Shear Strengthening of RC members

为研究外贴FRP布加固钢筋混凝土梁的抗剪性能，进行了9根CFRP布和AFRP布加固钢筋混凝土梁抗剪加固试验。这项研究的重点是有效利用玻璃钢板材来防止板材脱粘。所有钢筋混凝土梁具有相同的截面、受弯钢筋和2800 mm的净跨度。由于所有梁的设计都是在纵向钢筋屈服之前进行剪切破坏，因此没有设置箍筋。其中4根梁用碳纤维布加固，另外4根梁用AFRP布加固。使用的玻璃钢片材是单向的，其中主要纤维保持垂直于梁的纵轴。为避免FRP片材与混凝土脱粘，采用了不同的缠绕方式，将一定长度的FRP片材锚固在梁的顶面上。主要试验变量为FRP片材的锚固长度。对不同研究者提出的计算FRP片材对受剪承载力贡献(Vf)的设计方法进行了讨论，并与试验结果进行了比较。从试验结果中得出以下结论：1)外贴CFRP和AFRP片材对提高RC梁的抗剪强度是有效的。与对照组相比，CFRP最大提高了123%，AFRP最大提高了118%。2)研究表明，采用粘结锚固的FRP比U型缠绕的FRP更有效，提供粘结锚固是防止板材剥离的有效方法。3)在梁的顶面设置粘结锚固，降低了界面粘结应力。4)设置粘结锚固长度，FRP片材破坏时的有效应变比U型缠绕梁提高了100%以上。

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.