Nonlinear micromechanical modeling of tuff stone masonry for dynamic response analysis

Masonry is a composite material made of prismatic elements (i.e. stones, bricks or blocks) and mortar or dry joints. Masonry assemblages are typically used to form load-bearing or partition walls, as well as vaults, domes and retaining walls. Different computational strategies are currently available to simulate mechanical behavior of masonry structures, but experimental data are needed to assess the accuracy of numerical and analytical models. In this study, a micromechanical finite element (FE) model is proposed for tuff stone masonry, which has been used from ancient times to the present for construction of buildings and infrastructures (e.g. arch bridges and water distribution networks). The arrangement of stones was set up according to the running masonry bond scheme. The micromechanical modeling approach allowed the authors to distinctly simulate the behavior of stone units and mortar joints, as well as their interaction. The FE model was developed within LS-DYNA computer program to predict masonry response to quasistatic, dynamic and even impulsive loads such as blast and impact. Material properties and volumetric stress‒strain behavior of constituents (i.e. stones and mortar) were properly defined by means of laboratory test results. The nonlinear micromechanical FE model was then calibrated to get an effective reproduction of the experimental behavior of masonry specimens under different load patterns, hence assessing its numerical robustness. A satisfactory experimental-numerical comparison in terms of force‒displacement diagrams and crack patterns was found. Local limit states associated with different failure modes of masonry constituents were statistically characterized for each load pattern. Finally, the influence of material properties was assessed. This investigation was first based on a sensitivity analysis where material properties were changed according to statistical variability from experimental evidence. Then, a stochastic FE analysis was carried out by simulating material properties in compliance with discrete and continuous probability models. That procedure accounted for the actual inhomogeneity of masonry constituents. Key masonry properties such as peak resistance and ultimate displacement were statistically characterized, evaluating the propagation of material uncertainties to the macroscopic level. The micromechanical model presented in this paper will be used for dynamic response analysis of masonry walls subjected to blast loading.