近场地震下考虑土-结构相互作用的梁式桥基于性能的抗震设计

Seismic damage experience show that: the main reason for collapse of beam-bridge subjected to near-fault ground motions is the shortage of capacity of deformation and energy consumption. Effects of near-fault ground motions on beam-bridge can not be accurately determined by only selecting one of strength, displacement and energy to be the single index. Meanwhile, effect of deformation and energy consumption of basement on the special seismic response of beam-bridge can become significantly by considering near-fault ground motions. And, soil-structure interaction (SSI) can not be neglected. So, based on the method of FEMA440 considering SSI, the equivalent SDOF model considering constraints of foundation soil is established and one elasto-plastic dynamic program is prepared. So, effects of near-fault ground motions, SSI, dynamic parameters of restoring force model on the special seismic response of equivalent SDOF and MDOF beam-bridge can be studied by inputting a large number of near-fault ground motions and equivalent pulse. Then, the elasto-plastic response spectra and energy response spectra can be obtained by considering characteristics of near-fault ground motions and SSI. Based on above research and improved seismic damage model which is chosen to be the quantitative tool, the performance-based seismic design, which synthesizes all the indexes of strength, displacement and energy, is established for beam bridge by considering near-fault ground motions and SSI.

震害经验表明：梁式桥在近场强震作用下倒塌的主要原因是变形和耗能能力的不足，如果仅仅依靠强度、位移或能量作为梁式桥抗震设计的单一指标，都不足以确定近场强震对梁式桥破损程度的影响。而近震效应又使得基底变形与耗能对梁式桥特殊地震响应的影响更为显著，此时的土-结构相互作用(SSI效应)更不容忽视。本课题基于FEMA440计算SSI效应的方法，建立考虑土体约束的等效SDOF模型，编制相应的弹塑性动力分析程序，再选取大量的典型近场强震记录及其等效脉冲作为输入，研究近场地震动特性、SSI效应和恢复力模型动力参数对等效SDOF约束模型和MDOF梁式桥的特殊地震响应的影响，进而统计能考虑近震效应和SSI效应的弹塑性反应谱和地震能量反应谱。在此基础上，以改进的地震损伤性能评估模型作为性能目标的量化工具，建立能考虑近震效应和SSI效应的影响，并综合强度、位移、能量三重指标的梁式桥基于性能的抗震设计方法。

近震效应使得基底变形与耗能对梁式桥特殊地震响应的影响更为显著，此时的土-结构相互作用更不容忽视。本项目主要工作如下：（1）依据国内外规范对近场地震动的定义，收集了215条近场地震动记录，进而对近场地震弹塑性反应谱进行了参数影响研究，得到了地震动特性和恢复力模型动力参数等因素对近场地震弹塑性反应谱的影响规律。（2）合理选取四类场地320条强震记录，研究了地震动特性和恢复力模型动力参数对弹塑性SDOF体系的地震能量响应及其分配规律的影响，建立了适用于我国梁式桥抗震设计的地震总输入能谱、能量折减系数谱、滞回耗能谱和滞回耗能比谱。(3) 在前人建议的模态分析Pushover法的基础上，针对我国大跨铁路桥梁中的高桥墩，提出了能考虑高阶振型影响的改进能力谱法，并以内昆线花土坡铁路特大桥8#墩为实例，验证了改进方法评估高桥墩抗震性能的合理性。(4) 改进了正规化累积耗能参数，得到了基于损伤性能指标的等效位移延性系数，并以此对桥梁抗震的地震损伤模型进行了探讨。在此基础上，提出了考虑残余位移影响的梁式桥基于性能的抗震设计方法，并给出了具体算例。