Patent Grant
8646976
The present invention relates in general to structural bearings for transferring large vertical loads to a supporting structure without physical connection between the bearing feet and the supporting structure. More particularly, the invention relates to a structural bearing that transfers little or no lateral load to the support structure in response to external lateral loads exerted upon the supported load.
In various industrial contexts, it is commonly required to provide structural bearings for supporting vertical loads while preventing transfer of significant lateral forces to the supporting structure. Examples include structural bearings in bridges and larger buildings that must be able to carry large vertical loads without allowing transfer of lateral loads to the supporting structure due to wind loads, seismic loads, or expansion or contraction induced by temperature changes. As well, it is commonly desirable to prevent the development of lateral reactions against supporting structures and foundations that can otherwise develop in some structures due to inherent structural characteristics. For example, ‘rigid frame’ building structures can in some cases exert lateral forces against supporting structures or foundations, even under vertical loading alone.
In such situations, prevention of lateral load transfer to the supporting structure, or prevention of lateral reactions in rigid frame structures, is commonly achieved by allowing the bearings to move laterally relative to the supporting structure, with such lateral movement being facilitated by rollers of some type, or the bearings may be slide bearings using a low-friction material such as PTFE (polytetrafluoroethylene).
In other scenarios, it is necessary to temporarily support large vertical loads on a supporting structure without transferring lateral loads, such as in conjunction with cantilevered mobile drilling rigs used to drill closely-spaced oil wells, particularly in extremely cold conditions. In such drilling operations, multiple wells are drilled at linear spacings of 10 or 12 feet, with the wellheads being disposed within a heated enclosure. The roof of the wellhead enclosure has hatches spaced to match the well spacing. Well drilling is carried out using a wheel-mounted or track-mounted mobile drilling rig having a cantilevered superstructure that carries a typically sliding rig floor. The mobile rig is positioned adjacent to the wellhead enclosure with the cantilevered superstructure extending over and beyond the wellhead enclosure. The mobile rig is movable parallel to the line of wells, such that it can be longitudinally aligned with each well location as required.
When the mobile rig is longitudinally aligned with a selected well, the free end of the cantilevered superstructure must be supported before the rig floor and mast section can be laterally positioned over the well and drilling operations commenced. For this purpose, a heavy girder is installed adjacent to the wellhead enclosure on the side opposite the mobile rig. The cantilevered superstructure is provided with two or more telescoping support legs that can be extended to bear upon the girder, without any mechanical connection or anchorage to the girder. When it is desired to move to a new well location, the support legs are retracted vertically away from the girder, and the mobile rig can then be relocated as required.
The girder is typically supported by spaced columns such that the top of the girder is at an elevation well above the roof of the wellhead enclosure, which may put the girder 25 or 30 feet above the ground. The vertical load exerted on the girder by each support leg during well-drilling operations can be in the range of 500,000 to 600,000 pounds. These large vertical loads create high frictional resistance across the contact interface between the support legs and the girder, such that large lateral loads exerted on the drilling rig structure by wind or seismic forces will react in part against the girder. This is undesirable not only because of the resultant torsional stresses induced in the girder, but also because of the resultant large bending moments induced in the structural columns supporting the girder (not to mention lateral loads and bending moments induced in the piles or other foundation systems supporting the columns).
For the foregoing reasons, there is a need for improved structural support bearings that will transfer large vertical loads to a supporting structure without allowing the transfer of significant lateral loads the supporting structure, but also without requiring lateral displacement at the contact interfaces between the support bearings and the supporting structure. The present invention is directed to this need.
The present disclosure addresses the foregoing need by providing a structural bearing apparatus for supporting vertical loads while preventing the transfer of significant lateral loading to the supporting structure without relative movement at the contact interface between the bearing and the supporting structure, and which will automatically return to a neutral or centered position upon removal of lateral loads acting on the supported vertical load. In one embodiment, the structural bearing incorporates:
As used in this patent document, the term “neutral position” (or, alternatively, “centered position”) means a position assumed by the described component when the structural bearing is not subjected to lateral loads.
In a preferred embodiment, the structural bearing is adapted to similarly respond to lateral loading in a second direction (typically but not necessarily perpendicular to the first direction). In this preferred embodiment, the structural bearing further includes a middle bearing plate and a second (or upper) load-bearing lateral displacement means, positioned between the first (or lower) load-bearing lateral displacement means and the upper bearing plate, such that when the supported vertical load is subjected to lateral loading in both the first and second directions:
In this embodiment, the structural bearing includes additional centering means, for returning the middle bearing plate and the upper lateral displacement means to their neutral positions upon removal of the lateral loads causing lateral displacement thereof.
In one embodiment, the lower and upper load-bearing lateral displacement means are provided in the form of roller beds each comprising roller means in the form of a plurality of elongate rollers mounted in a retaining frame or cage, with the elongate rollers in each roller bed having parallel and coplanar rotational axes.
However, the present invention is not limited to lateral displacement means using elongate rollers. By way of non-limiting example, lateral displacement means in alternative embodiments could comprise different roller means, which (by way of non-limiting example) could be provided in the form of multiple sets of wheel-like rollers mounted on parallel axles, or in the form of a ball bearing bed comprising ball bearings disposed within a suitable retaining frame or cage.
Other alternative embodiments may use the lateral displacement means may comprise a lubricated steel slide plate, with the slide plate being slidable relative to the bearing plates above and below it. Lubrication of the slide plate could be provided by a suitable grease or oil, or alternatively by applying a low-friction material or coating to the surfaces of the slide plate (and/or the surfaces of the associated bearing plates). Lateral displacement means in accordance with such alternative embodiments may be best suited (but not necessarily restricted) to applications requiring support of comparatively light vertical loads, with lateral displacement means using heavy-duty rollers or ball bearings being a preferred choice for (but not restricted to) applications requiring support of heavier vertical loads.
In one embodiment, each centering means comprises helical springs arranged so as to be compressed in response to lateral loading and corresponding lateral displacement of the associated lateral displacement means or bearing plate, such that upon removal of the lateral load, the compressed springs will automatically restore the associated lateral displacement means or bearing plate to its initial position as the springs rebound to their unstressed states. However, the present invention is not limited to centering means using helical compression springs. By way of non-limiting example, centering means in alternative embodiments could comprise springs that are put into tension rather than compression in response to lateral displacement of associated lateral displacement means or bearing plates. Other embodiments could use springs of a type different from helical springs.
Moreover, centering means for use with structural bearings in accordance with the present invention do not necessarily have to use springs of any type. By way of non-limiting example, further alternative embodiments may be devised using hydraulic cylinders, screw jacks, or other known devices that can be shortened or elongated in response to a force exerted by lateral displacement of an associated bearing plate or lateral displacement means, and which will naturally rebound or will be otherwise restored to a neutral or unloaded state upon removal or relaxation of the applied lateral force, thereby moving the displaced bearing plate or lateral displacement means back to a neutral or centered position (by means of suitable mechanical linkages). Centering means in accordance with still further embodiments may be adapted to mobilize gravity forces to re-center the bearing plates and lateral displacement means upon removal of lateral loads.
Embodiments of the invention will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which:
In the illustrated embodiment, structural bearing 10 comprises a lower bearing plate 20 having an upper surface 21 and a lower surface 25, with lower surface 25 being intended for resting on a structural support (such as girder 245 shown in
Preferably but not necessarily, lower bearing plate 20 comprises an upper plate 20U overlying a lower plate 20L, as shown in
Also as best seen in
In the illustrated embodiment, lower roller frame 31 comprises parallel side members 32 extending between parallel end members 33, with side members 32 being adapted (e.g., with suitable bearing means) to support rollers 34 in rotatable fashion. Persons skilled in the art will appreciate that end members 33 are not essential to the invention, and also that lower roller frame 31 in alternative embodiments may have side members 32 that are not parallel.
Lower bearing plate 20 is also provided with a first centering means for biasing lower roller bed 30 toward a neutral or centered position relative to lower bearing plate 20. Persons skilled in the art will readily appreciate that the first centering means can be provided in a variety of forms using known concepts and technologies, and the present invention is not limited by or restricted to the use of any particular type of centering means. However, as shown in
Each spring rod 42 passes through an opening 38A in a lug member 38 projecting laterally outward from a medial region of a corresponding side member 32 of lower roller frame 31, such that for each pair of helical springs 40, one spring 40 is disposed around the corresponding spring rod 42 on each side of the corresponding lug member 38 on lower roller frame 31. As illustrated, each spring rod 42 will preferably carry a washer 41 on either side of and adjacent to the corresponding lug member 38 to facilitate uniform application of compressive force into springs 40.
Accordingly, when lower roller bed 30 is moved in either direction between lower fence members 22, one helical spring 40 on each side of lower roller bed 30 will be compressed between a corresponding lug member 38 and a corresponding abutment 24. Removal of the external force causing the movement of lower roller bed 30 will in turn relieve the compressive load in the compressed springs 40, which as a result will urge lug members 38, and lower roller bed 30 with them, back toward the neutral or centered position relative to lower bearing plate 20.
As will be described later in this specification, the illustrated embodiment of structural bearing 10 comprises second, third, and fourth centering means using helical compression springs similar to the first centering means described above. For enhanced clarity and to distinguish between the various centering means and related components, the first centering means may be alternatively referred to as the inner lower centering means, and helical springs 40 may be alternatively referred to as inner lower springs 40. Similar alternative terminology will also be used for the other centering means described later herein.
Referring to
As illustrated in
To facilitate centering of middle bearing plate 60 relative to lower bearing plate 20, structural bearing 10 preferably incorporates a second (or outer lower) centering means generally similar to the first (or inner lower) centering means described previously, and as best understood with reference to
Removal of external force F1 will relieve the compressive load in compressed outer lower springs 50A, which as a result will urge middle bearing plate 60 back toward a neutral or centered position relative to lower bearing plate 20.
Middle bearing plate 60 may be adapted to accommodate lateral displacement relative to lower bearing plate 20 without vertical separation when structural bearing 10 is in a suspended condition (such as, for example, when incorporated into a vertically extendable support leg 215 as in the mobile cantilever drill rig 200 shown in
In the illustrated embodiment, however, this is accomplished by forming abutments 24 on lower bearing plate 20 with outwardly-extending elongate flanges 24A as shown in
In alternative embodiments, intended for use in service conditions in which structural bearing 10 will at all times rest on a supporting structure and therefore will not be suspended, there will be no necessity for means for preventing vertical separation between lower and middle bearing plates 20 and 60. In such service conditions, rollers 34 will at all times maintain compressive contact with upper surface 21 of lower bearing plate 20 and with lower surface 65 of middle bearing plate 60. In such alternative embodiments, the second (or outer lower) centering means may be unnecessary, depending on the magnitude of the vertical load applied to structural bearing 10. Provided that it has sufficient strength, the first (or inner lower) centering means by itself may be effective to center middle bearing plate 60 as well as lower roller bed 30 upon removal of loads or conditions causing lateral displacement thereof in the first direction. As mentioned previously, when lower roller bed 30 is laterally displaced relative to lower bearing plate 20 in the first direction, middle bearing plate 60 will be resultantly displaced a corresponding amount in the same direction relative to lower roller bed 30, due to the fact that rollers 34 roll equally relative to both upper surface 21 of lower bearing plate 20 and lower surface 65 of middle bearing plate 60. Therefore, if middle bearing plate 60 is in compressive contact with rollers 34, the action of the first centering means to urge lower roller bed 30 back toward its neutral or centered position will have a corresponding effect on middle bearing plate 60, barring slippage between rollers 34 and lower surface 65 of middle bearing plate 60.
As shown in
As illustrated in
As shown in
Each inner upper spring rod 82 passes through an opening 78A in a lug member 78 projecting laterally outward from a medial region of a corresponding side member 72 of upper roller frame 71, such that for each pair of helical springs 80, one spring 80 is disposed around the corresponding spring rod 82 on each side of the corresponding lug member 78 on upper roller frame 71 (preferably with washers 81 on each side of lug member 78).
Accordingly, when upper roller bed 70 is moved in either direction between upper fence members 62, one helical spring 80 on each side of upper roller bed 70 will be compressed between a corresponding lug member 78 and a corresponding abutment 64. Removal of the external force causing the movement of upper roller bed 70 will in turn relieve the compressive load in the compressed springs 80, which as a result will urge lug members 78, and upper roller bed 70 with them, back toward the neutral or centered position relative to middle bearing plate 60.
It will be immediately apparent that upper roller bed 70, the third centering means, fence members 62, and abutments 64 in the illustrated embodiment are similar in configuration and construction to lower roller bed 30, the first centering means, fence members 32, and abutments 34, respectively. However, the direction of travel of upper roller bed 70 is transverse to the direction of travel of lower roller bed 30. Accordingly, the illustrated embodiment of structural bearing 10 accommodates lateral loading in two directions, and is auto-centering in both directions upon removal of the lateral loads.
Referring to
As illustrated in
To facilitate centering of upper bearing plate 100 relative to middle bearing plate 60, structural bearing 10 preferably incorporates a fourth (or outer upper) centering means, which as shown in
Removal of external force F2 will relieve the compressive load in compressed springs 90A, which as a result will urge upper bearing plate 100 back toward a neutral or centered position relative to middle bearing plate 60.
Upper bearing plate 100 may be adapted to accommodate lateral displacement relative to middle bearing plate 60 without vertical separation when structural bearing 10 is in a suspended condition. In the illustrated embodiment, this is accomplished by forming abutments 64 on middle bearing plate 60 with outwardly-extending elongate flanges 64A as shown in
In alternative embodiments, intended for use in service conditions in which structural bearing 10 will at all times rest on a supporting structure and therefore will not be suspended, there will be no necessity for means for preventing vertical separation between middle and upper bearing plates 60 and 100. In such alternative embodiments, the fourth (or outer upper) centering means may be unnecessary, for reasons essentially as set out previously with respect to alternative embodiments not requiring the second (or outer lower) centering means.
As shown in
Structural bearing 10 is provided with mounting means (generally indicated by reference number 110) for mounting structural bearing 10 to a supported structural element, such as (by way of non-limiting example) to the lower end of a support leg 215 as in the mobile cantilever drill rig 200 in
As illustrated in
To accommodate this movement, mounting means 110 projects upward through opening 123 in top member 122 of fixed cover 120. In order to protect against entry of contaminants through opening 123 regardless of the lateral position of the movable subassembly, a travelling cover 125 with an opening 126 is mounted to mounting means 110 in any suitable fashion, such that travelling cover 125 extends over top member 122 of fixed cover 120, and such that the perimeter edge 127 of travelling cover 125 will always overlap top member 122 of fixed cover 120 regardless of the lateral position of the movable subassembly. In the illustrated embodiment, travelling cover 125 is mounted to mounting means 110 by interposing a base plate 112 between upper bearing plate 100 and mounting brackets 114, such that travelling cover 125 can be fastened to base plate 112 along the periphery of opening 126 in travelling cover 125. Optionally, and as best seen in
Persons skilled in the art will appreciate that the protective cover means described and illustrated herein are by way of example only, and that alternative suitable cover means can be readily devised without departing from the principles and concepts of the present invention. Moreover, it is to be understood that protective cover means are not essential to the present invention, and do not form part of the broadest embodiments of the invention.
It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the scope and teaching of the present invention, including modifications which may use equivalent structures or materials hereafter conceived or developed. To provide one particular and non-limiting example, and as previously suggested herein, alternative embodiments can be devised to accommodate lateral displacement either way from a centered or neutral position but only in two opposite directions (e.g., lateral displacement to the north or south, but not to the east or west). Such alternative embodiments would require only one roller bed, disposed between a lower bearing plate and an upper bearing plate. Accordingly, such embodiments would substantially correspond to the illustrated embodiment, but without the middle bearing plate, the upper roller bed, and the third and fourth centering means. For variant assemblies that will not be suspended, and for which no means for preventing vertical separation between the lower and upper bearing plates will be necessary, it may be sufficient to provide only a single centering means.
Another alternative embodiment would accommodate operational conditions where anticipated lateral displacement of one bearing plate relative to another (e.g., lateral displacement of the middle bearing plate relative to the lower bearing plate) would be in one direction only, relative to a centered or neutral position (e.g., lateral displacement to the north but not to the south). In this embodiment, each associated centering means would need only a single compression spring on each side of the assembly.
In a variant combining the two alternative embodiments described immediately above, the principles of the present invention could be applied to accommodate lateral displacement from the neutral position in two opposite directions (e.g., north and south) and only one transverse direction (e.g., east). A further variant would accommodate lateral displacement from the neutral position in only a single direction (e.g., to the north, but not to the east, south, or west); in such embodiments, only a single roller bed would be required, with upper and lower bearing plates.
In yet further alternative embodiments, intended for service conditions in which the auto-centering structural bearing will always be supported from below and will not be suspended, there will be no need for means for preventing vertical separation between adjacent bearing plates, such as lugs 66 on abutments 68 or lugs 104 on abutments 102.
It is to be especially understood that the invention is not intended to be limited to any described or illustrated embodiment, and that the substitution of a variant of a claimed element or feature, without any substantial resultant change in the working of the invention, will not constitute a departure from the scope of the invention. It is also to be appreciated that the different teachings of the embodiments described and discussed herein may be employed separately or in any suitable combination to produce desired results.
In this patent document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the terms “connect”, “engage”, “couple”, “mount”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure. Relational terms such as “parallel”, “perpendicular”, “coincident”, “intersecting”, and “equidistant” are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring substantial precision only (e.g., “substantially parallel”) unless the context clearly requires otherwise.
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