Experimental and numerical study of precast concrete joints with buckling-restrained knee braces and self-centering tendons

This study proposes an innovative precast concrete (PC) beam-column connection system for seismic-prone
areas, integrating unbonded post-tensioned (PT) connections with buckling-restrained knee braces (BRKBs) to enhance both stiffness and self-centering capabilities while managing energy dissipation. To evaluate key parameters, including strength, stiffness, ductility, and self-centering efficiency, three scaled-down jointed beamcolumn PC specimens were subjected to reversed cyclic loading: an unbonded PT PC specimen without BRKB, and two unbonded PT PC specimens with BRKBs of differing core dimensions. The results indicated that the  unbonded PT PC connection with BRKB1 exhibited 30 % greater initial stiffness and 47 % higher relative selfcentering efficiency compared to the cast-in-place (CS) specimen. However, BRKB1 demonstrated 21 % less energy dissipation at a drift of 2.75 % due to its design, where the BRKB core primarily provides energy dissipation.At the same time, self-centering is achieved through the unbonded PT tendons. In contrast, energy dissipation in the CS specimen was achieved through the formation of plastic hinges, allowing for greater plastic deformation. The relative self-centering efficiency was calculated based on the ratio of residual displacement to peak displacement during cyclic loading. Finite analysis via SeismoStruct software further validated these findings, showing strong agreement with experimental results, with a peak force difference of only 6.88 %. These findings underscore the effectiveness of BRKB integration in unbonded PT systems for enhancing seismic resilience in PC structures, providing not only improved structural safety but also advantages in post-earthquake repair.