مقاوم سازی برشی تیرهای بتن مسلح به روش نصب در نزدیک سطح با استفاده از میله‌های ساخته شده از صفحات الیاف کربن

This experimental study is intended to evaluate the effectiveness of a Near Surface Mounted (NSM) technique using bars made of carbon fabrics (BMCF) for shear strengthening of RC beams. To delay the onset of BMCF debonding, a new anchorage is also developed and tested. When the amount of NSM FRP in shear strengthening of RC beams is low, the shear failure is likely to be due to debonding of individual FRP rod and in this case improved bond properties as well as proper anchoring of the FRP rods are likely to delay the failure of the beam. In this project an innovative bars made of carbon fabrics is produced by wrapping an FRP sheet around a wooden rod. BMCF provide a larger perimeter to cross sectional area ratio with respect to conventional FRP rods for the same amount of FRP used, providing potentially higher bond strength. In addition, the circular shape of BMCF is not only convenient for production but also suitable for NSM shear strengthening as noted by previous researchers. Another key advantage of introducing the BMCF is that it allows the incorporation of a novel anchor system that can be used to improve the performance of NSM BMCF reinforcement for shear strengthening of RC beams in applications with low FRP percentage. A distinguished benefit of the proposed anchor system is that it only requires the access to the beam sides for installation. This means that the proposed anchorage system can be conveniently applied to RC beams whose top and/or bottom face is inaccessible. A set of six shear deficient beam specimens were designed. All specimens had the same internal reinforcement arrangements. They were 200 mm wide, 250 mm high and 1650 mm long. One half of each beam was designed to be weak in shear as the test shear span while the other half was designed as the strong shear span. Only the test shear span was strengthened in shear with NSM BMCF with or without proposed end anchorages. The amount of steel shear reinforcement in the two sides was designed to ensure that shear failure would occur in the test span. All beams were simply supported at the ends and tested under a concentrated monotonic load applied at the mid-span. Test results presented in this paper have confirmed that the use of BMCF is an effective technique for improving the shear capacity of RC beams. The increase in the shear capacity was between 25 to 30% for beams strengthened with simple BMCF, and ranged between 41% and 48% for beams strengthened with anchored BMCF, compared with the reference beam. Beams strengthened with BMCF with end anchors exhibited excessive flexural cracking at their mid spans. The use of the end anchors also significantly enhanced the maximum strain in the BMCF. The load–deflection response of beams is presented, in addition to selected strain measurements. Performance and the failure modes of the test beams are studied and discussed.