Forensic Investigation of a Failed Steel Tube Chair

A legal firm had asked us to perform a forensic investigation on a steel tube chair that failed when a 180 pound individual sat down. We conducted the evaluation using generally accepted engineering analysis practices and modern finite-element elastic-plastic large-deflection three-dimensional computer analyses.

We determined that the failure was due to gross plastic deformation of the material in the bend, which had been deformed during fabrication. The failure occurred when the bending moment applied to the tube exceeded its plastic moment capacity. A three-dimensional finite element analysis was performed to evaluate the structural integrity. The results were compared to the relevant American National Standard, requiring that dynamic loads be included in the structural adequacy of such chairs. The results showed that the chair did not meet these requirement in the “as-built” condition, and was structurally defective per the American Standard.


We Perform Forensic Investigations on Equipment including Forklifts, Conveyors, Racks, and other Industrial / Process Equipment.


(412) 835-5007

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