MILLAUVIADUCT

MILLAU VIADUCT

NAME : ROHIT DIGRAYEAR : 1ST YEAR M.ARCH (P.M.)

LONG SPAN STRUCTURE

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.

INTRODUCTION

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.

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.

SPECIFICATIONS

CONSTRUCTION OF PIERSEach 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. TEMPORARY PIERS

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.

STEEL DECKS

They 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 DECK

7 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 CONSTRUCTIONAfter 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.

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.

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!

ATTACHMENT OF CABLES

WINDSCREEN

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.

REFERENCES

www.leviaducdemillau.comWikipediaCnrsm.creteil.iufm.frwww.enerpac.com/html/Projects/Millau/Millau_Launching_Systems.htmlwww.fosterandpertners.com/projects/millau-viaductMegastructures-Millau viaduct – national geographic.Google images