GB2578935A - Improvements in or relating to anchor bolts - Google Patents

Abstract

An anchor bolt comprises a shank 21 with a first (distal) end having an external helical thread 22 for substrate engagement, and a second (proximal) end with a drive head portion 32 for driving it into a substrate such as concrete. The second end also has an internal thread for receiving a machined bolt (40, Figure 4) enabling fixture of components to the anchor bolt. The drive head portion may be a hexagonal, square or pentagonal recess, and the internally threaded portion may be of a smaller nominal diameter than the recess and be located distal relative to the proximal recess. Alternatively, the diameter of the threaded portion may be larger than the nominal diameter of the shaped recess and the shaped recess located distal relative to the proximal threaded portion. A flange 31 may be located at, and may be flush with, the proximal end of the shank. The anchor bolt may be produced by thread rolling a blank to plastically form the external thread, cold forming an inside drive surface to form the drive portion and drilling and tapping to form the internal thread. May be used to anchor machinery where headroom restricts lifting of the machinery.

Description

Improvements in or relating to Anchor Bolts

Field of the Invention

[1] The present invention relates to fasteners such as screwbolts in general s and to anchor bolts in particular. Anchor bolts are used in a number of industries, particularly the construction industry, where a fastening is required to fix a first structure to another structure.

Background to the Invention

[2] Whilst concrete has some considerable strength in resisting compressive loads, it has relatively poor tensile or torsional strength. Conventional threaded fixing devices such as screws are difficult to secure in masonry substrates since it is difficult for a conventional thread to find secure location within a bore in such a substrate. In order to provide security for structures paced on or otherwise attached to a concrete base or structure, further elements need to be provided. Metallic piles can be fixed into concrete during placement of the concrete prior to setting but, more commonly, studding or screwbolts are typically employed. Studbolts can be secured within concrete, using one of extra cement, screwthread attachment or by the use of expanding bolt sections which become securely embedded within the concrete.

[003] In a typical situation, for example in an engineering facility, lathes, milling machines -frequently in excess of one tonne in weight will be attached to a floor by means of studding. The studding, for example of having an M10 thread, will stand proud from a floor or other body by approximately 5 -20cm. An apertured foot to a piece of equipment, such as a lathe or similar machine, will be attached to the studding by having the apertured foot placed about the studding, the aperture conveniently comprising a circular hole or a slot, to allow for alignment. Given that the studding is fixed within the floor, it will be appreciated that the equipment will need to be raised above the studding, necessitating the use of substantial lifting gear or hoists, although in many situations fork lift trucks can be employed. It will also be realized that the area will need to have sufficient above machine room to enable lifting gear to be employed, precluding certain areas from providing suitable operating space for such equipment.

[4] Conventional threaded fixing devices such as screws are difficult to secure in masonry substrates since it is difficult for a conventional thread to find secure s location within a bore in such a substrate. Conventional screw thread fixings are accordingly conventionally secured within bores in masonry substrates by first lining the bore with a lining of relatively soft material into which the threaded fixing can cut its own thread, at the same time compressing the lining against the walls of the bore within the masonry substrate. A typical example of such a io lining is that sold under the trade mark Rawlplug. Such linings are available in fibrous and plastics material form and in a wide variety of configurations reflecting a very considerable activity in the art over the years to improve upon the security and ease of use of screw threaded fixing devices used with such liners.

[5] Adopting a somewhat similar principle, alternative forms of fixing device are of metallic material and structured so as to be expansible after introduction into a bore in a masonry material whereby compressive forces against or impingement into the internal surfaces of the bore resist withdrawal of the fixing device from the bore. Reflecting similarly substantial activity in the art, a wide variety of such devices is available. For example, various devices of this kind are available under the above-mentioned trade mark Rawlplug and under the trade marks Fischer and Hilti.

[6] GB2344629 (C Bickford) discloses an improved fixing device having a three thread helical thread arrangement, wherein the outer threads are smaller in height that the central thread and each of the sets of three parallel threads are separated by land gaps. Each thread has a helical angle of between 30° and 50°. The fixing device of GB2344629 is not particularly suitable for use with very soft substrates such as end grain timber. GB2386405 (C Bickford) discloses a thread rolled fixing device having a pair of spaced apart helical ridges, wherein the height of the ridges is increased from zero to full height over the first full turn and then from full height to zero height over the last full turn. US5531553 (C Bickford) discloses a masonry fixing device which comprises a steel shank which in the form of the blank is right circular cylindrical form. A ridge-grooveridge configuration extends helically along the lower portion of shank and comprises a pair of parallel opposed ridges upstanding from an adjacent land. Each ridge defines with the adjacent ridge a groove. At least the forward end of s the lower portion of shank is configured so as to provide a self-tapping facility.

In use, the fixing device is introduced into a pre-drilled bore in a masonry substrate such as brickwork by turning so as to form a thread on the interior walls of the bore. The axial dimension of the land is at least 50% of the blank diameter with the result that relatively large amounts of substrate material are io disposed between the edge-groove-ridge configurations when the fixing device is in place.

Object of the Invention [7] The present invention also seeks to provide a screwbolt for use as a ground anchor The present invention therefore seeks to provide an improved anchor bolt arrangement which overcomes or, at least, reduces some of the above-mentioned problems of the prior art. The present invention also seeks to provide a method of making such ground anchors.

Statement of Invention

[8] In accordance with a first aspect of the present invention, there is provided an anchor bolt assembly comprising an anchor bolt and machined bolt, wherein the anchor bolt comprises a generally cylindrical shank with an axis, said shank having a substrate engagement portion at a distal end, and a coupler engagement/drive head portion at a proximal end portion; wherein the substrate engagement portion comprises a helical thread and the coupler engagement/ head portion comprises a drive means whereby to enable rotation of the anchor bolt about its axis; wherein the proximal portion includes an internal thread whereby to permit engagement with the machined bolt, to enable fixture of components therewith.

[009] Conveniently, the coupler engagement/drive head portion comprises a shaped recess. Preferably, the coupler engagement/drive head portion comprises a hexagonal recess.

[010] In one embodiment, the internal thread of the proximal portion is of a reduced diameter relative to a diameter of the shaped recess and the internally threaded portion is distal relative to the shaped recess of the proximal portion.

[011] In an alternative embodiment, the internal diameter of the shaped recess of the proximal portion is of a reduced diameter relative to a diameter of the internal thread of the proximal portion and the shaped recess portion is distal relative to the internally threaded proximal portion.

1.0 [012] In a further embodiment, the anchor bolt is further provided with a flange element operably positioned about a proximal end of the shank. When a flange is provided, a greater area is provided for a component to be attached to, whereby to provide a more secure base for clamping. Conveniently, the flange element is flush with the proximal end of the shank [13] In accordance with a further aspect of the invention, there is provided a method of manufacturing an anchor bolt, comprising the following steps; providing a circularly cylindrical anchor bolt blank to a thread rolling mechanism to define a helical bore wall engagement configuration about a first, distal end of the blank, by a thread rolling apparatus, as is known; thread-rolling the anchor bolt blank between a fixed die and a displaceable die, the two dies being spaced apart by a gap therebetween, said gap being equal to the core diameter of the blank, moving the displaceable die in a reciprocating fashion such that the blank is plastically deformed whereby to provide an external screwthread; cold forming the inside drive surfaces whereby to provide an anchor bolt drive surface; drilling a recess; tapping the recess with a thread to permit screwfastening with a machined bolt. The components may be protected by simple plating techniques, such as zinc plating, or may need to be subjected to more rigorous techniques such as the nitriding of screwbolt components followed by the application of a Sheradizing process.

[14] The anchor bolt is selected such that it is sized and dimensioned to provide appropriate resistance to directional tensile loads, in use. Conveniently, the screwbolt comprises a twin helix threaded shank, which is known to provide a good grip on the inside surface walls of holes in masonry. The present invention has applications across a range of construction sectors including repair work, especially in communication networks such as vehicular highways, railways and tunnelling. The secure substrate anchoring together can provide an s increased efficiency and improved costs in many major engineering facilities, manufacturing plant and the like around the world.

Brief Description of the Figures

[015] For a better understanding of the present invention, reference will now be io made, by way of example only, to the Figures as shown in the accompanying drawing sheets, wherein:-Figure 1 illustrates a known two-part ground anchor; Figure 2 shows a twin helix ground anchor screwbolt; Figure 2a shows the footings of a piece of equipment secured to the ground by is way of an anchor screwbolt of Figure 2; Figures 3a and b show an axial view and a part section/part plan view from one side of a flanged anchor bolt in accordance with one aspect of the present invention; Table 1 comprises a set of recommended dimensions for a screwbolt shown in zo Figure 3a, b; Figure 4 shows a first anchor bolt fastening an item of steelwork to a concrete base in accordance with the present invention in part cross-sectional view / part perspective view; Figures 4b & 4c show side views of two variant anchor bolt assemblies in accordance with the present invention; Figure 5 shows a set of three anchor bolts in accordance with the invention; Figures 6a -6c show a 20mm screwbolt in accordance with the invention in views from one side, proximal end and with machined bolt in place; Figure 7 shows a proximal end view of a 16mm screwbolt in accordance with the 30 invention; Figures 8a -8b show a proximal end view and a side view of a flanged 12mm screwbolt in accordance with the invention; Figures 9a, 9b show the flanged 12mm screwbolt in accordance with the invention respectively with an M5 machined bolt with a butterfly head and an M5 machined bolt with an hexagonal socket head; Table 2 comprises a set of failure forces relating to tensile tests performed in s two types of concrete for differing anchor bolts in two types of concrete; Figures 10 shows a process step for forming an external thread; and, Figures 10a & 10b show die elements used in the thread forming process.

Detailed description of the Preferred Embodiments

io [016] There will now be described, by way of example only, the best mode contemplated by the inventor for carrying out the present invention. In the following description, numerous specific details are set out in order to provide a complete understanding to the present invention. It will be apparent to those skilled in the art, that the present invention may be put into practice with is variations of the specific.

[17] Referring now to Figure 2, there is shown a screwbolt 20 as is known, with the screwbolt acting as a ground anchor in accordance with the invention, prior to placement in concrete or like base support material. The ground anchor 20 comprises a screwbolt comprising a shank 21, with a twin-ridge thread 22 and an external fastening thread 23. Figure 2a shows how the ground anchor has been inserted into a bore 24 defined in a concrete support surface 25 and fastened thereto. The footing 26 of a piece of equipment, partition, etc., lies upon the surface of the concrete 25, the footing is clamped down by the use of threaded nut 28 with washer 27 acting upon an upper surface of the a flange 26.

The forces F, arising from the footing act directly onto the surface of the concrete.

[18] Figures 3a and 3b show a first embodiment 30 of the invention having a flange at the head or proximal end of the screwbolt. The flange 31 is detailed in plan view, with an internal hexagonal recess 32 to permit the screwbolt to be screwed into bore 24 within the concrete 25, the recess being coaxial with a central axis of the screwbolt (not indicated). It will be appreciated that the recess could instead be of a square section, of a pentagonal section for security reasons or otherwise. The hexagonal recess extends to a depth D and then reduces in diameter, but is provided with an internal screwthread 34, which continues for a depth C. The flange has a diameter H and a thickness G; the shank has a diameter A and a threaded section 22 that extends for a distance D, with a proximal end having a conical edged flat end 33.

[019] Figure 4 shows how a flanged anchor bolt 30 in accordance with the present invention is set into a concrete base 25. However, this concrete base 25 is covered, with a layer of asphalt 43, which asphalt is compressible and should not bear weight of equipment etc.. Accordingly, upon insertion of the screwbolt, io the screwbolt is rotated by way of a hexagonal key manually -or a powered nut-runner with a hexagonal drive key -until the outside face of flange 31 of the anchor bolt corresponds in distance from the concrete as the surface 44 of the asphalt is distant to the concrete. The steelwork 41 to be secured to the concrete is then placed over the upstanding flange 31, such that the central is recess of the flange is coaxial with an aperture associated with the steelwork 41, whereby a fixing threaded fastener 40 can be placed in and secured to the anchor bolt 30, whereby all the forces 45 due to a weight arising from an item of plant / equipment acts through the anchor bolt 30. In a variant, the drive means could be provided externally to the recess.

[020] Figure 5 shows a flanged 12mm diameter flanged anchor screwbolt 51, a non-flanged 16mm diameter flanged anchor screwbolt 52 and a non-flanged 20mm diameter flanged anchor screwbolt 53. Figure 6a details a side view which clearly shows a groove 61 between two parallel spaced apart screwthreads 62 upstanding from the shank 63 of the anchor bolt 53. Figure 6b details the hexagonal recess 64, together with the reduced diameter yet coaxial internally screwthreaded portion 65. Figure 6c shows how the load from a nut 40 and washer 63 apply forces F through a section of plate steelwork 41, to the anchor bolt, whereby, as discussed above in relation to an asphalt surface, the anchor bolt support can provide support at a distance distinct to a base concrete (or other type of firm support medium), enabling intermediate surfaces to be utilised, which may be important for certain processes associated with a particular type of plant. Figure 7 shows a still further view of screwbolt 52, detailing at its proximal end a hexagonal drive internal surface 64, together with the reduced inside diameter, internally screwthreaded surface 65. This fixing corresponds to the flanged "below ground anchor", the absence of the flange means that it does not offer a large surface for bearing the weight, but may well find application where a flange is too obtrusive.

[021] Figure 8a shows the anchor bolt 51 in perspective view of the distal flange 31 together with central aperture with hexagonal inside walls 64 together with reduced diameter internally threaded section 65. Figure 8b shows the anchor bolt in side perspective view; the groove 61 inside of the upstanding screwthread ridges 62 is clearly visible. Figure 9a and 9b show anchor bolt 51 io with a butterfly bolt head 22 for M5 screwthread fixing bolt 40 and hexagonal drive head 92 respectively, for clarity, no washer element is provided, but details on a particular type of washer -shakeproof, locking etc. will be selected by the skilled man, based on a perceived or actual need.

[22] Applicants have performed some testing of the anchor bolts and initial is results have shown that the below ground anchor bolts in accordance with the invention are capable of undergoing substantial tensile forces prior to failure. The largest test anchor bolt having a diameter of 20mm and a threaded length of 170mm was threaded in a bore of 20mm diameter within C5060 concrete failed after the application of mean force of 120KN. As is known, the site and, particularly, the condition of the concrete into which the anchor bolt is inserted is often the determining factors. Table 2 shows the mean results of a number of tests that have been performed with different anchor bolts in different types of concrete. It will be appreciated that tensile testing -i.e. pull out testing always entails maximum design load stress testing anticipated in construction to confirm that industry standards have been achieved, to check the suitability and allowable loads of an anchor type and check they have been installed correctly.

[23] The screwbolt may be exposed to processing fluids associated with manufacture that may be particularly corrosive and the components may need to be protected by simple plating techniques, such as zinc plating, or may need to be subjected to more rigorous techniques such as that described in Applicants patent EP2914756 where nitriding of screwbolt components is followed by the application of a Sheradizing process, conveniently in a non-oxidising atmosphere, preferably a nitrogen atmosphere.

[024] The actual anchor bolt is formed by thread rolling with a helical bore wall engagement configuration by a thread rolling apparatus, as is known. With s reference to Figure 10, a thread-rolling station 100 comprises a fixed die 101 and a displaceable die 102; the two dies are spaced apart by a gap G therebetween being equal to the core diameter of the product being rolled. The displaceable die is displaceable in reciprocating fashion indicated by Z. In use, a blank 103 is inserted between the fixed and moving dies by manual or io mechanical means as is known in the thread-rolling art. The reciprocating action of the moving dye then carries the blank between them and during this time, the blank is plastically deformed to the face of the dies as the blank rolls along the faces thereof. This gives rise to formation of the helical bore engagement configuration: die grooves 104 give rise to ridges 62 in the anchor bolt and die is ridges 105 give rise to grooves 61 in the anchor bolt. In the case of the example shown in Figure 11, both helical ridges are formed on the shank with identical helix angles with the result that the ridges are, of course, parallel one to another and separated by the same pitch throughout the extent of the helix. Both ridges serve as a screw thread for enabling removal of the anchor bolt device. Both ridges are of generally frusto-conical form in cross-section. Each ridge has an upstand from the surrounding basal surface of the shank which is uniform throughout the helix, with both upstands being the same as one another. The first and second ridges define a helical groove forming part of helical engagement configuration. Once the anchor bolt has been formed, the inside hexagonal drive surfaces can be formed by cold forming, as is known for the formation of hexagonal drives. In order to provide the internally threaded recess, again a standard process of drilling followed by tapping with the appropriate thread can be simply and easily implemented.