Behaviour of FRP-to-concrete interfaces between two adjacent cracks: A numerical investigation on the effect of bondline damage

Abstract

The bond behaviour between FRP and concrete has been commonly studied using simple pull-off tests on bonded joints where an FRP plate bonded to a concrete prism is pulled at one end to induce debonding failure. Knowledge gained from such studies has been directly employed in predicting debonding failure in FRP-plated concrete beams induced by major flexural cracks, but significant differences exist between the two scenarios. The chief difference lies in the interaction between adjacent flexural cracks in a flexural member which is absent in a joint pull-off test. This interaction may be approximated using an FRP-to-concrete bonded joint where the FRP plate is pulled at both ends. This paper presents a numerical study into this bonded joint problem, with the main objective being to clarify the effect of bondline damage during slip reversals on the ultimate load. The study shows that such damage has a significant effect on the predicted bond behaviour and ultimate load when the ratio between the end loads is larger than 0.7, particularly when the bond length is reasonably large. An important implication of the present study is that in the modelling (e.g. finite element modelling) of debonding behaviour of FRP-plated RC beams where multiple cracks exist, the FRP-to-concrete interface should be represented using a bond-slip model with appropriate consideration of the damaged behaviour during slip reversals in order to achieve accurate predictions.