DISCRETE CRACKING OF MASONRY WALLS

The behaviour of a masonry wall with an opening, confined by frames, is analysed. In particular, crack evolution is investigated under enforced displacements. Cracking is modelled by means of a discrete approach and fracture energy concept. A plasticity model is adopted to describe the localised constitutive relation between stresses and relative displacements measured at crack faces. In this model, a modified Coulomb friction law and a non-associated softening flow rule are adopted. In particular, special attention is given to the effects, on the overall behaviour of the walls, of: i) the crack resistance in tension and in shear and ii) the non-linear compressive behaviour of the bricks. Two new yield surfaces are developed where the friction coefficient is made to decrease with the increase of the compressive stresses. It is found that the shear strength of the mortar joints has a major influence both on the peak loads and on the collapse mechanisms numerically obtained. These results are compared to experimental and numerical results obtained by other authors.