Thickness of tensile strips (tr) presents positive influence on ultimate load and ductility 20 for the lateral stress of concrete benefits from the axial force of tensile strips.
The tensile strip with large thickness brings high ultimate resistance and ductility.
Moreover, even very thin tensile strip can effectively improve mechanical behavior of specimens.
Therefore, the tensile strip is suggested to have the same thickness with the steel tube, as long as the welding requirements are satisfied. In addition, the yielding strength of stiffeners (yr)f has little influence on ultimate load and ductility (Fig. 20(g)).