•  Buckling-restrained braces with multiple round steel cores have been developed as a new seismic resisting element for building structures. 
•  Loading tests were conducted on full-scale test specimens to reveal the performance of the proposed brace. 
•  Finite element analysis simulations were conducted to analyze in detail the structural performance of the proposed brace.

  The use of buckling-restrained braces (BRBs) have been increasing in Japan and abroad to improve the seismic performance of building structures. Various sections of steel members are used for the core member of BRBs. Recently, BRBs with round steel bar cores have been proposed. 

  This study developed a new type of BRB using multiple round steel bar cores. It is composed of some primary stiffening tubes that directly restrain buckling of the round steel cores and a secondary stiffening tube that restrains the overall brace buckling. Two configurations of BRB have been developed. Particularly, in the second configuration, the secondary stiffening tube of the square steel section is utilized outside the primary stiffening tube group to reduce the total weight of BRB. The loading tests using real-size test specimens revealed the good performance of the proposed BRB. Furthermore, computer simulations based on the finite element analysis clarified the detailed behavior of each BRB component, which is useful for the structural design of BRB. 

  Seismic resistant technology to reduce the earthquake damage to buildings is an important research topic for realizing safe and comfortable societies. The results of this research will contribute to the progress of related research fields.

[1] Sijin Zhang, Hiroshi Tagawa, Xingchen Chen, Study on buckling-restrained braces using multiple round steel core bars, Journal of Constructional Steel Research, Volume 199, 2022, 107573, https://doi.org/10.1016/j.jcsr.2022.107573. 

[2] Sijin Zhang, Hiroshi Tagawa, Xingchen Chen, Buckling-restrained brace with multiple steel bar cores using SHS outer tube, Journal of Constructional Steel Research, Volume 211, 2023, 108175, https://doi.org/10.1016/j.jcsr.2023.108175.