Investigation of shear span to depth ratioo and beam height variation in strengthening of reinforced concrete beams witth insufficient shear capacity using mechanical steel stitches

In this study, the performance of mechanical steel stitches (MSS), an innovative method for strengthening reinforced concrete beams with inadequate shear capacity, was investigated in two parts experimentally and comparatively. The variations in the shear span-to-effective depth ratio (av/d= 2.5, 3.3, and 4.9) and beam height (h = 250 and 360 mm) were examined. In experimental studies, beams with inadequate shear capacity were strengthened with concrete having an approximate compressive strength of 17 MPa, along with longitudinal (3Ø16 tension and 2Ø12 compression) and transverse (Ø6/1.5d) reinforcements. Apart from reference beams, beams were strengthened with 6 mm diameter MSS at various spacings (~d/1.4, d/2, d/2.5, d/3, d/5) and anchorage depths of 10Ø. In the first part of the study, experimental beams measuring 125x250x2500 mm were prepared to investigate the av/d ratio. For the av/d=2.5 test group, there was 1 reference beam and 5 beams strengthened with varying intervals. Similarly, for av/d=4.9 test group, there was 1 reference beam and 4 reinforced beams tested. The results were compared with strengthened concrete beams strengthened with MSS (mechanical steel stitches) having an av/d=3.3 obtained from the literature. The study concluded that applying MSS to beams with av/d=2.5 increased shear capacity by 40% to 86% compared to reference beams. In contrast, beams with av/d= 3.3 showed an increase in shear capacity ranging from 29% to 54%. For beams with the highest av/d ratio (av/d=4.9), the impact of MSS application on shear capacity was more limited, ranging from -1.8% to 15%. MSS demonstrated better performance at lower av/d ratios. However, as the av/d ratio increased from 2.5 to 4.9, the demand for shear force in the beams decreased, leading them to behave more like flexural beams, resulting in increased flexural cracks that reduced the effectiveness of MSS. In the second part of the study, five experimental beams measuring 125x360x2500 mm were prepared to investigate the effect of beam height variation, all having an av/d ratio of 3.3. These beams were compared with beams of dimensions 125x250x2500 mm also with an av/d ratio of 3.3. At the end of the study revealed that in beams with a height of 360 mm, compared to beams with a height of 250 mm, there was a lesser increase in shear capacity ranging from 5% to 27% across different MSS intervals. However, this difference arose primarily due to both experimental groups having the same MSS ratio. The higher contribution of concrete to shear capacity in taller beams inherently increases the total shear capacity. Therefore, while the effect of MSS on shear capacity per se remains nearly the same, its relative contribution to the total shear force decreases, leading to a perception that MSS contributes less to shear capacity.