Miami Pedestrian Bridge Collapse: Computational Forensic Analysis

Abstract

On March 15, 2018, a pedestrian concrete truss bridge in Miami, Florida, collapsed during construction. The failure of this bridge caused multiple casualties and raised many serious concerns regarding the design and construction of the bridge, including the emerging concept of accelerated bridge construction (ABC). The causes of failure of this bridge have not yet been comprehensively investigated. This paper used high-fidelity computational simulation to investigate the behavior of critical structural members of the bridge during construction. Four important construction stages (prestressing, transportation, relocation, and retensioning) were simulated to identify dominant factors that could have contributed to the failure of the bridge. A recent investigation report from the National Transportation Safety Board (NTSB) attributed the collapse to flawed design at the failed joint at the northern end of the bridge, but the specific sequence of mechanisms that led to collapse was not identified. Based on simulation and demand/capacity analysis, this work shows that the horizontal component of the retensioning force overcame the resistance of the joint and caused it to slide with respect to the deck. As sliding progressed, dowel action between the deck and joint became fully mobilized, crushing and damaging concrete locally within the joint and the deck. The evolving damage (to the cold joint and adjacent joint and deck concrete) prompted more sliding and led to a vicious cycle that culminated in the collapse of the entire bridge. Parametric studies investigated the effects of the coefficient of friction at the cold joint, prestressing forces in the deck, and retensioning forces applied to the northern diagonal member on the collapse behavior of the bridge. The results from the analysis and simulations provide important insights into the collapse mechanism and highlight lessons that could be learned for preventing similar catastrophic failures in the future.