New hybrid FRP strengthening technique for rectangular RC columns subjected to eccentric compressive loading

Abstract

In this study, a new hybrid technique for the strengthening of rectangular reinforced concrete (RC) columns under eccentric compressive loading is described, and its effectiveness is assessed experimentally. This technique combines two carbon fiber-reinforced polymer (CFRP) systems for complementary purposes: strips of CFRP wet layup sheets with a certain prestress level using a mechanical device in an attempt to introduce effective concrete confinement, and CFRP laminates applied according to the near surface mounted (NSM) technique to increase the flexural capacity of the RC columns. The effects of the cross section aspect ratio and flexural strengthening ratio of CFRP laminates were investigated in terms of the load carrying capacity of this type of RC columns. All specimens had a height of 1,080 mm, and 3 cross sections were considered, 120 × 120 mm2, 240 × 120 mm2, and 480 × 120 mm2, representing cross section aspect ratios (large/small edge) equal to 1, 2, and 4, respectively. All columns were subjected to eccentric compressive loading until failure. The results show that the new hybrid strengthening technique can enhance the performance of rectangular RC columns in terms of load carrying capacity and ductility under eccentric loading. The cross section aspect ratio played an important role in the confinement effectiveness of the strengthened system. When the cross section aspect ratio increases, the benefits provided by the proposed technique in terms of maximum axial strength and lateral deformability at the peak load of all columns decreased. The load carrying capacity and lateral deformability of the tested RC columns increased with the flexural strengthening ratio. In addition, an analytical model is proposed to evaluate the maximum strength and the axial load–lateral displacement response of rectangular RC columns strengthened according to the newly proposed technique, and a good predictive performance was obtained.