Nonlinear Elastoplastic Analysis of Semirigid Steel Frames at Elevated Temperature: MP Approach

Abstract

An elastoplastic analysis of semirigid steel frames subjected to elevated temperature is presented. Within the discretized structural framework, an updated Lagrangian approach is used to incorporate the nonlinear geometric effects on the equilibrium and constitutive conditions. Modeling of elastoplastic behavior is based on the generalized plastic hinge concept for beam-column elements that obey piecewise linearized yield criteria. Under the proportional temperature variation, the analysis for finite temperature increment becomes the standard form of a nonlinear complementarity problem in mathematical programming (MP) formalism. An iterative predictor–corrector scheme coupled with an MP-based method is used in the analytical procedures. Numerical studies are carried out on rigid and semirigid frames. It is found that the benefits of using a full-strength rigid connection over the semirigid one are not unlimited, particularly on the frames with fire-unprotected columns.