Long term wireless ambient monitoring of heritage buildings

Motivated by the preservation of an artistic treasure, the fresco of the "Cycle of the Months" on the second floor in an historic tower, Torre Aquila, a wireless sensor network (WSN) has been developed and installed for permanent health monitoring. The monitoring scheme covers both static and dynamic evaluation of the tower structural integrity from local to global scale and consists of 17 nodes, including 2 long length fiber optic sensors (FOS), 3 accelerometers and 12 environmental nodes. The system has been working for 1.5 years and has been debugged and updated both as to hardware and software. This paper focuses mainly on the ambient vibration analysis used to investigate the performance of the sensor nodes and structural properties of the tower. Initial ambient vibration monitoring shows that cyclic environmental factors, such as traffic flow, are not the dominant cause of tower vibration; and the vibration levels of the tower in different axes are not large enough to be a critical issue calling for attention under current conditions. It proves that the WSN is an effective tool, capable of providing information relevant to safety assessment of the tower.