Phd in STRUCTURAL AND GEOTECHNICAL ENGINEERING

Thesis title: Micromechanical and macromechanical approaches for the analysis of periodic masonry structures

In European countries, preservation of masonry architectural heritage is a felt concern. The most fascinating landscapes are characterized by a large presence of masonry structures that have become part of country cultural identity. This justifies the lively interest towards the development of efficient computational tools to assess the structural capacity of masonry buildings. Among the available modeling strategies, finite element models seem to be suitable tools to characterize the evolution of the nonlinear mechanisms occurring in the material under typical loading conditions. This work focuses on finite element modeling of masonry structures at different scales. A micromechanical model, based on a damage-plastic constitutive law for masonry mortar joints, is developed to reproduce the structural response of unreinforced masonry arches, by studying global force-displacement response curves and collapse mechanisms. The proposed model is implemented in finite element procedures, where the mesh-dependency problem is efficiently overcome by adopting nonlocal integral formulations. To prove the efficiency of the adopted model, the response of experimentally tested walls and arches is numerically reproduced. Then, some parametric analyses on arches are performed with the aim of analyzing the effect of most relevant geometrical and mechanical parameters on the global structural response. Subsequently, the use of macromodeling technique based on smeared crack constitutive laws for the cyclic in-plane analysis of masonry panels is explored. The numerical investigation is focused on two material macromechanical models (total strain cracking and crack and plasticity) that show some limitations when analyzing the behavior of masonry structures subjected to in-plane cyclic loading. A modified version of the Drucker-Prager model including cohesive softening is introduced to overcome these shortcomings. It is proved that the numerical results correlate better with the experimental outcomes. In particular, attention is focused on two different techniques adopted to overcome the mesh-dependency of the finite element solution: fracture energy regularization and nonlocal integral approach. A single-fixed smeared crack is implemented in finite element procedures adopting these two different techniques. Numerical applications are performed to prove the robustness and stability of these two approaches.