Seismic design method for multi-story SMA braced frames based on inelastic displacement ratio

Superelastic shape memory alloys (SMAs) can recover large inelastic deformation meanwhile dissipating energy under loading reversals. This property makes them an attractive alternative for developing structures with desirable self-centering (SC) capability. For SMA braced frames (SMABFs), which have not been codified in current seismic provisions, their deformation demand under earthquakes needs to be estimated with confidence in the phase of seismic design, retrofit or upgrade. In this work, the inelastic displacement ratio, i.e. C_R, is explored to address current issue. The fundamental behavior of SMABFs is understood by analyzing the equivalent single-degree-of-freedom (SDOF) systems, with the purpose of evaluating and discussing the influence of fundamental period (T), strength reduction ratio (R) and hysteretic parameters of systems (including the secondary stiffness ratio α and the hysteresis width β) on C_R. The regression of C_R is further conducted to be a function of T, R, α, and β. Subsequently, a C_R-based seismic design procedure is developed for multi-story SMABFs. Two frame structures of 3 and 6 stories are utilized to verify the proposed design procedure. The seismic analysis results indicate that the mean responses of designed structures agree well with prescribed performance targets. Although SMABFs are focused in this study, the proposed method could also shed light on the other types of SC structures.