An indirect method to calibrate the interfacial cohesive material law for FRCM-concrete joints

The cohesive material law (CML), i.e., relationship between the interfacial shear stress and slip between a fiber reinforced composite and the substrate, is a fundamental tool to model the structural behavior of composite-strengthened elements. A crucial problem that researchers working in the field of strengthening applications with fiber reinforced cementitious matrix (FRCM) composites face is how to obtain the CML. A direct method to determine the CML could be applied if the longitudinal strain is measured along the bonded length. However, since the critical interface for some FRCM composites appears to be the interface between the fibers and matrix, measuring the fiber strain in FRCM composites is a difficult task due to the presence of the matrix that embeds the fiber textile. To overcome this difficulty, an indirect method is proposed in this paper. The parameters of the CML are determined by fitting experimental data in terms of peak load measured for different composite bonded lengths. The procedure is applied to single-lap shear test results previously published by the authors. The CML obtained shows good correlation with the CML obtained from direct calibration of strain profiles measured along the bonded length and is able to predict the experimental load responses.