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

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 (θ max) 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 (u y). For taller TP-BRBFs, the initial gap is suggested to be (8.5–12) u y 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 0.25 k e , where k e is the initial stiffness of the TP-BRB. Moreover, an estimation formula to calculate the minimum value of θ max and an iteration design procedure were proposed for taller TP-BRBFs. [Display omitted] • Effects of the post-onset stiffness on performances of TP-BRBFs was investigated. • Excessively reducing the initial gap and increasing the additional stiffness are irrational. • Recommended values to the initial gap and the additional stiffness of TP-BRBs are provided. [ABSTRACT FROM AUTHOR]