Application of the Granular Micromechanics Approach to Bimodulus Materials in Structural Members

Many materials, such as masonry and concrete, exhibit bimodulus behavior characterized by different stiffness properties in tension and compression. Classical beam models for such materials often assume sharp transitions and neglect axial force effects. In this study, a granular micromechanics framework is adopted to overcome these limitations. The model is `rst applied to simple beam con`gurations to examine the influence of the stiffness ratio in tension to compression (n) on neutral axis positioning and internal force distribution. Additionally, the thrust line (LT) is computed based on stress `eld reconstruction. The results clearly show that, unlike monomodular materials (where the neutral axis remains centered) bimodular materials demonstrate a noticeable shift in the neutral axis. The granular micromechanics model captures this shift accurately and provides a physically consistent basis for understanding its cause. Moreover, the framework enables precise evaluation of axial and shear force development due to material asymmetry. Using this model, we determine a representative stiffness ratio (n) that governs the asymmetry between tension and compression. As n increases, the LT path converges toward the theoretical trajectory de`ned by Heyman’s no-tension model, providing a solid bridge between microstructural mechanics and classical theory. Finally, the robustness of the identi`ed stiffness ratio is veri`ed by applying it to arches with varying geometries. For each con`guration, the LT obtained through granular micromechanics is compared with Heyman’s solution. The results con`rm that once n exceeds a critical threshold (approximately 20), the LT remains consistently aligned with that of the idealized no-tension formulation, validating the model across a wide range of structural forms.