PSI - Issue 64

Luigi Petti et al. / Procedia Structural Integrity 64 (2024) 637–644 Petti L., Lupo C., D’Angelo T., Dallocchio P. & Guizzetti D. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Knowledge of the past is essential for human development, both economically and socially. For this purpose, the preservation and conservation of the cultural heritage is necessary and fundamental due to their inestimable value. Italy is internationally renowned for its extensive tangible and intangible heritage. It is the country with the highest number of UNESCO sites (UNESCO World Heritage Centre - World Heritage List) and boasts a significant portion of the world's artistic and cultural heritage. In this within, a relevant evidence is provided by the Greek and Roman architecture, as well as the extensive architectural heritage and monuments left by the Renaissance. The well-known strong influence of Greek culture in Italy, is represented by the various archaeological sites located in the southern part of the country, see Marconi C. (2012). Among these sites, the Valley of Temples in Sicily (see Badami A.A. (2017)) and Paestum in Campania (see Mangone F et al (2019)) stand out for their magnificent Temples. While most of them survive today in the form of ruins, the three Greek temples located in Paestum (southern Italy) are still standing and are exceptionally well preserved, despite some apparent seismic deficiencies. The three temples of Paestum are, actually, the best example of well-preserved Greek architecture. In fact, the archaeological site of Paestum together with the other sites of Velia, the National Park of Cilento and Vallo di Diano and the Certosa di Padula, was recognized as UNESCO world heritage in 1998. These monumental structures are often located in areas susceptible to high natural hazards such as earthquakes, landslides, floods, etc., to which must be added the obvious degradation of the material caused by aging, atmospheric phenomena, etc. In addition to these well-known issues, it is necessary to consider the new hazards and risks associated with human activities and climate-change, see Bonazza A. et al (2018), European Commission (2022), Crowley K. et al (2022). As well described in Sesana E. et al, (2021), the impact of climate change on cultural heritage is generated by significant variations in temperature, precipitation, and wind. An increase of precipitation and humidity, coupled with higher temperatures, may produce accelerated corrosion processes of materials, biological deterioration, cracking, as well as the formation of salt crystals causing efflorescence and subflorescence. The intensification of wind, particularly when associated with sand, salt, and atmospheric contaminants, could result in surface erosion, water infiltration and structural damage. An increase of temperature fluctuations could lead to more freezing and thawing cycles causing more frequently thermoclastism phenomena. On the other hand, human activities have also changed over the centuries, creating other hazard to heritage. For example, infrastructures have very often been built, causing significant interference with heritage sites; in the past much of the heritage have been altered or destroyed due to the lack of rules and regulations for its protection and preservation (see Pickard R. (2001)); and nowadays, the increasing number of tourists has an impact on heritage preservation, as described in Pedersen A. (2002). Of course, all of this is compounded by the complexity of implementing the most appropriate conservation strategy and the economic burdens involved. The need to preserve the heritage finds crucial support in innovative methods and technologies that can improve our understanding of the buildings’ health state and its evolution , for the purpose of monitoring any critical conditions or in order to anticipate them through proactive maintenance activities. In this respect, an innovative experimental monitoring strategy has recently been developed and applied to the Temple of Athena in Paestum (Southern Italy, ca. 500 BC), in the frame of a joint research project by the Department of Civil Engineering (DICIV) of the University of Salerno (UNISA), the Archaeological Park of Paestum and Velia (PAEVE) and Leica Geosystems S.p.a. (LGS). The aim of the monitoring activities is to evaluate the causes that led to the evolution of a crack pattern affecting some drums of one of the columns of the temple and part of the stylobate, which were struck by thunderbolt in the 70s, and to assess the static behaviour. In particular, this paper describes the criticalities of the temple and the installed monitoring network, and focuses on the preliminary results of the ongoing monitoring activities. The results were obtained through an approach of data analysis based on signal processing techniques, Fourier theory, and correlation analysis. The aim of the analyses is to control any potential evolution in the structural behaviour by removing the influence of the environmental conditioning on the response of the structure and of the devices. To this end, the strategy involves correlation analyses using different approaches. In particular, this includes the consideration of different time windows and possible response delays, analysing both the raw signals and the signals filtered with an approach based on Fourier theory.