Retrofitting of RC Frames by Steel Braced Frames Utilizing a Hybrid Connection Technique

Abstract

This study presents a new connection technique to retrofit existing RC frames by steel braced frames. The proposed connection which is called the “hybrid connection” plays two important structural roles. The first role is to provide connection between an existing RC frame and a steel braced frame. The second role is to increase shear strength and axial compression capacity of boundary RC columns of retrofitted frames. The hybrid connection consists of steel plates, high-strength bolts, and high-strength grout. Experimental investigations were conducted on four one-bay one-story RC frames and one one-bay two-story RC frame which were retrofitted by the proposed method. Moreover, one one-bay one-story RC frame was tested as a non-retrofitted benchmark frame. Experimental results of the specimens indicated that the proposed hybrid connection transferred relatively high direct shear forces between the RC frames and the installed steel braced frames to obtain lateral capacity of the steel braces. In addition, the proposed hybrid connection prevented possible shear failure of the boundary RC columns with the help of the utilized steel plates. Taking into consideration experimental results and observations, simplified design approaches are presented to estimate lateral strength of fundamental failure mechanisms of retrofitted RC frames.