Structural Health Monitoring Using Smart Sensors - ideals ...

its spatial gradient, which is claimed to change according to the health of a structure
(Farrar et al., 1994; Nagayama et al., 2005; Pandey et al., 1991; West, 1984), needs spatial
information. Independent data processing without data sharing among nodes cannot utilize
such spatial information. On the other hand, collaboration of all of the smart sensors in the
whole network is neither practical nor desirable due to substantial communication and
power requirements. Collaboration in local communities, which are spatially large and
dense enough to capture local structural condition, is thus essential for SHM using a dense
array of smart sensors.
Redundancy
Because measurement error, inaccurate modeling, numerical error, etc. introduce
uncertainty in SHM results, SHM algorithms on smart sensor networks should possess
redundancy. For example, more than one set of smart sensors monitor a given element and
make their own judgments on the damage existence; the judgments are then compared
with each other to examine their consistency. Redundancy is an effective means to deal
with the uncertainty, which is problematic for most SHM algorithms.
Multiple functions
Smart sensor networks should preferably achieve multiple tasks, for example,
continuous SHM of a structure, baseline measurement for SHM, monitoring of rare events
such as earthquakes, and sensor calibration. Inclusion of other tasks such as traffic
monitoring and local weather monitoring further enhances the value of smart sensor
systems and makes introduction of smart sensor systems more attractive from a cost/
benefit perspective.
5. Desirable platform characteristics specific to SHM of civil infrastructure
Appropriate sensor availability
Appropriate sensors need to be available for smart sensors. Acceleration and strain
are among the most important measurands for SHM, while velocity, displacement,
temperature, humidity, wind velocity, and wind direction as well are sometimes measured
in full-scale structural monitoring (Ko & Ni, 2005; Wong, 2004). Sensors for these
measurands are needed on smart sensor platforms. One of the most commonly adopted
sensors on smart sensor prototypes is an accelerometer. The applicability of
accelerometers on smart sensors to civil engineering applications is, however, not
necessarily clear. Strain sensor adoption to smart sensors is not common (Arms et al.,
2004; Lynch & Loh, 2006; Nagayama et al., 2004). Sensors being capable of accurately
capturing structural behavior and environmental conditions need to be developed or
customized under the constraint of limited resources of smart sensors, especially battery
power.
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