Strength of Masory Walls under Static Horizontal Loads: B.E. Analysis and Experimental Tests

The Boundary Element Method is applied to the static analysis of two masonry walls previously subjected to experimental tests carried out in situ in two different stages. The walls were brought to the point of collapse by applying horizontal loads simulating the seismic actions and then, after being repaired by injections of cement mixtures, they were subjected to a new loading process culminating, as the first one, in the occurrence of the mechanism of collapse. In the numerical analysis, carried out under the plane-stress condition, masonry is regarded as a no-tension material with infinite strength in compression and a path-dependent criterion, corresponding to an elasto-plastic material behaviour, is adopted to model the no-tension solution. Linear boundary elements and linear triangular cells are used to transform the solving boundary integral equations into linear algebraic equations. The numerical results are obtained through an iterative incremental process based on the initial stress method: at each step, the no-tension condition is enforced by computing an initial stress field which is used to iterate the solution until the state of no-tension is achieved everywhere. The nonlinear behaviour is modelled by succesively correcting the loading conditions and leaving the elastic stiffness matrix unchanged. The B.E. results, in terms of displacement diagrams and internal stress states, are compared with the measurements and the crack patterns recorded during the experimental tests.