非一致地震激励下大跨度桥梁随机振动时域显式法#br#

对于大跨度桥梁结构，地震激励的空间效应不应忽略。考虑到随机地震激励的非平稳特性，为提高计算效率，有必要在时域内直接开展非一致地震激励下大跨度桥梁的随机振动分析。基于相对运动法，推导非一致地震激励下结构动力响应的时域显式表达式，提出可考虑非一致地震激励的时域显式直接法，可快速获取结构响应的统计矩；同时提出高效的时域显式随机模拟法，可进一步获取非一致地震激励下结构响应的平均峰值等更全面的统计信息，并可有效实现结构的动力可靠度分析。以某主跨1200m悬索桥为工程实例，开展顺桥向非一致地震激励下的随机振动分析，分别研究地震激励的行波效应、失相干效应和局部场地效应对桥梁关键响应标准差、平均峰值和结构抗震动力可靠度的影响。研究结果表明，对于该桥主梁跨中和主塔塔顶顺桥向位移，非一致地震激励下的响应标准差和平均峰值均小于一致地震激励下的结果；而对于该桥主塔塔底内力，非一致地震激励下的响应标准差和平均峰值有可能大于一致地震激励下的结果，其中弯矩和剪力的平均峰值增幅分别可达21.6%和19.5%；此外，地震激励的空间效应对该桥的体系失效概率也有较大影响。

Random vibration analysis of long-span bridges under non-uniform seismic excitations by explicit time-domain method

For long-span bridges, the spatial variability effects of seismic excitations should be taken into account. In view of the non-stationarity of seismic excitations, to improve the computational efficiency, it is necessary to carry out the random vibration analysis of long-span bridges in the time domain with non-uniform ground motion. Based on the relative motion method, the explicit time-domain expression of the dynamic response of a structure under non-uniform seismic excitation was first deduced, and an explicit time-domain method was then proposed for fast calculation of the statistical moments of structural responses under non-uniform seismic excitations. Meanwhile, using the explicit time-domain expressions of dynamic responses, an efficient Monte-Carlo simulation method was further proposed for obtaining the mean peak values of structural responses and for analyzing the dynamic reliability of the structure with non-uniform ground motion. Taking a long-span suspension bridge with a main span of 1200m as a practical example, the random vibration analysis of the bridge under longitudinal non-uniform seismic excitations was conducted in the present study. The traveling-wave effect, the incoherence effect and the local site effect on the standard deviations and mean peak values of critical responses and structural seismic dynamic reliability were studied, respectively. The results show that, for the longitudinal displacements at the mid-span section of the bridge girder and at the top sections of the ain towers, the standard deviations and mean peak values of the responses under non-uniform seismic excitations are smaller than those under uniform seismic excitation. However, for the internal forces at the bottom sections of the main towers, the standard deviations and mean peak values of the responses under non-uniform seismic excitations may be larger than those under uniform seismic excitation, and the mean peak value of the bending moment and the shear force may be 21.6% and 19.5% larger, respectively. In addition, it can be observed that the spatial variability effects of seismic excitations have great influences on the failure probability of the bridge system.