Frp Composites for Shear Strengthening of Rc Beams

ABSTRACT Fiber Reinforced Polymer (FRP) composite systems can be used for shear strengthening of reinforced concrete (RC) members. The present study investigated the shear performance and the modes of failure of simply supported RC T-beams externally strengthened in shear with FRP composites. Two different FRP-based strengthening systems were investigated, namely, externally bonded FRP sheets and Near Surface Mounted (NSM) FRP rods. The latter is a novel technique on which no literature is available to date. The experimental program consisted of testing eleven full-scale, T beams. The beams were grouped into three series. The first series was tested to investigate the influence on the shear capacity of the concrete surface roughness and of the carbon FRP sheets axial rigidity. The second series focused on the capability of externally bonded CFRP reinforcement to enhance the ultimate capacity of beams that already have adequate internal steel reinforcement. In addition, a beam with internal glass FRP stirrups was tested in this series. In the third series, the novel shear strengthening system of NSM CFRP rods was evaluated. The test results confirm that externally bonded CFRP sheets and NSM CFRP rods can be used to increase significantly the shear capacity, with efficiency that varies depending on the tested variables. The test results were used to validate a previously proposed shear design approach. Khalifa, A., L. De Lorenzis, and A. Nanni, "FRP Composites for Shear Strengtheneing of RC Beams,” Proc., 3rd Inter. Conf. on Advanced Composite Materials in Bridges and Structures, Ottawa,Canada, J. Humar and A.G. Razaqpur, Editors, 15-18 Aug. 2000, pp. 137-144. 2 INTRODUCTION Externally bonded carbon fiber reinforced polymer (CFRP) sheets continue to show great promise for use in shear strengthening of existing reinforced concrete (RC) beams (Taerwe et al. 1997). Some of the parameters that may affect the shear capacity of the strengthened beams such as concrete surface roughness prior to CFRP application, and CFRP sheets axial rigidity are investigated in this study. Furthermore, an alternative strengthening system is described and evaluated. This system will be referred to as near-surface mounted (NSM) FRP rods. NEAR-SURFACE MOUNTED FRP RODS NSM FRP rods are emerging as an alternative to externally bonded FRP laminates for external strengthening of RC structures. Embedment of the rods is achieved by grooving the surface of the member along the desired direction. The groove is filled half way with epoxy paste, the FRP rod is then placed in the groove and lightly pressed, so forcing the paste to flow around the rod and fill completely between the rod and the sides of the groove. The groove is then filled with more paste and the surface is leveled. Details of the final product are illustrated in the sketch of Fig. 1.