Seismic Performance of a Y-Shaped Irregular Bridge Subjected to Strong and Multidirectional Ground Motions

A 1/20 scale model of a Y-shaped irregular bridge was designed, and shaking-table tests were performed to simulate its failure mechanism and performance characteristics when subjected to a multidirectional strong earthquake. The results showed that the irregular bridge structure could accelerate in the horizontal direction when subjected to vertical excitation. For both unidirectional and multidirectional excitation, the acceleration response of the pier top was more significant in the transverse direction than in the longitudinal direction. For the variable-section and branching curved beams (i.e., ramp), the response to three-dimensional excitation was equivalent to the direct superposition of the responses to bidirectional excitation and single vertical excitation. With multidirectional excitation, the girder and ramp were more prone to structural collision. However, the likelihood of structural collision was not increased with multidirectional excitation than with bidirectional excitation. The displacement of the pier and beam was very large at the junction of the variable-section main beam and branching curved beam, so bearing failure and falling beams easily occurred. Multidirectional excitation generally increased the vertical acceleration response of the two piers and pier top at the irregular bridge branch, demonstrating the need to consider shock absorption and isolation in designing these locations