GB2034436A - Elastomeric stack spring with viscous or friction damping - Google Patents

Abstract

A resilient mounting having high internal damping comprises a stack of parallel metal sheets having elastomer 53, 69 vulcanized between them and, within the elastomer, at least one chamber filled with energy absorbing material, for example, a viscous fluid, pitch, tar, sand, or visco-elastic elastomer 54. The chamber may include flow guides, or interdigitated plates. The plates may extend in a direction perpendicular to those shown. <IMAGE>

Description

SPECIFICATION Bearing device with high internal shock absorption for constructions The present invention relates to a bearing device having a high internal damping in order to render the structures supported or their foundations less sensitive to the effects of dynamic stresses whatever their origin (strong gusts of wind, braking effect of heavy vehicles) and possibly of earth tremors, par ticularly for structures requiring very high security, such as atomic power stations.

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, 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. They are consequently unsuitable for withstanding the forces of braking or of the wind.

So-called "metal-hooped elastomer" supports are also known which are constituted by a superposition of layers of elastomer separated by steel sheets to which these layers adhere to prevent crushing thereof. Upon a relative lateral displacement of the structure and the foundation, the support undergoes a distortion and its elasticity at least partly prevents the transmission of the horizontal force which provoked the displacement.

Although this known device spontaneously returns the structure and its foundation into mean position, it has the drawback 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 supported.

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.

A bearing device for a structure on its foundation comprising a stack of parallel sheets between which are vulcanized layers of elastic elastomer is, according to the invention, characterised in that spaces are arranged between at least two sheets within the contour of these layers, which spaces are filled at least with a substance capable of absorbing at least a part of the energy which entails its deformation.

Such a substance may be a viscous fluid, such as pitch or tar, or formed by angular particles such as sand, absorbing the energy in a closed volume by internal friction and friction against the walls of this volume. Grains of this type may also be included in a viscous substance.

This substance is preferably a visco-elastic elastomer having a high internal damping and compatible, chemically and with regard to vulcanization, with the elastic elastomer.

Such known elastomers having a high creeping under pressures such that pressure exerted by the structure on its foundation, cannot be used alone between the parallel sheets. However, their confinement between the sheets and the elastic elastomer which surrounds them enables their property of damping to be fully utilized without risk of creeping.

The spaces made inside the layers of elastic elastomer may also extend through the reinforcing sheets, i.e. may constitute cavities inside the bearing device.

Within the contour of each layer of elastomer, the spaces receiving the damping substance may have any contour; the contour may in particular be circular and multiple, thus defining sorts of pellets of the substance absorbing the energy.

In each layer of elastic elastomer, the contour of the space receiving the absorbent substance is preferably parallel to that of said elastomer and, preferably still, similar thereto.

By giving, in each layer, the two respectively elastic and visco-elastic elastomers adjacent surfaces, without this being a limiting choice, a bearing device is obtained of which the internal damping may be two to four times that of a similar conventional device comprising only elastic elastomer.

Moreover, bearings comprising a damping substance of the viscous or visco-elastic type have a rigidity in distortion which is a function of the speed of the deformations imposed; this rigidity is the greater as the phenomena are more rapid. Thus, such bearings supporting structures oppose a considerable rigidity against the action of the braking of heavy vehicles or strong gusts of wind, then limiting the displacement of these structures, whilst they lend themselves flexibly to the slow thermo-hygrometric actions avoiding the high stresses in the structure.

By the US Patent 3 920 231 and the Dutch Patent application 77 12269 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 assembly acting as a spring use is made of the liquid incompressibility for limiting distortion of said spring and stiffening the same. Howeverthe liquid used is unable 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.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings, in which: 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 vertical section of a variant embodiment of that shown in Figs. 1 and 2.

Fig. 4 shows a variant of Fig. 3 in partly enlarged section.

Fig. 5 shows another variant in axial vertical section.

Fig. 6 is a partial plan view of the embodimen shown in Fig. 5.

Figs, 7 and 8 are vertical sections of two variant embodiments of bearings according to the invention.

Referring nowt 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 eitherthe forward movement or the return movement of the structure, according to the invention, pellets 3 are housed in the layers of elastomer. Such pellets may be made of sand composed of angular grains agglomerated by a highly viscous substance such as pitch, or solid but easily deformable or destructible. A relative displacement 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 the 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" assuming that the maximum horizontal displacement of one sheet with respect to the other is equal to the thickness of 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 four 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.

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 from the space which contracts towards the one which expands.

In order to increase this effect of braking by circu lation of the viscous liquid (Fig. 4), two sets of concentric frames (or rings) 41 and 42 may be alternately fixed to two consecutive or non-consecutive sheets 33 or to the end sheets 31 and 32, the intermediate sheets 33 then being hollowed at their centre. 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 expaned parts.

The bearing shown in Fig. 3 may also be made in two parts, namely the annular peripheral part made in a vulcanization mould 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 boxshaped 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 diameters. These discs are surrounded by a cylindrical ring 70 made of two separate halves joined at70a 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 precedingiy filled with very viscous liquid 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 dash 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 effect only due 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 elastomer 54 with a high internal damping is entirely surrounded by the elastomer 53 with elastic behaviour, is capable of mobility in all directions of the plane of the reinforcing sheets. To limit this mobility, in at least one direction between the support and the structure supported, resisting stops suitable for the forces encountered may be provided.

The shape of the bearings in plan (rectangular, square, circular, even annular with two elastic rings surrounding a plastic ring) depends on the shape and the mass of the structure supported.

Claims (13)

1. A bearing device interposed between a struc to rue and its foundation, comprising a stack of parallel metal sheets between which are vulcanized layers of elastic elastomer without creeping, wherein spaces are arranged between two sheets, at least within the contour of these layers, said spaces filled at least with a substance capable of absorbing at least a part of the energy which provokes its deformation.

2. A device as claimed in Claim 1, wherein the filling substance is a viscous fluid.

3. A device as claimed in Claim 1, wherein the filling substance comprises agglomerated solid grains.

4. A device as claimed in Claims 1 and 2, wherein said space is provided with solid elements provoking, by laminating, the deformation of the viscous fluid.

5. A device as claimed in Claims 1 and 2, wherein the opposite sheets limiting the space enclosing the viscous fluid are fast with solid elements provoking, by relative displacement, a circulation of the said fluid.

6. A device as claimed in Claim 5, wherein the solid elements are in the form of concentric closed contours alternately fast with the opposite sheets.

7. A device as claimed in Claim 4, wherein the solid elements are plates parallel to the sheets and alternately fast, on the one hand, with one of the two sheets closing the space enclosing the viscous fluid and on the other hand, with the peripheral wall of said space wall made of the stack of sheets and elastomer layers.

8. A device according to claim 7, wherein the said space is a cylindrical cavity closed by a lid having a boss carrying a plurality of staggered flat concentric discs which are intercalated between flat half-rings the periphery of which is supported by two elastic half-cylinders adapted to the diameter of said cylindrical cavity.

9. A device as claimed in Claim 1, wherein the filling substance is a vulcanized visco-elastic elastomer adhering to the sheets in the same manner as the elastic elastomer.

10. A device as claimed in Claim 9, wherein each layer of elastic elastomer makes at least one closed space enclosing the visco-elastic elastomer.

11. A device as claimed in Claim 8, wherein each closed space being unique, its contour is parallel to the outer contour of the elastic elastomer of the layer.

12. A device as claimed in Claim 9, wherein the intermediate sheets are coated laterally by the elastic elastomer.

13. A device as claimed in Claim 9, wherein the mobility parallel to the planes of the sheets is limited in one direction by at least one stop.