| Name | Millau Viaduct |
|---|---|
| Who | |
| Owner | Public Authority:Direction des Routes, France, Arrondissement interdepartemental
des ouvrages d'art de l'autoroute A75, Millau, France Concessionaire: Compagnie Eiffage du Viaduct de Millau, Millau, France |
| Design | Michel Virlogeaux, Greisch, Arcadis, Thales E et C |
| Architect | Foster & Ptnrs |
| Contractor | Eiffage TP Eiffel Construction Metallique |
| Where | Millau, France |
| Latitude | N 44 05' 00" |
| Longitude | E 03 01' 17" |
| Why | Takes 4 lanes of A75 between Clermont-Ferrand and Beziers by-passing Millau. Part of the link between northern Europe and Spain |
| Millau is at the confluence of the rivers Tarn and Dourbie. | The bridge strides over the deep valley connecting the two plateau - with the River Tarn 275 m. below. |
| What | Read more..... |
| How to read the bridge | Read more..... |
Back |
| What | |
|---|---|
| Overall type | Multi-span cable stayed bridge. |
| Width | 32 m. |
| Length | 2.46 km. |
| Span | 8 spans - 2 side spans at 204 m. and 6 middle spans at 342 m. |
| Height of towers | Deck is 275 m. above River Tarn and pylons or masts above the deck are 87 m. tall. |
| Materials | Towers: Reinforced concrete with some prestressing Deck: Steel box girder Cables: Steel |
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| How to read the bridge | Read more about the book metaphor... |
|---|---|
| The chapters |  |
| Chapter 1 | Suspension system |
| Paragraphs | Towers: Piers with 2 longitudinal dividing shafts below deck level and pylons or masts above deck level. Supporting cables: 11 pairs of stay cables each side of each pylon. |
| Sentences | Towers: Piers have variable cross section - shape influenced by architect but within engineering constraints.
Pylons shaped as longitudinal A frames. Cables: Consist of 51 to 91 steel strands depending on location. |
| Words | Tower: Piers built in sections using self climbing forms with linked tower crane.
Pylons were precast and erected on the bridge. Cables: Each strand contains 7 wires triple protected against corrosion. |
| Letters | Steel: Iron, carbon with other additives such as chromium etc Concrete: Cement, sand, aggregate and water Reinforced concrete: Concrete is strong in compression but weak in tension where it has to be reinforced with steel bars |
| Chapter 2 | Deck |
| Paragraphs |
Bridge deck: Aerodynamic steel box girder. Tied to piers by vertical prestressing tendons
in line with the 2 fixed bearings on each shaft and the pylons above. Surfacing: Road surfacing on top flange of bridge deck for traffic surface. Street furniture: All services including signing, lighting and power supply. |
| Sentences | Deck: Triangulated cross brace stiffening at 4.17 m. intervals along the length. 2 vertical webs to strengthen deck during erection. |
| Words | All components including steel plate, stiffeners and welds making the box girder, members of lattice cross girders and joints. |
| Letters | Steel: Iron, carbon with other additives such as chromium etc Concrete: Cement, sand, aggregate and water Reinforced concrete: Concrete is strong in compression but weak in tension where it has to be reinforced with steel bars |
| Chapter 3 | Foundations |
| Paragraphs | Each pier is founded on 4 "artificial wells" which are 4 to 5 m. diameter and 9 to 16 m. deep. Bearings are spherical and covered with a special hard wearing composite. |
| Grammar | Technically the bridge is a way of taking forces from up in the air down to the ground.
So imagine the flow of those forces through the structure.
Think of a truck standing on the brdge and how its weight is transmitted through the bridge to the ground.
This bridge is elegant because its structural grammar is slender and aesthetically pleasing.
It has the 'wow' factor. Multiple spans of cable stayed bridges produce special difficulties - they behave quite differently from the more conventional 3 span bridges (i.e. with 1 main span and 2 side spans). Interactions between the spans are more complex, especially under varying patterns of live loads. The various solutions are highly influenced by the type of connections between the deck and the towers (the piers below and the pylons above at Millau). Sideways wind loads are critical but such a long bridge has also significant longitudinal movements mainly due to temperature variations. There are therefore contradictory requirements for the piers: they have to to resist very high lateral wind forces whilst at the same time they must be sufficiently flexible along the length of the bridge to allow longitudinal movement. Various solutions have been tried (see References below: Virlogeux 2001). The solution at Millau is both elegant and structurally efficient. The piers split into two shafts along the length of the bridge and the deck is fixed to the shafts by vertical prestressing tendons on each shaft and the pylon above with the shape of an inverted V. As a consequence some of the bending from the deck is transferred to the towers so that the bridge has increased longitudinal rigidity and the deck section is more slender. The box section for the lower part of each pier resists the wind as a giant cantilever. |
| Erection | A major innovation was the launching of the box girder and the subsequent erction of the pylons.
The girders were launched from each end. Temporary intermediate supports were installed
at the mid-points of each span except for the span where the two ends met - the closing span.
Each girder had its first leading pylon mounted with 6 of the final 11 cables installed to reduce
the bending moments in the girders during the launch. A highly innovative system was developed
to make sure the piers were not simply 'pushed over' as the girder moved over them.
Each support had specially designed active wedge shaped launching bearings with horizontal jacks and sensors
connected to a central computer which controlled the movement of the girders to ensure they each moved
incrementally the same amount. The pylons were transported one by one onto the deck by two crawlers and lifted up from a horizontal position using a support tower. The cables were then installed between the pylons and the deck. All this was done in varying weather condition 275 m, in the air. Wind loading was of critical importance. For more details of the jacking system used during the launch of the girders click here |
| References | Virlogeux M, "Bridges with Multiple Cable-Stayed Spans", Structural Engineering International, 1/2001, 61-82 Virlogeaux M et al, "Millay Viaduct, France", Structural Engineering International, 1/2005, 4-7 |
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