Precise finite element verification of the unreliability of using multi-layers of FRP on CFRP-debonding in RC beams

Abstract

The nonlinear behaviour of an adhesive material that connects layer of carbon fibre reinforced polymer (CFRP) to a reinforced concrete (RC) beam is numerically simulated in this study. To the author’s knowledge, how debonding increases significantly with increasing FRP thickness has not yet been studied theoretically only with few experimental studies that directly say this information. The work is conducted via a finite element approach using the commercially available software ABAQUS 6.13. Firstly, the 3D finite element model is introduced and all the suitable elements, material properties, damage initiation and evolution, and failure criteria are presented. Initially, the numerical model is validated by using the experimental study of a CFRP strengthened beam, which is chosen from literature. The model is shown to accurately capture slip at the interface of the strengthening material and resultant debonding. Furthermore, the tensile strain profile along the CFRP sheet is studied and, which has shown a reverse trend to the interfacial slip profile. Using the validated model, a detailed study is conducted with regards to the effects of multiple CFRP layers on the ultimate capacity and failure mode of the strengthened RC beam. It is found that adding two layers similar to the thickness of one layer will not change the response of the beam. However, this makes the beam behave with less ductility. Furthermore, the difference between the two cases is that the damage of one layer is concentrated at the FRP free end for a short distance. While, for two layers it is also at the free end but extended to a longer distance to the centre of the beam what causes earlier debonding. It is also found that adding one layer of CFRP to strengthen a RC beam can improve the ultimate capacity by 22%. But adding more CFRP layers does not increase the ultimate capacity or change the failure mode. In addition, it will reduce the total deflection of the beam. The study has also found that the interface bond-stresses are non-uniformly distributed along the reinforced boundaries and the shear stresses values exhibit peak values of 1 to 2 times greater than or 1 to 0.5 times less than the mean values predicted by the classical beam theory. Moreover, during the simulation, no de-lamination was observed between the superimposed CFRP plates for the two layers of CFRP.