Analytical Model and FE Implementation for FRCM-Retrofitted Flat Masonry Under Direct Shear Tests

This study presents an analytical and numerical framework to describe the debonding behavior of fiber-reinforced cementitious matrix (FRCM)-reinforced flat masonry elements under direct shear tests. A sawtooth shear stress–slip law, initially proposed for Steel Reinforced Grout (SRG) systems by two of the authors, is calibrated for a PBO-FRCM system based on the experimental results available in the literature. These recent experimental outcomes on flat masonry pillars serve to validate the model by capturing essential interface behaviors, including residual strength and pseudo-linear hardening. Furthermore, a finite element (FE) model of the specimens has been developed to simulate the interface response, allowing for a comparison between numerical predictions and experimental results. The sawtooth law is implemented directly in commercial FE software without the need for custom coding. Additionally, a mesh sensitivity analysis was performed to verify numerical stability and identify the optimal discretization parameters for consistent model response. Results show good agreement among experimental observations, the sawtooth analytical model, and FE simulations. The analytical model slightly underestimates the experimental peak load by about 4–6%, while the FE predictions differ from the experimental results by less than 10%, confirming the reliability of the proposed modeling framework.