Postbuckling mechanics of square slender steel plates in pure shear: Examining the role of second order effects

Thin (slender) steel plates possess strength beyond the elastic buckling load which is commonly referred to as the postbuckling capacity. Semi-empirical equations based on experimental tests of plate girders have been used for decades to predict the ultimate postbuckling strength. However, several recent studies have shown that the current models for predicting the ultimate shear buckling capacity of thin plates are based on some incorrect assumptions of their mechanical behavior. As a result, the current design equations provide an approximate (albeit generally conservative) estimate of capacity based upon a range of test data parameters upon which they are founded. This paper explores the fundamental behavior of thin plates under pure shear. Such a fundamental examination of shear postbuckling behavior in thin plates is important because it will enable design procedures that can optimize a plate's shear strength and load-deformation performance for a wider range of loading and design parameters. Using finite element analyses (which are validated against available results of previous tests), outputs such as von Mises stresses, principal stresses, and principal stress directions are examined on both surfaces of a buckled plate acting in pure shear. The internal bending, shear, and axial stresses in the plate's finite elements are also evaluated. In this study, these evaluations are performed for a simply-supported plate with aspect ratio equal to 1.0 and slenderness equal to 134-future work will examine a wider range of plate parameters. Results show that localized bending in the plates due to the out-of-plane postbuckling deformations appear to be a significant factor in the ultimate shear buckling capacity of the plate. Also, the compressive stresses continue to increase beyond elastic buckling in some regions of the plate, contrary to current design assumptions. Overall, this study provides new insights into the mechanics of shear postbuckling behavior of thin plates that can be exploited for improved design modifications compared to designs currently allowed in current practice.