Area contact truss strut joint

Abstract

A strut joint of a truss features a contact trough on an inner chord face being in an area contact with a rotationally symmetric strut end surface having a contact radius of at least half a strut height. The rotation axis of the strut end surface and the trough is substantially perpendicular to the struts protrusion direction and the chord's protrusion direction. The area contact provides for snug contact irrespective deviations from a predetermined strut joint angle between strut end and chord. An optional interposing structure may extend the area contact in between two opposite strut end surfaces of a single strut joint.

Description

CROSS REFERENCE

The present Application claims priority from Provisional Application of the same title and inventor, filed Mar. 08, 2005, Ser. No. 60/659,988, which is hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to trusses having chords and struts. More particular, the present invention relates to trusses having strut joints with rotationally symmetric area contact between strut and chord.

BACKGROUND OF INVENTION

The load carrying capacity of a truss greatly depends on the rigidity of the strut joints where web struts of a truss are combined with the chords. A prior art truss 10 as shown in FIG. 1 includes top and bottom chords 11 combined along their respective inner chord faces 111 via a number of web struts 12. The ends of the web struts 12 define at their attachment locations on the inner chord faces 111 together with the chords 11 the strut joints 13. The web struts 12 are attached to the chords 111 in varying strut joint angles SA with respect to the strut tilt axes TA. To keep the buckling resistance to a maximum, the truss 10 is preferably a planar structure symmetric with respect to a symmetry plane SP. The strut tilt axes TA are consequently preferably perpendicular to the symmetry plane SP.

Strut joints 13 are also preferably symmetric with respect to symmetry plane SP. Prior art strut joints 13 of prior art FIGS. 2, 3 have one ore two tapered end surfaces 121. In cases of single tapered end surfaces 121 as in FIG. 2, there exists a high likelihood of line contact LC between end surfaces 121 and inner chord faces 111, which may result from limited truss 10 assembly precision and/or assembly deviations from predetermined strut joint angles SA.

In case of two tapered end surfaces 121, there may be an additional rounding between the two tapered end surfaces 121 as shown in FIG. 3. Such prior art strut end configuration is designed to make the strut joints 13 independent of above mentioned deviations of predetermined strut joint angle SA and to provide a standardized strut end configuration. Even rounded strut end surfaces 121 provide only line contact LC with the inner chord faces 111. Due the small tip radius that is substantially smaller than the strut's height half HH, indentations of the strut tip radii into the contacting chord face 111 may even be worth than in a configuration of prior art FIG. 2.

Exclusive Line contact LC, especially between the strut end surfaces 121 and the inner chord faces 111 has very little compressive load transmission capability resulting in a deformation of both inner chord faces 111 and chord end surfaces 121. As a result, the joint plates 14 commonly laterally and oppositely nailed or screwed onto the chords 11 and the struts 12 at the strut joints 13, end up as load transmitting elements, whereby the nail or screw connections become additionally shear stressed. This may eventually reduce the overall stiffness and load carrying capacity of the truss 10. Therefore, there exists a need for strut joints with area contact between the strut ends and the chord that is highly independent of strut angle offset. The present invention addresses this need.

SUMMARY

A well known truss used in architectural construction includes a number of web struts combined with top and bottom chords in several strut joints along inner chord faces. The struts are oriented with varying strut joint angles with respect to the respective chord. In the present invention, area contact is established in the strut joints between rotationally symmetric strut end surfaces being in a snug contact with correspondingly shaped contact troughs provided at the inner chord surfaces. Strut ends and troughs may have a standardized configuration that complies with a range of the strut joint angles. The troughs may be cut into the chord whereby the chord grain is interrupted and/or may be pressed into the inner chord faces whereby the chord grain is compress but remains substantially continuous.

In alternate embodiments, an interposing structure may be added to the strut joint. It may be placed between the strut ends and the chords to either partially extend the trough surface for an enlarged area contact with the strut end. Alternately, the interposing structure may provide entire trough surface whereby a reduction of the chord's cross section due to the trough is circumvented while the advantageous area contact is maintained. The interposing structure may rest on the inner chord face. Positioning of the interposing structure may be provided by a positioning groove fabricated into the inner chord face and/or a corresponding positioning feature of the interposing structure. The interposing structure may be part of a prefabricated assembly including lateral joint plates. The preassembly may clamp along the chords in a friction contact and be aligned with a positioning label on the chords indicating the predetermined position of the strut joint. As a favorable result of the area contact, overall truss stiffness and load carrying capacity may be improved without increasing dimensions of struts and/or chords

A chord fabrication system may include a trough fabrication device positioned along a chord fabrication path to fabricate the troughs at predetermined positions along the chords. In addition or alternately, a position defining device may fabricate the positioning grooves and/or positioning labels into the chords.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a representative prior art truss.

FIG. 2 is the perspective view of a first representative prior art strut joint with the removed foreground plate.

FIG. 3 is the perspective view of a second representative prior art strut joint with removed foreground plate.

FIG. 4 is the perspective view of a first embodiment of the present invention with removed foreground plate and interrupted chord grain.

FIG. 5 is the strut joint of FIG. 4 with continuous chord grain.

FIG. 6 is a second embodiment of the present invention including an interposing structure placed between two adjacent strut end surfaces of a strut joint.

FIG. 7 is a third embodiment of the present invention including an interposing structure placed between the strut end surfaces and the chord.

FIG. 8 schematically depicts a chord fabrication system for fabricating chords in accordance with the present invention.

DETAILED DESCRIPTION

The present invention introduces improved strut joints 23 of FIGS. 4-7 with area contact at least in an interface between a chord trough 212 and a strut end surface 221 between the modified struts 22 and inner chord faces 211 of modified chords 21 as depicted in FIGS. 4, 5. Area contact may also extend directly between adjacent modified chord end surfaces 221 of a modified strut joint 23 as illustrated in FIGS. 6, 7.

Primary area contact is provided between at least rotationally symmetric strut end surfaces 221 and corresponding at least rotationally symmetric contact troughs 212. The contact troughs 212 are rotationally symmetric with respect to a trough axis 212A that is substantially perpendicular to the truss symmetry plane SP, a chord protrusion direction CD, a strut protrusion direction PD and parallel to the strut tilt axes TA. As a result, the struts 22 may be combined with the inner chord faces 211 in a primary area contact irrespective their strut joint angle SA.

Contact troughs 212 and strut end surfaces 221 are at least rotationally symmetric but preferably cylindrical and may have a contact radius CR that is at a maximum for a predetermined range of strut joint angle SA, within which the struts 22 may be assembled while exclusively maintaining area contact between strut end surfaces 221 and their respective contact trough 212. More particular, a strut end surface 221 may have an end surface angle EA. The end surface angle EA may have a symmetric axis ESA, which may be in an angle with respect to its respective web strut's 12 protrusion direction PD. In such a case the end surface angle EA and the end surface symmetry axis ESA may be selected such that the respective strut end surface 221 extends at least up to a peripheral trough edge TEP and a strut contact line SCL between two oppositely contacting strut end surfaces 221. More particularly, two adjacent troughs 212 of a strut joint 23 including two struts 22 may share a single central trough edge TEC in case of which the strut contact line SCL may substantially coincide with the central trough edge TEC.

In the case of the end surface symmetric axis ESA being collinear with the strut protrusion direction PD, the end surface angle EA may be selected for a given strut joint angle SA and a trough angle TAN of the respective truss joint 23 such that the respective strut end surface 221 extends at least up to a peripheral trough edge TEP and the strut contact line SCL. More particular, all struts 22 of a truss may have a substantially equal end surface angle EA such that for the strut joint angle SA being in a range between a maximum and a minimum at a number of truss joints 23, each of the end surfaces 221 of the respective truss extend et least up their respective peripheral trough edge TEP and their respective strut contact line SCL. In this preferred case, fabrication of troughs 212 and strut end surfaces 221 may be accomplished with respective standards for individual strut 22 lengths and at varying trough 212 locations along the inner chord face 211.

The end surface angle EA may be up to 180 degrees and the contact radius CR at least half a height SH of a strut side face 229 substantially perpendicular to the rotation axis of the end surface 221. Having the contact radius CR at least half the height SH provides for a maximum area in the interface between trough 212 and respective end surface 221, which in turn assists in reducing contact pressure and deformation in the strut joint 23 resulting in an increased overall stiffness of a truss having strut joints 23.

In case of the chord 21 being made of wood as shown in FIG. 4, contact troughs 212 may be fabricated with well known cutting techniques resulting in interrupted chord grains 213 in the vicinity of the trough 212. Alternately and also in case of a wooden chord 21 as shown in FIG. 5, contact troughs 212 may be fabricated with non-cutting fabrication techniques resulting in substantially continuous chord grains 213 in the vicinity of the troughs 212. Continuous chord grains 213 may improve the chord's 21 strength and/or splicing tendency in the vicinity of the trough 212 as may be well appreciated by anyone skilled in the art. A non-cutting fabrication technique may be a pressing technique as may be well appreciated by anyone skilled in the art.

In the first embodiment of the invention described under FIGS. 4, 5, line contact exists along the strut contact line SCL directly between the strut end surfaces 221. As strut joint angles SA become smaller, the strut contact line SCL may become increasingly loaded. In a second and third embodiment of the invention depicted in FIGS. 6, 7, a secondary area contact is provided directly between the adjacent strut end surfaces of a single strut joint 23. The secondary area contact is above the level of the inner chord faces 211 by an interposing structure 24 placed at least between the two adjacent strut end surfaces 221 and on top of the inner chord face 211 adjacent a through 212. The interposing structure 24 rests with a flat contact face 243 on the inner chord face 211. The interposing structure 24 may be positioned on the inner chord face 211 via a protruding positioning feature 241 fitting in a chord groove 214. The interposing structure 24 may have plate connect features 244 for attaching and positioning the joint plates 14 with the interposing structure 24.

In the second embodiment of FIG. 6, the interposing structure 24 has at least one but preferably two contact surfaces 242 corresponding to and extending from the contact troughs 212 while the interposing structure 24 is in assembled position on the inner chord face 211. In the third embodiment of FIG. 7, the interposing structure 24 may provide primary and secondary area contact with fully interposing surfaces 242. The strut end surfaces 221 contact solely the interposing structure 24 and the inner chord faces 211 may feature only positioning grooves 214.

The interposing structure 24 may be combined with two opposing joint plates 14 of a strut joint 23 in a preassembly that may provide sufficient stiffness for a friction based damping onto the chords 21. The use of such preassembly may ease the truss fabrication process. The friction based damping and positioning of the preassembly may eliminate the need for a positioning groove 214 such that the inner chord face 211 may remain continuous. A positioning label 26 may be substituted for the positioning groove. A reference mark may be provided at the preassembly to position the preassembly with respect to the previously fabricated positioning label 25. The positioning label 25 may give also information about a required length of the strut 22 to be assembled at the respective strut joint 23.

A chord fabrication system 300 schematically depicted in FIG. 8, may fabricate chords 21 from chord raw material 2 along a fabrication path 302 as is well known in the art. Such chord fabrication system 300 may include a fabrication device 301 for fabricating the contact troughs 212 and/or positioning grooves 214 and/or positioning labels 25 at predetermined positions along the chord 21 and in accordance with the teachings above.

Accordingly, the scope of the invention described in the Figures and the Specification above is set forth by the following claims and their legal equivalent:

Claims

1. A strut having a rotationally symmetric end surface, said rotationally symmetric end surface having a contact radius of at least half of a height of a strut side face and having an end surface angle of up 180 degrees, wherein a rotation axis of said end surface is substantially perpendicular to said strut side face.

2. The strut of claim 1, wherein said end surface is in an area contact with a trough on an inner face of a chord, said end surface and said trough being part of a strut joint, and wherein said strut is in a strut joint angle to said chord.

3. The strut of claim 2, wherein said strut contacts a second of said strut in a strut contact line.

4. The strut of claim 3, wherein said end surface angle is selected such that said strut contact line is within said end surface.

5. The strut of claim 3, wherein a number of said strut joint are part of a truss and wherein a number of said strut of said truss have said end surface angle substantially equal and selected in conjunction with a maximum and a minimum of said strut joint angle and selected in conjunction with a trough angle such that said number of said end surfaces extend at least up to a peripheral edge of a respective of said trough and a respective of said strut contact line.

6. The strut of claim 1, wherein said end surface is in contact with an interposing trough surface of an interposing structure.

7. The strut of claim 1 being made of wood.

8. A chord comprising a rotationally symmetric contact trough on a face of said chord, said contact trough being rotationally symmetric with respect to a trough axis, said trough axis being substantially perpendicular to a protrusion direction of said chord.

9. The chord of claim 8 being made of wood and wherein said chord has interrupted chord grains in a vicinity of said contact trough.

10. The chord of claim 8 being made-of wood and wherein said chord has substantially continuous chord grains in a vicinity of said contact trough.

11. The chord of claim 8, wherein said trough is in an area contact with an end surface of a strut, said end surface and said trough being part of a strut joint, and wherein said strut is in a strut joint angle to said chord.

12. The chord of claim 8, further comprising an interposing structure adjacent said contact trough and on top of said chord face, said interposing structure having a contact surface corresponding to and extending from said contact trough.

13. The chord of claim 8, wherein said contact trough is provided by an interposing structure placed on said chord face.

14. A truss having a strut joint comprising a strut having a rotationally symmetric end surface in an area contact with a rotationally symmetric trough on an inner chord face, said end surface and said trough having a rotation axis substantially perpendicular to a symmetry plane of said truss, and wherein said strut is in a strut joint angle to said chord.

15. The truss of claim 14, wherein said end surface has a contact radius of at least half of a height of strut side face and an end surface angle of up 180 degrees.

16. The truss of claim 14, wherein said strut contacts a second of said strut in a strut contact line within said strut joint.

17. The truss of claim 16, wherein said end surface angle is selected such that said strut contact line is within said end surface.

18. The truss of claim 16, wherein a number of said strut joint have said end surface angle substantially equal and selected in conjunction with a maximum and a minimum of said strut joint angle and selected in conjunction with a trough angle such that said number of said end surfaces extend at least up to a peripheral edge of a respective of said trough and a respective of said strut contact line.

19. The truss of claim 14, wherein said chord is made of wood and wherein said chord has interrupted chord grains in a vicinity of said contact trough.

20. The truss of claim 14, wherein said chord is made of wood and wherein said chord has substantially continuous chord grains in a vicinity of said contact trough.

21. The truss of claim 14, further comprising an interposing structure adjacent said contact trough and on top of said chord face, said interposing structure having a contact surface corresponding to and extending from said through, and wherein said contact surface is in an area contact with said end surface.

22. The truss of claim 14, wherein said trough is provided by an interposing structure placed on said inner chord face.