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THE MILLAU VIADUCT
Geoffrey Kieme Gitau, 7432798
Peter Tadros, last name and student number
Sarmad Iftikhan, 7432763Mohammed Kassim Ali, 7433794
ABSTRACTThe Millau Viaduct is one of the greatest Civil Engineering projects in Europe. The main
fascination towards this project is the fact that its very high above the ground and yet
construction was finished within three and a half years only. Its a great money making machine
for the construction company, EIFFAGE, who put their own money for construction under
concession from the French governent. Its a great tourist attraction and thus promoting
Millaus economy drastically. The Millau Viaduct sets new standards of bridge building,having; a steel deck being built away from the bridge, tallest piers in the world and pylons that
are 700 tonnes each.
KEYWORDSCables, concrete, construction, cost, deck, Eiffage, Eiffel, loading, materials, Millau, piers,
Pylons, road, steel, Viaduct.
INTRODUCTION
One of the biggest and most beautiful structural marvels ever to be conceived by mankind,connecting Europe and the Mediterranean, The Millau Viaduct, at 343m high is the tallest
bridge in the world, so tall that it glides over the clouds.
Figure 1: Millau Viaduct over the clouds.
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The Millau Viaduct (French: Le Viaduc de Millau) is a triumph of engineering, imagination and
will. The initial rough design by a French architect was for the Bridge to have 9 piers; the
insanity of the design led the French government to bring in a Mastermind. Lord Norman
Foster, Britains most famous and finest architect. He instead designed the bridge with two less
piers and thus for the bridge to touch the valley at seven points only.
The structure coasted around 320 million euros, financed and constructed by the EIFFAGE
group themselves under concession from the French government for 75 years. The EIFFAGE
had to sell some of their offshore properties to assure a smooth and a steady construction of the
Viaduct.
Search for a beautiful yet durable structure led to the choice of a multi cable-stayed viaduct with
lean piers and a very light deck. From the start, the construction team faced four daunting
challenges: One; build the tallest piers in the world on a hilly land, two; put a thirty six
thousand tonnes freeway on top of the piers, three; erect seven steel pylons each weighing seven
hundred tonnes and four; they had to do this all hundreds of meters above ground, so high that
you would still be looking up if you were standing on the Eiffel Tower.
Construction on the Viaduct began on 10th October 2001 and was intended to take three years,
but irregular weather conditions delayed the schedule. A revised schedule aimed for the bridge
to be opened in January 2005.
The viaduct was inaugurated by President Chirac on 14th December 2004 to open for traffic on
16th December, a few weeks ahead of schedule.
Table 1: The important statistics on the Millau Viaduct (Janberg, N 2004)
Statistics : The Millau Viaduct Bridge
Total length of the roadway 2,460 m (8,071 ft)
Number of piers 7
Height of the shortest pier: Pier 7 77 m (253 ft
Height of the tallest pier: Pier 2 343 m (1,125 ft)
Height of each Pylon 87 m (285 ft
Number of shrouds 154
Average height of the roadway 270 m (886 ft)
Thickness of the roadway 4.20 m (13 ft 9 in)
Width of the roadway 32.05 m (105 ft 2 in)
Total volume of concrete used 85,000 m (111,000 cubic yards)
Total weight of the bridge 290,000 metric tons (320,000 short tons)
Estimated daily traffic 10,00025,000 vehicles
Horizontal radius of curvature of the road
deck
20 km (12 mi)
DESIGNThe Viaduct 343m high to the top of the pylons is the biggest and the most beautiful civil
engineering structure on the A75 motorway crossing the Tarn valley. The bridge also holds the
title of the worlds longest multi-span cable stayed bridge with a total length of 2460m, slightly
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curved in plan with radius of 20km and a constant upward slope 3% from north to south. Road
Layout and deck section. (Steel Bridge, 2004),(Structurae),(50Detail.de).
Figure 2. Elevation view of the viaduct.
Road Layout and deck section
The cross section of the deck is a trapezoidal steel box girder. In the core centre there are two
vertical rods 4m apart and 4.2m deep. As the structure and core are entirely made of steel it
consists a mass of 36,000 metric tons (40,000 short tons), is 2,460m and 32m wide. It comprises
eight spans. The two of them are 240m and the other six are 342m. These spans are composed
of 173 central box beams. The central beams have a 4m cross-section and a length of 15-22m
(49-72ft) for a weight of 99 tons. In strong wind conditions, the deck has an air foil shape
providing negative lift. (Steel Bridge, 2004),(Art of Design).(Enerpac)
Figure3. Functional cross-sectional of the deck.
Pylons
The seven masts, each 87 m (290 ft) high and weighing around 700 metric tons (770 short tons),
are set on top of the pylons. Between each of them, eleven stays (metal cables) are anchored,
providing support for the road deck. (Steel bridge, 2004).
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Figure 4. Elevation and cross-section of pier and pylon.
Cables
Each span is arranged in a single plane in half-fan pattern supported by eleven pair of cables.
Depending on their length, the stays were made of 55 to 91 high tensile steel cables, or strands,
formed of seven strands of steel. Each strand has triple protection galvanization. The idea is to
avoid running water which, in high winds, could cause vibration in the stays and compromise
the stability of the viaduct. (Steel bridge, 2004).
Figure 5. General view of the cables.
The materials
The pylons and the deck, entirely made of metal, are made of steels of grade S460 and S355.
B60 concrete is used to construct the piers. This concrete was chosen due to its strength,
durability and high mechanical resistance. (Steel bridge, 2004).
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CONSTRUCTIONConstruction of such an enormous structure unsurprisingly came with a puzzle on how to
actually pull of the design in the most economical manner. Its huge distance and the fact that it
was way above the ground was the biggest concern. At such heights construction is almost
impossible and weather change is a constant threat.
The Piers
The piers had to be brought up to support the bridge. The bridge was covering a distance of
around 2500m, a single or two piers couldnt support weight the bridge, thus by careful
calculations, seven piers were to be built.
Each pier was treated as a separate worksite. A total of seven formwork systems were installed
on the site. The concrete for the foundation of the piers and the latter was produced in nearby
plants so as to reduce transportation costs and assuring the concrete is as fresh as possible. The
foundation of the piers consisted of four bored piles ranging in depths of 9m to 16m. The
foundation piles were then concealed after construction so as not to corrupt the look of the
Viaduct.
Figure 6. Head Of A Pier
The piers closest to struts were first initially erected so as for the launch of the deck to start
while the remaining piers were being constructed. The formwork of the piers was a
revolutionary self-climbing device using hydraulics; this significantly reducing the cost of the
manual labour. Checks were made by GPS to ensure a precision of 5mm in both X and Y
directions after an every four meter rise. The tallest piers built for the bridge are 245m and
223m high and these are the tallest piers ever built in the world to date. The top 90m of the piers
are split into two so as to allow contraction and expansion due to weather changes and also to
increase the visual beauty of the Viaduct.
Temporary Piers
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The deck of the Viaduct was launched by a hydraulic technology from ENERPAC, a US
Multinational that specializes in large scale Hydraulic Systems. The hydraulic system was
designed and built by Enerpacs Construction Centre of Excellence in Madrid, Spain. This
system is designed to push the 27.35m wide deck from both sides onto the seven concrete piers.
Temporary metal piers were placed to support the launching. The first of the seven temporsrypiers was erected using cranes but the rest were raised using a hydraulic telescopic system also
designed and built by Enerpac.
Figure 7. Overview of temporary and permanent piers.
The Deck
The deck was constructed of steel from the Eiffel Company. Steel parts were manufactured in
the factory and then transported to the worksite. There they were welded together to create the
skeleton of the deck and thus pushed along the piers. The state of the art deck is a two-lane dual
highway with a 32.05m width.The deck of the Millau Viaduct consists of a trapezoidal profiles
metal box girder with a maximum height of 4.2m at the axis with an upper orthotropic decking
made up of 12-14mm thick on the greater part of the main spans (Steelbridge Article, June
2004).
The Pylons
Before the pylons were connected to the bridge, the whole deck was dramatically flexible as its
made from steel. The Pylons and the cables were installed to pull the deck straight. Each pylon
is 90m high and weighs 700tonnes. A technique used in ancient Egypt to erect odalisques in the
sand. On top of the road deck two enormous steel cranes were installed capable of raising a
1000tonnes. Each pylon is then lifted, as it raises, it rotates little by little until its vertical, its
then lowered safely into its anchorage point.
Hydraulic Systems
The enormous yet light deck was pushed by means of hydraulic devices on each pier which first
lifted and then pushed the deck. Each system consists of a lifting cylinder with a capacity of 250tonnes, lifting the deck of the supporting structure of the pier, and two or four skates, each
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equipped with two 60 tons cylinders which retract to launch the deck at a maximum of 600mm.
All this relies on a system of single-acting lock nut cylinders supporting both the launching
process and the deck. Each push cycle moves the deck 600mm and takes 4 minutes.
Figure 8. Initial, Lifting, Launching, Lowering and Final Position of the hydraulic system.
There were 24 support cylinders of 600 tonnes. Valves were used to make the cylinders
independent of each other so as to control the height and the angle of the deck, each system
having an independent control centre for the skates and the jacking cylinders.
The Nose of the Deck
As the deck is being pushed forward, naturally it curves downwards thus approaching the next
deck below the suitable level. To control this problem, an independent nose recovery system is
built at the end of the deck. This system consists of four 270 tons cylinders pulling the noseupwards to the level of the skate. Another hydraulic system allows the nose-end to pivot.
Figure 9. Nose of the deck at work
The cylinders extend, pulling the spindle bar and raising the nose. The nose is blocked with
respect to the column by means of the nuts and the cylinders are withdrawn. The cylinders
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extend again, repeating the operation until the support area of the nose passes beyond the level
of the balancing device. The Bridge is moved forward by operating the balancing device until
the support area of the nose reaches the balancing device. The cylinders withdraw until the nose
rests on the balancing device and finally the skate support device is withdrawn from the nose.
PROJECT MANAGEMENTMillau Viaduct is the tallest bridge in the world with the height of 342m over the tarn valley
connecting the small city of Millau in Paris to Bziers. Millau Viaduct is the longest cable
bridge in the world with a total length of 2460m of steel deck.and also technically, known as
A75, the last link of Clemont Ferrand-Bziers motorway (Buonomo, M, Servant, C, Virloguex,
M, Cremer, J-M, Goyet, V, & Del Forno, J-Y 2004)
Background of the Companies Involved
Eiffage was formed in 1992, that is made up from several companies such as Fougerolle
(founded in 1844), Quillery (founded in 1863), Beugnet (founded in 1871) and La Societe
Auxiliaire d' Enterprises Electriques et de Travaux Public, better known as SAE (founded in1924). Effage Company is one of France's top construction and civil engineering groups.
During the 1980s the plan had been decided but it took ages to study a perfect way of
construction, a least costing one and a durable design. Finally in 2001 the design of the bridge
had been proposed which actually looks like the one that had been constructed.
Figure 10. The Completed Millau Viaduct
The Eiffage Company proposed the idea to build the Millau Viaduct; it is the same company
that constructed the Eiffel tower. The contract was to construct the bridge with a booth (Tallest
booth in the world) that contains eighteen lanes and is six kilometres far from the bridge to the
north side. The profit from the booth will belong to the company.
The Eiffage Company chose a design that made them construct the bridge with 50% concrete
and 50% steel. Meanwhile the Millau Viaduct was upright the tarn river; a steel deck that was
used to make the road surface was a perfect choice in sense of weight and price. This gave them
the chance to transfer less weight to the site as well as using less cable to handle the light
weighted road.
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Time Management
The Eiffage Company had considered time as a big factor and that was one of the leading
reasons in choosing to build a steel deck instead of a concrete oneSteel gave Eiffage the
flexibility to start building the piers as well as the deck and thus saving time. On the other hand
if they used concrete they had to build the piers first then get started with the deck. Building the
Millau Viaduct had to be in an accurate way such as placing the piers and the exact location ofthe road surface. the global positioning system (GPS) has played a big role in positioning the
piers. Hydraulic jack system was used to move and put them in place. And that was used for the
piers matter. What hold the Millau viaduct is 7 piers that distance of 342m difference between
each, except for the two end spans with 204m each.
It took Effiage 38 months to accomplish the construction of the Millau Viaduct. The
construction began on the October 10.2001 and was considered to be done in 3 years. But the
weather conditions such as wind stress and others didnt allow the bridge to finish on time and
therefore, a new schedule had been calculated, and the target was to inaugurate it on the January
of 2005 . The viaduct was officially capitalized by President Chirac on December 14 2004 and
opened to traffic on December 16 2004; a few weeks ahead of the revised schedule.
Timeline
16 October 2001: work begins
14 December 2001: laying of the first stone
January 2002: laying pier foundations
March 2002: start of work on the pier support C8
June 2002: support C8 completed, start of work on piers
July 2002: start of work on the foundations of temporary, height adjustable roadway
supports
August 2002: start of work on pier support C0 September 2002: assembly of roadway begins
November 2002: first piers complete
2526 February 2003: laying of first pieces of roadway
November 2003: completion of the last piers (Piers P2 at 245 m (804 ft) and P3 at 221
m (725 ft) are the highest piers in the world.)
28 May 2004: the pieces of roadway are several centimetres apart, their juncture to be
accomplished within two weeks
2nd half of 2004: installation of the pylons and shrouds, removal of the temporary
roadway supports
14 December 2004: official inauguration 16 December 2004: opening of the viaduct, ahead of schedule
10 January 2005: initial planned opening date
Cost Management
The Eiffage Company stated that constructing the bridge would approximately cost about 300
million .the Bridge users will provide the income for the company while the construction of the
bridge amounted to around 394 million and extra 20 million for the toll plaza which was placed
6 km north of the bridge. For 75 years the income for the bridge will belong to the company
which is till 2080 on the other hand if they achieved profit from the income, by 2044 the
government will be taking over the bridge till 2044.
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Resource Management
Materials. The design of the bridge has given several advantages, such as producing a quality of
board and lightens for the structures, while during construction, decrease amount work on the
site, they had builded a factory near the site to bond the steal segmented deck ,to reduce the
volume and the amount of materials that will be needed and used on the site.
Steel. The amount of steel that has been used in the site was 36,000 tons of metal frame, 7 times
the Eiffel tower.
Steel Wire Ropes. The steel cables had played a big role in the bridge, in such that it will be
attached on the pillars and give the whole support to carry the weight of the pillar and the sides
of the deck. They were sustained on the midway between in each pillar to handle it.
This technique had been normally used thru bridge construction history, and it became a special
use for those with a greater number of instalments, as in the case of the Millau viaduct.
Figure 11: Cables tensors steel.
Concrete. The concrete was used to make the 7 piers that took amount of 205000 tonnes of B60
concrete, 40 times the Eiffel tower.
Safety Barriers. The Millau viaduct is prepared with a safety barriers to tough to shocks for
trucks, Transparent wind screens with the height of 3 m. the lighting ensures a perfect vision for
the drivers.as well as placing a emergency telephones are placed every 400 m in case of
accidents or breakdown.
Engineers involved with this structure
Designer - Michel Virlogeux - Overall concept
Architect - Lord Norman Robert Foster
Technical advisors to the owner:
Jean-Claude Foucriat - Steel
Jean Piccardi - Steel
Franois Schlosser - Geotechnics
Equipment/Machinery
Enerpac Company was the company that supported the project with the hydraulic machines thathelped to construct the bridge in faster and easier way.
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There are two main parts for the of the telescopic system, a 12m base of a cubic structure which
accommodate the whole system, the system equipped with toothed racks which are installed at
its vertices in meters. The second is the lifting mechanism which consists of hydraulic cylinders
and hydraulic control systems. The four vertices of the cube are used to place the hydraulic
cylinders which are anchored to supports and linked to the tooth racks. The successive insertion
of locking chocks in the toothed rack allows the pier structures and hydraulic machinery to bedisplaced in vertical directions.
1000mm lifting steps
The process of operating the system is simple plain;using the chocks the cylinders are locked in
the toohed rack which supports the cylinders while the sturucture of the pier is left alone.then
oil is pumped into the cylinders by the operators who use a software which includes all the
safety options.pumping the oil pumped produce a thrust against the structure of the pier by
raising the rams.this raises the structure of the piers.
The cylinders contains a stroke of 1100 mm and the toothed rack has cut every 1000mm , the
extra 100mm is available to ensure for the possible unexpected circumstances.
MAINTENANCEIn summary Maintenance are all actions which have the objective of retaining or restoring an
item in this case the Millau Viaduct bridge to a state which it can perform its required function.
Maintenance Aspects in Design
Figure 12: Elevation of the Viaduct
The viaduct comprises of seven concrete piers and steel pylons. The concrete used in the piers
is B60 grade. This concrete was chosen more for its durability than for its high mechanical
resistance (The Millau Viaduct official website, Eiffage). The top of the piers is split into two
shafts, to allow for contraction and expansion effects due to temperature changes, and above
where the pier splits, the concrete is pre-stressed using eight cables. The steel deck of the
viaduct and pylons are made from S355 and S460 grade steel. These grades were chosen due to
their high tensile strength; the maximum load that a material can support without fracture when
being stretched, divided by the original cross-sectional area of the material (Foster & Partners
Projects)
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Usually cable stayed bridges have a set of cables called backstays which tie the pylons to the
ground to transfer the load from the bridge. In contrast to this the Millau Viaduct does not have
any backstays and all set of cables are anchored to the spans of the bridge deck itself. This
means stresses and loading in each section are transferred to the adjacent sections and the
pylons deflect towards the most heavily loaded span. In order to reduce the vertical movement
in the deck the piers and pylons are fully fixed to the deck. This is achieved from the connectionof four large spherical bearings on each pier. This also reduces the forces which are transferred
to the adjacent spans. The piers and pylons were therefore designed to have high stiffness to
allow for a more slender and flexible deck as shown in Figure 2 below
Figure 13; Cross section of the Millau Viaduct deck.
Above the bearings there is a frame which continues up to the pylons providing further rigidity
as shown below. The pylons have an overall height of 87m and consist of an A frame with legs
38m tall. The upper mast section is 49m high where the cables are anchored but the top 17m of
the upper mast section provides no structural function (The Millau Viaduct official website,Effiage)
Figure 14: Pier, deck and pylon connection.
Each pylon supports 11 pairs of steel cables which are arranged in a semi fan arrangement in asingle plane with anchor points spaced equally on the deck 12.51m apart in the central
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reservation following the curve of the bridge. This arrangement allows support from the cables
along the majority of spans of the deck. Each cable consist of a collection between 45-91 1 T15
cable strands which have been protected by a white PEHD outer casing which has been
equipped with a double helical weather strip to prevent water running down the cables reducing
vibrations (Buonomo et al. June 2004). The tension in the stays is stated in (The Millau
Viaduct official website, Eiffage) as being between 900 tonnes and 1200 tonnes thereforeproviding more rigidity.
Beyond the deck the parapets are extended 2.2m away from the road and are 3m high see Fig 2.
This is to discourage people from looking over the edge of the bridge and slowing down too
much to take photos. The parapets are deigned to reduce the wind load by 50% (Caetano, E et
al Flamand, O. et al. 2004)
Maintenance aspects of Construction Materials
The choice of materials to be used in construction determines the cost in maintaining a
structure. In this case the material of choice is steel, so to therefore reduce the cost of
maintenance the quality of steel to be used has to be tough and of good quality to avoid anyunpredictable repercussions. Three main steel types are used to achieve this.
1. Thermo mechanically rolled steel which has high yield strength and retains good weld
ability and high thickness without preheating.
2. Longitudinally profiled steel plates also known as variable thickness plates. This
varying thickness is important since it prevents the bridge from collapsing through
weight reduction, it also helps to lower the cost of fatigue, performance and number of
welds to be used.
3. Weathering steel plates are low alloy steels coated with a protective layer that prevents
damage due to atmospheric pressure, therefore reducing the cost of maintenance on
repainting and increases the permanence of the structure (IBELL, T.2004)
Durability.In the contract it was stated that the bridge had to be designed for a useful life of
120 years. This meant that all structural parts had to be long wearing. As previously mentioned
grade B60 concrete was used and was chosen for its good durability properties. Each steel
strand within the cables is protected by galvanization, a petroleum wax coating and an extruded
polythene covering. On top of this, the collection of strands is protected from moisture and UV
fatigue damage by a plastic outer casing.
The deck has been designed to resist fatigue over time by using 14mm steel sheets on the upper
decking which is then covered in 4mm of bitumen and sealed at 400c to protect it from the riskof corrosion.
Serviceability. In order to monitor the viaduct over its life a network of accelerometers,
anemometers, inclinometers and temperature sensors are fixed to the piers, deck pylons, and
stays. This sends data to a central monitoring station where movements of the Viaduct are taken
to measure creep, the components resistance to wear and tear over time and the responses of the
structure in extreme wind conditions. The system can make measurements to high degrees of
accuracy, especially in critical areas of the structure such as pier 2, the highest of the bridge.
Another aspect of maintenance is constant inspection undertaken to ensure the performance of
the bridge is safe. Throughout the inspection any damage of the bridge can be detected and
repaired. Inspection is done in the following four ways; visual inspection, electromagneticinspection, x-ray inspection and ultrasonic inspection. The last three are used to detect any
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internal damages not visible to the human eye such a road crack, broken wires, abrasion and
corrosion. Ultrasonic inspection is the most effective of the three as it can control the entrance
of the cable into their elements and therefore any crack inside can be located.
SAFETY
Loading
Loading is critical to safety of the bridge as it gives one a true estimate of the loads and stress
levels a bridge can withstand. So in the case of the viaduct although the bridge was designed to
French standards, In this report the analysis the loading is using (BS 5400-2, 2006), the British
standards for steel, concrete and composite bridges. The loads taken into account encompass
dead loads, super imposed loads dead loads, live traffic loads, secondary live loading including
skidding and impact loads, wind loads and temperature loads.
Load combination and factors. Each load type is not considered individually, but in various
combinations that provide the designers with worst case scenarios to check the adequacy of the
bridge design. They are five load combinations.
1. Permanent loads plus the primary live loads
2. Combination 1 plus wind loading and temporary erection loads where erection is
considered. Traffic loads can replaced by construction traffic loads
3. Combination 1 plus loads induced due to the changes in temperature plus temporary
erection loads where considered. Traffic loads can be replaced by construction traffic
loads.
4. Permanent loads plus secondary live loads and primary live loads associated with them.
Secondary live loads are considered separately and do not have to be in combination.5. Permanent loads plus loads due to friction at supports.
6.
Dead loading and superimposed dead loading. As a collective, dead loads are referred to as
permanent loads. The dead loads of the bridge deck refers to the steel box girder, plus the wind
shields as these are always present and would never be removed. The pylons and cables could
also be considered as dead loads after construction is finished, as they would not be removed.
The super imposed dead loads are the deck surfacing, steel and concrete impact barriers,
lighting hand rails and drainage fittings. All of this are not structural elements and could be
potentially removed at various points through the bridges life.
In order to calculate the nominal and design dead load one has to use the weight and span of thesteel deck stated on the viaducts official website as 36,000 tonnes and 2460m respectively.
From the same reference the thickness of the bitumen layer is given as 4mm with a density
approximated to the same as asphalt of 2300 kg/m3. Its assumed the lower bitumen layer
covers the whole deck surface up to the outer edge of the hard shoulder (total width of 27.8m)
The total weight of the upper special bituminous concrete surface material over the whole deck
is stated as 9500 tonnes (BS 5400-2, 2006) resulting into the following
Tab
le 2. Dead Loads
Load type Nominal (KN/m) SLS load KN/m ULS load (KN/m)Dead 146.3 146.3 169.98
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Super imposed dead;bitumen
2.51
SID bituminous concrete 38.62
Total super imposed dead 41.13 49.36 79.18
The above table shows that the dead loading due to steel is within the permissible stress levels
of the steel grades used in the construction of the viaduct.
Secondary live loading. This is a loading combination that is associated with traffic loads on the
viaduct. Because the curve of the Millau Viaduct is greater than 1000m centrifugal loading can
be ignored. Other loads considered are horizontal loading caused by braking of either HA
vehicles (personal vehicles) or HB vehicles (PSVs) according to (BS5400 6.10) it is applied
longitudinally at the road surface in one notional lane only. From the same reference the HA
loading which has a nominal uniformly distributed load (UDL) of 8Kn/m of the loaded length
of 2460m plus 750KN maximum over the width of the notional lane and loaded length. For HB
loading it would be 450KN over two axles of the HB vehicle 1.8m apart.
Secondary loading also considers accidental loading such as skidding and collision with the
parapets, for skidding the loading is taken as a 250KN point load acting parallel to the surface
but in any direction and in one notional lane only. Both the local and global effects due to
loading from collision with parapets are covered under the sub topic Accidents and
Vandalism.
Wind loading and natural frequency. The location and height of the viaduct means it is exposed
to high wind speeds, strong gusts and adverse funneling effects from the valley. Although the
wind loading analysis in (BS5400 5.3) does take into account relevant variables such as
topography factors and gust factors which could account for this. They can only be applied tobridges up to 200m long and up to 300m above sea level. Therefore the British standards would
not be sufficient for a bridge as long and as high as the viaduct.
The wind loading was a critical factor in the design of the bridge. Comprehensive wind tunnel
studies mentioned in (Buonomo et al. June 2004) were undertaken to find the stresses and
deflections of the structure under wind loading. Funneling and gusting due to the topography
was also taken to account and the aerodynamics of each part of the structure was tested
including the torsional effects on the deck. The actual aero foil shape of the deck; see Figure 2
was designed to reduce wind load effects and the parapets halve the wind load on the road. The
transverse displacement under serviceability limit state design was calculated to be 0.6m and
the vertical displacement under SLS was 0.75m as stated in (Buonomo et al. June 2004).
The natural frequency of the bridge needed to be found as the light structure combined with
high wind speeds could cause great acceleration and deflections of the bridge. Different
dynamic tests were undertaken to analyse the natural frequency of the bridge including the
installation of 21 accelerometers and 4 seismographs on the deck for the ambient vibration and
free vibrations tests. Another method called the Polymax method identified 20 natural
frequency modes in the range of 0.1Hz to 0.8Hz which are acceptable levels (Caetano, E et al
Flamand, O. et al. 2004)
Temperature Loading. They are two ways in which temperature variations causes stresses in the
bridge, the first being expansion and contraction caused by changes in the effective temperature
around the bridge. The effective temperature is the average found using the ratios of different
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temperatures and cross sectional areas at different levels on the bridge. A maximum, minimum
and overall effective temperature range can be found. The effective temperature range of the
Mill au Viaduct is stated as being a maximum of 40c (The Millau Viaduct official website,
Effiage), so the deflection can be calculated.
(1)
So there can be approximately 0.6m movement at each end of the structure. This means the
stress in the deck due to any possible restraint is (BS 5400-2, 2006).
(2)
This is within the permissible stresses of the steel grades mentioned earlier. Because of the high
rigidity of the piers and pylons and the fixed bearing connection to the deck, high stresses in
some of the piers could occur due to temperature variations in the deck. During design this
deflection was found to be above the resistance levels of the concrete in the two ends of the
piers so the splitting of the section into two shafts was designed to accommodate for this.
Similarly the bottom section of the metal pylons has been split into two shafts.
Figure 15. The split section design in the piers
The other temperature effect is the stresses and bending induced in the deck from localized
differences in temperature between the top and bottom of the deck. The average temperature for
the Millau is 10.5c, which is within a safe range. Using British Standards the following graphs
can be produced showing the temperature difference which arise in the steel deck (BS 5400-2,
2006)
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Figure 16. Deck temperature distribution graph.
Loading used in Structural Assessment. The intensity of the live loading can be found and
converted to a transverse UDL. This is then used in combination with the dead and
superimposed dead loading mentioned above and converted to transverse UDLs to analyse the
transverse bending moments in the deck. As there are 11 pairs of cables set 12.51m apart with
the larger spans between the two central cables and the outer cables and pylons. The large spans
are approximated to 30.6m so the maximum longitudinal length that a support would have to
carry would be 30.6m (at the pylons)( BS 5400-2, 2006)
Figure 17. Longitudinally spacing of supports
Figure 18: Transverse loading arrangement with key
(3)
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Figure 19. Transverse bending moment diagram.
This would not be the worst case scenario on the deck as the asymmetrical loading would create
a torsion which is a particular problem on the Millau Viaduct due to the single plane of cable
supports providing low torsional rigidity. The pylons and piers also lie within this plane which
provides less torsional stiffness than if there were two pylons or an A or H frame arrangement.
(BS 5400-2, 2006)
Figure 20. Torsional loading arrangement
The torsional moments are reduced by the steel deck cross section which has high torsional
rigidity provided by the box girder, steel cross bracing and trapezoidal deck shape.
Accidents and Vandalism.
The bridge must also be safe guarded against intentional damage. Because the viaduct is such a
great landmark and symbol of pride for France, one could think that no one would want to
damage it. However its possible some people will. If anyone were to try and damage the bridge
by driving into the barriers, they have been designed to take high impact loads without doing
damage to other parts of the bridge. Hypothetically if an aircraft were to hit the bridge, they
would most likely be failure of the structure. During construction of the bridge deck could
withstand the bending stresses associated with cantilevering from one of the piers, showing the
super structure of the bridge could stay up if a section of the deck or pylon were to be damaged
(Buonomo et al. June 2004)
SUSTAINIBILITY PRACTICESOne of the main purposes to build the Millau Viaduct was to avoid the traffic .the only way to
make French people go the south cost was through long ways around the valley and drive in a
very narrow area to avoid traffic and that takes a lot of time. Specialized engineers and
ecologist had to design a way to decrease the damage that have done by the toxic pollution from
the heavy traffic. The viaduct had successfully reduced the number of the traffic for the past
years, especially in holidays season where the French usually spend in south cost. (Godfrain
2006)
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The Eiffel Company have use special concrete known as b60 concrete by the engineers that will
give the piers more durable comparing to high mechanical resistance. Millau Viduct deck is
made by 100% steel and that makes it so light, recommended by buonomo et al. (2004),the
piers that support the viaduct from The valley of the river tarn near Millau in southern France
and its design that it just be supported with seven pillars passing through the valley. And that
shows that viaduct is an environmental-friendly bridge. The valley of the river tarn near Millauin southern France
Cable stayed to balance the weight of the metal long road surface so that the piers will support
the roadbed which is also made of metal in the Millau viaduct. Eiffel Company had the idea to
use multiple pillars of metal cable to help and support the load. The benefit behind using cable
stayed is to reduce the longitudinal flexion of the redistributing effort via the stays as
recommend by the Eiffel Company. The cable has uncountable spirals that involve eleven in
each as the resolve to fight the combination effects of rain and wind which leads to vibration.
(Infotua, April 2004).
Building the Millau Viadtuct with steel was a magnificent idea, because practically all steel has
the ability to weld together. The best part was Eiffel Company have done all the accumulatedand painted in indoor workshop, which gave the quality and safety to workers who avoided
welding all the parts together in this height.
Figure 21: The Millau Viaduct
Moreover another major advantage of steel is that it could be recycled within a large amount.
Secondly by using steel it made constructing the bridge with less stone aggregate and with less
water. Thirdly and more important it has done in a very dry area with a gorgeous natural
landscape.
The idea of structure of the lightweight steel was to make it half the weight of structure of
concrete, which helped to deliver few trucks loaded with material that is needed in the site, and
that gave less fuel consumption and less pollution from exhaust emissions.
Finally, the structure of the steel didnt require a heavy and amount of foundations, actually it
took fewer pylons and cables to support it comparing if they used concrete structure .which
gave a big benefit to reduce the total cost of the price of the project.
Risk assessment
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As bridges are complex structures with a multitude of components and structural forms, a
comprehensive management system is required. Risk assessment can be defined as the
qualitative or quantitative value of risk related to a concrete situation and a known hazard. For
the Millau Viaduct Bridge case, the main types of risk assessments are:
Risk assessment in structural designThe Millau Viaduct is a multi-span cable-stayed bridge. Having the multiple spans, there are no
back stays as with most cable-stayed bridges to enable the pylons to have a rigid support. Due
to the height of bridge, the pylons have a relatively low bending stiffness compared to the piers.
Moreover, pylon have a bending moment caused by the cables, one leg of the pylon will
experience tension and the other compression. These forces can be transferred to the ground by
the split piers. By cables, the steel deck is set into compression. The pre-stressed concrete deck
is used due to its good compressive strength and durability.
However, it is mentioned that the deck is made of steel. A concrete deck is possible to crack
under its own weight which may lead to problems during its service ability life time. Preventingsuch cracking during the launch would require pre-stressing the deck in advance using tendons
and also completely arising the pylons and cables before launching; effectively pre-stressing the
deck super structure. It was time consuming, thus was considered most efficient and effectual
option.
It was seen that the steel deck moved in a wavy form during the construction but did not create
any lasting effect due to its high ductility. The single plane of cable stays introduces potential
problems associated with torsion. Undesirable live loading on one side of the cables and no live
loading on the other side will result in torsion. Using an 'A' shaped frame or other similar pier
design fixed to the deck itself would provide torsion restraint limiting the torsion effects in
between spans. (Steel Bridge, 2004).
Figure 22. deformed shape of Millau vVaduct.
Risk assessment in public safety.
In the case of the Millau viaduct bridge, risk assessment of public safety can be defined as the
characterization of potential undesirable effects or results of human exposures to environmental
hazards. Driving on the bridge itself can pose accidents to occur. Hence, safety measures are
done before and after construction of the bridge as well as during the construction of the bridge.
(Steel Bridge, 2004).
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One of the safety measures includes provision of an emergency telephone every 400 meters on
the bridge. Besides that, a 24-hour surveillance system incorporating such as video recording of
traffic, weather stations and programmable message boards are installed. Some other safety
measures are specially designed for safety barriers to resist truck impacts and wind-breaking
screens to reduce the wind factor problem. This is because; the engineers and architects must
also consider the disaster factor, for example, occurrence of storms and hurricanes etc. Risk ofdamages occurring is also present. If that happens, the authorities should consider the damages
cost and repairing cost. (Steel Bridge, 2004)
Figure 23. Safety measures during construction.
SOCIAL IMPACTSDuring the first eighteen months of construction, an estimation of more than five hundred
thousand tourists visited the bridge under construction. According to Godfrain (2006), more
than a million motorists have used The Millau Viaduct just for the sole purpose of admiring it.
Figure 24. The Millau Viaduct as a great tourists attraction.
Impacts on Society
Locals had expected the bridge to cut down their income as drivers will no longer pass by the
town of Millau but contrarily more and more tourists, photographers, journalist kept pouring in.
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More and more hotels, restaurants and shops have been built in Millau just to suit the needs of
the travellers and thus increasing the economy of Millau.
Jos Bov, a union leader who is France's leading opponent of globalization, organized the
destruction of a McDonald's restaurant to protest the Americanization of France. Nevertheless,
the McDonalds was rebuilt within few months and went on with business as usual.
On a National Scale, the French government has started using the bridge as a selling tool for
France. The Tour de France announced that its annual bicycle race will be routed under the
bridge next year
An Ad campaign by the French government intended to lure the foreign investments to France
by using the Millau Viaduct as a symbol of modernity. The campaign concludes with the line,
The new France, where the smart money goes. Undeniably, the bridge is a rare example of
private money financing a project so dear to France.
The construction of Millau Viaduct came to a total of approximately three hundred and twentymillion euros, which was not provided by the government of France, instead by the Engineering
company of the Viaduct, the company was not stable enough financially to afford the
construction of The Viaduct, thus leading them to sell some of their offshore properties to raise
money. However, this will be repaid by tolls over 75 years. It takes around six-seven dollars to
cross the bridge for a normal car and around thirty one dollars for a truck and thus making this
bridge a very profitable investment.
The Millau Viaduct serves its purpose to relieve traffic congestion at Rhone Valley which
connects Northern Europe with Spain and Portugal. It allows travellers to reach their destination
quickly while enjoying the beautiful scenery at the same time. The Viaduct lessens the time
taken to travel from Paris to Bziers up to three hours.
Since the building of the Millau Viaduct, the traffic on The A75 Motorway has increased by
more than 20%. Despite having various routes to choose from for tourists travelling from
Northern to Southern France, majority choose the A75 Motorway Route as its the cheapest and
the most beautiful.
After the completion of The Millau Viaduct, more than one hundred and fifty construction
workers and welders from The Millau Vidauct were employed by the EIFFAGE to work on
other projects. Since the company is also managing the Bridge, it has employed people to work
at the toll-gate and engineers perform maintenance on the Viaduct. This has led to a reductionof the unemployment rate from 10.2% to 9.1% (Republique Francais, n.d.).
Environmental Impacts
The Millau Viaduct has decreased air pollution dramatically. It only takes twenty minutes for
vehicles to cross through The Viaduct compared to the initial three hours at Rhone Valley
before the construction of Millau.
The construction of the motorway has had positive ecological impacts as it clears the rainwater
in clarification tanks before supplying it to the nearby countryside. The EIFFAGE company has
employed Ecologists and Engineers to make sure that the Viaduct causes no harm to the
environment.
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CONCLUSIONSThe Millau Viaduct is certainly an engineering success and pride of France. With seven piers
only and a deck made up of hundred percent steel, it certainly revolutionized the concept of
Bridge Designing and construction. Such a task was not easy to carry out but with expertise of
Europes best Engineers the Viaduct was completed with no major accidents or fatalities withina staggering period of 38 months.
Steel was used for the deck as it is lighter and less costly as compared to concrete. The Millau
Viaduct has definitely promoted the economy of Millau drastically as its a major tourist
attraction now in France.
The bridge was opened in 16th December 2004, a few weeks ahead of its schedule. The bridge
has provided various job opportunities for the locals; jobs for maintenance, toll attendants and
security personnel.
Imagine standing on top of the Eiffel tower and yet looking up at the Viaduct, a bridge thatglides over the clouds and a bridge that glows in the dark. The Millau Viaduct is definitely an
engineering marvel and sets new levels of bridge designing and construction.
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