Subassemblage test and gusset rotation response of buckling-restrained braced steel frames

Abstract

Gusset rotation would cause adverse influence on the buckling-restrained brace (BRB) end zone and even lead to premature buckling of the BRB end zone. However, limited studies to date referred to the gusset rotation response. To evaluate the cyclic behavior and gusset rotation response, five 1/2-scaled buckling-restrained braced frame (BRBF) subassemblages with various gusset connections, i.e., pinned gusset connection, bolted gusset connection, welded gusset connection, pinned-welded gusset connection, and pinned-bolted gusset connection, were conducted under horizontal cyclic loading. The effects of gusset connection type on the failure modes, horizontal initial stiffness, energy dissipation and rotation response of specimens were analyzed in detail. It showed that all specimens performed plump and stable hysteresis behavior. The upper gusset rotation of the specimen with pinned gusset connection was larger than that of bolted gusset connection, followed by welded connection. Meanwhile, the finite element (FE) models were established and validated by test results. Furthermore, the standard FE model of a full-scale one-story one-bay steel moment BRBF with a single diagonal BRB was developed and then extended to a large number of models to investigate the contribution of various parameters on the upper gusset rotation. Finally, the gusset rotational formulae for predicting its response, as the steel moment BRBF reached to either 2.0% or 3.0% drift, were proposed on the basis of the results of the extensive parametric analysis. It could be used to determine the rotation of the BRB end zone, and the flexural moment acting on the BRB end zone and corresponding practical design procedure can be finally derived to avoid the potential premature failure of the BRB end zone.