Analisi non lineari di pannelli murari con elementi finiti equilibrati

In the analysis of masonry walls the accurate definition of the stress components at the brick-mortar interface is of particular importance. In these regions it is more important to have a rigorously equilibrated definition of the stress state rather than a rigorously compatible description of the strain state: this result can be obtained by directly modelling the stress fields and making use of the principle of the minimal complementary energy. An equilibrium approach was previously developed by Zavelani Rossi (2001) based on the definition of linear stress subfields in quadrangular finite elements. The state of stress over each triangular sub-element is rigorously kept under control through a check at the element corners, so that possible critical situations at the inner boundaries can be evidenced. Fractures along the boundary of the elements are identified according to the values of the shear and normal stress components along the contact surface. Using this model three different typologies of masonry structures have been analyzed: a dry stone masonry panel subjected to constant vertical load and progressively increasing horizontal load (Oliveira, 2002); a dry brick masonry panel with an asymmetric rectangular opening subjected to the same load conditions as the previous one (Vermeltfoort el al., 1993); some stone masonry prisms with three leaves subjected to compression or “shear” loads (Pina-Henriques et al., 2004). The numerically predicted crack pattern is generally in good agreement with the experimental findings; the estimated load carrying capacity is comparable to that supplied by compatible finite element models.