Failure Mechanism in TRM-Strengthened Damaged Concrete Based on Three-Dimensional Mesoscale Modeling

The behavior of textile-reinforced mortar (TRM) composites in different substrates depends on the strength of the textile, the matrix, and the substrate. Simulating three key failure modes—TRM debonding, textile fracture, and matrix cracking—within a single model presents significant challenges, because the model should consider material nonlinearity and the intricate interactions at the dual interfaces (textile–matrix and TRM–matrix), and the impact of substrate degradation. In this paper, this challenge was addressed through a combined experimental and computational approach, involving single-lap shear tests on externally bonded TRM-strengthened concrete members (before and after fire damage) and the development of a mesoscale three-dimensional finite-element (FE) model to examine the failure mechanisms. Single-layer shear tests designed for concrete before and after fire damage provided important baseline data for calibrating the mesoscale FE model of TRM-strengthened concrete, ensuring accurate matrix–textile interaction and failure mode simulations. A realistic concrete mesostructure was generated using a random-walk algorithm. The mortar matrix and textile were modeled explicitly, with cohesive contact employed to simulate their bond-slip behavior. The mortar (inorganic) matrix was modeled using the concrete damage plasticity model, while the carbon and glass fibers are represented as orthogonal materials. The model’s effectiveness and accuracy were verified by comparing experimental and numerical load–slip curves and failure modes. A parametric study investigated the effects of warp fiber, weft fiber, mortar matrix, and concrete. The results clarify the failure mechanism of TRM-strengthened concrete and inspire practical applications.