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Bridges are one of the most critical components of any transport infrastructure network, and their serviceability during earthquakes is vital to ensure the safety of society. To be able to overcome bridge failure, code committees started to focus on different methods to design bridges under the effect of seismic forces. One of the challenges associated with Eurocode 8 and AASHTO-LRFD, which is not effectively addressed by code committees, is to withstand the failure of irregular bridges with unequal pier heights from seismic forces.

EC8 currently uses “moment demand-to-moment capacity” ratios to insure simultaneous failure of piers on bridges supported by piers of unequal heights, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These regulations are not entirely valid, especially for bridges with piers of relative height of 0.5 or less, where in the case of earthquakes, they can experience a combination of shear and flexure failure modes. In this case, the shorter piers often result in a brittle shear failure, while longer piers are most likely to fail due to flexure.

This study aims to evaluate the adequacy of EC8 and AASHTO-LRFD design procedures for regular seismic behavior, by modeling various irregular bridges using shear-critical fiber-based beam-column elements. In this work the behavior of several irregular monolithic and bearing-type bridges is investigated. In addition, different methods of regularizing the bridge performance are examined in order to balance damage, with the ultimate aim of obtaining a simultaneous or near-simultaneous failure for all piers irrespective of the different heights and failure modes experienced.

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