16.04: High strength steel (HSS) S690 in highway bridges: Comparative design

ABSTRACTThe use of High Strength Steel (HSS) S690 in highway bridges decks is not yet widespread. A research program investigated the optimal use of HSS S690 within bridges was conducted.A comparative design is presented for a 21.5 m wide highway bridge, with a typical 80 m long span and a composite steel‐concrete twin plate girder deck. Two designs are compared, using the Eurocodes: Design (A) adopted standard S355 NL steel grade whereas Design (B) uses HSS S690 QL or QL1 on the main girders.Comparison between the two designs shows that using S690 enables reductions of 25% on the steel weight and about 65% on full penetration welding volume, compared to design with S355. The deck can be slender using HSS and have thinner plates, but it is more susceptible to local buckling phenomena. Brittle fracture is slightly less dimensioning using HSS, but girders are likely to be much more prone to fatigue, which proves to be the main issue of the design together with the local buckling phenomena.The critical fatigue welded joints are analysed according to EN 1993–1‐9. For plate girders with transverse stiffeners, fatigue presents a major design constraint, namely on span sections, due to allowable plate stresses range near the welded joints.Standard fatigue load model FLM3 with the damage equivalent factor concept is used for fatigue design of several plate girder details. Fatigue resistance of the welded joint between the transverse stiffeners and the bottom tension flange proved to be the most relevant aspect of the design of the composite steel‐concrete twin plate girder deck designed for HSS S690.