Zhang, Quan and Lu 2021
In this study, a modified approach to buckling-restrained braces was introduced to reduce residual drift in structures. This assembled self centering buckling-restrained brace (ASCBRB), comprises prestressed disk-spring groups and a steel case assembled with the use of steel bolts. Due to its higher seismic performance, easier routine maintenance, ability to be replaced and a higher bearing capacity to brace weight ratio, the proposed ASCBRB is more favorable in use as an earthquake prevention device compared to conventional buckling-restrained braces (BRBs). Four different specimens of this proposed system were tested under cyclic loading to verify their self-centering capacity and flag-shaped hysteretic behavior. The results showed that the proposed device exhibited significantly smaller residual drift compared to traditional buckling-restrained braced frames.
System Concept
The energy dissipating part of the proposed system consists of a core-filler-shim-guide plate group. Buckling behavior is mainly restrained by the guide and filler plates while the shim plates installed between them reduce friction that is caused by deformation during compression.
The self centering part of the system comprises prestressed disk springs with link stoppers and outer and inner components. The hat-shaped element composed of channel and cover plates in the outer section ensures the device achieves a high moment of inertia to further reduce buckling. While in compression, the blocking members of the inner screws would contact the link stoppers which causes a linear force-displacement behavior in the braces along the disk springs.
The proposed system is designed to ensure damage is concentrated on the core and guide plates. This helps reduce permanent damage as the core and guide plates can be easily detached by removing the steel bolts.
Experimental Study, Results and Discussion
The experiment was conducted on four different specimens: assembled BRB (ABRB), the assembled SC brace (ASCB) and two ASCBRBs. The braces had the same design parameters but had different arrangements of the prestressed disk-spring groups and core plates. A servohydraulic actuator of 2,000 kN load bearing capacity and 200 mm deformation capacity was used to apply cyclic loading on the specimens.
There were no buckling failures observed in the outer tube, blocking members, twin screws, or cover plates among all specimens which were easily replaceable. However, a local buckling was in the core plate and a permanent deformation in the guide plates of ASCBRB were observed. The ASCB exhibited relatively good resilience with a low energy-dissipating capacity and the ABRB specimen had relatively good energy dissipating capacity but with fairly low ultimate ductility.
Following the quasi-static experiment, a seismic performance simulation was conducted on the braced frames at a 6-story office building. The data portrayed that the ASCBRBF had similar seismic performance to the traditional BRBF while the residual drift was largely reduced to 0.1%. As proven by the results, the proposed ASCBRB frames were able to demonstrate higher seismic performance compared to the BRB frames while possessing other advantages such as easy long-term maintenance and replaceability.
Reference
Zhang, Hongmei, et al. “Experimental Hysteretic Behavior and Application of an Assembled Self-Centering Buckling-Restrained Brace.” Journal of Structural Engineering, vol. 148, no. 3, Mar. 2022, p. 04021302.