基于耐震时程法的大跨度钢桁拱桥易损性分析

An Endurance Time Method Based Fragility Analysis for Long-span Steel Truss Arch Bridge

为克服复杂桥梁结构在地震易损性评估时需要进行大量非线性时程分析的不足,提出一种基于耐震时程法(ETM)的易损性分析方法用于桥梁结构易损性的快速评估。首先,基于ETM合成了若干条耐震时程曲线(ETA),将其与概率地震需求模型相结合。随后,考虑桥梁模型的不确定性,借助OpenSEES建立一座大跨度上承式钢桁拱桥的有限元模型样本库,并分别使用ETM和增量动力分析(IDA)法对其中的桥梁模型进行时程分析并得到典型构件的易损性曲线,将二者结果进行对比以验证ETM的适用性。最后,利用验证后的方法分析该桥各构件纵向地震下的易损性。结果表明:ETM与IDA所得结果的相对误差基本控制在5%以内,说明基于耐震时程的易损性方法可有效兼顾分析效率和计算精度;在纵向地震作用下,上承式钢桁拱桥的引桥墩和交界墩在50%中等损伤概率下的地震动强度指标仅为0.597g和0.972g,远小于其他构件,说明混凝土桥墩为最易损构件;拱肋和立柱在地震作用下发生破坏的概率较小,但拱顶和拱脚相对薄弱;设置固定支座的短立柱在纵向地震作用下易发生损伤,可通过改变拱上立柱的支座布置形式进行优化。

To overcome the deficiency of large numbers of nonlinear time history analysis for seismic fragility assessment of complex bridge structures,a fragility analysis method based on endurance time method(ETM)is proposed for rapid assessment of bridge fragility.Firstly,several endurance time accelerations(ETA)are synthesized according to ETM and combined with probabilistic seismic demand model.Subsequently,a sample library of finite element model for a long-span steel-truss deck arch bridge is established by using OpenSEES software with the consideration of bridge model uncertainties.ETM and incremental dynamic analysis(IDA)methods are employed to carry out nonlinear time history of the bridge models to obtain the fragility curves of typical components,and the applicability of ETM is validated by comparing the results of the two methods above.Results show that the relative error between ETM and IDA is basically controlled within 5%,indicating that the fragility method based on ETM can effectively take into account both analysis efficiency and calculation accuracy;Under the action of longitudinal earthquake,the seismic indexes(i.e.,0.597g and 0.972g)of approach pier and junction pier of steel-truss deck arch bridge with 50%moderate damage probability are much smaller than that of other components,illustrating that concrete piers are the most vulnerable members.The failure probability of arch ribs and columns under earthquake is small while the vault and arch foot are relatively weak.Short columns with fixed supports are susceptive to be damaged subjected to the longitudinal earthquakes,which can be optimized by changing the support layout of columns.