考虑弯曲－屈曲耦合失效模式的液化场地桥梁桩基强震反应分析方法

Case studies of several major earthquakes have clearly documented that this phenomenon has significantly damaged the pile foundations of bridges in liquefiable soils, which are designed using current modern method. Advisory investigation, case studies, model and field tests, theoretical method, numerical simulation, and criterion analogy will be adopted to investigate the seismic response of reinforced concrete pile-column pier of bridges under well understanding its performance in the previous study. Attention is paid to the failure mechanisms involving coupling of structural bending and buckling under combined lateral and vertical loading and its negative influence. A novel simplified analysis method of the seismic response of nonlinear soil-pile-bridge structure system in liquefiable ground was proposed in this proposal, which can be utilized to identify and avoid the structural failure coupling of bending and buckling. Suggestions for improving China’s current seismic code for designing bridges in liquefiable ground will be proposed. The study would greatly help improve understanding of failure mechanism and accurately predicting the seismic behavior for bridges pile foundation under strong earthquakes, which is significant in engineering practice as well as in theory research.

基于现代设计理念的桥梁桩基在液化场地破坏频发的工程背景，针对延性抗震性能研究较充分的钢筋混凝土桩柱式桥墩，依托咨询调研、震害调查、模型试验与原型测试、理论解析与数值模拟、规范比照等综合研究方法，关注侧向荷载（运动荷载和惯性荷载）和竖向荷载联合作用下桩的强震反应基本规律与失效机制，突出桩的弯曲－屈曲耦合作用及其影响效应，致力于桩的弯曲－屈曲耦合失效的有效防控，着眼于桩－土－桥梁结构强非线性动力耦合体系，聚焦提出便于推广且易于数值实现的液化场地桥梁桩基强震反应分析方法，对我国现行规范液化场地桥梁抗震设计方法提出初步的改进建议。这对于客观认识桩基桥梁结构强震反应规律与失效机制，精准分析桥梁桩基动力反应特性，科学完善现行液化场地桥梁桩基抗震设计规范，有效实施强震下桥梁桩基抗震设计等，无疑具有重要理论和现实意义。

历次震害调查显示，土体液化造成液化场地桩基失效的主要模式有弯曲失效、沉降破坏和屈曲失效。针对液化场地桩基的弯曲失效和沉降破坏问题，国内外学者已开展了大量的研究工作，并颁布多项抗震设计规范。然而，针对液化场地桩基屈曲失效机制的研究相对较少，且多集中于研究轴向荷载对桩基屈曲失效的影响，忽略了惯性荷载和轴向荷载耦合作用可能诱发的桩基屈曲失效问题。为此，项目以液化场地嵌岩桩为研究对象，通过开展多重荷载解耦的振动台对照试验，揭示了液化场地桩基屈曲失效原因，提出了桩基屈曲临界荷载计算方法，查明了影响桩基地震反应的关键地震动参数，发展了易于工程应用的液化场地桩基屈曲失效判别方法。研究成果对于客观认识桥梁桩基强震反应规律与失效机制，精准分析桥梁桩基竖向承载力，科学完善现行液化场地桥梁桩基抗震设计规范，有效实施强震下桥梁桩基抗震设计等，无疑具有重要的理论和现实意义。