Effect of Substructure Irregularity on the Seismic Vulnerability of Short-Span Bridges

Seismic performance and dynamic characteristics of bridge structures are highly influenced by their geometric properties. This paper aims at studying the impact of substructure irregularity on the seismic vulnerability of multicolumn-bent short-span bridges by estimating the capacity of bridge components. For this purpose, incremental dynamic analyses have been performed on two five-span bridge configurations, chosen according to a real case study. The studied bridges present supported on seat-type abutments and differ according to pier heights: regular and irregular substructures with equal and different heights, respectively, have been considered. Pounding of the bridge superstructure portion and nonlinear backfill soil behavior are accounted for in nonlinear time history analyses. Spectral acceleration of the first fundamental period and peak ground velocity are considered as intensity measures, while failure criteria consisted on maximum columns drift ratio and deck unseating at abutments. The performed analyses revealed a response of the irregular bridge significantly worser than the regular one. Besides, the two failure criteria affect the seismic vulnerability of the regular bridge almost equally and for the irregular bridge, column damage is always recognized to be the main reason of the structural collapse.