Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Reexamination Certificate
1999-03-26
2001-08-14
Novosad, Christopher J. (Department: 3671)
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
C052S704000, C411S354000, C411S267000, C411S268000, C411S270000
Reexamination Certificate
active
06273646
ABSTRACT:
FIELD OF THE INVENTION
THIS INVENTION relates to the tensioning of tendons. More particularly it relates to a method of pre-stressing a tendon. It also relates to a barrel, to a pre-stressing kit and to a setting tool suitable for use in the method.
SUMMARY OF THE INVENTION
The Inventor is aware that pre-stressed or pretensioned tendons, e.g. lengths of wire rope or steel rods, are often used in the construction and mining industries. For example, in the mining industry, tendons, e.g. in the form of lengths of wire rope, are often used for support, e.g. for the hanging wall, in an underground mine. This can be achieved by drilling a hole in the hanging wall and anchoring an end of the tendon in the hole, e.g. adhesively or mechanically. A bearing element, e.g. an apertured plate, is positioned over the end portion of the tendon protruding from the hole in the hanging wall. The tendon may be tensioned using a barrel and wedge system. This entails positioning a barrel having a hole therethrough over the end portion of the tendon in abutment with the bearing element. The tendon is tensioned to a predetermined level and the barrel is secured to the tensioned tendon by a wedge arrangement positioned between the barrel and the tendon. Hence, the tension in the tendon urges the barrel against the bearing element which in turn is urged into abutment with the hanging wall to support the hanging wall.
In order to install the barrel, use is made of a tensioning jack. The tensioning jack includes a nose which abuts the barrel, a gripping formation which grips the protruding end of the tendon and displacement means for displacing the gripping formation and nose in opposite directions to tension the tendon.
One problem associated with this system is that difficulty can be encountered in setting or blocking of the wedge, i.e. in urging the wedge between the barrel and the tensioned tendon. In addition, once installed there is no indication that the tendon has been correctly tensioned.
It is an object of this invention to provide means which the Inventor believes will at least alleviate this problem.
According to one aspect of the invention there is provided a method of pre-stressing a tendon using a barrel and wedge system which includes the steps of
positioning a barrel having a hole therethrough over the tendon;
applying a tensile load to the tendon; and
applying via a setting member an oppositely disposed force to a spacing member which is configured to transmit said oppositely disposed force to the barrel until a predetermined force is achieved at which stage the setting member urges the wedge arrangement between the barrel and the tendon to secure the barrel in position on the tendon.
The method may include the step of positioning at least part of the wedge arrangement in the hole such that it is a loose fit between the barrel and the tendon prior to applying a load to the tendon, the spacing member being configured to maintain a clearance between the setting member and the wedge arrangement until the predetermined force is achieved at which stage the spacing member permits the setting member to engage the wedge arrangement and urge it between the barrel and the tendon.
The spacing member may fail structurally at the predetermined load which results in the tendon being tensioned to the desired tension. Preferably the structural failure of the spacing member at the predetermined load will be sudden or catastrophic thereby allowing the degree of pretensioning to be controlled fairly accurately.
The spacing member may fail in shear.
According to another aspect of the invention there is provided a barrel for use in pre-stressing a tendon, which includes
a body having a hole therethrough; and
a spacing member connected to the body and configured to transmit a load from a setting member to the body.
The spacing member may be configured to fail structurally when a load in excess of a predetermined load is applied thereto.
The body may be generally circular cylindrical in shape, the hole extending axially therethrough and having a diameter which decreases over at least part of its length towards a leading end of the body. The leading end of the body may be rounded.
The spacing member may be annular in form.
The spacing member may be in the form of a shear ring.
An annular recess may be provided in the body immediately adjacent the shear ring into which recess at least part of the material of the shear ring is displaced, in use, when the shear ring fails.
The barrel may include indicating means to indicate that the spacing member has failed and hence that a tendon has been tensioned or pre-stressed to the required tension. The indicating means may include a filler material in the recess which filler material is at least partially displaced when the shear ring fails. The filler material may be configured at least partially to absorb shock loads when the shear ring shears. In one embodiment of the invention, the filler material may be an epoxy. In another embodiment of the invention, the filler material is a metal such as a aluminum. In yet another embodiment of the invention, the filler material is a synthetic plastics material.
The shear ring may be formed integrally with the body. In a preferred embodiment of the invention, the shear ring may be defined between a pair of axially spaced apart annular recesses in the body.
According to yet another aspect of the invention there is provided a pre-stressing kit which includes
a barrel as hereinbefore described; and
a wedge arrangement, at least part of which is receivable, in use, in the hole in the body between the body of the barrel and a tendon extending therethrough.
According to still yet another aspect of the invention there is provided a pre-stressing kit which includes
a barrel having a body through which a hole extends;
a wedge arrangement, at least,part of which is receivable, in use, in the hole in the body of the barrel between the body and a tendon extending therethrough; and
a spacing member which is configured, in use, to transmit a force from a setting member to the body of the barrel until a predetermined force is reached at which stage the spacing member permits the setting member to urge the wedge arrangement between the body of the barrel and the tendon to secure the barrel in position on the tendon.
The spacing member may be formed integrally with the body.
The wedge arrangement may include a plurality of wedge elements.
According to a further aspect of the invention there is provided a setting device for use in pre-stressing a tendon using a barrel and wedge system, the barrel of which includes a body and a spacing member in the form of a shear ring fast with the body, the setting device including
a nose having a leading end and defining an annular radially inwardly open channel-shaped formation adjacent the leading end; and
a shear ring engaging member which is floatingly mounted and held captive in the channel-shaped formation and which is configured to engage and transmit a load to the shear ring of a barrel.
The shear ring engaging member may be in the form of a discontinuous ring.
The nose and the discontinuous ring may include complementary formations configured to cause the discontinuous ring to contract diametrically when the discontinuous ring and nose are urged towards one another in use.
The setting device may be in the form of a tensioning jack and includes a gripping formation for gripping a tendon and displacement means for displacing the gripping formation and the nose in opposite directions.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings.
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patent: 5397202 (1995-03-01), Shrader et al.
patent: 5486079 (1996-01-01), Martin et al.
patent: 5511909 (1996-04-01), Calandra, Jr.
patent: 5525013 (1996-06-01), Seegmiller
patent: 5556233 (1996-09-01), Kovago
patent: 5586839 (1996-12-01), Gillespie
patent: 5785463 (1998-07-01), Eaton et al.
patent: 5802788 (1998-09-01), Ozawa et al.
Grinaker- LTA Limited
Ladas and Parry
Novosad Christopher J.
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