GB2274124A - Reinforcement tendon - Google Patents

Description

2274124 REINFORCEMENT TENDON This invention relates to a

reinforcementtendon, capable of use as a so-called roof bolt in the reinforcement of underground strata, or alternatively as reinforcement rods for concrete structures such as pillars, beams, roofs, floors, stairways etc.

Roof bolts are used extensively in mining or tunnelling operations for the stabilization of overlying strata, by the drilling usually of an array of bolt holes at prescribed angles, to lengths of e.g. 5 - 15 m, with each bolt hole being adapted to receive a bolt conventionally anchored at its inner ends by the bursting of an epoxy resin cartridge, and thereafter with tension applied to the bolt, typically by a nut secured on an end fitting of the bolt. Conventionally, such bolts have been of steel and of section slightly less than that of the hole to provide relatively trouble free insertion but, with the lengths involved, these bolts are awkward to manhandle particularly into an overhead hole, as well as presenting transportation problems underground particularly if coal mining is involved where a coal face may be several miles from a supply shaft.

In the construction industry, steel reinforcing bars, usually with external ribs, are used extensively in the formation of structures, with the bars embedded within the structures, and/ unlike the mining industry where temporary roof support is all that is required, long term satisfactory performance is required by the construction industry, which is problematical with steel reinforcing bars due to corrosion and/or chemical attack from constituents of the concrete, while again, with the number of reinforcing bars involved, attendant weight factors usually require plant such as cranes to lift and locate the bars prior to the pouring of the 4 concrete.

According to the present invention, there is provided a reinforcing tendon comprising an elongate member of synthetic plastics material comprising a plurality of glass fibre, pultruded strands to provide a relatively rigid tendon of desired profile, with a plurality of strand spacers located at predetermined axial distances along the tendon and serving to maintain the individual glass fibre strands in predetermined, spaced relationships, and means to displace the strands to non-parallel dispositions.

is Thus, the invention provides what is in effect a skeletal tendon of relatively lightweight, synthetic plastics material that is easier to handle than prior art, steel tendons, and which is able to sustain the same tensile loads, as the strand spacers maintain the glass fibre reinforcing strands in predetermined optimum positions within the tendon and hence for example the tensile strength of a roof bolt is known to a greater or lesser extent, and is consistent.

In practice, -to produce a roof bolt the skeletal tendon is inserted into the bore hole and cement grout is then injected into the bore hole, which grout encapsulates the tendon so that, after the grout has set, the composite element formed by the tendon and grout is a roof bolt. to which the required tension may then be applied. For example, with the 3 reinforcing tendon in the form of a roof bolt, the displacement of the strands to non-parallel dispositions results in the formation of grout wedges between the external periphery of the tendon and the internal periphery of a bore hole to assist in location of the tendon within the bore hole.

In practice, to produce a concrete structure, a tendon, or a plurality of tendons in a suitable array, are laid, usually horizontally, before the concrete is poured over the tendon(s) to embed the latter within the structure.

The strand spacers are preferably themselves of synthetic plastics material, conveniently of washer or annular configuration, with a plurality of peripheral notches each capable of housing, and locating, one strand. The strand spacers may be "external", or both "external" and Hinternal".

is Thus, in one embodiment of a tendon employing a number, e.g. 14 glass fibre strands, the "external" strand spacers would be provided with. e.g. 14 notches to keep the inner core of the tendon free of glass fibre strands by confining the strands to an annular zone adjacent the periphery of the tendon.

Conversely, with a combined "external" and "internal" spacer, the internal spacer is typically provided with 7 notches, the latter serving to maintain the inner strands in the inner core zone of the tendon and clear of the outer periphery. The strands are conveniently retained in the notches of the external spacers, or the combined external and inner spacers, by providing first tie wires in close proximity to each strand spacer and surrounding the strands.

The means to displace the strands is located approximately mid-way of two adjacent strand spacers, and preferably takes the form of a constricting means.

Preferably, the constricting means is a second tie wire surrounding the strands.

Each of say 14 strands is preferably woven in such a way as to ensure complete cementitious grout encapsulation thus optimising the compressive strength of the grout and the tensile strength of the glass fibre strands.

The strand spacers and strands are woven to provide a desired profile and dimension that result in a test load failure 267 to 550 Kn when encapsulated in cementitious grout as per BC Test RM/CON/92/B.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side elevation of a reinforcement tendon in accordance with the invention; Figure 2 is an enlarged view of one end portion of a first embodiment of tendon of Figure 1; Figure 3 is an enlarged view of one intermediate portion of the first embodiment of tendon of Figure 1; Figure 4 corresponds to Figure 3 but shows a second embodiment; Figure 5 is a view on one face of an outer spacer; Figure 6 is an end view of the spacer of Figure 5; Figure 7 is a view on one end face of an inner spacer; and Figure 8 is an end view of a composite spacer.

In the drawings, a reinforcing tendon 1 comprising an elongate member 2 of synthetic plastics material comprising a plurality of glass fibre, pultruded strands 3 to provide a relatively rigid tendon 1 of desired profile, with a plurality of strand spacers 4, or 4 and 5, located at predetermined axial distances D along the tendon 1 and serving to maintain the individual glass fibre strands 3 in predetermined, spaced relationships, can be seen in Figures 2 to 4, and to define an end portion 5 and an intermediate portion 6.

Figures 2 and 3 illustrate an embodiment in which the strands 3 have a straight lay, and Figure 4 illustrates an embodiment in which the strands 3 have a spiral lay.

Also illustrated in Figure 2 is the possibility of providing the terminal end of the end portion 5 with an end fitting in the form of an externally threaded tube 7 to receive a washer and nut (not shown) so that tension may be applied to the tendon 1, when the latter constitutes a roof bolt. Also illustrated in Figures 2 to 4 are a series of first steel tie wires 8 located in close proximity to, but at opposite sides of each strand spacer 4, or 4 and 5, and a second series of steel tie wires 9 which displace the strands to a non-parallel disposition by bringing the strands 3 together at locations approximately mid-way between two adjacent strand spacers 4, or 4 and 5. With this arrangement and again considering the tendon 1 in the form of a roof bolt, then as can be seen in Figure 4, a bore hole 10 is provided in rock strata 11, with annular grout wedges 12 defined between the external periphery of the tendon 1 and the internal periphery of the bore hole 10, so that when tension is applied to the tendon 1, by tightening a nut on the threaded tube 7, to maintain the integrity of the strata 11, the grout wedges 12 along the length of the tendon assist in resisting the tendon 1 being pulled from the bore hole 10.

In Figures 5 and 6 is illustrated an outer spacer 4 of synthetic plastics material, provided with fourteen peripheral notches 13 and hence capable of accepting up to fourteen strands 3 to maintain them in an optimum spaced relationship at an outer zone of the tendon 1, with the strands 3 retained in the notches 13 by the proximity of the first series of tie wires 8.

In Figure 7 is illustrated an inner spacer 5 having seven notches 13 adapted to accept up to seven strands 3 to maintain them in an optimum spaced relationship at an inner zone (or core) of the tendon 1.

Figure 8 illustrates the possibility of combining a strand spacer 4 with a strand spacer 5 to provide a composite spacer in circumstances where it is desired to maintain the spacing of both inner strands 3 and outer strands 3.

7

Claims (11)

1. A reinforcing tendon comprising an elongate member of synthetic plastics material comprising a plurality of glass fibre, pultruded strands to provide a relatively rigid tendon of desired profile, with a plurality of strand spacers located at predetermined axial distances along the tendon and serving to maintain the individual glass fibre strands in predetermined, spaced relationships, and means to displace the strands to non-parallel dispositions.

2. A tendon as claimed in Claim 1, wherein the strand spacers are of synthetic plastics material.

3. A tendon as claimed in Claim 1 or Claim 2, wherein the strand spacers are of washer, or annular, configuration.

4. A tendon as claimed in any preceding Claim, wherein the strand spacers are provided with a plurality of peripheral notches each capable of housing, and locating, one strand.

5. A tendon as claimed in any preceding Claim, wherein first tie wires are located in close proximity to each strand spacer, with the first tie wire surrounding the strands, to retain the strands in the notches.

6. A tendon as defined in any preceding Claim, wherein the means to displace the strands is located approximately mid-way of two adjacent strand spacers.

7. A tendon as defined in any preceding Claim, wherein the means to displace the strands is a constricting means.

8. A tendon as defined in Claim 7, wherein the cosntricting means is a second tie wire surrounding the strands.

9. A tendon as defined in any preceding Claim, wherein a smaller diameter, inner strand spacer is located in a receiving aperture of a larger diameter, outer strand spacer.

10. A tendon substantially as hereinbefore described with reference to Figures 1 to 3 and 5 to 8 of the accompanying drawings.

11. A tendon substantially as hereinbefore described with reference to Figures 1 and 4 to 8 of the accompanying drawings.