Mechanics-based identification of in-plane flexural and shear failure in URM walls from crack patterns: A diagnostic framework

Unreinforced masonry (URM) buildings constitute a substantial share of the global building stock and remain highly vulnerable to seismic loading owing to their brittle response and negligible tensile capacity. Flexural and shear failures are the most prevalent in-plane mechanisms governing deformation capacity and collapse potential, making reliable identification of the governing failure mode from crack patterns essential for damage assessment and retrofit decisions. However, interpretation of cracking morphology remains inconsistent in practice, since it requires linkage to the governing stress state and contextual parameters rather than appearance alone. This review synthesizes the mechanics of flexural and shear crack formation in URM walls under in-plane loading, as influenced by axial load ratio, aspect ratio, boundary conditions, and masonry anisotropy, and examines transitional and mixed-mode responses that often cause post-earthquake misclassification. A mechanics-based diagnostic framework is then proposed for crack-based identification of failure mechanisms, operationalized as a sequential decision tree linking crack morphology, spatial distribution, deformation kinematics, and governing parameters. A quantitative crack dominance ratio (CDR) is proposed as a practical indicator for mixed-mode classification using experimentally validated thresholds. The framework is illustrated against three experimental cases, producing classifications consistent with reported failure modes, and key research gaps are identified.