Issue 46

A. Maione et alii, Frattura ed Integrità Strutturale, 46 (2018) 240-251; DOI: 10.3221/IGF-ESIS.46.22 241 the resistant elements, the constructive typology, the state of conservation, material degradation and mechanical properties together with a proper knowledge about the foundation soil and the possible interaction with adjacent buildings. In this phase an integrated approach is crucial to critically manage multi-source information provided by visual inspections, historical documents and instrumental investigations [3]. An interesting experimentation of such an approach has been carried out by the authors in the framework of the Italian ARCUS-MiBACT Project on the “Assessment of the seismic safety of National Museums of Italy” [4] supported by the Ministry of the Cultural Heritage (MiBACT). The project, aimed at assessing the seismic safety of a historic masonry building [5, 6], and applied to the Capodimonte Museum in Napoli (Fig. 1) and to other National museums, has been developed according to the Italian Guidelines on Cultural Heritage [1]. In particular, this paper is focused on the approach developed by the authors to achieve a proper characterization of the constructive features of the horizontal structures upon the first level of the Museum, most of them strongly modified in the '50s of the last century to host the exposition of the painting collection of the Museum [7]. It is well known in fact, also on the basis of the recognition of seismic damage, that the horizontal structures strongly influence the seismic behaviour of masonry buildings. This is due to their properties of mass and stiffness which affect the entity and the repartition of the seismic forces among the vertical walls, while the effectiveness of their connection with the vertical structures ensures the occurrence of a global behaviour preventing the out-of-plane mechanisms of the walls [8- 11]. Besides, this effectiveness has the same importance even for other structural typologies of buildings, e.g. timber and r.c. systems [12, 13]. Figure 1 : External view from east side of the Capodimonte Museum. Hence, the identification of the constructive typology of the horizontal structures is a crucial aspect in defining proper models of the seismic behaviour of masonry buildings and can also help to optimize energy and structural aspects in retrofitting [14]. However, when cultural heritage buildings are involved, some difficulties can arise in the acquisition of the data required by a proper characterization of these structures. In these cases, in fact, the execution of direct inspections and testing is usually not compatible with the needs to preserve the historical and artistic values inherent to painted ceilings or remarkable floors, while other difficulties can be related to the possibility to access these structures safely. To this aim, non-destructive testing (NDT) methodologies have lately gained increasing interest, mainly due to the continuous improvement of technologies characterized by a low impact on the structures [15-20]. In particular, for the presented case study, the lack of clear information concerning the renewal of the spaces on the first level, arranged for the new museum use [7], was another reason for providing a diagnostic investigation plan. Infrared thermography proved to be a useful method to answer critical questions related to the interpretation of the structural role of some vaults and also to overcome the difficulty to approach these structures; mostly the use of a scaffolding to go hand knocking on their intrados and listening the acoustic vibrations is generally not allowed in such places hosting museums because of the risks for the precious contents. Infrared thermography, instead, does not require contact with the tested object and allows preserving its integrity [21-23] and it seems to be very promising in order to obtain also quantitative data thanks to the recent advances in thermographic signal processing. This technique is usually carried out according to two distinct approaches depending on the existing thermal contrast between the investigated object and the background. The passive approach detects the thermal radiation emitted by its surface under natural conditions, without employing any