Numerical evaluation of cracking and crushing in ancient masonry towers

In the present paper a comparative numerical study of two XIII century masonry towers preserved in Alba (Italy) is described. The buildings have been recently analyzed and monitored because of an emerging damage pattern, also due to some seismic events during the last few years. Nondestructive evaluation techniques have been adopted to assess the present situation of the towers without perturbations. Such investigations revealed the presence of concentrated damage zones as well as the deviation of one of the towers from verticality. Both towers have been analyzed through a preliminary linear elastic analysis, and a good agreement has been found with in situ measurements of the stress level by means of flat jack tests. This model validation allowed proceeding with the nonlinear analysis in order to evaluate cracking and crushing in the masonry. In the case of “Torre Sineo”, an increasing tilt mechanism has been simulated. Cracking and crushing of the masonry have been both taken into account, as well as the influence of geometrical nonlinearity. The opening of sub-vertical radial cracks anticipate compression crushing, while the evolution of the top displacement shows an almost linear evolution with respect to the tilt of the basement. The numerical simulations have also predicted the damage in correspondence to the main openings. On the other hand, the main vertical crack detected in “Torre Astesiano” has been taken into account by vanishing the elastic modulus in the corresponding narrow band. In this case the analysis reveals that, although the static stress field is not influenced in a sensible way, damage is responsible for high strain localization in the cracked area and for a change of the dynamic properties of the tower. In both cases, the numerical analysis has given a valuable picture of possible damage evolutions, providing useful hints for the prosecution of structural monitoring.