# Development of a New Rubber Buckling-Restrained Brace System for Structures
## 1 Introduction
The parametric study concerning equivalent damping aided in several conclusions for optimal brace behavior. First, a larger brace sectional area results in higher equivalent damping. Likewise, a larger brace cross-sectional area results in higher damping under small lateral displacements, while a brace having a smaller cross-sectional area sees higher damping under large lateral displacements. Finally, if a larger BRB is to be employed, the steel must have a lower yield stress to maximize the equivalent damping. Given the limited available variance in steel strength, a designer can only practically affect the stiffness of the braces by varying the cross-sectional areas. [PERSON] and [PERSON] (2009) investigated the seismic performance of steel moment-resisting frames (MRFs) retrofitted with various bracing systems. The main MRF was designed with a lateral stiffness that did not accompany drift limitations in severe seismic regions. The bracing systems were special concentrically braced frames (SCBFs), megabraces (MBFs), and BRBFs. Their combination led to eight retrofitted models [43]. It was found that the maximum story drifts in MBFs is 70%, 50% lower than MRFs and SCBFs. Although BRBFs have a slightly higher reduction in maximum story drifts than MBFs, their total weights are greater than those of MBFs (18.45 vs. 13.5). They concluded that MBFs are the most cost-effective bracing systems. [PERSON], [PERSON], and [PERSON] (2014) compared the seismic performance of BRBFs and shape memory alloy-traced frames (SMA BFs). Four different bracing configurations (including diagonal, split-X, chevron-V, and inverted-V) were tested using incremental dynamic analysis (IDA) under twenty various ground motion records. In the SMA BFs, the beams and columns were the same as BRBFs, while the BRBs were replaced by super-elastic SMA bar segments that were connected to rigid links. The SMA BFs were designed to have the same natural period as the BRBFs [44]. [PERSON] et al. drew the following conclusions from the study:  
1. The responses of BRBFs are only slightly sensitive to higher modes. 2. The SMA braces are effective in reducing maximum inter-story drifts. 3. Both SMA BFs and BRBFs satisfy design drift limits
4. The inelastic responses of SMA BFs are distributed more evenly than BRBFs, which mitigate structural damages. 5. SMA BFs experience negligible residual drifts due to the re-centering capacity of shape memory alloy braces. 6. SMA BFs are more sensitive to the frequency content of earthquakes. Under severe earthquakes, SMA braces undergo complete phase transformation, which allows them to dissipate more energy [44]. [PERSON] and [PERSON] (2004) modeled five-story and ten-story structures furnished by BRB to investigate the effect of BRBs on the seismic responses of buildings. Nonlinear time-history analyses were performed using scaled El Centro and Mexico City earthquakes. The same number of BRBs with yield stresses of 14.5 and 35 ksi (100 and 240 MPa) were distributed throughout the structures using four different methods: (a) distribution proportionally to story stiffness, (b) same-sized BRB in every story, (c) distribution proportional to inter-story drift resulting from pushover analysis, and (d) distributed proportional to story shear. The results proved that BRBs produced better structural performance. They also proposed a design procedure based on the hypothesis of equivalent damping by plastic deformation of the BRBs. A model structure designed in accordance with the proposed method exhibited maximum displacements that corresponded well with target displacements [45]. In similar research, [PERSON] et al. (2004) studied a performance-based seismic design procedure for SDOF and MDOF model structures furnished by BRBs. Both three- and five-story model structures were built according to the direct displacement design method under nonlinear time history analysis.