Bracing design requirements for inelastic members

Using properly spaced and designed bracing can substantially increase the buckling capacity of a member. A brace needs to satisfy both stiffness and strength requirement. Significant research has been done for the bracing requirements of elastic members. Relatively little work has been performed for the bracing design of inelastic members. This research focuses on the brace design requirements for structures that rely on plastic redistribution or energy absorption. The finite element analysis results for lateral bracing behavior in inelastic beams are presented. The research focuses on the lateral bracing requirements to achieve a specified rotation capacity in braced members subjected to uniform moment and moment gradient. The brace stiffness and lateral brace force requirements for inelastic steel members are evaluated considering the effects of unbraced length, flange slenderness and web slenderness. The results show that the current AISC-LRFD requirements for brace stiffness are adequate and not sensitive to rotation capacity. Brace forces, however, increase as rotation capacity increases. Brace forces also increase significantly when local flange and web buckling occur. The factors affecting beam rotation capacities and lateral brace forces are discussed. A design formula for beam rotation capacities is proposed. The lateral bracing behavior of inelastic beams under cyclic loading were investigated both experimentally and analytically. The bracing requirements for inelastic columns were also considered.