Strong-axis and weak-axis buckling and local bulging of buckling-restrained braces with prismatic core plates

The performance of new type Buckling-Restrained Braces (BRB) is evaluated. The new type BRB is efficient since the steel core is constructed with prismatic steel plates that are straight throughout its length. Connection plates attaching the BRB to gusset plates are welded perpendicular to the steel core plates; this configuration is different from conventional BRBs in which the core plates also serve as the connection plates. Since the steel core plates are prismatic, construction of new type BRBs saves material and reduces the cost of manufacturing. Four full-scale new type BRBs were tested under quasi-static cyclic loading with either a single core plate or dual core plates using either bolted or welded connections to gusset plates. The hysteresis curves exhibited stable behavior with positive incremental stiffness; the ratio of maximum compression to tension capacity and the cumulative inelastic deformation were satisfactory. There was no rupture or instability and at failure the core plates achieved maximum tensile strains between 3.2% and 4.2%. Failure modes included core plate buckling about the strong or the weak axis and local bulging. The strong and weak axis buckling behavior is modeled using a strut-and-tie model. The local bulging behavior about either the strong or the weak axis is modeled using plastic analysis. Recommendations are presented for preventing strong axis buckling of the steel core and local bulging of the steel casing about the strong axis.