Optimal design of steel buckling-restrained braces considering stiffness and strength requirements

Abstract

This paper is concerned with the optimal (or least weight) design of steel buckling-restrained braces against global buckling. First, the global buckling prevention criterion of steel buckling-restrained braces (BRB) is reconstituted to take on a symmetric expression, i.e., (Pcr/Pu−1)[Mr/(v0Pu) −1] ≥ 1, so as to provide clarity on the equal importance of the stiffness and strength requirements of the restraining member, where Pcr is the elastic buckling load, Mr the yield moment resistance, and v0 the initial imperfection of the restraining member whereas Pu is the ultimate compressive load of the core under cyclic axial loads. It is shown herein that the optimal design of the restraining member satisfies (1) the boundary of the global buckling prevention criterion, and (2) the relationship between the stiffness term Pcr/Pu and the strength term Mr/(v0Pu) in view of the maximum feasible cross-sectional height-to-thickness ratio as specified by the adopted design code recommendation. The satisfaction of these two conditions furnishes a unique optimal design of the restraining member. The optimal design can be expressed as an explicit equation in terms of the second moment of area of the restraining member. A design example is presented to illustrate the material (or weight) efficiency of all-steel BRB designs based on the proposed design equation.