Inelastic Buckling of Reinforcing Bars

Abstract

A special beam‐column element is developed for the finite element inelastic buckling analysis of reinforcing bars in concrete columns. The material considered is elastic‐plastic‐strain hardening. A strain reversal rule is also included to model the unloading from compression once buckling occurs. The element is used to trace the post‐buckling load‐deflection path of a reinforcing bar supported laterally by sufficiently stiff ties of the column and initially loaded axially to the yielding load. The post‐buckling load‐deflection path depends on the slenderness ratio of the bar. For a very small slenderness ratio, an interesting [straightening] phenomenon is present after the buckling at the yielding load, followed by a second buckling at a higher load. For a larger slenderness ratio, the post‐buckling load carrying capacity may or may not exceed the yielding load. A critical slenderness ratio is found by equating the maximum load to the yielding load.