GB2257444A

GB2257444A - Anchor grip for tendon

Info

Publication number: GB2257444A
Application number: GB9113986A
Authority: GB
Inventors: Geoffrey Dean
Original assignee: CCL Systems Ltd
Current assignee: CCL Systems Ltd
Priority date: 1991-06-28
Filing date: 1991-06-28
Publication date: 1993-01-13
Also published as: GB9113986D0

Abstract

The surface of an anchor grip 2, 3 is provided with a friction layer the better to grip an elongate rope K received therein. The friction layer may be a sprayed on metal, alloy, cermet or ceramic. <IMAGE>

Description

ANCHOR GRIPS The invention relates to anchor grips for use in the tensioning of wires, rods, cables or stranded elements in say prestressed concrete structures. Such grips may take a variety of forms, such as compression grips, wedge grips. In one example, the grip comprises a body having a central passageway, a wedge device comprising a plurality of tapered wedge elements within the passageway, the elements having a bore to receive and engage the wire to be gripped. The elements may comprise a plurality of interwoven strands which may be made of metal or of plastics or composite e.g. KEVLAR (KEVLAR is a registered trademark) or carbon fibre; or the like. While it is possible to provide threads on the inside surface of a grip to bite into the element to be gripped, this will not provide a good grip if the element presents a smooth surface.This is often the case with plastics rope where the individual strands are bonded together by set resin which also forms an outer sheath.

It is one object of the invention to provide an anchor grip adapted to grip an element, even if the element presents a smooth surface. The invention is based on the discovery that if a layer of friction material is interposed between the rope and the gripping region of the anchor element then a good grip can be obtained. It is further based on the realisation that the friction layer can be provided by rough particles of material bonded to the gripping region.

In one aspect of the invention there is provided a connection comprising a wire rope or the like and an anchor grip therefor, wherein the grip is engaged with the rope by means of an interposed friction layer.

Preferably the friction layer has first been bonded to the gripping region of the anchor grip and the layer comprises a material which is a metal, alloy, cermet, ceramic or the like applied to a preformed region of the grip. Specific materials include tungsten carbide, Inconel nickel alloys; nickel aluminium alloys, nickel chromium or cobalt alloys with additions of boron, silicon, carbon, aluminium, tungsten carbide etc; molybdenum based powders; alumina; magnesia and zirconia. The anchor grip (or just the gripping region) may be based on iron, nickel, copper, or their alloys; alloy and non-alloy steels, and the like.

In a much preferred feature of the invention the friction layer is applied by flame spraying. Preferably the material is deposited in the region of the grip followed by fusing to bond the deposited material on to the grip. The flame spraying may be carried out using a torch working with oxygen/fuel gas e.g.

oxygen/acetylene. Other systems include gas wire spraying, arc spraying, gas powder spraying, plasma spraying, and the like.

The coating formed comprises a rough surface with good adhesion to the substrate and provides a roughened, almost abrasive surface. The hardness of the applied material and the thickness of the applied layer will depend on the rope to be gripped.

Where the rope has a smooth external surface as in the case of a KEVLAR rope, the friction layer preferably cpmprises a flame sprayed nickel chromium boron alloy. Where the rope comprises wire strands, the friction layer preferably comprises flame sprayed tungsten carbide.

Preferably the anchorage grip comprises co-operating segments, each of which has an applied friction layer.

In another aspect the invention also includes the anchor grip carrying a friction layer as defined.

The invention further includes a method of making an anchor grip to grip the surface of a rope or the like, the method including the step of bonding a friction layer on the region of the grip intended to contact the smooth surface.

The shape of the gripping region will usually correspond to that of the surface to be gripped. The connection may be at the end of a rope, as in an anchorage, or it may join two ropes in the manner of a splice. The connection may be made before the rope is installed in an installation or afterwards.

In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a transverse section of a connection; Figure 2 is an enlarged view of a wedge element of the grip; Figure 3 is a section of a connection of a grip and a flat KEVLAR wire rope having 400,000 filaments; and Figure 4 is a sectional view of an individual wedge for steel strand.

The rope K of Figure 1 is made of a plurality of strands of KEVLAR fibre bonded together by a set resin which also forms a sheath. An anchor grip G comprises an elongate barrel 1 having a wedge gripping device 2 comprising a plurality of tapered wedge elements 3. As shown in Figure 2, each of the elements formed of say-mild steel, has a smooth flat interior surface, whereas one normally would have expected biting thread teeth. The surface has a friction layer F thereon formed by flame spraying a powder of nickel chromium boron alloy so bonding the powder to the surface to leave an abrasive sandpaper like finish. When such a grip is used to terminate a KEVLAR rope the particles grip the smooth surface in a way not otherwise possible.

Figure 3 shows a grip connecting a flat KEVLAR wire rope and Figure 4 shows a wedge for a steel strand rope.

Claims

1. A connection comprising an elongate rope or the like and an anchor grip therefor, wherein the grip is engaged with the rope by means of an interposed friction layer.

2. A connection according to Claim 1, wherein the friction layer has first been bonded to the grip.

3. A connection according to Claim 1 or 2, wherein the friction layer comprises a material which is a metal, alloy, cermet, ceramic or the like applied to a preformed region of the grip.

4. A connection according to Claim 3, wherein the friction layer was applied by flame spraying.

5. A connection according to Claim 3, wherein the material was deposited in the region of the grip followed by fusing to bond the deposited material on to the grip.

6. A connection according to any preceding Claim, wherein the rope has a smooth external surface and the friction layer comprises flame sprayed a nickel boron.

7. A connection according to Claim 6, wherein the rope comprises resin bonded KEVLAR strands.

8. A connection according to any of Claims 1 to 5, wherein the rope comprises wire strands and the friction layer comprises flame sprayed tungsten carbide.

9. A connection according to any preceding Claim, wherein the anchorage grip comprises co-operating segments, each of which has an applied friction layer.

10. An anchor grip comprising a body having a gripping region to grip a portion of a rope or the like, wherein a friction layer is present on the surface of the gripping region.

11. An anchor grip according to Claim 10, wherein the friction layer comprises a material which is a metal, alloy, cermet, ceramic or the like applied to a preformed region of the grip.

12. An anchor grip according to Claim 10 or 11, wherein the friction layer was applied by flame spraying.

13. An anchor grip according to Claim 10, 11 or 12, wherein the friction layer comprises nickel boron or silicon carbide.

14. A method of making an anchor grip to grip the surface of a rope or the like, the method including the step of bonding a friction layer on the region of the grip intended to contact the smooth surface.

15. A method according to Claim 14, wherein the applied layer comprises a material which is a metal, alloy, cermet, ceramic or the like.

16. A method according to Claim 14 or 15, wherein the layer comprises an alloy such as tungsten carbide or nickel boron.

17. A method according to any of Claims 14 to 16, wherein the bonding is performed by flame spraying the material on to the region of the grip.

18. A method according to any of Claims 14 to 17, wherein the bonding is applied by depositing the material on to the region followed by fusing of the deposited material.