# Development of a New Rubber Buckling-Restrained Brace System for Structures
## 6 BRB and RBRB Experimental and Hysteresis Response Results
### RBRB Experimental Results  
The failure mode of RBRB was comparable to that of BRB. However, the failure in RBRB occurred within the core with less displacement, attributed to the excessive stiffness and resistance of the rubber components, in contrast to BRB, wherein the test was finished due to failure of the core. RBRB exhibited sustained stability as its rubber blocks continued to resist the applied load. Figure 32 indicates the local buckling in the RBRB core. Figure 33 illustrates the failure stage in the weakest point of the core due to the core reaching maximum strength capacity.  
Figure 28: Local buckling of BRB core.  
Figure 29: Failure of BRB core after testing.  
Based on the results shown in Figure 34, the rubber in the test remained completely elastic during and after the testing process, indicating no signs of damage that could compromise its functionality. This characteristic represents a significant advantage compared to BRB systems, where all systems collapsed following core failure.  
The obtained force-displacement relation hysteresis curve for conventional RBRB is shown in Figure 35. The graph shows that the maximum force reached by the BRB was 177 kN (at 8 mm displacement) under tension and  
compression. Additionally, the backbone curve was plotted, and polynomial formulations were derived and are presented in Figure 36. Also, the RBRB results before the failure follow the same BRB kinematic hardening behavior [87] with better performance in terms of increased strength due to the rubber resistance.  
The behavior of the proposed RBRB is discussed in two main phases. Phase 1 shows the behavior of RBRB before failure in the main core, and phase 2 indicates the behavior of the device after core failure. In phase 1, the steel core, rubber components, and concrete were performed in parallel and shared the duty to carry the load. In phase 2, after the plastic core failed by being ruptured, the load-bearing duty was on the rubber components. The load was transferred from the core to steel dividers, then to the rubber components, and finally to the concrete. This process proves the claimed hybrid behavior of the RBRB system.  
The phase 1 load-displacement curves are shown in Figure 37. The maximum load and displacement under tension are 177 kN (in 8 mm) and 18 mm, respectively. Under compression, the maximum load was 224 kN, and the maximum displacement reached 17 mm. This behavior was anticipated based on the rubber material test result under volumetric compression, whose strength aids in increasing the steel resistance in load-bearing.  
Figure 34: Core failure and rubber components of RBRB.  
Figure 33: Core failure of RBRB.  
Figure 35: Hysteresis curve of experimental RBRB.  
Figure 36: Full backbone curve of experimental RBRB.  
Figure 37: Hysteresis curve in phase 1 of experimental RBRB.  
As shown in Figure 38, on the other hand, in phase 2, the performance is similar to an independent rubber damper and had a perfect linear behavior curve in the load-bearing under cyclic loading, which follows the same behavior of rubber material. It reached a maximum load of 85 kN (42 mm displacement) under tension and 63.5 kN (42 mm displacement) under compression.