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 can 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. Thus, proper evaluation of the seismic demand and capacity of each structural component involved in the seismic loads path is crucial to assess the fragility of these bridges.The objective of the paper is to investigate the seismic vulnerability of SCC bridges with dual load path accounting for model parameter uncertainty. A benchmark model of a three-span SCC bridge with relatively slender piers is considered for this purpose. Monte Carlo Simulation with Latin hypercube sampling is used to build a probabilistic model of the seismic demand and capacity at the different bridge components. This paper considers both uncertainties of the seismic action and of model parameters defining geometrical, mechanical, structural and inertial properties of the bridges considered. Comparison between the response variability induced by seismic input uncertainty and by model parameter uncertainty sheds light on the importance of accounting for the latter when evaluating the safety of the class of SCC bridges considered in this study.
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