Seismic capacity of continuous steel-concrete composite bridges with dual load path behaviour

This paper analyzes the transverse nonlinear seismic behaviour of multi-span continuous steel-concrete composite bridges with abutment restraint and dissipative piers. These structural systems have a “dual load path” behaviour and their failure may occur in the piers or in the deck, depending mainly on geometry and stiffness distribution. An analytical continuous bridge model is developed, and a variational formulation of the seismic problem is employed to derive the properties of an elasto-plastic single-degree-offreedom system equivalent to the bridge. This permits to obtain analytical expressions for describing the post-elastic system behaviour, the global dissipative capacity, and the failure modalities, and also to make explicit the relationship between the seismic deck and pier capacity and the bridge properties. The proposed analytical formulation is applied to the analysis of a set of continuous multispan steel-concrete composite bridges with different geometry. The accuracy of the simplified model is tested and validated by comparison with the results of incremental dynamic analysis performed on three-dimensional nonlinear finite element models.