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with the potential for self-diagnosis and self-calibration capabilities, thus reducing that amount of information
that needs to be transmitted over the network. Indeed, a National Research Council report recently
noted that the use of networked systems of embedded computers and sensors throughout society could
well dwarf all previous milestones in the information revolution.
This paper is comprised of two parts. Part one focuses on two smart damping strategies that have
already been implemented in full-scale civil engineering applications. The first, the variable orifice
damper, has been or is being installed in 11 buildings in Japan. The second smart damping strategy discussed
herein considers magnetorheological (MR) fluid dampers, one of the most promising of the
smart devices. These two classes of smart dampers mesh well with application demands and constraints
to offer an attractive means of protecting civil infrastructure systems against severe earthquake and
wind loading. The second part of the paper is directed toward the future of smart sensors. A brief review
of existing systems is provided, followed by an outline of some of the challenges and opportunities
offered.
VARIABLE-ORIFICE DAMPERS
One means of achieving a smart damping device is to
use a controllable, electromechanical, variable-orifice ^--
valve to alter the resistance to flow of a conventional ^»
hydraulic fluid damper. Such a device, schematically L J
shown in Fig. 2, typically operates on approximately
50 watts of power. The concept of applying this type
Flgure 2> Schematic Of variable-orifice damper
of variable-damping device to control the motion of bridges experiencing seismic motion was first discussed
by Feng and Shinozuka (1990), Kawashima and Unjoh (1993) and Kawashima et al. (1992).
Subsequently, variable-orifice dampers have been studied by Symans et al. (1994) and Symans and
Constantinou (1996) at the Multidisciplinary Center for Earthquake Engineering Research in Buffalo,
New York.
Sack and Patten (1993) conducted experiments in which a hydraulic actuator with a controllable orifice
was implemented in a single-lane model bridge to dissipate the energy induced bv vehicle traffic. These
studies were followed by a full-scale experiment conducted on a bridge on interstate highway 1-35 to
demonstrate this technology (Patten 1998, Patten, et al. 1999; Kuehn et al. 1999) shown in Figs. 3-4.
Figure 5 shows the effectiveness of the SAVA system. This experiment constitutes the only full-scale
implementation of structural control in the USA.
Conceived as a variable-stiffness device, Kobori et al (1993) and Kamagata and Kobori (1994) implemented
a full-scale variable-orifice damper in a semiactive variable-stiffness system (SAVS) to investigate
semiactive control at the Kajima Technical Research Institute. The overall system, shown
schematically in Fig. 6, has SAVS devices installed on both sides of the structure in the longitudinal
direction. The results of these analytical and experimental studies indicate that this device is effective in
reducing structural responses.
More recently, a smart damping system was installed in the Kajima Shizuoka Building in Shizuoka,
Japan. As seen in Fig. 7, semiactive hydraulic dampers are installed inside the walls on both sides of the
building to enable it to be used as a disaster relief base in post-earthquake situations (Kobori, 1998: