梁桥地震易损性分析方法

Analysis on Seismic Fragility for Beam Bridge

通过地震易损性分析,可以得到梁桥结构在不同地震危险性水平下发生不同破坏模式的概率,从而可以定量评估梁桥结构的抗震性能。首先介绍了当前常用的基于概率性地震需求模型和基于频数的分析方法求解地震易损性曲线的思路,并从理论上分析了两种方法的优缺点。在此基础上,以一座两跨钢筋混凝土简支梁桥为背景,考虑地震动的不确定性,以地面峰值加速度(PGA)和位移漂移(drift)为指标,分别表征地震强度和工程需求,从而由上述两种方法建立相应的需求模型,并研究了上述指标对需求模型的影响。进而,计算上述两种方法对应的易损性曲线,采用Kolmogrov-Smirnov(K-S)距离定量度量两种情形下易损性曲线的偏离程度,并分析了易损性曲线之间的差异及其原因。研究结果表明,概率性地震需求模型引入了3条基本假设,在不同的PGA区间,这3条基本假设得到不同程度的满足,尤其是其中地震需求的对数标准差保持不变这一假设,是使得梁桥易损性计算结果误差较大的重要原因;频数分析方法虽然与实际情况比较接近,但也存在计算量较大的不足。此外,研究结果还表明,结构损伤程度越严重,由上述两种方法获得的易损性曲线偏离程度越大。本研究成果可为实际梁桥结构地震易损性分析方法选择、计算结果判别,以及梁桥结构抗震性能评价提供理论指导。

Through seismic fragility analysis,the probability of different damage modes occurring in beam bridge structure at various seismic hazard levels can be obtained.Therefore,the seismic performance of beam bridge can be evaluated quantitatively.Firstly,after introducing the prevalent concepts of deriving seismic fragility curves based on probabilistic seismic demand models and frequency-based analysis methods,the merits and drawbacks of these two approaches were analyzed theoretically.Based on this,taking the two-span reinforced concrete simply supported beam bridge for example.The uncertainty of seismic motion,ground peak acceleration(PGA)and displacement drift were used as indicators to respectively characterize seismic intensity and engineering demand.The above two methods were used to establish corresponding demand models.The influence of above indicators on the demand models was explored.Furthermore,the fragility curves corresponding to above two methods were calculated.The Kolmogorov-Smirnov(K-S)distance was used to quantitatively measure the deviation degree of fragility curves under two scenarios.The differences among fragility curves and the causes were analyzed.The findings reveal that the probabilistic seismic demand model introduces 3 basic assumptions,which are satisfied to varying degrees in different PGA intervals.In particular,the logarithmic standard deviation of seismic demand remains unchanged is the significant source of error in beam bridge fragility calculation.Although the frequency analysis method aligns more closely with reality,it has the disadvantage of computational complexity.In addition,the study finds that the degree of deviation in fragility curves obtained by the two methods increases with the severity of structural damage.In summary,the study result can provide theoretical guidance for the selection of practical seismic fragility analysis methods for beam bridge structure,calculation result interpretation,and seismic performance assessment on beam bridge structure.