ABSTRACT
After 1994 Northledge and 1995 Kobe earthquake, it has been widely-recognized as an important issue to improve poor seismic performances of existing buildings. For this reason, many retrofitting techniques has been studied and developed. Recently, several rehabilitations with hysteric damper such as buckling restrained braces (BRBs) have been reported (Tena-Colunga, 1997, Hasegawa, 2006, Di Sarno, 2006). Some of them include several techniques to connect these braces to original beam-to-column connection (Ichikawa 2006). However, little attention have been given to the effective techniques for attaching braces to column bases in the past. There are several reasons for this. One of them is that actual seismic performance of column base with braces, such as resisting mechanism against seismic load has not been clarified. Many old middle-rise buildings which need seismic rehabilitation have exposed type column bases. Most of their column bases don’t have sufficient stiffness and strength. Therefore, to achieve requested structural improvement with additional components such as BRBs, retrofitting technique including repair of original column base may be required. On the other hand, for steel moment frame with BRBs, effects of rigidity of column bases on global performance have not been clarified. So, in this study, prior to evaluation of performance of column bases with braces such as strength and restoring force characteristics subjected to earthquake load and developing retrofitting techniques, In order to investigate the effects of rigidity of column base on seismic performance of steel moment frames retrofitted with BRBs, a series non-linear response analysis of middle-rise steel moment frames retrofitted with BRBs was carried out.
