A new strengthening technique for increasing the load carrying capacity of rectangular reinforced concrete columns subjected to axial compressive loading

In this work, a new technique for the efficient confinement of reinforced concrete (RC) columns of rectangular cross-section is described and its effectiveness is assessed experimentally. This technique is based on the concept of applying strips of carbon fiber reinforced polymer (CFRP) wet layup sheets with a certain prestress level using a mechanical device. The influence of the cross-section aspect ratio of columns on the axial stress-strain response, strain field in the CFRP and strength increase provided by the different adopted strengthening configurations was investigated. All specimens had a height of 1100 mm, and three 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. Four types of columns were tested: conventional RC columns (reference columns), fully-wrapped columns, partially-wrapped columns, and columns strengthened according to the new technique. All columns were subjected to axial compression loading until failure. The experimental results show that the cross-section aspect ratio has a significant effect on the confinement effectiveness that CFRP strengthened systems can provide to RC columns of rectangular cross-section. The maximum axial strength and axial strain at the peak load of all columns significantly decrease when the cross-section aspect ratio increases. Based on the obtained experimental results, it is shown that the proposed technique is more efficient in terms of increasing the load carrying capacity of rectangular RC columns than CFRP-based conventional strengthening techniques.The first author would like to thank Erasmus Mundus Programme and TecMinho to provide financial and scholarship supports. The support from the FCT in the scope of PTDC/ECM-EST/1882/2014 project is also acknowledged. Moreover, the authors would like to thank the collaboration of Casais and CiviTest companies for the collaboration on the preparation of the RC columns, and Clever Reinforcement Company for providing the CFRP sheets and adhesives. Also gratefully acknowledge the technicians of laboratory of the structural division of the Department of Civil Engineering of Minho University