If it is decided to provide an opening in the beam at post-construction stage, the opening zone needs to be strengthened for avoiding premature beam failure. Fiber reinforced polymer (FRP) has been found to be effective for external strengthening in such cases due to a number of advantages, such as excellent strength to self-weight ratio, high tensile strength, large fatigue resistance capacity, and high durability.
This study presents a numerical analysis that studies the effect of providing openings in RC cantilever beams and possible external carbon fiber reinforced polymer configurations to restore their stiffness. This research includes thirty-eight RC double cantilever beams under symmetrical case of loading, which were studied by using ANSYS finite element software version 14.0. Different parameters were investigated including opening dimensions (length and height), location of the opening, configuration of the used CFRP sheets around the opening, and number of CFRP layers (1, 2, 3 and 4). The study program was conducted in five groups. In group (R), one solid beam without opening was taken as a reference beam. In group (A), nine unstrengthened beams have web openings with various lengths and heights (from 200 mm to 400 mm) where analyzed. In group (B), six unstrengthened beams have openings, 300x300 mm and 400x400 mm dimensions, located at various distances from the support (300, 400, 500 and 600 mm) where studied. In group (C), sixteen RC beams have openings where externally strengthened with various CFRP sheets configurations and analyzed. While, in group (D), six RC beams with the largest opening dimensions, 400x400 mm, were externally strengthened with various number of CFRP sheets layers.
All beams in this study were analyzed under concentric load at free-end of the cantilever. For all analyzed beams, the obtained deflections, stresses and strains in concrete and longitudinal reinforcement, and strains in CFRP layers as well as cracking, yielding and failure loads were studied and discussed. Numerical results showed the effect of the presence of web openings and their strengthening using CFRP sheets on the behavior of the analyzed RC cantilever beams. Also, the numerical results declared the effect of the studied parameters on the behavior of such reinforced concrete cantilever beams provided with web openings. The shear capacities of the beams analyzed in this study were calculated according to some of analytical models and compared with corresponding numerical results. Finally, the most important results were concluded, and some valuable recommendations were given.