Seismic design and performance evaluation of steel braced frames with post-tensioned and disc-spring-based self-centering buckling-restrained braces

In this study, we focus on two types of self-centering buckling-restrained braces (SC-BRBs), which are post-tensioned (PT) SC-BRB and disc-spring-based SC-BRB, and develop a seismic design method for steel braced frames with these braces according to the displacement-based design theory. The whole independent parameters that describe the hysteretic behavior of the SC-BRBs are first determined. Then nonlinear time history analysis (NLTHA) is conducted to explore the effects of these hysteretic parameters on the ductility demands of the nonlinear single-degree-of-freedom (SDOF) system. Based on the analysis results, a ductility demand spectral model is developed, followed by a nonlinear displacement ratio spectral model. Subsequently, the seismic design procedure for SC-BRB frames is proposed based on the two spectral models. Finally, a total of 24 six-story steel frames with the two types of SC-BRBs, two target inter-story drifts, and different parameter combinations are designed at the maximum considered earthquake (MCE) level. The pushover analysis and NLTHA results indicate that a smaller strength ratio β and a larger initial stiffness ratio αs are beneficial for reducing the base shear and obtain an economical design when the designed frames achieve the same target inter-story drift. Considering the initial stiffness of the SC-BRBs is highly sensitive to machining errors, it is recommended that the value of β be taken within 0.25 to reduce the influence of the initial stiffness uncertainty of the braces on seismic design results. Moreover, controlling β within 0.25 also helps to reduce the higher-mode effect and peak floor acceleration responses of the designed structures effectively.