A numerical model for environmentally induced deterioration of masonry structures

A great attention is nowadays devoted to preserve cultural heritage against deterioration. The causes of this deterioration process can be generally subdivided in two main groups: mechanical and physico-chemical deterioration actions. The well-known mechanical deterioration of the masonry, in terms of the more meaningful phenomena, i.e. damage and friction toughness, it has been extensively studied numerically and experimentally in literature; Less attention has been devoted to the simulation of the chemical processes, which involve the diffusion of the aggressive species and water into the masonry structures. Decisive for the damaging process of salts in porous media is the interaction of the salt with the humidity in the masonry: under specific conditions the salt crystallization appear inducing stress into the masonry pores. The aim of this work is to look at the deterioration of masonry in a unified framework which accounts for both the mechanical and the chemical part of the problem and their coupling. Few are the contributions in this direction specifically for masonry while some contributions can be found for other materials, such as the concrete. In particular, here, a model for the analysis of masonry structures which couples the mechanical deterioration process with the environmental damage is presented. In order to deal with real masonry structure, the implementation of the model is developed by an efficient multilevel strategy that solves a simplified modeling of local interaction brick-brick through iterative nested solutions defined at different levels of mechanical definition. The local model is based on a discrete Lagrangean description where each brick is a rigid body and each joint is a nonlinear interface characterized by normal and tangential stress components. The environmental damage is modelled with the diffusion of penetrating agents inside the masonry and is described with a diffusion equation. The constitutive relations for stresses involve mechanical damage, chemical damage and friction. On the other hand, the mass flux of external agents depends on the concentration and on the mechanical damage. Numerical tests show the effectiveness of the proposed approach.