GB1604125A

GB1604125A - High-load bearing for bridges and similar structures

Info

Publication number: GB1604125A
Application number: GB22973/78A
Authority: GB
Original assignee: Watson Bowman Associates Inc
Current assignee: Watson Bowman Associates Inc
Priority date: 1977-07-05
Filing date: 1978-05-26
Publication date: 1981-12-02
Also published as: BR7803576A; NZ187434A; FR2396919B1; AU3680278A; FR2396919A1; JPS5417447A; CH630682A5; SE7805330L; ES470268A1; SE438514B; DE2825606A1; AU516757B2; PH16573A; CA1100714A; JPS62125115U; ZA782235B; NO782244L

Abstract

The bearing which can be subjected to high loading and is intended for bridges and other structures comprises an upper and a lower slab (2, 3) and an elastomeric cushion (4) which receives the load and is located between the slabs. The cushion (4) has a constricted portion on its periphery. The bearing is provided with means which prevent a translatory movement between the upper and lower slabs (2, 3), but permit a tilting movement between them. The invention provides a device (15, 16) to delimit or to prevent a lateral expansion of the base and top surfaces of the cushion (4) without preventing its periphery from bulging outwards. A bearing of this type permits, with the same dimensions, greater loading and ensures better stability. <IMAGE>

Description

(54) HIGH-LOAD BEARING FOR BRIDGES AND SIMILAR STRUCTURES (71) We, WATSON-BOWMAN ASSOCIATES INC., a corporation organised under the laws of the State of Delaware, U.S.A., of 1280 Niagara Drive, Buffalo, State of New York, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates primarily to an improvement in bearings of the type described and claimed in U.S. Patents 3,806,975 and 3,921,240. The bearings described in these patents are primarily intended for the support of the decks of bridges or piers and abutments wherein rotational and/or translational motion takes place between the bridge deck and the pier or abutment.However, the present invention also provides an improvement which is useful with bearings of somewhat similar general construction wherein there may be no rotation or translational movement between the bridge deck and the pier or abutment. The invention also is useful with bearings which support other structures such as buildings. The principal objective of the invention is to assure that the bearing will have the capability of sustaining very heavy loads and that the load carrying capability will be stabilized.

In bearings of the aforesaid type, an elastomeric ad, generally 1/4 to 5 inches thick is fitted between two flat plates which in turn are secured between the bridge deck or some other structure and the pier, abutment or some other foundation. In the type of bearings described in the aforesaid patents, a third plate is mounted for sliding movement relative to one of the plates and anchored to the structure of the foundation to accommodate translational movement, and means are provided to minimize shearing strains in the elastomer without interfering with necessary rotation between the first and second plates and compression of the elastomer by the weight of the structure.

The preferred type of elastomer pad is circular, and the lateral edge of the pad preferably is concave. In practice, the elastomer pads which have been used in this type of bearing have been biconical (i.e.

they resemble a pair of conical sections, one inverted over the other).

Variations have been encountered in the load capabilities of the elastomer paid. This is evidenced by the load deflection curve for the bearings wherein the deflection of a bearing under load is greater in some instances than in others. It now has been discovered that these variations can be attributed to variations in the bonding of the elastomer pad to the aforesaid plates above and below it, which is believed to have allowed the upper and lower surfaces of the biconical pad to spread laterally under load, to some extent irreversably.

The present invention provides a highload bearing comprising upper and lower plates, a load bearing elastomer pad between said plates, the elastomer pad having a groove extending around its periphery, a cooperating bearing member constructed and arranged to substantially prevent shearing movement between the plates but permitting rotational movement between the plates, and means mechanically restraining the elastomer pad to at least limit lateral expansion of the upper and lower surfaces of the elastomer pad under load without preventing bulging of the periphery of the elastomer pad.

In a preferred form the invention also provides a safety element which protects the bearing pad from the hazard of overload and from separation from the aforesaid plates during rotation. Briefly, the structural means comprises means secured to the plate which provides a mechanical interlock with the elastomer pad so as to exert a force opposed to lateral growth of the upper and lower surfaces of the biconical or similar pad when it is compressed.Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure I is a cross section through a preferred form of the new bearing; Figure 2 is a plan view of a plate used in the bearing of Figure 1;ion 1; Figure 3 is a side elevation of the bearing pad of the bearing of Figure 1, when partly compressed; Figure 4 is a side elevation of the bearing pad of the bearing of Figure 1, when further compressed; and Figures 5-10 are cross sections through the bearing pad and adjoining plates of other embodiments of the bearing of the present invention.

As shown in Figure 1, the bearing comprises three steel components, a square top plate 1, a square upper bearing plate 2 and a lower beanng plate 3. A circular bearing pad 4 is positioned between the upper plate 2 and the lower plate 3 and a low friction plastics sheet 5 is positioned in a recess 6 in the top of upper plate 2 to reduce friction between upper plate 2 and top plate 1. The top plate 1 and the lower beanng plate 3 are fitted with concrete anchors 7 and 7' to secure them respectively to a bridge pier 8 and a bridge deck 9 although it will be understood that the bearings can be used in other kinds of construction.The top plate 1 is provided with depending side plates 10 and 11 which extend along opposite sides of the upper bearing plate 2 to substantially confine relative sliding movement between the top plate and the upper bearing plate and thus between the bridge deck 9 and the pier 8, to a single direction. However, it will be understood that other arrangements can be used, for example, to allow sliding movement in all directions, by omitting plates 10 and 11 or to substantially prevent sliding movement in all directions, depending upon the requirements of the structure.

The bearing is equipped with a pin 12, integral with the lower bearing plate 3 engaged in a cylindrical collar 13. As described in U.S. Patents 3,806,975 and 3,921,240 in connection with Figure 2 thereof the disclosure of which patents is incorporated herein by reference; this is one embodiment of a cooperating bearing member which serves to substantially to prevent shearing movement between the two bearing platens.

The bearing pad 4 is made from polyurethane elastomer, preferably 85 to 95 durometer, Shore A and is of biconical shape. The dimensions of the pad 4 depend on the weight the pad is expected to support, but typically the external diameter is 4 to 60 inches and the diameter at the midpoint 14 is typically 1/8 to 2 inches less than the diameter of the pad.

In accordance with the present invention, the upper plate 2 is provided with a depending circular ring 15 which extends around the bearing pad, but whose internal diameter is slightly larger than the initial diameter of the bearing pad 4, that is the diameter before the pad is compressed.

Preferably, a clearance of 1/32 to 3/8 inch is provided. Similarly, the lower plate 3 is provided with a raised ring 16 of the same diameter and it allows the same clearance.

The arrangement is such that, as initially assembled, the bearing pad does not contact either of the rings 15 and 16. However, as the bearing is compressed by the weight of the structure, two phenomena are observed.

First, as illustrated in Figure 3, the tapered sides of the pad bulge outwardly and towards each other. Ultimately, if the bearing is compressed sufficiently, the tapered sides of the pad 4 bulge outwardly to the extent that they contact the rings 15 and 16.

However, the bearings are designed so that this does not occur at the design load. Thus the ring provides a safety factor which comes into effect if the bearing is overloaded. At that stage the shape factor of the pad is increased and it is substantially prevented from undergoing further compression.

The second phenomenon which is observed is that the diameter of the bearing pad 4 may increase slightly on its top and bottom surfaces, as described above, but growth is limited by the rings 15 and 16.

A third phenomenon is observed if the bearing is rotated or tilted. In this situation, the bearing pad is compressed more on one side than on the other side. When this occurs, the outwardly bulging tapered sides may contact the rings 15 and 16 in the area of greatest compression. When that occurs, further compression in that area is restricted in effect by changing the shape factor of the pad.

A further advantage of the invention follows from this arrangement. Because overcompression during tilting is avoided, it is possible to use relatively softer elastomer than otherwise would be possible. During rotational movements, soft elastomers can stretch a little, if needed, in the area opposite the compressed areas, and therefore, avoid separation from the plates 2 and 3, which otherwise might occur. As a result, the bearings can be rated for greater rotational movement than otherwise might be allowed.

The overall effect of the invention is to increase the rated loadings of the bearings.

For example, it is presently believed that bearing pads which were rated at 2500 psi can now be rated at 3800 psi.

Alternatively, improvements in the bearings can be provided by other means which reduce the growth of the upper and lower surfaces of the pad 4. This is provided by a variety of mechanical interlock arrangements which provide an internally facing vertical or inclined surface of the upper plate 2 and/or the lower plate 3 which abuts an outwardly facing vertical or inclined surface of the bearing pad 4 internally of the perimeter of the bearing pad. Several forms of abutting surfaces are illustrated in Figures 5-10.

WHAT WE CLAIM IS: 1. A high-load bearing comprising upper and lower plates, a load bearing elastomer pad between said plates, the elastomer pad having a groove extending around its periphery, a cooperating bearing member constructed and arranged to substantially prevent shearing movement between the plates but permitting rotational movement between the plates, and means mechanically restraining the elastomer pad to at least limit lateral expansion of the upper and lower surfaces of the elastomer pad under load without preventing bulging of the periphery of the elastomer pad.

2. A high-load bearing according to Claim 1 in which said restraining means comprises at least one projection from at least one of said plates into at least one corresponding groove in the upper and/or lower surface of the elastomer pad.

3. A high-load bearing according to claim 1 in which said restraining means comprises at least one projection from at least one of said surfaces of said load bearing elastomer pad into at least one corresponding groove in one or each of said plates.

4. A high-load bearing according to any one of Claim 1 in which said restraining means comprises means projecting from one or each said plates and surrounding the periphery of said elastomer pad so that when the pad is under load the periphery is supported by the projecting means.

5. A high-load bearing according to Claim 4 in which a lateral clearance is provided between a corresponding periphery of the surface of the elastomer ad and said projecting means when said bearing is not under load, whereby the elastomer pad is permitted limited lateral expansion before abutting said projecting means.

6. A high-load bearing according to Claim 5 in which said lateral clearance is 1/32 to 3/8 inch.

7. A high-load bearing according to Claim 4, 5 or 6 in which said elastomer pad and said projecting means are circular.

8. A high-load bearing according to any one of Claims 1 to 7 in which said load bearing elastomer pad is biconical.

9. A high-load bearing according to any one of Claims 1 to 7, in which said peripheral groove extends from the upper surface to the lower surface of said load bearing elastomer pad.

10. A high-load bearing substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bearing pads which were rated at 2500 psi can now be rated at 3800 psi. Alternatively, improvements in the bearings can be provided by other means which reduce the growth of the upper and lower surfaces of the pad 4. This is provided by a variety of mechanical interlock arrangements which provide an internally facing vertical or inclined surface of the upper plate 2 and/or the lower plate 3 which abuts an outwardly facing vertical or inclined surface of the bearing pad 4 internally of the perimeter of the bearing pad. Several forms of abutting surfaces are illustrated in Figures 5-10. WHAT WE CLAIM IS:

1. A high-load bearing comprising upper and lower plates, a load bearing elastomer pad between said plates, the elastomer pad having a groove extending around its periphery, a cooperating bearing member constructed and arranged to substantially prevent shearing movement between the plates but permitting rotational movement between the plates, and means mechanically restraining the elastomer pad to at least limit lateral expansion of the upper and lower surfaces of the elastomer pad under load without preventing bulging of the periphery of the elastomer pad.