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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After the event of 1972, the damaged drum was subjected to an important restoration activity. In fact, the current configuration of the column is the result of a restoration of the block through the relocation of the destroyed parts. Some studies conducted between 2005 and 2006, with the aim of developing a scheduled maintenance plan for the Temples of Paestum, investigated the crack pattern on the aforementioned column. For this purpose, a monitoring activity was carried out from 2008 until 2010 by a team of the University of Naples - Federico II, to control the evolution of the crack pattern. The study highlighted that no substantial changes were detected during the observation period. However, in 2021, a notable evolution of the crack pattern on the restored drum of the column 4 of the east colonnade was recognised. This evolution showed the need to develop an ad-hoc monitoring plan to safeguard the temple. For this purpose, the Archaeological Park of Paestum & Velia with the Department of Civil Engineering of the University of Salerno started dedicated monitoring activities. These activities involve a direct periodic survey of the crack pattern on the block using very high-resolution orthophotos, as well as continuous monitoring of the colonnade of the east facade through sensors. The high-resolution photo allows to control the punctual evolution of the crack patterns, while the continuous monitoring enables the evaluation of possible evolution related to a global mechanism that involves the colonnade. The activities related to the monitoring network are carried out with the support of Leica Geosystems S.p.a..

Fig. 4. View of the drum of column 4 of the east facade of the Athens Temple (left) and a zoom of the crack pattern (right).

3. Monitoring Network The activities started in 2021 demonstrated the necessity for the implementation of a strategy to complement the detailed survey of the crack pattern through high-resolution photography. In particular, a continuous monitoring system was considered necessary to control the evolution of the overall static behaviour of the colonnade. In this way it is possible to have a cross-check on the effects that changes in the overall staticity of the facade may have on the cracked wall, and vice versa. The monitoring network was installed at the end of March 2023 and it is composed by five sensors with function of distance meter and triaxial tilt meter. In particular, the sensors communicate wirelessly with the gateway, which transmits data to the cloud via UMTS connection. The measurements are carried out with a sampling time of 1 hour. The sensors are placed on the top of the column, on the abacus, with the laser pointed downwards, with the objective to monitor eventual relative displacement between the column and the stylobate, as well as tilt variation. In particular, the devices are characterised by the following accuracy and resolution: • Angles, full 360° tilt, with an accuracy of ±0.002° and a resolution of ±0.0001°; • Distance, from 5 cm up to 100 m, with an accuracy of ±1mm and a resolution of ±0.1mm. The devices are also integrated with an internal temperature sensor. Figures 5 shows the location of the sensors. The choice to install the sensors on the internal side of the colonnade was made in order to respect the authenticity of the heritage. In addition, visitors are currently not permitted to enter the temple.