Using model updating techniques to assess bond-slip effects on the behaviour of Reinforced concrete beams externally strengthened with CFRP

Carbon Fibre Reinforced Polymer (CFRP) composites are now widely used in strengthening and repair of concrete structures damaged by natural or human caused disasters. The highly complex nature of the Reinforced Concrete (RC) structural elements strengthened with CFRP (four different materials: concrete, steel reinforcement bars, CFRP and adhesive grout), means there is no reliable analytical model that closely represents the true behaviour of these structural elements. The authors' previous studies demonstrated that using model updating techniques it was possible to successfully address some of the modelling issues with RC beams strengthened with CFRP. There appeared to be some discrepancies with larger diameter bars in the beams. The main reason for this discrepancy was bond-slip between the reinforcing steel bars and the concrete. This paper addresses this issue by modelling the bond between the reinforcement bars and the surrounding concrete as joint elements that connect the steel reinforcements and concrete through "springs". Model updating was used to vary the constants of the spring at various locations along the length of the beam. Good agreement with experimental results was obtained using model updating method by generating spring constants for one system and applying that solution to similar systems with different parameters.