previous paragraphs, all steel elements must pass a series of
checks before they can be put into use.
Factories that produce metal carpentry and subsequently manufacture the
structures can only process steels from production plants that meet all quality
12 The ability of a material to absorb energy and to deform plastically before rupture is defined as the area below the stress/deformation curve of a tensile test.
171
criteria according to UNI EN 9001 and that possess a CE marking and a
Declaration of Performance.
Subsequently in the factories, once the structural elements have been rolled,
further tests are carried out in order to verify that these manufacturing
processes have not altered the properties of these materials.
The factory acceptance checks for the type of structures covered by the thesis
consist of:
Geometric checks:
Completeness of the structure: Check the presence of each single
element constituting the structure according to the executive design
and therefore the bearing structure, bolts, ladders, signal cages and
hand rails;
Verify that the individual elements of the load-bearing structure
respect the dimensions and configurations indicated in the executive
project. These elements are:
o Steel columns (also check the plate for anchoring the column to
the plinth)
o Beams:
Check the conformity of the type of profile produced with
that present in the structural design (UPN);
Check that the cuts have been made at the points indicated
in the executive project;
Check that the welds have been carried out in conformity
with the design instructions in accordance with EN ISO
23277.
172
Check the arrangement of the modules according to the
design drawing
Check that the dimensions of the non-load-bearing structural
elements are in accordance with the design drawings, these elements
are:
o Ladder
o Hand rail
o Signal cage
The last geometric check consists in verifying the compatibility of the holes
for the realization of the bolted unions.
Checks on the treatments carried out on the steels:
For this type of structure, the treatment that is performed is the
galvanization. It is necessary:
Check that the hot-dip galvanizing procedure has been carried out in
accordance with EN 1090-2;
Visual inspection to check that there are no oxidation phenomena;
Check that the thickness of the layer complies with the design
specifications.
Documentation to be requested at the time of acceptance of the structure at
the factory:
Request the CE marking certificate and the Declaration of
Performance issued by the steel production plant (and check that the
173
type of steel used for the construction of the structure coincides with
the one present in the material specifications of the executive project);
Certification of execution of welding processes according to UNI EN
ISO 4063: 2011 and verify that the welders are trained according to the
indications given in UNI EN ISO 9606-1-2017;
Manual for assembly of the structure on site.
174
CHAPTER 7: ACCEPTANCE OF THE STRUCTURE
AND CONSTRUCTION OF THE PLINTH AT THE
BUILDING SITE
This chapter describes the procedures for accepting the metal structure on
site according to Italian regulations. European standards cover the processes
of production and supply of materials, in order to ensure a common standard
for what concerns the products marketed in Europe. However, with regard
to the procedures for acceptance, sampling and subsequent performance of
laboratory tests, the national standards are referred to. In Italy, reference is
made to the technical standards for construction NTC 17-01-2018.
In the chapter will also briefly describe the procedure for the construction of
the plinth on site and the subsequent phase of assembly of the structure
arrived on site from the processing center (factory).
7.1 Acceptance of the structure materials on-site before starting the
construction
Acceptance on site of the structure materials means the acceptance of its
individual components by the site manager. The on-site acceptance checks
for these structures will therefore cover:
Steel for metal structures
Bolts
Concrete
Steel for concrete reinforcement
175
7.1.1 Steel
The acceptance procedure for the structures on building site of shipping lots
of a maximum of 30 tons must be equipped by:
o Identification mark (unalterable over time and without the
possibility of tampering)
o Different identifiers for products having different
characteristics even if manufactured in the same factory.
If these 2 elements are not present, the product is absolutely not usable on
site.
In Italy, on-site supplies of pre-welded, pre-shaped or pre-assembled
elements made by a processing center must be accompanied by a declaration
on the Transport Document of the details of the declaration of activity issued
by the Central Technical Service of the Higher Council of LL.PP with the logo
of the center itself and the attestation of the internal control tests carried out
by the technical director of the processing center.
The Site Manager must carry out checks on each type of supply at the
laboratories in accordance with art. 59 of Presidential Decree no. 380/2001.
The qualitative and quantitative validity of the on-site checks must then be
checked by the Inspector who, if not, is required to have the tests provided
for by the standard carried out and/or completed.
7.1.1.1 Steel for metal structures:
Only qualified steels with an identification mark are allowed on site, with
mandatory controls both in the processing centers and on site.
176
On-site inspections are managed by the Site Manager and consist in taking
from each supply a maximum of 30 tons of at least 3 samples, of which, one
is on the maximum thickness and the other one is on the minimum thickness
as shown in the figure (X - chapter 6). From these tests will be obtained the
test tubes for the tests of:
o Traction
o Resilience
o Chemical composition
If the outcome of the testing is negative, the standards require tests to be
carried out on a further 10 tests to verify the acceptance of the tests before
refusing the supply.
All samples must be taken in the presence of the site manager or a trusted
technician.
Samples must be labelled and accompanied by explicit documents, the
request for testing signed by the site manager must be delivered to the
laboratory by the site manager himself.
For supplies coming from a processing center (as is generally the case for the
type of metal structure in question), the site manager must make sure that
the center meets all the requirements (chapter 6) and if adequate samples to
be tested are not delivered to the worksite, he may himself go to the
processing center to carry out the relevant checks and arrange for samples to
be taken. In this case, the sampling is carried out by the technical director of
the processing center.
The site manager must ensure, by means of indelible markings and labels,
that the samples to be tested in the laboratories are actually those taken by
177
him and must sign the related request for tests and deliver the samples
personally or by a technician of his choice.
7.1.1.2 Steel for concrete reinforcement:
Acceptance checks on site for concrete reinforcing steel are mandatory and
must be carried out by the site manager within 30 days of delivery of the
material and in any case before it is put into use.
Acceptance checks are carried out on each shipment lot of a maximum of 30
tons from the same factory and consist of 3 pieces of the same diameter and
of 3 with different diameters. The following tests shall be carried out on these
samples:
o Traction
o Elongation and bending
o Adherence
o Chemical composition
If the identification mark and accompanying documentation do not show
that the material comes from the same establishment, checks are extended to
all batches from other plants.
The strength, elongation and bending values of each sample of the same
diameter must be comprised in the values listed in the standards. If the value
of the results of the tests carried out on one of the samples obtained from the
three lengths is lower than the prescribed value, an additional sample shall
be taken.
If the average of the previous two and the new one does not meet the
acceptance criteria, 10 additional samples must be taken from different
178
products in the presence of the manufacturer, who may also be present
during the performing of the tests at the laboratory.
If the average of the 10 results is not greater than the characteristic value and
the individual values are not included between the minimum and maximum
value of the values indicated in the standard, the shipment lot must be
rejected, with notification to the Central Technical Service by the site
manager.
Sampling must be carried out by the site manager (or by a technician of his
choice) who will label the samples and draw up and sign a specific sampling
report.
For supplies (shaped or assembled elements) coming from the processing
centers, the site manager checks the requirements and, if adequate samples
to be subjected to laboratory tests are not supplied to the site, he can go to the
same plant, carry out the relative checks and order the collection of samples
(carried out by the technical manager of the processing center) to be sent to
the laboratory. In both cases:
The request for tests to the Laboratory, as per art. 59 of Presidential Decree
no. 380/2001, must be signed by the Works Manager and must contain all
useful information on the structures involved in the sampling.
The samples must be delivered to the testing laboratory by the site manager
or by a technician of his choice.
The test certificates must show the identification mark recorded by the
laboratory on the samples tested.
7.1.1.3 Bolts
The acceptance of the bolts on site must also be carried out by the site
manager. 3 samples are taken for every 1500 pieces. The number of samples,
179
taken and tested within the same work, may not be less than three. For works
for which the use of a quantity of pieces not exceeding 100 is envisaged, the
number of samples to be taken is identified by the site manager. The tests are
the same as those carried out in chapter 6, regarding the operations of
acceptance of the bolts in the factory.
7.1.2 Concrete
The acceptance check of the concrete is made by taking a quantity of concrete
from the mix when it is poured in place.
A quantity is taken to allow the packaging of 2 samples that will be subjected
to compression resistance tests, providing with their average the
"Withdrawal Resistance" used for the associated type A and type B checks.
These samples must be collected in the presence of the site manager, who
will identify the samples by means of indelible initials and labels and will
draw up and sign the appropriate sampling report.
The request for tests to the laboratory must be signed by the site manager
and must contain precise information on the position in the facilities affected
by each sampling and must report the details of the "Record of Withdrawal",
the certification issued by the laboratory must refer to this Record.
In this case too, the samples must be delivered to the laboratory by the site
manager or by a technician of his choice.
The Site manager is obligated to carry out systematic checks during
construction to verify the conformity of the characteristics of the concrete
used with respect to that established by the project and experimentally
verified during the preliminary assessment: he must in any case prescribe
further samples compared to the minimum prescribed whenever changes in
the quality of the concrete should occur.
180
These acceptance checks, performed on homogeneous mixtures at the
Laboratories referred to in art. 59 of Presidential Decree 380/2001, are
conducted on the basis of the quantity of homogeneous concrete concerned.
Type A control:
This control refers to a quantity of homogeneous concrete mixture of less
than 300 m3 used in structural works. Each control is represented by a
maximum sampling every 100 m3 and for each day of casting.
For constructions with less than 100 m3 of homogeneous mixture jet (as in the
case of the structures subject to the thesis), for which it is allowed to derogate
from the obligation of daily sampling, the number of samples can be reduced
to a minimum of 3.
The check is successful if the following inequalities are verified:
๐ 1 โฅ ๐ ๐๐ โ 3,5 (๐/๐๐2)
๐ ๐ โฅ ๐ ๐๐ + 3,5 (๐/๐๐2)
where:
R1 the minimum value of the withdrawals
Rm Average resistance of samples
Rck Design characteristic strength (or concrete strength class)
For this type of control, the circular explaining the standard specifies that, if
the number of concrete samples delivered to the laboratory is less than six
181
per homogeneous mixture, the laboratory, having conducted the tests, issues
the required certification but must inform the workโs director that the
number of samples taken is not sufficient to perform the type A control
provided for in the Ministerial Decree 17-01-2018.
Type B control:
This type of statistical acceptance check is mandatory for quantities of
homogeneous mixture greater than 1500 m3 used in structural works and is
followed with a frequency of one check every 1550 m3. For the structures
under investigation, this check is therefore not necessary.
The standard specifies that the work or part of the work that does not comply
with the acceptance checks cannot be accepted until the conformity has been
definitively removed by the manufacturer, who must check the
characteristics of the concrete put in place by using other means of
investigation as prescribed by the site manager and in accordance with what
is indicated in the control of the strengths of the concrete in place.
If the additional checks confirm the results obtained, a theoretical and/or
experimental safety check of the structure affected by the quantity of non-
conforming concrete must be performed on the basis of the reduced strength
of the concrete.
If this is not possible, or if the results of this investigation are not satisfactory,
the work can be de-qualified, a consolidation work can be executed or the
work can be demolished.
Acceptance checks are mandatory and the inspector is required to check their
validity, quality and quantity; if this is not the case, the inspector is required
to have tests performed that certify the characteristics of the concrete,
182
following the same procedure that is applied when the limits set by the
"acceptance checks" are not respected.
In-situ resistance checks:
When the "acceptance tests" are not satisfactory or when the inspector deems
it appropriate, or when it is necessary to evaluate "a posteriori" the properties
of a concrete already in place and hardened, it is possible to carry out
resistance tests on the concrete through a series of both destructive and non-
destructive tests: these tests, however, cannot replace the acceptance tests.
First of all, by means of non-destructive tests such as SONREB (combined
sclerometer-ultrasound method), zones of structures with homogeneous
resistance are identified, delimited and then, by means of "core drilling",
cylindrical samples are taken in order to obtain a reliable estimate of the
resistance of a test area with at least 3 samples (core samples) with a diameter
between 75 and 150 mm (preferably 100 mm) from which cylindrical samples
with twice the diameter height are obtained.
Properly prepared (test surfaces ground with diamond discs and parallel to
each other and orthogonal to the directions), the specimens are subjected to
a compressive rupture test to determine the average value of the structural
cylindrical resistance in place, which must be at least 85% of the design
(average acceptable value, compared to the design strength and potential
resistance of samples taken in the casting phase and matured in the
laboratory under normalized conditions of temperature and humidity).
For concrete class Rck = 30 N/mm2 (C25/30)
Circular no. 617/2009 states:
183
o Obtained the average value of the cylindrical resistance of the
core samples fcm
o Considering that:
๐๐๐ = ๐๐๐ + 8 (๐/๐๐2)
where:
๐๐๐ = 0,83. ๐ ๐๐ per core sample having h = 2D
Must result an average value of the cylindrical resistance in place
๐๐๐๐๐๐.๐ โฅ 0,85. ๐๐๐ (๐/๐๐2)
๐๐๐๐๐๐.๐ โฅ 0,85. (0,83๐ ๐๐ + 8) (๐/๐๐2)
๐๐๐๐๐๐.๐ โฅ 27,96 (๐/๐๐2)
In the case of cylindrical core samples with a height equal to the
diameter fck = Rck
7.2 Construction of the plinth on site
Once the materials have been accepted on site, the structure is put into
operation. The plinth is made and then the steel structure is mounted on it.
The plinth is a continuous surface foundation and is used when the
structures in elevation are of the frame type. They are placed with the center
of gravity on the vertical resultant of the forces transmitted to allow the
uniform distribution of the loads of the structure to the laying surface. The
184
function of the plinth is to distribute the load over a larger footprint to
prevent the columns from sinking into the ground.
From a geometric point of view, the plinths can be divided into:
High
Short
Deformable
Rigid
From a mechanical point of view, depending on the choice, the behavior of
the plinth changes, both its interaction with the ground below and therefore
the distribution of tensions.
In general, the various categories of plinths are divided into:
๐ โฅ 4โ great thinness
โ
2โค ๐ โค 4โ medium thinness
๐ โคโ
2 small thinness
Plinths, but more generally foundations, must not lay directly on the ground
because the reinforcements could oxidize. A layer of concrete with a low
cement content, called "lean concrete", is realized, with a thickness varying
from 5 to 10 cm, whose task is to provide the leveled base of support to the
foundation structures and to avoid the direct contact of the reinforcement
steel with the ground, as well as the permeation of rising water.
The process for the realization of the plinth begins with the excavation in the
grounding the positioning of the formwork, where the reinforcing irons
185
(including coach screws) will be positioned first and then followed by the
casting of concrete.
Before casting, the formwork must be cleaned inside and preferably covered
with a layer of release agent to allow it to detach from the concrete once it
has hardened, and the formwork walls must be perfectly sealed.
It is also important to ensure that the walls of the formwork do not open
under the pressure of the concrete, which must maintain its position and
shape unchanged.
The design of the reinforcement cage and the positioning of the
reinforcements must be deduced from the design documents supplied by the
designer and it is important that during the assembly phase of the
reinforcements and formwork's the spacers are prepared. Spacers are special
elements that separate the reinforcements from the walls of the formworks,
keeping them in position during the casting and ensuring the correct
execution of the iron cover. It is also advisable to make sure that the steel rods
are closely linked to each other to prevent movement during the casting.
Concrete can be transferred into the formwork directly by means of slides or
pipes, or with the aid of a motor pump that allows obstacles or differences in
level to be overcome. To make a good casting, the formwork must be filled
slowly, thus avoiding the formation of air bubbles in the material.
During the casting process, the concrete introduced into the formwork
always contains a quantity of embedded air, which must be absolutely
eliminated in order to obtain a durable and high-quality mix. This is achieved
by compacting or constipation, which is normally carried out by mechanical
means.
186
This can be done by means of a vibrator, i.e. by immersing a tapered element
called a needle in the concrete, which produces a vibration of the material,
making it easier for air bubbles to escape, or by means of a vibration
transmitted to the concrete by the formworks.
Figure 101: Excavation scheme forformworks
Formworks can be of different types and consist of different materials, such
as steel, plastic, wood and resins and new materials.
The profiles of the columns, in the lower part of support to the plinth, are
welded to a horizontal perforated plate that acts as a load distribution plate
that can be stiffened by lateral fins as shown in the image below.
187
Figure 102: Plinth-column coupling detail
The column is fixed with a series of coach screws that are drowned in the
concrete. The coach screws are made up of bars bent into hooks in the lower
part and threaded in the upper part emerging from the foundation and are
positioned with extreme precision before the casting by means of a
positioning bar.
Figure 103: Executive project drawing for plinth-column coupling
188
At the end, the column is positioned by bolts and washers that allow it to be
plumbed leaving the column raised by a height of about 6-8 cm from the
plinth. The structural continuity is ensured through the realization of an
integrative jet with anti-shrinkage expansive mortar.
Figure 104: Example of the introduction of anti-shrinkage expansive mortar
7.3 Assembling of the structure on-site:
Once the construction project has been submitted to the plant in charge of the
production of the structures, it will then be the task of that plant or processing
center to provide instructions for the assembly of the structures on site.
The document in which the indications are given about the steps to be
followed for the assembly of the structure, as well as the order in which they
have to be performed, is called Assembly Plan. In conjunction with the
assembly plan, a safety plan must also be drawn up with measures to prevent
accidents during assembly.
189
The assembly is carried out by the factory itself or can be hired companies
specializing in the assembly of metal structural works.
7.3.1 Analysis and assessment of possible risks
During the assembly phase of the structure, it is necessary to take preventive
measures against the risks arising from the assembly operation itself.
The assembly of metal structures for railway signaling is often conducted at
night at time intervals that vary according to line and traffic regulations, as
the power supply of the line section concerned must be cut off. Possible risks
include:
Falls from height
Blows, impacts, compressions
Slips, level falls
Heat, flames (in case of on-site welding processes)
Electricity
Noise
Shearing, crushing
Manual handling of loads
The personal protective equipment that is made available is generally:
Helmet
Safety footwear with anti-crushing toecap
Gloves
Noise protection care (earplugs or ear muffs)
Fall protection equipment
190
Eyewear
Respiratory protection masks
Protective clothing
In consideration of these risks, it is necessary to draw up a safety and accident
prevention plan.
7.3.2 Instructions for workers
The assembly work must be carried out by physically trained workers under
the guidance of an experienced technician (assembly assistant).
During the assembly work, the personnel in charge must be divided into
clearly defined tasks for which they must have received information and
training appropriate to the functions performed.
As a general rule, the assembly work involves the following activities, which
must be conducted by a sufficient number of assigned workers:
For the structures under examination, it is preferable, where
possible, to reach the point of installation by specialized
trucks in terms of costs and logistical operations, otherwise
railway wagons are used which are additionally equipped
on board with equipment for handling loads.
Pre-assembly at the foot of the work of the elements and
security systems;
Lifting of single or pre-assembled elements by means of
lifting equipment;
191
Preparation of the accident prevention arrangements on the
ground and harnessing of the pieces;
Reception, positioning and stabilization of the elements on
site;
Installation of safety guards (parapets, nets, etc.).
The following rules must be observed during assembly:
o The installation operations must be directed by a designated
person (team leader);
o For lifting, special equipment must be used with tie rods, sling
bars and tools suitable for the weight of the elements;
o Before each operation, it must be checked that the lifting
equipment is supplied with the appropriate equipment for the
type of element to be lifted;
o During all manoeuvres, the crane operator must act with the
utmost care, avoiding sudden movements or accelerations.
Each manoeuvre must be preceded by an acoustic signal;
o Elements that show anomalies in the systems for attaching to
the lifting equipment or for removing the guards on site must
be discarded;
o The anchoring devices must be installed on the individual
elements during construction or pre-assembly on the ground of
the carpentry;
o The safety devices and their accessories must be stored,
transported and handled with care to avoid their deterioration;
o Methods that reduce the risk of falling to a minimum must be
used during installation;
192
o Anchorage systems and personal fall protection equipment for
the personnel in charge of their installation must be provided
and set up during construction or pre-assembly on the ground
of the carpentry;
7.3.3 Emergency procedures
The documentation to be made available includes instructions on emergency
procedures indicating the weather conditions under which, in relation to the
activities carried out, the work must be stopped.
The maximum wind speed allowed in order not to interrupt the assembly
work must be determined on site taking into account the surface area and
weight of the elements as well as the particular type of lifting equipment
used.
As a rule, lifting equipment must not be used if the wind speed exceeds 60
km/h.
When atmospheric discharges due to storms in progress that may affect the
work area are foreseen, operations must be suspended immediately.
Any instability during the assembly phases must be promptly assessed by
the person in charge, who must arrange for reinforcement of the temporary
support instruments or, if necessary, the immediate evacuation of the danger
zone.
7.3.4 Mounting of structures
The structures are assembled with the help of equipment suitable for lifting
the structural elements. The company in charge of assembly must provide a
193
detailed list of the main equipment, such as fixed cranes, mobile cranes or
other machinery providing the routes and areas required for these machines.
It is the responsibility of the site manager or the person responsible to
provide information about the situation of the terrain on site and any other
risks of which the company in charge of assembly must be informed in order
to take the right precautions and make the appropriate logistical decisions.
Before starting the lifting operations, the operators must carry out the
following checks:
Check the lifting axes of the foundation plinth on which the
structure is to be mounted;
Check that the foundation bolts have been correctly
assembled, with regard to positioning, number, bolt circle,
bolt diameter and protrusion from the foundation, length of
threads and good flow of the washers and locking nuts;
Provide for good lubrication of the threads of the bolts and
nuts;
Check that the elevation measured on the anchor plate is
correct;
Check that the parts of the lifting equipment are working
properly.
When installing the various pieces and/or elements of the metal structures, it
is necessary to pay attention to the verticality of the column(s), to the
elevation of the laying surface and to the position in the plan so as to avoid
any demolition in the event of unacceptable installation errors.
For these structures, it is not possible to define any a priori procedure
regarding the assembly methods, as the sizes of the elements are very
194
variable and therefore also the different solutions for their transport to the
building site.
Implementing rules for bolted unions
It is advisable that the parts to be bolted on site are marked in such a way as
to be able to reproduce in the final assembly the same positions that they had
in the factory when the holes were reamed.
During the assembly phase, it is important to be careful not to create greater
eccentricities than the bolt-hole play. Usually the use of steel dowel pins is
used to put the parts in the right position. The steel pins are used to create
very precise unions and couplings, they are cylindrical or conical elements
that, placed in the appropriate holes, make torsionally and axially joined two
different pieces.
Figure 105: Example of steel dowel pins
Bolts can be tightened with key bolts until the plates between the head and
the nut are in contact. The nut is then rotated between 90ยฐ and 120ยฐ with
tolerances of 60ยฐ more.
For a correct operation, it is important that the contact surfaces on assembly
are clean, i.e. free of oil, paint, rolling scales or grease stains. As a rule,
195
cleaning is carried out by sandblasting; simple brushing of the contact
surfaces is permitted for joints mounted on site.
For the tightening of the bolts, torque wrenches are used by hand, with or
without a torque limiting mechanism, or pneumatic wrenches with a torque
limiting mechanism; however, all of them must be such as to guarantee an
accuracy of no less than ยฑ 5%.
Figure 106: Example of torque wrench
When tightening the bolts, it is recommended to proceed as follows:
Tighten the bolts, with a torque equal to about 60% of the
prescribed torque, starting from the innermost bolts of the
joint and proceeding to the outermost ones;
Repeat the operation, as described above, tightening the
bolts completely according to the specifications on the
constructive project.
To check the efficiency of the tightened joints, the torque applied can be
checked in one of the following ways:
196
The torque required to turn the nut further by 10ยฐ is measured
with a torque wrench;
After marking the nut and bolt to identify their relative
position, the nut must first be loosened with a rotation of at
least 60ยฐ and then tightened again, checking whether the
application of the prescribed torque returns the nut to its
original position.
If even one bolt in a joint does not meet the tightening requirements, all other
bolts must also be checked.
197
CHAPTER 8: COMMISSIONING OF THE
STRUCTURE AT THE BUILDING SITE
As with the procedures for the acceptance of structures on site, there are no
European standards for commissioning. Therefore, for the testing of the
structures it will be necessary to refer to the national standards in which the
structure will be built. Below is reported the Italian procedure regarding the
commissioning procedure.
The technical standards for Italian constructions define testing as the
procedure aimed at assessing and evaluating the performance of structural
works and components. In the event of a positive outcome, the test procedure
ends with the issue of the Test Certificate.
The static test must be carried out during the work in progress and these
structures may not be put into operation before that. The static tests of all
civil engineering works include the following requirements:
Checking of the prescribed provisions for works carried out with
materials regulated by Presidential Decree no. 380 of 6 June 2001, laws
no. 1086/71 and no. 64/74 with different materials;
Inspection of the work during the construction phases of the structural
elements and of the work as a whole, in particular for these structures
is important to verify:
o The completeness of the structure (if all the constructive
elements figuring on the executive project have been assembled
and correctly installed on the load-bearing structure)
o Verticality of the columns (for example through the plumb-bob
technique);
198
o State of the welded joints (visual inspection)
o Checks by means of a wrench torque that the tightening torque
of the bolts corresponds to that indicated in the construction
plan.
o Verification of compliance with the safety distances of the
assembled structure from the elements under voltage
according to EN 501101.
It is the task of the tester to check that the design requirements have
been implemented and that the experimental checks have been carried
out.
Examination of material testing certificates, divided into:
o Verification of the number of samples taken and their
conformity with the prescriptions in chapter 11 of DM 17-
01-2018 (described in chapter 6 of this thesis regarding
factory acceptance and in chapter 7 regarding on-site
acceptance);
o Check that the results of these tests have been successful in
accordance with the standards.
Examination of the certificates of inspections in the production plants
and during the production cycle;
Checking the reports and results of any load tests carried out by the
site manager.
The tester also has the task of:
Examining the design of the structure, the general layout, the
structural and geotechnical design, the calculation schemes adopted
and the actions considered;
199
Examining the investigations carried out in the design and
construction phases.
The tester may also require:
Studies, investigations, experiments and research useful to convince
himself of the safety, durability and testability of the work as:
o Load tests
o Testing of materials also by non-destructive methods
o Programmed monitoring of significant quantities
describing the behavior of the work, possibly even after
it has been tested.
In general, the structural elements, once installed, are no longer able for
testing neither controllable and therefore the static test is a test being
performed during the construction.
8.1 Load tests
As mentioned above, load tests are not compulsory, but can be requested by
the tester and it is always the latter who must define the program of such
tests, indicating the loading procedures and expected performance which
must in any case also be submitted to the attention of the manufacturer and
the designer as well as to the site manager who is also responsible for their
material implementation.
Load tests are tests designed to verify the behavior of structures under
operational actions in order to induce maximum operational stresses for rare
200
characteristic combinations. The test results are judged by the tester and must
be assessed on the basis of the following factors:
The increase in deformation is approximately proportional to the
loads;
During the test, no fractures, cracks, deformations or disruptions
occur that compromise the safety or the preservation of the work;
The residual deformation after the first application of the maximum
load does not exceed a portion of the total deformation commensurate
with the foreseeable initial inelastic settlements of the structure. If, on
the other hand, these limits are exceeded, the subsequent load tests
must indicate that the structure tends towards elastic behavior;
The elastic deflection shall not be greater than the calculated
deflection.
If the tester requires it, dynamic tests and breaking tests on structural
elements may be added.
As can be seen from the standards, there is no distinction between the
different materials that perform a certain load bearing function and therefore
the test is extended to all the load bearing structures (columns and beams)
whatever the material used for this purpose.
201
CHAPTER 9: CONCLUSIONS
With this thesis a process has been defined for the realization of these
structures, starting from the input documents up to the turnkey delivery of
the structure with a multidisciplinary approach ranging in different fields of
civil engineering such as geotechnics and structural design. Every single
phase of the process has been faced, providing on each occasion the
motivations behind each choice and consideration.
The structures that are the subject of the thesis, in addition to having to meet
the criteria of technical design and construction, must also comply with the
indications and restrictions imposed by the regulations of the railway
system. It was therefore also a work of integration at the regulatory level.
Particular attention has been paid to the different inputs to be provided to
the different stakeholders involved in the construction of these structures,
which may not be as familiar with the railway sector or with the types of
structures described in this thesis.
For example, this was the case in Morocco with regard to the factories in
charge of the production of these structures, which faced this type of
production for the first time. It was therefore essential to pay particular
attention to the inputs and indications provided so as not to be faced with
delays and cost increases.
202
APPENDIX A: Examples of cross sections located in
the Casablanca triangle
This appendix contains a brief analysis of the cross-sections of a section of
the Moroccan line, with some considerations regarding the installation of the
structures.
In this specific case, there was no information about the electric traction
elements in the drawings therefore no information about the contact wire
height. Consequently, at the design stage, the height of the columns was set
at 10m as a precautionary measure.
The image below shows part of the plan view of the line section in question,
while the other figure is a close up.
203
From section number 9 to section number 36 it can be noticed that there are
3 tracks alongside each other with non-constant interaxis, and with the
presence of a side wall.
The side wall is located at a minimum distance from the nearest rail of 1.46
m (section nยฐ35) and at a maximum distance of 4.83 m (section nยฐ20).
Cross section nยฐ20
204
Cross section nยฐ 35
In section 35, the side wall would not allow the installation of any structure
between the track and the wall itself, as it is positioned too close to the inner
edge of the nearest rail.
The height of the wall in relation to the rolling plane, however, being 1.96 m,
would allow the position of structures in elevation positioned beyond that
wall. Obviously, inspections and surveys on site would be necessary to
understand the real feasibility of such a hypothesis, as it is not possible to
define it just from the cross sections.
In section 20, however, depending on the type of structure that needs to be
installed, there may be space for structures.
As for the interaxis, still considering the same line section, the distance
between the two left tracks varies between 3.50 m and 3.70 m from section 9
to section 22, while it remains constant by 3.69 m from section 23 to section
36.
Section number 36 has the maximum distance between sections 9-36 between
the rightmost tracks. This distance is 5.72m, which subtracts one track gauge
(half of one track and half of the other) and places the inner rails at a distance
of 4.29m.
205
At this distance, it would be possible to verify the feasibility of installing the
structures, considering that the minimum distance must be respected for
both tracks.
As can be seen in cross section 36, in this specific case a possible solution
should also be studied to divert or incorporate the project well to any
foundations of the structures.
Cross section nยฐ 36
From cross section number 37 to section number 43, in addition to the wall,
already present in the previous sections, the project also provides for a
retaining wall with an L-section of 3.70 m high and 3.00 m wide, which
should not create problems at the design stage, as a possible solution would
still be to place the foundation plinth beyond the retaining wall, always
respecting the minimum safety distances. Again, no assumptions can be
made about the type of structures.
It can therefore be said that cross sections are an important tool during the
preliminary stages of the project, but they are not sufficient to allow valid
design assumptions to be made without integration with the staking
procedures.
206
Crosse section nยฐ 43
207
References
Cherkaoui, T.-E., and Asebriy, L. (2003). Le risque sismique dans le Nord du Maroc. Traveaux Inst. Sci. Traveaux de lโInstitut Scientifique, sรฉrie gรฉogr. , 225โ232. Babak, P. and al. (2017). Seismic wave amplification by topographic features: A parametric study. Soil Dynamics and Earthquake Engineering., 503-527 Meletti, C. and Valensise, G. (2004). Zonazione sismologica ZS9 โ App.2 al Rapporto Conclusivo. Istituto Nazionale Di Geofisica E Vulcanologia.( ordinanza PCM 20-03.03 n 3274) Criteri generali per l'individuazione delle zone sismiche e per la formazione e l'aggiornamento degli elenchi delle medesime zone. Gazzetta Ufficiale n. 108 del11 maggio 2006 (O.P.C.M. 28 aprile 2006 n. 3519) CENELEC, en 50124 (2017). Railway applications โ Insulation coordination CENELEC, en 50126 (2017) Railway applications โ The Specification and Demonstration of Reliability, Availability, Maintainability and Safety (RAMS) CNR - AEI - CEI EN 50128 (2002). Railway applications Communications, signaling and processing systems - Software for railway control and protection systems CENELEC en 50126 (2003). Railway applications โ Communication, signaling and processing systems โ Safety related electronic systems for signaling CEI en 50119 (2010) Railway applications - Fixed installations - Electric traction overhead contact lines. Martino, A (2017). Storia della Normativa e della tecnica ferroviaria e Segnali ferroviari italiani, www.rsifn.it. Valfrรจ, V (2011). Il segnalamento di manovra nella impiantistica FS Volume I โ CIFI Guida P.L. and Milizia E., (2016) Impianti Ferroviari Volume I, Lucio MAYER โ CIFI, Ristampa SNCF (2013). Sรฉcuritรฉ De Lโexploiatation Sur Le Chemin Ferrรฉ National Franรงais. Report annuel Baker, C. and al, (2019). Transient aerodynamic pressures and forces on trackside and overhead structures due to passing trains. Part 2 Standards applications. Birmingham Centre for Railway Research and Education, University of Birmingham Reglement De Construction Parasismique (R.P.S (2002). Ministรจre de lโAmรฉnagement du Territoire, de lโUrbanisme, de lโHabitat et de lโEnvironnement. Riggio, A,. and Carlucci R,. Topografia Di Base Fondamentali della geomatica per la misura e rappresentazione del territorio