近场脉冲地震下考虑模型不确定性的桥梁时变抗震分析

Time-dependent seismic performance of bridges considering modeling uncertainties under near-field pulse-like ground motions

为了研究近场脉冲地震下桥梁结构的时变抗震性能,以一座常规连续梁桥为研究对象,引入氯离子侵蚀模型,在考虑多种不确定性因素基础上,采用拉丁超立方抽样建立不同服役时期的时变模型样本,运用增量动力分析方法,从能力、需求以及倒塌等方面对算例桥梁的时变抗震性能进行了研究和评价。结果表明:近场脉冲型地震下结构的抗震需求明显大于远场地震;氯离子侵蚀导致钢筋锈蚀后力学性能发生改变,箍筋对核心混凝土约束能力减弱,锈蚀纵筋屈服强度及极限拉应变都降低,导致桥墩的变形能力下降;与地面运动的不确定性相比,模型参数的不确定性对结构的抗震需求均值及离散性影响均不大;随着服役时间延长,钢筋锈蚀加剧,桥墩出现倒塌破坏的概率加大。

In order to study the time-dependent seismic performance of bridge under near-field pulse-like ground motions,a conventional continuous bridge considering chloride attack was taken as an example.In order to consider the vary uncertainty factors in the model,Latin hypercube sampling method was adopted to establish time-dependent model samples at different times.Then the time-dependent seismic performance of the bridge from the aspects such as capacity,demand and collapsed in the earthquake were studied and evaluated with incremental dynamic analysis.The results show that the seismic demand of structure in near-field pulse-like pulse earthquake is obviously greater than that in far field earthquake.As the mechanical properties of reinforcement changed after corrosion due to chloride attack,the constraint ability of stirrup to core concrete is weakened and yield strength and ultimate tensile strain of longitudinal reinforcement are reduced,which led to decline of the deformation ability of pier.Compared with the uncertainty of ground motion,the uncertainty of model parameters has little influence on the mean value and discreteness of seismic demand.With the extension of service time and the increment of corrosion of the steel,the probability of collapse of bridge pier increases.