Shear Strengthening of RC members

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To investigate shear behavior of RC beams strengthened with externally bonded FRP sheets, nine RC beams strengthened using CFRP and AFRP sheets for shear upgrading were tested. This study was focused on effective utilization of FRP sheets to prevent debonding of sheets. All RC beams have the same cross section, flexural reinforcements and a clear span of 2800 mm. Since all the beams were designed to fail in shear before yielding of longitudinal reinforcements, stirrups were not provided. Four beams were strengthened using CFRP sheets, while the other four beams were upgraded using AFRP sheets. FRP sheets used were unidirectional, where principal fibers were kept perpendicular to the longitudinal axis of the beam. Different wrapping methods were used to avoid debonding between FRP sheet and concrete such that FRP sheets are anchored with certain length on the top surface of beams. The main experimental variables are the anchorage length of FRP sheets. Design methodologies proposed by different researchers, to calculate FRP sheet contribution to shear capacity (V_f), is also discussed and compared with experimental results.From the results of experiments, the following conclusions are made.1)Effectiveness of externally bonded CFRP and AFRP sheets for enhancement of shear strength of RC beams was confirmed. Maximum 123 % increase for CFRP and 118 % increase for AFRP in shear capacity were observed as compare to that of the control beam.2)It is confirmed that FRP with bonded anchorage is much more effective than U-wrap scheme, and that provision of bonded anchorage of sheet is an effective way to prevent sheet debonding instead of full wrapping of sheet.3)Bonded anchorage of sheet at the top surface of beam resulted in a decrease of interface bond stress.4)Provision of bonded anchorage length showed an increase of more than 100 % in effective strain of FRP sheet at failure, as compare to U-wrap beams.