Cables are critical load carrying members of cable-stayed bridges; monitoring tension forces of the cables provides valuable information for SHM of the cable-stayed bridges. Monitoring systems for the cable tension can be efficiently realized using wireless smart sensors in conjunction with vibration-based cable tension estimation approaches. This study develops an automated cable tension monitoring system using MEMSIC’s Imote2 smart sensors. An embedded data processing strategy is implemented on the Imote2-based wireless sensor network to calculate cable tensions using a vibration-based method, significantly reducing the wireless data transmission and associated power consumption. The autonomous operation of the monitoring system is achieved by AutoMonitor, a high-level coordinator application provided by the Illinois SHM Project Services Toolsuite. The monitoring system also features power harvesting enabled by solar panels attached to each sensor node and AutoMonitor for charging control. The proposed wireless system has been deployed on the Jindo Bridge, a cable-stayed bridge located in South Korea. Tension forces are autonomously monitored for 12 cables in the east, land side of the bridge, proving the validity and potential of the presented tension monitoring system for real-world applications.
Due to their cost-effectiveness and ease of installation, smart wireless sensors have received considerable recent attention
for structural health monitoring of civil infrastructure. Though various wireless smart sensor networks (WSSN) have
been successfully implemented for full-scale structural health monitoring (SHM) applications, monitoring of low-level
ambient strain still remains a challenging problem for wireless smart sensors (WSS) due to A/D converter resolution,
inherent circuit noise, and the need for automatic operation. In this paper, the design and validation of high-precision
strain sensor board for Imote2 WSS platform and its application to SHM of a cable-stayed bridge are presented. By
accurate and automated balancing the Wheatstone bridge, signal amplification of up to 2507-times can be obtained.
Temperature compensation and shunt calibration are implemented. In addition to traditional foil-type strain gages, the
sensor board has been designed to accommodate a friction-type magnet strain sensor, facilitating fast and easy
deployment. The sensor board has been calibrated using lab-scale tests, and then deployed on a full-scale cable-stayed
bridge to verify its performance.
Rapid advancement of sensor technology has been changing the paradigm of Structural Health Monitoring (SHM)
toward a wireless smart sensor network (WSSN). While smart sensors have the potential to be a breakthrough to current
SHM research and practice, the smart sensors also have several important issues to be resolved that may include robust
power supply, stable communication, sensing capability, and in-network data processing algorithms. This study is a
hybrid WSSN that addresses those issues to realize a full-scale SHM system for civil infrastructure monitoring. The
developed hybrid WSSN is deployed on the Jindo Bridge, a cable-stayed bridge located in South Korea as a continued
effort from the previous year's deployment. Unique features of the new deployment encompass: (1) the world's largest
WSSN for SHM to date, (2) power harvesting enabled for all sensor nodes, (3) an improved sensing application that
provides reliable data acquisition with optimized power consumption, (4) decentralized data aggregation that makes the
WSSN scalable to a large, densely deployed sensor network, (5) decentralized cable tension monitoring specially
designed for cable-stayed bridges, (6) environmental monitoring. The WSSN implementing all these features are
experimentally verified through a long-term monitoring of the Jindo Bridge.
Long-term structural health monitoring (SHM) systems using wireless smart sensors for civil infrastructures such as
cable-stayed bridges has been researched due to its cost-effectiveness and ease of installation. Wireless smart sensors are
usually powered by high capacity batteries because they consume low power. However, theses batteries require regular
replacements for long-term continuous and stable operation. To overcome this limitation of wireless smart sensor-based
SHM, considerable attention has been recently paid to alternative power sources such as solar power and vibration-based
energy harvesting. Another promising alternative ambient energy source might be a wind-generated power; in particular,
it can be very useful for structures in windy area such as coastal and mountainous area. In this study, the feasibility of the
wind-powered generation for wireless smart senor nodes is investigated by through experimental and analytical
approaches, and the possibility of practical application to actual SHM system of a cable-stayed bridge is discussed.