Buckling Restrained Braces - Issues and Solutions

This paper describes some design issues relating to buckling restrained braced frames (BRBFs) including: (i) BRB system capacity under both axial compression and out-of-plane (OOP) frame deformations, (ii) BRB demand estimation, (iii) brace inertial effects, (iv) gusset plate (GP) weld strength, (v) frame element requirements near the gusset plate, (vi) frame ratchetting considerations, (vii) frame demands, (viii) load paths into the frame, and (ix) BRB quality control. Methods to address these issues are proposed. As part of this, a simple method for BRB system design considering BRB stability and frame out-of-plane deformation effects is described. The method seeks to prevent yielding in the BRB system except for within the core inside the BRB restrainer/casing. It uses standard equations with which engineers are familiar. The method discourages brace/gusset plate regions which are too flexible (where instability may occur as a result of axial force), or which are too stiff (where yielding may occur due to out-of-plane frame deformations thereby compromising the performance in later in-plane deformation cycles).