ABSTRACT

Many bridges in seismic prone regions suffer from serious foundation exposure caused by scouring of the riverbed. In this study, the seismic performance of a bridge at various scour depths is assessed using a nonlinear static procedure based on the capacity spectrum approach. The performance limit of the bridge is identified in the capacity spectrum. The level of seismic intensity, characterized as peak ground acceleration, required to reach this performance limit is determined accordingly. The influence of riverbed scour on the seismic performance of a bridge is assessed by comparing the seismic intensities correlated to the performance limit at different scour depths. Results emphasize that for a bridge originally equipped with sufficient foundation strength, an improved seismic performance is observed when the scour depth is shallow. Once the scour depth exceeds a critical level, the seismic performance of the bridge is controlled by unexpected damage in the foundation. The seismic intensities correlated to the performance limit of the bridge decreases, and the seismic performance declines rapidly when the scour depth increases. The influence of structural properties and soil profile type on the seismic performance of a bridge at different scour depths is also investigated. The minimum scour depth, which causes the difference in seismic performance limit of a bridge from the original design, reduces with a decrease in the superstructure mass or soil-foundation system strength. The findings of this study help engineers evaluate the need for foundation retrofitting, particularly to ensure satisfactory seismic performance for bridges that undergo riverbed scour.

摘要

地震多发地区的许多桥梁因河床冲刷而遭受严重的地基暴露。在这项研究中，桥梁在不同冲刷深度的抗震性能是使用基于容量谱方法的非线性静态程序评估的。网桥的性能限制在容量范围内确定。相应地确定达到该性能极限所需的地震烈度水平，以峰值地面加速度为特征。河床冲刷对桥梁抗震性能的影响是通过比较不同冲刷深度下与性能极限相关的地震强度来评估的。结果强调，对于最初配备足够基础强度的桥梁，当冲刷深度较浅时，可以观察到改善的抗震性能。一旦冲刷深度超过临界水平，桥梁的抗震性能就会受到基础意外损坏的控制。与桥梁性能极限相关的地震烈度降低，随着冲刷深度的增加，抗震性能迅速下降。还研究了结构特性和土壤剖面类型对不同冲刷深度下桥梁抗震性能的影响。引起桥梁抗震性能极限与原设计差异的最小冲刷深度随着上部结构质量或土基系统强度的降低而减小。本研究的结果有助于工程师评估基础改造的必要性，特别是确保经受河床冲刷的桥梁具有令人满意的抗震性能。