Growing public concern regarding the health of the aging civil infrastructure has spurred research in structural health
monitoring (SHM). Recent advances in wireless smart sensor (WSS) technology has significantly lowered the cost of
SHM systems and resulted in WSS being successfully implemented at full-scale. However, assuring accurate timesynchronized
WSS nodes in a network is still a challenging problem. Generally, WSS synchronization is realized by
communicating a sensors' CPU clock information over the network. However, such a synchronization approach
becomes more challenging as the network size increases. Reliable communication is not easily achieved due to longer
communication distance, larger numbers of sensors, and complexity of a distributed sensor network. Moreover, CPU
clocks may not be sufficiently reliable for accurate
time-synchronization due to substantial tolerance errors in crystal
and/or temperature effects. In this study, the use of low-cost GPS receivers for time synchronizing WSSs is explored to
resolve these issues. GPS sensors offer the potential to provide high-accuracy synchronization --- nano-second level
even with low-cost GPS receivers. The GPS-assisted time synchronization approach overcomes network communication
limitations to realize time-synchronization in large-scale networks of WSS.
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.
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