Abstract

Floods, bridge scour, and flood-associated loads have caused over sixty percent of bridge failures in the U.S. Current practices for the vulnerability assessment of instream bridges under the effect of such flood largely rely on qualitative methods, such as visual inspection, without considering uncertainties associated with structural behaviors and flood loads. Recently, numerical methods have been investigated to quantitatively consider such uncertainty effects by adapting fragility analysis concept that has been well established in the earthquake engineering area. However, river hydraulics, geotechnical uncertainties of foundation, variable scour-depth effects, and their significance in structural fragility of bridges have rarely been systematically investigated. This study proposes a comprehensive fragility analysis framework that can effectively incorporate both flow hydraulics and geotechnical uncertainties, in addition to commonly considered components in flood-fragility analysis of bridges. The significance of flow hydraulics and geotechnical uncertainties has been demonstrated through a real-bridge case study. Conventional fragility curves with maximum scour depth may not represent actual vulnerability during floods, as the scour may not reach to the maximum in many cases. Therefore, fragility surface with two intensity measures, i.e. flow discharges and scour depths, is introduced for real-time vulnerability assessment during floods in this study.

摘要

在美国，洪水、桥梁冲刷和洪水相关荷载造成了美国超过 60% 的桥梁故障 目前在此类洪水影响下对河道桥梁进行脆弱性评估的做法主要依赖于定性方法，例如目视检查，而没有考虑不确定性与结构行为和洪水荷载有关。最近，已经研究了数值方法，通过采用在地震工程领域已经很好地建立的脆弱性分析概念来定量地考虑这种不确定性影响。然而，河流水力学、基础岩土工程的不确定性、可变冲刷深度效应及其在桥梁结构脆弱性中的重要性很少被系统地研究。本研究提出了一个综合的脆弱性分析框架，除了在桥梁洪水脆弱性分析中通常考虑的组件外，还可以有效地结合流动水力学和岩土工程的不确定性。流动水力学和岩土工程不确定性的重要性已通过真实桥梁案例研究得到证明。具有最大冲刷深度的传统脆弱性曲线可能无法代表洪水期间的实际脆弱性，因为在许多情况下冲刷可能不会达到最大值。因此，本研究引入了具有两种强度测量的脆弱面，即流量和冲刷深度，用于洪水期间的实时脆弱性评估。流动水力学和岩土工程不确定性的重要性已通过真实桥梁案例研究得到证明。具有最大冲刷深度的传统脆弱性曲线可能无法代表洪水期间的实际脆弱性，因为在许多情况下冲刷可能不会达到最大值。因此，本研究引入了具有两种强度测量的脆弱面，即流量和冲刷深度，用于洪水期间的实时脆弱性评估。流动水力学和岩土工程不确定性的重要性已通过真实桥梁案例研究得到证明。具有最大冲刷深度的常规脆弱性曲线可能无法代表洪水期间的实际脆弱性，因为在许多情况下冲刷可能不会达到最大值。因此，本研究引入了具有两种强度测量的脆弱面，即流量和冲刷深度，用于洪水期间的实时脆弱性评估。