Transverse seismic behaviour of composite bridges with abutment constraints

The performance of multi-span steel-concrete composite bridges in recent seismic events has shown that these structures are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures, which are expected to yield, but also in the components of the superstructure involved in transferring the seismic loads. Current codes allow the design of regular bridges by means of linear analysis based on response spectrum modified through a reduction factor reflecting their structural ductility capacity. In bridges whose superstructure transverse motion is restrained at the abutments, the sequential yielding of the piers may cause a substantial change of the stiffness distribution. As a consequence, force distributions and displacement demand may notably differ from the predictions provided by linear analysis. The objective of this paper is to assess the influence of piers-deck stiffness ratio in the post-elastic seismic behaviour of continuous composite bridges and to evaluate the suitability of simplified linear elastic analysis in estimating the actual structural behaviour. Parametric analysis results are presented for a common bridge typology. The dependence of the response on the parameters is studied by means of nonlinear incremental dynamic analysis. The results are finally compared with those obtained by using linear dynamic analysis. Main focus is posed on curvature demand of the piers, bending moments along the deck and reaction forces in correspondence of the piers and the abutments.