Note: Descriptions are shown in the official language in which they were submitted.
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SEALED ~kS:~u~ SE:ISMIC ISOLATOR
The invention presented herein is a device for lessening
the destructive forces transmittable to buildings, structures,
or heavy equipment during earthquakes. The outstanding
features of the device are in its simplicity, versatility,
reliability, low costs, and being virtually maintenance-free.
It is suitable to be used for practically all types of
buildings, including family homes, commercial and apartment
buildings, and power generation stations.
As in all existing seismic isolation schemes, a super-
structure is founded on an Upper Foundation Mat. The Sealed
Pressure Seismic Isolator works by sealing of f the Isolator
Gallery, which is the space between the Upper and Lower
Foundation Mats, and then pressurizing it. The net uplift
pressure reduces the downward loads and, in turn, the
frictional forces at the base plates.
In the drawings which illustrate ~ ts of the
invention, Figures 1 and 2 illustrate the setup for a family
home and for an industrial plant, respectively. Figures 3, 4
and 5 show a variety of base att~, L.
In Figure 1, the house is founded on the Upper Foundation
Mat 1, and then onto the Exterior Curtain Wall 2 which
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encloses the entire Isolator Gallery and is anchored to the
Short Base Plate 4. The Long Base Plate 5 is supported by
the Lower Foundation Mat 6 which may have a water-proof surface
or cover.
A Pressure Seal 3 is attached to the Short Base Plate to seal
off the gap from the Long Base Plate. This Seal comprises a
pressurizing hose which, when inf lated, undergoes a vertical
expansion and presses against the rubber seal. Interior walls
or pillars 7 are added where required.
In Figure 2, the Isolator Gallery of an industrial plant
is shown to be compartmentalized into pressure chambers, with
the high water pressure at the central zone 1 being stepped
down to a medium-low pressure zone. Interior curtain walls 5
enclose the entire central zone. Water at atmospheric
pressure is maintained outside the exterior curtain walls 6,
which enclose the edges of the foundation mat, thereby forming
a natural pressure seal to the pres6urized system.
The non-symmetric heavy load situated directly above zone
2 in Figure 2 is counteracted by a medium-high pressure zone 2.
The aim is to brin~ the net weight in zone 2 down to a value
similar to that found in zone 3. This is an important feature
of the present invention. It reduces the torsional in-plane
rotation of the Upper Foundation Mat as augmented by asymmetric
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loads . SUCh 21 roiation causes excessive displ ~, at the
corners of the mat and often leads to failure.
Figures 3, 4 and 5 identify different att~ Ls at the
base plates. In Figure 3, an rubber pad 6 is embedded in
between the Short Base Plate 4 and the Long Base Plate 5 to
increase the resilience in the vertical direction. Pressure
Seal 3 is affixed to Base Plate 4.
In Figure 4, a group of hard or flexible rollers 6 are
inserted between the base plates 4 and 5, thereby reducing
further the frictional force. The use of ball-bearing
rollers under dynamic seismic condition is acceptable when the
structural weights have already been reduced by the uplifting,
sealed pressures.
In Figure 5, a rubber pad 6 is cdded in an assembly
formed by a pair of Short Base Plates 4. A group of rollers 7
is inserted above the ~ong Base Plate 5. This system has
added resilience for attenuating vertical shocks, and has extra
low frictional force to facilitate ~i Ls in the horizontal
direction .
Pressurization of the sealed pressure chambers may be
achieved by elevated water tanks, as shown in Figures 1 and 2,
and/or by cylinders of compressed air, all connected to the
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Isolator Gallery.
Pressurization may al90 be designed to be triggered by the
initial motions of an earthquake, which as a rule requires a
few seconds before reaching its destructive peak motion.
These initial motions can activate a motor or valve, or
possibly a detonation of a small charge, all for the purpose of
allowing water to flow from the tanks to the Isolator Gallery.
Nominally low pressures only, even at zero value, may then be
maintained on a regular basis at the underside of the Upper
Foundation Mat. This will lessen leakage, if any, in the
ple62~uLized system.
Even without such automatic activation devices, the full
hydrostatic pressure required for constant seismic isolation is
merely 4 to 8 psig, which is low comparing even to the ordinary
household water supply at the 50 to 60 psig range. Leakage,
if any, will be negligible.
~ ince maintenance is hardly re~uired, the Isolator Gallery
for homes and ordinary buildings may be reduced in height to a
crawl-space, or less, for further savings.
In a sealed pressure system, the pressurizing f luid may be
water, gas, any other liquid, or any cornbination thereof.
Also, all Long Base Plates may be attached to the top of the
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Lower Foundation Mat, or attached to the bottom oi~ the Upper
Foundation Mat, as desired.
The use of the present invention eliminates the need for
expensive alternatives such as the Elastomeric Bearings with
low-friction sliding plates as used by the French for the
Roeberg Nuclear Plants in South Africa.
The Koeberg-type low frictional force is readily and
;nPl~rpnF:ively achieved by the present invention. With the
structural weights being reduced by the uplifts at the pressure
chambers, the resulting frictional forces at the base plates
will be equivalent to those produced by the full weight under a
low coefficient of friction.
The present invention is based on the physical fact that
in a seismically isolated system it is the base shear, not the
structural mass, which detprmi neR the dynamic response. An
earthquake simply cannot transmit more force to a structure
than through the base shear, which is the friction force
itself. Therefore, there exists a one-to-one correlation
between the effective friction force and the horizontal seismic
dynamic force transmittable to the superstructure, regardless
of mass.
The pressuri~ed chambers will also act as giant shock
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ab~orbers for seismic vibrations in the vertical direction.
Downward shocks would cause bleeding of the pressurized liquid
and a momentary increase of the sealed uplift pressures, which
cancel out the downward shock. Likewise, upward shocks would
create a partial vacuum or momentary de-pressurization, which
restores the weight and thereby cancels out the vertical
acceleration .
Non-uniform horizontal translations would still occur in a
symmetrical plant layout, as asymmetric loads would result from
overturning or rocking motions caused by shocks in the
orthogonal horizontal direction. The present invention, being
self-ad~usting for vertical shocks, safely resolves this major
and thorny problem.
For achieving a low, basic friction for use with the
present invention, base plates may be made of low friction
material such as graphite, bronze, oxide-filmed steel, or steel
plates lubricated by powered mica, etc.
The distinguishing features of the Sealed Pressure
Seismic Isolator may be summarized as follows:
1) Attenuating Horizontal Vibrations. The upward pressures
exerted by the pressure chambers reduce the downward loads,
effectively achieving an equivalence of a low friction
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coefficient at the bearing plates.
2) Being effective for earthquakes of all magnitudes. It may
start from a ground horizontal motion of 596 g (gravitational
acceleration) or lower. In contrastr the low-friction steel
plates start to function only at a 20~ g, at which point most
homes would have collapsed.
3 ) Low Costs . They are merely small fraction6 of those of
low-friction plates. This enables seismic isolation to become
an affordable household feature.
4 ) Attenuating Vertical Vibrations . The pressure chambers
act as shock absorbers f or vertical shocks through momentary
pressurization or de-pressurization. It is especially
effective for counteracting localized vertical shocks induced
by orthogonal rocking motions.
5) Reducing Risks of Torsion in Asymmetric Plants. The
upward pressure of a pressurlzed chamber placed underneath an
asymmetric heavy weight would reduce the torsional moment
produced by the said weight, thus minim; ~ing the dangerous
horizontal rotation of the mat.
6) Re-centering of Plant after a Major Earthquake. By a
moderate increase of the sealed pressures to counteract most of
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the structural weight, re-centering is readily performed
through lateral jacking. Without such a re-centering, most of
the connecting pipes etc. will be very much failure-prone after
being locked in permanently displaced configurations by an
earthquake .
7) Safety for After-shocks. Most major earthquakes world-
wide had severe after-shocks. A sliding plate seismic
isolator may fail in an after-shock, when the Upper Foundation
mat has already been badly misplaced and rotated under the main
quake. The present invention will avoid such failure through
an immediate re-centering.
8) Secure Scheduling. Expensive construction delays are
avoided by using the present invention: manufacturers are
plentiful; material sources are local; manufacturing processes
are simple; special acceptance tests are not required; delivery
is immediate; and the installation is straight-forward and does
not require special tools.
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