ANUB-Aggregates: a fully automatic NURBS-based software for advanced local failure analyses of historical masonry aggregates

Masonry structures constitute the great majority of buildings in historical centers where construction activities were carried out by adding structural portions to pre-existing ones: as a result, masonry aggregates are currently the most common structural typology in such contexts. The structural behavior of masonry aggregates, which are complex systems of different buildings interacting with each other, is generally affected by several factors, such as the different steps of construction, uncertainties about interlocking between walls, presence of different and irregular masonry textures and multi-leaf walls, which make such a structural typology very difficult to study. During recent seismic events in Italy, a wide number of local collapses has been observed in masonry aggregates of historical centers, highlighting the important role of local mechanisms in the seismic assessment of such structures. In this paper, an efficient software called ANUB-Aggregates (Adaptive Nurbs Upper Bound limit analysis for masonry Aggregates) is proposed for the seismic assessment of partial failure mechanisms in historical masonry aggregates. The theoretical core of this program is a kinematic NURBS-based limit analysis with meta-heuristic mesh adaptation. The use of NURBS allows studying aggregates containing vaulted structures, or any other typology of curved elements, without additional computational effort. Moreover, the mesh adaptation scheme assures the representation of the correct collapse mechanism by finding the real position of fracture lines. Starting from the three-dimensional model of the whole aggregate, the code ANUB-Aggregates provides the analysis of more macro-elements interacting with each other with different interlocking hypotheses, evaluating both simple and complex failure mechanisms. As proof of the effectiveness of this applicative, the analysis of two historical masonry aggregates is presented.