Proceedings Article | 3 April 2012
KEYWORDS: Bridges, Sensing systems, Sensors, Data acquisition, Structural health monitoring, Relays, Finite element methods, Remote sensing, Reliability, System identification
DuraMote is a MEMS-based remote sensing system, which is developed for the NIST TIP project, Next Generation
SCADA for Prevention and Mitigation of Water System Infrastructure Disaster. It is designed for supervisory control
and data acquisition (SCADA) of pipe ruptures in water distribution systems. In this project, a method is developed to
detect the pipe ruptures by analyzing the acceleration data gathered by DuraMote which consists of two primary
components; the first, "Gopher" contains the accelerometers and are attached to the water pipe surface noninvasively,
and the second, "Roocas" is placed above ground supplying the power to, and retrieving the data from the multiple
Gophers, and then transmit the data through Wi-Fi to a base station. The relays support the Wi-Fi network to facilitate
the transmission. A large scale bridge provides an ideal test-bet to validate the performance of such a complex
monitoring system as DuraMote for its accuracy, reliability, robustness, and user friendliness. This is because a large
bridge is most of the time subjected to susceptible level of ambient vibration due to passing loads, wind, etc. DuraMote
can record the acceleration time history arising from the vibration making it possible to estimate the frequency values of
various bridge vibration modes. These estimated frequency values are then compared with the values computed from
analytical model of the bridge for the verification of the accuracy of DuraMote. It is noted that such a verification
method cannot be used practically by deploying DuraMote on a water distribution network since the dynamic behavior
of a pipe network, either above or underground, is too complex to model analytically for this purpose, and in addition,
the network generally lacks conveniently recordable ambient vibration. In this experiment, the performance of DuraMote
system was tested being installed on the Hwamyung Bridge, a 500 m long RC cable stayed bridge in Korea for long term
monitoring. In total, the system consisted of 24 accelerometers, 13 Gophers, 10 Roocas, 5 relays, and 1 base station. As
it happened, the bridge was subjected to heavy rain, winds, and a typhoon during the experiment allowing the DuraMote
to demonstrate extra ordinary robustness and durability. Indeed, in spite of the rough weather, acceleration data was
continuously recorded from which natural frequencies, mode shapes, and other structural parameters were calculated.
This opportunity would not have happened if the experiment was planned for a shorter duration.
