MILLAU VIADUCT

MILLAU VIADUCT

The Millau Viaduct is a cable-stayed bridge that spans the valley of the River Tarn near Millau in southern France .

It is the 12th highest bridge deck in the world.

It was built to reduce traffic of small town Millau as the motorway connecting Paris and Spain passed through Millau.

INTRODUCTIONThe Millau Viaduct is a cable-stayed

bridge that spans the valley of the River Tarn near Millau in southern France .

It is the 12th highest bridge deck in the world.

It was built to reduce traffic of small town Millau as the motorway connecting Paris and Spain passed through Millau.

MAJOR ENGINEERING CHALLENGES

1) BUILD THE TALLEST BRIDGE PIERS IN THE WORLD.

2) PUT 36000TON FREEWAY ON TOP OF IT.

3) ERECT 7 STEEL PYLONS HUNDREDS OF METER ABOVE THE SOLID GROUND.

SPECIFICATIONSMILLAU VIADUCT

Crosses : River Tarn Design : Cable-stayed bridgeTotal length : 2.5 km longWidth : 32 mLongest span : 342 mHighest pier : 245 mCurved radius : constant 20 km

Construction of piers

Each pier is treated as a worksite in its own right so that construction of all the seven bridges can take place independently.

The geometry of the piers varies from one pouring step to the following pouring step and is tapering entire way up.

The shape of the mould was changed at every 4m height to fit the profile and reinforcing concrete method was used in raising the pier.

The formwork was of self-climbing type for outer surfaces and craneassisted for the inner surfaces as the risk factor was to be taken care of.

Altimetric checks by GPS ensured a precision of the order of 5mm in both X and Y direction.

• The installation of the deck by successive launching operations requires the erection of 7 temporary piers.

• These piers consists of a metal framework of a square section of 12mx12m whose members are tubes of 1,016mm diameter.

• They introduced this piers between the two pillers as the span between the two piers was large and deck could not support itself.

Temporary piers

Steel DecksThey opted for steel deck over the conventional concrete block,as it is not economical and safe to lift concrete over such heights.Fabrication of the deck section was done on steel factory .Around 2200 sections each weighing upto 90 tonnes and were some were 22 long.

Launching the deck7 temporary piers help support the weight of the deck,as the longest deck could support was half the span.

Two deck segments were launched from each end of the bridge

Hydraulic launchers•Computerized launchers push the pre-fabricated deck segments on to the piers.•Each cycle moves the deck 600 mm.• Total of 5000 cycles required.•The cycle is repeated every 4 minutes

NOSE RECOVERY•Weight of steel box girder deck sags as span is completed.•Nose recovery system attached to raise the deck to the level of the next pier.•This aligns the deck for the level and curvature of the next pier.•The precision carried out in the nose recovery system was due to the use of GPS system as the accuracy was upto 4mm.

PYLON CONSTRUCTION

After the deck construction was finished it was time to erect the pylons to provide cable support for the bridge.The temporary piers were supporting the deck but due to the flexibility of the steel the deck was very undulating, the deformations were quite large.So the 90 m tall and 700 ton pylons were installed as fast as possible.The pylons and cables were needed to straighten the undulated deck.

For placing the pylons steel engineer Marc Buonomo used a technique which was practiced in the ancient Egypt.In this Egyptian method the pylons were lifted slowly using a hydraulic machine.As they were being lifted they were also made to pivot by two temporary steel towers,both of them secured by a cable.As the bridge is lifted it also pivots untill it is vertical and it is erected .

Connection between pylon , deck and the pier

An inverted Y shape ha been adopted for the pylons,which are metal,and which are oriented longitudinally as extensions of the split shafts of the piers.This arrangement gives the pylons the required high degree of rigidity.

ATTACHMENT OF CABLES

With all seven pylons in place it was time to attach the cables stays that would straighten the rippling deck and give it the strength to endure the traffic load.The roadway weighs over 40000 tonnes and the 154 cable stays should prevent it from sagging or collapsing.These cable stays are made of 91 individual steel strands and have breaking strength of 25000 tonnes.These stays are strong enough to hold 25 jumbo jets all at full throttle!

WIND SCREEN

An issue that presented itself after the bridge was completed was the fact that the wind speed at the level of the bridge was “upto 151 km/hr”,which is significantly more than the wind speed that would be found at ground level.This would cause serious issues driving on the bridge because the high wind speeds would push vehicle to the side, making driving dangerous.This problem was addressed by the inclusion of windscreens that reduced the affect of the “wind by 50%”,effectively causing wind speeds on the bridge to reflect those on the ground.

GRADING OF MATERIALS

The deck and the pylons,entirely of metal,are made of steel of grade S355 and S460.The piers are constructed in B60 concrete.This concrete was chosen more for its durability than for its high mechanical resistance.

REFERENCESwww.leviaducdemillau.comWikipediaCnrsm.creteil.iufm.frwww.enerpac.com/html/Projects/Millau/Millau_La

unching_Systems.htmlwww.fosterandpertners.com/projects/millau-viadu

ctMegastructures-Millau viaduct – national geographic.Google images

PAURIN SHAH

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