墩台洪水冲刷对RC桥梁构件和整体抗震性能的影响

Influence of flood-induced pier and abutment scour on seismic performances for component and entire structure of the reinforced concrete bridges

跨水域桥梁结构的约束边界和动力特征在经历洪水冲刷后会发生改变,为探讨墩台洪水冲刷对桥梁构件和整体抗震性能的影响,以我国西部地震活跃区某跨河的钢筋混凝土(RC)桥梁工程为例,根据算例桥梁桥址处的历史水文数据对流经河流的洪水危险性进行概率性统计分析。通过建立桥墩和桥台的冲刷深度风险评估曲线,分别以超越概率2%、50%和98%对应的冲刷深度来表征严重、中等和常规的洪水冲刷工况,在此背景下探讨了不同工况下的桩−土相互作用和台−土相互作用的模拟方法。采用OpenSees程序建立了算例桥梁的非线性有限元模型,通过输入100条地震波进行桥梁动力响应计算。基于计算结果分析了墩台洪水冲刷对桥梁构件、系统易损性以及构件损伤顺序的影响规律。研究结果显示,随着墩台洪水冲刷程度的增加,桥墩地震损伤概率逐渐减小,桥台和桩基地震损伤概率明显增大,支座地震损伤概率有一定增加但变化不大。此外,桥梁结构系统层次的地震易损性随洪水冲刷程度增加而增大。不同桥梁构件的损伤顺序和级差会随洪水冲刷程度的增加而发生明显改变,特别是,严重冲刷后不易修复的桥台和桩基可能率先发生破坏。研究结果对理解墩台冲刷情况下RC桥梁的抗震性能具有较好的工程实用价值,特别是跨水域桥梁进行构件能力保护设计时有必要提前考虑运营阶段墩台冲刷效应的影响。

The constraint boundaries and dynamic characteristics of the bridge structures across the water region will change after the flood-induced scour.In order to investigate the effect of flood-induced pier and abutment scour on seismic performances of bridge components and the entire structure,a case study of an RC bridge engineering across a river in an earthquake-prone region of western China was conducted.The probabilistic statistical analysis was performed on the flood risk of the river based on the historical hydrological data of the river that across the case-study bridges.By developing the risk assessment curves of flood-induced scour depth for the pier and abutment,flood-induced scour conditions were characterized as severe,moderate,and typical using exceedance scour depth of probability 2%,50%and 98%,respectively.In this context,the modeling methods of pile-soil-interaction and abutment-soil-interaction under three different scour conditions were discussed.A nonlinear finite element model of the case-study bridge was developed using the OpenSees program.Then,100 seismic waves were inputted for dynamic response calculation of the bridges.Based on the calculated results,the influences of flood-induced pier and abutment scour on component and system fragility of the bridges,as well as the sequences of component damage,were investigated.The results show that with the increasing degree of flood-induced scour,the damage probability of the bridge pier gradually decreases,while that of the abutment and pile increases significantly.The damage probability of bearings increases but the change is not significant.In addition,the seismic fragility of the bridge structural system increases with increasing flood�induced scour degree.The damage sequence and grade difference of various bridge components also change significantly with increasing degree of flood-induced scour degree.In particular,the difficult-to-repair abutments and piles may be damaged first after the severe scour.The research results have significant practical engineering value for understanding the seismic performance of the RC bridges under the pier and abutment scour.Especially,it is necessary to consider the impact of pier and abutment scour during the operation phase of the bridges when designing the capacity protected members of the bridges across the water region.