A Novel Easy Apply Method on Strengthening Rc Shear Deficient Members: 45º Angled Mechanical Steel Stitches

Abstract

Purpose: It is known in the literature that beams with low shear capacity are strengthened by different techniques. This study investigated the strengthening of beams with low shear capacity with a new Mechanical Steel Stitches (MSS) technique. It is seen in a limited number of studies in the literature that the shearing capacity of beams is improved by using MSSs, which stand out as being fast, applicable, and economical. However, the effective MSS application spacing should be determined before using the MSS strengthening method in real practice. To solve this problem, in the beams with insufficient shear capacity produced within the scope of this study, the change of the MSS spacing was investigated by keeping constant that the MSS application angle 45º, the MSS diameter (Ø6) and the MSS anchorage depth (10 Ø). Thus, its effect on beam shearing capacity could be observed depending on the changing MSS spacing and suggestions were made about the optimum MSS application spacing that should be in practice. Study design/methodology/approach: In this study, a total of 5 test beams with geometric dimensions of 125x250x2500 mm were produced, one of which was for reference and 4 of which was strengthened with MSS, and tested in a four-point bending setup. In the test beams, 3Ø16 in the tension zone and 2Ø12 in the compression zone are used as longitudinal reinforcements. Stirrups of Ø6mm diameter with 90º hooks at 350mm spacing were used as transverse reinforcement. In order to represent the existing building stock, beams with a concrete compressive strength of 16.65 MPa were produced. After observing shear damage on the reference beams, based on the effective height (d=215mm), experiments were carried out for the MSS spacings approximately d/5 (45mm), d/2.5 (90mm), d/1.7 (130mm) and d (220mm), respectively. Findings: In the test beams with different MSS spacings, up to 53.74% increase in shear capacity was observed compared to the reference beam. When compared with the results obtained in previous studies in the literature, it has been confirmed that the optimum MSS angle should be 45º. The highest capacity increase (53.74%) was seen in the beam with d/5 (45mm) spacing. In addition, it has been determined that for the strengthening with MSS to be effective, the MSS spacing should be equal to or smaller than d/2 in order to be able to cover the inclined cracks formed on the beam by at least one MSS. Originality/value: In this study, it was observed that MSS application, which is a patented strengthening method, significantly increased the load carrying capacity of beams with insufficient shear capacity (53.74% increase in shear strength). In addition, an innovative method has been presented as an alternative to traditional strengthening methods with its fast, practical, economical and easy application. As a result, it has been seen that reinforced concrete beams with insufficient shear capacity in practice can be strengthened by taking into account the optimum MSS spacing and other parameters (anchorage depth, MSS angle, MSS diameter, etc.) obtained in this experimental study.