FRP-to-concrete bond-slip behaviour under dynamic loading

Strengthening reinforced concrete (RC) structures by externally bonded FRP composites has been widely used for static loading and seismic retrofitting since 1990s. More recently many studies on strengthening concrete and masonry structures with externally bonded FRP for improved blast and impact resistance in protective engineering have also been conducted. The bond behaviour between the FRP and concrete plays a critical role in a strengthening system with externally bonded FRP. However, the understanding of how the bond between FRP and concrete performs under high strain rate is severely limited. Due to the dynamic characteristics of blast and impact loading, the bond behaviour between FRP and concrete under such loading is very different from that under static loading. This paper presents a study on the dynamic bond-slip behaviour based on both the numerical analysis and test results. A dynamic bond-slip model is proposed in this paper.

Bond behavior of NSM FRP strips between two adjacent cracks in concrete beams: A numerical study

Strengthening RC structures with near-surface mounted (NSM) fibre reinforced polymer (FRP) composites has a number of advantages compared with that with externally bonded (EB) FRP sheets/plates. As with EB FRP, the performance of the bond between NSM FRP and concrete is one of the key factors affecting the behaviour of the strengthened structure. This paper presents a numerical investigation into the behaviour of NSM FRP loaded at its both ends to simulate the NSM FRP-toconcrete bond between two adjacent cracks in RC members. The main objective of this study is to quantitatively clarify the effect of the bondline damage during slip reversal on the ultimate load (bond strength). The results show that the bondline damage has a significant effect on the load-carrying capacity of the NSM FRP-to-concrete bonded interface and should be considered in FE modeling of the interface.

Mitigation of concrete cover separation in frpstrengthened RC beams using FRP U-jackets

Concrete cover separation is a common failure mode of reinforced concrete (RC) beams strengthened with a fibre-reinforced polymer (FRP) plate bonded to the tension face (FRP-plated RC beams). Plate-end FRP U-jackets have previously been explored as a mitigation measure to delay or suppress concrete cover separation, although its effectiveness needs further clarification. The paper presents the first systemic experimental study on the use of FRP U-jackets of different forms for mitigating the concrete cover separation failure. A total of ten full-scale FRP-plated RC beams were tested. The test results show that both the ultimate load and the ductility of the beams were enhanced by the U-jackets. Among the forms of U-jackets explored, those inclined at 45o are the most effective.

Effects of unconfined concrete strength on FRP confinement of concrete

Research has shown that fibre reinforced polymer (FRP) wraps are effective for strengthening concrete columns for increased axial and flexural load and deformation capacity, and this technique is now used around the world. The experimental study presented in this paper is focused on the mechanics of FRP confined concrete, with a particular emphasis on the influence of the unconfined concrete compressive strength on confinement effectiveness and hoop strain efficiency. An experimental programme was undertaken to study the compressive strength and stress-strain behaviour of unconfined and FRP confined concrete cylinders of different concrete strength but otherwise similar mix designs, aggregates, and constituents. This was accomplished by varying only the water-to-cement ratio during concrete mixing operations. Through the use of high-resolution digital image correlation to measure both axial and hoop strains, the observations yield insights into the mechanics of FRP confinement of concretes of similar composition but with varying unconfined concrete compressive strength.