Innovative Material Using Mechanical Steel Stitches in Shear-Deficient Reinforced Concrete Beams With Different Concrete Strengths

Shear damage in beams limits ductility and leads to a sudden loss of load-bearing capacity. Thus, shear strengthening is essential for maintaining structural performance. Although many conventional methods exist, they are practically restrictive due to implementation difficulties, architectural constraints, and high costs. Therefore, there is a need for strengthening techniques that are both economical and easy to implement. In this study, the results of a series of experimental studies on strengthening using mechanical steel stitches (MSS), which is an innovative method, are presented. A total of 24 beams with four different concrete compressive strengths, named R5, R10, R15, and R20, were tested, 4 of which were reference beams and 20 were reinforced with MSS. MSS spacings were chosen as a function of effective depth as d/3, d/2.5, d/2, d/1.7, and d/1.4. As a result of the four-point bending test of the reference and strengthened beams, the load-displacement relationship, stiffness, ductility, and energy dissipation capacity were calculated, and their experimental behavior and failure modes were evaluated. As a result of the study, depending on the MSS spacing, as the compressive strength of the concrete increases, the effectiveness of the MSS on the shear capacity increases by up to 15%. When the yield stiffnesses were examined, a transition between 2% and 26% occurred, depending on the concrete compression strength. Thus, shear strengthening is essential for maintaining load-carrying capacity and structural performance. In the analytical calculation, it was observed that all beams strengthened with MSS contributed between 6% and 69% in the load-carrying capacity compared to the reference beams. When the damage analysis at the end of the experiment was examined, by increasing the MSS spacing, the failure mode of the beams changed from a diagonal tension failure to a splitting failure.