Earthquake Engineering Research - HKU Libraries - The University ...

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Observation
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Figure 1. Kyobashi Seiwa Building with AMD Installation.
One of the most promising new methods for
protecting civil infrastructure systems is
found in smart damping (also known as
semiactive control) systems. These systems
offer the reliability of passive devices, yet
maintain the versatility and adaptability of
fully active systems without requiring the
associated large power sources. In fact,
many can operate on battery power, which is
critical during seismic events when the main
power source to the structure may fail.
According to presently accepted definitions,
a smart damping device is one which cannot
inject mechanical energy into the controlled
structural system (i.e., including the structure
and the control device), but has properties
that can be controlled to optimally reduce the responses of the system. Therefore, in contrast to
active control devices, smart damping devices do not have the potential to destabilize (in the bounded
input/bounded output sense) the structural system. Studies have shown that appropriately implemented
smart damping systems perform significantly better than passive devices and have the potential to
achieve, or even surpass, the performance of fully active systems, thus allowing for the possibility of
effective response reduction during a wide array of dynamic loading conditions (Dyke et al. 1998;
Spencer et al. 2000). Examples of such devices include variable-orifice fluid dampers, controllable friction
devices, variable stiffness devices, adjustable tuned liquid dampers, and controllable fluid dampers
(Spencer and Sain 1997).
In addition to being adaptable, smart structures can have the possibility of using their sensors to become
self-monitoring. The ability to continuously monitor the integrity of structures in real-time can provide
for increased safety to the public, particularly for the aging structures in widespread use today. Detecting
damage at an early stage can reduce the costs and down-time associated with repair of critical damage.
Observing and/or predicting the onset of dangerous structural behavior, such as flutter in bridges,
can allow for advance warning of such behavior and commencement of mitigating control or removal
of the structure from service for the protection of human life. In addition to monitoring long-term degradation,
assessment of structural integrity after catastrophic events, such as earthquakes, hurricanes, tornados,
or fires, is vital. These assessments can be a significant expense (both in time and money), as
was seen after the 1994 Northridge earthquake with the shear number of buildings that needed to have
the moment-resisting connections inspected. Additionally, structures internally, but not obviously, damaged
in an earthquake may be in great danger of collapse during aftershocks; structural integrity assessment
can help to identify such structures to enable evacuation of building occupants and contents prior
to aftershocks. Furthermore, after natural disasters, it is imperative that emergency facilities and evacuation
routes, including bridges and highways, be assessed for safety. However, a significant number of
sensors are required to efficaciously monitoring of civil infrastructure systems.
Recent advances in sensors, wireless communication, MEMS, and information technologies have made the
dream of inexpensive, powerful, ubiquitous sensing for structural health monitoring a readily achievable
near-term goal. To assist in dealing with the large amount of data that is generated by such a dense
array of sensors, on-board processing at the sensor level allows a portion of the computation to be done
locally on the sensor's embedded microprocessor. Such an approach provides for an adaptable, smart sensor,