Mazziotti, Alessandra (2016) Structural analysis of historical masonry buildings. [Tesi di dottorato]

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The structural analysis of masonry historical buildings is still a challenging task, basically due to: the difficult numerical modelling of the nonlinear behaviour of masonry material, with almost no tensile strength; the arrangement of blocks and mortar joints frequently uncertain and variable; the complexity of morphology; the difficult modeling of the geometry, which drives to three-dimensional models characterized by a large number of degrees of freedom. The above considerations justify the need for specific modelling and analysis strategies to be developed and established for historical buildings. The most widely used strategies are affected by some limitations and different levels of accuracy. In this study the structural analysis of different types of historical buildings, under seismic loads, is performed by comparing different analysis approaches and pointing out some their criticalities. In the first part of the thesis (Chapter 2), the seismic capacity of multi-storey masonry buildings is evaluated, comparing different modelling strategies, such as simplified methods (equivalent frame, macro-modelling) and FE method. Four case studies characterized by different geometry (overall height, storey number, slenderness of spandrels and piers, etc.) are analyzed. The results are compared with the horizontal collapse multipliers computed with the limit analysis. The latter has proved to be a powerful simple method to check the results of more complex analysis, often less manageable and influenced by the implemented modelling. A simplified formula is proposed to apply the limit analysis and it was found to provide a good approximate measure of the seismic capacity of the building, being only noted the geometrical characteristics of the walls. The second part of the thesis focuses on the seismic behavior of masonry churches. The dynamic behavior is first investigated on a sample of fourteen case studies (Chapter 3), then an impressive case study: the gothic cathedral of Santa Maria del Mar, is analyzed by means of different analysis methods. The dynamic analyses of the fourteen masonry churches reveals a considerable dispersion of the vibration modes, which provide very small contribution in terms of participating mass. It leads to low values of the base shears (computed through the response spectrum analysis) and, consequently, to the possibility of adopting reduced forces to be applied on the masonry churches. The Santa Maria del Mar church was analyzed carrying out: linear static analysis, modal analysis, non linear (push-over )analysis and non linear dynamic analysis. The comparison between all these analysis methods provides a convincing picture of the structural weaknesses of the cathedral.

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