Combinations of NSM and EB CFRP strips for flexural strengthening of concrete structures

Abstract

The purpose of this study is to investigate the flexural strengthening effectiveness of beams reinforced with near-surface mounted (NSM) carbon-fibre-reinforced polymer (CFRP) strips and externally bonded reinforcing (EBR) CFRP strips. To accomplish this objective, a total of nine concrete T beams were tested and two groups of experimental study were carried out, one for the beam series reinforced with NSM CFRP strips and the other for the beam series combined reinforced with NSM and EBR strips. From this study, it is found that the flexural stiffness and strength of the beams reinforced with NSM and EBR strips were significantly improved compared with the beams strengthened only with NSM CFRP strip. The maximum increase of flexural strength was 347% compared with the control beam. Failure of the beam reinforced with NSM and EBR strips is initiated by debonding EBR strips attached on the bottom face, and it is succeeded by a partial separation of NSM strips along the longitudinal direction and secondly failure of NSM strips. As the load increases, diagonal cracks are formed and eventually sudden explosive failure occurs with the separation of concrete cover in the shear region. The maximum tensile strains measured in the NSM and EBR CFRP strips of the beam reinforced with T-shape strips were noticed in the range 8200–11 600 με and 7000–8900 με respectively. This result shows that the NSM and EBR strips have good combination to resist applied load and the combined reinforcement of NSM and EBR strips can appropriately redistribute the total stress subjected to the concrete beam to the EBR and NSM strips.