Parametric study of continuous steel-concrete composite bridges exhibiting dual load path

The performance of multi-span steel-concrete composite (SCC) 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 (piers), which are expected to yield, but also in the other components (e.g., deck, bearings, and abutments) involved in transferring the seismic loads. Current seismic 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 with superstructure transverse motion restrained at the abutments, the sequential yielding of the piers can lead to a substantial change in the stiffness distribution. As a result, force distributions and displacement demand can significantly differ from the predictions provided by linear analysis. Bridges experiencing this drastic change in stiffness distribution are commonly referred to as “dual load path bridges”. The objectives of this study are to assess the influence of piers-deck stiffness ratio and of soil-structure interaction effects on the post-elastic seismic behavior of continuous SCC bridges and to evaluate the suitability of simplified linear elastic analysis in estimating the actual structural behavior of SCC bridges with regular geometry. Parametric analysis results are presented and discussed for a common bridge typology. The dependence of the response on the parameters is studied by nonlinear multirecord incremental dynamic analysis (IDA). The results are finally compared with those obtained by using linear multi-record IDA. Main focus is on curvature demand of the piers, bending moments along the deck and reaction forces at the piers and the abutments. The results presented in this study suggest that simplified linear elastic analysis based on inelastic response spectra can produce very inaccurate estimates of the actual structural behavior of SCC bridges with dual load path. 3 INTROD