公路桥梁地震设计状况荷载组合分项系数研究

为了在保障桥梁目标可靠度指标的前提下，确定最优的地震设计状况荷载组合分项系数，使桥梁结构以最为经济的抗力方式抵御外加荷载，从而对现行的桥梁设计规范地震设计状况进行优化，为今后公路桥梁地震设计状况荷载组合计算提供理论依据和指导意见，以2座连续刚构桥为依托工程，建立空间动力有限元模型，采用Monte-Carlo法并基于动态称重（WIM）系统模拟随机车流，进行了数条地震波增量动力分析（IDA）；采用Ferry Borges荷载组合理论求解地震设计状况组合效应分布，依据直接积分法求解桥梁结构的失效概率，从而确定荷载效应分项系数与可靠度指标影响面关系。研究结果表明：荷载效应分项系数的取值与目标可靠度指标的选取息息相关，忽略汽车荷载的地震设计状况风险分析，将严重低估桥梁结构的实际失效概率。为指导高烈度区连续刚构桥的地震设计状况设计，对于E2工况下的地震动输入，地震作用重要性系数λ₁取1.0，桥梁结构跨径对汽车荷载效应分项系数取值产生较大的影响，故选取β_s=3.1~3.4作为Ⅷ度区连续刚构桥地震设计状况设计时目标可靠度指标建议值，汽车荷载分项系数Ψ_Q的建议取值为0.76；地震基本烈度对汽车荷载分项系数存在一定的影响，在同样的目标可靠度指标建议值下，对于Ⅶ度区地震设计状况，汽车荷载分项系数Ψ_Q的建议取值为0.652。

Partial Coefficient of Load Combination in Seismic Design of Highway Bridge

Determination of the optimal partial coefficient of load combination for earthquake design condition can help guarantee the target reliability index of the bridge,enabling the bridge structure to resist the applied loads in the most economical way.The current bridge design code for earthquake design condition is optimized to provide a theoretical basis and guidance for the calculation of load combination for earthquake design condition of highway bridges in the future.Under the premise of the bridge target reliability index,the most economical means was used to resist the applied load.Based on two continuous rigid frame bridges,the Monte-Carlo method was used to simulate random traffic flow based on a weigh in motion(WIM)system.A space dynamic finite element model was established,and several seismic wave incremental dynamic analyses(IDA)were carried out.The Ferry Borges load combination theory was used to solve the combined effect distribution of seismic design condition.The failure probability of the structure was calculated according to the direct integration method,and the relationship between the load effect partial coefficient and the reliability index influence surface was determined.The results show that the risk analysis of seismic design condition under the vehicle load will seriously underestimate the actual failure probability of the bridge structure,and the value of the load effect component coefficient is closely related to the selection of the target reliability index.In order to guide the design of the seismic design of a continuous rigid frame bridge in a highintensity area,for the ground motion input in the E2 state,the importance coefficient λ1 of the seismic action is taken as 1.0.The bridge span has a great influence on the value of the vehicle load effect component factor,so βs=3.1~3.4 is selected as the recommended value of the target reliability index for the design of the seismic design of a continuous rigid frame bridge in the Ⅷ degree area,and the recommended value of the vehicle load partial coefficient ΨQ is 0.76.The basic intensity of the earthquake has some influence on the vehicle load component coefficient,and the recommended value of the car load partial coefficient ΨQ in the Ⅶ degree zone seismic design condition is 0.652 under the same recommended target reliability index.