Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BEARING DEVICE WITH HIGH INTERNAL
DAMPING FOR CONSTRUCTIONS
TECHNICAL F]ELD
The present invention relat;es to a bearing device
having a high internal damping in order to render the
structures supported or their foundations less sensi~
tive to the effects of dynamic stresses whatever their
origin (strong gusts of wind, braking effect of heavy
vehicles) and possibly of earth tremors, particularly
for structures requiring very high security, such as
atomic power stations.
BACKGROUND ART
To reduce the destructive effect of earth tremors,
bearing devices have already been proposed which allow
the supported structure to slide with respect to its
foundation when the stress exceeds a certain threshold.
Bearing devices are also known whereby viscous
materials are forced between parallel plates, when
subject to stress.
The drawback of such devices is that, for example
in the case of an earth tremor, the structure is moved
and must be returned into position, for example with
the aid of jacks, since these devices do not comprise
return means for returning the structure and its founda-
tion into mean position. They are consequently unsuit-
able for withstanding the forces of braking or of the
wind.
So-called "metal hooped elastomer" supports are
also known which constitute a superposition of layers
of elastomer separated by steel sheets to which these
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layers adhere to prevent crushing thereof. Upon a relative lateral
displacement of the structure and the foundation, the support under-
goes a distortion and its elasticity at least partly prevents the
transmission of the horizontal force which provoked the displace-
ment.
Although this known device spontaneously returns the
structure and its foundation into mean position, it has the draw-
back of a low damping effect. In the case of successive tremors,
an accumulation of energy is produced in the elastomer and, by the
effect of resonance or "see-saw" effect, the force transmitted
may increase until the structure is ruined. In fact, experience
has shown that the broad spectrum of the earth tremors includes
the proper oscillation frequency or frequencies of the structure
support~d.
SUMMA~Y OF INVENTION
The invention enables the effect of damping of the sudden
stresses to be associated with the effect of return to a mean
position in the bearing connection between a structure and its
foundation.
According to one aspect of the invention there is pro-
vided a bearing device interposed between a structure and its
foundation comprising a continuous upper plate and a continuous
lower plate respectively contacting said structure and foundation;
a stack of spaced apart parallel continuous metal sheets between
and spaced apart from said plates; and a further stack of layers
each comprising a central visco-elastic elastomer and a peripheral
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strictly elastic elastomer sandwiched between and vulcanized to
said plates and sheets for tight adherence thereto.
According to another aspect of the invention there is
provided a bearing device interposecl between a structure and its
foundation comprising a continuous upper plate and a continuous
lower plate respectively contacting said structure and foundation;
a stack of spaced apart parallel metal sheets between and spaced
apart from said plates; a further stack of layers of elastic
elastomer sandwiched between and vulcanized to said plates and
sheets for tight adherence thereto, each of said layers having at
least one aperture therewithin; a filling of the spaces internally
comprised in the apertures of said layers, said filling comprising
a viscous fluid capable of absorbing, by shearing and lamination,
at least part of the energy provoking its deformation; and includ-
ing an intermediate flat plate disposed in each of said apertures,
said intermediate flat plates having beveled side edges, there
being a narrow gap between one of the faces of said intermediate
flat plates and the respective adjacent ones of said sheets and
upper and lower plates, and a peripheral channel between said
beveled side edges of said intermediate flat plates and the
respective adjacent walls of said apertures.
According to a further aspect of the invention there is
provided a bearing device interposed between a structure and its
foundation comprising a continuous upper plate and a continuous
lower plate respectively contacting said structure and foundation;
a stack of spaced apart parallel metal sheets between and spaced
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apart from said plates; a further stack of layers of elastic
elastomer sandwiched between and vulcanized to said plates and
sheets for tight adherence thereto, each of said layers having at
least one aperture therewithin; a filling of the spaces internally
comprised in the apertures of said layers, said filling comprising
a viscous fluid capable of absorbing, by shearing and lamination,
at least part of the energy provo]cing its deformation; and wherein
each of said metal sheets has at least one aperture therewithin,
said apertures in said layers and sheets being superposed upon
each other to form a cavity; and including a third stack of spaced
apart parallel plates disposed in said cavity between and spaced
apart from said upper and lower plates, said plates of said third
stack being fastened alternately to one of said upper and lower
plates and the sidewalls of said cavity, said viscous fluid filling
the spaces internally comprised in said cavity~
According to yet another aspect of the invention there
is provided a bearing device interposed between a structure and its
foundation comprising a continuous upper plate and a continuous
lower plate respectively contacting said structure and foundation;
a stack of spaced apart parallel metal sheets between and spaced
apart from said plates; a further stack of layers of elastic
elastomer sandwiched between and vulcanized to said plates and
sheets for tight adherence thereto, each of said layers having at
least one aperture therewithin; a filling of the spaces internally
comprised in the apertures of said layers, said filling comprising
a viscous fluid capable of absorbing, by shearing and lamination,
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at least part of the energy provoking its deformation; and includ-
ing circulation means affixed to the plates and sheets disposed
on the upper and lower ends of said apertures which limit the
spaces enclosing said viscous fluid for provoking, by relative
displacement of said plates and sheets, a circulation of said
viscous fluid.
According to a still further aspect of the invention
there is provided a bearing device interposed between a structure
and its earth foundation, comprising: a stack of parallel, con-
tinuous and coextensive metal sheets; annular layers of elasticelastomer at least coextensive with said metal sheets, each
annular layer being interposed between and vulcanized to two of
said metal sheets for tight adherence thereto; and layers of
viscoelastic elastomer of the same thickness as said annular layers,
each of said layers of viscoelastic elastomer being interposed
between and vulcanized to two of said metal sheets for tight
adherence thereto and filling the apertures of said annular layers,
whereby said annular layers of elastic elastomer prevent creeping
of said layers of viscoelastic elastomer and said layers of visco-
elastic elastomer absorb at least part of the energy provokingdistortion of the device.
By the United ~tates Patent 3,920,231 assemblies are
known which comprise capacities each made of a superposition of
annular elastomer layers and steel sheets closed by metal plates
and filled with a more or less viscous liquid. In such an
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assembly acting as a spring use is made of the liquid incompress-
ibility for limiting distortion of said spring and stiffening
the same. However the liquid used is incapable of internal
damping. On the contrary in the present invention owing to high
viscosity of the matters used a spring damping effect is obtained
which is all the more large as the distortion speed of the spring
is high.
BRIEF DESCRIPTION OF DRAWINGS
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The invention will be more readily understood on reading
the following description with reference to the accompanying
drawings, in which:
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Fig. 1 is a view in perspective of an element of a
first embodiment of the invention.
Fig. 2 is a section along the plane II of Fig. 1.
Fig. 3 is a view in vertic:al section of a variant
embodiment of that shown in Fiqs. 1 and 2.
~ ig. 4 shows a variant of Fig. 3 in partly en-
larged section.
Fig. 5 shows another variant in axial vertical
section.
Fig. 6 is a partial plan view of the embodiment
shown in Fig. 5.
Figs. 7 and 8 are vertical sections of -two ~ariant
embodiments of bearings according to the invention.
BEST MODE OF CARRYING OUT THE INVENTION
Referring now to the drawings, Figs. 1 and 2 show
superposed sheets 1 which are connected together in
manner known per se by layers of elastic elastomer 2
vulcanized against the opposite faces of these sheets.
The elastomer being flexible, i.e. having a low
coefficient of elasticity, the lower sheet resting on a
foundation and the upper sheet supporting a structure,
said latter may move horizontally in any direction over
a distance corresponding to about the height of the
stack. After displacement, the elastomer assures the
return of the structure to its original position.
To dampen either the forward movement or the
return movement of the structure, according to the
invention, pellets 3 are housed in the layers of elas-
tomer. Such pellets may be made of sand composed of
angular grains agglomerated by a highly viscous sub-
stance such as pitch, or solid but easily deformable or
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destructible. A relative disp:Lacement of the sheets is
thus braked by the friction inside the pellets of the
grains against one another and by the external friction
of the superficial grains against -the faces of the
sheets.
In the embodiment shown in Fig. 3, the structure 4
rests on its foundation 5 via t:he stack 6. The latter
comprises, between the thick end sheets 31 and 32,
respectively connected to the structure and to the
foundation, a stack of thinner sheets 33 and of layers
of elastomer 34 hollowed out to form the superposed
spaces 35 in their central zone.
These spaces may be of any contour, preferably
parallel to that of the bearing, which is generally
circular or rectangular.
Each cavity contains a plate 36 of which the edges
36a are bevelled to 45 D assuming that the maximum
horizontal displacement of one sheet with respect to
the other is e~ual to the thickness o the layer of
elastomer. The spaces existing in each cavity are
filled with pitch (in liquid hot condition), or other
highly viscous matter, via tubes 37 and 38 (the former
for filling, the latter for evacuation of air~ and
channels 39 and 40 pierced in the sheets 33 and plates
36. At the manufacturing stage, these spaces may also
be filled with an elastomer of suitable composition
without any vulcanizing substance, so that it remains
visco-elastic whilst the layers 34 containing the
vulcanizing substance adhere to the sheets 33 as well
as 31 and 32.
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In such an embodiment, the damping by friction is
produced on the one hand in the narrow gaps 44 between
the upper face of the plates 36 and the lower faces of
the sheets, and on the other hand, in the peripheral
channel 40 of each cavity, under the action of the flow
of the viscous matter, passing upon a distortion of the
bearing ~rom the space which contracts towards the one
which expands.
In order to increase this effect of braking by
circulation of the viscous liquid (Fig. 4), two sets of
concentric frames (or rings) 41 and 42 may be alter-
nately fixed to two consecutive or non-consecutive
sheets 33 or to the end sheets 31 and 32, the intermed-
iate sheets 33 then being hollowed at the center.
Annular conduits 43 are thus arranged in cavities
inside the bearing, which conduits, upon distortions of
said bearing, drive the viscous matter from their
contracted parts towards their expanded parts.
The bearing shown in Fig. 3 may also be made in
two parts, namely the annular peripheral part made in a
vulcanization mold and the central part constructed in
the central space of this peripheral part between the
end closing sheets 31 and 32.
The embodiment shown by Figs. 5 and 6 is box-shaped
and comprises a bottom 57, an upper wall 58 having a
central circular aperture and a lateral wall made of
intermediate sheets 59 embedded in elastic elastomer
69.
The inner cylindrical cavity is closed by a lid 60
having a central downwardly directed boss 61 fast with
concentric plat discs 62,63,64 having decreasing dia-
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meters. These discs are surrounded by a cylindrical
ring 70 made o~ two separate halves joined at 70a and
each embedding the flat half-rings 65 and 66, the inner
diameter of the second being larger than the one of the
former. Owing to a hole 67 pierced in the lid 60 (and
an air escape not shown) the cylindrical cavity is as
preceedingly filled with very viscous li~uid such as
pitch.
In use, when, under action of a lateral force, by
distortion of the elastomers 69 and 70, the whole is
distorted, as schematized by the dashed and dotted line
68, the high viscous matter included between the discs
62, 63, 64 and the half-rings 65 and 66 is squeezed and
sheared what largely increases the damping ef~ect only
du~ to viscosity.
In Fig. 7, intermediate sheets 52 are distributed
between the end reinforcing sheets 51. Two consecutive
sheets are separated by a thin layer of elastomer: a
peripheral part 53 is made of elastic elastomer having
a relatively low damping and an inner part 54 made of
visco-elastic elastomer with high internal damping,
which the elastomer 53 prevents from creeping between
the sheets which imprison it. In the case of Fig. 8,
the first elastomer 53 coats the intermediate sheets,
this protecting them and further reducing the risks of
creeping of the elastomer 54.
Finally, such an embodiment, in which the elasto-
mer 54 with a high internal damping is entirely sur-
rounded by the elastomer 53 with elastic behavior, is
capable of mobility in all directions of the plane of
the reinforcing sheets. To limit this mobility, in at
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least one direction between the support and the structure supported,
resisting stops suitable for the forces encolmtered may be provided.
~ he shape of the bearings in plan (rectangular, square,
circular, even annular with two elastïc rings surrounding a plastic
ring? depends on the shape and the mass of the structure supported.
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