Tension stiffening and crack formation in reinforced concrete members with fiber-reinforced polymer sheets

Models to estimate crack spacings and tension stiffening effects in reinforced concrete (RC) members with externally bonded fiber-reinforced polymer (FRP) sheets are presented. Due to the lack of experimental evidence on the tension stiffening effect of FRP sheeting, a theoretical approach based on the concept of tension chords is introduced. Crack formation and the tension stiffening of tension chords with FRP sheets are subjected to parametric analyses using bond stress-slip relations. The analytical results are then reduced into simple model equations. In addition to the FRP sheet, the bond characteristics between steel bars and concrete is also modeled according to a concept of average bond. These models are incorporated into the distributed stress field model, enabling reasonable estimations of the crack widths and the tension stiffening effects in RC members with the FRP sheets.