The seismic behaviour of Maniace castle, Syracuse: a first numerical comparison between the current condition and a hypothetical complete reconstruction

The seismic behaviour of Maniace Castle, built on the Ortigia island in Syracuse (Italy) during the thirteenth century by Emperor Frederick II, was investigated by a numerical approach with the aim of comparing different strategies for structural reinforcement. The original building consisted of a square perimeter made by 4 m thick limestone masonry walls and round towers at the corners, embedding a large hypostyle hall. The roof of this main hall was supported by a system of arches, five on each side span. The current state of the castle is the result of subsequent interventions following the explosion that devastated the interior of the castle in 1704. Accordingly, at present the indoor hall consists of only 2/5 of the original covered area, and the primitive structural concept has greatly changed, since the double symmetry of the plant was substantially lost. Buttresses and transverse walls were added to improve the mechanical response to horizontal loads. Previous studies, both experimental and numerical, proved that the interior columns supporting the arches experience a level of vertical stress that is quite high in comparison to the actual strength. The situation is particular serious accounting for the seismicity of Syracuse, as a the significant increase in axial stress in the columns due to their flexural deformation might occur. In the present study, the behaviour of the castle is studied by means of a detailed full 3D FE model, both under vertical and lateral loads. The results of the analysis are used for a proposal of reconstruction of the hypostyle hall, bringing it back to the original geometrical configuration of the XIII century, by the use of modern building materials.