Influence of Unit Irregularity on the Shear Behavior of Rubble Stone Masonry Walls

The increasing availability of high-resolution geometric data has enabled microscale simulations of rubble stone masonry with varying levels of geometric fidelity; however, the influence of geometric simplification on predicted mechanical behavior remains unclear. This study investigates the effect of unit shape irregularity on the shear response of rubble stone masonry walls using a microscale rigid block modeling framework. Stones are represented as rigid polyhedral units, and mortar joints are discretized into tetrahedral elements, with interactions governed by elasto-plastic contact laws with softening. An automated workflow is developed to generate models from point clouds and to apply multiple geometry simplification techniques while preserving global geometric characteristics. The approach is validated against shear-compression tests, showing good agreement and robust performance in predicting force-displacement response and failure patterns. Results indicate that mechanical response is strongly influenced by geometric characteristics. A convexity index shows a negative correlation with force capacity, while a sphericity index correlates with displacement capacity, reflecting a transition toward shear-dominated failure with increasing rounding of units. These findings highlight the importance of accurate shape characterization in microscale modeling, with implications for empirical assessment methods and the design of rubble stone masonry structures.