GB2122276A

GB2122276A - Improvements in bearings for structures

Info

Publication number: GB2122276A
Application number: GB08319851A
Authority: GB
Inventors: Edward Robert Fyfe
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-06-09
Filing date: 1983-07-22
Publication date: 1984-01-11
Also published as: GB8319851D0; GB2122276B; GB2099932A; GB2099932B; CA1186359A

Abstract

A bearing for supporting a structure such as a bridge from a pier or embankment has, for accommodating misalignment of the bearing with the expected direction of longitudinal movement of the structure and/or non- linear movement such as may occur with a curved bridge, includes two plate members (10, 16) which have between them a layer of resilient material (14) and a layer 52 of low-friction material which accommodates vertical, horizontal, rotating and tilting forces between the two members, a further layer of low friction material (32) being interposed between the plate 16 and a plate member (26) which is secured to the bridge, to accommodate longitudinal movement. <IMAGE>

Description

1 GB 2 122 276 A 1

SPECIFICATION

Improvements in bearings for structures The present invention is concerned with improve- 70 ments in or relating to bearings for structures, such as bridges and elevated roadways.

My prior US patent specifications Serial Nos: 3 806

975 and 3 921240 disclose and claim a high load structural bearing which includes a layer of an elastomer between two parallel plates to accommo date vertical, horizontal, tilting and rotation forces applied to the bearing by the structure which it supports. Excessive horizontal shear forces applied to the elastomer layer are resisted by a shear restricting element, while expected horizontal longi tudinal movements of the supported structure are accommodated by sliding movement that takes place between two bearing members arranged for this purpose. These bearings have now obtained complete engineering and commercial acceptance, and are used extensively in many different kinds of structures, principally bridges and elevated road ways.

While such a bearing is being installed it is 90 essential that the direction of sliding which it is designed to permit be aligned accurately with the expected direction of movement of the supported structure, since otherwise there is a danger that excessive sideways forces, sufficient to cause binding of the sliding members, will be applied to the bearing. Even when the installation is performed by skilled and conscientious operators there is a danger of misalignment occuring, for example while the surrounding cement is being poured if the bearing is not held rigidly in position during the operation.

In recent years the designers of bridge structures and the like have become more venturesome in curving the structures for both practial and aesthetic reasons, and are attempting designs with an amount and/or degree of curvature that would not previously have been corntemplated. This has placed a requirement on the bearings to accommodate the resulting nonlinear movements of the structure, e.g. with temperature changes. Moreover, it is difficult to predict in practice with any degree of accuracy the average direction of such movements, adding to the above-mentioned difficulty of ensuring that the bearing has been installed with the optimum align- ment for free sliding.

It is therefore an object of the invention to provide a new bearing for structures able to accommodate a degree of misalignment that would damage or disable a prior art bearing.

In accordance with the present invention there is' provided a supporting bearing for the support of a structure such as a bridge or elevated roadway, the bearing comprising a plate member on which the structure rests for supportthereby; another plate member; a layer of resilient material interposed between the first-mentioned and another plate member and supporting the latter from the former for vertical, horizontal, tilting and rotational movements; and 130 a layer of low-friction material interposed between the first-mentioned plate and the layer of resilient material to facilitate movement of the firstmentioned plate relative to the layer of resilient material upon application of horizontal misalignment forces thereto.

Particular preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings,wherein:- Figure 1 is a plan view of a first embodiment, parts thereof being broken away as necessary to show the construction thereof; Figure 2 is a section taken on the line 2-2 of Figure 1; Figure 3 is a section taken on the line 3-3 of Figure 1; Figure 4 is a section similar to Figure 2 of a second embodiment; Figure 5 is a section similar to Figure 2 of a third embodiment; Figure 6 is a cross-section of a small portion of a guide means of the structure of any of Figures 1-5 to show a modifiation; and Figure 7 is a similar cross-section to Figure 6 of another modification.

Referring nowto Figures 1 to 3 a first embodiment particularly suitable for use as a bridge bearing consists of a lower plate 10, usually of circular shape in plane. The plate usually is embedded in the concrete work (not shown) of the bridge structure and is provided with a single axially-disposed, downwardly-extending anchor pin 12 for embedding in that concrete. An annular bearing element 14 of a suitable elastomeric material is sandwiched between the lower plate 10 and an upper bearing plate 16 which is of rectangular shape in plan, the element 14 being surrounded at its circumferential boundaries with the respective plates by respective circular limiting rings 18 and 20 that extend toward one another. A horizontal shear restricting mechanism as disclosed in my prior patents Serial Nos. 3 806 975 and 3 921240, consists of a pin 22 extending upward axially from the lower plate 10 and embraced by a sleeve 24 extending downward from the upper plate 16; this mechanism permits vertical, tilting and rotational movements between the two plates 10 and 16 under control of the element 14 and also a limited amount of horizontal movement, while pre- venting the application of excessive horizontal shear forces to the element.

The unavoidable longitudinal movements of the structure supported by the bearing are accommodated by permitting longitudinal sliding movement between the upper bearing plate 16 and an uppermost plate 26 the latter plate being fixed rigidly to the supported structure; in this embodiment is is provided with a plurality of parallel upwardlyextending anchor pins 28 which are embedded in the said supported structure. The two plates 16 and 26 have sandwiched between themselves a layer 30 of a low-friction material, such as tetrafluroethylene and a thin sheet 32 of highly polished stainless steel, the latter being fastened as by continuous welding to the under surface of the uppermost plate 26. The plates 2 GB 2 122 276 A 2 16 and 26 are constrained in their relative movement along a longitudinal axis 34 by downwardly extending guide bars 36 fixed to the undersurface of the uppermost plate, the opposed vertical edge faces of the plate 16 and the guide bars 36 being provided with respective strips 38 and 40 of low friction material e.g. tetrafluorethylene.

The bearing is provided at each end with a buffer stop consisting of a buffer support 46 fastened to the plate 26, a buffer plate 48 that is disposed to engage the facing edge of the plate 16, and a buffer pad 50 of elastomeric material interposed between the sup port 46 and plate 48. As the bearing reaches its extreme position at either end the plate 16 engages the plate 48, which moves toward the support 46 compressing the pad 50, the plate being guided in such movement by rods 52 moving in corresponding bores in the support.

To prevent misalignment between the axis 34 and the actual direction of attempted sliding movement of the plate 26 over the plate 16 causing unaccept able binding between the plate 16 and the bars 36 to an extent that could seriously damage and eventual ly even destroy the bearing, the low friction strip 40 is mounted on a thin metal backing strip 42, which is in turn mounted on a strip 44 of an elastomeric material that is thus interposed between the low friction strip 38 and the respective vertical edge of the plate 16 along the whole length of the plate. If there is any small misalignment of the sliding movement for the reasons explained above, or such misalignment appears because the sliding move ment is along a non-linear path, then this is accom modated by expansion or compression in the elas tomeric strips, so that the sliding takes place without binding.

In some alternative embodiments each low friction strip 38 is bonded directly to the elastomer strip 44, and in others the strips simply lie alongside one another and are fastened in place by bolts that are threaded into the guide bars 36.

Alternatively, or in addition, an elastomer strip 44 may be interposed between the low friction strip 40 and the respective guide 36, as illustrated in broken lines in Figure 2. The invention is illustrated as applied to a bearing in which straight-line sliding is provided between straight sliding surfaces, but it will be apparent to those skilled in this particular art that the invention is also applicable to designs with which the sliding surfaces are curved.

In the embodiment of Figure 3 each strip of elastomer material is semi-confined within a longitu dinal slot 46 in the respective vertical edge of the plate 16, while in the embodiment of Figure 4 each strip 44 is wholly confined within its slot 46, the strip and the slot being of substantially the same cross sectional dimensions; in some embodiments the unconfined elastomer strip may be larger in cross section than the slot so that it must be compressed for insertion therein and is therefore precompressed to a corresponding extent.

In a commercial range of bearings for load capaci ties from 100 to 8,000 KIPS the upper plate 16 varies in width from 18.1 cm to 162.6 cm, and in thickness from 1.27 cm to 5.08 cm respectively, while the 130 elastomeric layer 14 varies in thickness from about 1.3 cm to about 10.1 cm. The elastomer strips vary in thickness from about 1.2 cm to 3 cm and are intended to accommodate deviations of up to about -i:15 degrees each, based on a permitted compressability of about 15%. A suitable material forthe unconfined structure of Figures 1 and 2 is a urethane of about 95 Durometer hardness and about 15,000 p.s.i. strength. Other material such as polyethers can be used. The semi-confined and confined structures of Figures 3 and 4 respectively permit the use of lower hardness materials such as chloroprene, natural rubber and ethylene propylene materials. For example, a fully confined structure can use natural rubber of about 50 Durometer and 1500 p.s.i. Other values for bearings of the load range indicated above can be calculated by those skilled in the art.

In some embodiments it may be desired to use a material of strength and hardness that for the preferred dimensions of the strips 44 does not give the required amount of deflection, and in such cases the modification of Figure 5 or 6 may be used. Figure 5 shows an arrangement in which each strip 44 is provided with a plurality of spaced bores such as 47 extending from the surface contacting the plate 16 to that contacting the low friction strip 40, while Figure 6 shows an arrangement in which the face of the strip 44 contacting the plate 16 is provided with a plurality of spaced recesses 48. In both of these arrangements the shape factor and the deflection characteristic of the strip is altered by the presence of the bores or recesses. Yet other embodiments may use a mixture of bores and recesses.

It is preferred thatthe amount of misalignment accommodated by the resilient mounting of the guide means be not greater than about 1-2 degrees, since otherwise the amount of deformation of the low friction rubbing strips 38 and 40 that is required becomes somewhat larger than is considered desir- able. However, there is still the possibility that the amount of misalignment encountered in practice exceeds this figure, and such greater misalignment can be met by another system to be described below. Thus, it is found with bearings of my prior invention that with the structure illustrated, in which the annular bearing element 14 is confined around its circumferential boundary by limiting rings 18 and 20, that there is no need to fasten the bearing element to the plates 16 and 26, the load of the supported structure being ample to retain the element in its operative position.

Normally the friction between the materials of the element 14 and the cast steel surface of the plate 16 is quite high, and this friction is reduced to a low value, for example by interposing between the element and the plate a low- friction layer, consisting in this embodiment of a thin layer of polished stainless steel 50 fastened to the surface of the plate 16, as by continuous welding, and a thin layer 52 of a low friction material, such as polytetrafluorethylene, aff ixed to the immediately adjacent surface of the element 14, so that the layers 50 and 52 are in sliding contact with one another. If now a larger misalignment is encountered that cannot be accommodated by the resilient mountings 44, then the plate 16 and 3 GB 2 122 276 A 3 the element 14 are able to slide relative to one another without damage to the element. Some transverse distortion of the element 14 will take place, but it is circular in plan and such distortion therefore takes place in a chord-shaped portion thereof, so that a very substantial misalignment must be present before any appreciable area of the element is adversely affected. Even this small trans verse distortion can of course be avoided by provid ing a suitably-sized gap between the element edge and the ring 18 where the distortion is anticipated. It will be noted that the low-friction layer 52 extends over the edge of the element 14 where it contacts the limiting ring 18, so as to facilitate rotation between the element 14 and the plate 16 that will usually result from misalignment and accompany the above-described transverse distortion.

If the polished metal layer 50 is provided only a thin layer is required, for example about 1.5 mm thick. The degree of polish required is at least about RMS, and it may be possible instead to polish the surface of the plate 16 to the required degree.

However, in commercial practice it will usually be more economical to provide the polished sheet as a separate light-weight element rather than attempt to polish the surface of a relatively heavy disc. The low friction material suggested for the element 52 and the strips 38 and 40 is polytetrafluorethylene since this is now a widely commercial ly-available material, but in some embodiments it may be preferred to use a filled one of these materials because of its increased load capacity, despite the usual increase in friction coefficient for such materials; the higher friction can in some embodiments be reduced by use of a suitable grease between the metal and low 100 friction layers.

In some embodiments of the invention it may be preferred to employ the low friction layer 52 be tween the plate 16 and element 14 on place of the resilient mounting of the low-friction layers 38 and/or 40 as the method of accommodating the expected misalignment.

Claims

1. A supporting bearing for the support of a 110 structure such as a bridge or elevated roadway, the bearing comprising:

a plate member on which the structure rests for support thereby; another plate member; a layer of resilient material interposed between the first-mentioned and another plate member and supporting the latter from the former for vertical, horizontal, tilting and rotational movements; and a layer of low-friction material interposed between 120 the first-mentioned plate and the layer of resilient material to faciliate movement of the first-mentioned plate relative to the layer of resilient material upon application of horizontal misalignment forces thereto.

2. A bearing as claimed in claim 1, wherein the said layer of lowfriction material is a layer of polytetrafluorethylene and the surface of the firstmentioned plate member engaged by the low- friction material is polished.

3. A bearing as claimed in claim 2, wherein the said polished surface of the said first-mentioned plate member is provided by a thin metal layer fastened to the respective surface of the said first- mentioned plate member.

4. A bearing as claimed in anyone of claims 1 to 3, wherein the layer of resilient material is surrounded at least at its junction with the firstmentioned and another plate member with respec- tive restraining rings upstanding from the plate members.

5. A bearing as claimed in claim 4, wherein the layer of low-friction material extends over the respective edge of the layer of resilient material to facilitate rotation of the respective plate member 15 relative to the layer of resilient material.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1984. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

f.

IP 1 1

5. A bearing as claimed in claim 4, wherein the layer of low-friction material extends over the respective edge of the layer of resilient material to facilitate rotation of the first-mentioned plate member relative to the layer of resilient material.

6. A bearing as claimed in anyone of claims 1 to 5, and including horizontal shear restricting means extending between the first-mentioned and another plate memberfor preventing the application of excessive horizontal shearforces to the layer of resilient material as the result of horizontal movements.

7. A supporting bearing for the support of a structure such as a bridge or elevated roadway, constructed and arranged for use substantially as described herein with reference to any of the examples illustrated in the accompanying drawings.

New claims or amendments to claims filed on 16th August 1983 Superseded claims 1 to 6 New or amended claims:- CLAIMS (Filed on 16 August 1983) 1. A supporting bearing for the support of a structure such as a bridge or elevated roadway, the bearing comprising:

a plate member on which the structure rests for support thereby; a radially-unconstrained layer of resilient material interposed between the first-mentioned and a further plate member and supporting the latter from the former for vertical, horizontal, tilting and rotational movements; horizontal shear restricting means extending between the first-mentioned and further plate members for preventing the application of excessive horizontal shear forces to the layer of resilient material as the result of horizontal movements between the plate members; and a layer of low-f riction material interposed between one of the plate members and the layer of resilient material to facilitate transverse movement of the respective plate member relative to the layer of resilient material upon application of horizontal misalignment forces thereto.

2. A bearing as claimed in claim 1, wherein the layer of low-friction material is a layer of polytetrafluorethylene and the surface of the respctive plate member engaged by the low-friction material is polished.

3. A bearing as claimed in claim 2, wherein the polished surface of the respective plate member is 4 GB 2 122 276 A 4 provided by a thin metal layer fastened to the respective surface of the respective plate member.

4. Abearing as claimed in anyone of claims 1 to 3, wherein the layer of resilient material is sur rounded at least at its junction with the first mentioned and another plate member with respec tive restraining rings upstanding from the plate members for restraining the extent of transverse movement between the layer of resilient material and the respective plate member.