Inelastic stability of diagonal braces in building frames

Abstract

The inelastic behavior of diagonal braces in building frames subjected to relative horizontal end displacements is investigated both theoretically and experimentally with particular reference to the post-buckling behavior. The analysis is based on commonly adopted piecewise linear approximate moment-thrust interaction curves and bilinear elastic-plastic moment-curvature relations. The maximum loads as well as the horizontal load-displacement curves observed in the experimental investigation agree well with the theoretical prediction for short braces. In the medium range, the stable branches of the horizontal load-displacement1 curves are followed by a steep unloading branch, with initially positive slope which becomes infinite at a point beyond which the curves become unstable. The maximum experimental loads are smaller than the theoretical predictions and occur consistently in the vicinity of the point of infinite slope in the theoretical horizontal load-displacement curves. The experimental curves start to deviate from the theoretical curves shortly before reaching this point, showing rapid increase in the displacement. Finally, long braces behave elastically until the maximum loads are attained at the termination of the elastic state. For practical purposes, a simple means for predicting the carrying capacity of diagonal braces is recommended in view of these findings. © 1978.