Reduced formulation for post-elastic seismic response of dual-load path bridges

The paper analyzes the transverse seismic behaviour of multi-span bridges with dissipative piers and a continuous deck transversally restrained at the abutments. 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. A simplified analytical model and formulation are defined in order to derive the properties of an elastoplastic single-degree-of-freedom system equivalent to the bridges, which can be used for design purposes or for preliminary analyses. Analytical expressions are proposed for describing the post-elastic system behaviour, the global dissipative capacity, and the failure modalities. These expressions can be written in terms of non-dimensional characteristic parameters to shed light on the relationship between the seismic capacity and the bridge properties. The proposed analytical formulation is applied to the analysis of a set of continuous multi-span steel– concrete composite bridges with different static schemes and stiffness distributions. The accuracy of the simplified model is tested by comparison with the results of incremental dynamic analysis performed on three-dimensional nonlinear finite element models