# Development of a New Rubber Buckling-Restrained Brace System for Structures
## 1 Introduction  
Recently, construction methods have tended to use lateral bracing systems in the form of tension only or rigid tension-compression steel bracing to increase the stiffness of structures. While conventional cross-bracing can be used for both lateral loading, the cyclic compressive force applied to steel braces in a seismic event occurrence has resulted in the recent development of the Buckling-Restrained Bracing (BRB) system to enhance seismic performance by addressing buckling and low energy dissipation in traditional braces by providing stable, symmetric yielding under tension and compression. However, previous studies on BRBs showed that during a severe vibration, by failure of the main core, braces are not able to perform further in load bearing and are required to be changed or repaired, which causes difficulty for maintenance and retrofitting in the structure. Despite structures being furnished with other vibration dissipation systems such as viscous dampers [1; 2] or variable stiffness bracing [3], BRBFs exhibit very favorable energy-dissipating characteristics. However, low post-yield stiffness of the braces leaves this system vulnerable to unfavorable behavioral characteristics such as maximum story drift and residual story drift. Furthermore, in order to increase the strength of high-rise buildings against earthquakes, it is required to enlarge the BRB cross-sectional area, which leads to an increase in the total weight and occupied area of the building. For a larger BRB, the steel must have a lower yield stress to maximize the equivalent damping. Given the limited available variance in steel strength, the only practical solution for a designer is to affect the stiffness of the brace by varying the cross-sectional areas of the brace. The concept of Buckling-Restrained Braces (BRBs) originated in Japan during the early 1980s, initially referred to as buckling-inhibited or unbonded braces [4]. These types of braces received initial approval in the United States a few years after the Northridge earthquake occurred in 1994 [5]. Although BRBs could be diverse in design and configuration, the main concept among the BRBs remains identical. The brace consists of one ductile steel core, which is supposed to yield under tension and compression. To prevent global buckling in the core, it is placed inside a steel case's mainly hollow section, which is named the hollow steel section (HSS), and then this hollow gap between the core and restrainer case can be filled with various mortars such as concrete or just remain as a void cavity. Before this mortar is cast, an un-bonding material or an air gap should be provided so the core segment becomes able to move easily through the system and the axial load can be transferred between the core and hollow steel section (HSS) [6]. One investigation focused on how to assemble the BRB elements by modifying the size, configuration, and material. We also performed an extensive analysis of the BRBs' stability and analyzed a range of factors that may affect the BRBs' performance. The authors proposed a simplified seismic calculation method to design this kind of bracing system and developed new methods for using existing steel sections [7]. Based on several benefits of steel plate-assembled BRBs, for instance, performance stability and simple fabrication, the number of studies conducted on them have been increasing. To address the issue of the problems of local buckling of end connection and random failure locations of steel core components in plate BRBs, [PERSON], et al. (2009) produced perforated steel plate Buckling-Restrained Braces (or PBRBs). They investigated PBRB energy absorption and its parameters. Their results proved the excellent performance of PBRBs, such as energy consumption mechanisms, by fixing failure location, having stable energy consumption capacity, and showing good hysteresis curve performance, which enhanced the seismic performance of the conventional BRB [8]. [PERSON] et al.