ZA200610844B - Teltale and overstress indicator for tendon lock-off devices - Google Patents
Teltale and overstress indicator for tendon lock-off devices Download PDFInfo
- Publication number
- ZA200610844B ZA200610844B ZA200610844A ZA200610844A ZA200610844B ZA 200610844 B ZA200610844 B ZA 200610844B ZA 200610844 A ZA200610844 A ZA 200610844A ZA 200610844 A ZA200610844 A ZA 200610844A ZA 200610844 B ZA200610844 B ZA 200610844B
- Authority
- ZA
- South Africa
- Prior art keywords
- tendon
- groove
- indicating
- overstress
- bore
- Prior art date
Links
- 210000002435 tendon Anatomy 0.000 title claims description 30
- 239000004033 plastic Substances 0.000 claims description 8
- 229920003023 plastic Polymers 0.000 claims description 8
- 238000009434 installation Methods 0.000 claims description 4
- 230000000750 progressive effect Effects 0.000 claims description 2
- 239000003795 chemical substances by application Substances 0.000 claims 1
- 239000000463 material Substances 0.000 description 4
- 239000011435 rock Substances 0.000 description 4
- 238000010276 construction Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 229920002379 silicone rubber Polymers 0.000 description 1
- 239000004945 silicone rubber Substances 0.000 description 1
Landscapes
- Piles And Underground Anchors (AREA)
Description
TELLTALE AND OVERSTRESS INDICATOR
FOR TENDON LOCK-OFF DEVICE IC 08 / I VR 4h a
This invention relates to a device provided with indicating means for locking a tendon under desired tensions. The invention is concerned primarily with rock anchors, but is also applicable to other tendons such as prestressed reinforcing elements for concrete in the construction industry.
Rock anchors comprise an elongate tendons, such as a rod or cable, means to secure the distal end of the tendon in a bore in the hanging wall, a load distributing washer and a device lockable along the proximal end of the tendon for tensioning the tendon. The locking device, referred to as a "lock-off barrel" in the art, comprises a body with a through bore having a tapered portion through which the tendon can pass, and a cone comprising a plurality of locking wedges for gripping the tendon received in the tapered portion of the bore.
The tendon has a breaking point under tension of 10 to 30 tonnes, depending on thickness and material, but prior to this limit reaches a plastic point at which the material starts to deteriorate irreversibly.
This invention seeks to provide a lock-off barrel with an overstress load indicator.
One aspect of the invention provides a locking device for a tendon comprising a body with a through bore having a tapered portion through which the tendon can pass, and a cone comprising a plurality of locking 3s wedges for gripping the tendon received in the tapered portion of the bore, wherein at least one substantially circumferential groove is formed in the exterior of the body such that the groove will collapse when a predetermined overstress limit is reached.
C2724FABCHEM 21.12.2006 page 2
Closing of the groove indicates that the tendon has been tensioned excessively. In this regard the predetermined limit may be at approximately the plastic point or limit of thé tendon to indicating that it has been overstressed. When overstressed, the tendon may be replaced or the indicator may be used as an warning that further anchors should be installed or that the roof or hanging wall may collapse undesirably.
A plurality of overstress indicating grooves, each having its own collapsing point, may be formed in the body to provide a progressive indication of the stresses on the tendon.
Preferably an elastomeric or plastics indicating ring is seated in the or each groove. In use the ring will be extruded out of the groove when the groove collapses to provide a readily visible indication thereof.
The overstress load indicating groove is preferably continuous, although discontinuities or ungrooved portions may be provided or formed to achieve desired stress indicating limits.
The overstress load indicating groove is preferably used with other load indicators for indicating proper prestressing of the tendon on installation. Such other load indicators may be grooves with indicating rings, shear rings and the like.
Further features, variants and/or advantages of the invention will emerge from the following non-limiting description of an example of the invention made with reference to the accompanying schematic drawings and from the claims, which are to be regarded as an integral part of this description.
Figure 1 shows a partly sectioned side view of an embodiment of lock-off device of the invention, prior to installation:
Figure 2 shows a partly sectioned side view of the device of Figure 1, after installation; 3s Figure 3 shows a partly sectioned side view of the device of Figure 1, after it has been overstressed; and
Figure 4 shows an underplan view of the device of Figure 1.
C2724FABCHEM 21.12.2006 page 3
B2006/71084%
The drawings show a lock-off device 10 for a tendon, also known as a lock-off barrel, for a cable strand rock anchor. The device comprises a barrel body 12, a locking cone member 14, a tensioning load-indicator 16 and an overstress load indicator 17.
The body 12 has a round cylindrical rear portion 12.1, a rounded nose portion 12.2, a tapered bore 18 that narrows from the rear end to the nose end, a tension load indicating annular groove 20 near the rear end, and an overload indicating groove 21 near the front end. The grooves 20 and 21 are configured and dimensioned, ie. width of groove, shape of groove base and thickness of material between groove and bore 18, such that each will collapse when a predetermined load is applied to the device in use. :
The locking cone 14 has a taper corresponding to the taper of the bore 18 and comprises three annular wedges 14.1 that have a smooth outer side and, on the inner sides, a part of a round bore formed with teeth to engage a cable or rod. A circlip 14.2 holds the three wedges together. :
The load indicators 16 and 17 are each O-rings of suitable plastics, such as silicone rubber, that is visible in an underground mine working under suitable conditions. For example the plastics may be photoluminescent or :phosphorescent or made of a material that is reflective and easily visible under poor light conditions.
Also shown in Figure 1 is a nose portion 22 of a jack used to set the device in use. The nose has an outer portion 24 that will engage the barrel body in use and an inner plunger 26 that is relatively movable to the outer portion 22. The jack, as is well known in the art, also has: a clamp to engage a tendon or strand being tensioned; a ram that act such that the clamp pulls the strand and pushes against the rear end of the barrel; and a further ram to push the plunger against the locking cone to force the cone along the bore and cause the cone to grip the strand.
Figure 2 shows the device of Figure 1 when it has been set, ie. the tendon on which it is mounted has been tensioned to at least a predetermined extent. As can be seen the groove 20 has been compressed, the load indicator 16 extruded from the groove to become more visible, the locking
C2724FABCHEM 21.12.2006 page 4
~ cone 14 pushed towards the nose end of the barrel and the barrel collapsed axially by the width of the groove to the length indicated by arrow B.
Additionally and importantly, by collapsing the groove the barrel has deformed to form an annular rib 28 in the tapered bore 18. The rib is positioned behind the locking cone when set, so that the cone cannot be removed from the barrel. This prevents preactivation of the lock-off barrel, ie. compressed so that the load indicating groove 20 is collapsed, either with or without the locking cone installed. If the locking cone is not installed prior to preactivation, then the extent of the rib 28 is such that the cone cannot be inserted into the barrel at least sufficiently that it will be wholly received within the barrel. If the locking cone is installed prior to preactivation, then the rib 28 prevents the locking cone from opening sufficiently to thread a strand of appropriate cross-section through the bore therein.
The load indicating groove 21 is configured and dimensioned to collapse at a much higher strain on the tendon. For example, the groove 20 may collapse when the tendon is tensioned to 14 tonnes, a figure specified by a mine engineer, and the groove 21 may collapse at about 20 tonnes for a tendon having a plastic limit of about 20 to 21 tonnes and a breaking point of about 25 tonnes. These are typical figures for one type of rock anchor <and are given to illustrate and not limit the invention.
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 scope of the invention as defined in the claims.
C2724FABCHEM 21.12.2006 page 5
Claims (6)
1. A locking device for a tendon comprising a body with a through bore having a tapered portion through which the tendon can pass and a cone comprising a plurality of locking wedges for gripping the tendon received in the tapered portion of the bore, wherein at least one substantially circumferential groove is formed in the exterior of the body such that the groove will collapse when a predetermined overstress limit is reached.
2. The device of claim 1, wherein the predetermined limit is at approximately the plastic point or limit of the tendon.
3. The device of either of claims 1 or 2, wherein a plurality of overstress indicating grooves, each having its own collapsing point, are formed in the body to provide a progressive indication of the stresses on the tendon.
4, The device of any one of claims 1 to 3, wherein an elastomeric or plastics indicating ring is seated in the or each groove.
5.. The device of any one of claims 1 to 4, wherein the overstress load indicating groove is used with other load indicators for indicating proper prestressing of the tendon on installation.
6. A lock-off device substantially as herein described with reference to the drawings. DATE 21 December 2006 / LES/FISHER & CO. Applicant's Agents C2724FABCHEM 21.12.2006 page 6
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA200610844A ZA200610844B (en) | 2006-12-19 | 2006-12-19 | Teltale and overstress indicator for tendon lock-off devices |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA200610844A ZA200610844B (en) | 2006-12-19 | 2006-12-19 | Teltale and overstress indicator for tendon lock-off devices |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| ZA200610844B true ZA200610844B (en) | 2009-10-28 |
Family
ID=41449759
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| ZA200610844A ZA200610844B (en) | 2006-12-19 | 2006-12-19 | Teltale and overstress indicator for tendon lock-off devices |
Country Status (1)
| Country | Link |
|---|---|
| ZA (1) | ZA200610844B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017214639A1 (en) * | 2016-06-09 | 2017-12-14 | Ncm Innovations (Pty) Ltd | Progressive load indicator |
-
2006
- 2006-12-19 ZA ZA200610844A patent/ZA200610844B/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017214639A1 (en) * | 2016-06-09 | 2017-12-14 | Ncm Innovations (Pty) Ltd | Progressive load indicator |
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