Pier F. Giordano1, Filippo Ubertini2, Nicola Cavalagli2, Alban Kita2, Luís F. Ramos3, Maria G. Masciotta3
1)  Politecnico of Milano
Department of Architecture, Built environment and Construction Engineering,
Piazza Leonardo da Vinci 32, 20133 Milan, Italy
2)  University of Perugia
Department of Civil and Environmental Engineering,
Via G. Duranti 93, 06125 Perugia, Italy
3)  University of Minho
Department of Civil Engineering,
Campus de Azurém, 4800-058 Guimarães, Portugal

Keywords: Historical masonry structure, Structural Health Monitoring, Seismic induced
damages, Environmental effects, Operational Modal Analysis, Sonic Test.

Abstract. The San Pietro bell tower belongs to a monumental complex of exceptional historical, cultural and artistic value and is considered one of the landmarks of Perugia, Italy. The preservation of this structure has been considered an essential issue over centuries and even more nowadays. For this reason, a permanent vibration-based Structural Health Monitoring (SHM) system able to detect anomalies in the structural behavior by means of statistical process control tools has been installed in the tower. The SHM system is based on the continuous identification of the natural frequencies of the bell tower and on the statistical analysis of their variations. Environmental parameters, i.e. temperature and humidity, are monitored as well for compensation purposes. The aim of this paper is to present the results of the most recent investigations carried out on the monument after the 2016-2017 Central Italy earthquake sequence whose effects were perceived also in Perugia, in spite of the significant distance from the epicenter of the main shocks (about 70 km). In particular, ambient vibration test and sonic tests were performed. Moreover, the dependence of the dynamic parameters on the environmental factors is studied by means of AutoRegressive output with an eXogenous input (ARX) models. The comparison of results in pre- and post-earthquake conditions allows detecting the modifications in the structural behavior of the tower.