断层错动诱导的地表破裂永久位移对跨断层桥梁结构会造成严重破坏,准确预测断层错位的永久位移对跨断层桥梁结构抗震性能评估具有重要意义.首先结合反向传播神经网络(BPNN)提出具有较高精度的断层错位量预测模型,然后通过低频成分叠加高频成分方法人工合成断层面两侧地震动(简称跨断层地震动),最后以某主跨为538 m的跨断层大跨钢桁架悬索桥为研究对象,利用有限元软件ABAQUS建立考虑桩-土相互作用(m法)的全桥计算模型,探究断层位置和跨越角度对悬索桥地震响应的影响.结果表明:基于BPNN提出的方法能精确预测断层位错永久位移,对比已有的回归公式具有更高的精度,为人工合成跨断层地震动的准确性提供了保障;断层相对位置会显著影响桥梁结构的地震响应,与近断层地震动作用相比,在跨断层地震动作用下,悬索桥的塔底剪力、弯矩、相对位移以及扭矩响应增加了22.79%、154.1%、139.36%和265.48%;断层跨越角度对悬索桥动力响应影响明显,其响应均以跨越角度θ=90°呈规律对称分布,塔顶纵向位移、塔底纵向弯矩、塔底纵向剪力以及塔底扭矩最大值均出现在θ=90°,分别为0.81 m、282.45 MN?m、3.96 MN和6.14 MN?m.研究成果可为跨断层悬索桥抗震分析提供一套简便、可靠的人工地震动合成方法,也揭示了跨越角度和断层位置对跨断层悬索桥地震响应的影响.
Fault dislocation can lead to permanent ground rupture displacement and cause severe damage to bridge structures crossing fault.Accurate prediction of the permanent displacement caused by faults displacement is of great significance for assessing the seismic performance of cross-fault bridge structures.In this study,a high-precision model for predicting fault displacement based on BPNN(backpropagation neural network)was proposed.The model is used to generate artificial earthquake ground motions(referred to as cross-fault ground motions)by combining low-frequency and high-frequency components.The 538 m long-span steel truss suspension bridge crossing an active fault is taken as the research object,and the full-bridge calculation model considering pile-soil interaction was established using the finite element software of ABAQUS.Finally,the influence of fault rupture permanent displacement on the seismic responses of suspension bridges crossing faults was explored by studying the impact of fault location and fault-crossing angle on the seismic responses of the suspension bridge.The research results indicate that the proposed method based on BPNN can accurately predict the fault rupture permanent displacement caused by fault movement.Compared with existing regression formulas,this method has higher accuracy and provides a guarantee for artificially synthesizing fault-crossing ground motions.The relative position of the fault has a significant impact on the seismic response of the bridge structure.Compared with the effect of near-fault seismic motion,the tower base shear,bending moment,relative displacement,and torsional response of the suspension bridge under fault-crossing ground motions increased by 22.79%,154.1%,139.36%,and 265.48%,respectively.In addition,the fault-crossing angle also has a significant impact on the dynamic responses of the suspension bridge.The response is symmetrically distributed with a regular pattern at the crossing angle θ=90°.The maximum longitudinal displacement on the top of tower,tower bottom longitudinal moment,tower base longitudinal shear force,and tower base torsional moment all appear at θ=90°,with values of 0.81 m,282.45 MN?m,3.96 MN,and 6.14 MN?m,respectively.The results of this study can provide a simple and reliable method for artificially synthesizing seismic motion for seismic analysis of suspension bridges crossing faults and reveal the effects of fault-crossing angle and fault location on the seismic response of suspension bridges crossing faults.