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CROSS REFERENCE TO RELATED APPLICATION 
     This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/ZA03/00032, filed Feb. 25, 2003, and claims priority of South African Patent Application 2002/1531, filed Feb. 25, 2002. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an anchor device. 
     As used herein the expression “anchor device” designates a load carrying device which is capable of yielding in a controlled manner when the load on the device increases above a predetermined limit. 
     Without being restrictive in any way an anchor device, as defined, may be used as a rock bolt to reinforce a rock face or as a reinforcing element in a concrete structure such as a bridge or building. 
     SUMMARY OF INVENTION 
     According to a first aspect of the invention there is provided a method of forming an anchor device which includes the steps of:
     (a) locating an elongate member at least partly within a tubular member; and   (b) simultaneously deforming the elongate member and the tubular member at least at one location whereby withdrawal of the elongate member from the tubular member is inhibited.   

     At least a portion of the elongate member and of the tubular member may be deformed into a substantially sinusoidal shape. 
     The elongate member and the tubular member may be deformed at each of a plurality of locations which are spaced from each other in a longitudinal direction of the elongate member. 
     The method may include the step of securing a restraining component to an end of the elongate member which extends from the tubular member. 
     The tubular member may be at least one pipe and the elongate member may be selected from the following: a rod and a cable. 
     The invention also provides an anchor device which includes a tubular member, and an elongate member at least partly inside the tubular member, the tubular member and the elongate member being shaped, in a complementary manner, at least at one location whereby withdrawal of the elongate member from the tubular member is inhibited. 
     The arrangement may be such that the elongate member can only be withdrawn from the tubular member by deforming the elongate member. 
     The anchor device may include a restraining component at an end of the elongate member which protrudes from the tubular member. 
     The elongate member may be any appropriate element or elements and, for example, may be selected from a rod and a cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is further described by way of example with reference to the accompanying drawing wherein: 
         FIG. 1  depicts, from the side and in cross section, an anchor device according to the invention; and 
         FIG. 2  is an enlarged detail view of the circled portion of  FIG. 1 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The accompanying drawing illustrates from the side and in cross section an anchor device  10 , according to the invention, installed in a hole  12  which is formed in a rock face  14 . 
     The anchor device includes an elongate tubular member  16  which is in the nature of a thin wall steel pipe and an elongate load bearing member  18  which is inserted into the pipe with one end  20  protruding from the pipe. 
     The member  18  may be a steel rod or a cable. 
     A restraining component  22  is secured to the protruding end  20  and bears against a load distributing washer  24  which in turn acts against a surface of the rock face  14  which surrounds the hole  12 . 
     The restraining device varies according to the nature of the elongate member  18 . For example if the elongate member is a steel rod then the protruding end  20  may be threaded and the restraining component  22 , which is then in the nature of a nut, is threadedly engaged with the end  20 . Alternatively if the member  18  is a cable or is formed from a number of wires then the restraining component  22  may be in the nature of a lug or ferrule which is crimped onto the protruding end in situ at an installation site. 
     The anchor device  10  is formed, under factory conditions, by inserting the elongate member  18  into the pipe  16  when the pipe is of a regular shape ie. is not deformed. The pipe, which encloses the elongate member over a substantial portion of the length of the elongate member, is placed in a suitable press and is deformed in one or a plurality of steps into the shape shown in the drawing. The deformed pipe has peaks and troughs with a generally smooth transition between each peak and adjacent trough thereby imparting to the pipe an overall generally sinusoidal shape. 
     The undulations or sinusoidal peaks are spaced apart by a distance  26  which varies according to requirement. 
     The hole  12  is formed in the rock face using any appropriate technique known in the art and the anchor device  10  is placed in the hole with the pipe  16  embedded in grout or other settable material  28  which fills the hole. The settable material is normally injected into the hole using any suitable placement apparatus after the pipe has been inserted into the hole. 
     If the restraining component  22  is a nut then the washer and the nut are engaged with the protruding end  20  after the settable material is injected into the hole through its mouth. On the other hand if the restraining component is in the nature of a lug or similar device which is applied under factory conditions to the protruding end then the load distribution washer  24  may initially be displaced slightly from the rock face  14  to allow the settable material to be injected into the hole through its mouth or, alternatively, the washer  24  may have an aperture or passage formed through it and the settable material may be injected through the aperture or passage into the hole  12 . 
     Ideally, once the material  28  has set, the component  22  is advanced along the member  18  to prestress the member. This may however not be possible if the component is crimped under factory conditions to the end  20 . It is preferable therefore to attach the component to the end  20  in situ, at the installation location. 
     When the anchor device is embedded in the settable material, the material, whether grout, resin or of a different type, bonds to the exterior surface of the pipe which is thereby held firmly in position. 
     If there is movement of the rock face relatively to the bulk of the rock in which the hole  12  is formed then the load which is carried by the member  18  increases. The member  18  is therefore placed under increasing tensile stress. The rock face  14  can only move however when the load carried by the member  18  is so high that the element is deformed through the sinusoidal passage which is defined by the pipe  16 . It is evident that the point at which yielding takes place is dependent on a number of factors including the material from which the elongate member is made, the dimensions and shape of the member, the clearance between the member and the inner wall of the pipe, and the number, depth and spacing of the formations in the pipe and the member. 
     The elongate member slides through the pipe by deforming as it passes through the undulations to provide a controlled yielding action with the pipe remaining behind and fully embedded in the settable material. An appropriate lubricant may be applied to the elongate member, before it is inserted into the pipe. This helps to ensure that a smooth sliding action takes place as yielding occurs, particularly if the yield rate is high ie. when the member  18  moves very rapidly, for example during a seismic event. 
     The length of the anchor device may be substantial. This makes the anchor device suitable for use in reinforced concrete applications for example in bridges and structures. With this type of application the member  18  will generally be a cable or comprise a plurality of high tensile winds which may be helically twisted, at least slightly. The installation and operation of the anchor device, in a reinforced concrete application, for all practical purposes, are the same as what has been described hereinbefore with reference to the use of the anchor device in a body of rock except that the device is cast in position. 
     The pipe  16  is rigid and if the anchor device is made to a substantial length it may be difficult to install the device particularly in an underground situation or in a location in which there is limited space. To impart a degree of flexibility to the anchor then, as is shown more clearly in the inset drawing, the member  18  may be a cable and the pipe  16  may comprise a plurality of relatively smaller lengths  16 A,  16 B, . . . which are separated from each other along the length of the cable by means of suitable spacers  30 , which may be made from a flexible plastics material. Each individual pipe length is sinusoidally deformed, with the cable inside, in the manner which has been described and is fixed in position when it is embedded in the settable material. However, before installation, it is possible to bend or flex the anchor device, at least to a limited degree, by bending one pipe section to a limited extent relatively to an adjacent pipe section. The use of the spacers does not adversely affect the strength of the anchor device nor the yielding action thereof.

Summary:
An anchor device which includes a pipe ( 16 ), an elongate member ( 18 ) which is partly inside the pipe and which has an end ( 20 ) which protrudes from the pipe ( 16 ), and a restraining component ( 22 ) which is engaged with the protruding end ( 20 ). The pipe ( 16 ) and the elongate member ( 18 ) are shaped with a plurality of deformations along their respective lengths such that the elongate member ( 18 ) can only be withdrawn from the tubular member ( 16 ) by further deforming the elongate member ( 18 ).