SELF-CENTERING BUCKLING RESTRAINED BRACE DEVELOPMENT AND APPLICATION FOR SEISMIC RESPONSE MITIGATION

Abstract

A self-centering buckling restrained brace (SC-BRB) has been developed which returns to near zero displacement when axial force is removed through the action of pretensioned shape memory alloy (SMA) rods and dissipates significant seismic energy through a buckling restrained brace (BRB) component. The SC-BRB can be substituted in place of conventional braces or BRBs to provide enhanced seismic performance that is expected to reduce business downtime and repair costs. A prior experimental program has shown that the SC-BRB is a viable seismic brace with enhanced performance. This paper explores the design space for the SC-BRB and its application in realistic building scenarios. A parametric computational study was conducted on 147 braces examining the effect of varying key design variables such as strength, self-centering ability, SMA pretension, SMA gage length, and SMA material properties. Three prototype buildings with five different levels of self-centering capability were then designed. The fifteen resulting structures were subjected to a suite of 44 ground motions scaled to two levels of seismic hazard. The results show that the SC-BRB structures exhibit virtually no residual drift even if the braces don’t have full self-centering capability. Brace configurations with SMA pretension force between 50% to 150% of the BRB yield force can still reliably self-center the building while reducing the demands on surrounding framing by limiting brace overstrength.