Using a new method in order to reduce the effects of higher modes in self-centering rocking steel brace frame systems

Modern damage-free systems are part of modern lateral seismic structures. These structures have minimal residual displacement and dissipate earthquake energy through replaceable fuses. self -centering rocking steel braced frame systems that have been investigated in this research are considered among these modern seismic systems. In self-centering rocking structures as well as other tall structures, the effect of higher modes can cause irreparable damages in the structure. In this research, an attempt has been made to reduce the effects of higher modes by using buckling restrained columns and braces (BRCs and BRBs) as energy dissipating fuses instead of standard columns and braces in self -centering rocking structures. Five 12-story structures were investigated, including;self -centering rocking steel braced frame system and four other structure with placement of BRBs and BRCs at the base, one-third, middle and three-quarter of the height. To investigate the seismic behavior of these structures, several analyses has been performed in OpenSees software under 22 far field records according to FEMA P695. Geometric and material nonlinearities is considered in the modeling. The results show the improvement of the seismic performance and the reduction of the effects of higher modes in the case of using BRBs and BRCs in the stories, compared to the case of the common self-centering rocking bracing system.