LoRa-Based Precision Wireless Structural Health Monitoring System for Bolted Joints in a Smart City Environment

Smart City is a cutting edge technology driven city aimed at making our everyday lives safer and more convenient. Like every city it is comprised of structures. To uphold their safety these structures have to undergo periodical maintenance checks. However, checks are done manually, thus consume a significant amount of time and financial resources. Remote Structural Health Monitoring (RSHM) is a perfect solution for a Smart City, however limited research is done in applying Internet of Things (IoT) sensor nodes for permanent RSHM in applications that use bolted joints as a main fastening method. Most of the proposed solutions are not suitable, since either additional structural modifications are required, they violate standards, provide poor wireless communication range or still require human intervention. Therefore, this paper proposes an IoT sensor node named TenSense M30, which leverages Long Range (LoRa) communication technology to enable wide communication coverage and long life for monitoring the health of bolted joints in a Smart City environment. TenSense M30 has a miniature footprint and can be used as an add-on to current structures. Mechanical, hardware and embedded designs are presented and evaluated by means of simulation and practical tests. Results show that TenSense M30 is capable of precisely monitoring the pre-tension load of bolted joints, has a secured non-line of sight communication channel with a distance of 800 meters, has an expected lifetime of greater than 5 years powered by a number of coin cell batteries, and is safe under the pre-tension load.