Redundancy Analysis of Unbraced Network Arch Bridges

Abstract

The redundancy of a structural system is its ability to support loads even after a failure of one or several structural components. Redundancy analysis is vital to assess the safety and reliability of network arch bridges, particularly in the context of extreme events such as hanger replacement and hanger loss. Even though the Post-Tension Institute (PTI) offers specific design guidelines on handling abrupt cable loss and replacement for cable-stayed bridges, it failed to address the issue of gradual collapse comprehensively. However, comparable guidelines are lacking in the AASHTO design practices. While system factors for simple bridge systems have been extensively investigated, there is a lack of research on corresponding system factors for complex structures such as network arch bridges. Recently, an attempt was made to establish a step-by-step procedure to compute the system factors for a steel box tied arch bridge structure system. However, no studies were found to determine the system factors for freestanding network arch bridges. The lack of research or documentation outlining a specific methodology to establish the system factors for unbraced network arch bridges underscores the need for further research to establish design standards that prioritize the safety and resilience extreme circumstances. To address this knowledge gap, a parametric investigation is currently being conducted to develop a definitive procedure for determining the system factors for straight and moderately skew (skew<20ﾰ) unbraced network arch bridges using finite element analysis (FEA). A 265 ft long, 96.5 ft wide, and 18ﾰ skew unbraced network arch bridge constructed in Detroit, Michigan, was used as the prototype and evaluated its performance during the hanger replacement scenario under dead load conditions. The results of the analysis indicate that the sequential replacement of hangers in a straight and moderately skew unbraced network arch bridges can be performed under its own weight without impacting the structural integrity.