砂土场地桥梁群桩基础延性抗震性能分析

Ductile Seismic Performance Analysis of Bridge Pile-group Foundations in Sand

采用严格的增量动力分析(IDA)方法对砂土场地桥梁群桩基础的延性性能开展了系统研究。基于砂土中单墩-群桩基础体系振动台试验验证了数值模拟方法;以实际工程为背景,考虑与结构、土体相关的9个参数,建立了一系列分析模型;将7条实际地震记录作为输入,进行了系统的增量动力分析。基于计算结果,对地震下桥梁群桩基础的损伤破坏过程进行了验证,提出了表征群桩基础延性性能的位移、转角、强度3个指标,并揭示了各性能指标随结构、土体参数的变化规律。结果表明,群桩基础在易修复状态下的平均位移延性系数为2.52,平均水平承载力为首次屈服状态的1.41倍;极限状态下平均位移延性系数为3.62,平均水平承载力为首次屈服状态的1.47倍,延性性能可观且稳定;承台转动引起的桥墩漂移率最大不超过0.7%,不控制抗震设计。

In this paper,the rigorous incremental dynamic analysis(IDA)method is employed to systematically investigate the ductile seismic performance of pile-group foundations(PGFs).A shake-table test on the pier-PGF system in sand is firstly used to validate the numerical modelling technique.Based on the engineering practice,a series of analytical models are then established considering the variation of nine structural/geotechnical parameters.Seven ground motion records are selected for the implementation of IDA.Finally,the seismic failure process of PGFs is validated and three performance indicators in terms of displacement,rotation and strength are proposed.And the impact of each parameter on the proposed performance index is investigated.It is found that for PGFs in the easy-to-repair state,the average displacement ductility is 2.52 and the average lateral strength is 1.41 times of that of the first-yield state.The average ultimate displacement ductility of PGFs is 3.62 and the average ultimate lateral strength is 1.47 times of that of the first-yield state.The maximum drift ratio of the pier induced by pile-cap rotation is less than 0.7%.