A Simulation of the Millau Viaduct

University essay from KTH/Mekanik; KTH/Mekanik

Author: Cathrina Bergsjö; Marcus Pettersson; [2016]

Keywords: ;

Abstract: Cable-stayed bridges have become very popular over the last ve decades due totheir aesthetic appeal, structural eciency, the limited amount of material usageand nancial benets. The rapid increase of new techniques creating longer spans,slender decks and more spectacular design has given rise to a major concern ofthe dynamic behavior of cable-stayed bridges. This has resulted in a more carefulmodelling procedure that will represent the reality in the most particular way. Amodel is simply an approximation of the reality, thus it is important to establishwhat simplications and approximations that are reasonable to make in order forthe model to be as accurate as possible.The Millau Viaduct is a cable-stayed bridge unique of its kind. At the time thatit was built it was breaking many records: span length, height of deck above thefoundations and the short construction time in just three years. Due to the slendernessof the structure, the extreme height and the location in a deep valley, theviaduct is naturally subjected to external loads. This thesis attempts to describea performed dynamic nonlinear analysis of two models of the Millau Viaduct usingthe FEA packages SAP2000 and BRIGADE/Plus. The models have been renedin order to be compared between the programs and to the reality i.e. the measuredmode shapes and frequencies obtained from reports.The viaduct required many specically designed solutions in order to obtain theelegance and the aesthetic appeal. Approximations in geometry has been essentialdue to the many details that the viaduct consists of, but the details are nonethelessimportant to capture to get the structural mechanics correct. The support conditionshas been considered as important as these were designed to allow for movementthat were caused by a combination of the external loads and the slenderness of thestructure. The most critical support conditions were the deck-pier connection inwhich the piers are split into two columns equipped with spherical bearings allowingfor angular rotation. The two shafts were modelled by one single column and thespherical bearings were simulated by creating two alternative models; one assignedwith a pinned constraint to allow for the angular rotation and the second, since thissupport condition is in fact rigid has been assigned as xed.The SAP and BRIGADE models showed to be consistent with each other, thoughthe beam theories, Euler-Bernoulli were applied to the SAP model and Timoshenkoin BRIGADE. The alternative models with the dierent constraints generated fairresults yet diers signicantly from each other. Alternative approaches towards themodelling have been addressed in the conclusions.

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