Stability of stainless steel unequal-leg angles with imperfect supports

Recent experimental work completed at the University of Wisconsin-Madison subjected hot-rolled and laser-fused 304 austenitic stainless steel unequal-leg angles, ranging in length from 10 inches to 148 inches, to uniform compression with fxed supports. The angles failed in flexural-torsional buckling with variable degrees of flexural and torsional deformations. This paper reports on the fnite element modeling validation of the flexural-torsional buckling failures. Early work implemented a simplifed approach that isolated the angle column with perfect fxed-fxed boundary conditions and incorporated measured material properties, cross-section dimensions, and geometric imperfections. This method accurately simulated the appropriate non-linear stiffness, deflection patterns, and ultimate capacities associated with the torsion-dominated buckling failures. However, the same analysis approach was not able to reproduce the reduced ductility and capacity associated with the flexure-dominated failures in this test series. Further investigation noted that the reusable loading brackets did not provide a perfect fxed support. This was a consequence of incomplete contact at the supports at the commencement of flexural buckling combined with an imperfect bearing surface. Due to the signifcantly high ratio of measured to nominal yield strength of the stainless steel angles, the reusable loading brackets were permanently deformed. Finite element models accounting for the incomplete contact and separation between the nonplanar bearing plates and the stainless steel angle reproduced the reduced ductility and loading capacity captured in the experimental testing. This modeling technique was used to complete a parametric study to provide data on unequal-leg angles, which highlighted the importance of defning the appropriate material model to capture accurate buckling behavior.

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