基于汶川地震震害调研的典型公路桥梁地震易损性研究

As one of the critical steps in assessing seismic risk of transportation system, developing seismic bridge vulnerability model is very important for making up bridge seismic retrofit strategy and post-earthquake emergency response. In view of the disadvantages existing in current researches for dealing with bridge seismic vulnerability, it is known that a better seismic vulnerability model for typical highway bridges is the approach in which empirical statistics and numerical calculation are combined together. Based on the damaged bridge data collected from the 2008 Wenchuan earthquake, a classification criterion for highway bridges is recommended. A mixed ground motion intensity prediction method is proposed based on the observed ground motion date and existing attenuation model, and then the empirical seismic vulnerability models for typical highway bridges are developed by using Bayesian statistical method. The baseline finite element models for typical bridge samples are built in which boundary and transient dynamic effects are considered. The components limit states and theirs probability characteristics for considering multiple failure modes are assessed and defined. Based on the multi-dimensional probabilistic seismic demand analysis, analytical seismic vulnerability models for typical highway bridges are developed. Bridge parameters sensitivity analysis is performed and the simplified analysis flowchart for seismic vulnerability of typical highway bridges is proposed. The results from the study will further reveal bridge dynamic behavior and seismic response mechanism, improve the accuracy and efficiency of bridge vulnerability analysis, and provide the reference and basis for the guidelines of bridge seismic assessment and retrofit in the future.

桥梁地震易损性模型作为交通系统地震风险评估中的关键环节，对于桥梁抗震加固修复决策及震后紧急响应评估具有重要指导意义。鉴于既有桥梁地震易损性研究不足，采用经验统计和数值模拟相结合的方法，建立更加完善和精确的典型公路桥梁地震易损性模型：通过大量的汶川地震桥梁震害调研资料分析，建立典型公路桥梁分类准则，基于实测地震数据和地震动衰减模型提出地震动强度混合预测方法，采用贝叶斯统计方法建立典型公路桥梁经验型地震易损性模型；建立考虑边界效应及瞬态动力效应的典型桥梁样本基准有限元模型，评估界定多重破坏模式下构件极限状态及其概率特征，应用多维概率性地震需求分析方法，建立典型公路桥梁分析型地震易损性模型；开展桥梁参数敏感性分析，提出基于修正系数的典型公路桥梁易损性简化计算方法。研究成果将进一步揭示桥梁动力学行为和地震响应机理，提升典型公路桥梁易损性分析的精度和效率，为后续桥梁抗震评估及加固决策提供参考和依据。

桥梁地震易损性模型作为交通系统地震风险评估中的关键环节，对于桥梁抗震加固修复决策及震后紧急响应评估具有重要指导意义。针对既有桥梁地震易损性研究不足，采用经验统计和数值模拟相结合的方法，建立更加完善和精确的典型公路桥梁地震易损性模型。主要研究工作及结论如下：.(1) 基于汶川地区典型公路桥梁调研资料，依据不同上部结构支承形式、墩柱形式和设计规范，将公路规则梁桥细化为8种桥型并开展模型参数化研究，针对每种桥型分别建构桥梁样本作为各类桥型代表，基于OpenSees建立桥梁样本的非线性动力有限元模型，运用增量动力分析方法，分析得到各类桥梁的全桥系统地震易损性模型。基于计算得到的地震易损性模型参数，拟合提出适用我国公路规则梁桥的中位值简化计算公式，并给出对数标准差建议值。.(2) 进一步进行斜交角度变换建构新的桥梁样本，对相同斜交角下桥梁样本进行分析并建立易损性模型，重点研究斜交角与易损性参数之间的关系。研究发现：易损性模型中位值大致随斜交角的增加而减小，对数标准差则呈相反趋势。以计算得到的易损性模型参数为样本，拟合提出适用我国斜交梁桥的中位值修正系数公式，并给出对数标准差建议值。研究表明：提出的简化计算方法具有较高的准确性，结果可为后续桥梁地震风险评估及加固规范修订提供参考依据。.(3) 在充分考虑结构和材料等桥梁参数不确定性基础上，基于Plackett -Burman 设计方法生成一系列桥梁样本。比较输入参数对地震响应的贡献，刷选出影响桥梁地震响应的显著性参数；进一步针对显著性参数进行中心复合设计，基于非线性时程分析建立桥梁各构件在不同的地震动强度下的响应面模型，采用蒙特卡罗抽样方法计算得到桥梁构件的易损性曲线。结果表明：生成的响应面方程可以高效地替代复杂的非线性时程分析，提高了地震易损性分析的计算效率，具有较好的工程应用价值。.(4) 采用基于多样条分析思想的估计方法、蒙特卡洛抽样的频率点回归方法以及二维概率密度函数积分的频率点回归方法，分别建立了近远场地震动激励下桥梁墩柱地震易损性模型。研究结果表明：在相同地震动强度作用下，墩柱在近断层地震动作用下发生完全破坏的概率较高，墩柱在远场地震动作用下发生其余三种损伤的概率较高；在同时考虑延性系数和残余变形两个损伤指标时，墩柱易损性中位值与单一损伤指标相比有较大幅度的减小，研究表明该方案可以更为准确地评估墩柱的地震风险。