Seismic assessment of bridges with different configuration, degree of irregularity and dynamic characteristics using multimodal pushover curves

Abstract eng:
In seismic assessment of structures the pushover curve is a key tool, in the sense that it provides a good description of the strength and the available ductility of the structure, both combined in a single diagram. The present study assesses the seismic performance of bridges with different configuration, degree of irregularity and dynamic characteristics. The first structure is a 638m-long multispan bridge with significant curvature in plan, unequal pier heights and different types of pier to deck connections. The second one is an overcrossing bridge with three spans and total length 100m, typical in modern motorway construction in Europe, which although ostensibly a regular structure is found to exhibit a rather unsymetric response. The third one is a 247m-long three-span bridge with small curvature in plan and piers of unequal height that are monolithically connected to the deck. The bridges are assessed using response spectrum, ‘standard’ and modal pushover analyses, as well as the more rigorous non-linear response history analysis (NL-RHA). Multimodal pushover curves are derived for each bridge using modal pushover analysis. Dynamic pushover curves are also derived to investigate the accuracy and efficiency of both multimodal and ‘standard’ pushover curves for the selected bridges. The study shows that the multimodal pushover curve reasonably matches the ‘dynamic’ pushover curve derived from the more rigorous NL-RHA in all cases. On the contrary, ‘standard’ pushover analysis is found to be valuable only for the assessment of the actual inelastic response of the bridge with regular response, where the influence of higher modes was found to be insignificant. An important issue regarding the applicability of modal pushover method to bridges is not only the influence of the modal participation factor on the response of the structure but also the boundary conditions at the abutments that affect the torsional response of the bridge.

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