Traditionally, structural safety has been assessed on a factor-by-factor basis—evaluating each load effect and failure mode separately—according to predefined engineering categories. While this segmented approach simplifies design calculations and other engineering approaches related, it often overlooks interactions among different hazards and failure mechanisms, potentially resulting in overly conservative safety margins or, conversely, unrecognized risks. Two bridge-failure case studies illustrate these shortcomings:
1. Silver Bridge (Ohio River, 1967) [1]. The National Transportation Safety Board (NTSB) concluded that the collapse was caused by corrosion-assisted fatigue rather than by corrosion or fatigue in isolation. Because inspections traditionally focused on either corrosion or fatigue separately, the compounded effect went undetected until failure.
2. Fern Hollow Bridge (Pittsburgh, 2022) [2]. Over the two decades preceding collapse, routine inspections evaluated structural safety and corrosion as independent issues—none identified the imminent danger. On the day of failure, ambient temperatures reached the year’s low, well below the ductile-to-brittle transition temperature of the steel. A subsequent transportation-agency report noted that hundreds of analogous steel bridges in northern U.S. climates may face the same risk.
This presentation outlines a multi-hazard, multi-mechanism evaluation framework that accounts for concurrent interactions among environmental loads (e.g., temperature extremes, corrosion) and mechanical drivers (e.g., fatigue, fracture) while integrating fracture-mechanics principles to quantify how coupled damage mechanisms evolve under realistic service conditions [3–10]. By embedding these interactions into a unified safety assessment, the proposed methodology aims to improve predictive accuracy and prioritize mitigation strategies for aging infrastructure across the nation.