近断层地震下在役简支梁桥横向抗震性能分析

Seismic Performance Analysis of Existing Simply Supported Bridges Subjected to Near-fault Ground Motions in the Transverse Direction

摘要:

为了研究材料劣化对近断层区简支梁桥横向抗震性能的影响，揭示支座+挡块组合隔震效果随桥梁服役时间的变化规律，以汶川地震中某实际桥例为背景，考虑钢筋锈蚀和混凝土碳化的时变特点，建立了桥例非线性时变分析模型，采用时程分析研究了桥梁不同构件的劣化损伤规律，并对挡块强度的时变影响规律进行了参数分析。结果表明：随着服役年限的增长，墩柱抗弯能力不断减小，损伤程度不断加剧；材料劣化提高了挡块的相对限位能力，使得支座位移下降，但由于墩柱损伤加剧，桥梁整体抗震性能下降；挡块强度越大，其限位能力越强，但会降低支座的"隔震"效果，增大墩柱塑性变形，且服役时间越长，挡块强度的增大对墩柱越不利。当挡块强度取20%~30%支反力时，不同服役年限下的支座和主梁位移都能得到有效的控制，而桥墩也处于可修复的损伤状态，对于桥例而言是合理强度取值，且与美国Caltrans规范吻合。

Abstract:

To investigate the influence of material degradation on the lateral seismic behavior of simply supported bridges in the near-fault area and to reveal the variation of the combination isolation effects of bearing + shear key with respect to the service time, an actual bridge subjected to the Wenchuan earthquake was taken as an example and a nonlinear time-dependent analysis model of the bridge was established considering the time-varying characteristics of steel corrosion and concrete carbonation. Time history analysis was applied to study the deterioration trend of various members of the bridge. A parametric study was conducted to examine the time-varying influence of the shear key strength. Results show that the flexural resistance of the pier column is continuously reduced and the damage level increased as the service life increased. The material degradation improves the relative displacement-control capacity of the shear key, which causes the decrease of bearing displacement. However, the overall seismic performance of the bridge decreases due to the increased damage of the pier. The shear key’s great strength corresponds to its strong displacement-control capacity. However, the increased strength of the shear key will reduce the isolation effects of the bearing and increase the plastic deformation of the pier. As the service time increases, the increased strength of the shear key will be more disadvantageous for the pier. When the strength of the shear key is designed to be 20%-30%, the displacement of the bearing and the girder in different service years can be effectively controlled, and the damage of the pier is also in a repairable state. The 20%-30% shear key strength is a reasonable strength value for the bridge example used in this paper and is consistent with the Caltrans recommendation in America.