Effect of Height on Retrofitting of Existing Steel Frames Using Buckling Restrained Brace Frames

Recent earthquakes indicate the importance of retrofitting existing structures to achieve an acceptable level of performance. Several different methods for retrofitting of existing structures were used by structural designers; Use of bracing systems is a cost-effective method for seismic retrofitting of existing steel frames. In particular, Buckling Restrained Braces (BRBs) are workable choices to be used because of their large energy dissipation capacity especially under moderate to severe earthquakes. Buckling restrained braces yield in tension and compression, exhibits stable and predictable hysteretic behavior. In this paper two existing structure with different heights are retrofitted with BRB. At next stage vulnerability assessment is done according to ASCE 41-06 with pushover analysis by SAP2000 software and compare the seismic parameters with each other to evaluate effect of height in retrofitted buildings with BRB. By having focus on results, it's observed that, Stiffness of four story building that retrofitted with BRB is larger than eight story but Earthquake energy that dissipated by eight story BRB is more also, four story BRB may undergo less lateral displacements than eight story BRBF and ductility of eight story is larger, so with increasing height, effective stiffness will decrease but ductility will increase. So it's better to use of BRB for retrofitting high raise building in moderate to high seismicity regions.