AU2015249143A1 - Fastening with load indicator - Google Patents

Abstract

H:\p1w\1nterwoven\NRPortbl\DCC\PLW\873' 1502 _.DOC-27/10/2015 - 10 A fastening for installation in concrete or the like has an indicator for visually indicating a loss or reduction in anchoring capacity of the fastening. The indicator comprises a spring washer interposed between a head of the fastening and a component being clamped by the fastening, the washer being deformable from an unstressed state to a compressed state upon setting of the fastening to a required loading and being returnable to or towards its unstressed configuration in response to loss or reduction of said loading to thereby cause a visual indication of such loss or reduction to be given. In one embodiment, the visual indication can be provided by an indicator cap applied to a head of the fastening and displaceable in response to return of the washer from its compressed state. In another embodiment, the visual indication is provided colouring a part of the washer in a bright colour which is observable upon return of the washer from its compressed state. Figure 1

Description

FASTENING WITH LOAD INDICATOR

[0001] The present invention relates to a fastening having an indicator to visually indicate unintended loosening of the fastener under load conditions. More particularly, but not exclusively, the invention relates to a masonry anchor or a screw-threaded type fastener as used in building construction and having a visual load indicator.

[0002] One widely used form of masonry anchor is an expansion anchor comprising an expansion sleeve which is forced into tight engagement with the wall of a hole drilled into masonry by an expansion cone which is drawn into the sleeve by tightening of the anchor bolt. General anchors of this type are marketed by the present applicants under their trade mark "DYNABOLT". To ensure that the anchor is set tightly within the hole to carry a specified design loading, the anchor needs to be set within the hole to a specified preloading which is basically a tensile loading within the bolt which draws the expansion cone into the expansion sleeve to expand the sleeve circumferentially into very tight anchoring engagement with the wall of the hole. In practice this is achieved by tightening the anchor bolt to a prescribed torque by use of a torque wrench or torque driver. Although tightening of the anchor bolt to the prescribed torque normally provides an indication that the anchor has been set to the necessary preload for secure anchorage, that is not always the case. Although there is a relationship between driving torque and preload in such anchors in ideal conditions, this can be influenced by extraneous factors such as an unusually rough surface against which the bolt is tightened or grit or dirt between the head of the bolt and the underlying surface; under these conditions for instance, setting the bolt to a specified torque might not achieve the required preload and as a consequence the anchor might not be properly set within the hole.

[0003] One of many possible uses of expansion anchors of the type discussed above is for anchoring temporary braces or props for precast concrete wall panels in building construction and these are sometimes referred to in the industry as brace anchors. The temporary braces are anchored at their upper ends to erected wall panels and base slabs at their lower ends, and support the panels in their erected condition until such time as the panels are interconnected to form a coherent self-supporting structure and which might not occur for days or weeks following erection. If the braced panels are subject to substantial loading, a high wind loading for instance, there is a risk that the loading might cause anchors to pull out of the holes in the panel or slab if the anchors have not actually been set to the required preload, leading to potentially catastrophic consequences if the bracing for a panel was to fail.

[0004] Another type of fastening frequently used in precast concrete construction and concrete construction cast in-situ involves the use of an internally-threaded ferrule set into the concrete during casting to form an anchoring point for a bolt or threaded rod and nut installed following casting to anchor another component to the cast concrete. Under certain dynamic loading conditions, that anchorage may also loosen.

[0005] The present invention in its preferred embodiments relates to a visual indicator associated with the anchor or other fastening to provide a visual indication that the fastening has loosened. Although a principal usage of the particularly preferred embodiment of the invention is with anchors for fixing temporary bracing (so-called brace anchors) as discussed above, it is to be understood that the invention also has applicability in a wide variety of other situations.

[0006] According to the present invention there is provided a fastening having an indicator for visually indicating a loss or reduction in anchoring capacity of the fastening following setting of the fastening, the indicator comprising a spring washer interposed between a head of the fastening and a component being clamped by the fastening, the washer being deformable from an unstressed state to a compressed state upon setting of the fastening to a required loading and being returnable to or towards its unstressed configuration in response to loss or reduction of said loading to thereby cause a visual indication of such loss or reduction to be given.

[0007] In the preferred embodiment the indicator comprises a base within which the washer is mounted and which is adapted to lie against the surface of the component to be clamped such that in the set condition of the fastening the compressed washer lies within a rim of the base. In one form, the indicator has an indicator cap adapted to be applied to the head of the fastening after setting, the cap when applied to the head being locked to the base, the arrangement being such that subsequent return of the washer to or towards its unstressed state upon loss or reduction in anchoring loading following setting will cause at least a part of the indicator cap to separate from the base to provide the visual indication. In another form at least part of the surface of the washer is concealed when the washer is in its flattened compressed state when the fastening is set and restoration of the washer to or towards its unstressed state arising from loss or reduction of the loading exposes that part for visual identification of the condition. In this other form, preferably the exposed part is of a bright colour to facilitate visual identification of the condition from a remote position.

[0008] In one form the fastening is a masonry anchor having utility in anchoring temporary braces in the erection of precast concrete wall panels in building construction. In another form the fastening is a bolt or other threaded fastening for installation into a component such as an internally-threaded ferrule.

[0009] The present invention also provides a load indicator as defined above for use in conjunction with a fastening such as a masonry anchor or threaded fastening.

[00010] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: [00011] Figure 1 is an exploded view of an indicator of a preferred embodiment associated with a bolt of an expansion anchor; [00012] Figure 2 is a section showing the indicator in a condition in which the anchor has been set into masonry to a required loading; and [00013] Figure 3 is a view showing the underside of an indicator cap of the indicator.

[00014] Figure 1 of the accompanying drawings shows in exploded form a load indicator associated with the bolt 2 of a masonry anchor of expansion type as discussed earlier. The bolt itself is shown in Figure 1 in somewhat schematic form, with a hexagonal head 2 and shank 4 extending from the head 2. Threading present on the shank to threadedly engage an expansion cone is not shown and likewise the expansion sleeve itself is not shown. The load indicator comprises a rimmed base 6, preferably of metal, and a Belleville washer 8 both mounted on the shank of the bolt beneath the head. As is well known, a Belleville washer is a spring washer of generally frustoconical shape in its unstressed state, and under compressive loading is deformed into a flattened state. The base 6 is cupped and of a diameter to receive the washer 8 when in its compressed flattened state (see Figure 2).

[00015] The indicator also comprises an indicator cap 10, preferably of plastic, and an ejector coil spring 12 associated with the head of the bolt.

[00016] The anchor is supplied preassembled with the Belleville washer 8 and base 6 adjacent the head 2 of the bolt and also with the expansion sleeve and expansion cone, the latter being threadedly engaged with the bolt towards the end of the shank. However the indicator cap 10 and ejector coil spring 12 are supplied separated from the anchor. The anchor is applied in conventional manner by passage through a component to be fastened, a base plate of a temporary brace for example, and into a hole predrilled into the masonry with the underside of the base being against an outer surface of the component being fixed; the bolt is tightened to a prescribed torque to fix the anchor within the hole in the masonry by expansion of the expansion sleeve into tight contact with the wall of the hole. During tightening of the bolt the applied loading will cause the Belleville washer 8 to flatten from its generally frustoconical unstressed state into its compressed flattened state in which it sits within the base with its upper surface substantially flush with the rim of the base and against the underside of the bolt head as shown in Figure 2.

[00017] When the anchor has been set to the required torque, the ejector spring 12 and indictor cap 10 are applied to the head 2 of the bolt. The rim of the base 6 is formed with outwardly-directed locking teeth at its upper end and the indicator cap 10 is formed with an inwardly-directed lip formation at its lower end and which snaps into locking engagement with the teeth of the base 6 when the cap 10 is pushed downwardly onto the bolt head 2 against the bias of the ejector spring 12 which is thereby held compressed when the cap is applied; alternatively, the locking teeth may be on the cap to engage with a suitable locking formation on the base. The lower end part of the cap including its inwardly-directed lip (or locking teeth in the alternative) is coupled to the remainder of the cap by a peripheral zone of weakness 14 which is of a strength sufficient to withstand the axial loading applied to the indicator cap by the ejector spring when compressed. The integrity of the zone of weakness also serves to provide a tamper-evident effect when the cap has been installed.

[00018] In alternative arrangements, the cap may be coupled to the base by a threaded connection between the two or by a push/twist connection similar to a bayonet connection.

[00019] In a variant a compression spring having the function of the spring 12 could be formed integrally with the base 6 to reduce the number of parts; in that case the spring may consist of spring fingers.

[00020] In use, provided the anchor remains firmly seated within the hole in the masonry, the anchor with applied indicator cap will remain in the state shown in Figure 2. If however due to insufficient preloading such as for the reasons discussed earlier, the anchor loosens in the hole, the compressive loading within the Belleville washer 8 releases to an extent sufficient to apply a differential loading between the upper part of the cap 10 via the bolt head and the lower part of the cap via its locking engagement with the base, the loading being sufficient to break the wall of the cap along the zone of weakness 14; it is to be noted that the cap is reinforced at its underside with ribs 16 as shown in Figure 3 to ensure that the cap breaks and thereby separates under the applied differential loading, rather than just deforms. When the zone of weakness is broken, the coil spring 12 is able to eject from the bolt head the main body of the cap 10 above the zone of weakness or at the very least to cause substantial and observable displacement of the main body of the cap. Either the absence of the cap or its substantial displacement from its regular position is visually identifiable such that on periodic inspection of the anchors the loosening of the anchor will be apparent to enable appropriate remedial action to be taken.

[00021] Although separation of the cap by breaking at a line of weakness is preferred, however in an alternative, separation could occur by breaking the locking connection with the base.

[00022] In an alternative embodiment of the invention, the indicator cap and associated ejector spring is omitted and, instead, visual indication of a loosening effect is given by observation of the configuration of Belleville washer if that returns from its normally flattened configuration under compressive loading to, or towards, its frustoconical configuration should the anchor loosen. To achieve this, that part of the outer surface of the washer which when in its flattened compressed condition is concealed against the underside of the bolt head is painted or is otherwise of a bright colour. If however the anchor loosens, restoration of the washer to, or towards, its generally frustoconical state will then expose that brightly coloured surface to provide a visual indication that the anchor has loosened.

[00023] Although the two embodiments described are alternatives, nevertheless it is envisaged that the second embodiment may be of particular value when the anchor is installed in a position remote from the ground where the showing of a bright colour resulting from the exposure of the Belleville washer may make it easier to observe from the ground than displacement of the indicator cap of the first embodiment.

[00024] Although both embodiments as described use a Belleville washer, other types of spring washer could alternatively be used to carry out the functions of the Belleville washer as described.

[00025] It is to be understood that the indicators described herein are capable of application in a variety of anchoring situations not just the anchorage of temporary bracing for concrete wall panels although that is a primary usage. The indicators also have utility with other types of masonry anchor than the specific type of expansion anchor described. For example the second embodiment could be used in conjunction with an expansion anchor of the type in which the expansion cone is formed integrally with the shank of the anchor with the shank being threaded at its outer end for engagement with a nut (which then forms the head of the anchor), the described indicator being used in conjunction with that nut. Indicators of either embodiment could be used in conjunction with masonry anchors of the type which operate by cutting a coarse thread into the wall of the hole during application, and even anchors which are set within the hole by a so-called chemical action usually involving the application of a strong two-part epoxy adhesive.

[00026] Indicators of either embodiment can also be used in conjunction with other types of fastening such as a bolt driven into an internally-threaded ferrule set into concrete during casting as discussed earlier; when the ferrule is used in conjunction with a threaded rod and nut, rather than a bolt, the indicator used would likely be in accordance with the second embodiment.

[00027] It should also be understood that the visual load indicators as described also have utility in a wide variety of other fasteners used in building construction or, indeed, more general engineering construction.

Claims (13)

1. A fastening having an indicator for visually indicating a loss or reduction in anchoring capacity of the fastening following setting of the fastening, the indicator comprising a spring washer interposed between a head of the fastening and a component being clamped by the fastening, the washer being deformable from an unstressed state to a compressed state upon setting of the fastening to a required loading and being returnable to or towards its unstressed configuration in response to loss or reduction of said loading to thereby cause a visual indication of such loss or reduction to be given.

2. A fastening with indicator according to claim 1, wherein the indicator comprises a base within which the washer is mounted and which is adapted to lie against the surface of the component to be clamped such that in the set condition of the fastening the flattened compressed washer lies within a rim of the base.

3. A fastening with indicator according to claim 2, wherein the indicator further comprises an indicator cap adapted to be applied to the head of the fastening after setting the fastening, the cap when applied to the head of the fastening being locked to the base, the arrangement being such that subsequent return of the washer to or towards its unstressed state upon loss or reduction in said loading following setting will cause at least a part of the indicator cap to separate from the base to provide the visual indication.

4. A fastening with indicator according to claim 3, wherein the indicator cap is locked to the base via a zone of weakness in the cap such that restoration of the washer to or towards its unstressed state causes the cap to break and separate at said zone of weakness.

5. A fastening with indicator according to claim 3 or claim 4, further comprising a compression spring acting on the cap to cause displacement of the cap following separation.

6. A fastening with indicator according to claim 1 or claim 2, wherein at least part of the surface of the washer is concealed when the washer is in its compressed state when the fastening is set and restoration of the washer to or towards its unstressed state arising from loss or reduction of said loading exposes said part for visual identification of the condition.

7. A fastening with indicator according to claim 6, wherein the said part is of a bright colour to facilitate visual identification of the condition from a remote position.

8. A fastening with indicator according to any one of claims 1 to 7, wherein the spring washer is a Belleville washer which is flattened when in its compressed state.

9. A fastening with indicator according to any one of claims 1 to 8, wherein the fastening is a masonry anchor.

10. A masonry anchor with indicator according to claim 9, wherein the anchor is an expansion anchor of the type having an expansion sleeve and expansion cone driven into the sleeve to set the anchor.

11. A masonry anchor with indicator according to claim 9 or claim 10 when used to anchor temporary braces in the erection of precast concrete wall panels in building construction.

12. A fastening with indicator according to any one of claims 1 to 8, wherein the fastening is a bolt or other threaded fastening for installation into a component such as an internally-threaded ferrule.

13. A load indicator for use with a fastening, the indicator being as defined in any one of claims 1 to 8.