# Seismic Response Analysis of Multi-Story Steel Frames Using BRB and SCB Hybrid Bracing System
SCBs can be based on shape memory alloys (SMAs) or post-tension technology supplemented by damping sources, exhibiting a flag-shape (FS) hysteresis. The first SMA-based SCB can be traced back to the work by [PERSON] et al. [29]. In their study, the SMA-based SCBs consisted of a pair of superelastic SMA cables which were prestressed to a desirable extent to provide recentering capacity and energy dissipation ability, respectively, and then they were tested within a scaled reinforce concrete frame. [PERSON] et al. [30] invented an innovative SCB which explored the large elastic behavior of aramid tendons and friction damper. According to the test, the SCB exhibited full FS behavior and suffered from high axial strain level while resulting in zero structural damage. Through extensive analyses on FS single-degree-of-freedom (SDOF) systems, [PERSON] et al. [39] pointed out the benefits of increasing energy dissipation and post-yield stiffness in improving the seismic performance of self-centering structures. Researchers have proposed various improvement schemes for systems using SCBs. Such as [PERSON] and [PERSON] [22] tuned the relative amount of the prestressed and un-prestressed SMA cables to meet the energy dissipation and post-yield stiffness of SCB at a desirable level. In another work, the authors [40] introduced friction mechanism in SMA-based SCBs to increase the damping behavior of self-centering hysteresis. The testing results of the reduced-scale brace specimen detected that the FS cyclic behaviors were repeatable for many loading cycles without any property degradation. [PERSON] et al. [41] explored the friction damper, in which the friction surfaces were created inside in the SCBs to generate a plump hysteresis. Further, the SCBs were tested within a reduce-scale frame on shaking table and they performed as expected in a series of strong earthquakes and maintained a stable FS hysteresis with high damping capacity. As have been revealed by prior studies, BRBFs have the problem of generating excessive residual deformations after earthquakes, while the self-centering concentrically braced frames (SCCBFs) have relatively low energy dissipation capability. This work comprehensively compares the seismic behavior of BRBFs, SCCBFs, and concentrically braced frames (CBFs) using hybrid bracing systems. The idea of combing BRBs and SCBs in a braced frame has never been proposed by earlier studies. To validate the proposed idea, nonlinear static and time-history analyses were carried out on the bracing system using BRBs, SCBs, and a combination of them. In the comparative analysis, interested seismic response parameters include maximum story drift ratio, maximum floor acceleration, and residual story drift ratio. Through the comparative study, it indicates that the BRBFs are featured with excessive residual deformation and that the SCCBFs are characterized by larger deformation demand. However, when the BRBs and SCBs are utilized together as the hybrid bracing system, the protected frame structures respond with improved performance, including reduced maximum deformation, controlled maximum floor acceleration, and minimized residual deformation. As well as should be noted is that, although this paper primarily analyzed the seismic performance of multi-story CBFs, the associated observations and conclusions might also provide some insights into the similar self-centering structures and systems.