Analysis of the confinement of RC hollow columns wrapped with FRP

This paper presents a theoretical model for the analysis of fiber-reinforced polymer (FRP) confined hollow reinforced concrete (RC) sections as found in many tall bridge piers. FRP confinement systems effectiveness have been studied focusing on solid columns while very little has been done about hollow sections. In order to study the behavior of square hollow sections subjected to combined axial load and bending, a total of 7 specimens have been tested, representing, in a scale 1:5, typical square hollow bridge piers. The strengthening scheme consisted of unidirectional Carbon FRP laminates applied in the transverse direction. The proposed model is able to estimate confinement effectiveness in the case of hollow sections. Relevant parameter was the relative wall thickness. Theoretical results, in excellent agreement with authors' sets of experimental data, show that FRP jacketing can enhance the ultimate load and the ductility also in the case of hollow concrete cross sections.