Keywords: non-linear analysis, numerical modelling, static assessment, masonry building, cultural heritage, strengthening techniques.

The assessment of the structural behaviour of monumental masonry buildings is a challenging task that in recent decades has attracted the interests of a plethora of researchers all over the Europe [1]. Because of the uncertainties that affect both the structural behaviour and mechanical properties of masonry material, historical buildings can hardly be reduced to a standard structural scheme, which make their whole static and dynamic behaviour too complicated to be interpreted by simple mechanical models. In addition, due to the difficulty of gathering experimental data on the mechanical properties of in-situ materials it is also quite difficult to perform reliable, or comprehensive, quantitative strength evaluations on the whole fabric [2].

This paper aims to provide a contribution to the issue of modelling and analysis of historical masonry buildings of cultural relevance, presenting a careful use of numerical analyses to deal with practical engineering problems in the field of historical constructions. As an illustrative example, the Italian Medieval Castle of San Niccolò (Toscana, Italy) is analysed, and its structural behaviour under static loads is assessed. In the past the building exhibited significant damage and a cracking pattern that required restoration works. The structural evaluation of the Castle under vertical loads before and after the strengthening was performed to assess the causes of the damage. To this end three-dimensional non-linear analyses were performed: the masonry non-linear behaviour was examined through proper constitutive assumptions, characterized by elasticity, damage and friction. The standard finite element modelling strategy was used based on the concepts of homogenized material and a smeared cracking constitutive law. The analysis of the Castle included its structural evolution, i.e. the damage and the crack pattern before the restoration works were analysed and used as reference to identify a global numerical model. The main concept for assessment in the present study was the achievement of an adequate knowledge of the structural static behaviour [3]. After calibrating the numerical model to fit the damage state before the restoration works, non-linear analyses were performed to assess the effectiveness of the past strengthening. Results highlighted that the works, conceived as to mitigate the exhibited damage, were not able to eliminate the causes. New restoration works are required to offer a proper remedial strategy. Conclusions and suggestion for researchers and professionals were then obtained.

1

M. Betti, A. Vignoli, "Modelling and analysis of a Romanesque church under earthquake loading: assessment of seismic resistance", Engineering Structures, 30(2): 352-367, 2008. doi:10.1016/j.engstruct.2007.03.027

2

G. Bartoli, M. Betti, P. Spinelli, B. Tordini, "An 'innovative' procedure for assessing the seismic capacity of historical tall buildings: the 'Torre Grossa' masonry tower", Proceeding of the 5th International Conference on Structural Analysis of Historical Constructions, New Delhi, 929-937, 2006.

3

M. Corradi, A. Borri, A. Vignoli, "Experimental study on the determination of strength of masonry walls", Construction and Building Materials, 17(5): 325-37, 2002. doi:10.1016/S0950-0618(03)00007-2

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