US20110232216A1

US20110232216A1 - Beam having internal tensioning and methods

Info

Publication number: US20110232216A1
Application number: US13/031,926
Authority: US
Inventors: Jonathan R. Schroeder; Kevin Bischel
Original assignee: Pacific Bearing Co
Current assignee: Pacific Bearing Co
Priority date: 2010-03-03
Filing date: 2011-02-22
Publication date: 2011-09-29

Abstract

A structural support member is provided. The structural support member includes a tensioning mechanism for applying a preload to a beam member of the structural support member. The tensioning mechanism acting on a loading pin causing the beam member to bend.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application No. 61/310,151, filed Mar. 3, 2010, the entire teachings and disclosure of which are incorporated herein by reference thereto.

FIELD OF THE INVENTION

This invention generally relates to structural beams and methods of controlling deflection of structural beams due to external loads.

BACKGROUND OF THE INVENTION

Elongated structural members are used all over to construct structures as well as to provide supports for other devices. For instance, elongated structural members might be used in the construction of a building, for forming a frame upon which machine tools are mounted, or maybe for forming a guide track for guiding a trolley or carriage.
Some structural members are formed from extruded materials such as aluminum. Because they are extruded they can be basically infinitely long. In many situations long spans of the structural member might be unsupported. These unsupported regions will deflect vertically due to the weight of the structural member itself under loading due to gravity. Unfortunately, this will cause an otherwise straight structural member to sag and no longer be straight. This can be particularly problematic when forming structures or guides as mentioned above.
Further, when weight is loaded onto the unsupported regions of the structural member, the additional weight will increase the amount of deflection caused by gravity increasing the sag in the structural support member. While the design of the extrusion can be modified to increase rigidity, unfortunately it is impractical to design extrusions for each specific load.
Additionally, when the load is non-uniformly located along the length of the unsupported region of the structural support member, the extrusion process will not be able to be modified to compensate for these variables.
The invention provides methods and apparatuses to compensate for this problem of undesirable sag or deflection of a structural support member due to gravity.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention relate to structural support members that prevent or counteract deflection of a beam member when loaded with weight. In one embodiment, a structural beam arrangement including a beam member and a mechanism for preloading the beam member is provided. The beam member extends longitudinally between opposed first and second ends along a longitudinal axis. At least one tensioning mechanism is attached to the beam member proximate the first end at a first attachment location and the second end at a second attachment location. A first intermediate loading pin is attached to the beam member at a third attachment location. The tensioning mechanism acts on the first intermediate loading pin to impart a first preload on the beam member between the first and second attachment locations such that the beam member is bent absent any additional external loading. This preloading counteracts any subsequent loading of the beam member.
In a more particular embodiment, the beam member has a vertical height that is generally perpendicular to the longitudinal length of the beam member. The first attachment location is at a different vertical height than the third attachment location. The second attachment location is at a different vertical height than the third attachment location. The first and second attachment locations are on the top vertical side of the first intermediate loading pin.
In some embodiments, the tensioning device may include a continuous cable as part of the tensioning mechanism that extends substantially between the first and second attachment locations. The continuous cable passing vertically below a bottom side of the first intermediate loading pin. The bottom side is opposite of the top side and faces generally vertically away from the first and second attachment locations.
In an alternative embodiment, the continuous cable passes through the first intermediate loading pin vertically below the top side of the first intermediate and vertically above a bottom side of the first intermediate.
The location of the intermediate loading pin can be varied along the length of the beam member. In some embodiments, the first intermediate loading pin is equally spaced between the first and second attachment locations along the longitudinal length of the beam member.
In alternative embodiments, the first intermediate loading pin is unequally spaced between the first and second attachment locations.
In alternative embodiments, the tensioning mechanism need not utilize a cable but could include a single tensioning rod extending between the attachment locations or a plurality of tensioning rods including one rod extending between an intermediate loading pin and the first attachment location and another rod extending between the intermediate loading pin and the second attachment location.
Further embodiments contemplate counteracting deflection due to a complex external loading arrangement. In such embodiments, a second intermediate loading pin (or more loading pins) is included. The first and second intermediate loading pins are offset from one another along the longitudinal axis extending the length of the beam member between the first and second attachment locations.
The same tensioning mechanism may act on both intermediate loading pins. Alternatively, each loading pin may be acted on independent of all the other loading pins. Alternatively, some pins may be independent acted upon while other pins are acted on by a single loading device together. Further, preloading of the various intermediate loading pins can be in opposite directions. For instance, the first loading pin could be loaded in a vertically upward direction and the second loading pin could be loaded in a vertically downward direction.
Further yet, the magnitudes of the first and second preloads may be different.
Not only might the loading pins be positioned at different longitudinal positions along the length of the beam member, but the different loading pins could additionally or alternatively be located at different vertical heights perpendicular to the longitudinal length of the beam member.
Some embodiments of the present invention permit adjustment of the preloading on the intermediate loading pin(s). For instance, when using a tensioning rod, one end of the rod might be threaded such that it can interact with a nut to increase or decrease the tension within the rod to adjust the load acting on the corresponding intermediate loading pin.
Further, when using a cable, the device may include attachment mechanisms to couple the tensioning cable to the beam member. At least one of the attachment mechanisms permits adjustment of the tension of the cable. In a more particular embodiment, at least one of the attachment mechanisms includes an eyebolt, one end of the cable being connected to the eyebolt. Adjustment of the position of the eyebolt relative to the beam member adjusts the tension of the cable.
In further embodiments, the attachment mechanisms might pivot relative to the beam member.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic simplified illustration of a structural support member including a tensioning system according to an embodiment of the present invention;

FIG. 2 is a schematic simplified illustration of an attachment mechanism for attaching a tensioning cable to a beam of a structural support member according to an embodiment of the present invention;

FIG. 3 is a simplified cross-sectional illustration of a beam of a structural support member according to an embodiment of the present invention illustrating one embodiment of a loading pin attached to the beam;

FIG. 4 is a simplified cross-sectional illustration of a beam of a structural support member according to another embodiment of the present invention utilizing an eyebolt as a loading pin for preloading the beam; and

FIGS. 5-8 are alternative embodiments or arrangements of structural support members according to the present invention.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified representation of a structural support member 100 according to an embodiment of the present invention. The structural support member 100 is configured to counteract external loading thereon to provide a substantially straight structural support member when subject to the external loading.
The structural support member 100 is generally an assembly that includes a beam 102 (or beam member) and a tensioning system 104. The tensioning system 104 acts on the beam 102 to counteract any external loading provided by an external load 106, such as illustrated schematically by arrow 106 in FIG. 1.
The beam 102 is preferably formed from an extruded aluminum. The beam 102 is also preferably a rectangular tube of extruded aluminum. However, other materials and other shapes could be used while remaining within the teachings and scope of embodiments of the present invention. For, non-exhaustive, example, the beam 104 could be formed from plastics, steal, or other materials. Further, the beam could take other forms in cross-section such as being an I-beam, T-shaped or U-shaped. Further, the beam 102 need not be extruded.
The tensioning system 104 preloads the beam 102 to counteract any deflection of the beam 102 due to load 106. Preferably, the tensioning system 104 is configured to counteract load 106 such that the beam 102 remains substantially straight once loaded with zero beam deflection at the point of loading.
The preload 108, illustrated as an arrow in FIG. 1, provided by the tensioning system 104 is provided by tension within the tensioning system 104.
In the illustrated embodiment, the tensioning system 104 includes a tensioning cable 109 that extends between and is tensioned between opposed attachment mechanisms 110, 112 at first and second attachment locations. In the illustrated embodiment, cable 109 is a continuous cable extending from attachment mechanism 110 to attachment mechanism 112. To generate the preload 108, the cable 109 acts on loading pin 113 at a third attachment location causing beam 102 to bend.
Both attachment mechanisms 110, 112 are on a same (top) side of loading pin 113. Cable 109 passes on an opposite (bottom) side of loading pin 113. In FIG. 1, attachment mechanism 110, attachment mechanism 112 and loading pin 113 are located first, second and third distances D1, D2 and D3 from bottom surface 114, respectively. In FIG. 1, first and second distances D1, D2 are substantially equal and are greater than third distance D3.
This arrangement causes a bend in cable 109 at loading pin 113 such that cable 109 extends at an angle, at least in part, relative to the longitudinal length of beam 102 and particularly top surface 116. This bend in cable 109 causes the tension present in cable 109 to apply preload 108 to loading pin 113. With the configuration of FIG. 1, this causes beam 102 to bend vertically upwards or crown absent any external loading.
The amount of tension in cable 109 and angle α defined by the two segments of cable 109 on opposite sides (left and right) of loading pin 113 adjusts the amount of preload 108.
In FIG. 1, the attachment mechanisms 110, 112 are simply eye bolts 120, 122 passing through apertures in end plates 124, 126. The use of eye bolts 120, 122 allows for easy adjustment of the tension within cable 109. Nut arrangements 128, 130, on the opposite side of plates 124, 126 can be used to draw eyebolts 120, 122 away from one another to increase the tension or can be adjusted to allow eyebolts 120, 122 to come towards one another to reduce the tension in cable 109. In some embodiments, only one of the attachment mechanisms 110, 112 need be adjustable.
However, in alternative embodiments, the cable 109 could take other forms. For instance, the cable 109 could include cooperating attachment structures to couple with attachment mechanisms 110, 112, such as for example, clips or hooks attached to opposed ends of cable 109. Further, the cable 109 could be replaced by a plurality of cables extending between attachment mechanisms 110, 112. Further yet, the cable 109 could be replaced by a plurality of substantially rigid linkages such as turn buckles or rigid rods.
Further, as illustrated in FIG. 2, a schematic representation of an alternative attachment mechanism 210 is illustrated. This attachment mechanism 210 does not require end plates. Instead, the eyebolt 110 is attached to a pivot arrangement 220 operably coupled to beam 102. The pivot arrangement 220 allows the eyebolt 110 to rotate about axis 222 so that the threaded shaft 132 of the eyebolt 110 stays axially aligned with the portion of the cable 109 connected thereto. This allows for more direct adjustment of the tension within cable 109. However, in other embodiments, other attachment mechanisms could be used. For instance, a similar arrangement as shown in FIG. 2 could be used, however, the eyebolt 110 may be prevented from pivoting relative to beam 102. This would be a simpler design. Further, because any in tension adjustment would adjust the angle of eyebolt 110 relative to beam 102 only slightly, because eyebolt 110 is already angled relative to beam 102 (measured by shaft 132), the need for pivoting action would not be necessary.
Loading pin 113 could take numerous forms. In FIG. 3, the loading pin 113 is illustrated as a pin passing through and externally welded to vertical sidewalls 134, 136. Alternatively, the loading pin 113 could merely be in the form of a threaded bolt passing through vertical sidewalls 134, 136. Further yet, a rod passing through sidewalls 134, 136 having mushroomed ends could suffice. As illustrated in FIG. 4, the loading pin could be in the form of an eyebolt 213 attached to bottom wall 138
Returning to FIG. 1, while being illustrated as passing below loading pin 113, other arrangements of cable 109 relative to loading pin 113 could be provided. For instance, the cable 109 could pass through an aperture formed through loading pin 113. All that generally be required is that the loading pin 113 vertically restrains cable 109 such that preload 108 can be generated.
Further embodiments of structural support members will now be discussed.
FIG. 5 illustrates an alternative structural support member 300 having a loading pin 313 offset from the opposed first and second ends 350, 352 of the beam 302. In this embodiment, external load 306 is not centered between first and second ends 350, 352. As such, loading pin 313 is a length L2 from first end 350 and loading pin 313 is a length L3 from the second end 352 with length L2 being less than length L3. This arrangement places loading pin 313 closer to external load 306 such that the preload 308 provided is better applied to compensate for any deflection that would have otherwise been caused by external load 306.
FIG. 6 illustrates an alternative structural support member 400 having a plurality of loading pins 413, 414, 415. These loading pins 413, 414, 415 allow for a customized compensation profile. This allows for preloads 408, 409, 410 to be applied to beam 402. Further, in this embodiment, two separate cables 422, 424 placed in tension are used to generate preloads 408, 409, 410. Cable 422 acts on loading pin 413 much like the embodiment of FIG. 1. Cable 424 acts on both loading pins 414, 415. By providing separate cables 422, 424, a different preload magnitude for preload 408 can be applied to loading pin 413 as opposed to a preload magnitude for preloads 409, 410 applied to loading pins 414, 415. In this arrangement, where two loading pins are acted on by a single cable, typically the preloads applied to those loading pins will be substantially equal in magnitude.
Cable 424 has several sections. More particularly, three sections. A first section 430 extends between attachment mechanism 432 and loading pin 414. A second section 434 extends between loading pins 414, 415. A third section 436 extends between the loading pin 415 and attachment mechanism 438. In the illustrated embodiments, loading pins 414, 415 are spaced a same distance from their corresponding attachment mechanisms 432, 438, respectively and a same distance from bottom surface 440 such that the angle between the first and second sections 430, 434 and the second and third sections 434, 436 are the same generating the same preload magnitude.
The previous embodiment could include a third cable such that each loading pin 413, 414, 415 is associated with its own cable for better fine adjustment of the preloading profile.
Further, while the various attachment mechanisms at a give end of beam 402 are shown vertically displaced from one another, they could alternatively be laterally spaced from one another such that they are all at the same vertical distance from bottom surface 440.
FIG. 7 illustrates a further alternative embodiment of a structural support member 500 according to principles of the present invention. In this embodiment, the beam 502 is preloaded in opposite directions.
More particularly, a first cable 509 acts on a first loading pin 513 to generate a preload 508 oriented in a vertically upward direction. However, a second cable 516 acts on a second loading pin 518 to generate a preload 520 oriented in a vertically downward direction. This will create a preloading profile that will generally cause the beam 502 to be generally “s-shaped” absent any external loading on the structural support member 500. More particularly, absent external loading, preload 508 will cause a first portion of beam 502 to deflect vertically upward creating a crowned portion of beam 502 while preload 520 will cause beam 502 to deflect vertically downward creating a dipped (upside down crown) portion of beam 502.
The tension in cables 509, 516 can be varied to adjust the magnitudes of preloads 508, 520 such that the deflections at loading pins 513, 518 may be different.
FIG. 8 is a further embodiment of a structural support member 600. This embodiment is similar to FIG. 1 and FIG. 6. In this embodiment, each cable 609, 610 are connected to attachment mechanisms that are laterally offset from one another at a give end of the beam 602. Both cables are not coupled to a same attachment mechanism at a given end.
In some embodiments, such as when the beam forms a channel, such as a box-beam construction or a C- or U-shaped channel, the structural support member may be filled with a foam material to assist in dampening of vibration of the beam as well as the tensioning mechanism such as cables or rods.
Further, these principles were tested as will be explained further.
A 4 inch by 4 inch by 21.5 foot aluminum beam was tested.
The beam 102 was supported using a simple support spaced 240 inches apart and 9 inches from each end of the beam 102. The loading pin 113 was a ½ inch diameter pin. The bottom of the pin was 3.3 inches from the attachment mechanisms 110, 112 in the vertical direction. The system used tensioning rods rather than a tensioning cable. The rods were threaded on each end. The beam had a moment of intertia of 4.853841 inch⁴, a cross-sectional area of 1.9376 inch, aluminum density of 0.0975 lb/inch³, a unit weight of 0.188906 lb/inch.
A first test was done to check the deflection of the beam absent any tensioning of the tensioning rods. A 25.45 pound weight was placed on the center of the beam and a deflection of 0.159 inches was measured resulting in 0.00625 inch/lb of applied weight. Next, a 10.35 pound load was applied resulting in a deflection of 0.065 inches resulting in a 0.00628 inch/lb of applied weight. Thus, the beam deflection acted substantially linearly as expected based on ideal beam deflection formula for a beam with simple supports. However, estimated deflections were about 5% lower than the measured values.


	Estimated center
	deflection caused	Estimated	Measured
Applied Weight	by beam weight	Deflection	Deflection	Error
Lbs	Inch	Inch	Inch	%

25.45	−0.16813	−0.151006	−0.159	5.03
10.35	−0.16813	−0.061411	−0.065	5.52

After the initial analysis of the beam 102 without any preloading, tensioning rods 113 were installed and tensioned to a minimum amount. A raise in the height of the center of the beam of 0.033 inches occurred. This indicated an estimated upload of 5.267 lbs at the center.
The nut at the end of the tensioning rod 113 was tightened causing the center of the beam 102 to rise. The following results were determined.


					Change	Center
					in	Height	Change
		Change	Total	Estimated	Estimated	with	in Height
	Center	in Height	Change	Center	Upload	25.45 Lb	due to
Nut	Height	by Turn	in Height	Upload	per turn	Applied	25.45 Lb
Turns	Inch	Inch	Inch	Lbs	Lbs	Inch	Inch

0	5.256	N/A	0	0	N/A	N/A	N/A
1	5.273	0.017	0.017	2.7	2.7	5.115	0.158
2	5.293	0.020	0.037	5.9	3.2	5.134	0.159
3	5.313	0.020	0.057	9.1	3.2	5.154	0.159
4	5.332	0.019	0.076	12.1	3.0	5.175	0.157
5	5.356	0.024	0.100	16.0	3.8	5.195	0.161
6	5.379	0.023	0.123	19.6	3.7	5.215	0.164
7	5.397	0.018	0.141	22.5	2.9	5.239	0.158
Average	N/A	0.020			3.215		0.159
St. Dev		0.002545			0.406199		0.00237

From the data, it can be seen that with the tensioning rods, the beam continued to act linearly so that a 25.45 lb weight continues to cause a 0.159 inch deflection.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A structural beam arrangement comprising:

a beam member extending longitudinally between opposed first and second ends;

at least one tensioning mechanism, the tensioning mechanism being attached to the beam proximate the first end at a first attachment location and the second end at a second attachment location; and

a first intermediate loading pin attached to the beam member at a third attachment location, the tensioning mechanism acting on the first intermediate loading pin to impart a first preload on the beam member between the first and second attachment locations such that the beam member is bent absent any additional external loading.

2. The structural beam arrangement of claim 1, wherein the beam member has a vertical height that is generally perpendicular to a longitudinal length of the beam member, the first attachment location being at a different vertical height than the third attachment location, the second attachment location being at a different vertical height than the third attachment location, the first and second attachment locations being on the top vertical side of the first intermediate loading pin.

3. The structural beam arrangement of claim 2, wherein the tensioning mechanism includes a continuous cable extending substantially between the first and second attachment locations, the continuous cable passing vertically below a bottom side of the first intermediate loading pin, the bottom side being opposite of the top side and facing generally vertically away from the first and second attachment locations.

4. The structural beam arrangement of claim 2, wherein the tensioning mechanism includes a continuous cable extending substantially between the first and second attachment locations, the continuous cable passing through the first intermediate loading pin vertically below the top side of the first intermediate loading pin and vertically above a bottom side of the first intermediate loading pin, the bottom side being opposite of the top side and facing generally vertically away from the first and second attachment locations.

5. The structural beam arrangement of claim 1, wherein the first intermediate loading pin is equally spaced between the first and second attachment locations in a direction parallel to a longitudinal length of the beam member extending between the first and second attachment locations.

6. The structural beam arrangement of claim 1, wherein the first intermediate loading pin is unequally spaced between the first and second attachment locations in a direction parallel to a longitudinal length of the beam member.

7. The structural beam arrangement of claim 1, wherein the tensioning mechanism includes a pair of tensioning rods, one of the tensioning rods extending between the first attachment location and the first intermediate loading pin and the other one of the tensioning rods extending between the second attachment location and the first intermediate loading pin.

8. The structural beam arrangement of claim 1, further including a second intermediate loading pin, the first and second intermediate loading pins being offset from one another along a longitudinal axis extending the length of the beam member between the first and second attachment locations.

9. The structural beam arrangement of claim 8, further including a second tensioning mechanism acting on the second intermediate loading pin to impart a second preload on the beam member.

10. The structural beam arrangement of claim 9, wherein the second preload acts in a generally opposite direction as the first preload.

11. The structural beam arrangement of claim 10, wherein the magnitudes of the first and second preloads are different.

12. The structural beam arrangement of claim 8, wherein the first and second intermediate loading pins are at different vertical heights.

13. The structural beam arrangement of claim 1, further including a second intermediate loading pin and a third intermediate loading pin, the first, second and third intermediate loading pins being offset from one another along a longitudinal length of the beam member extending generally between the first and second attachment locations.

14. The structural beam arrangement of claim 13, wherein at least two of the intermediate loading pins are at different vertical heights relative to one another in a direction perpendicular to the longitudinal length.

15. The structural beam arrangement of claim 1, wherein the tensioning mechanism includes an elongated rod attached to the beam member at the first and second attachment locations, the elongated rod passing vertically below the intermediate loading pin and the first and second attachment locations being vertically above the loading pin.

16. The structural beam arrangement of claim 15, wherein at least one end of the elongated rod is threaded and includes a nut thereon, the nut operably acting on the beam member such that adjustment of the location of the nut relative to the elongated rod increases the magnitude of the preload.

17. The structural beam arrangement of claim 1, wherein the tensioning mechanism includes a cable and a pair of attachment mechanisms, one of the attachment mechanisms operably coupled to beam member at the first attachment location and the other one of the attachment mechanisms operably coupled to the beam member at the second attachment location, the attachment mechanisms operably coupling the cable to the beam member, the cable acting on a first side of the loading pin, the attachment mechanisms being positioned on an opposite side of the loading pin as the side upon which the cable acts.

18. The structural beam arrangement of claim 17, wherein at least one of the attachment mechanisms permits adjustment of the tension of the cable.

19. The structural beam arrangement of claim 18, wherein at least one of the attachment mechanisms includes an eyebolt, one end of the cable being connected to the eyebolt, adjustment of the position of the eyebolt relative to the beam member adjusting the tension of the cable.