Behavior and design of laterally braced inelastic compression members

This paper presents a numerical study of the inelastic response of laterally braced geometrically imperfect columns under uniform compression. The study employs the pseudo load method of inelastic analysis in which the load deflection behavior of the member is traced from the beginning of loading to ultimate failure. The compression member to be analyzed is pinned at both ends and is supported at some intermediate point by a brace. The brace is modeled as a spring and its location can vary within the length of the compression member. Although this spring brace is assumed to behave in an elastic fashion' the compression member being braced can experience inelasticity. The inelastic behavior of this braced compression member as well as the lateral bracing requirements and the effect of brace location on the ultimate strength of the braced member are investigated. Contrary to the usual design practice in which the braced point is assumed to be rigid and undergo no lateral movement' studies have shown that such a so-called fully-braced condition is rarely realized. As a result' the actual strength of the compression member will fall below its code-specified value. To ensure a safe design' due considerations must be given to the proper design of the brace. Design equations for the stiffness and strength of a brace required to develop at least 90% of this code-specified design compressive strength for the braced member are proposed.