punching mechanism in reinforced concrete frames retrofitted by steel frame

In recent years, steel elements such as shear walls and steel braces have been frequently applied as the lateral load resisting system in design and retrofit of structures. the low-cost construction, quick installation, high energy absorption potential, etc. have made this system an appropriate system for retrofitting of existing structures (rutherford et al., 2006), since these systems are currently has found many usages in buildings retrofitting in countries such as: the united states,japan and canada. the early experimental investigations by sugano and fujimura pointed out the efficiency of retrofitting rc frames by steel braced frames (sugano, 1981). kawamata and ohnuma (1981) proposed a technique for retrofitting rc frames by eccentric steel braces. generally, by reviewing the associated works, the connections betweenrc frames and steel frames can be classified into two main types including direct and indirect connections. ohishi et al. (1988) and sekiguchi et al. (1988) have suggested the indirect connection for retrofitting rc frames by steel braced frames. in the indirect connection, a steel braced frame is installed inside an rc frame using studs, anchors and highstrength grout. anchors are installed in the epoxy-injected holes provided on the boundary elements of rc frames. studsare welded on the boundary of the steel braced frame. finally, the high-strength grout fills the provided space between the rc frame and the steel braced frame, to strongly interlock the anchors and studs.