NSF PR 98-48 - September 19, 1998
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ENGINEERS DESIGNING SMART BUILDINGS TO REACT TO SHAKES
AND QUAKES
Earthquakes, windstorms, traffic and explosives cause
motion that can be catastrophic to buildings or bridges.
National Science Foundation (NSF)-funded engineers
Billie Spencer Jr. and Michael Sain at the University
of Notre Dame are designing systems that counteract
damaging structural responses to such events. These
"smart buildings" adjust to changing conditions without
requiring massive amounts of energy to do so.
"This type of research is important because it pioneers
a novel concept for the optimal performance and safety
design of buildings and other civil infrastructures,
particularly those under the threat of earthquakes
and other natural hazards," said Chi Liu, National
Science Foundation program manager.
Acts of nature, terrorism or even traffic create ever-changing
forces on most structures. Buildings rely primarily
on strong materials and a structure that dissipates
energy to resist damage. Increasingly, though, mechanical
means are being explored.
Traditionally, buildings are built to sustain damage
in order to survive during severe earthquakes, according
to Spencer. "You wouldn't want that in your car --
for it to break every time you go over a pothole."
To prevent such damage, manufacturers put shock absorbers
in the suspension of automobiles to dampen the effect
of thumps and bumps. Engineers are using the same
concept, to design shock absorbers for buildings.
However, the best systems must adapt quickly to change.
"When controlling buildings during non-critical times,
you want to have the dampers soft so there are no
jerky movements, which helps protect the contents.
But during an earthquake you want increased damping,"
Spencer said. In other words, during stable periods,
building designers seek the soft, cushy, boat-like
ride of a luxury car, but during a catastrophic event,
they seek the tight-suspension control of a sports
car.
The shock absorber Spencer and Sain are developing
for use in buildings relies on the same premise as
the shock absorber most used in cars with a piston
in an air- or fluid-filled cavity. Unlike your car,
however, the associated damping forces can be automatically
adjusted.
Spencer and Sain's shock absorber uses an oil suspension
of tiny iron particles. The viscosity of the fluid
-- and the magnitude of the damping effect -- can
be modulated by creating a magnetic field.
"The fluid is like water or a light oil, but when
it is in the presence of a magnetic field it becomes
thick like pudding," Spencer said. Sensors in the
building can determine -- in real time -- the way
the building is moving and modulate the damping forces
on a series of the smart shock absorbers.
Another important feature of Spencer and Sain's system
is that it requires very little power; each shock
absorber requires only about 50 watts. The system
could easily run on batteries, especially important
during earthquakes where power is frequently interrupted.
In tests, a three-story structure exposed to the same
forces as the 1940 El Centro earthquake showed that
the magnetically adjusted shock absorber was much
more effective than, for example, a shock absorber
without any on-line provision for adjustment. The
magnetically controlled damper reduced the peak effect
of horizontal displacement and acceleration on the
third floor by almost 75 percent and 50 percent, respectively.
The displacement relates directly to the health of
the building - if it is too large, the building may
not return to its normal shape. The acceleration,
on the other hand, relates to the protection and comfort
of building occupants - forces which are felt by persons
and which can be tolerated by expensive equipment.
Spencer and Sain are working with Lord Corporation
to develop the details of the technology. They presented
their work at several international conferences this
past summer.
Editors: For more information, see: http://www.nd.edu/~quake/
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