Flexural Performance of Reinforced Concrete Beams with Openings Strengthened by Varying Thickness Steel Tubes

This study investigates into the influence of opening size and steel tube thickness on the structural properties of reinforced concrete beams, particularly those with utility ducts and pipes.Four reinforced concrete beams were subjected to comprehensive testing, including a reference beam devoid of openings and three specimens featuring square openings of varying intensities.The evaluation encompassed crucial parameters such as load-deflection response, ultimate failure load, cracking load, cracking pattern, stiffness criteria, and ductility index.Employing the Digital Image Correlation (DIC) method, detailed analyses of cracking behavior were conducted.Unstrengthened beams exhibited a reduction in ultimate load capacity and stiffness, approximately 11.18% and 19.8% lower, respectively, compared to the control beam.Introduction of a steel tube significantly enhanced the performance of opening beams, manifesting in improved cracking load, cracking formation, ultimate capacity, stiffness, and ductility index, thereby promoting more ductile behavior.Strengthened beams with 2 and 3 mm-thick steel tubes demonstrated an approximate 9.27% and 28.47% increase in ultimate load compared to their unstrengthened counterparts.Beams featuring 3 mm-thick steel tubes exhibited behavior akin to the reference beam in terms of load-vertical displacement curves, albeit with a 14.12% disparity in ultimate load capacity.Despite a somewhat identical crack morphology across all tested beams, unstrengthened beams displayed higher crack width and deflection than their strengthened counterparts.