ZA201100863B - Load indicator - Google Patents

Description

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LOAD INDICATOR

TECHNICAL FIELD

This invention relates to a load indicator and is concerned primarily, though not exclusively, with a device for indicating tensile loads applied to a tendon member, such as a rock anchor or anchor bolt, having a shank, a head towards one end of the shank and a barrel member movable along and lockable onto the shank to tension the shank.

BACKGROUND ART

Tendon members are used in underground mine warkings to tension the hanging wall and thereby inhibit the hanging wall from collapsing while the working is still in use. The tendon members must be tensioned properly to be effective. Until recently the tension was monitored by observing or controlling the forces applied by a jack or other tool used to tension the tendon member. Now it is more common to use load indicating lock-off barrels, such as that disclosed in South African Patent No. 97/8519, which has a ring that shears when a preset tension is reached, and that disclosed in South African Patent No. 88/0320, which has a barrel with a deformable zone formed by a circumferential groove that closes when a preset tension is reached. Neither barrel is able to indicate tensions to which the tendon member has been subjected after installation. Knowledge of such tensions would be extremely useful for determining both the structure of the rock of the hanging wall, its stresses and its changes over time, as well as the performance characteristics and quality of the installed tendon member.

Typically the installation tension ranges from 80 to 200 kN (kilo Newtons), while the load capacity of the anchor ranges from 250 to 380 kN.

Thus, the invention seeks to provide a load indicator for tendon members that can indicate the performance of the tendon member in use, such as the tensions to which it is subjected over time after installation, and can indicate the installation tension.

M £20117 00863

DISCLOSURE OF THE INVENTION

According to a first aspect of the invention there is provided a load indicating device for a tendon member, the load indicating device comprising a socket member and a spigot member that can be forced into the socket member, the extent to which the spigot member is forced into the socket member indicating the tension applied to the tendon member.

In an embodiment, the load indicating device is integral with a locking device for a tendon member.

In an embodiment, the tendon member comprises a shank having a distal end and a proximal end, head means for locking the distal end of the shank, the locking device movable along the shank from the proximal end towards the distal end and being selectively lockable to the shank

In an embodiment, the socket member is threaded onto the shank between the locking device and the head means, with the spigot member being arrangeable between the locking device and the head means such that it tends to be forced into the socket member when tension is applied to the shank between the head means and the locking device.

Either the spigot member or the socket member may be integral with the locking device.

Preferably the spigot member has a substantially central through bore, so that the load indicating device can be threaded on to the tendon member.

Preferably the spigot member is engaged with the socket member sufficiently to ensure that the members do not separate during normal handling prior to tensioning of the tendon member.

Preferably the spigot member is tapered along at least a portion of its length, so that the force required to move it deeper into the socket member increases as it progresses into the socket member.

+ -2011/ 00863

Preferably marking means is provided to indicate the extent to which the spigot member has been inserted into the socket member. Preferably the spigot member has longitudinally spaced markings that may extend helically or substantially circumferentially. Preferably the markings are coloured. Preferably the coloured markings are arranged in colour to correspond substantially to the colour arrangement of a rainbow. Preferably the rainbow colours range from blue to red and are arranged such that red indicates maximum load Preferably a marking is provided to indicate that a desired installation tension has been achieved; this marking may correspond to a first (blue) marking on the spigot member or may be a separate marking with a readily visible marking, such as a white coloured marking. Preferably, the outer surface of the spigot member may comprise at least one groove to accommodate the markings. Preferably the markings are fluorescent or reflective, so that they are readily visible in poor light conditions.

According to a second aspect of the invention there is provided a load indicating device in combination with a tendon member, the tendon member comprising a shank having a distal end and a proximal end, head means for locking the distal end of the shank, and a locking device movable along the shank from the proximal end towards the distal end and being selectively lockable to the shank, and the load indicating device comprising a socket member and a spigot member that can be forced into the socket member, the socket member being threaded onto the shank between the locking device and the head means, and the spigot member being arrangeable between the locking device and the head means such that it tends to be forced into the socket member when tension is applied to the shank between the head means and the locking device.

Further features, variants and/or advantages of the invention will emerge from the following non-limiting description of examples of the invention made with reference to the accompanying schematic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a partly sectioned view of a first embodiment of load indicating device integral with a lock-off barrel threaded on

° -*2011/ 00863 to the shank of a rock anchor, only a portion of which is shown;

Figure 2 shows a partly sectioned side view of a second embodiment of load indicating device integral with a lock- off barrel threaded on to the shank of a rock anchor, only a portion of which is shown; and

Figure 3 shows a graph of displacement against tension for a rock anchor fitted with a load indicating device of the invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

In the drawings the same or similar parts have the same reference numbers, certain parts having sub-numbers to identify them as part of a component or as substantially equivalent parts in different embodiments.

Figure 1 shows a rock anchor locking and load indicating device 8 comprising a load indicating device 10 integral with a lock-off barrel 12 The lock-off barrel 12, as conventional, has a cylindrical body 20 formed with a tapered bore that receives a plurality of arcuate, tapered wedges 22 that lock on to a shank 36 of an anchor 35 when pushed into the body 20.

The load indicating device 10 comprises a spigot member 16 and a socket member 18. The spigot member 16 is integral with the body 20 of the lock-off barrel 12, has an axial bore 24, is threaded on to the shank 36 and is formed with a plurality of spaced circumferential grooves 26. Colour is applied to the base of each of the grooves 26 using reflective coloured tape wrapped around the spigot, though coloured reflective or fluorescent paint may also be used if desired. The spigot member 16 has a tapered nose 28 at its free end remote from the lock-off barrel 12.

The socket member 18 comprises a cylindrical tube 30 that is flared at one end 32 and has a rounded nose 34 at the other end. The leading end of the spigot member 16 is engaged in the flared portion 32 of the socket member 18, so that the spigot member 16 and socket member 18 are joined to each other sufficiently not to separate during normal or expected handling.

2°2011/ 00863

In practice, the socket member 18 is initially cylindrical and the flare 32 is formed when the tapered nose 28 of the spigot member 16 is forced into the free end of the socket member 18. The spigot member 16 is relatively harder than the socket member 18, and this is done by a choice of suitable materials or by hardening the spigot member 16, as desired.

The spigot member 16 has a slight outward taper from its free end towards the lock-off barrel 12, so that the force required to move it deeper into the socket member 18 increases as it progresses into the socket member 18.

The drawing also shows a section through a portion of a domed washer 38 used as a loading member that abuts the mouth 50 of the hanging wall surrounding a bore into which a rock anchor 35 is inserted.

In practice, the device 8 is assembled as shown in the drawing. A rock anchor 35 is made up by securing a locking head (not shown) to one end of a suitable shank 36, fitting a domed washer 38 and then the device 8 to the shank 36 and binding the device 8 to the shank 36, so that the anchor 35 is complete and ready for insertion into a bore in a hanging wall when required.

The anchor 35 is installed by inserting the locking head into a bore in hanging wall, moving the device 8 along the shank 36 until the washer 38 is near to the mouth 50 of the bore, and then tensioning the shank 36 using a jack that grips the shank 36 and pushes the device 8 along the shank 36 so that it is forced against the washer 38. Force is applied until the spigot member 16 has been pushed to a required depth into the socket member 18, indicated by the first groove 26.1 adjacent the free end of the spigot member 16 being adjacent to the end of the socket 18

This tells the installer that the anchor 35 has been correctly tensioned, and the installation can be easily checked visually by an inspector.

In use, as the hanging wall tends to sag or drops as the earth moves then the load indicating device 10 yields by the spigot member 16 progressing into the socket member 18. The yield strength or resistance to yielding increases as the spigot member 16 moves into the socket member 18 The movement of the spigot member 16 into the socket member 18can be inspected periodically or when desired to determine how much the hanging wall has dropped, the tensile load supported by the

” £°2011/ 00863 anchor 35 and whether the anchor 35 has performed as intended.

Figure 2 shows a load indicating and locking device 8.1 comprising a load indicating device 10.1 and a lock-off barrel 12.1. The load indicating device 10.1 comprises a tubular socket 18.1 one end of which engages a boss 21 on the lock-off barrel and a spigot 16.1 that is engaged in the other end of the socket. The spigot has a tapered end 28.1 that fits into the socket and an opposed hemispherical end 34.1. This is assembled, used and functions in much the same way as the embodiment of Figure 1, other than that the load indicating device can be attached to any desired lock-off barrel, which needs to be modified to have a boss 21 to engage the socket.

Figure 3 shows a graph of displacement against tension for a rock anchor fitted with a load indicating device of either of Figures 1 or 2. In this event the displacement is a measure of the movement of the spigot member into the socket.

As can be seen the displacement and load, and hence yield characteristic, are substantially linear and confined within upper and lower limit lines 36.1 and 36.2.

This continues until point 38 where the domed washer starts to deform: first to be substantially flat and then with further loading to be domed in the opposite direction. Further loading cause the spigot to move further into the socket in a substantially linear manner until point 40 when the shank of the rock anchor fails.

The invention is not limited to the precise details described above and shown in the drawings. Modifications may be made and other embodiments developed without departing from the spirit of the invention. For example, the load indicating device 10 may be formed as a separate component so that it can be used with a lock-off barre! of choice that need not be modified in any way.

Claims (20)

CLAIMS Co

1. A load indicating device for a tendon member, the load indicating device comprising a socket member and a spigot member that can be forced into the socket member, the extent to which the spigot member is forced into the socket member indicating the tension applied to the tendon member.

2. The load indicating device of claim 1, wherein the load indicating device is integral with a locking device for a tendon member.

3. The load indicating device of claim 2, wherein the tendon member comprises a shank having a distal end and a proximal end, head means for locking the distal end of the shank, the locking device movable along the shank from the proximal end towards the distal end and being selectively lockable to the shank

4. The load indicating device of claim 3, wherein the socket member is threaded onto the shank between the locking device and the head means, with the spigot member being arrangeable between the locking device and the head means such that it tends to be forced into the socket member when tension is applied to the shank between the head means and the locking device.

5. The load indicating device of any one of claims 2 to 4, wherein either the spigot member or the socket member is integral with the locking device.

6. The load indicating device of any one of the preceding claims, wherein the spigot member has a substantially central through bore, so that the load indicating device can be threaded on to the tendon member.

7. The load indicating device of any one of the preceding claims, wherein the spigot member is engaged with the socket member sufficiently to ensure that the members do not separate during normal handling prior to tensioning of the tendon member.

8. The load indicating device of any one of the preceding claims, wherein the spigot member is tapered along at least a portion of its length, so that

> *201 -e011/ 0086 3 the force required to move it deeper into the socket member increases as it progresses into the socket member.

9. The load indicating device of any one of the preceding claims, wherein marking means is provided to indicate the extent to which the spigot member has been inserted into the socket member.

10. The load indicating device of claim 9, wherein the spigot member has longitudinally spaced markings that may extend helically or substantially circumferentially.

11. The load indicating device of either claim 9 or claim 10, wherein the markings are coloured.

12. The load indicating device of claim 11, wherein the coloured markings are arranged in colour to correspond substantially to the colour arrangement of a rainbow.

13. The load indicating device of claim 12, wherein the rainbow colours range from blue to red and are arranged such that red indicates maximum load.

14. The load indicating device of either claim 12 or clam 13, wherein a marking is provided to indicate that a desired installation tension has been achieved.

15. The load indicating device of claim 14, wherein the marking corresponds to a first marking on the spigot member or may be a separate marking with a readily visible marking.

16. The load indicating device of claim 15, wherein the readily visible marking comprises a white coloured marking.

17. The load indicating device of any one of claims 10 to 16, wherein the outer surface of the spigot member comprises at least one groove to accommodate the markings.

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18. The load indicating device of any one of claims 10 to 17, wherein the markings are fluorescent or reflective, so that they are readily visible in poor light conditions.

19. A load indicating device in combination with a tendon member, the tendon member comprising a shank having a distal end and a proximal end, head means for locking the distal end of the shank, and a locking device movable along the shank from the proximal end towards the distal end and being selectively lockable to the shank, and the load indicating device comprising a socket member and a spigot member that can be forced into the socket member, the socket member being threaded onto the shank between the locking device and the head means, and the spigot member being arrangeable between the locking device and the head means such that it tends to be forced into the socket member when tension is applied to the shank between the head means and the locking device.

20. A load indicating device substantially as herein described and illustrated. DATED THIS 2"° DAY OF FEBRUARY 2011 4 £ Ze GILFILLAN INC. FOR THE APPLICANT