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Development of Wireless Structural Sensing and Control Devices Validation Tests of the Wireless Structural Monitoring System Decentralized Wireless Structural Control

Development of Wireless Structural Sensing and Control Devices
Capitalizing on recent advances in wireless communication, micro-electro-mechanical systems (MEMS), and integrated circuits, low-cost modular structural monitoring and control systems can be designed. It is envisioned that in the future, these wireless sensors will be able to acquire measurement data, communicate with each other, and make real-time intelligent decisions for monitoring or controlling a civil structure. As part of Prof. Yang Wang's PhD research, which was co-advised by Prof. Kincho H. Law at Stanford University and Prof. Jerome P. Lynch at the University of Michigan, a prototype wireless structural health monitoring (SHM) system has been developed.



The prototype wireless unit is designed in such a way that the unit can serve as either a sensing unit (i.e., a unit that collects data from sensors and wirelessly transmits the data), an actuation unit (i.e., a unit that calculates control forces and issue commands to the actuators), or a unit for both sensing and actuation. Following figure shows the overall hardware design of the prototype wireless sensing unit and two optional off-board auxiliary modules for conditioning analog sensor signals and generating actuation signals.

Validation Tests of the Wireless Structural Monitoring System
Through collaboration with Prof. Chin-Hsiung Loh's group at National Taiwan University, the prototype wireless monitoring system was instrumented on a half-scale laboratory structure in June 2005. A 6-DOF large-scale shaking table in National Center for Research on Earthquake Engineering (NCREE), Taiwan is used to excite the structure with various ground motions. Data acquisition and onboard computation capabilities of the wireless monitoring system were validated through the tests.



In collaboration with Prof. Chung Bang Yun's group at Korean Advanced Institute of Science and Technology (KAIST), large-scale field validation tests were completed at Geumdang Bridge in Icheon, South Korea. Wireless sensors were deployed along the concrete box girder bridge spanning 122m. The bridge has also been instrumented with a high-quality cable-based monitoring system for baseline validation. Learning from the first bridge test in December 2004, the sensor signal conditioning module was developed. Later test in July 2005 proved that the module greatly improved the data quality for the low-amplitude and noisy vibration signals at the bridge deck.




In March 2006, another field validation test for the wireless structural sensing system was conducted at Voigt Bridge, San Diego, CA, in collaboration with Prof. Ahmed Elgamal's group at the University of California at San Diego. Up to 20 wireless sensing units were employed for the field test. A wire-based system was installed on the bridge, prior to the instrumentation of the wireless sensing system. Comparison of the measurement results from the wired and wireless system is first conducted. With the wireless system conveniently re-deployed to a different configuration, the operating deflection shapes (ODS) of the bridge deck are extracted from the wireless sensor data.

Decentralized Wireless Structural Control
In traditional structural control systems, coaxial wires are normally used to provide communication links between sensors, actuators and controllers. For a large scale structure, wired control systems require high instrumentation cost, are difficult to reconfigure, and potentially suffer from a single-point failure at the controller. With the rapid emergence of wireless communication and embedding computing technologies, a natural extension of the wireless sensing technology is to explore its applicability for semi-active or active control devices by eradicating expensive cable installation and centralized bottleneck associated with traditional control systems.

Traditional Centralized Cabled Control System			Future Decentralized Wireless Control System

In a wireless feedback structural control system, the wireless units not only collect structural response data in real time, but also communicate with other units, make optimal control decisions, and issue commands to structural actuators. Compared with wired control systems, the difficulties faced by a wireless feedback control system include the shorter communication range and longer communication latency. To overcome these constraints of wireless communication, decentralized structural control strategies are being investigated. In the decentralized control system, a controller unit may only require neighborhood sensor data for sub-optimal control decisions. We develop decentralized structural control algorithms for embedment in the wireless units. Experimental tests and numerical simulations have been conducted to verify the performance of the wireless sensing and control system. The tests were conducted in National Center for Research on Earthquake Engineering (NCREE), Taiwan, as a joint effort with Prof. Chin-Hsiung Loh's group at National Taiwan University.

Copyright © 2007, Laboratory for Smart Structural Systems, Georgia Institute of Technology