A team of our engineers and architects is attending the Institution of Civil Engineer’s Fifth International Conference on Forensic Engineering in London, of which Thornton Tomasetti was also a sponsor. A variety of investigation methodologies and case studies were presented during the first day. The big topics were risk assessment and risk management as a way to determine and mitigate future risks and learn from past failures. Dr. Robert Ratay summarized the conference theme: studying failures is important for improving codes, standards and our practice in general. Therefore, it is critical to get to the root cause of the failure to assure that the necessary lessons are learned.
From left, Robert Glynn, Marguerite Pinto, Mariachiara Faliva, Francesca Brando and Liling Cao
On the conference’s second day, Marguerite Pinto, a project director based in our Philadelphia office, presented the methodology we often use for determining the cause of structural failure. Our investigation of the I-35 West bridge collapse in Minneapolis, Minnesota was presented as a case study. To determine the cause of the collapse, we combined a set of analysis results using finite element models and hand calculations into one non-linear model to simulate what occurred on the day of collapse. The collapse model contains the non-linear material properties, loading scenario and findings from the inspection history of the bridge. As such it captures the actual demands upon and capacities of the bridge prior to collapse. This combination of a priori and a posteriori knowledge was used to drive the analysis and trace the actual behavior at the bridge’s various bifurcation points. The results from the analytical model compare well with the video, which helps to verify the collapse initiation theory. The completed collapse model proved to be a valuable tool for comparing various theories as to the cause of the collapse, and confirmed that the theory presented by the National Transportation Board does not tell the whole story.
— Mariachiara Faliva, Associate
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