Analyzing reliability missteps: The collapse of the Francis Scott Key Bridge — Target reliability, redundancy, and extreme load combinations

The collapse of the Francis Scott Key Bridge, a significant case study in structural engineering, is a stark reminder of the catastrophic consequences of overlooking critical design principles. This paper examines the interplay between system and element target reliability, structural elements' criticality, load modifiers' application, and redundancy's role within the limit state and reliability-based design frameworks. Through a comprehensive analysis of the bridge collapse, the study uncovers critical failures in understanding and implementing these principles, significantly contributing to the disaster. It underscores the nuanced differences between system-level and element-level reliability, highlighting that misconceptions and underestimations can lead to severe vulnerabilities. Furthermore, the paper explores how the failure to acknowledge the criticality of structural components and the correct application of load modifiers, combined with insufficient redundancy, set the stage for this failure under extreme loading conditions, a prevalent issue in the Eastern United States. In addition, an innovative integrative target reliability selection is proposed. The findings underscore the immediate need for a holistic approach to structural reliability that integrates comprehensive risk assessments and redundancy strategies. This study aims to enhance structural engineering practices by shedding light on the errors in reliability analysis that led to the bridge's failure, offering insights that could prevent future infrastructural collapses.