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sensors. New algorithms must be developed that can utilize the smart sensor's on-board processor to
deal with the large amount of data that will be generated by a monitoring system employing a dense
array of sensors. Additionally, eliminating redundant information from neighboring sensors may be
necessary. Such an approach reduces that amount of information that needs to be transmitted over the
network. To date an appropriate framework on which to build structural health monitoring and control
strategies does not exist. Other critical issues include errors in synchronization of on-board clocks
among sensors, delays in transmission due packet collisions (20-30% of the data packets can be lost),
short transmission range, inability to simultaneously transmit and acquire data, and limited memory
capabilities.
CONCLUSIONS
This paper provides an update of smart structures technology, including both smart dampers and smart
sensors. Although in their infancy, control strategies based on smart damping devices appear to cornbine
the best features of both passive and active control systems and to offer a viable means of protecting
civil engineering structural systems against earthquake and wind loading. In particular, they provide
the reliability and fail-safe character of passive devices, yet possess the adaptability of fully active
devices. Full-scale implementations for two smart damping systems were presented. The variable orifice
damper has been or is being installed in 11 buildings in Japan. Magnetorheological (MR) fluid
dampers have been installed last year in a building in Japan and on a bridge in China. These two classes
of smart dampers have been shown to mesh well with application demands and constraints to offer an
attractive means of protecting civil infrastructure systems against severe earthquake and wind loading.
To investigate both local and global damage criteria, a dense array of sensors is anticipated to be
required for large civil engineering structures. Rapid advances in sensor, wireless communication,
Micro Electro Mechanical Systems (MEMS), and information technologies have the potential to significantly
impact structural health monitoring. The emerging technology of smart sensors, allows a portion
of the computation to be done locally on the sensor's embedded microprocessor. This paper presented
the basic ideas behind smart sensors, some of units developed to date, and indicated certain needs to
takes advantages of smart sensors for structural health monitoring. The Berkeley-Mote smart sensors
are an open hardware/software platform that will provide the impetus for the development of the next
generation of structural health monitoring and control systems.
ACKNOWLEDGMENT
The author gratefully acknowledges the partial support of this research by the National Science Foundation
under grant CMS 99-00234 (Dr. S.C. Liu, Program Director) and the Lord Corporation. The author
would also like to thank Dr. Takuji Kobori for providing the information and photographs regarding the
full-scale implementation of semi-active hydraulic dampers by the Kajima Corporation and thank Dr.
Y.Q. Ni for providing the photographs regarding the full-scale implementation of MR dampers on the
Dongting Lake Bridge.