Study of Rupture Mechanism in Concrete Girder Strengthened by External Fiber Reinforced Polymer Using Crack Analysis

In the concrete beam strengthened by using fiber-reinforced polymer (FRP) sheet, the failure of the beam in the design standard is considered as the delamination of the FRP sheet at the end of the concrete beam or break of the FRP sheet when its maximum strain reaches. However, as cracks always happen in bending concrete beam, the failure is predicted to occur between two adjacent cracks. This failure also occurs in concrete near the adhesive zone instead of delamination of the FRP sheet. By analyzing the crack formation of a concrete beam under flexure, the average strain of the FRP sheet at failure is assumed as the ratio of crack width and distance between two adjacent cracks. This assumption is consistent with the comparison of experimental data from the literature. The proposed maximum strain value values from assumption have a lower value than the strain of FRP sheet specified in design specification ACI 440-2R which is determined from pulling tests. Tests of FRP strengthened concrete beam under flexure rupture were conducted in the laboratory. The failure morphologies confirm that cracks of concrete beam affect significantly rupture type.