Static/Dynamic Analysis of Locally Buckled Frames

Abstract

The static and dynamic behavior of plane frames composed of thinwalled steel members is presented. Frame analysis includes post‐local‐buckling and/or first‐order geometric nonlinearities. Post‐local‐buckling behavior is included using the effective width concept which includes both axial and bending stresses. Direct iteration is used to calculate the effective cross section properties for members that have locally buckled. An “exact” elastic stiffness matrix, finite element geometric stiffness, consistent mass and Rayleigh damping matrix formulation is used to discretize the dynamic equilibrium equations. The nonlinear dynamic equations are solved using a modified Newton‐Raphson iteration strategy coupled with Newmark's time integration scheme. Static and dynamic analyses of a two‐bay, two‐story frame are considered. Static problem results are presented to demonstrate the accuracy of the formulation and the influence of local buckling and/or first‐order geometric nonlinearities. Dynamic simulations are based on subjecting the two‐story, two‐bay frame to a sway pulse loading to simulate wind pressure. The dynamic results include linear elastic, local buckling, and/or first‐order geometric nonlinearity.