地裂缝活动作用下城市立交桥地震易损性分析

Seismic vulnerability of urban overpasses under active ground fissures

摘要:

城市立交桥等线型结构无法彻底避免地裂缝活动的影响。基于地裂缝场地上盘对地震动的放大效应,考虑地裂缝与桥梁结构的交角,得到结构非线性动力时程分析时的非一致地震动输入的上盘放大系数。地裂缝两侧的沉降差使得连续桥内力显著变化,导致桥墩的轴力增大且在地震作用下桥墩顶部的水平力增大。针对西安地裂缝场地与地裂缝活动特征,以三跨城市立交桥为例,采用park模型作为桥墩的损伤指标,考虑结构与地震动的不确定性,对立交桥进行不同场地条件的易损性分析。研究表明,地裂缝活动使得跨骑地裂缝的城市立交桥桥墩在地震作用下的失效概率相比于非地震缝场地显著增大,且桥墩的失效概率与其位置有关。

Abstract:

Urban overpasses and other linear structures can not completely avoid the impact of ground fissure activities. Considering the amplification effect of hanging wall on the ground motion in ground fissure sites and the intersection angle between the ground fissure and the bridge structure, the hanging wall magnification factor of the structure used for nonlinear dynamic time-history analysis under non-uniform ground motions was obtained. The differential settlement on both sides of the ground fissure causes significant change of internal force of the continuous bridge, resulting in the increase of axial force of the pier and the increase of horizontal force at the pier top under earthquake. According to the characteristics of ground fissure activities and ground fissure sites in Xi'an, a three-span urban overpass was taken as an example to carry out the vulnerability analysis of the overpass under different site conditions. The uncertainty of the structure and ground motions were considered, and the Park model was adopted as the damage index of bridge pier. The results showed that the ground fissure activity makes the failure probability of urban overpass pier crossing the ground fissure significantly higher than that in non ground fissure sites, and the failure probability of pier is related to its location.