In this work, a new technique for the efficient confinement of reinforced concrete (RC) columns of rectangular crosssection 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 mm×120 mm, 240 mm×120 mm and 480 mm×120 mm, 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.

An experimental program was carried out to investigate the behavior of RC beams flexurally strengthened using the NSM technique with CFRP laminates. Four beams were tested, a reference beam without CFRP, and three beams flexurally strengthened using different percentage of laminates. The experimental results show that NSM CFRP laminates is an effective solution to increase cracking, yielding and maximum loads of beams failing in bending. Furthermore, the high tensile strength of the CFRP was effectively mobilized. By increasing the CFRP percentage, the load carrying capacity of the NSM beams increased, while the ductility level decreased. Taking into account the experimental results, the predictive performance of the analytical formulation proposed by the ACI was assessed considering two methodologies to determine the maximum strain that can be applied to the CFRP: i) the ACI proposal; ii) the equation proposed by Barros et al. (2007). ACI formulation provides safe results by using both methodologies, but the Barros et al. equation ensures better predictions. A numerical strategy was used to evaluate the load-deflection relationship of the tested beams and to highlight the influence of the longitudinal bars percentage, the CFRP percentage and the concrete strength on the NSM flexural strengthening effectiveness of RC beams.

In this work, 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 of introducing an effective concrete confinement; CFRP laminates applied according to the near surface mounted (NSM) technique for increasing 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 1080 mm, and three cross-sections were considered, 120×120 mm 2 , 240×120 mm 2 and 480×120 mm 2 , 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 showed 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 on 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 decrease. The load carrying capacity and lateral deformability of the tested RC columns have increased with the flexural strengthening ratio. Moreover, an analytical model is proposed for evaluating the maximum strength and the axial load-lateral displacement response of rectangular RC columns strengthened according to the new proposed technique, and a good predictive performance was obtained.