Advanced framework for post-flood assessment of steel truss bridges under data-constrained conditions: integrating engineering insights and empirical fragility models

Bridges are vital components of a country’s infrastructure, playing a crucial role in transportation networks. However, natural hazards such as floods significantly threaten their stability and serviceability. The increasing frequency and intensity of floods due to climate change have heightened concerns about the serviceability of bridges after the floods. Despite their critical importance and high risk of vulnerability to floods, limited research has examined the failure mechanisms and their contributing factors on steel truss bridges, as one of the most widely used types of bridges. This knowledge gap remains a major challenge in the field. Previous studies have primarily assessed bridge vulnerability to floods through qualitative analyses or finite element modeling, often overlooking the specific failure characteristics of collapsed bridges and their empirical fragility curves. Addressing this limitation, the present study investigates the catastrophic 2019 Poldokhtar flood (one of the most devastating floods in Iran in recent decades) and its impact on eight steel truss bridges. Through extensive field investigations and the development of empirical fragility curves, this research provides a detailed assessment of bridge performance during extreme flood events. The study identifies key failure mechanisms and damage scenarios based on visual inspections, engineering judgment, and empirical analyses. Furthermore, to overcome data scarcity and site-specific uncertainties, this study introduces a novel flood intensity measure relating floodwater height to bridge deck elevation. This practical indicator enables consistent comparison across different hydraulic conditions and serves as a valuable tool for evaluating bridge vulnerability under real-world flood scenarios.