Paper Title
SEISMIC PERFORMANCE OF NATURALLY BUCKLING BRACED FRAMES

Abstract
Abstract - Naturally buckling braces (NBBs) had been previously developed to significantly improve the seismic performance of conventional buckling braces (CBBs). Previous experimental studies have verified that NBBs enable to postpone local buckling behavior, pinching effect and brace fracture of CBBs thereby enlarging the overall ductility of the member. This study conducts an analytical investigation of seismic performance of naturally buckling brace frame (NBBF) buildings compared to that of the counterpart SCBF systems with CBBs through nonlinear response history analyses. The design procedures and accurate numerical models of NBBFs were established and compared to the typical design procedures of SCBFs. Three-, nine- and twenty-story prototype buildings of the NBBF and SCBF were designed, and their dynamic responses under the events at various hazard levels were examined and compared. The results verified that the NBBF general provided a positive post-yield stiffness under the pushover analysis. In dynamic analyses, the NBBFs were verified to have more uniformed distribution of story drifts throughout the height which helped to reduce the maximum story drifts under the events at all hazard levels. The NBBFs would have greater residual drifts after earthquakes compared to the counterpart SCBFs, but the residual drift levels were minor and still met the limit state for immediate operation (IO). The demands of floor accelerations and story shears of the NBBFs were smaller than that of the counterpart SCBFs. The fragility analyses verified that the energy dissipation was advanced, and the failure modes and structural collapse were significantly postponed or event prevented in NBBFs compared to SCBFs. Keywords - Naturally Buckling Braces, Seismic Performance Evaluations, Special Concentrically Braced Frames