Shear behavior of reinforced concrete beams strengthened with a 45° inclined MSS technique: Parametric study of shear Span-to-depth ratio and beam height

Current methods for strengthening reinforced concrete beams with insufficient shear capacity have structural and practical limitations. This study experimentally investigated the performance of a 45° inclined Mechanical Steel Stitches (MSS) technique under four-point loading. 17 beams (3 reference, 14 strengthened) with shear span-to-depth ratios (a<inf>v</inf>/d = 2.5, 3.3, 4.9) and section heights (250, 360 mm) were tested, while a group with a<inf>v</inf>/d = 3.3 and 250 mm height was adopted from the literature for comparison. Beams were evaluated in terms of maximum load, displacement, energy dissipation, stiffness, ductility, and failure modes. Results showed that MSS was highly effective, particularly at low a<inf>v</inf>/d ratios. The maximum capacity increase reached 86.2% for a<inf>v</inf>/d = 2.5, decreasing to 50.6% at a<inf>v</inf>/d = 3.3 and 14.9% at a<inf>v</inf>/d = 4.9, where diagonal cracks intersecting MSS anchor holes limited the contribution. The optimum MSS spacings were determined as d/2.5 for a<inf>v</inf>/d = 2.5 and d/5 for a<inf>v</inf>/d = 3.3 and 4.9. Increasing beam height from 250 to 360 mm reduced MSS effectiveness by 5.4–27.5%. All reference beams failed in brittle diagonal tension, while strengthened beams exhibited splitting (43%) or combined diagonal tension–splitting (29%). Decreasing MSS spacing shifted failure from diagonal tension to splitting. Overall, the inclined MSS technique proved effective and practical for strengthening shear-deficient beams, offering guidance for design and application. © 2025 Taylor & Francis Group, LLC.