Abstract
In recent years, applications of buckling restrained braces (BRBs) in reinforced concrete (RC) frames have attracted much attention. It is necessary to reduce the damage in the BRB connections in RC frames to make the BRBs more effective in dissipating earthquake energy. In this paper, it is proposed to use an unconstrained gusset plate and a hinge relocation technique to control the damage to RC beam-column joints. The structural behavior of RC beams with BRB connections and relocated plastic hinges is investigated by both cyclic loading tests and finite element analysis. In the tests on RC beams with BRB connections, the BRB axial force was simulated by a force-controlled actuator to simplify the boundary condition of the test setup. Two different details of BRB gusset connections were examined. In one method, the gusset plate was fastened to the end of the RC beam by post-tensioned steel rods, whereas it was embedded in the RC beam and anchored there by a stud group in the other method. The test results confirmed that the proposed hinge relocation scheme is effective in controlling the locations of plastic hinges in RC beams so as to prevent the BRBs from being dislocated from the entire structural system as a result of the beam end failure at extreme earthquake scenarios. Both gusset connection details performed satisfactorily by providing sufficient strength and large stiffness to minimize the deformation loss in the BRB connections.
Detailed finite element analysis was carried out to reproduce and extend the understanding of the test results. In the analysis, the posttensioned steel rods, the embedded studs and the bond-slip behavior between the embedded gusset plate and the concrete were explicitly modelled. The analysis results agree well with the test results. A parametric study was performed to determine the flexural strength demand for the beam sections that are subjected to the BRB-induced tensile force but are not expected to yield. The results show that the strength ratio, βh, should be no less than 1.14 for the BRB connection to remain essentially elastic.
