Enhancing Safety and Performance in Temporary Brackets: Insights into Forensic Analysis and Construction Errors

Abstract

On August 17, 2021, a steel bracket of an under-construction bridge in Anhui, China, experienced a catastrophic failure. This incident raised significant concerns about the design and construction of temporary structures. In response to the discovery of multiple construction errors in the debris, a novel, comprehensive investigation was undertaken. The present study involved an on-site survey, joint capacity analysis, and advanced finite-element modeling to elucidate the specific sequence of failures. The primary cause of the initial failure was identified as the absence of welding and two missing bolts in a particular connection area. The results of the redundancy assessment by nonlinear analysis suggest that the shear resistance contribution of the additional welding reinforcement in the bolt connection accounts for more than 50%, and safety was still ensured even without connecting bolts. The results also indicate that the six-bolt design could lead to bolt slippage before the upper chord reaches its yield point. Further, even the eight-bolt design, which was recommended based on joint capacity analysis and elastic analysis, may not be sufficient to prevent premature brittle failure in the bolts. However, since collapse resistance is governed by ultimate strengths, the revised bracket design, incorporating the necessary mechanisms, requires a minimum of 11 bolts. This adjustment accounts for the impact of various processing techniques on the steel’s performance. The new design exhibited a 175% increase in load-carrying capacity before bolt slippage occurred, even in the presence of the same construction errors. The innovative matching mechanism effectively mitigated premature failure, primarily by preventing bolt slippage prior to the yielding of ductile members.