Influence of post-onset stiffness on seismic responses of BRBFs with gap-supported protections

Abstract

A Buckling-restrained brace with gap-supported tendon protection (TP-BRB) is a new buckling-restrained brace with post-onset stiffness. The critical design parameters of the TB-BRB are the values of the initial gap and the additional stiffness. In this paper, 3-, 6-, 9-, and 12-story frame buildings were designed with two types of bracing members: Buckling-restrained braces (BRBs) and TP-BRBs. Nonlinear time-history analyses were conducted to investigate the influences of the initial gap and the additional stiffness. The results illustrate that the TP-BRBFs exhibit smaller maximum story drift (θmax) and residual story drift than BRBFs, and the formers show a more uniform distribution of lateral deformation than the latter. For lower TP-BRBFs, a decrease of the initial gap is an effective way to improve their seismic performances, and the initial gap is recommended to be the difference between the maximum axial deformation of the TP-BRBs under maximum considered earthquake and its yield deformation (uy). For taller TP-BRBFs, the initial gap is suggested to be (8.5–12)uy in the premise of cables remaining elastic under maximum considered earthquake. On the other hand, an excessive additional stiffness would reduce the potentiation of TP-BRB on the seismic performances, and it increases manufacturing costs of the TP-BRB. The additional stiffness of the TP-BRB is recommended to be less than 0.25ke, where ke is the initial stiffness of the TP-BRB. Moreover, an estimation formula to calculate the minimum value of θmax and an iteration design procedure were proposed for taller TP-BRBFs.