One of the challenges associated with AASHTO-LRFD and Eurocode 8 is predicting the failure of irregular bridges supported by piers of unequal heights, which is not effectively addressed by codes committee. EC8 currently uses "moment demand-to-moment capacity" ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 and AASHTO-LRFD design procedures for regular seismic behavior, various irregular bridges will be simulated through a non-linear pushover analysis using shear-critical fiber-based beam-column elements. The research will investigate the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and investigate different ways of regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all unequal piers irrespective of the different heights and failure mode experienced.
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