FRP can significantly improve the shear strength of beams, but the height of FRP is different, and the bearing capacity of reinforced concrete is also different. Therefore, this adverse effect should be considered in the design.

In this paper, the test results of 12 test beams (4 contrast beams and 8 reinforced beams) are analyzed. The shear behavior and failure mode of the diagonal section of beams strengthened with U shaped CFRP and GFRP beams are studied. The reinforcement effect of CFRP and GFRP is compared. The reasons for the difference are preliminarily analyzed. According to the “cost performance” of materials, suggestions are put forward from an economic point of view.

1. Fiber reinforced polymer(FRP) composite can significantly improve the shear strength of beams, but the height of FRP is different, and the bearing capacity of reinforced concrete is also different. Therefore, this adverse effect should be considered in the design.

2.When the negative bending moment section of the beam is reinforced by FRP, the negative bending section of the beam is not only pulled up in the upper part of the beam and the tension of the longitudinal reinforcement is larger, so the longitudinal reinforcement will produce large cyclic tensile stress on the concrete around it. Stress concentration will also occur at the top of the fiber bar at the bottom of the flange plate, that is, the longitudinal reinforcement. The combination of the two causes the slanting cracks to cross the fiber bar and develop at the top of the longitudinal tendons toward the loading point, but not as the contrast beam, the critical slanting cracks all the way through the wing plates to the top of the beam. Because of this, the horizontal projection length of the critical inclined crack is less than that of the unreinforced beam, which will also affect the number of stirrup and the contribution of the stirrup to the cross section bearing capacity of the beam. Therefore, the effect of the FRP sheet on the inclined section bearing capacity of the beam is comprehensive, not the simple superposition of the bearing capacity of the oblique section of the beam before the reinforcement of the FRP sheet.

3.The failure of reinforced beams is caused by the peeling of fiber sheets, so the brittleness is more obvious and the damage is more abrupt. Therefore, considerable safety reserve should be left in the reinforcement design.

4.From the economic point of view, the use of GFRP instead of CFRP or 2 kinds of fibers can achieve the same reinforcement effect and more economical for the reinforcement members with the characteristics of FRP stripping failure.