Automatic detection of local collapse mechanisms in historical masonry buildings: Fast and robust FE upper bound limit analysis

A fast and robust FE upper bound limit analysis approach is proposed, aimed at predicting the spectral acceleration that triggers local failure mechanisms on historical masonry constructions. Structural verifications are made in agreement with the Italian building code, without assuming pre-assigned local failure mechanisms and with masonry unable to withstand tensile stresses. Structural elements are discretized through infinitely resistant hexahedrons coupled with quadrilateral interfaces obeying a Mohr-Coulomb failure criterion and where all plastic deformation is lumped. Two different horizontal load distributions are investigated, namely constant and reverse linear along the height. Several different in-plane directions of the seismic entrance are considered. The kinematic limit analysis problem, written in its standard form, is solved using a consolidated linear programming routine. In function of the tensile strength, the collapse acceleration and the active failure mechanism are found automatically. Through iterative extrapolation, the results for the no-tension material model are deduced. Finally, a novel filtering algorithm is proposed that considers active exclusively the elements belonging to the failure mechanism, thus allowing the estimation of the spectral acceleration responsible for the collapse. The procedure is applied on two complex historical buildings located in northern Italy.