Strengthening shear deficiency in undamaged reinforced concrete beams using innovative 45° mechanical steel stitches

In this study, beams with insufficient shear capacity were reinforced with U-shaped Mechanical Steel Stitches (MSS), which is an innovative approach. MSSs were applied at an angle of 45 degrees along the shear span on both faces of the beam body. A total of eight shear beam specimens, one of which is a reference and the other seven with different MSS spacing, were examined under vertical loads. The diameter, anchorage depth and mechanical properties of the MSSs and the geometry, longitudinal and transverse reinforcements of the reinforced concrete beam were kept constant. By changing the MSS intervals (from d/5 to d), the change was investigated in terms of strength, ductility, stiffness and energy consumption capacities. As a result of the study, 54% increase in shear capacity was observed in the beam with the most tightened MSS spacing (d/5). However, the nominal yield and total energy consumption capacity increased by 144% and 366%, respectively, compared to the reference beam. While splitting damage was most frequently observed in the MSS application with d/5, the damage turned into diagonal tension collapse, which is more abrupt and brittle as the spacing increases to d/2 range. As the MSS interval in beams increased from d/5 to d/2, the nominal yield stiffness of the beams showed a decreasing trend between 2.1% and 21.2% compared to the reference beam. Based on the experimental results, the developed novel strengthening methods can applicable to beams if the interval of MSS spacing is tightened enough.