Effect of opening size and location on the punching shear behavior of interior slab-column connections strengthened with CFRP strips

This research study is aimed at evaluating the effects of carbon fiber reinforced polymer (CFRP) strengthening on the punching shear behavior of two-way reinforced concrete (RC) slabs strengthened with CFRP strips having openings varying in size and location. In the scope of the research study, series of experiments are conducted on eight test specimens of CFRP strengthened two-way square RC slabs having openings with variable locations and sizes. In the experimental study, the specimens (with dimensions of 2000 × 2000 × 120 mm) are tested by applying an axial load from the top of a square column (200 mm × 200 mm) located at the center of the test specimen. Each test specimen has one opening with the dimensions of 300 × 300 mm or 500 × 500 mm located adjacent or 300 mm far from the central column in a parallel or diagonal position. The test specimens are strengthened with four CFRP strips (150 mm wide) located under the slab next to the opening of the specimen. Additionally eight U shaped CFRP strips (150 mm wide) located at the corners of the opening are used to further retrofit the test specimens. The effects CFRP strengthening and varying size and location of openings on the punching shear behavior of the test specimens are considered by examining the slabs' bearing capacities and stiffnesses obtained from the results of the experiments in comparison to the results of a former experimental study. Furthermore, the experimental results obtained from the study are used to evaluate the accuracy of the available code equations to predict the punching shear capacity of flat slabs. From the comparison, it is observed that the punching shear capacities of the retrofitted test specimens significantly increased with respect to the punching shear capacities of the bare specimens with opening tested in a former study. Moreover, it is also observed that the several equations proposed by structural codes underestimate the punching shear capacities of the test specimens.