Effect of the DYB on the seismic response of steel concentric bracings

Even though steel Concentric Braced Frames (CBF) provide buildings with large strength and stiffness and the use of pinned beam-to-column connections makes their fabrication eco-nomical, the poor dissipation capacity of steel braces and the low redundancy of the structure make CBFs prone to storey collapse mechanisms. In this paper, the Double-stage Yield BRB (DYB) is proposed to replace conventional steel concentric braces in order to improve the ductility of CBFs. This damper yields in tension and compression exhibiting fat hysteresis loops and large ductility capacity. In addition, it is characterized by a two-stage yielding. The double-stage yielding mitigates the lack of redundancy of the structural type and promotes a global collapse mechanism. In fact, even if the DYBs of one storey yield before the others, the internal forces will increase in the whole structure between the first and the second yield stages of DYB, thus forcing yielding of the DYBs of the other stories. The goal of this paper is to investigate the effect of the insertion of the DYB on the seismic perfor-mance of CFBs. To this end, a steel frame with DYBs is designed according to a method derived from that stipulated in Eurocode 8 for conventional CBFs. The behaviour factor q is set equal to 4.5. To examine the influence of the properties of the DYBs on the structural response of the frame, different values of the ratio YS between first and second yield forces of the DYBs are considered. Finally, the seismic response of the obtained frames is evaluated by nonlinear dynamic analysis and verified ac-cording to Eurocode 8 acceptance criteria.