Effect of Stirrup Spacing on Strengthening Beams With Insufficient Shear Capacity Using Innovative Mechanical Steel Stitches

Abstract

This study investigates experimentally and analytically the effect of stirrup spacing variation on the behavior of reinforced beams in the 45 degrees-inclined innovative mechanical steel stitches (MSSs) application for the strengthening of reinforced concrete beams with insufficient shear capacity. Within the scope of the experimental study, four-point loading tests were carried out under vertical loads by selecting stirrup spacing (250, 350, and 450 mm) and MSS spacing (d/3, d/2.5, d/2, d/1.7, and d/1.4) as variable parameters (d is effective depth of beam). In this context, a total of 12 beam specimens with dimensions of 125 x 250 x 2500 mm each with 250 and 450 mm stirrup spacing were produced, one reference specimen with each stirrup spacing and specimens reinforced with five different MSS spacings were tested; in addition, the test results of a reference beam with 350 mm stirrup spacing and beams reinforced with six different MSS spacings in the literature were used for comparison. Within the scope of the analytical study, the MSS spacing required for the beams to reach the flexural capacity was investigated by selecting the ratio of tensile reinforcement and the presence/absence of compressive reinforcement as variable parameters. In the study, the changes in failure mode, strength, ductility, stiffness, and energy consumption capacities of beams due to different stirrup and MSS spacings were analyzed. According to the experimental results obtained at the end of the study, it was observed that the reference beam with 250 mm stirrup spacing carried 32% and 35% more load than the reference beams with 350 and 450 mm spacing, respectively. Tightening the MSS up to 75 mm increased the shear capacity of beams with 450, 350, and 250 mm stirrup spacing up to 46.1%, 37.4%, and 23.5%, respectively. As the stirrup spacing of the reinforced beams decreased, the contribution of the MSS application to the shear capacity decreased. In addition, the failure mode of the beams changed from diagonal tension mode to splitting mode by increasing the MSS spacing. According to the analytical results, it was observed that MSS contributed more to the flexural capacity in beams with low longitudinal reinforcement ratio, and the performance of MSS was significantly improved in the absence of compression reinforcement.