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ROAD AND RAILWAY CONSTRUCTION
MSC COURSE
2016/2017 AUTUMN SEMESTER
RAILWAY SLEEPERS
SZÉCHENYI ISTVÁN UNIVERSITY Zoltán MAJOR junior lecturer
Several researches of different modes of rail failures show that railway sleeper take significant part as other components like rail, ballast, etc. Inspection and maintenance of sleeper is therefore required to insure that the sleeper keeps in good condition to: 1. maintain track gauge and rail inclination 2. distribute and transmit forces to the ballast bed or slab track 3. provide adequate strength both in the vertical and horizontal direction 4. insulate electrically one rail from the other 5. dampen rail vibration and reduce the influence of sound and impact waves on the environment
Railway sleeper has been developed for over hundred years, and according to the nature of its purpose, sleeper need to be durable enough to resist the heavy traffic loads. Traditionally, railway sleeper were always made from wood, and it had continued for 50 years. With the intense steel production, steel sleeper was used for about 50 years. But nowadays, concrete sleeper is widely chosen with a demand for increased axle loads. The first concrete sleeper was introduced at the end of 19th century, and the first concrete sleeper experiment was made in Germany in 1906 between the line Nuremberg and Bamberg. In the period of World War II the production of concrete sleeper was largely increased, and in 1939 the steel sleeper was stopped producing.
Types of sleeper
• According to material aspects, sleeper can be sorted as wooden, steel and reinforced concrete sleeper.
Wooden sleeper
• Wooden sleeper is only suitable for low speed lines with the speed limit of 160 km/h. Acceptable species of wood for this type of sleeper are European oak, beech, pine and etc. Nowadays in some countries, wooden sleeper is being replaced by concrete sleeper.
The advantages of wooden sleeper are:
• Easy to handle
• Good resilience
• Good electrical insulation
• Easily adapted to non-standard situations
The disadvantages are:
• Expensive
• Non reusable due to preservative chemicals
Steel sleeper
The advantage of steel sleeper is:
• Easy to manufacture and install
But the main disadvantages are:
• Low transverse resistance
• Difficult to maintenance
• Sensitive to chemical attacks
British Steel steel sleeper
Normal gauge, 250 kN axel load, weight: 77 kg.
Steel sleeper
Profil H [mm] B [mm] C [mm] D [mm] F [mm]
Pr 51 75 120 232 9 7
UIC 28 90 150 260 12 7
SW 82/54 100 145 260 9 7
Y- shaped steel sleeper
An unusual form of tie is the Y-shaped tie, first developed in 1983. Compared to conventional ties the volume of ballast required is reduced due to the load-spreading characteristics of the Y-sleeper. Noise levels are high but the resistance to track movement is very good. For curves the three-point contact of a Y steel tie means that an exact geometric fit cannot be observed with a fixed attachment point.
KRUPP Y- shaped steel sleeper
Cross-section
A [mm] B [mm]
60E2
St98-Y-No-600-60 600 1160
A [mm] B [mm]
60E2
St98-Y-Üre-600-60
St98-Y-Üli-600-60
185 745
Switch with Y- shaped steel sleepers
Concrete sleepers
Prestressed concrete is a method for
overcoming concrete's natural weakness in
tension. It can be used to produce beams,
floors or bridges with a longer span than is
practical with ordinary reinforced concrete.
Prestressing tendons (generally of high
tensile steel cable or rods) are used to
provide a clamping load which produces a
compressive stress that balances the tensile
stress that the concrete compression
member would otherwise experience due to
a bending load. Traditional reinforced
concrete is based on the use of steel
reinforcement bars, rebars, inside poured
concrete. Prestressing can be accomplished
in three ways: pre-tensioned concrete, and
bonded or unbonded post-tensioned
concrete.
Difference between the pre-stressed and the reinforced concrete sleepers
Pre-tensioned concrete is cast around steel tendons—cables or bars—while they are under tension. The concrete bonds to the tendons as it cures, and when the tension is released it is transferred to the concrete as compression by static friction. Tension subsequently imposed on the concrete is transferred directly to the tendons. Pre-tensioning requires strong, stable anchoring points between which the tendons are to be stretched. Thus, most pre-tensioned concrete elements are prefabricated and transported to the construction site, which may limit their size. Pre-tensioned elements may be incorporated into beams, balconies, lintels, floor slabs or piles
Reinforced concrete is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength and/or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not.
The advantages of concrete sleeper compared to wooden sleeper are: • Longer life cycle time • Cheaper • Lower maintenance cost of fastening • Smaller lateral displacement on account of large
weight
But concrete sleeper still has some disadvantages: • Vulnerable to impact • difficult to handle because of large weight • difficult to maintain longitudinal level due to higher
inertia moment and lower elasticity
In general, concrete sleeper can be divided into reinforced twin block concrete sleeper and prestressed monoblock concrete sleeper. They are presented in detail in the following section.
• Reinforced twin block sleeper is a type of sleeper where two concrete blocks are connected to each other through a steel rod or rigid steel beam. It was first developed in France. Increased lateral resistance and lower weight are the main advantages of this sleeper type. It can be used under various loading conditions and its service life is about 50 years. Recently it is being used in France, Belgium, Denmark, Netherlands, Greece, etc.
The advantages of this type are:
• Better lateral displacement resistance
• More elastic behaviour
• Easy to handle due to low weight
The disadvantages are:
• Require elastic fastening
• Declination of sleeper to the track centre
• Require special insulating accessories
• Defect because of corrosion and fatigue of steel
• Load distribution and flexibility less satisfactory
Prestressed monoblock sleeper which consists of one prestressing reinforced concrete beam was developed in UK. It can be used for high speed railway and heavy loading. And the service life would be also about 50 years. Nowadays it is used in USA, Canada, Sweden, Australia, England, Germany, China and etc.
The advantages are:
• Maintain track gauge in a good manner
• Longer life time
• Load distribution better than twin block
• Good surface for maintenance inspection staff
The disadvantages are:
• Require elastic fastening
• Require special insulating accessories
• No reinforcement against shear and torsional forces
Hungarian concrete sleepers
Type of sleeper: LW
Axel load 22,5 t
Allowed speed 200 km/h
Length 2500 mm
Width 300 mm
Height 232 mm
Height under the rail 214 mm
Height at middle of the sleeper 175 mm
Function Mainline sleeper
Type of sleeper: LM
Axel load 22,5 t
Allowed speed 200 km/h
Length 2420 mm
Width 280 mm
Height 190 mm
Height under the rail 181 mm
Height at middle of the sleeper 150 mm
Function Mainline sleeper
Type of sleeper: F40
Axel load 22,5 t
Allowed speed 200 km/h
Length 2420 mm
Width 295 mm
Height 225 mm
Height under the rail 216 mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper
Type of sleeper: LSZ
Axel load 22,5 t
Allowed speed 200 km/h
Length 2700 mm
Width 295 mm
Height 225 mm
Height under the rail 216 mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper széles nyomtáv esetén
Type of sleeper: LI
Axel load 22,5 t
Allowed speed 200 km/h
Length 2420 mm
Width 295 mm
Height 225 mm
Height under the rail 216 mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper (nyombővítésre alkalmas)
Type of sleeper: FV
Axel load 22,5 t
Allowed speed 140 km/h
Length 2900 mm
Width 291 mm
Height 225 mm
Height under the rail 216 mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper fonódó vágányok esetén
Type of sleeper: LT
Axel load 22,5 t
Allowed speed 140 km/h
Length 2420 mm
Width 280 mm
Height 190 mm
Height under the rail 181mm
Height at middle of the sleeper 171 mm
Function Mainline sleeper terelősín alkalmazásával
Type of sleeper: TM
Axel load 22,5 t
Allowed speed 140 km/h
Length 2420 mm
Width 280 mm
Height 190 mm
Height under the rail 181 mm
Height at middle of the sleeper 150 mm
Function Mainline sleeper
Type of sleeper: TF
Axel load 22,5 t
Allowed speed 140 km/h
Length 2420 mm
Width 280 mm
Height 177 mm
Height under the rail 177 mm
Height at middle of the sleeper 150 mm
Function Mainline sleeper fa betétekkel
Type of sleeper: TSZ
Axel load 22,5 t
Allowed speed 140 km/h
Length 2420 mm
Width 280 mm
Height 177 mm
Height under the rail 177 mm
Height at middle of the sleeper 150 mm
Function Mainline sleeper fa betétekkel
Type of sleeper: L2
Axel load 25 t
Allowed speed 250 km/h
Length 2600 mm
Width 300 mm
Height 235 mm
Height under the rail 215 mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper
Type of sleeper L4
Axel load 25 t
Allowed speed 200 km/h
Length 2600 mm
Width 300 mm
Height 235 mm
Height under the rail 215(1:40) / 211(1:20) mm
Height at middle of the sleeper 185 mm
Function Mainline sleeper
L4 sleeper
B70 sleeper
Type of sleeper B 70
Axel load 25 t
Allowed speed 250 km/h
Length 2600 mm
Width 300 mm
Height 234 mm
Height under the rail 214 mm
Height at middle of the sleeper 175 mm
Function Fővonali beépítés
B70 sleeper
Non-conventional concrete sleepers / Development of concrete sleepers
Wide ties Concrete monoblock ties have also been produced in a wider form (e.g. 57 cm (22 in)) such that there is no ballast between the ties; this wide tie increases lateral resistance and reduces ballast pressure. The system has been used in Germany where wide ties have also been used in conjunction with the GETRAC A3 ballastless track systems.
Type of sleeper: BBS 1
Axel load 25 t
Allowed speed 160 km/h
Length 2400 mm
Width 570 mm
Height 233 mm
Height under the rail 214 mm
Height at middle of the sleeper 225 mm
Function Mainline sleeper
Frame sleeper comprise both lateral and longitudinal members in a single monolithic concrete casting. This system is in use in Austria; in the Austrian system the track is fastened at the four corners of the frame, and is also supported midway along the frame. Adjacent frame ties are butted close to each other. Advantages of this system over conventional cross tie ties are reduced ballast pressure (up to half), increased lateral resistance, and increased support of track. In addition, construction methods used for this type of track are similar to those used for conventional track.
R65 type frame sleeper
Fabrication Methods
Concrete tie production is similar to other precast, prestressed concrete members except in terms of the repetition and quantity of concrete ties which are produced during a single casting. Depending on the fabrication method used, hundreds of ties can be cast concurrently. The three methods of fabrication historically used in the world are the long-line method, stress-bench method, and the individual form method. The most common fabrication method used today is the long-line method; the other two methods are less common for major manufacturing facilities and are typically used for one off castings such as turnout ties, therefore those fabrication methods will not be presented.
Long-Line Method
The long-line method describes the process in which ties are produced end to end in a line, with continuous strands of prestressing steel running through the ties. Casting beds containing the forms are stationary and equipment moves along the length of each bed. A variation of this method, in which forms are placed on train cars called lorries, which allows the ties to move between the different production steps, is termed the Grinberg method.
The long-line fabrication process can be highly automated, but still requires a labor force with a size dependent on the number of casting beds in operation and the number of forms in each bed. Workers are typically broken down into crews performing specific tasks which may include utility application, steel layout, casting, sawing, stripping, and final preparation. A turnaround time of less than 24 hours is typical for this method. A typical tie manufacturing facility will consist of a lay down area, casting building occupied by several prestressing beds, and a concrete batch plant. The facility is typically serviced by an over head gantry cranes and interior rail systems to transport completed ties out of facility.
Prestressing beds support tie forms and ties during curing process while prestressing forces and jacking equipment is supported by “dead men” anchors at ends of beds. Form sections contain several tie cells set side by side, with multiple form sections placed end to end. For one tie manufacturer visited, the form sections contained 6 tie cells with 60 form sections set in a single prestressing bed; therefore 360 ties could be cast at a single time. Ties were cast upside down for the reasons including: • Decrease occurrence of air voids and poor concrete consolidation, • Cast-in-place fastener components can be set in form prior to casting, • The bottom of a tie tends to be the only flat surface which makes it the easiest to have as a form free surface to provide an opening for concrete placement and finishing.
Material properties
In order to capture the crushing and cracking of sleeper, the most critical parameters should be analysed such as the maximum tensile stress and strain which can be used to determine crack propagation of sleeper especially in static situation. Because stress and strain relation is relevant to material properties, the properties of concrete and steel used as input value in finite element analysis
Stages of pre-tensioning
Pre-stressing technology has been developed for many years, and it is divided into pre-tension and post-tension. For concrete railway sleeper, pre-tensioning is widely used where tension is applied to tendons before casting of concrete. The stages of pre-tensioning are mainly described below.
The pre-tensioning is carried out in a prestressing bed equipped with end anchorages which take up tension. The high strength reinforcement tendons are pulled between two end anchorages which are fixed upon the prestressing bed before concrete sleeper is cast in the form. Once the concrete has attained a sufficient prestressing strength, the tendons are cut from the end anchorages, and the tensile force is transferred to the concrete through the tendons, because of the bonding between the concrete and the embedded reinforcement.
The stages of the pre-tensioning procedure are summarized in the following:
1) Anchoring of tendons against the end abutments
2) Placing jacks
3) Applying tension to the tendons
4) Casting of concrete
5) Cutting of the tendons
Steel forms
Pre-stressing wires and plastic dowels
End abutment and anchors
Concreting
Compaction of the concrete
Cutting of the sleepers
The finished sleeper
Storage of the sleepers
https://www.youtube.com/watch?v=2QQsaPYssVU
Design of prestressed concrete sleeper Concrete sleeper has been used in some countries for more than fifty years. Sleeper is used to maintain rail gauge and rail inclination, as well as transmit loading and reduce ballast pressure. After World War II, in order to carry higher axle load and sustain higher speed, prestressed concrete sleeper started to be introduced and is now widely used especially in Europe and Asia. The use of prestressed 60MPa concrete ensures that sleepers are able to withstand variable loading conditions. Moreover, small cracks which can appear through accidental damage close automatically, preventing the degradation of the reinforcing steel and any damage to the integrity of the sleepers.
DESIGN OF SLEEPERS
In the practices, analysis of sleepers comprises four steps:
• Considering a dynamic coefficient
• Calculating rail seat loads
• Assuming a stress distribution pattern under the sleeper
• Applying static equilibriums to a structural model of sleepers.
Dynamic coefficient factor
• In the practices wheel load is considered to be static, taking into account a dynamic coefficient factor. Researchers all over the world have recommended several formulae and values for the calculation of the dynamic coefficient.
Rail seat load
The exact magnitude of the load applied to each rail seat depends upon the following parameters:
• the rail weight,
• the sleeper spacing,
• the track modulus per rail,
• the amount of play between rail and sleeper,
• and the amount of play between sleepers and the ballast.
As a train moves along the track, the load from an axle is distributed amongst several ties due to the rigidity of the track. A single tie typically carries between 45 to 55 percent of an axle load directly above it. Factors affecting this load distribution are the tie spacing, fastening system, rail stiffness, and ballast and sub-grade conditions with tie spacing having the largest effect.
Stress distribution pattern under sleeper
The exact contact pressure distribution between the sleeper and the ballast and its variation with time is an important item in the structural design of sleepers. In order to calculate the sleeper bending stresses several approaches have been proposed.
baFp
4d
ba
2a2F
4d
2F
2aapMs
2dapTmax
2baF
2otF
2ba
2otFMk
Uniform distribution of bearing pressure
8d
ba
2aFMs
a2
2
2da
spTmax
3ba
k FM
Triangular distribution of bearing pressure
Support condition vs. bending moment
Failure Mechanisms of concrete sleepers
• The three primary failure mechanisms of concrete ties observed by the rail industry are rail seat abrasion, flexural cracking from center binding and rail fastener failure. Of these three, rail seat abrasion is the most perplexing and difficult to prevent. Failures may be related to concrete tie materials, design, or a combination of the two. Installation and maintenance practices also contribute to a tie’s resistance to these failure mechanisms.
Rail Seat Abrasion
AREMA defines rail seat abrasion (RSA) as the gradual wearing away of the cement paste from the concrete, resulting in an uneven aggregate bearing surface beneath the tie pad.However, RSA may degrade the concrete uniformly across the entire interface depending on the mechanism causing the deterioration.
Flexural Cracking (Center-Binding)
While inadequate tie flexural capacity is predominantly an issue of the past, cases of ties cracking at the top center location due to negative moment have been observed on mainline tracks. Two factors contribute to the ballast support conditions which cause this center bound condition. First, as the tie develops uniform ballast support in response to ballast consolidation negative moment occurs at the tie center. Secondly, over time cyclic loading applied to the track causes ties to oscillate and deform vertically within the track structure; this deformation produces pumping action which ultimately allows ballast to abrade the bottom of the tie and pulverize the ballast beneath the tie.
Fastener Failure
While many rail fastener configurations exist, a commonality between them is their shared purpose of providing a restraining force known as toe load to the rail. However, over time due to the effect of cyclic loading, fatigue of fastener components such as the spring clip and ductile iron shoulder occurs, allowing movement of the rail, deterioration of pads, and a decrease in the fastener toe load applied to the rail.
In addition to a decreased toe load, polymer insulators located between the rail and spring clip are subjected to abrasion from cyclic loading. Over time this abrasion wears away insulating material, creating voids and allowing for excess movement between the rail-tie interface in the form of rail rocking side-to-side and slip in the longitudinal direction of the rail. This excessive movement and space between the tie and rail further exacerbates the issues related to rail seat abrasion by providing an abrasive motion and allowing for the intrusion of water and abrasive agents such as rail grit or sand .
Control tests of railway sleepers
Size control
Loading under the rail seat
positive moment
Loading at the middle of the sleeper
negative moment
Breaking under the rail seat
Breaking at the middle of the sleeper
Shan Li:
Railway Sleeper Modelling with Deterministic and Non-deterministic Support Conditions
Stockholm, 2012
https://www.diva-portal.org/smash/get/diva2:510879/FULLTEXT0
1.pdf
REFERENCES
ThyssenKrupp GfT Gleistechnik:
Oberbauhandbuch Teil 1
REFERENCES
• https://en.wikipedia.org/wiki/Prestressed_concrete
• https://en.wikipedia.org/wiki/Railroad_tie
REFERENCES
J. M. Sadeghi and M. Youldashkhan:
INVESTIGATION ON THE ACCURACY OF THE CURRENT PRACTICES IN ANALYSIS OF RAILWAY
TRACK CONCRETE SLEEPERS
http://ijce.iust.ac.ir/files/site1/user_files_6k93w6/javad-A-10-136-2-2c53cef.pdf
REFERENCES
Concrete sleepers and other concrete elements for railway construction
http://www.railone.hu/Vasuti_betonalj_katalogus.pdf
REFERENCES
http://www.mabatrack.com/hu/Produkte/productcat/0/product/0.html
REFERENCES
• LICHTBERGER, B. :
Track compendium, Eurailpress Tetzlaff-Hestra GmbH & Co. KG, Hamburg, 2005, 634 p.
REFERENCES
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