Many reinforced concrete (RC) bridges with hollow section piers were built in Europe between the 1950s and the 1970s. These bridges are now in need of a seismic upgrade to improve their response under earthquake conditions. This paper reports on a study to investigate the upgrade and retrofit of existing RC piers with rectangular hollow cross section using fiber reinforced polymer (FRP) materials applied in the transverse direction. To study the behavior of rectangular hollow cross sections subjected to combined axial load and bending, 7 scaled specimens representing, in reduced scale, typical square hollow bridge piers were tested. The paper discusses the outcomes of the performed tests focusing on the analysis of cross section curvature, member deformability, specific energy, and model restraints. Results showed that the failure of hollow members was strongly affected by the occurrence of premature mechanisms such as compressed bars buckling and concrete cover spalling. The FRP confinement delayed these mechanisms, increasing strength and ductility.