Effect Of anchors on FRP-Concrete Bond Behavior In EBR and EBROG Joints

Document Type : Original Research

Authors
M. Garakyaragh
D. Mostofinejad
Isfahan University of Technology
10.22034/23.5.8
Abstract
Fiber-reinforced polymer (FRP) sheets are lightweight and offer high tensile strength and durability under harsh environmental conditions. For this reason, FRP sheets are used extensively for the strengthening of concrete structures. Concrete structures reinforced with FRP composites commonly experience debonding failure of the reinforcement sheet before the tensile capacity of the FRP sheet has been fully utilized. One method used to prevent the debonding of FRP sheets is the use of FRP anchors. FRP anchors are made by rolling the FRP sheet and impregnating it with epoxy resin as a matrix. One end of the FRP anchor then is placed into a hole drilled in the concrete and the other end is fanned out across the FRP composite. In this research the bond technique, method of fan application, length of fan part, the anchor cross-section to reinforcement sheet cross-section ratio, and converting the failure mode to FRP rupture for straight FRP anchors were investigated. The FRP anchors were examined by the externally-bonded reinforcement (EBR) method and the externally-bonded reinforcement on grooves (EBROG) technique. To strengthen the specimens, FRP with a net thickness of 0.131 mm (SikaWrap-230C), a bond length of 70 mm, and a width of 48 mm was used. In the EBROG technique, two grooves with widths of 10 mm, depths of 10 mm, and spaced 20-mm apart were cut on the concrete surface. The matrix phase of the composite was Quantom-EPR 3301 epoxy resin. FRP composites were prepared by the wet lay-up method. To determine the bond behavior of FRP anchors, 15 single-lap shear tests on T-shaped specimens were conducted. The results showed that, in EBR method an increase in the anchor cross-section had a positive effect on the bond strength, so an increase of about 58% in bond strength of the EBR-60-3 specimens was observed. The failure mode in EBR specimens was debonding. The load-slip curves of the EBR joints showed that in the first part, the load increases sharply and linearly up to the initiation of debonding; In the second part, slippage increased significantly and the slope of the curve decreased. The use of straight FRP anchors significantly increased the bond strength and the final slip values compared to the control specimens. In the EBROG method, anchors with a cross-section ratio of twice eliminated the debonding and the failure mode for this group was the rupture of the FRP sheet. The load-slip curves for the EBROG method ascended and did not exhibit the almost two-line behavior of the EBR specimens. The load-slip curves consisted of an ascending branch with an initial slope that was greater than at the end. The slippage of the EBROG specimens was significantly lower than for the EBR specimens. This small amount of slip versus the high bond strength reveals the high stiffness of the bond. A comparison of the EBR and EBROG methods shows that the EBROG eliminated debonding at lower FRP fan and bond length values. Also, the bond strength of the EBROG specimens with FRP anchors increased by 136% compared to the EBR specimens. In this research, an embedment depth of 50 mm transferred stress to the concrete without pulling out the fibers.

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Modares Civil Engineering journal
Volume 23, Issue 5
November and December 2023
Pages 115-127