Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 53 1 2021 03 21 Numerical and experimental study of failure mode of CFRP strengthened concrete under tension and shear loading Numerical and experimental study of failure mode of CFRP strengthened concrete under tension and shear loading 35 56 4257 10.22060/ceej.2021.19027.7033 FA Roza Rahbari Department of Civil Engineering, Engineering Faculty, International Imam Khomeini University, Qazvin, Iran Mahmood Naderi Department of civil engineering, Faculty of engineering, International Imam Khomeini university, Qazvin, Iran Journal Article 2020 09 17 Today, the use of carbon fiber reinforced polymers (CFRP) is used as an efficient method for the reinforcement of concrete structures. Concrete structures strengthened with CFRP sheets may have a failure due to debonding mechanisms. In this study, the bond strength and failure mode of CFRP strengthened concrete in tensile and shear stresses are investigated using nonlinear finite element and experimental methods. Because in the study of mechanical behavior of concrete strengthened with CFRP sheet, the assumption of homogeneity of concrete leads to unrealistic results, so in this study, a mesoscale model is used to model concrete. The mesoscopic model of concrete includes three-phase inhomogeneous material consisting of aggregate, mortar, and Interfacial Transition Zone (ITZ). Tests performed include "pull-off" and "twist-off" to determine tension and shear bond strength. The results show that the tension and shear strength of the finite element model is 18% and 13% higher than the results of the "pull-off" and "twist-off" tests, respectively, which are due to laboratory influencing factors and ignoring They are acceptable in numerical modeling of this difference. Also, the tensile strength of the numerical and experimental models is 34% and 33% lower than the shear strength, respectively. According to the obtained results, the debonding in the CFRP strengthened concrete sample was from the substrate concrete. The results show that the micro-cracks, followed by debonding in the mortar and ITZ phases of concrete, due to high porosity and lower strength than the aggregate phase, spread easily. Today, the use of carbon fiber reinforced polymers (CFRP) is used as an efficient method for the reinforcement of concrete structures. Concrete structures strengthened with CFRP sheets may have a failure due to debonding mechanisms. In this study, the bond strength and failure mode of CFRP strengthened concrete in tensile and shear stresses are investigated using nonlinear finite element and experimental methods. Because in the study of mechanical behavior of concrete strengthened with CFRP sheet, the assumption of homogeneity of concrete leads to unrealistic results, so in this study, a mesoscale model is used to model concrete. The mesoscopic model of concrete includes three-phase inhomogeneous material consisting of aggregate, mortar, and Interfacial Transition Zone (ITZ). Tests performed include "pull-off" and "twist-off" to determine tension and shear bond strength. The results show that the tension and shear strength of the finite element model is 18% and 13% higher than the results of the "pull-off" and "twist-off" tests, respectively, which are due to laboratory influencing factors and ignoring They are acceptable in numerical modeling of this difference. Also, the tensile strength of the numerical and experimental models is 34% and 33% lower than the shear strength, respectively. According to the obtained results, the debonding in the CFRP strengthened concrete sample was from the substrate concrete. The results show that the micro-cracks, followed by debonding in the mortar and ITZ phases of concrete, due to high porosity and lower strength than the aggregate phase, spread easily. https://ceej.aut.ac.ir/article_4257_c5e1ab9c931df8f5e4c5a8aa53837d52.pdf