Seismic performance of steel braced frames with rotational self-centering energy-dissipating braces

A rotational self-centering energy-dissipating brace (R-SCEDB) with variable stiffness is proposed to improve the post-earthquake recoverability of steel braced frames and mitigate inter-story drift concentration under strong earthquakes. The brace consists of physically independent friction-based energy dissipation (ED) systems and disc spring-based self-centering (SC) systems, allowing damaged ED components to be replaced without dismantling the SC systems. A restoring force model and an efficient OpenSees model are developed and validated against cyclic test results. Nonlinear response-history analyses are then performed on the six-story buckling-restrained braced frame (BRBF), self-centering buckling-restrained braced frame (SCBRBF), and R-SCEDB frame (R-SCEDBF) designed with identical lateral strengths. Twenty ground motions scaled to the design basis earthquake (DBE) and maximum considered earthquake (MCE) levels are used, followed by incremental dynamic and parametric analyses. The test results demonstrate stable frictional energy dissipation, nonlinear elastic restoring behavior, and flag-shaped hysteresis, while the numerical analyses reveal the activation of second-stage stiffening. At the MCE level, the R-SCEDBF exhibits the most uniform inter-story drift distribution, with median and 84th-percentile drift concentration factors of 1.62 and 1.78, respectively. The probability of exceeding a residual inter-story drift of 0.2% is nearly zero for the R-SCEDBF, compared with 91% and 21% for the BRBF and SCBRBF, respectively. Parametric analyses show that increasing the contribution of the ED system reduces peak inter-story drift and floor acceleration while maintaining negligible residual deformation. Earlier activation of second-stage stiffening moderately improves drift uniformity, whereas excessive stiffness amplification increases floor acceleration and force demands on the primary frame. Based on these findings, preliminary design recommendations are proposed for the key hysteretic parameters.