Abstract:Intermediate crack induced debonding (IC debonding) is a common failure mode of RC beams strengthened with externally bonded FRP reinforcement. Although extensive research has been carried out on IC debonding, much work is still needed to develop a better understanding of the failure mode and a more reliable strength model. This paper presents an advanced finite element (FE) model based on the smeared crack approach for predicting IC debonding failure. Existing FE models of the same type are generally deficient in capturing localized cracks (both their pattern and widths). This deficiency is overcome in the proposed FE model through the accurate modeling of interfaces between the concrete and both the internal steel and the external FRP reinforcements. The capability and accuracy of the proposed model are demonstrated through comparisons of its predictions with selected test results. The importance of accurate modeling of localized cracking is also explained using numerical results obtained from the FE model.

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.

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