• masonry structures
• monumental buildings
• nonlinear analysis
• FEM modelling
• macroseismic analysis
• historical constructions
• structural analysis

The historical monumental masonry buildings play a fundamental role in the World Cultural Heritage, especially in the European country. They are generally characterised by a limited initial knowledge (e.g. geometrical, structural and historical features), by large dimensions and great structural complexity and heterogeneity. The structural complexity is a natural consequence of a usually long constructive genesis characterised by additions, transformations and demolitions realised during centuries, determining a great heterogeneity in the geometrical-structural features and widespread irregularities. Further, the constructive phases are not properly documented (or not documented) since they are often a consequence of practical needs and not of systematic planning, making it hard to comprehend the morphological evolution. Besides being difficult to reconstruct through the only historical analysis commonly adopted for ‘ordinary’ historical buildings, such an intricate construction process determines a structural behaviour similar to structural aggregate, composed of several Structural Units (SU), more than to single building. Therefore, the procedures commonly adopted for the structural evaluation of ordinary buildings are often partially ineffective if applied to the present building typology, or extremely demanding in time and economic resources.
The scientific literature currently faces the theme of the analysis of historical buildings according to different ‘scales’ and several procedures; however, a complete methodology properly calibrated and accounting for all the peculiarities of monumental buildings is still missing. The present thesis has been developed to analyse the behaviour and the specific features of this building typology and propose a proper methodology for the investigation and the structural assessment finalised to the possible planning of retrofitting interventions. A multi-step multidisciplinary procedure, characterised by a progressive increase of the knowledge level and analysis detail, was elaborated and tested on a representative case study: the Certosa di Calci monumental building near Pisa (Italy).
The first fundamental step of the proposed procedure consisted of multidisciplinary and integrated knowledge analysis, comprehensive of the contribution of more fields – e.g. historical-critical analysis, geometrical and structural survey, in situ investigations – essential to determine a sort of ‘state of the art’ of such complex buildings. Regarding the Certosa di Calci, different sources’ contributions – e.g. archival documents, iconographic sources, bibliographic references, geometrical/architectural/structural issues – were compared and elaborated in a synergic and iterative process. The final aims were to reconstruct the morphological evolution, comprehend the aggregate’s inner behaviour, and identify the SUs within the monumental complex. Different disaggregation criteria were accounted, looking for a compromise between homogeneity of the inner geometrical and structural features and reliability of the structural behaviour.
The subdivision of a monumental building into its SUs allowed to approach it as an urban aggregate, resorting to the macroseismic risk analysis commonly adopted for large-scale evaluations. A procedure and a specific survey and evaluation form were elaborated, based on the scientific literature's approaches for other building typologies, properly modified to fit the considered case. An index risk was achieved for each SU through the proposed form, consequently determining a sort of ‘priority list’ within the aggregate, allowing identifying the areas to be more urgently in depth-analysed to design retrofit interventions.
According to the progressive deepening line, the following step in the procedure was to execute numerical analyses useful to detail the in-aggregate behaviour and the phenomena related to the units’ interaction according to some recurrent aggregation cases. Finite Element Method models of some representative SUs were defined, adopting some necessary simplifications, and preliminarily validated through linear analyses. Later, nonlinear static analyses were performed to investigate the structural behaviour of the SUs both as single buildings and as aggregates according to different configurations, analysing the interaction phenomena and their influence over the global capacity.
Finally, the work focused on developing a simplified numerical model to simulate the in-aggregate behaviour once knowing the complex FEM models' result. A proper investigation of the stresses transferred through the contact area between two adjacent SUs was performed. It was needed to propose a reliable simplified approach based on the detailed numerical model of a unit and the simulation of the interaction with the adjacent ones through a set of nodes and springs. The influence of parameters such the mass and stiffness definition, and the connection among the numerical model and the simplified one were analysed, looking for a good compromise between result’s accuracy and speed in terms of model definition and analysis execution.
In conclusion, the methodology proposed allows a complete and coherent analysis of the structural capacity of a historical masonry monumental building, according to different detail levels and, consequently, different aims.