185 / 2022-04-30 21:18:27

Factors Affecting the Ductility of CFRP-to-concrete Bonded Joints with End Anchors: A Theoretical Study

CFRP-concrete,end anchorage,ductile failure,analytical solution

Strengthening of reinforced concrete (RC) structures by using externally bonded (EB) carbon fiber reinforced polymers (CFRP) laminates has gained increasing popularity within last few decades due to the high strength-to-weight ratio and excellent durability performance of CFRP. However, as the concrete substrate is often the weak layer in the bonding interface, an abrupt premature debonding happening within the concrete substrate is the predominant failure mode. As such, the load-carrying capacity of the CFRP-to-concrete bonded joints is much less than the strength of the CFRP laminate, which results in a very low material efficiency. To tackle this problem, researchers have proposed different mechanical anchors, such as FRP spike anchors, self-anchorage buckles and hybrid anchors etc. to constrain the slip of the bonding interface, thus improving the ultimate load-carrying capacity. However, existing experimental research have shown that bonded joints with end anchorages could still exhibit brittle failure mode. Through an analytical study, the anchorage stiffness and strength were identified as two factors affecting the ductility of the bonded joints. However, as the interfacial bond behavior, such as the ultimate deformation of the bonded joints is governed by the local bond-slip relation, the interaction between the anchorage and the bonded interface, as well as the maximum deformation of the bonded joints with end anchorage will be also affected. Unfortunately, the effect of the bond-slip model on the ductility hasn’t been thoroughly investigated.



Against this background, this study conducted a theoretical study to reveal the factors affecting the bond behavior of CFRP-to-concrete bonded joints with end anchorage. The anchor was simplified as a spring with non-linear force-displacement behavior. As such, the classical interfacial fracture mechanics can be employed to derive closed-form solutions for the interfacial bond behavior. Then a finite element analysis was conducted to validate the accuracy of the presented analytical solution. Results show that the obtained analytical solutions are valid in predicting the bond behavior of CFRP-to-concrete bonded joints with end anchorages, given the force-displacement behavior of the anchorage is known (Figs. 1-3). It is also found that though the stiffness and force of plastic plateau in force-displacement relation of the anchor are important in determining the ductility (Figs. 4-5), the relation between the ultimate interfacial slip and anchorage deformation also shows significant influence. When the ultimate interfacial slip is less than the maximum anchorage deformation, the anchor will fail before the full debonding of the bonded joints. As such, the anchorage performance is not sufficient, and a brittle failure will occur (Fig. 6). Therefore, while designing the anchor, factors, such as the anchor stiffness, force of plastic plateau in the anchor’s force-displacement relation, the local bond-slip relation of CFRP-to-concrete bonded joints and CFRP strengthen should be considered to get a ductile failure mode of the bonded joints.