BACKGROUND TO THE INVENTION

THIS invention relates to a wall support strap.

One well known wall support strap which is widely used in underground mining operations to provide localised support, typically for a hanging or side wall in a mine working, is the so-called "Oslo" strap. This has a number of round bar steel tendons which are held together in a spaced apart, parallel array by means of "pigtail" strap members. These are round steel bars which, at regular intervals, are bent to form loops or pigtails. The tendons pass through the loops and welds connect the tendons to the strap members at each loop.

Although the known Oslo straps work well in practice, they are expensive to manufacture. This is mainly because of the difficulty in forming the pigtail loops in the strap members. In practice it has proved difficult to automate the formation of the loops so the necessary bending work is often carried out manually. SUMMARY OF THE INVENTION

According to this invention there is provided a wall support strap comprising a plurality of tendons which are held together in spaced apart, generally parallel relationship by means of spaced apart, generally parallel strap members which extend transversely to the tendons, at least some of the strap members comprising a generally flat, elongate strip formed with longitudinally extending slits at longitudinally spaced apart slit positions, strip material on one side of the slit being deformed, in a direction transverse to the length of the strip, relative to strip material on the other side of the slit so as to define openings in the strip through which the tendons pass.

Other features of the invention are defined in the appended claims.

When compared to known Oslo straps, the wall support strap of the invention is advantageous in that the manufacture of the strap members, and the overall assembly of the wall support strap, can be carried out in an automated and economical manner.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a perspective view of a wall support strap according to a first embodiment of the invention;

Figure 2 shows a plan view of one strap member of the wall support strap seen in Figure 1 ;

Figure 3 shows a view at the line 3-3 in Figure 2; Figure 4 shows a view at the line 4-4 in Figure 3; Figure 5 shows a perspective view of a wall support strap according to a second embodiment of the invention; Figure 6 shows a plan view of one strap member of the wall support strap seen in Figure 5; Figure 7 shows a view at the line 7-7 in Figure 6; Figure 8 shows a view at the line 8-8 in Figure 7; Figure 9 illustrates an end region of a modified support strap according to the invention; Figure 10 shows a detail of a strap member seen in Figure 9; Figure 11 illustrates an end region of another modified support strap according to the invention; Figure 12 illustrates an end region of a further modified support strap according to the invention; and Figure 13 illustrates an end region of a further embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Figures 1 to 4 illustrate a wall support strap 10 according to a first embodiment of the invention. The wail support strap 10 is elongate and rectangular in overall shape and includes four spaced apart, generally parallel tendons 12 extending in the long direction of the support strap and a series of spaced apart, generaiiy parallel strap members 14 which sen/e to connect the tendons and space them apart from one another. In this embodiment, each tendon is provided by a length of round steel bar, and the tendons are spaced apart from one another at a 100mm centre to centre spacing by the strap members 14 which are themselves arranged at a 200mm centre to centre spacing.

Each strap member 14 is provided by a generally flat steei strip 16, in this case of 350mm overall length. At regular intervals, in this case 100mm intervals, slits 18 are formed at slit positions on the longitudinal centre line of each strip 16, for example by a punching operation. Strip material on one side of each slit is deformed in one direction out of the genera! plane of the strip and strip material on the other side of each slit is deformed in an opposite direction out of the genera! plane of the strip. With the general plane of the illustrated strip horizontal, materiai 20 in a zone on one side of each slit has been deformed upwardly relative to the genera! plane 22 of the strip and material 24 in a zone on the other side of the slit has been deformed downwardly relative to the general p!ane 22. After deformation, openings 26 transverse to the length of the strip are then defined by the respective zones of deformed material 20, 24.

The slitting/punching and deformation operations are conveniently carried out in an automated manner on a length of steel strip which is cropped to length to form the individual strap members 14. Thereafter, the individual strap members are laid out in a suitable jig such that the openings 26 are in alignment. The tendons 12 are then threaded through the aligned openings. Tack welds, a typical one of which is indicated by the numeral 28, are then applied at each intersection between a tendon and a strap member to connect the assembly of tendons and strap members securely to one another to form the unitary wail support strap 10.

Figures 5 to 8 illustrate a second embodiment of wall strap according to the invention. Components in these Figures corresponding to components seen in Figures 1 to 3 are designated by the same reference numerals. The second embodiment differs from the first in that, in each strap member 14, the strip 16 is formed with pairs of parallel, longitudinally extending slits 30 at slit positions situated at intervals along the length of the strip. The slits of each pair are equally spaced on opposite sides of the longitudinal centre line of the strip, !n this case, a zone 32 of strip material between the slits 30 of each pair is deformed in one direction (upwardly in Figures 7 and 8) and zones 34 of material between the slits and longitudinal side edges 36 of the strip are deformed in an opposite direction (downwardly in Figures 7 and 8) relative to the general plane 22 of the strip. After deformation, openings 26 transverse to the length of the strip are defined by the respective zones of deformed material.

In the assembled wall support strap 10 of the second embodiment, the tendons 12 are threaded in the jig through the aligned openings and tack welds are applied at each tendon/strap member intersection to secure the assembly together. Typical welds are indicated by the numeral 28 in Figure 6.

Persons skilled in the art and familiar with conventional Oslo straps will understand that, in use, wall support straps 10 are fixed at their ends to a hanging wall or roof in a mine working to restrain the rock surface and hold back rock fragments which may have broken from the surface and would otherwise fall dangerously from the wall. The straps are, as in conventional practice, fixed to the wail by means of so-called "split sets" or rock bolts which are anchored in holes drilled into the face. This is typically achieved by arranging washer plates associated with the split sets or rock bolts such that they overlap one or more strap members and/or tendons of the support strap and press the support strap against the face.

Support straps 10 will typically be used to provide micro or localised support for the hanging wall or roof of a mine working, but it will be understood that they could also be used beneficially on a side wall or even a footwatl or floor, in a typical case, the overall length of the wall support strap, corresponding to the lengths of the tendons, could be 1.5m to 2.5m or more.

The illustrated embodiments have only four tendons, but there may be more or less tendons in other embodiments, in which case the strap members 14 will be of appropriate length and will have a corresponding number of openings 26.

In a typical installation, the washer plate may only bear on a central region at each end of the support strap 10. In this situation, ends of the strap members which are not contacted by the washer plates, and tendons located towards the sides of the support strap 10, are not directly supported against the hanging wall. This in turn means that side portions of the strap members, and the tendons located towards the sides have a reduced ability to restrain the rock surface and any loose fragments at the surface. For this reason, strap members 14 situated at or towards the ends of the strap 10, i.e. in end regions of the strap, may be made stronger in tension and bending than intermediate straps 14 which are located between the end regions. The stronger strap members are then better able to support tendons located towards the sides of the strap which are not directly contacted by the rock bolt washer plates, and these tendons are in turn better able to perform the required surface restraining function.

In one example, all the strips 16 may have the same width, say 25mm, but the strips of one or more strap members 14 which are at or towards the end of the support strap may be thicker than the strips of the intermediate strap members. The strips of the end strap members could for example be 3mm thick while the strips of the intermediate strap members may be only 1.6mm or 2mm thick.

Other possible examples are illustrated in Figures 9 to 12. In Figures 9 and 0, that strap member 14 which is second from each end of the support strap 10 has a channel shape in cross-section with the tendons fixed, typically by welding, in part-circular recesses 40 formed in the edges of the iegs 42 of the channel. During installation the rock bolt washer is arranged to bear on the channei-shaped strap members 14. The extra strength of these members, attributable to their channel shapes, allows them to provide adequate support to the tendons 12 located towards the sides of the support strap 10. In a typical example, each channel-shaped strap member is bent from 2mm steel plate with dimensions 44 and 46 of 50mm and 10mm respectively.

Figure 11 shows another possibility in which the relevant strap members 14 have a curved shape. These members have a greater width than the intermediate strap members and cou!d also be made of thicker steel or be made in a channel shape or other suitable cross-sectional shape.

In the example illustrated in Figure 12, the relevant strap members 14 again have a greater width than the intermediate strap members, and could again be of thicker steel and/or be made in a channel shape or other suitable cross-sectional shape.

It will be understood that in each case the endmost strap members 14 could also be made stronger than the intermediate strap members, for example by being of thicker material or with any suitable cross-sectional shape to enhance their bending strength.

It is also possible for the bending strength of any or all of the strap members 14 to be enhanced, for example by pressing dimple shapes into them. This possibility is indicated in Figures 1 to 3 and 5 to 7, in which the broken lines 50 indicate elongate dimples pressed into the strips 16 between the slit positions.

Figure 13 illustrates another embodiment of the invention. This is similar to the embodiment seen in Figure 1 , except that one of the straps, designated 14.2, has been omitted, and two further bars 60 are provided. The bars 60 have ends welded at 62 to the tendons 12, as illustrated, and are angled with respect to the tendons over the major part of their lengths. The extra bars 60 are typically provided at positions where the strap 10 is mounted to the wail by means of roof bolts or split sets, and provide extra strength at these positions.

Many other variations are possible within the scope of the invention. For example, while the openings 26 in the illustrated examples are formed by deforming strip material on opposite sides of each slit in opposite directions, it would also be possible to form suitable openings merely by deforming one or more zones of material in one direction only. Referring to the first embodiment, the openings could be formed by deforming only the zones 20 out of the general plane of the strip, leaving the other zone 24 undeformed. in general however, deformation in opposite directions is preferred since this will involve a smaller amount of deformation of each zone in order to create an opening of the required size, and therefore subject the strip material to less stress. in other variations it would be possible to make the strips out of material other than steel, for example a suitable grade of plastic. Also, the diameter of the tendons could vary from application to application.