衔接GMPE的城市燃气管网连通易损性分析

Seismic connectivity fragility analysis for urban gas network using GMPE

为合理评估城市燃气管网在不同地震动强度下的连通性,以地震动预测方程(GMPE)为输入依据,通过蒙特卡罗模拟方法给出了考虑地震动不确定性的城市燃气管网连通易损性计算方法.首先,在某设定震级下,基于地震动预测方程(GMPE)确定燃气管网各点的输入地震动强度指标(峰值加速度P ga和峰值速度P gv),同时采用正态分布抽样来模拟随机误差变量的分布以体现不确定性.然后,利用蒙特卡罗模拟方法确定燃气管网系统各单元失效概率,再通过震后的管网中未通气的节点数量比例来定义连通性的损失指标.最后,计算得到多个设定震级下损失指标的超越概率和连通易损性曲线.本研究基于该流程以中国华北某城市燃气管网作为实例进行连通易损性分析,同时针对地震动预测方程中不确定性的影响进行了对比研究.计算结果表明,该市燃气管网在考虑地震动不确定性时的震后各个破坏状态对应的震级均值比不考虑时小接近0.5级,且在不同震级下连通性能超过某破坏状态的概率也偏大.本研究所建议的连通易损性分析流程可以为城市评估整体燃气管网的概率地震风险提供参考,同时较好考虑了地震动的区域差异性和不确定性.

To comprehensively evaluate the connectivity of urban gas network under different ground motion intensities,the method of seismic connectivity fragility analysis was proposed based on Monte Carlo simulation which uses the ground motion prediction equation(GMPE)as input.Firstly,the input ground motion intensity measurements(P ga and P gv)of each site of the gas network were determined based on GMPE conditioned on a given target magnitude.The distribution of random residual was simulated by normal distribution sampling to represent the uncertainty of the ground motion.Then,the Monte Carlo simulation was used to determine the failure probability of each element in the gas network system,and the loss index of connectivity was determined by the number of blocked nodes in the gas network after the earthquake.Finally,the seismic connectivity fragility curves of the gas network were obtained by calculating the loss index exceedance probability at different magnitudes.The gas network of a city in North China was taken as an example to evaluate its seismic connectivity fragility performance based on the proposed method,and the influence of uncertainty in GMPE was compared and analyzed.Calculation results show that the mean value of magnitude corresponding to each failure state of the gas network was 0.5 smaller when the uncertainty of ground motion was taken into account.Larger connectivity failure exceedance probability could also be observed at different magnitudes.The seismic connectivity fragility analysis method proposed in this study could provide constructive strategy for urban cities to evaluate the probability seismic risk of the whole gas network,and comprehensively take into account the seismic regional differences and uncertainties of ground motion.