Millau Viaduct, France

Recent Structures Worldwide: An Introduction Both our regular readers, the IABSE members, as well as it may be. IABSE is the prime professional organization for new readers who may be getting this special issue of “Struc- structural engineers truly committed to the exchange of tural Engineering International” at the Structures Congress knowledge and to the advancement of the practice of struc- 2005 in New York City, will be delighted to go through this tural engineering worldwide, as reflected in this and in every Recent Structures series, aimed at showcasing a wide range of SEI issue, and, if you are not a member yet, I invite you to structures recently completed. They all share common fea- join! tures: they were challenging to design and to build, uncon- This carefully selected group of recent structures, many of ventional in their own way, and innovative. They were built which will be presented by their designers at Structures Con- all over the world, and in many cases by a truly global part- gress 2005, is certain to stimulate our creativity. I invite you to nership of designers, detailers, fabricators and constructors. read the articles, and to attend the Congress. While in New As structural engineers in a world where country borders are York, hometown to some of the best and internationally rec- increasingly just a line on a map, we strive to feed on the ex- ognized structural engineering firms, don’t forget to visit the perience of other engineers, geographically or by specialty local outstanding structures, both new and old. both near and far from us. Designs conceived in Switzerland For more information on the Congress, which is organ- are executed in Japan, software developed in the USA creates ized by the Structural Engineering Institute, please visit a barrier-free language for the exchange of data in Europe. www.asce.org/conferences/structures2005. I am looking for- Bridge technologies get applied to long-span building roofs, ward to greeting you in New York City! architectural aspects traditionally found in building design become a driving force for signature bridges. In a rapidly evolving world, becoming aware of sophisticated analysis Maria Grazia Bruschi techniques and new construction materials and methods as Member, IABSE SEI Editorial Board they develop will influence our next project, small or large as Member, Steering Committee Structures Congress 2005 Millau Viaduct, France Michel Virlogeux, Consult. Eng. and Designer, Bonnelles, France; Claude Servant, Tech. Dir., Eiffage TP,Neuilly sur Marne, France; Jean-Marie Cremer, Dir., Bureau Greisch, Liège, Belgium; Jean-Pierre Martin, Proj. Dir., Eiffage TP,Millau, France; Marc Buonomo, Dir., Eiffel, Lauterbourg, France Fig. 1: View of Millau Viaduct near completion (Photo: Phototheque Eiffage /D. Jamme) Introduction the South, at an altitude of about 720 m, The basic idea was to design a very selecting a road alignment was not an slender bridge, thus cable-stayed, with The Millau Viaduct is the major bridge easy task, and the more so considering a series of equal spans which would on the A75 motorway between Cler- that the lower portions of the hills are look logical from the city of Millau, mont-Ferrand and Béziers, which will made of unstable soil, mainly clay. from where the lower part of the Tarn be part of a new link between North- valley cannot be seen due to the multi- ern Europe and Eastern Spain (Fig. 1). After eliminating different options it ple river bends. Several other solutions The city of Millau is located at the con- was decided to erect a viaduct passing were developed with his design team fluence of two rivers, the Tarn and the directly from plateau to plateau, 275 m at SETRA (French national highway Dourbie Rivers, that cut two deep val- above the Tarn River. The concept of department) in 1992–1993. leys in the old Massif Central plateau. the final structure that was erected, a As the motorway had to pass from a cable-stayed bridge with eight spans Through a quasi-brainstorming com- plateau on the North, at an altitude of suspended from seven pylons, was first petition, in 1993–1994, several design- about 600 m, to the Larzac Plateau on proposed by Michel Virlogeux in 1990. ers and architects had the opportunity 4 Structures Worldwide Structural Engineering International 1/2005 2460 m 204 m 342 m 342 m 342 m 342 m 342 m 342 m 204 m Béziers Clermont Ferrand South Alt. North Alt. 90 m 675 m 601 m 77 m C8 C0 145 m P7 245 m 230 m P6 P1 P4 P5 P3 P2 Tarn River SNCF train track Fig. 2: Bridge elevation to analyse the SETRA solutions and 3,00 m 3,50 m 3,50 m 1,00 m 1,00 m 3,50 m 3,50 m 3,00 m propose new ones. Finally a quasi-competition was organized between five design teams, each in charge of one type of solution, the five families of solutions being derived from those pro- 3,00 m posed by SETRA and enhanced by the new ideas that came from the brain- 4,20 m storming competition. The design teams were appointed to develop the solu- 14,025 m 4,00 m 14,025 m tion that was as close as possible to their proposals made during the brain- 32,050 m storming competition. In July 1996, the jury selected a cable-stayed bridge with Fig. 3: Cross-section of bridge deck multiple spans. The project was developed between 1997 and 1998 by the a streamlined orthotropic steel box- vehicles arriving on the bridge; and of winning team which included Sogelerg girder with two vertical webs required fairings intended to improve both the (now Thalès Engineering and Consult- by the selected erection technique. Tri- aerodynamic streamlining and aesthet- ing), EEG Simecsol (now Arcadis), angulated cross-beams, spaced at 4,17 m ic quality (Fig. 4). SERF, and Foster and associates, to- longitudinally, were preferred to full gether with Michel Virlogeux. In actu- diaphragms. This box-girder carries ality, there were two parallel projects, two lanes of traffic in each direction Piers one in prestressed concrete and one in with 3 m wide shoulders to increase steel. the distance between the traffic and The design of the bridge results from Due to the high global cost of the mo- the bridge edge, in order to reduce the major structural demands; to balance torway, the French government decid- risk of vertigo (Fig. 3). The box-girder unsymmetrical live loads in the multi- ed that the bridge would be built with- is equipped, in addition to classical ple cable-stayed spans, as well as to in a concession. Three major groups barriers, with wind screens designed to adapt to the length variations due to took part in the competition in 2000– limit the wind velocity on the viaduct temperature effects in the box-girder. 2001, and the concession for 75 years to the value at the approach ground To resist the high bending moments was awarded to Compagnie Eiffage du level, in order to avoid wind shocks to due to their extreme height, the piers Viaduct de Millau, a specific company were designed as wide strong box-sec- created for this occasion. Construction tions that split into two flexible shafts work began on October 10, 2001. As in the upper last 90 m (Fig. 5). the group Eiffage includes a steel con- structor, Eiffel Construction Métallique, The box-girder deck is tied down to the steel solution was preferred. Con- the pier by vertical prestressing ten- struction was carried out by Eiffage dons in line with the two fixed bearings Travaux Publics and Eiffel under the on each shaft, and the pylon, above, supervision of an independent check- has the shape of an inverted V. Under er, a joint venture of SETEC and SNCF the effects of unsymmetrical live loads (the French railways). The final detail or extreme wind loads, the vertical load design was developed by Greisch (for on each bearing can reach 100 MN. To the steel parts of the bridge), Arcadis, reduce the bearing size, spherical Mau- Thalès E and C, SERF and Eiffage TP. rer bearings covered with a new com- posite material which can resist stress- Bridge Cross-Section es up to 180 MPA under ultimate loads were used. The Millau Viaduct, 2460 m in length, The piers have a variable cross-section, consists of eight spans; two side spans the shape of which has been designed 204 m long, and six intermediate spans by the architect in close collaboration 342 m long (Fig. 2).The cross-section is Fig. 4: View of wind-screen with the engineers to allow for ease in Structural Engineering International 1/2005 Structures Worldwide 5 10,00 m 16,00 m 90,00 m 244,80 m Fig. 7: Launching of girder with front pylon and cables in place 27,00 m 17,00 m Fig. 5: Typical pier elevation construction despite its variations. Four panels have fixed dimensions, and the other four change slightly in each seg- ment, including their orientation. This allowed for an erection with external self-climbing forms developed by Peri, and classical internal shutters moved by the tower crane. Fig. 8: Launching operations nearing completion The two taller piers are 245 m (P2) and rary supports, each in the shape of a tu- 223 m (P3) high. The tallest tower bular truss, were installed in each span crane, for P2, reached a height of 275 except for the closure span. In the in- m. It was therefore necessary that each termediate spans, these temporary sup- tower crane was fixed to the corre- ports, 12 m by 12 m, were at mid-span sponding pier, step by step, according with two lines of launching equipment to the construction progress (Fig.

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