AU2016222506A1 - Removable Anchor Bolt Assembly and Method - Google Patents

Abstract

A removable anchor bolt assembly comprising a bolt and a plug for engagement with a thread of the bolt; the plug formed as a coil spring; at least one end of the coil spring provided with a sharp projection extending beyond a notional cylinder defined by an outer diameter of the coil spring and, wherein the sharp projection leaves a scored groove along a surface of a bore hole when the anchor assembly is driven into the borehole for use. ci -~ 0 -~0 0 C ) cc 0 04 c 1~* ~ f. 00 \u. LI) ~ *~* .0. ~ ** _~ >

Description

TECHNICAL FIELD [0001] The present invention relates to fasteners and, more particularly although not exclusively, to removable fasteners for temporarily securing equipment to a structural surface.

BACKGROUND [0002] Anchor bolts have been in common use since at least the early part of the twentieth century. Two methods, mechanical and chemical, of securing a bolt in hole in a borehole are known. Perhaps the most common is that of the screwing action of the bolt acting to expand a plug or sleeve inserted into the borehole so that the friction between the expanded plug or sleeve and the surface of the borehole secures the bolt. An alternative arrangement mostly found in mining applications, is the use of an adhesive plug, activated by rotation of the bolt.

[0003] In mechanically secured bolts employing an expanded sleeve, the end of the bolt projecting from the sleeve is formed as tapered enlarged diameter bell which is partially drawn into the sleeve as a nut at the outer end of the bolt is advanced along the bolt thread. When the bolt is no longer required, it is cut off at the surface of the structure into which it was inserted, leaving a portion of the bolt and all of the sleeve in the borehole. At best this leaves a visible trace in the fagade but may also lead to corrosion.

[0004] A particular arrangement of a plug know in the prior art in US5006023 is a plug formed as a short section of a coil spring. As can be seen for example in figure 1 or 2 of US5006023, at a near end of the coil spring the wire of the coil is formed into a projecting extension lying approximately in line with the surface of a notional cylinder defined by the outside diameter of the spring. The tapered end of the threaded bolt engages with the coils of the spring and rotation of the bolt then expands the spring, provided that the projecting extension of the spring prevents rotation of the plug. It will be noted that the extension (26) presents a smooth surface to the inside of a borehole in which the device is placed making gripping to prevent rotation doubtful.

[0005] A similar arrangement is shown in EP2208897 in which a coil spring is provided with a tab or tang formed in the proximate end of the wire of the coil spring. One disadvantage of this latter arrangement is the relatively complicated manufacturing process required to produce the plate from the wire of the spring. Another is that the plate causes the initial assembly of the plug to the end of the bolt prior to insertion in the borehole, to force the axis of the plug somewhat out of alignment with the axis of the bolt, making insertion somewhat difficult in some boreholes. On the other hand, the diameter of some boreholes formed in a friable material such as concrete may turn

2016222506 02 Sep 2016 out of uneven or somewhat enlarged diameter from that nominally required for the anchor assembly, making it difficult to prevent the plug from rotating in the borehole.

[0006] In particular forms a related problem is control of the insertion depth. Mistakes relating to insertion depth should be avoided or minimised as such mistakes can lead to poor anchoring strength.

[0007] It is an object of the present invention to address or at least ameliorate some of the above disadvantages.

Notes [0008] The term “comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of “having” or “including”, and not in the exclusive sense of “consisting only of’.

[0009] The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.

SUMMARY OF INVENTION [00010] Accordingly, in one broad form of the invention, there is provided a removable anchor bolt assembly comprising a bolt, and a plug for engagement with a thread of the bolt; the plug formed as a coil spring; at least one end of the coil spring provided with a sharp projection extending beyond a notional cylinder defined by an outer diameter of the coil spring and, wherein the sharp projection leaves a scored groove along a surface of a bore hole when the anchor assembly is driven into the borehole for use.

[00011] Preferably, the assembly further includes a depth indicator associated with the bolt.

[00012] Preferably, the depth indicator is removably associated with the bolt.

[00013] Preferably, a proximate end of the bolt is provided with an hexagonal head, an unthreaded shank section and a threaded section; the depth indicator formed as a tubular sleeve of friable material around the unthreaded shank section.

2016222506 02 Sep 2016 [00014] Preferably, outer diameter of the threaded section of the bolt decreases from a first outer diameter at a proximate end of the threaded section to a second smaller outer diameter at a distal end; the second smaller outer diameter sized to engage with at least one coil at a proximate end of the coil spring of the plug.

[00015] Preferably, the sharp projection is formed by an angled cut of an end of wire of the coil spring of the plug at least at the proximate end of the coil spring.

[00016] Preferably, the end of the wire at the proximate end is bent outwardly relative the notional cylinder prior to being provided with the angled cut.

[00017] Preferably, the bend of the wire is substantially normal to the notional cylinder.

[00018] Preferably, the sharp projection engages with the scored groove to prevent rotation of the plug in the bore hole when the bolt advances into the plug by rotation of the bolt.

[00019] Preferably, progressive engagement of the thread of the bolt with the coils of the coil spring of the plug forces an increase in the outer diameter of the coil spring; the coils spring being pressed against the surface of the borehole.

[00020] Preferably, force of the outer diameter of the coils of the coil spring of the plug against the surface of the borehole acts to prevent withdrawal of the anchor bolt assembly from the borehole to a predetermined axial load.

[00021] Preferably, the bolt of the anchor bolt assembly may be removed from the borehole after use by contra-rotation of the bolt.

[00022] In another broad form of the invention, there is provided a method of securing equipment to a surface of a wall by means of a removable anchor bolt assembly; the method including the steps of:

- drilling a borehole into the surface,

- passing a bolt of the anchor bolt assembly through an aperture in a part of the equipment,

- assembling a plug of the anchor bolt assembly to a distal end of the bolt,

- inserting the bolt and plug into the borehole; a sharp projection of the plug forming a scored groove along a surface of the borehole,

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- applying rotation to a hexagonal head of the bolt until the part of the equipment is drawn into contact with the surface; rotation of the bolt causing enlargement of an outer diameter of the plug, and wherein the plug is in the form of a coil spring, a proximate end of the coil spring modified by a bend and cut of wire forming the coil spring to produce the sharp projection.

[00023] Preferably, the indicated depth is indicated by a distal end of an indicator spacer contacting the equipment.

[00024] Preferably, the borehole is drilled to a nominal diameter of the bolt of the anchor bolt assembly.

[00025] Preferably, an outer diameter of the coil spring is equal to the nominal diameter of the bolt.

[00026] Preferably, the sharp projection projects beyond the outer diameter of the coil spring by a percentage of the nominal diameter of the bolt.

[00027] Preferably, the percentage is in a range of 5 to 8percent.

[00028] In a further broad form of the invention, there is provided a method of forming a plug of a removable anchor bolt assembly; the plug in the form of a coil spring provided at least at one end with a sharp projection; the projection formed as a modification of wire of the coil spring by the steps of:

- bending an end of an extension of the wire to form a projecting wire section extending substantially radially beyond an outer diameter of the coil spring,

- cutting the projected wire section wire at an angle to the axis of the projecting wire section, and wherein the sharp projection forms a scored groove in a surface of a borehole when the anchor bolt and plug are inserted into the borehole for use.

[00029] Preferably, the method further includes the step of inserting the bolt and plug into the borehole to an indicated depth.

[00030] Preferably, the sharp projection projects beyond an outer diameter of the coil spring by a percentage of the outer diameter; the percentage lying in the range of 5 to 8percent.

BRIEF DESCRIPTION OF DRAWINGS [00031] Embodiments of the present invention will now be described with reference to the accompanying drawings wherein:

2016222506 02 Sep 2016 [00032] Figure 1 is a side view of a bolt and plug of a removable anchor bolt assembly according to a preferred embodiment of the invention;

[00033] Figure 2 is an end view of a plug of the anchor bolt assembly of figure 1 showing the process of forming a sharp projection on the coil spring forming the plug, [00034] Figure 3 is an end view of a borehole showing a scored groove formed by inserting the plug of figures 1 and 2 into the borehole, [00035] Figure 4A is a sectioned view of the anchor bolt assembly of figure 1 inserted partially in a borehole for use, [00036] Figure 4B shows the disposition of the bolt in the borehole after rotation to engage with plug of the assembly, [00037] Figure 5 is a side view of the coil spring forming the plug of the anchor bolt assembly, [00038] Figures 5 A and 5B are end views of two preferred embodiments of the coil spring of the plug of Figure 5.

DESCRIPTION OF EMBODIMENTS

First Preferred Embodiment [00039] With reference to Figures 1 to 5, a removable anchor bolt assembly 10 according to the invention, comprises a bolt 12, fitted with a spacer 50 and a plug 14, the latter in the form of a section of a coil spring. The bolt 12 is provided typically with a hexagonal head 16, an unthreaded shank 18 and a threaded section 20 which decreases from a maximum outer diameter efi (the nominal diameter of the bolt) at a proximate end 22, to a smaller diameter at a distal end 24. The second smaller outer diameter of the bolt 12 at the distal end 24 is sized to engage with at least one turn of coil 26 at a proximate end 28 of the coil spring of the plug 14. The pitch of the coils of the coil spring and that of the thread of the bolt are substantially the same.

[00040] Refening now also to Figures 5 and 5A, at least the proximate end 28 of the coil spring of the plug 14 is provided with a, preferably, sharp projection 30 extending by a distance h beyond a notional cylinder 32, defined by the outer diameter di of the coil spring. As best seen in Figure 2,

2016222506 02 Sep 2016 the sharp projection 30 may be formed by an angled cut 34 of an end of the wire of the coil spring at the proximate end 28 of the plug 14. The sharp projection 30 is formed to prevent rotation of the plug 14 when the anchor bolt 12 is rotated to engage with, and advance into, the plug 14 as explained more fully below.

[00041] As can be seen from Figure 2 the sharp projection 30 may be formed by firstly bending an extension 36 (shown in dashed lines) of the end of the wire of the coil spring, so as to project substantially radially beyond an outer diameter of the coil spring. The projecting wire extension 36 is then cut at an angle to form the sharp projection 30. Typically the sharp projection 30 projects beyond the outer diameter of the coil spring by 0.3 to 0.5mm.

[00042] With reference now to Figures 4A and 4B, in use a fitting, such as for example a bracket 40 of scaffolding (not shown) may need to be secured to the surface 42 of a wall 44. A borehole 46 to the nominal size of the anchor bolt 12 of the anchor bolt assembly 10, is drilled into the wall 44. Typically the diameter d4 of the borehole 46, if drilled in friable material such as concrete, will be a little larger that the nominal size d3 of the drill. Thus for example, for an Ml 6 anchor bolt, the borehole diameter d4 typically turns out to be about 16.7mm in diameter (d4=d3+Ad where Ad-3~5%> di). To prevent rotation of the plug 14 when the anchor bolt 12 is rotated to firstly engage with, and then advance into the coils of the plug in expanding di, it is particularly preferred that the sharp projection 30 projects and also ‘bites’ into the surface 48 of the borehole 46. For an M16 bolt, the amount of projection of the sharp projection 30 is preferably approximately 0.4mm. [00043] In use, depending on the size of the aperture in the bracket 40, the bolt 12 may firstly be passed through the aperture in the bracket 40 and the plug 14 then threaded onto the distal end 24 of the bolt sufficient to retain the plug on the end of the bolt, and the assembly of bolt and plug pushed into the borehole 46.

[00044] As shown in Figures 1 and 4A, the bolt 12 is supplied with a depth control indicator, preferably in the form of a tubular spacer 50, formed of some friable material such as a polymer, paper or cardboard and which is easily removed by on site personnel. The spacer 50 is positioned under the hexagonal head 16 of the bolt and controls the depth to which the bolt and plug assembly should initially be inserted to the designated depth before rotating the bolt 12 in the borehole.

[00045] As shown in Figure 4A, in a first step, the assembly of bolt 12 and plug 14 is inserted into the borehole 46 to the point at which the distal end of the spacer 50 is in contact with the bracket 40. The spacer 50 is then removed from the shank of the bolt.

[00046] As the plug 14 at the end of the bolt 12 is pushed into the borehole 46, the sharp projection 30 leaves a scored groove 52 along the surface 48 of the borehole as best seen in Figure 3, and the enlargement inset of Figure 4A.

2016222506 02 Sep 2016 [00047] In a following step, the bolt is rotated and, given the groove 52 is deep enough, engagement of the sharp projection 30 within the groove 52, will prevent the plug 14 from rotating in the borehole 46. As the bolt 12 is rotated, it engage with, and advances into and through the coils of the coil spring of the plug 14 as shown in Figure 4B.

[00048] The advance of the bolt 12 through distance A progressively forces an increase in the outer diameter of the coils from the initial diameter di to (h due to the increasing diameter and wedging effect of the tapered bolt. Thus the coils of the spring are pressed into the surface 48 of the borehole with sufficient force to prevent extraction of the bolt to a predetermined maximum holding load. For an M16x90mm bolt for example, this holding force is of the order of 26kNewtons in a wall of concrete with compressive strength of 32Mpa.

Second Preferred Embodiment [00049] As shown in Figures 5 and 5A by dashed lines, both ends of the coil spring forming the plug 14, may be provided with projections 30 and 30a formed as described above, thus providing two scored grooves as the plug is inserted into a borehole. The two projections may be diametrically opposed as shown in Figure 5, 5A or may be offset as shown in Figure 5B.

Third Preferred Embodiment [00050] In this further preferred embodiment, a removable anchor bolt assembly again comprises a bolt and a plug in the form of a steel coil spring as described above, but in this embodiment the coil spring is not provided with projections. Instead, the assembly includes an additional component in the form of a secondary coil spring formed of a high friction polymer material.

[00051] The secondary coil spring is of similar pitch to that of the steel coil spring but is of slightly larger outer diameter. This polymer spring is threaded onto the steel coil spring, in effect leaving projecting ridges between the coils of the steel coils. An end of the polymer spring is formed so that it nests against the distal end of the wire forming the steel coil spring and prevents the steel coil spring rotating within the coils of the polymer spring when they are fully assembled together.

[00052] When this anchor bolt assembly is inserted into a borehole to an initial depth as described for the embodiments above, the friction contact of the polymer ridges with the walls of the borehole prevents the plug from rotation, allowing rotation of the bolt relative to the plug to cause expansion of the steel coil spring and retention of the bolt in the borehole.

2016222506 02 Sep 2016

Industrial Applicability [00053] The anchor bolt assembly of the invention according to the first embodiment above, provides a more reliable means of securing fittings to the wall of a structure. An additional advantage of the system in use is that the bolt is easily removed from the wall by unscrewing, leaving a considerable depth of borehole which may be filled with grouting. If the plug coil spring being made of hot-dipped galvanized or stainless steel or aluminium, this will prevent its corrosion. Given a separate supply of plugs, bolts removed after completion of a project, may be used again. This further provides an environmental advantage over those anchor bolts which cannot be removed but must be cut at the surface of the structure. This firstly leaves an entry point for concrete cancer and, secondly leaves unusable bolt heads as waste.

[00054] Moreover, the manufacture of an anti-rotation part of the plug is simplified providing a significant cost saving.

2016222506 02 Sep 2016

Claims (21)

1. A removable anchor bolt assembly comprising a bolt, a depth indicator and a plug for engagement with a thread of the bolt; the plug formed as a coil spring; at least one end of the coil spring provided with a sharp projection extending beyond a notional cylinder defined by an outer diameter of the coil spring and, wherein the sharp projection leaves a scored groove along a surface of a bore hole when the anchor assembly is driven into the borehole for use.

2. The assembly of claim 1 further including a depth indicator associated with the bolt.

3. The assembly of claim 2 wherein the depth indicator is removably associated with the bolt.

4. The assembly of claim 2 or 3 wherein a proximate end of the bolt is provided with an hexagonal head, an unthreaded shank section and a threaded section; the depth indicator formed as a tubular sleeve of friable material around the unthreaded shank section.

5. The assembly of any one of claims 1 or 2 or 3 or 4 wherein outer diameter of the threaded section of the bolt decreases from a first outer diameter at a proximate end of the threaded section to a second smaller outer diameter at a distal end; the second smaller outer diameter sized to engage with at least one coil at a proximate end of the coil spring of the plug.

6. The assembly of any one of claims 1 to 5 wherein the sharp projection is formed by an angled cut of an end of wire of the coil spring of the plug at least at the proximate end of the coil spring.

7. The assembly of claim 6 wherein the end of the wire at the proximate end is bent outwardly relative the notional cylinder prior to being provided with the angled cut.

8. The assembly of claim 7 wherein the bend of the wire is substantially normal to the notional cylinder.

9. The assembly of any one of claims 1 to 8 wherein the sharp projection engages with the scored groove to prevent rotation of the plug in the bore hole when the bolt advances into the plug by rotation of the bolt.

10. The assembly of any one of claims 1 to 9 wherein progressive engagement of the thread of the bolt with the coils of the coil spring of the plug forces an increase in the outer diameter of the coil spring; the coils spring being pressed against the surface of the borehole.

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11. The assembly of claim 9 wherein force of the outer diameter of the coils of the coil spring of the plug against the surface of the borehole acts to prevent withdrawal of the anchor bolt assembly from the borehole to a predetermined axial load.

12. The assembly of any previous claim wherein the bolt of the anchor bolt assembly may be removed from the borehole after use by contra-rotation of the bolt.

13. A method of securing equipment to a surface of a wall by means of a removable anchor bolt assembly; the method including the steps of:

- drilling a borehole into the surface,

- passing a bolt of the anchor bolt assembly through an aperture in a part of the equipment,

- assembling a plug of the anchor bolt assembly to a distal end of the bolt,

- inserting the bolt and plug into the borehole; a sharp projection of the plug forming a scored groove along a surface of the borehole,

- applying rotation to a hexagonal head of the bolt until the part of the equipment is drawn into contact with the surface; rotation of the bolt causing enlargement of an outer diameter of the plug, and wherein the plug is in the form of a coil spring, a proximate end of the coil spring modified by a bend and cut of wire forming the coil spring to produce the shaip projection.

14. The method of claim 13 further including the step of inserting the bolt and plug into the borehole to an indicated depth.

15. The method of claim 14 wherein the indicated depth is indicated by a distal end of an indicator spacer contacting the equipment.

16. The method of any one of claims 13 to 15 wherein the borehole is drilled to a nominal diameter of the bolt of the anchor bolt assembly.

17. The method of any one of claims 13 to 16 wherein an outer diameter of the coil spring is equal to the nominal diameter of the bolt.

18. The method of any one of claims 13 to 17 wherein the sharp projection projects beyond the outer diameter of the coil spring by a percentage of the nominal diameter of the bolt.

19. The method of claim 18 wherein the percentage is in a range of 5 to 8percent.

2016222506 02 Sep 2016

20. A method of forming a plug of a removable anchor bolt assembly; the plug in the form of a coil spring provided at least at one end with a sharp projection; the projection formed as a modification of wire of the coil spring by the steps of:

- bending an end of an extension of the wire to form a projecting wire section extending substantially radially beyond an outer diameter of the coil spring,

- cutting the projected wire section wire at an angle to the axis of the projecting wire section, and wherein the sharp projection forms a scored groove in a surface of a borehole when the anchor bolt and plug are inserted into the borehole for use.

21. The method of claim 20 wherein the sharp projection projects beyond an outer diameter of the coil spring by a percentage of the outer diameter; the percentage lying in the range of 5 to 8percent.

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Fig. 4A Fig. 4B