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Title:
SHAFT COUPLINGS AND RELATED METHODS
Document Type and Number:
WIPO Patent Application WO/2012/000112
Kind Code:
A1
Abstract:
A coupling, for connecting two shaft sections, comprising a plurality of connection pieces featuring recesses to receive projections extending from the ends of both the shaft sections, and an assembly mechanism which secures the connecting pieces together.

Inventors:
VICKARS, Robert Alfred (6220 9th Avenue, Burnaby, British Columbia V3N 2T6, CA)
VICKARS, Jeremiah Charles Tilney (1430 Nanaimo Street, New Westminster, British Columbia V3M 2G4, CA)
Application Number:
CA2011/050394
Publication Date:
January 05, 2012
Filing Date:
June 27, 2011
Export Citation:
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Assignee:
VICKARS DEVELOPMENTS CO. LTD. (6220 9th Avenue, Burnaby, British Columbia V3N 2T6, CA)
VICKARS, Robert Alfred (6220 9th Avenue, Burnaby, British Columbia V3N 2T6, CA)
VICKARS, Jeremiah Charles Tilney (1430 Nanaimo Street, New Westminster, British Columbia V3M 2G4, CA)
International Classes:
F16D1/04; E02D5/56; F16B7/04; F16D1/02; F16L21/06; F16L23/14
Foreign References:
US0034769A
CA2438774A1
US2187314A
US6814525B1
US20080063479A1
US7090437B2
US1435028A
GB2177479A
Attorney, Agent or Firm:
MANNING, Gavin, N. et al. (480 - The Station601 West Cordova Stree, Vancouver British Columbia V6B 1G1, CA)
Download PDF:
Claims:
We claim:

1. A coupling for coupling first and second shaft sections, the coupling comprising:

one or more first projections projecting from an end of the first shaft section;

one or more second projections projecting from an end of the second shaft section;

two or more connecting pieces each configured with recesses to receive at least one of the first projections and at least one of the second projections; and an assembly mechanism configured to clamp the connecting pieces together to couple the first and second shaft sections

2. A coupling according to claim 1 , wherein the first and second projections have non-round cross-sections in planes perpendicular to longitudinal axes of the first and second shaft sections respectively and the recesses limit relative rotation of the first and second shaft sections by engaging edges of the first and second projections.

3. A coupling according to claim 1 or 2, wherein at least one of the first and second shaft sections has a uniform cross section along its length except for the projections.

4. A coupling according to claim 1 or 2, wherein at least one of the first and second shaft sections has a round cross section in a middle part of the shaft section and a square or rectangular cross section at one or both ends of the shaft section.

5. A coupling according to claim 1 or 2, wherein at least one of the first and second shaft sections has a round cross section and at least some of the projections are square or rectangular in cross section.

6. A coupling according to any one of claims 1 to 5, wherein a maximum width of the projections is 1½ or less times a maximum width or diameter of the shaft section on which the projections are located.

7. A coupling according to any one of claims 1 to 5, wherein a maximum width of the connecting pieces is equal to or less than a maximum width or diameter of the shaft sections.

8. A coupling according to any one of claims 1 to 7, wherein a maximum width of the coupling, when assembled, is three or less times a maximum width or diameter of the shaft sections.

9. A coupling according to any one of claims 1 to 8, wherein a sum of the ultimate shear strengths of the first projections is at least equal to an ultimate tensile strength of the first shaft section.

A coupling according to claim 9, wherein a sum of the ultimate shear strengths of the second projections is at least equal to an ultimate tensile strength of the second shaft section.

11. A coupling according to claim 10, wherein the sum of the ultimate shear

strengths of the second projections exceeds the ultimate tensile strength of the second shaft section by a factor of at least 1.1.

A coupling according to any one of claims 1 to 10, wherein an aggregate ultimate tensile strength of the connecting pieces is at least equal to an ultimate tensile strength of each of the first and second shaft sections.

A coupling according to claim 12, wherein an aggregate ultimate tensile strength of the connecting pieces is at least 1.1 times an ultimate tensile strength of each of the first and second shaft sections.

14. A coupling according to any one of claims 1 to 13 wherein the connecting pieces comprise a material having a tensile strength greater than that of a material of the first and second shaft sections.

15. A coupling according to any one of claims 1 to 14 wherein the connecting pieces are made from a material having a tensile strength of at least 500 MPa.

16. A coupling according to any one of claims 1 to 15, wherein a torque capacity of the assembled coupling exceeds that of each of the first and second shaft sections.

17. A coupling according to any one of claims 1 to 16 wherein, when the first and second projections are engaged in corresponding recesses of the connecting pieces, ends of the first and second shaft sections are spaced apart by a gap.

18. A coupling according to claim 17 wherein the assembly mechanism comprises an assembly member extending through the gap.

19. A coupling according to claim 18 wherein the assembly member comprises a bolt.

20. A coupling according to any one of claims 1 to 17 wherein the coupling pieces are each penetrated by an aperture and, when the coupling is assembled, the apertures of the coupling pieces are aligned with a gap between end portions of the first and second shaft sections.

21. A coupling according to claim 20 wherein the assembly mechanism comprises an assembly member extending through the apertures and the gap.

22. A coupling according to claim 21 wherein the assembly member comprises a bolt.

23. A coupling according to any one of claims 1 to 22, wherein at least one of the connecting pieces is C-shaped in cross-section.

24. A coupling according to any one of claims 1 to 22, wherein the connecting pieces comprise two connecting pieces which are each C-shaped in cross-section.

25. A coupling according to any one of claims 1 to 22, wherein the connecting pieces comprise at least two connecting pieces which are L-shaped in cross-section.

26. A coupling according to claim 25, wherein the connecting pieces comprise four connecting pieces which are L-shaped in cross-section.

27. A coupling according to any one of claims 1 to 26 wherein ends of the first and second shaft sections comprise a plurality of faces and one or more of the connecting pieces are configured to engage a plurality of the faces.

28. A coupling according to claim 27 wherein the ends of the first and second shaft sections are square or rectangular in cross section and at least one of the connecting pieces comprises a right-angle corner so as to receive at least one corner of each of the first and second shaft sections, the at least one of the connecting pieces having faces on either side of the right angle corner and to contact faces of the shaft sections that are adjacent to the right angle corner.

29. A coupling according to claim 27 wherein the ends of the first and second shaft sections are square or rectangular in cross section and at least one of the connecting pieces comprises a channel having side walls configured to contact two opposing faces of each of the first and second shaft sections.

30. A coupling according to claim 29 wherein the channel comprises two side faces and a bottom face and the recesses comprise recesses in at least the two side faces.

31. A coupling according to claim 30 wherein the first and second projections comprise projections on each of four faces of the ends of the first and second shaft sections respectively and the recesses comprise recesses in the bottom face of the channel.

32. A coupling according to claim 31 wherein the recesses comprise grooves

extending across the side and bottom faces of the channel.

33. A coupling according to any one of claims 1 to 26 wherein ends of each of the first and second shaft sections comprise three or more faces and the connecting pieces comprise flat connecting pieces each arranged to engage a corresponding one of the faces of each of the shaft sections.

34. A coupling according to any one of claims 1 to 33 wherein the first and second shaft sections are hollow.

35. A coupling according to claim 33 comprising a torque-transmitting member engageable in bores of the first and second shaft sections.

36. A coupling according to any one of claims 1 to 16 wherein ends of the first and second sections comprise torque-transmitting structures that are held in engagement with one another when the coupling is assembled.

37. A coupling according to claim 36 wherein the torque-transmitting structures comprise interdigitating teeth on ends of the first and second sections.

38. A coupling according to any one of claims 1 to 37 wherein the first and second projections extend circumferentially around the ends of the shaft sections.

39. A coupling according to claim 38 wherein the first and second projections extend helically around around the ends of the shaft sections.

40. A coupling according to any one of claims 1 to 26 wherein the ends of the shaft sections each comprise a pair of opposing faces and the first and second projections respectively include projections on both of the opposing faces of the first and second shaft sections.

41. A coupling according to any one of claims 1 to 26 wherein surfaces of the

projections facing away from the ends of the first and second shaft sections are inclined toward the end of the respective shaft section.

42. A coupling according to any one of claims 1 to 26, wherein the assembly

mechanism comprises a sleeve dimensioned to slide over the connecting pieces when the first and second projections are engaged in the recesses of the connecting pieces.

43. A coupling according to claim 42 wherein the sleeve comprises one or more soil displacing members or helical screws.

44. A coupling according to any one of claims 1 to 26 wherein the first shaft section comprises a socket at the end of the shaft section and the socket is configured to receive the end of the second shaft section.

45. A coupling according to claim 1 , wherein the assembly mechanism is selected from the group consisting of a clamp, a clip, straps, wires, pins, welding the connecting pieces together, locking the connecting pieces together, interdigitating the connecting pieces together, and combinations thereof.

46. A coupling according to claim 45 wherein one of the first projections is provided by a rear face of the socket.

47. A coupling according to any one of claims 1 to 26 comprising a torque- transmitting tube configured to fittingly receive the ends of the first and second shaft sections so as to transmit torque between the coupled shaft sections.

48. A coupling according to any one of claims 1 to 47 wherein the coupling exceeds the first and second shaft sections in tensile strength and torque capacity.

49. A coupling according to claim 48 wherein the coupling exceeds the first and second shaft sections in resistance to bending.

50. A method for coupling shaft sections, the method comprising:

aligning first and second shaft sections co-axially, the shaft sections each having projections extending radially from at least one end thereof;

engaging the projections in recesses in two or more connecting pieces such that each of the connecting pieces extends between the shaft sections and engages at least one of the projections of each of the first and second shaft sections; and

securing the connecting pieces together.

51. A method according to claim 49 wherein the shaft sections comprise shaft

sections of a screw pier and the method further comprises:

providing a screw mounted on the first shaft section;

placing the screw in soil and turning the first shaft section to move the screw into the soil.

52. A method according to claim 51 wherein securing the connecting pieces together comprises sliding a sleeve over the connecting pieces wherein the screw is mounted on the sleeve.

53. A method according to claim 51 comprising coupling additional shaft sections to the first and second shaft sections.

54. A method for coupling shaft sections, the method comprising: aligning first and second shaft sections co-axially, the shaft sections each having projections extending radially from at least one end thereof;

sliding a sleeve over the ends of the shaft section and the projections; compressing the sleeve around the projections such that the ends of the shaft sections are held together and the projections engage with an inner surface of the sleeve.

55. A method according to any of claims 50 to 54 wherein the shaft sections

comprise sections of a screw pier.

56. A method according to claim 55 comprising, after coupling the shaft sections, rotating an upper one of the shaft sections to cause a screw on a lower one of the shaft sections to draw the coupling into the soil wherein the coupling transmits torque to drive the screw.

57. A method according to claims 56 comprising holding an upper end of the screw pier against longitudinal movement and turning the screw, thereby applying tension to the shaft sections, wherein the coupling transmits tension forces between the shaft sections.

58. A screw pier comprising a plurality of shaft sections and couplings according to any one of claims 1 to 49 coupling the shaft sections together.

59. Use of a coupling according to any one of claims 1 to 49 to couple sections of a screw pier.

60. Couplings and other useful apparatus comprising any new and inventive feature, combination of features, or sub-combination of features as described herein and/or illustrated in the drawings.

61. Methods comprising any new and inventive step, act, combination of steps and/or acts or sub-combination of steps and/or acts as described herein and/or illustrated in the drawings.

62. A coupling for coupling first and second shaft sections, the coupling comprising:

a first flange extending from an end portion of the first shaft section, the first flange being penetrated by a first set of apertures;

a second flange extending from an end portion of the second shaft section, the second flange being penetrated by a second set of apertures;

two or more connecting rods configured to couple the first flange with the second flange, each rod passing through one of the apertures in the first flange and a corresponding one of the apertures in the second flange; and

a torque transmitting coupling comprising a projection on the first shaft section and a socket on the second shaft section, the projection held in engagement with the socket by the connecting rods.

63. A coupling according to claim 62 wherein the projection extends axially from the end portion of the first shaft section and past the first flange, and the socket extends axially from the end portion of the second shaft section and past the second flange.

64. A coupling according to claim 62 or 63 wherein the torque-transmitting coupling limits relative rotation of the first and second shaft sections to within +1- 3 degrees.

65. A coupling according to any one of claims 62 to 64 wherein the first and second sets of apertures are spaced apart around the first and second flanges.

66. A coupling according to any one of claims 62 to 65 wherein the first and second sets of apertures are spaced apart evenly around the first and second flanges.

67. A coupling according to any one of claims 62 to 66 wherein an aggregate ultimate tensile strength of the connecting rods is at least equal to an ultimate tensile strength of each of the first and second shaft sections.

68. A coupling according to any one of claims 62 to 67 wherein the connecting rods are threaded at one or both ends.

69. A coupling according to any one of claims 62 to 68 wherein the connecting rods comprise a high-tensile-strength alloy.

70. A coupling according to claim 69 wherein the alloy has a yield strength of at least 80000 kpsi.

71. A coupling according to any one of claims 62 to 70 wherein the connecting rods extend substantially parallel to the first and second shaft sections.

72. A shaft section having a first end portion and a second end portion, the shaft section comprising:

at the first end portion of the shaft section, one or more first radially- projecting members penetrated by a first set of apertures;

at the second end portion of the shaft section, one or more second radially -projecting members penetrated by a second set of apertures;

a projection extending axially from the first end portion of the shaft section past the first members; and

a socket extending axially on the second end portion of the shaft section, the socket configured to receive the projection of another identical shaft section, the socket having a cross-sectional shape formed to non-rotatably engage with the projection of the other shaft section such that the apertures of the first set of apertures of the other shaft section are aligned longitudinally with the apertures of the second set of apertures of the shaft section. A shaft section according to claim 72 wherein the relative rotation of the two shaft sections when coupled together is limited to within +1- 3 degrees.

Description:
SHAFT COUPLINGS AND RELATED METHODS

Cross-Reference to Related Applications

[0001] This application claims priority from United States Patent Application No.

61/359339 filed on 28 June 2010 entitled SHAFT COUPLINGS AND RELATED METHODS and United States Patent Application No. 61/445515 filed on 22 February 2011 entitled SHAFT COUPLINGS AND RELATED METHODS which are incorporated hereby by reference. For the purposes of the United States, this application claims the benefit under 35 U.S.C. §119 of United States Patent Application No.

61/359339 filed on 28 June 2010 entitled SHAFT COUPLINGS AND RELATED METHODS and United States Patent Application No. 61/445515 filed on 22 February 2011 entitled SHAFT COUPLINGS AND RELATED METHODS.

Technical Field

[0002] The invention relates to couplings useful for coupling together sections of shafts and methods of using same. Some embodiments have particular application in coupling together shaft sections for helical piers to support the foundation of a structure, such as a building, and methods of using same.

Background

[0003] Vickars et al. US patent Nos. 5707180, 6264402, 6435776, and 6652195 which are hereby incorporated by reference for all purposes, disclose pile structures that include shafts encased in grout. The shafts may comprise a number of sections that are coupled together. The shafts may be shafts of a helical pier. Such pile structures may be used, for example, to provide support to structures, such as buildings.

[0004] In a typical helical pier, each shaft section comprises a socket at one end that can receive the other end of a connected shaft section. The socket is typically square in cross section and receives a square end of a connected shaft. A bolt passing through holes in the socket and connected shaft end secures the shaft sections together. [0005] The inventors have determined that it would be beneficial to provide couplings capable of transmitting increased tension between shaft sections in the helical piers used in piles of the general type described in the above-noted Vickars patents as well as in other applications.

[0006] The couplings currently used in most helical piers may be incapable of transmitting as much tension as would be desirable for some applications due to one or more of:

• The holes provided for bolting the shaft sections together reduce the strength of the shaft sections;

• The bolts used to secure shaft sections together are smaller in diameter than the shaft sections and can fail if the tension applied to the shaft exceeds the shear strength of the bolts;

• in general, cross- bolted connections tend to provide weak links at which failures tend to occur when shafts with bolted connections are made to withstand forces in one or more of shear, tension, bending and torque .

Strength of such prior art couplings can be increased by increasing dimensions of the couplings. However, this adds cost, weight and, if the couplings are made excessively large, can interfere with the installation and function of the shaft.

[0007] There remains a need in the above and other applications for couplings that are cost effective and capable of effectively transmitting tension and torque forces between coupled shaft sections. In some applications there is a desire to provide couplings that can transmit tension forces at least equal to or in excess of the yield strength of the coupled shaft sections. Brief Description of the Drawings

[0008] The accompanying drawings illustrate non-limiting example embodiments of the invention.

[0009] Figure 1 is a schematic view of a coupling according to an embodiment of the invention.

[0010] Figure 1A is a side elevational view of a shaft section according to an example embodiment.

[0011] Figures IB, 1C, and ID are possible cross-sections of a shaft section of the type illustrated in Figure 1A.

[0012] Figure 2 is a side elevational view and cross-sectional view of a coupling according to an example embodiment.

[0013] Figures 2A and 2B are respectively possible cross-sections of a shaft section and a coupling of the type illustrated in Figure 2. Figure 2C illustrates schematically an example projection having an angled flank.

[0014] Figures 3, 3A, 3B, and 3C are cross-sectional views through shaft couplings according to alternative embodiments.

[0015] Figure 4 is an elevational view of a helical pier incorporating shaft couplings according to an alternative embodiment.

[0016] Figure 5 is an isometric exploded view of a coupling according to a further alternative embodiment. [0017] Figures 6, 7 and 8A through 8E are cross sections through couplings according to further alternative embodiments.

[0018] Figures 9 is a cross-sectional view of a coupling according to another example embodiment and Figure 10 is a side elevation view of a shaft for coupling to another shaft with couplings as shown in Figure 9.

Description

[0019] Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well-known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention.

Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0020] In order to illustrate an example application of the invention, the following description describes some couplings being used to couple together shafts sections in screw piers and related methods. This choice of examples coincides with an aspect of the invention having significant commercial utility. However, the invention is not limited to application in coupling sections of screw piers.

[0021] Figure 1 illustrates schematically a coupling 10 that may be applied to couple together the ends 12A and 12B of first and second shaft sections 12. Coupling 10 comprises projections 14 that project outwardly (e.g. away from center-lines of shaft sections 12 or radially) and one or more members 16 that engage and extend between projections 14.

[0022] Projections 14 may be integral with shaft sections 12. In example embodiments shaft sections 12 are made of steel or another suitable metal and projections 14 are formed by forging, upsetting or otherwise deforming the material of shaft sections 12. In other example embodiments projections 14 are provided by welding or brazing pieces of material onto shaft sections 12. In some embodiments the material of projections 14 and shaft sections 12 is the same.

[0023] In some embodiments, shaft section 12, apart from projections 14, has a uniform cross-section and outside profile along its length. For example, shaft section 12, apart from projections 14, can have a uniform square (or rectangular) or round cross-section along its entire length. In some embodiments, the cross-sectional area of shaft section 12 is uniform along the length between projections 14.

[0024] Advantageously, the cross-sectional area of the connection between projections 14 and the remaining material of shaft sections 12 may be chosen so that the shear strength of projections 14 has a desired value. In some embodiments it is desired that the shear strength of projections 14 have at least a desired value relative to the ultimate tensile strength of shaft sections 12. Specific dimensions of projections 14 which achieve this objective will depend on the material of shaft sections 12 as well as the geometry of and number of projections 14 and the desired value. In some embodiments the desired value is: at least equal to the ultimate tensile strength of shaft sections 12, greater than the ultimate tensile strength of shaft sections 12 or at least some stated proportion to the ultimate tensile strength of shaft sections 12. The stated proportion may be in the range of 0.8 to 1.3 for example with example proportions of 0.85, 1.1, and 1.25.

[0025] As one example, for some kinds of steel the ultimate shear strength is approximately 0.75 times the ultimate tensile strength. In such cases the shear strength of projections 14 can be made to equal or exceed the tensile strength of shaft sections 12 by making the cross sectional area of the interfaces between projections 14 and a shaft section 12 at least approximately 1/0.75 = 4/3 or approximately 1.35 times the cross- sectional area of the shaft section 12 (or the thinnest part of shaft section 12 if the shaft section 12 has a variable cross-section). This may be adjusted by appropriate engineering factors. [0026] In some embodiments, the cross sectional area of the interfaces between projections 14 and a shaft section 12 are at least in the range of 1 to 2 times the minimum cross-sectional area of the portion of shaft section 12 that is subjected to tensile loads (e.g. the portion of the shaft section 12 between couplings 10).

[0027] Different embodiments may provide different numbers of projections 14. It is typically desirable to provide two or more projections 14 on the end of a shaft section 12 to be coupled although only one projection 14 is provided in some embodiments. In some embodiments there are from 2 to 5 projections 14 on each end of a shaft section 12 to be coupled. In some embodiments, projections 14 comprise a plurality of ridges on at least one end of a shaft section 12. For example there may be a suitable number of ridges having suitable sizes on each of two opposing faces of an end of a shaft section 12. In some embodiments the number of ridges is 5 or more. In other embodiments the number of ridges is 5 or fewer.

[0028] Coupling member or members 16 engage projections 14 on two coupled shaft sections. In some embodiments, engagement of coupling members 16 to projections 14 comprises receiving projections 14 in recesses formed in coupling members 16.

Coupling members 16 may be made from material(s) that are the same as or different from the material or materials of shaft sections 12 and projections 14.

[0029] Coupling members 16, in aggregate, may have an ultimate tensile strength having a desired relationship to the ultimate tensile strength of shaft sections. The ultimate tensile strength of coupling members 16 may, for example, have a desired value that is: at least equal to the ultimate tensile strength of shaft sections 12, greater than the ultimate tensile strength of shaft sections 12 or at least some stated proportion to the ultimate tensile strength of shaft sections 12. The stated proportion may be, for example in the range of 0.8 to 1.3 with example proportions of 0.85, 1.1 and 1.25. [0030] In some embodiments, the total cross sectional area, A c , of the coupling members 16 and the minimum cross sectional area, A s , of the tension-bearing part of shaft sections 12 is related by:

T c X A c > F T s X A s (1) where: T c is the tensile strength of the material of coupling members 16, T s is the tensile strength of the material of shaft sections 12, and F is a safety factor. In some embodiments F advantageously has a value such that F > 1 and preferably F > 1.25.

[0031] In some embodiments, coupling members 16 are made from a material having a tensile strength greater than that of the material of shaft sections 12. For example, in some embodiments, shaft sections 12 are made of mild steel and coupling members 16 are made of a high tensile strength steel. Coupling members 16 may be made, for example, of a material having an ultimate tensile strength of at least 500 MPa (as compared to about 400 MPa for mild steel).

[0032] In some embodiments, a minimum total cross-sectional area of the part of coupling members 16 that extend between projections 14 is at least equal to the minimum cross sectional area of the central portion of each shaft section 12 between its ends.

[0033] In addition to transmitting tensile forces between shaft sections 12, couplings 10 may transmit torques between shaft sections 12. Various example configurations and embodiments which provide for transmission of torque between coupled shaft sections 12 are described below.

[0034] It can be appreciated that couplings 10 may advantageously be configured so that the capacity of a shaft made up of sections 12 joined by couplings 10 in tension is not reduced by the presence of couplings 10. In some embodiments such a shaft is as strong in tension, torque, bending and shear as would be a continuous length of shafting having the same characteristics as shaft sections 12. In such embodiments, couplings 10 do not represent weak points. Such shafts may be safely tensioned to a level limited by the strength of the portions of shaft sections 12 between couplings 10. Engineering calculations involving the overall strength of such shafts are simplified since such calculations may be made without reference to any detailed characteristics of couplings 10.

[0035] An advantage of some embodiments of coupling 10 is that the total amount of metal in shaft sections 12 and coupling members 16 may be reduced in comparison to some prior art couplings. Another advantage of some embodiments of coupling 10 is that coupling 10 can be relatively small and compact in size while being able to transmit large tension forces and significant torques. For example, if the total cross-sectional area of projections 14 is equal to the cross-sectional area of shaft section 12, the width of coupling 10 may be about 1.414 times the width of shaft section 12. In some embodiments, the width of projections 14 can be made to be of some stated proportion to the width of shaft section 12 in order to keep the coupling compact while achieving a desired strength. Similarly, the width of coupling members 16 can be made to be of some stated proportion to the width of shaft section 12 in order to keep the coupling compact. In some embodiments, the total width of coupling 10, when assembled, is in the range of 1.5 to 3.0 times the width of shaft section 12.

[0036] While other embodiments may be designed for lighter loads, in some

embodiments, shaft sections 12 and coupling 10 are designed to carry tension loads of at least 20kN and shaft sections 12 and coupling 10 are configured to transmit torques of at least 2,000 N-m. In some embodiments couplings 10 can transmit higher torques and tensions. For example, a coupling 10 may be designed to withstand torques in excess of 20,000 N-m or 100,000 N-m and tensions of 400 kN or more. Thus, couplings as described herein may be used in heavy-duty applications for which light-duty coupling designs would be unsuitable. [0037] Figure 1A shows a shaft section 12 according to one example embodiment.

Projections 14 are provided at both ends 12A and 12B of shaft section 12. In this embodiment, the middle part 12C of shaft section 12 can be round in cross section whereas the ends 12A and 12B can be square in cross section. Such a shaft section may be fabricated, for example, by forging end portions of a round bar to have square cross sections. Projections 14 at ends 12A and 12B may also be square in cross section. Figure ID is a possible cross section of shaft section 12 at C-C showing a round middle part 12C. Figure 1C is a possible cross section of shaft section 12 at B-B showing a square shaft end 12A. Figure IB is a possible cross section of shaft section 12 at A-A showing a square projection 14. In some embodiments, the diameter of the round middle part 12C is equal to the width of square end 12A or 12B. In other embodiments, the diameter of the round middle part 12C is equal to the diagonal of square end 12A or 12B. In some embodiments, the cross-sectional areas of ends 12A and 12B are equal to or greater than the cross-sectional area of middle part 12C. In another example embodiment the cross-sectional areas of ends 12A and 12B are at least of some stated proportion to the cross-sectional area of middle part 12C. The stated proportion may be, for example, in the range of 0.8 to 1.3.

[0038] Figure 2 shows a coupling 20 according to one more detailed example embodiment. Coupling 20 comprises two shaft sections 22 A and 22B (collectively or generally shaft sections 22) respectively having ends 23A and 23B (collectively or generally shaft ends 23). Shaft sections 22 have a square (or other non-round) cross- section at least in ends 23. Projections 24 project on the outsides of shaft ends 23. In the illustrated embodiment, each shaft end 23 has two projections 24. In general, each shaft end 23 has one or more projections 24. Figure 2A is a cross section through a shaft 22 showing a square projection 24.

[0039] Each projection 24 has a square (or other non-round) cross-section. In the illustrated embodiment, projections 24 have the form of projecting flanges that extend around the circumferences of shaft ends 23. Where projections 24 and shaft sections 22 are square in cross section, shaft ends 23 may be symmetrical in relation to rotations of 90 degrees.

[0040] Coupling 20 comprises connecting pieces 25. Connecting pieces 25 have recesses 26 to receive projections 24 on shaft sections 22A and 22B. In some embodiments, connecting pieces 25 are long enough that tips 27 of shaft sections 23A and 23B are held spaced apart from one another when projections 24 are engaged in corresponding recesses 26 on connecting pieces 25. In other embodiments, connecting pieces 25 have lengths such that tips 27 of shaft sections 23 are held directly against one another.

[0041] Coupling 20 can be assembled by bringing shaft ends 23A and 23B together, placing connecting pieces 25 to engage projections 24 on both shaft ends 23 and holding connecting pieces 25 in place. Various holding means may be provided to hold connecting pieces 25 in place. For example:

• one or more bolts may be provided to clamp connecting pieces to one another (as shown for example in Figure 2);

• a sleeve may be slid over connecting pieces 25 after they are in place (as shown for example in Figures 3A to 3C);

• straps, wires, a clamp, a clip or the like may be fastened around connecting pieces 25 after they are in place;

• connecting pieces 25 may be welded to one another after they are in place;

• connecting pieces 25 may be configured to receive one or more pins, keys, or other retaining members to lock connecting pieces 25 together;

• connecting pieces 25 may be configured to interlock with one another and/or with projections 24 so as to hold connecting pieces 25 in place; and

• the like.

[0042] In the embodiment illustrated in Figure 2, a bolt 28A passes through holes 30 in connecting pieces 25 and is attached to a nut 28B to secure connecting pieces 25 around end portions of shaft sections 22A and 22B. One feature of the embodiment illustrated in Figure 2 is that no holes through shaft sections 22 are required (particularly in the tension-carrying portions of shaft sections 22 lying between projections 24). Bolt 28A passes through gap 29 between tips 27 of shaft sections 22 A and 22B.

[0043] Additional advantageous features of the embodiment illustrated in Figure 2 include:

• connecting pieces 25 can be identical to one another (thereby making assembly easier and requiring fewer different kinds of pieces);

• both ends of each shaft 22 may be the same as one another (thereby potentially simplifying manufacture of shaft sections 22);

• ends of connecting pieces 25 are interchangeable (thereby potentially simplifying manufacture of connecting pieces 25 and assembly of couplings 20).

• Shaft sections 22 do not need to be threaded or subjected to other expensive machining processes.

Some other embodiments may share one or more of these features. It is not mandatory that all embodiments share any of these features.

[0044] The flanks of projections 24 may be oriented at right angles to surfaces of shaft sections 22. However, it can be advantageous for the flanks 32 of projections 24 to be angled, for example as shown in Figure 2. When flanks 32 are angled as shown and the inside faces of recesses 26 have complementary angles, as shown, then tension on coupling 20 tends to cause connecting pieces 25 to be forced apart, thereby locking connecting pieces against bolt 28A. Figure 2C illustrates schematically a projection 24 having a flank angle Θ. In some embodiments Θ is in the range of about 3 to 5 degrees. In some embodiments the flank angle is negative, as illustrated by the dashed line in Figure 2C.

[0045] It is convenient but not mandatory that projections 24 are oriented to extend at right angles to the longitudinal center line of a shaft section 22. In some embodiments, projections 24 are angled slightly relative to the longitudinal centerline of the shaft section 22 and/or have flanks that are curved or chevron-shaped. In such embodiments, the inside faces of recesses 26 that bear against the flanks have a configuration matching that of the flanks so as to provide a broad area of contact between the inside faces of recesses 26 and the flanks when the shaft is placed under tension. In some embodiments projections 24 extend around the ends of shaft section 22 in a low-pitch helix (e.g. projections 24 have the overall form of coarse threads).

[0046] One or more connecting pieces 25 of a coupling 20 may be configured to contact two or more faces of each shaft section 22. For example, one or more connecting pieces 25 may be C-shaped or L-shaped or V-shaped in cross section. An advantage of embodiments in which one or more connecting pieces 25 contact two opposing faces of shaft sections 22 (for example, where one or more connecting pieces 25 is C-shaped in cross section) is that torque loads can be transmitted by the connecting pieces 25 without imposing extra forces on whatever mechanism is supplied to keep connecting pieces 25 in place. Such "wrap around" connecting pieces may be used alone, with one or more other wrap around connecting pieces or with one or more flat connecting pieces.

[0047] Figure 2B illustrates the case where two connecting pieces 25A and 25B are each C-shaped in cross section. One connecting piece 25A has a base 32 that extends across one face 34A of shaft 22 and has arms 33A and 33B that extend onto faces 34B and 34D of shaft 22. A second connecting piece 25B has a base 32 that extends across face 34C of shaft section 22 and has arms 33C and 33D that extend onto faces 34B and 34D of shaft section 22. Longitudinal channels 34 are defined between arms 33 of each connecting piece 25A and 25B. In this embodiment, recesses 26 may extend across arms 33 of connecting pieces 25A and 25B as well as across base 32. Connecting pieces 25A and 25B may together extend completely or nearly completely around the

circumferences of the ends of shafts 22.

[0048] In the embodiment illustrated in Figure 2B, shafts 22 cannot rotate relative to one another after they have been engaged in the channels of connecting pieces 25A and 25B, Thus the coupling 20 is capable of transmitting generous torque between shafts 22. [0049] Instead of, or in addition to a bolt such as bolt 28A connecting pieces 25 may be held in place by a sleeve as illustrated, for example, in Figures 3 through 3C. In the Figure 3 embodiment, a coupling 40 has two connecting pieces 45 which are both C- shaped in cross-section. Connecting pieces 45 are held in place by a sleeve 46. Sleeve 46 may be held in place over connecting pieces 45 by one or more of a clamp, set screw, bolt, pin, welding, deformation of some portion of sleeve 46, or the like.

[0050] Figure 3A, shows a coupling 40A comprising two connecting pieces 45A and two connecting pieces 45B. Connecting pieces 45A and 45B are all rectangular in cross section with connecting pieces 45 A wider than connecting pieces 45B.

[0051] Figure 3B shows a coupling 45B comprising connecting pieces 45C which are V- or L-shaped in cross section.

[0052] Figure 3C shows a coupling 45C comprising four connecting pieces 45D each having an L-shaped cross-section.

[0053] In all of Figures 3 through 3C coupling pieces have recesses (not shown) that engage projections on shaft sections to be coupled. In all of Figures 3 through 3C a sleeve 46 holds the connecting pieces in place. In embodiments which include a sleeve it can be advantageous for the flanks 32 of projections 24 to be angled, for example as shown in Figure 2. Where walls of recesses 26 have similar angles, the interaction of recesses 26 and projections 24 when tension is applied to pull coupled shaft sections 22 apart tends to force connecting pieces 25 outward into firm contact against inner walls of the bore of the sleeve.

[0054] A wide range of alternative embodiments are possible. For example:

• It is not necessary that projections 14 extend completely around the ends 23 of shaft sections 22. In some embodiments, projections 24 may be provided on two opposing faces of the ends of shaft sections 22. In some embodiments different projections 24 may be on different faces of shaft sections 22. • Ends 23 of shaft sections 22 may have cross-sectional shapes other than square. For example, ends 23 may be rectangular, pentagonal, hexagonal or the like.

• Alternative constructions may be provided for transmitting torque through a coupling as described herein. In such embodiments, ends 23 of shaft sections 22 may be round in cross-section. In some embodiments, ends 23 of shaft sections 22 are round in cross section while projections 24 are square in cross-section or have some other non-round shape. In some embodiments, ends 23 have splines, keyways, or other longitudinally-extending recesses or projections that engage corresponding recesses or projections of connecting pieces 25.

• It is not mandatory that there be multiple connecting pieces 16. For example, a coupling could comprise single connecting piece 16. As a specific example, a coupling may comprise a single C-shaped connecting piece that wraps around three faces of ends of each of two shaft sections being coupled.

[0055] In some embodiments, couplings as described herein are applied to couple shaft sections in helical piers. Such helical piers may be used, for example, in the context of pile structures as described in Vickars et al. US patent Nos. 5707180, 6264402, 6435776, and 6652195.

[0056] In some such embodiments shaft sections 12 are conveniently 3 to 10 feet in length. 4 foot long shaft sections 12 may be used in some applications. In some such embodiments connecting members 16 may be, for example, 9 inches or less in length. In some embodiments, connecting pieces for coupling ends of 2-inch square shaft sections are approximately 6 to 7 inches long. While not mandatory, making connecting pieces short relative to shaft sections 12 makes connecting pieces 16 easy to handle and relatively inexpensive. In some embodiments, even relatively short connecting pieces can provide couplings that fully develop the shaft sections in tension, torque bending and shear.

[0057] Figure 4 illustrates that soil displacing members or helical screws may be incorporated into couplings as described herein. Figure 4 shows a portion of a helical pier 50 comprising shaft sections 52A, 52B and 52C coupled by couplings 53. Each coupling 53 includes a sleeve 55 that holds in place coupling members (e.g. connecting pieces as described above). One or more helical screws 56 are mounted to one or more of sleeves 55. Helical screws 56 may be removably attached to sleeve 55 or permanently attached to sleeve 55. The helical screws may, for example, comprise angled and/or curved metal plates. In the illustrated embodiment, sleeves 55 are retained by providing pins, bolts or the like that pass through holes 57 in sleeves 55. Soil-displacing members such as disks, plates, projecting arms, circumferential flanges, one or more

longitudinally -extending radially-projecting plates, ridges, blades, or the like may optionally be mounted to one or more sleeves 55.

[0058] Figure 5 shows a coupling 60 according to another example embodiment.

Coupling 60 comprises first and second interlocking coupling pieces 62A and 62B (collectively or generally coupling pieces 62) that couple the ends 63 of shaft sections 64A and 64B. Coupling pieces 62A and 62B may advantageously be identical to one another although this is not mandatory. Each of ends 63 carry projections 65 that are spaced apart longitudinally along ends 63. In this example, ends 63 are square or rectangular in cross section.

[0059] Each coupling piece 62 comprises a base 67 and arms 68 projecting at right angles to base 67. In the illustrated embodiment, connecting pieces 62 each have four arms 68. Two arms 68 A and 68C are spaced apart from one another along one edge of base 67 and two arms 68B and 68D are spaced apart from one another along an opposing edge of base 67. Inner faces of base 67 and arms 68 define a channel 69 dimensioned to receive ends 63 of shaft sections to be coupled together. Arms 68 A and 68C are spaced apart from one another to leave a gap 70 A dimensioned to receive arm 68D of an opposing coupling piece 62. Arms 68B and 68D are spaced apart from one another to leave a gap 70B dimensioned to receive arm 68C of an opposing coupling piece 62.

[0060] A groove 72 A extends across base 67 and arms 68A and 68B. A groove 72B extends across base 67 and arms 68C and 68D. Grooves 72 A and 72B are dimensioned to receive corresponding projections 65. Groove 73A extends across base 67 at a level corresponding to gaps 70A and 70B. Groove 73B extends across base 67 at a level that is spaced along base 67 from arms 68C and 68D.

[0061] Coupling 60 may be assembled by bringing shaft section ends 63 together and sliding coupling pieces 62A and 62B transversely into place with projections 65 each received in a groove 72. In the illustrated embodiment, a part of each projection 65 on one face of shaft section end 63 is also received in a groove 73. In the illustrated embodiment at least one arm 68 from each coupling piece 62 is interdigitated between two arms 68 of an opposing coupling piece 62. Specifically, in the illustrated embodiment, arm 68C of each coupling piece 62 is interdigitated between arms 68B and 68D of the other coupling piece 62 and arm 68D of each coupling piece 62 is interdigitated between arms 68A and 68C of the other coupling piece 62.

[0062] After coupling pieces have been installed then they may be held in place by locking them to one another and/or to shaft sections 62 and/or by applying a clamp, strap, or other holding device. In the illustrated embodiment, projections 65 are interrupted by gaps 75 and corresponding grooves 76 are formed across arms 68. Gaps 75 and grooves 76 line up to form longitudinally extending slots when connecting pieces 62 are in place around shaft section ends 63. When coupling pieces 62 are in place, pins 77 may be pushed into the longitudinally -extending slots. Pins 77 prevent removal of coupling pieces 62. Pins 77 may be tapered and/or held in place by other means such as a pin, screw, weld, detent mechanism, spring, pawl, barb, or the like.

[0063] Couplings having the general layout shown in Figure 5 may have a wide variety of alternative constructions while still retaining features of the construction of coupling 60. For example, in one alternative embodiment, coupling pieces are configured such that arms on one side of a base are aligned with gaps between arms on the opposing side of the base. In another alternative embodiment, coupling pieces 62 have more than the four arms 68 illustrated in Figure 5. In another alternative embodiment, projections 65 are provided only on two opposing faces of shaft ends 63. In such embodiments, grooves 72 do not need to extend onto arms 68.

[0064] Figure 6 shows a coupling 20A that is similar to coupling 20 of Figure 2 except that one connecting piece 25 is attached to an end of each shaft section 22A and 22B in advance. The attachment is only required to hold the connecting pieces 25 in place prior to assembly. After assembly the coupling is retained by a bolt 28A and nut 28B or the like. Therefore, the attachment may be provided, for example, by spot welds, suitable adhesive or the like. Assembly of coupling 20A is simplified. One need only to mate the ends of each of shaft sections 22A and 22B with the connecting piece 25 that is attached to the other shaft section and then clamp the connecting pieces 25 toward one another with a bolt / nut 28A, 28B or other holding mechanism to complete the coupling. In an alternative embodiment, one connecting piece 25 is attached to the end of one of shaft sections 22A, 22B as described above and the other connecting piece 25 is provided as a separate piece.

[0065] Figure 7 shows a coupling 80 according to an embodiment wherein shaft sections 12 are tubular and have internal bores 81. Such tubular shaft sections 12 may have various cross-sectional shapes. For example, tubular shaft sections may be round, square, triangular, rectangular, polygonal, oval etc. Bores 81 may extend part or all of the way along shaft sections 12.

[0066] In some of the above embodiments torque is transmitted between shaft sections by engagement of connecting members with outer faces on the ends of shaft sections being coupled. Various alternative constructions may be provided for transmitting torque between coupled shaft sections 12. In some embodiments where one of these alternative constructions is applied, projections 14 and the outsides of the ends of shaft sections 12 are optionally round in cross section. Figure 8A illustrates a coupling 85A wherein torque is transmitted between shaft sections 12 by mechanical interference between structures 86A and 86B respectively on ends of the coupled shaft sections 12A and 12B. Connecting pieces 16 hold shaft sections end-to-end so that structures 86A and 86B remain engaged.

[0067] In coupling 85A structures 86A and 86B provide interdigitating projections (collectively 86). Projections 86 may have the form of castellations, as shown, gear teeth, or the like, In the illustrated embodiment, shaft sections 12 are hollow and projections 86 are formed on edges of the ends of the walls of shaft sections 12.

[0068] Figure 8B illustrates another example coupling 85B wherein at least the ends of shaft sections 12 are hollow to provide bores 88 that are non-round in cross section. A torque transmitting bar 89 is fittingly received in bores 88. Bar 89 may be kept in place bridging shaft sections 12A and 12B by, for example, one or more of: ends of bores 88 that abut ends of bar 89; stops 90 A within bores 88 that abut ends of bar 89; a flange 90B or other projection that abuts ends of shaft sections 12A and 12B to prevent bar 89 from sliding very far within bores 88; a bolt or pin passing through or projecting from bar 89 that may also be used to hold connecting members 16 in place. In some embodiments bar 89 has splines that engage internal splines (not shown) in bores of shaft sections 12A and 12B.

[0069] Figure 8C shows a coupling 85C that is similar to coupling 85B except that a torque-transmitting tube 92 is provided in place of (or optionally in addition to) bar 89. Tube 92 has a non-round bore 93 that fittingly receives ends of shaft sections 12A and 12B.

[0070] Figure 8D shows a coupling 85D in which a socket 95 is formed on one end of a shaft section 12A. Socket 95 is configured to receive an end of shaft section 12B. Socket 95 and the end of shaft section 12B have complementary cross-sections so that engagement of the end of shaft section 12B in socket 95 allows transmission of torque between shaft sections 12A and 12B. Connecting members 16A and 16B are configured with recesses 96 that receive the outside of socket 95. The outside of socket 95 may function as a projection 14 (optionally in conjunction with one or more additional projections 14 on the end of shaft section 12A). In the illustrated embodiment, two additional projections 14 are provided on the end of shaft section 12A while three projections 14 are provided on the end of shaft section 12B.

[0071] Figure 8E shows a coupling 85E which has been formed by deforming a heavy sleeve 98 around the ends of shaft sections 12A and 12B such that projections 14 are captured within the deformed sleeve 98. Sleeve 98 may be applied in-situ using a portable hydraulic press to crimp the walls of sleeve 98 against the ends of shaft sections 12A and 12B on either side of projections 14. Sleeve 98 and projections 14 may have complementary non-round cross-sections to facilitate transmission of torque between shaft sections 12A and 12B by way of sleeve 98. In some embodiments, shaft sections 12A and 12B may be hollow. In some embodiments, interdigitating castellations, gear teeth, or the like may be formed on edges of the ends of shaft sections 12A and 12B to facilitate transmission of torque between shaft sections 12A and 12B.

[0072] Figure 9 shows a coupling 100 according to another embodiment of the invention. Like a number of the other embodiments described herein, coupling 100 provides a first set of features for transmitting torque between shaft sections being coupled and a second set of features for transmitting tension forces between the shaft sections being connected. In the illustrated embodiment, tension is transmitted between first and second shaft sections 102A and 102B by way of tension rods 104. Tension rods 104 extend between fittings 106A and 106B (collectively or individually fittings 106) on shaft sections 102A and 102B respectively.

[0073] In the illustrated embodiments, each of fittings 106 comprises a flange 107 penetrated by apertures 108. Each tension rod 104 passes through corresponding apertures 108 in the two flanges 107. Apertures 108 are spaced apart around flanges 107. Preferably, three or more apertures are provided in each one of flanges 107 and three or more corresponding tension rods 104 extend between flanges 107. This helps to make connection 100 resistant to bending. Tension rods 104 may be spaced apart evenly around flanges 107. [0074] Flanges 107 may be welded onto the shaft sections or made to be unitary with the shaft sections. The attachment of each flange 107 to its corresponding shaft section 102 is sufficiently robust to withstand all expected forces that may be applied to flanges 107 by tension rods 104. Preferably the connection of flanges 107 to shaft sections 102 is such that under extreme tension forces, connected shaft sections 102 will fail before failure of the connections between flanges 107 and the shaft sections 102 to which they are attached.

[0075] Flanges 107 are affixed near the ends of shaft sections 102. Preferably, tension rods have a collective tensile strength at least equal to that of shaft sections 102 such that the tensile strength of the shaft sections 102 and not the tensile strength of tension rods 104 limits the maximum tensile loading of the resulting shaft.

[0076] Tension rods 104 may be threaded at one or both ends so that they can be secured in place between flanges 107 by way of nuts 111. In some embodiments, tension rods 104 comprise bolts having heads on one end and being threaded to receive one or more nuts 111 at a second end. In the alternative, tension rods 104 may be in the form of studs that are threaded at both ends to receive nuts 111. Alternative ways to keep tension rods 104 engaged between flange 107 may be provided. For example, heads may be formed on tension rods 104 while tension rods 104 are in place between flanges 107 by upsetting one end of the tension rods.

[0077] Tension rods 104 may comprise a high-tensile strength alloy, for example an alloy having a yield strength of at least 80000 kpsi. The alloy may, for example, comprise a high-strength steel alloy. For example, tension rods 104 may comprise grade 8 bolts.

[0078] In some embodiments, the cross-sectional area of each tension rod 104 is at least equal to the area A given by: A = (B xC)/(D xN) where B is the minimum cross sectional area of shaft sections 102 between flanges 107, C is the ultimate yield strength of the material of tension rods 104 and D is the ultimate yield strength of the material of shaft sections 102 at the location of the minimum cross sectional area and N is the number of tension rods 104 in each connection 100.

[0079] Preferably, tension rods 104 extend substantially parallel to shaft sections 102 when coupling 100 is assembled such that tension rods 104 do not bend in response to tension being applied to coupling 100. In some embodiments, tension rods 104 comprise a head or washer having a spherical profile that engages a corresponding recess in a flange 107 such that, under tension, tension rods 104 are self-aligning to the direction of tension and tend not to bend.

[0080] In the illustrated embodiment, coupling 100 comprises a projection 115 at the end of shaft section 102A and a socket 117 configured to receive and engage projection 115 at the mating end of second shaft section 102B. As shown in Figure 10, shaft sections 102 may be made to have a socket 116 at one end and a projection 115 at the other end. Multiple such shaft sections may be coupled together by couplings 100 to provide a shaft of a desired length.

[0081] The engagement of a projection 115 of one shaft section in a socket 117 of a connected shaft section transmits torque loads between the shaft sections. Preferably the fit of projection 115 in socket 117 is tight enough to prevent relative the coupled shaft sections from rotating enough to change the angle of tension rods 104 by a significant amount. For example, the fit may be sufficiently snug to maintain the tension rods parallel to logitudinal axes of the shaft sections within +1- 3 degrees.

[0082] As an alternative to a projection that is received in a socket, a coupling that uses tension rods to carry tension loads between shaft segments may have other features to transmit torque loads between shaft sections. For example, torque loads may be transmitted using features as shown in the other embodiments described above and illustrated in the accompanying drawings. Without limitation, such features may include: a sleeve having a through-passage or sockets on each end that non-rotationally receives projecting ends of the coupled shaft sections; and interdigitating teeth or other projections on the ends of the coupled shaft sections.

[0083] In use, the ends of two shaft sections are aligned with one another and brought together so that the torque transmitting features are engaged. Tension rods 104 are inserted through apertures 108 and then pre-tensioned sufficiently to hold the torque transmitting features in engagement using nuts or other fastenings.

[0084] Another aspect of the invention provides methods for coupling shaft sections together. An example embodiment of such a method comprises aligning two shaft sections having projections as described herein co-axially with ends of the aligned shaft sections proximate to one another. The method continues by applying connecting pieces having recesses to accommodate the projections to the ends of the shafts such that the projections on the shaft sections are engaged in corresponding recesses of the connecting pieces. The method is completed by securing the connecting pieces to one another and/or to one or both of the shaft sections. In some embodiments this last step comprises bolting the shaft sections together. In some embodiments the method comprises passing a bolt between ends of the shaft section and securing the connecting pieces to one another with the bolt. In some embodiments, securing step comprises sliding a sleeve over the connecting pieces and securing the sleeve in place.

[0085] Advantageously, shaft couplings as described herein may be designed so that a shaft assembled out of shaft sections connected by such couplings is fully-developed in all of shear, bending, torque and tension. That is, when such a shaft is subjected to loads in shear, bending, torque or tension to the point that the shaft fails, the failure of the shaft will occur in the material of the shaft and not at the couplings. Such couplings can be readily designed to provide a desired safety factor (for example, 25 %).

[0086] Another advantage of some embodiments is that shaft couplings according to such embodiments are simple to assemble in the field, have only a small number of parts, and cannot be assembled improperly. [0087] Advantageously, in some embodiments, connecting members and/or shaft sections comprise raw castings or forgings or rough-machined parts which do not require expensive finish machining operations to produce and which can be assembled in the field without the need for assembly personnel to concern themselves with tight- tolerance fits.

[0088] The features of example embodiments described herein may be combined in other combinations to yield other example embodiments. For example, an embodiment may be created by providing shaft sections having projections of one or more of the types as described herein, selecting a combination of one or more connecting pieces formed to receive the projections, and selecting one or more mechanisms for retaining the connection pieces in engagement with the projections. Some embodiments additionally include one or more mechanisms for facilitating transmission of torque between shaft sections selected from any of the example torque-transmission mechanisms disclosed herein. As another example, couplings like any of couplings 10, 20, 20A, 60, 80, or 85A through 85E may optionally have any compatible characteristics described above in relation to others of the described couplings and vice-versa.

[0089] Different aspects of the invention may be characterized in different ways. For example, some aspects provide couplings for coupling together shaft sections characterized by any one or more of the following:

• the coupling comprises connecting members or pieces that have recesses to

engage projections that project outwardly from the shaft sections and the coupling pieces are urged together by a bolt or other member that passes between ends of the shaft sections;

• the coupling comprises connecting members or pieces that have recesses to

engage projections that project outwardly from the shaft sections at least one of which engages two or more faces of two coupled shaft sections so as to serve as a path for transmission of torque between the shaft sections; the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections and the connecting members or pieces are held in place by a sleeve,

the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections and the connecting members and projections are dimensioned so as to fully develop the shaft sections in at least tension and torque.

the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections, the projections extend circumferentially around the ends of the shaft sections and the recesses extend circumferentially around the ends of the shaft sections (in some embodiment the bearing contact between sides of the recesses and faces of the projections extends for 360 degrees measured relative to a longitudinal centerline of the shaft sections. In some embodiment the bearing contact extends around the shaft sections through an angle of 330 degrees or more (again measured relative to a longitudinal centerline of the shaft sections).

the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections and ends of the shaft sections are shaped to provide members (e.g. teeth, castellations, or the like) that mechanically interfere with one another so as to facilitate transmission of torque between the shaft sections.

the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections, the shaft sections are hollow and the coupling comprises a bar slidably received in hollow ends of the shaft sections, the engagement of the bar with the bores in the shaft sections constraining rotation of the bar to facilitate transmission of torque between the shaft sections.

the coupling as described herein is applied as a coupling in a helical pier, the coupling comprises connecting members or pieces that have recesses to engage projections that project outwardly from the shaft sections and lacks a bolt, pin or other member passing transversely through any tension-bearing portion of either of the shaft sections.

methods comprise using couplings as described herein to transmit tension and/or torque in screw piers or similar apparatus.

[0090] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.