Church building represents a large portion of the Italian cultural heritage that have demonstrated to be particularly susceptible to damage and prone to partial or total collapse under earthquake loads (Lagomarsino 1999). The high seismic vulnerability of this type of building is due both to the mechanical properties of masonry materials, characterized by a very small tensile strength, and to the particular configuration (slender walls, lack of effective connections among the structural elements, etc.).
Each monumental building is characterized by its own history, often resulting in a composite fusion of additions and replacement of structural elements that gave origin to its final configuration. Besides the dynamic behavior of ancient buildings is normally too complicated to be interpreted with simple mechanical models and the process of extrapolating analytical procedures specifically developed for modern buildings is in most cases inadequate. Also, in ancient (monumental) buildings it is sometimes quite difficult to perform reliable quantitative strength evaluations, due to the difficulty of gathering experimental data on the resistance of the structural elements and even on the mechanical properties of the on site materials. Monumental historical buildings can hardly be reduced to any standard structural scheme because of the uncertainties affecting both the structural behavior and the mechanical properties (Binda et al. 2000). Therefore the study of masonry heritage buildings remains a challenging task as many recent studies confirm (Lourengo & Orduna 2003, Lourengo & Oliveira 2007).
To deal with these problems a double approach, with respect to a specific case study, is used. Firstly a global analysis of the building is made using the finite element technique. Specific assumptions on the material properties and on the non linear behavior of masonry are made to appraise the general properties of the building's structural response under earthquake loads. Next step is to apply the simplified schemes of the limit analysis on several significant architectonical elements of the building. Some elementary macroelements are analyzed, to this end, with reference to the mechanisms activated on similar buildings during past earthquakes. Comparing the results obtained with the global and local analyses could provide an accurate description of the building response under seismic loads. The paper suggests that comparing different approaches for the analysis of historical buildings is mandatory to cover the unavoidable unknowns that always affect building materials and mechanics.
The proposed approach is applied to an emblematic case study: the Basilica of Santa Maria all'Impruneta, located in Impruneta nearby Firenze, (Italy). As a first step, an in-situ survey of the building's state was made to obtain basic information for following
analyses. In particular an in-situ survey on the geometry (and on the structural details) aimed to identify any irregularities of the structure was made.
This is necessary also to localize possible collapse mechanisms that might be activated during an earthquake. The investigation consisted in a geometrical survey to identify the actual damage, a quality check up of connections wall to wall and wall to roof, and masonry texture characterization. This step was accompanied by an historical survey of the building over centuries in order to determine the original shape and to consider the church modifications over the centuries. The paper reports mainly, for brevity, results on the assessment of the seismic behavior of the church even though the research was extended to include the bell-tower.
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