FE-analyses to study the effect of temperature on debonding of externally bonded CFRP

The use of Externally Bonded Reinforcement based on Fiber Reinforced Polymers (EBR FRP) has become increasingly popular in the construction industry lately. Strengthening of existing concrete structures with FRP materials has proven to be a cost-effective and durable strengthening technique. The extensive amount of experimental, numerical and analytical research into this relatively new strengthening technique confirms the wide interest. By now, guidelines have become available for the construction industry [1,2] and numerous applications have been realized worldwide. Despite these developments, some questions have still remained unanswered. Debonding of the FRP, which generally governs the failure of a strengthened structure, has still not been fully understood and new developments, like anchoring and prestressing of FRP, are continuously going on. One of the questions that so far has received only little attention is the effect of the ambient temperature on the debonding behavior of externally bonded FRP [3]. Temperature changes will induce additional thermal stresses, due to the significant difference in the Coefficient of Thermal Expansion (CTE) between concrete (ac ˜ 10 × 10-6 /°C) and e.g. CFRP (af ˜ -1 × 10-6 /°C in the fiber direction). The material properties of the concrete, adhesive and CFRP and the bond between these materials will also change with changing temperature. This particularly applies for the adhesive, as the strength and stiffness will drop significantly when the glass-transition temperature is reached (Tg ˜ 45°C – 80°C for most cold curing epoxies). Both the difference in the coefficient of thermal expansion and the changing material properties may affect the load level at which debonding occurs.