Optimal use of high strength steel grades within bridge (OPTIBRI)

The project aims to generate guide lines for welded bridges using High Strength Steel. The quantification of the advantage of using HSS within bridges is performed on a 21.5 m wide highway bridge, with a typical 80 m long inner span and a composite steel-concrete twin plate girder deck. It presents clear fatigue and stability issues. An extensive experimental and numerical campaign of fatigue on HSS samples, welded plates and welded beams as well as an experimental and numerical study of multiaxial stressed plates allow a better understanding of HSS material and HSS welded joint behaviour with or without weld post treatment. The results enhance the need of an Eurocode review. Three designs of this bridge are compared: the first bridge design (A) uses only standard S355 steel grade whereas the second design (B) uses also HSS S690 QL steel but relies on current state of Eurocodes. Finally, the third design (C) is performed based on the real measured behaviour of HSS S690 QL steel and post treated welded joints. Through different variants of the design (C), the project results demonstrate the need of updating of Eurocode to take into account the enhanced material properties of HSS and the buckling of multiaxial stressed plates. The use of S690 QL in design B (C) enables reductions of steel weight of 25% (32%) on the steel deck and 34% (39%) on main girder compared to Design A and these designs save about 50% on full penetration welding volume compared to design A