An innovative bracing member with flag-shape hysteretic response for enhanced structural seismic performance

Structures designed according to modern seismic codes are expected to resist earthquake effects through controlled and ductile inelastic structural response. This implies that there will likely be extensive structural damage after a severe ground shaking, together with substantial residual deformations. To address this drawback of traditional yielding systems, an innovative bracing system that can undergo large axial deformations without structural damage while providing stable energy dissipation capacity and positive restoring force has recently been developed in Canada. This bracing member exhibits a repeatable flag-shaped hysteretic response with full re-centering capabilities, therefore eliminating residual deformations. In this paper, this new bracing technology is first described and preliminary full-scale experimental validations are presented. Experimental results confirmed that the concept performs as expected, exhibiting a full self-centering response with good energy dissipation. Results from an extensive analytical study that was performed to examine the seismic performance of 2- to 16-storey buildings are also summarized. The structures were located in the Los Angeles area and were designed according to ASCE-7 provisions. These numerical analyses showed that the structures equipped with self-centering braces exhibited similar maximum deformations as structures equipped with Buckling Restrained Braces (BRBs) but, unlike the BRBs, did not sustain any residual deformations. The structures equipped with the new self-centering brace experienced larger peak accelerations than their BRB counterparts. These acceleration peaks however occur at very high frequencies and would primarily affect stiff building contents.