Debonding Load and Effective Length in Concrete Elements Strengthened with FRP EBR Systems

This paper deals with the assessment of a design formulation to predict the end debonding load in Reinforced Concrete (RC) elements strengthened with Externally Bonded Reinforcement (EBR) made of FRP materials. The approach based on the fracture energy at the FRP-to-concrete interface has been considered and the 'design by testing’ procedure suggested in Eurocode 0 has been used for the statistical analyses in order to assess both mean and percentiles provisions for the debonding load. The statistical analyses have been developed by using a wide database of experimental debonding loads of bond tests on preformed and cured in-situ EBR FRP systems. The calibration factors have been distinguished for the two systems in order to better exploit the performance of each system one. A formulation for the effective length is proposed too. Comparisons with experimental distributions of strains along the FRP EBR systems have been used in order to assess the reliability of the proposed expression. The assessment of both formulations of debonding load and effective length has been developed within the review activities of the Italian Guidelines CNR DT 200/2004.