Sensing the health state of a city structural monitoring system by IoT wireless sensing devices

Barsocchi P., Cassarà P., Mavilia F., Pellegrini D.

Internet of Things (IoT)  Wireless sensing devices 

We are witnesses of technological ascent accomplished by the Internet of Things (IoT) in the new era of the shared informatization. Smart Cities make up certainly one of the major areas of IoT applications. Despite the several defi- nitions for this new concept, the aim is achieve a better use of public resources, increasing the quality of services and decreasing the costs of public services. Some initiatives of Smart Cities around the world have become reality [1]. Many components compose a smart city, e.g. smart transportation, smart energy, smart education, and smart building surely. A smart building consists in services offered to the occupants, resources distributed to the city and, in case of historical heritage, informations about its "health state" to municipalities. The core of a smart building, and more in general of a smart city, is represented by the IoT devices [2]. Physical objects connected over a network take part in Internet sharing information about themselves at any time. The marketplace offers several solutions for IoT developments, both in hardware and software. Developers have proposed simply and low-cost embedded systems, that allowed users to develop on their own monitoring and actuation systems [3]. The research in the structural health monitoring field (SHM) [4] takes advantage by the IoT paradigm. Indeed, the goal of SHM is to obtain informa- tion about the characteristics of a structure, its constituent materials, and the different parts that compose itself. The SHM needs of observations of a structure over the time, using measurements obtained with different kind of sensors (accelerometers, thermometers, hygrometer, extensometers) deployed along the whole structure to be monitored. Such procedures are recognized as a good way to test the state of conservation of a structure, and are also important aids in identifying when interventions are necessary. Exploiting low-invasive and aesthetically acceptable sensors becomes essential to widespread SHM applications. IoT technolo- gies have invaded SHM field providing an economical and relatively non-invasive instruments for real-time structural monitoring of buildings and monuments. Indeed, IoT-based sensors are able to monitor wide areas and transmit data to a remote server. We envisage their employment in a not too distant future in the monitoring of entire areas within a city, facilitating the management of maintenance operations and prompt interventions in the case of an emergency. The main issues that must be taken into account when an IoT-based sensor network is used for SHM applications are: the number and location of the sensors used to ac- quire data, the synchronization of the acquired data and the energy consumption of the nodes. The optimization of the number and location of sensors is a new challenge in these technologies, which typically involve a large number of redundant sensors. Moreover, the synchronization of the sampled data is essential in order to correlate data coming from different sensors deployed in the ancient monuments. Finally, adopting energy-efficiency policies becomes essen- tial for long term monitoring systems. In this paper we show how a long term monitoring infras- tructure based on the IoT paradigm can be achieved with off-the-shelf devices, where each sensing device is able of autonomously transferring data (3-axial acceleration, tem- perature and humidity) to a server. We deployed the sensing devices on the San Frediano bell tower in Lucca, collecting a large amount of data. Finally, we studied the structure behavior under external stresses, showing results in three particular conditions: environmental noise in a weekday, during the ringing of the bells and during a large event taken place in the city.

Source: ISTI Working papers, 2017