Development of Analytical Model for Bonding of CFRP Rod in Concrete Subjected to Cyclic Loads

Recent material science advances have resulted in the use of High-Performance Concrete (HPC) and Ultra-High-Performance Concrete (UHPC) in superstructures, which were chosen for their superior strength. However, under cyclic loads, these materials frequently show fatigue. Carbon-Fibre-Reinforced Polymer (CFRP) rods are replacing steel rebars due to their corrosion resistance and excellent strength-to-weight ratio and are thus gaining popularity in both infrastructural and superstructural design. However, due to a lack of understanding of their bond mechanics, modelling the interaction between CFRP rods and these advanced concretes in finite element simulations remains complex, particularly under cyclic loading. The bond behaviour of CFRP rods and both standard Grade 40 concrete and Ultra High-Performance Fibre-Reinforced Concrete (UHPFRC) under cyclic stresses is investigated in this work. A finite element model of connected concrete cube samples was built and analysed under cyclic stress, combining these concretes with CFRP rods. Furthermore, these samples were subjected to dynamic actuation testing to develop a traction-based constitutive model for the CFRP–concrete interface. In finite element models, an interface element devised for this study effectively approximated the binding, matching experimental data. The new analytical interface element improved simulation precision by 19% in displacement and 49% in pull-out force, resulting in a significant improvement in predicting the performance of the CFRP–UHPFRC bond under cyclic loading. The improved performance of the CFRP–UHPFRC bond under cyclic loading is attributed to the optimised interface model that enhances the bond integrity between CFRP rods and concrete.