Experimental study on seismic retrofit for existing R/C building by using CHS bracing

A new seismic retrofitting method for existing R/C buildings by using a circular hollow section (CHS) bracing is proposed. In the proposed method, a reinforcing frame composed of an H-section peripheral frame and pin-ended CHS bracings is placed on the outer surface of an R/C frame and connected to the R/C with mechanical anchors and high strength mortar. Experimental studies were carried out to evaluate the reinforcing effect. An FLD (Force Limiting Device 1 ), which is restrained not to buckle by the outer tube, is applied mainly as a reinforcing brace. For comparison, single tube braces and H-section braces are also applied to the proposed and conventional method. The proposed connection can transfer the shear force of the brace to the R/C frame. Consequently, the horizontal load carrying capacities of specimens agree with predicted values approximately for the reinforcement of a ductile R/C column. The design efficiency of the reinforcing frame for the brittle R/C column is also discussed.