Title of Invention	"METHOD, MEMBER, AND TENDON FOR CONSTRUCTING AN ANCHORING DEVICE"
Abstract	An anchoring device not accessible from one of its sides can be produced by making a cavity (11) of a particular shape and using tendons (4), each of which has an end portion (41) of adapted shape. The cavity may be made in different ways, especially by concreting an anchor member (1) having an opening (12) at one end, the anchor member and the cavity it contains each having an adapted shape. After the anchor member has been concreted and the tendons inserted in the cavity, the cavity is filled with an embedding mortar in order to block the ends of the tendons therein.

Title of Invention

"METHOD, MEMBER, AND TENDON FOR CONSTRUCTING AN ANCHORING DEVICE"

Abstract

An anchoring device not accessible from one of its sides can be produced by making a cavity (11) of a particular shape and using tendons (4), each of which has an end portion (41) of adapted shape. The cavity may be made in different ways, especially by concreting an anchor member (1) having an opening (12) at one end, the anchor member and the cavity it contains each having an adapted shape. After the anchor member has been concreted and the tendons inserted in the cavity, the cavity is filled with an embedding mortar in order to block the ends of the tendons therein.

Full Text	METHOD, MEMBER, AND TENDON FOR CONSTRUCTING AN ANCHORING DEVICE This invention relates to anchoring apparatus used in civil engineering, especially so-called blind anchoring devices accessible from only one side, and more particularly to a method of constructing such a device of the type having more than one tendon, as well as to an anchor member for constructing such a device. The invention further relates to a tendon of the type having one end intended to be inserted into an anchoring cavity of such an anchoring device. For certain anchoring devices having an anchor head with a tendon, prestressed or not, it is not possible to gain access to the anchoring device from the rear. This situation is encountered particularly in the case of a buried anchoring device where access is possible only from the surface of the ground, or when fluid-tightness or anticorrosion protection must be especially meticulous, so that the rear side of the device must be closed. This requirement prevents the use of a conventional anchor plate where the attachment of the tendon to the plate, e.g., with the aid of anchoring cones, calls for the development of new types of anchoring. U.S. Patent No. 5,056,284 shows an anchoring device accessible from only one side, the drawback of the device described there being that each tendon, hence the tube in which they are inserted, is held solely by longitudinal adhesion, thus greatly limiting the tractive stress which such an anchoring device can withstand and leading to a very great anchoring length to obtain a sufficient adhesion surface. Likewise, U.S. Patent No. 4,043,133 provides a tendon sheathing held solely by longitudinal adhesion to the surrounding earth. The tendons extend from the bottom end of the sheathing and are all attached to an anchor plate; the way in which this plate is inserted in the cavity, and the way in which the tendons are fastened to the plate, are not described. In case this embodiment can be produced, the transmission of the anchor force to the ends of the tendons in the surrounding earth through the injected sheathing is produced solely by longitudinal adhesion, without benefiting from the wedge effect as described below in connection with the present invention. Thus, there is a need for a method of constructing an anchoring device accessible from only one side which does not encounter the mentioned drawbacks of prior art anchoring devices, i.e., an anchoring device wherein the tendons are held so that the tractive stress on each of them at the level of the anchoring device is taken over by adhesion, this adhesion being appreciably favored by the confinement induced by the overall shape of the anchoring device, and by longitudinal mechanical blocking of the ends of the tendons due to the particular shape of these ends and their arrangement in a cavity of substantially tapering shape. There is further a need for an anchor member of a particular shape which, associated with a plurality of tendons also having a particular shape, makes it possible to construct such an anchoring device, as well as for a possibility of constructing such an anchoring device without the direct use of an anchor member. According to the present invention, the method of constructing an anchoring device according to the present invention, of the type initially mentioned, includes the steps of making a cavity in a surrounding structure, this cavity having a substantially oblong, tapering shape and having two ends, the area of the cross-section of the end disposed on the accessible side of the anchoring device being less than the area of the cross-section of another portion of the cavity, the cavity comprising an opening on the accessible side of the anchoring device; successively inserting through the opening of one end of each of the tendons, each of these tendons being made up of a traction rod having a first cross-sectional area and an end portion having a second cross-sectional area larger than the first cross-sectional area; and filling the cavity with an embedding material. The anchor member according to the present invention is of a substantially oblong, tapering shape and has two ends, the area of the cross-section of a first end being less than the area of the cross-section of another portion of the anchor member, the anchor member being made up substantially of a wall bounding a cavity of a shape substantially similar to that of the anchor member and provided with an opening having a first cross-sectional area at .the-first end of the anchor member and comprising a bottom wall at the second end, another cross-section of the cavity having another area larger than the first area. The tendon according to the present invention, of the type initially mentioned, is made up of a traction rod provided at the end thereof intended to be inserted in the cavity with an end portion, the area of the cross-section of which is larger than the area of the cross-section of the traction rod. Accordingly the present invention relates to a method of constructing an anchoring device having more than one tendon (4), said anchoring device being accessible from only one side, comprising the following steps: making a cavity (11) in a surrounding structure (2), said cavity having an oblong shape and having two ends, the area (512) of the cross section of the end disposed on the accessible side of the anchoring device being less than the area (511) of the cross section of another portion of the cavity, the cavity comprising an opening (12) on the accessible side of the anchoring device, successively inserting, through the opening (12) of one end, each of the tendons (4), each of said tendons being made up of a traction rod having a first cross-sectional area (540) and an end portion (41) having a second cross-sectional area (541) larger than said first cross-sectional area (540), and -filling the cavity (11) with an embedding material (50), this process being characterized in that, the insertion of each tendon (4) consists in pushing said tendon (4) into the guide tube (30), then into the cavity (11), until its end piece (41) comes in contact with the bottom surface of the cavity (11) which presents a surface (511) corresponding to the largest cross-sectional area of the cavity (11), the insertion of a tendon (4) is repeated until a number of tendons (4) have been installed in the same way, and a new end piece (41) to be installed may not have room at the bottom of the cavity (11); in that case, in order for the tendon in question to play its full part later on, it suffices if the end piece (41) is pushed down as far as possible in the cavity (11) until it comes up against one or more pieces (41) already installed or against the sidewall of the cavity (11), in order to anchor the guying or the prestressed element, a certain number N of tendons (4) must be inserted in the cavity (11), this insertion being preceded by a choice of tendons for which the following relations should exist: (N x S41) to allow the end pieces (41) to be disposed properly on the bottom of the cavity (11), and [ (N-l) x 840] + 841 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (812), and (N x 841)* > 812 for enabling blockage of the tendons (4) In the cavity (11) by preventing the mutually blocked end pieces (41) from coming out through the opening (12), wherein (N x 841)* represents generally the surface generated by the casing of the bundle of the N assembled end pieces (41), each having a cross-sectional area (S41). Accordingly the present invention also relates to an anchor member (1) for constructing an anchoring device having more than one tendon, said anchoring device being accessible from only one side, wherein said member is of substantially oblong, tapering shape and has two ends, the area of the cross section of a first end being less than the area of the cross section of another portion of the anchor member, said anchor member being made up substantially of a wall (10) bounding a cavity (11) of a shape substantially similar to that of said member and being provided with an opening (12) having a first cross-sectional area (S12) at said first end of the anchor member and comprising a bottom wall (14) at the second end, another cross section of said cavity having another area (Sll) greater than the first area (S12), this anchor member being intended to be used with a predetermined number (N) of tension members (4) each having one end intended to be inserted in an anchor cavity (11) of an anchoring device accessible from only one side, said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the area (S12) of the cross section of the opening (12) of the cavity (11) of the anchor member (1) is greater than the area made up of the sum of the areas (S40) of the cross-sections of (N-l) traction rods (40) added to the maximum area (S41) of the cross section of an end portion or of an end piece (41) of the tendons (4), but is smaller than [(N-l) x S40] + S41 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (S12) of the cavity (11). Accordingly the present invention also relates to a tendon (4) having one end intended to be inserted in an anchor cavity (11) of an anchoring device accessible from only one side, by a guide tube (30) said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the end portion or the end piece (41) has a convex lower end portion (44). Preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a preferred embodiment of an anchor member according to the invention, Figure 2 is a series of sectional views (A-L) representing steps in the method of constructing an anchoring device according to the invention, Figure 3A is a diagrammatic elevation of part of a tendon in a first embodiment of the invention, Figure 3B is a diagrammatic elevation of part of a tendon in a second embodiment of the invention, Figure 3C is a diagrammatic elevation of part of a tendon in a third embodiment of the invention, and Figure 3D is a diagrammatic view, partially in section, of part of a tendon in a fourth embodiment of the invention. For carrying out the inventive method, an anchoring cavity of a certain shape must first be obtained. The shape of this anchoring cavity is substantially oblong and tapering, with a first open end on the accessible side of the anchoring device and a second closed end on the non-accessible side of the anchoring device. Moreover, the cross-section of the first end of the anchoring device must be smaller than another cross-section of the cavity, whether this section corresponds to that of the second end or to an intermediate section of the cavity. Such a cavity may be obtained by several means or devices. A first means consists in using an anchor member comprising a prefabricated interior cavity having the required shape of the anchoring cavity. A preferred embodiment of such an anchor member is illustrated in Figure 1. The anchor member 1 consists essentially of a preferably thin wall 10 bounding an interior cavity 11. A first end of the anchor member 1, i.e., the top end of the member as viewed in the drawing, includes an opening 12, as well as means 13 for fastening a tubular sheath for protecting tendons, the use of which will be described below. The other end of the anchor member 1 is closed by a bottom wall 14. The outside shape of the anchor member 1, hence of the interior cavity 11, is substantially tapering, e.g., frustoconical or frustopyramidal, with the smallest cross-section close to the opening 12 and the largest cross-section close to the bottom wall 14. An inlet 15 is disposed close to the bottom wall 14, an injection tube 16 being attached or attachable to inlet 15. Similarly, an outlet 17 is disposed close to the opening 12, an exhaust tube 18 being attached or attachable to the outlet 17. The use of elements 15-18 will be described below. The tapering, frustoconical, or frustopyramidal outside surface of the anchor member 1 includes one or more anchor rings 19 disposed at the periphery of this surface, the purpose of which is to improve the transmission and distribution of the anchoring force to the surrounding structure. The embodiment shown in the drawing includes two such rings 19. The anchor member 1 may be made of synthetic material, of metal, or of concrete, its size depending essentially upon the extent of the anchoring device being considered. Figure 2A shows the first step in the inventive method of constructing an anchoring device using such an anchor member. While the surrounding concrete structure has not yet been made, an anchor member 1 is placed at the exact location where the anchoring device is to be constructed, the opening 12 being aimed in the direction of the future tendons. The anchor member 1 is held in place by temporary scaffolding or, preferably, by iron bars 20 of the concrete reinforcement. Preferably, although this is not indispensable to the invention, one or more circular iron bars 21, forming one or more hoops, are disposed about the anchor member 1 in order to improve the cohesion of the concrete at that location. In Figure 2B, it is seen that the concrete structure 2 intended to support the anchoring device has been conventionally poured about the anchor member 1. The anchor member 1 is thus completely surrounded and held in the concrete structure 2 except for its first end provided with the opening 12 which is flush with the top surface of the concrete structure 2 or, as shown here, projects slightly above that surface, and except for the ends of the injection tube 16 and exhaust tube 18, which remain accessible outside the concrete structure 2. It will therefore be noted that in this second step of the method, a cavity 11 of a certain shape has been produced within a concrete structure 2. As described until now, the cavity 11 has been produced using an anchor member 1 provided with a prefabricated cavity. A like cavity 11 in a concrete structure 2 may also be produced in other ways, e.g., by fabricating it in situ. For instance, provision may be made for a form capable of being dismantled, made of wood or some other material, having an outside shape corresponding to the desired shape of the cavity 11, and placed at the required location, about which form the concrete structure 2 is subsequently poured. As soon as the concrete is hardened, the form is dismantled through the opening 12 and extracted from the cavity 11 through that same opening. In a rather similar manner, a flexible, inflatable component may be used, which after inflation has the desired shape of the cavity 11 and is placed at the required location. After the concrete structure 2 has been poured, the inflatable component is deflated, leaving a cavity 11 of the required shape in the structure 2. Another procedure would be to produce the cavity 11 by drilling out such a cavity of the required shape in an existing structure 2. This drilling procedure would be reserved for anchoring directly in the earth or else for the installation of a new anchoring device on an existing structure 2. The cavity 11, produced in any one of the ways described, has two important dimensions, a passage area of the opening 12 designated S12 and a maximum cross-sectional area designated S11 (see Figure 1). During the third step of the method, shown in Figure 2C, the structural element 3 to be prestressed is placed or concreted, in a manner known per se, above the concrete structure 2, the structural element 3 preferably comprising a conduit or a sheathing tube 30, one end of which is situated opposite the opening 12 to be attached to the fastening means 13 adjoining the opening 12. The cross-section of the sheathing tube 30 or of the conduit contrived in the structural element 3 for the tendons corresponds substantially to the cross-section of the opening 12 of the cavity 11. The tube 30 or corresponding conduit includes at least one injection port 31 connected to an injection tube 32, at least one of the ports 31 preferably being disposed near the end of the tube 30 close to the opening 12, as well as at least one outlet connected to an exhaust tube, at least one of the outlets being disposed near the other end (not visible in the drawing) of the tube 30, hence near the structural element 3. The fourth step, shown in Figure 2D, consists in inserting the tendons. Here reference is made to Figures 3A-3D showing, by way of non-limiting examples, four designs of such a tendon 4. This tendon is substantially made up of a traction rod 40 and an end portion 41. The end portion 41 on the rod 40 is so designed that it has a cross-sectional area S41 larger than the cross-sectional area S40 of the traction rod 40, for reasons to be explained below. The other end of the rod 40 has no end portion of this kind and is made up for a normal anchoring device as known in the art. The traction rod 40 may be of any known type, consisting either of an undivided strand or of a plurality of strands assembled helically in order to constitute a traction cable. The undivided strand or the strands assembled into the traction rod 40 may be of steel, preferably of a steel having high resistance to traction, or of synthetic material, e.g., carbon-fiber- or Kevlar-based. The end portion 41 may be an end piece 41 of metal or synthetic material which is firmly fixed to the end of the traction rod 40. The choice of material of which piece 41 is made, as well as the way it is fixed to the traction rod 40, depend essentially upon the material and the manner in which the traction rod 40 is made. The end piece 41 essentially includes a central body 42 bounded by an upper portion 43 and a lower portion 44. The body 42 may have the shape of a right cylinder, with a circular cross-section as in Figure 3A or a polygonal cross-section, or else a frustoconical or frustopyramidal tapering shape, with a circular cross-section or a polygonal one as shown in Figure 3B. In the case of a tapering shape, the part with the smaller cross-section is that adjacent to the upper portion 43. The two portions 43 and 44 are preferably domed or formed of inclined planes so as to facilitate the sliding of an end portion being installed on another end portion already installed, as will be seen below. In another design, the end portion 41 may be formed by deformation or machining directly on the end of the traction rod 40. Figures 3C and 3D show examples of end portions of this type. In Figure 3C, the traction rod 40 is made up of an undivided strand, and the end portion 41 is obtained by deformation, e.g., by forging, dieing, or stamping, of the end of the traction rod 40. Figure 3D shows an example of an end portion 41 on a traction rod 40 made up of assembled strands. In this example, the end of each strand has been displaced from its normal position, it being possible to provide a ring or a binding just before this displacement in order to prevent the rest of the traction cable from untwisting. The displaced ends of the strands may be held in position by a supplementary holding part 45, e.g., a circular disk soldered or fixed in any other way under the displaced strands, or they may be left free. In a design not shown, the part for holding the displaced strands may consist of an element having the shape of two conical portions coupled at their bases, a first conical portion being inserted between the strands to displace them, while the second conical portion is used for the same purpose as the lower portion 44 described above. Thus, in any design of the end portion 41, it may also have a circular or polygonal shape and include upper and lower portions 43 and 44, as described previously. The described examples of end pieces 41 or of deformed end portions 41 are not limiting as regards either their shape or the way in which they are produced; any means may be envisaged for increasing the area of the cross-section of the end portion of the traction rod 40. When the following description speaks of end piece 41, it shall be understood that this may also be an end portion as described above. Returning to Figure 2D, it will be seen that a first tendon 4 has been pushed into the guide tube 30, then into the cavity 11, until its end piece 41 comes in contact with the bottom surface of the cavity 11. A second tendon 4 is being installed in the same way. Figure 2E shows the usefulness of the domed or inclined shape which may be provided on the upper and lower portions 43, 44 of the end piece 41. When a tendon 4 is being installed, it is quite possible for its end piece 41 to come up against another end piece of a tendon already installed. Owing to the domed or inclined shape of these portions, the second end piece does not jam against the first one but is moved away from it and slides against it until it arrives at its final position beside the first piece. Figure 2F shows that after a number of tendons have been installed, a new end piece to be installed may not have room at the bottom of the cavity 11; in that case, in order for the tendon in question to play its full part later on, it suffices if the end piece is pushed down as far as possible in the cavity until it comes up against one or more pieces already installed or against the sidewall of the cavity. In order to anchor the guying or the prestressed element, a certain number N of tendons 4 must be inserted in the cavity 11. Knowing that the cross-section of each traction rod 40 has an area S40 and that the maximum area of the cross-section of the end piece 41 equals S41 (see Figures 3A, 3B, 3C, and 3D), the following relations should exist: - to allow the insertion of the last tendon 4, i.e., to allow the last end piece 41 to pass into the guide tube 30 and into the opening 12: [(N-1)xS40] + S41 - to allow the end pieces 41 to be disposed properly on the bottom of the cavity 11: (NxS41) wherein S11 is the area of the cross-section of the cavity 11 having the largest area (Figure 1). When all the tendons 4 have been pushed through the conduit of the tube 30 so that all their end pieces 41 are accommodated in the cavity 11 as indicated above, the next step may be undertaken as shown in Figure 2G. During this step, a liquid embedding material 50 is inserted through the injection tube 16; this embedding material enters the cavity 11 through the inlet 15 and fills the empty spaces between the end pieces 41 and the ends of the traction rods 40 in the cavity 11 until it fills the cavity 11 at least partially. During this operation, the outlet 17 and the exhaust tube 18 serve to exhaust the air contained in the cavity 11 during its filling, as well as to check the filling level of the cavity 11. The cavity 11 is preferably filled until the liquid mass inserted reaches the level of the outlet 17. The embedding material contained in the cavity 11 then hardens into a rigid block 5 of high mechanical strength in which the end pieces 41 and the ends of the traction rods 40 are encased. In the following step, shown in Figure 2H, each of the tendons 4 is subjected to traction until the prescribed prestresssing tension is reached. This application of traction takes place in a conventional manner by acting on the other end of each tendon 4, i.e., of each traction rod 40, the tendons being pretightened simultaneously or in sequence. As may be seen in the drawing, the frustoconical or pyramidal tapering shape of the cavity 11, hence of the hardened mass in which the end pieces 41 and the ends of the rods 40 of the tendons 4 are encased, permits efficient wedge-shaped anchoring in the surrounding concrete structure. Contrary to the prior art devices mentioned earlier, this wedge shape prevents any possible axial movement of the hardened mass 5 and causes transmission of the anchoring forces into the surrounding structure 2 by axial compression and not by simple adhesion. The length of this anchoring device is therefore favorably reduced. Additional anchoring security is ensured by the particular arrangement of the end pieces 41 within the cavity 11. Considering that the end pieces 41 are disposed in a bundle in the cavity 11, the area of the cross-section generated by the casing of the bundle of assembled end pieces 41 is greater than the area of the opening 12 of the cavity 11. The bundle of end pieces 41 is therefore blocked in the cavity 11. Reverting to the expressions given above, - for enabling blockage of the tendons 4 in the cavity 11 by preventing the mutually blocked end pieces 41 from coming out through the opening 12, the relation should be: (NxS41)>S12 wherein (N x S41 ) represents generally the surface generated by the casing of the bundle of the N assembled end pieces, each having a cross-sectional area S41. In order to take into account that one or two end pieces 41 may possibly not have found their proper place, as indicated with respect to Figure 2H, the individual sections S41 and the passage section S12 must be of a size to block the end pieces 41 when the tractive force is exerted simultaneously on all the tendons 4. It should be noted that the step of pretightening the tendons 4 as just described may be carried out differently, especially in the case of simple guying, not pretightened. In a final step of the method, illustrated in Figure 2L, the empty space within the sheathing tube 30, or within the conduit made in the structural element 3, may be filled with a sealant 60 through the injection tube or tubes 32 and the inlet or inlets 31 in order to preserve the fluid-tightness of the pretightened system and to prevent corrosion of the pretightening elements. This last step is also optional, depending upon whether such protection 6 is required or necessary. It will therefore be noted that a very effective anchoring device is thus obtained, the longitudinal tractive force of each tendon 4 being taken over mainly by its end piece or portion 41 and transferred to the hardened block 5 of embedding material having high mechanical strength. Efficient transmission of this force is possible owing to the firm attachment of the end piece 41 on the traction rod 40; since this attachment may take place in the factory, its mechanical strength is very high. This force is then transferred by the oblique walls of the cavity 11 to the surrounding structure 2. By disposing one or more anchor rings on the anchor member 1, it is even possible to improve the mentioned anchoring effect in the surrounding structure 2. As mentioned, hoops 21 may be provided in order further to improve the cohesion of the surrounding structure 2 about the cavity 11. In addition to the mentioned longitudinal strength-each end of a traction rod 40 being held in the block 5 of embedding material-each rod 40 is held by radial compression as well. This type of anchoring device lends itself particularly well to prestressed anchoring of a prestressed structural element 3. It may also lend itself to anchoring of non-prestressed tendons, e.g., guys for staying a mast or pylon, in which case the guys need not be protected by a protective tube 30. Likewise, it is not indispensable for the cavity 11 to be contrived in a surrounding structure of concrete; a borehole in the earth or in rock whereby a cavity as required may be obtained might be provided instead. The foregoing description pertains to a cavity having a substantially vertical longitudinal axis, with its opening 12 at the top. Other geometric arrangements are also possible; the dimensions of the cavity 11 are to be adapted in order to obtain sufficient filling of the cavity 11 by the embedding material 50. WE CLAIM: 1. A method of constructing an anchoring device having more than one tendon (4), said anchoring device being accessible from only one side, comprising the following steps: making a cavity (11) in a surrounding structure (2), said cavity having an oblong shape and having two ends, the area (512) of the cross section of the end disposed on the accessible side of the anchoring device being less than the area (511) of the cross section of another portion of the cavity, the cavity comprising an opening (12) on the accessible side of the anchoring device, successively inserting, through the opening (12) of one end, each of the tendons (4), each of said tendons being made up of a traction rod having a first cross-sectional area (540) and an end portion (41) having a second cross-sectional area (541) larger than said first cross-sectional area (540), and -filling the cavity (11) with an embedding material (50), this process being characterized in that, the insertion of each tendon (4) consists in pushing said tendon (4) into the guide tube (30), then into the cavity (11), until its end piece (41) comes in contact with the bottom surface of the cavity (11) which presents a surface (511) corresponding to the largest cross-sectional area of the cavity (11), the insertion of a tendon (4) is repeated until a number of tendons (4) have been installed in the same way, and a new end piece (41) to be installed may not have room at the bottom of the cavity (11); in that case, in order for the tendon in question to play its full part later on, it suffices if the end piece (41) is pushed down as far as possible in the cavity (11) until it comes up against one or more pieces (41) already installed or against the sidewall of the cavity (11), in order to anchor the guying or the prestressed element, a certain number N of tendons (4) must be inserted in the cavity (11), this insertion being preceded by a choice of tendons for which the following relations should exist: (NxS41) to allow the end pieces (41) to be disposed properly on the bottom of the cavity (11), and [(N-l)x S40] + S41 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (SI2), and (NxS41)> S12 for enabling blockage of the tendons (4) in the cavity (11) by preventing the mutually blocked end pieces (41) from coming out through the opening (12), wherein (N x S41) represents generally the surface generated by the casing of the bundle of the N assembled end pieces (41), each having a cross-sectional area (S41). 2. A method as claimed in claim 1, wherein the cavity is made by installing a substantially oblong, tapering anchor member (1) having two ends, the area of the cross section of a first end being less than the area of the cross section of another portion of the anchor member, said anchor member being made up substantially of a wall (10) bounding a cavity (11) of a shape substantially similar to that of said member and provided with an opening (12) having a first cross-sectional area (SI2) at said first end of the anchor member and comprising a bottom wall (14) at the second end, another cross section of said cavity having another area (Sll) greater than the first area (S12), said anchor member (1) then being embedded or concreted in the surrounding structure (2), leaving said opening (12) free. 3. A method as claimed in claim 1, wherein the cavity (11) is made by installation of a template capable of being dismantled and having a substantially oblong and tapering outside shape, the surrounding structure (2) then being concreted about said template, the template then being dismantled by one of its ends, leaving a cavity (11) of substantially oblong and tapering shape in the concreted surrounding structure (2), as well as an opening (12) toward said cavity, the area (812) of the cross section of a portion of said cavity close to the opening (12) being less than the area (811) of the cross section of another portion of said cavity. 4. A method as claimed in claim 1, wherein the cavity (11) is made by installing an inflatable flexible part which, once inflated, has a substantially oblong and tapering shape, the surrounding structure (2) then being concreted about said inflated part, the part then being deflated, leaving a cavity (11) of substantially oblong and tapering shape in the concreted surrounding structure (2), as well as an opening (12) toward said cavity, the area (SI2) of the cross section of a portion of said cavity close to the opening (12) being less than the area (Sll) of the cross section of another portion of said cavity. 5. A method as claimed in claim 1, wherein the cavity (11) is made by boring a cavity of substantially oblong and tapering shape in the surrounding structure (2), said cavity having an opening (12), the area (S12) of the cross section of a portion of said cavity close to the opening (12) being less than the area (Sll) of the cross section of another portion of said cavity. 6. A method as claimed in one of the preceding claims, including after the step of making the cavity (11) a step of installing or concreting a structural element (3) to be prestressed, said structural element (3) comprising a longitudinal conduit (30) for the passage of the tendons (4), one end of said longitudinal conduit (30) communicating (13) with the opening (12) provided in the cavity (11) of the anchoring device. 7. A method as claimed in one of the preceding claims, comprising after the step of filling the cavity (11) with an embedding material (50) a step of tightening each of the tendons (4). 8. A method as claimed in claim 7, comprising after the step of tightening the tendons (4) a step of filling the longitudinal conduit (30) of the prestressed structural element (3) with a sealant (60). 9. An anchor member (1) for constructing an anchoring device having more than one tendon, said anchoring device being accessible from only one side, wherein said member is of substantially oblcng, tapering shape and has two ends, the area of the cross section of a first end being less than the area of the cross section of another portion of the anchor member, said anchor member being made up substantially of a wall (10) bounding a cavity (11) of a shape substantially similar to that of said member and being provided with an opening (12) having a first cross- sectional area (SI2) at said first end of the anchor member and comprising a bottom wall (14) at the second end, another cross section of said cavity having another area (Sll) greater than the first area (SI2), this anchor member being intended to be used with a predetermined number (N) of tension members (4) each having one end intended to be inserted in an anchor cavity (11) of an anchoring device accessible from only one side, said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the area (SI2) of the cross section of the opening (12) of the cavity (11) of the anchor member (1) is greater than the area made up of the sum of the areas (S40) of the cross-sections of (N-l) traction rods (40) added to the maximum area (S41) of the cross section of an end portion or of an end piece (41) of the tendons (4), but is smaller than [(N-1) x S40] + S41 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (S12) of the cavity (11). 10. An anchor member as claimed in claim 9, wherein the area (S11) of the maximum cross section of the cavity (11) is greater than the sum of the maximum areas (S41) of the cross-sections of the end portions or of the end pieces (41) inserted in said cavity. 11. An anchor member as claimed in one of the claims 9 or 10, wherein the area (SI2) of the cross section of the opening (12) of the cavity (11) is less than the area of the cross section made up of the assembly of the areas (S41) of the cross-sections of the end portions or of the end pieces (41) inserted in said cavity. 12. An anchor member as claimed in claim 9 having a frustoconical shape. 13. An anchor member as claimed in claim 9 having a frustopyramidal shape. 14. An anchor member as claimed in one of the claims 9 to 13 provided with an inlet (15) disposed in proximity to its bottom wall (14), said inlet being connected or connectible to a tube (16) for injecting a liquid or semi-liquid product (50). 15. An anchor member as claimed in claim 14 provided with an outlet (17) disposed in proximity to its opening (12), said outlet being connected or connectible to an exhaust tube (18). 16. An anchor member as claimed in one of the claims 9 to 15, wherein the opening (12) is provided with means (13) for fastening a guide tube (30) intended to contain tendons (4). 17. An anchor member as claimed in one of the claims 9 to 15 provided with at least one peripheral widening (19) on its outer lateral surface. 18. An anchor member as claimed in one of the claims 9 to 16 made at least partially of metal. 19. An anchor member as claimed in one of the claims 9 to 17 made at least partially of synthetic material. 20. An anchor member as claimed in one of the claims 9 to 17 made at least partially of concrete. 21. A tendon (4) having one end intended to be inserted in an anchor cavity (11) of an anchoring device accessible from only one side, by a guide tube (30) said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the end portion or the end piece (41) has a convex lower end portion (44). 22. A tendon as claimed in one of claim 21, wherein the end portion or the end piece (41) has a convex upper end portion (43). 23. A tendon as claimed in one of the claims 21 or 22, wherein the end portion or the end piece (41) has a tapering central portion (42), the area of the smallest-area cross section being adjacent to the upper end portion (43), while the area (S41) of the largest-area cross section is adjacent to the lower end portion (44). 24. A tendon as claimed in one of the claims 21 or 22, wherein the end portion or the end piece (41) has a right cylindrical central portion (42) having a constant cross-sectional area (41), bounded by an upper end portion (43) and a lower end portion (44). 25. A method of constructing an anchoring device substantially as hereinbefore described with reference to the accompanying drawings. 26. An anchor member substantially as hereinbefore described with reference to the accompanying drawings. 27. A tendon substantially as hereinbefore described with reference to the accompanying drawings.

Full Text

METHOD, MEMBER, AND TENDON FOR CONSTRUCTING AN
ANCHORING DEVICE
This invention relates to anchoring apparatus used in civil engineering, especially so-called blind anchoring devices accessible from only one side, and more particularly to a method of constructing such a device of the type having more than one tendon, as well as to an anchor member for constructing such a device. The invention further relates to a tendon of the type having one end intended to be inserted into an anchoring cavity of such an anchoring device.
For certain anchoring devices having an anchor head with a tendon, prestressed or not, it is not possible to gain access to the anchoring device from the rear. This situation is encountered particularly in the case of a buried anchoring device where access is possible only from the surface of the ground, or when fluid-tightness or anticorrosion protection must be especially meticulous, so that the rear side of the device must be closed. This requirement prevents the use of a conventional anchor plate where the attachment of the tendon to the plate, e.g., with the aid of anchoring cones, calls for the development of new types of anchoring.
U.S. Patent No. 5,056,284 shows an anchoring device accessible from only one side, the drawback of the device described there being that each tendon, hence the tube in which they are inserted, is held solely by longitudinal adhesion, thus greatly limiting the tractive stress which such an anchoring device can withstand and leading to a very great anchoring length to obtain a sufficient adhesion surface.
Likewise, U.S. Patent No. 4,043,133 provides a tendon sheathing held solely by longitudinal adhesion to the surrounding earth. The tendons extend from the bottom end of the sheathing and are all attached to an anchor plate; the way in which this plate is inserted in the cavity, and the way in which the tendons are fastened to the plate, are not described. In case this embodiment can be produced, the transmission of the anchor force to the ends of the tendons in the surrounding earth through the injected sheathing is

produced solely by longitudinal adhesion, without benefiting from the wedge effect as described below in connection with the present invention.
Thus, there is a need for a method of constructing an anchoring device accessible from only one side which does not encounter the mentioned drawbacks of prior art anchoring devices, i.e., an anchoring device wherein the tendons are held so that the tractive stress on each of them at the level of the anchoring device is taken over by adhesion, this adhesion being appreciably favored by the confinement induced by the overall shape of the anchoring device, and by longitudinal mechanical blocking of the ends of the tendons due to the particular shape of these ends and their arrangement in a cavity of substantially tapering shape. There is further a need for an anchor member of a particular shape which, associated with a plurality of tendons also having a particular shape, makes it possible to construct such an anchoring device, as well as for a possibility of constructing such an anchoring device without the direct use of an anchor member.
According to the present invention, the method of constructing an anchoring device according to the present invention, of the type initially mentioned, includes the steps of making a cavity in a surrounding structure, this cavity having a substantially oblong, tapering shape and having two ends, the area of the cross-section of the end disposed on the accessible side of the anchoring device being less than the area of the cross-section of another portion of the cavity, the cavity comprising an opening on the accessible side of the anchoring device; successively inserting through the opening of one end of each of the tendons, each of these tendons being made up of a traction rod having a first cross-sectional area and an end portion having a second cross-sectional area larger than the first cross-sectional area; and filling the cavity with an embedding material.
The anchor member according to the present invention is of a substantially oblong, tapering shape and has two ends, the area of the cross-section of a first end being less than the area of the cross-section of another portion of the anchor member, the anchor member being made up substantially of a wall bounding a cavity of a shape substantially similar to that of the anchor

member and provided with an opening having a first cross-sectional area at .the-first end of the anchor member and comprising a bottom wall at the second end, another cross-section of the cavity having another area larger than the first area.
The tendon according to the present invention, of the type initially mentioned, is made up of a traction rod provided at the end thereof intended to be inserted in the cavity with an end portion, the area of the cross-section of which is larger than the area of the cross-section of the traction rod.

Accordingly the present invention relates to a method of constructing an anchoring device having more than one tendon (4), said anchoring device being accessible from only one side, comprising the following steps:
making a cavity (11) in a surrounding structure (2),
said cavity having an oblong shape and having two ends, the
area (512) of the cross section of the end disposed on the
accessible side of the anchoring device being less than the
area (511) of the cross section of another portion of the
cavity, the cavity comprising an opening (12) on the
accessible side of the anchoring device,
successively inserting, through the opening (12) of one end, each of the tendons (4), each of said tendons being made up of a traction rod having a first cross-sectional area (540) and an end portion (41) having a second cross-sectional area (541) larger than said first cross-sectional area (540), and
-filling the cavity (11) with an embedding material (50), this process being characterized in that,
the insertion of each tendon (4) consists in pushing said tendon (4) into the guide tube (30), then into the cavity (11), until its end piece (41) comes in contact with the bottom surface of the cavity (11) which presents a surface (511) corresponding to the largest cross-sectional area of the cavity (11),

the insertion of a tendon (4) is repeated until a number of tendons (4) have been installed in the same way, and
a new end piece (41) to be installed may not have room at the bottom of the cavity (11); in that case,
in order for the tendon in question to play its full part later on, it suffices if the end piece (41) is pushed down as far as possible in the cavity (11) until it comes up against one or more pieces (41) already installed or against the sidewall of the cavity (11),
in order to anchor the guying or the prestressed element, a certain number N of tendons (4) must be inserted in the cavity (11), this insertion being preceded by a choice of tendons for which the following relations should exist:
(N x S41) to allow the end pieces (41) to be disposed properly on the bottom of the cavity (11), and
[ (N-l) x 840] + 841 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (812), and

(N x 841)* > 812
for enabling blockage of the tendons (4) In the cavity (11) by preventing the mutually blocked end pieces (41) from coming out through the opening (12), wherein (N x 841)* represents generally the surface generated by the casing of the bundle of the N assembled end pieces (41), each having a cross-sectional area (S41).
Accordingly the present invention also relates to an anchor member (1) for constructing an anchoring device having more than one tendon, said anchoring device being accessible from only one side, wherein said member is of substantially oblong, tapering shape and has two ends, the area of the cross section of a first end being less than the area of the cross section of another portion of the anchor member, said anchor member being made up substantially of a wall
(10) bounding a cavity (11) of a shape substantially
similar to that of said member and being provided with an
opening (12) having a first cross-sectional area (S12) at
said first end of the anchor member and comprising a bottom
wall (14) at the second end, another cross section of said
cavity having another area (Sll) greater than the first
area (S12), this anchor member being intended to be used
with a predetermined number (N) of tension members (4) each
having one end intended to be inserted in an anchor cavity
(11) of an anchoring device accessible from only one side,
said tendon being made up of a traction rod (40) provided
at its end intended to be inserted in said cavity with an
end portion (41) having a cross-sectional area (S41)
greater than the area (S40) of the cross section of said

traction rod (40), wherein the area (S12) of the cross section of the opening (12) of the cavity (11) of the anchor member (1)
is greater than the area made up of the sum of the areas (S40) of the cross-sections of (N-l) traction rods
(40) added to the maximum area (S41) of the cross section of an end portion or of an end piece (41) of the tendons
(4), but
is smaller than [(N-l) x S40] + S41
to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (S12) of the cavity (11).
Accordingly the present invention also relates to a tendon (4) having one end intended to be inserted in an anchor cavity (11) of an anchoring device accessible from only one side, by a guide tube (30) said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the end portion or the end piece (41) has a convex lower end portion (44).

Preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:
Figure 1 is a sectional view of a preferred embodiment of an anchor member according to the invention,
Figure 2 is a series of sectional views (A-L) representing steps in the method of constructing an anchoring device according to the invention,
Figure 3A is a diagrammatic elevation of part of a tendon in a first embodiment of the invention,
Figure 3B is a diagrammatic elevation of part of a tendon in a second embodiment of the invention,
Figure 3C is a diagrammatic elevation of part of a tendon in a third embodiment of the invention, and
Figure 3D is a diagrammatic view, partially in section, of part of a tendon in a fourth embodiment of the invention.
For carrying out the inventive method, an anchoring cavity of a certain shape must first be obtained. The shape of this anchoring cavity is substantially oblong and tapering, with a first open end on the accessible side of the anchoring device and a second closed end on the non-accessible side of

the anchoring device. Moreover, the cross-section of the first end of the anchoring device must be smaller than another cross-section of the cavity, whether this section corresponds to that of the second end or to an intermediate section of the cavity.
Such a cavity may be obtained by several means or devices. A first means consists in using an anchor member comprising a prefabricated interior cavity having the required shape of the anchoring cavity. A preferred embodiment of such an anchor member is illustrated in Figure 1. The anchor member 1 consists essentially of a preferably thin wall 10 bounding an interior cavity 11. A first end of the anchor member 1, i.e., the top end of the member as viewed in the drawing, includes an opening 12, as well as means 13 for fastening a tubular sheath for protecting tendons, the use of which will be described below. The other end of the anchor member 1 is closed by a bottom wall 14. The outside shape of the anchor member 1, hence of the interior cavity 11, is substantially tapering, e.g., frustoconical or frustopyramidal, with the smallest cross-section close to the opening 12 and the largest cross-section close to the bottom wall 14. An inlet 15 is disposed close to the bottom wall 14, an injection tube 16 being attached or attachable to inlet 15. Similarly, an outlet 17 is disposed close to the opening 12, an exhaust tube 18 being attached or attachable to the outlet 17. The use of elements 15-18 will be described below.
The tapering, frustoconical, or frustopyramidal outside surface of the anchor member 1 includes one or more anchor rings 19 disposed at the periphery of this surface, the purpose of which is to improve the transmission and distribution of the anchoring force to the surrounding structure. The embodiment shown in the drawing includes two such rings 19. The anchor member 1 may be made of synthetic material, of metal, or of concrete, its size depending essentially upon the extent of the anchoring device being considered.
Figure 2A shows the first step in the inventive method of constructing an anchoring device using such an anchor member. While the surrounding concrete structure has not yet been made, an anchor member 1 is placed at the exact location where the anchoring device is to be constructed,

the opening 12 being aimed in the direction of the future tendons. The anchor member 1 is held in place by temporary scaffolding or, preferably, by iron bars 20 of the concrete reinforcement. Preferably, although this is not indispensable to the invention, one or more circular iron bars 21, forming one or more hoops, are disposed about the anchor member 1 in order to improve the cohesion of the concrete at that location.
In Figure 2B, it is seen that the concrete structure 2 intended to support the anchoring device has been conventionally poured about the anchor member 1. The anchor member 1 is thus completely surrounded and held in the concrete structure 2 except for its first end provided with the opening 12 which is flush with the top surface of the concrete structure 2 or, as shown here, projects slightly above that surface, and except for the ends of the injection tube 16 and exhaust tube 18, which remain accessible outside the concrete structure 2.
It will therefore be noted that in this second step of the method, a cavity 11 of a certain shape has been produced within a concrete structure 2. As described until now, the cavity 11 has been produced using an anchor member 1 provided with a prefabricated cavity. A like cavity 11 in a concrete structure 2 may also be produced in other ways, e.g., by fabricating it in situ. For instance, provision may be made for a form capable of being dismantled, made of wood or some other material, having an outside shape corresponding to the desired shape of the cavity 11, and placed at the required location, about which form the concrete structure 2 is subsequently poured. As soon as the concrete is hardened, the form is dismantled through the opening 12 and extracted from the cavity 11 through that same opening. In a rather similar manner, a flexible, inflatable component may be used, which after inflation has the desired shape of the cavity 11 and is placed at the required location. After the concrete structure 2 has been poured, the inflatable component is deflated, leaving a cavity 11 of the required shape in the structure 2. Another procedure would be to produce the cavity 11 by drilling out such a cavity of the required shape in an existing structure 2. This drilling procedure would be reserved for anchoring directly in the earth or else for the installation of a new anchoring device on an existing structure 2. The cavity 11, produced in any one of the

ways described, has two important dimensions, a passage area of the opening 12 designated S12 and a maximum cross-sectional area designated S11 (see Figure 1).
During the third step of the method, shown in Figure 2C, the structural element 3 to be prestressed is placed or concreted, in a manner known per se, above the concrete structure 2, the structural element 3 preferably comprising a conduit or a sheathing tube 30, one end of which is situated opposite the opening 12 to be attached to the fastening means 13 adjoining the opening 12. The cross-section of the sheathing tube 30 or of the conduit contrived in the structural element 3 for the tendons corresponds substantially to the cross-section of the opening 12 of the cavity 11. The tube 30 or corresponding conduit includes at least one injection port 31 connected to an injection tube 32, at least one of the ports 31 preferably being disposed near the end of the tube 30 close to the opening 12, as well as at least one outlet connected to an exhaust tube, at least one of the outlets being disposed near the other end (not visible in the drawing) of the tube 30, hence near the structural element 3.
The fourth step, shown in Figure 2D, consists in inserting the tendons. Here reference is made to Figures 3A-3D showing, by way of non-limiting examples, four designs of such a tendon 4. This tendon is substantially made up of a traction rod 40 and an end portion 41. The end portion 41 on the rod 40 is so designed that it has a cross-sectional area S41 larger than the cross-sectional area S40 of the traction rod 40, for reasons to be explained below. The other end of the rod 40 has no end portion of this kind and is made up for a normal anchoring device as known in the art.
The traction rod 40 may be of any known type, consisting either of an undivided strand or of a plurality of strands assembled helically in order to constitute a traction cable. The undivided strand or the strands assembled into the traction rod 40 may be of steel, preferably of a steel having high resistance to traction, or of synthetic material, e.g., carbon-fiber- or Kevlar-based.

The end portion 41 may be an end piece 41 of metal or synthetic material which is firmly fixed to the end of the traction rod 40. The choice of material of which piece 41 is made, as well as the way it is fixed to the traction rod 40, depend essentially upon the material and the manner in which the traction rod 40 is made. The end piece 41 essentially includes a central body 42 bounded by an upper portion 43 and a lower portion 44. The body 42 may have the shape of a right cylinder, with a circular cross-section as in Figure 3A or a polygonal cross-section, or else a frustoconical or frustopyramidal tapering shape, with a circular cross-section or a polygonal one as shown in Figure 3B. In the case of a tapering shape, the part with the smaller cross-section is that adjacent to the upper portion 43. The two portions 43 and 44 are preferably domed or formed of inclined planes so as to facilitate the sliding of an end portion being installed on another end portion already installed, as will be seen below.
In another design, the end portion 41 may be formed by deformation or machining directly on the end of the traction rod 40. Figures 3C and 3D show examples of end portions of this type. In Figure 3C, the traction rod 40 is made up of an undivided strand, and the end portion 41 is obtained by deformation, e.g., by forging, dieing, or stamping, of the end of the traction rod 40. Figure 3D shows an example of an end portion 41 on a traction rod 40 made up of assembled strands. In this example, the end of each strand has been displaced from its normal position, it being possible to provide a ring or a binding just before this displacement in order to prevent the rest of the traction cable from untwisting. The displaced ends of the strands may be held in position by a supplementary holding part 45, e.g., a circular disk soldered or fixed in any other way under the displaced strands, or they may be left free. In a design not shown, the part for holding the displaced strands may consist of an element having the shape of two conical portions coupled at their bases, a first conical portion being inserted between the strands to displace them, while the second conical portion is used for the same purpose as the lower portion 44 described above. Thus, in any design of the end portion 41, it may also have a circular or polygonal shape and include upper and lower portions 43 and 44, as described previously.

The described examples of end pieces 41 or of deformed end portions 41 are not limiting as regards either their shape or the way in which they are produced; any means may be envisaged for increasing the area of the cross-section of the end portion of the traction rod 40. When the following description speaks of end piece 41, it shall be understood that this may also be an end portion as described above.
Returning to Figure 2D, it will be seen that a first tendon 4 has been pushed into the guide tube 30, then into the cavity 11, until its end piece 41 comes in contact with the bottom surface of the cavity 11. A second tendon 4 is being installed in the same way.
Figure 2E shows the usefulness of the domed or inclined shape which may be provided on the upper and lower portions 43, 44 of the end piece 41. When a tendon 4 is being installed, it is quite possible for its end piece 41 to come up against another end piece of a tendon already installed. Owing to the domed or inclined shape of these portions, the second end piece does not jam against the first one but is moved away from it and slides against it until it arrives at its final position beside the first piece.
Figure 2F shows that after a number of tendons have been installed, a new end piece to be installed may not have room at the bottom of the cavity 11; in that case, in order for the tendon in question to play its full part later on, it suffices if the end piece is pushed down as far as possible in the cavity until it comes up against one or more pieces already installed or against the sidewall of the cavity.
In order to anchor the guying or the prestressed element, a certain number N of tendons 4 must be inserted in the cavity 11. Knowing that the cross-section of each traction rod 40 has an area S40 and that the maximum area of the cross-section of the end piece 41 equals S41 (see Figures 3A, 3B, 3C, and 3D), the following relations should exist:
- to allow the insertion of the last tendon 4, i.e., to allow the last end piece 41 to pass into the guide tube 30 and into the opening 12:

[(N-1)xS40] + S41 - to allow the end pieces 41 to be disposed properly on the bottom of the cavity 11:
(NxS41) wherein S11 is the area of the cross-section of the cavity 11 having the largest area (Figure 1).
When all the tendons 4 have been pushed through the conduit of the tube 30 so that all their end pieces 41 are accommodated in the cavity 11 as indicated above, the next step may be undertaken as shown in Figure 2G. During this step, a liquid embedding material 50 is inserted through the injection tube 16; this embedding material enters the cavity 11 through the inlet 15 and fills the empty spaces between the end pieces 41 and the ends of the traction rods 40 in the cavity 11 until it fills the cavity 11 at least partially. During this operation, the outlet 17 and the exhaust tube 18 serve to exhaust the air contained in the cavity 11 during its filling, as well as to check the filling level of the cavity 11. The cavity 11 is preferably filled until the liquid mass inserted reaches the level of the outlet 17. The embedding material contained in the cavity 11 then hardens into a rigid block 5 of high mechanical strength in which the end pieces 41 and the ends of the traction rods 40 are encased.
In the following step, shown in Figure 2H, each of the tendons 4 is subjected to traction until the prescribed prestresssing tension is reached. This application of traction takes place in a conventional manner by acting on the other end of each tendon 4, i.e., of each traction rod 40, the tendons being pretightened simultaneously or in sequence. As may be seen in the drawing, the frustoconical or pyramidal tapering shape of the cavity 11, hence of the hardened mass in which the end pieces 41 and the ends of the rods 40 of the tendons 4 are encased, permits efficient wedge-shaped anchoring in the surrounding concrete structure. Contrary to the prior art devices mentioned earlier, this wedge shape prevents any possible axial movement of the hardened mass 5 and causes transmission of the anchoring forces into the

surrounding structure 2 by axial compression and not by simple adhesion. The length of this anchoring device is therefore favorably reduced.
Additional anchoring security is ensured by the particular arrangement of the end pieces 41 within the cavity 11. Considering that the end pieces 41 are disposed in a bundle in the cavity 11, the area of the cross-section generated by the casing of the bundle of assembled end pieces 41 is greater than the area of the opening 12 of the cavity 11. The bundle of end pieces 41 is therefore blocked in the cavity 11.
Reverting to the expressions given above,
- for enabling blockage of the tendons 4 in the cavity 11 by preventing the mutually blocked end pieces 41 from coming out through the opening 12, the relation should be:
(NxS41)*>S12
wherein (N x S41 )* represents generally the surface generated by the casing of the bundle of the N assembled end pieces, each having a cross-sectional area S41. In order to take into account that one or two end pieces 41 may possibly not have found their proper place, as indicated with respect to Figure 2H, the individual sections S41 and the passage section S12 must be of a size to block the end pieces 41 when the tractive force is exerted simultaneously on all the tendons 4.
It should be noted that the step of pretightening the tendons 4 as just described may be carried out differently, especially in the case of simple guying, not pretightened.
In a final step of the method, illustrated in Figure 2L, the empty space within the sheathing tube 30, or within the conduit made in the structural element 3, may be filled with a sealant 60 through the injection tube or tubes 32 and the inlet or inlets 31 in order to preserve the fluid-tightness of the pretightened system and to prevent corrosion of the pretightening elements. This last step is also optional, depending upon whether such protection 6 is required or necessary.

It will therefore be noted that a very effective anchoring device is thus obtained, the longitudinal tractive force of each tendon 4 being taken over mainly by its end piece or portion 41 and transferred to the hardened block 5 of embedding material having high mechanical strength. Efficient transmission of this force is possible owing to the firm attachment of the end piece 41 on the traction rod 40; since this attachment may take place in the factory, its mechanical strength is very high. This force is then transferred by the oblique walls of the cavity 11 to the surrounding structure 2. By disposing one or more anchor rings on the anchor member 1, it is even possible to improve the mentioned anchoring effect in the surrounding structure 2. As mentioned, hoops 21 may be provided in order further to improve the cohesion of the surrounding structure 2 about the cavity 11. In addition to the mentioned longitudinal strength-each end of a traction rod 40 being held in the block 5 of embedding material-each rod 40 is held by radial compression as well.
This type of anchoring device lends itself particularly well to prestressed anchoring of a prestressed structural element 3. It may also lend itself to anchoring of non-prestressed tendons, e.g., guys for staying a mast or pylon, in which case the guys need not be protected by a protective tube 30. Likewise, it is not indispensable for the cavity 11 to be contrived in a surrounding structure of concrete; a borehole in the earth or in rock whereby a cavity as required may be obtained might be provided instead.
The foregoing description pertains to a cavity having a substantially vertical longitudinal axis, with its opening 12 at the top. Other geometric arrangements are also possible; the dimensions of the cavity 11 are to be adapted in order to obtain sufficient filling of the cavity 11 by the embedding material 50.

WE CLAIM:
1. A method of constructing an anchoring device having more than one tendon (4), said anchoring device being accessible from only one side, comprising the following steps:
making a cavity (11) in a surrounding structure (2), said cavity having an oblong shape and having two ends, the area (512) of the cross section of the end disposed on the accessible side of the anchoring device being less than the area (511) of the cross section of another portion of the cavity, the cavity comprising an opening (12) on the accessible side of the anchoring device,
successively inserting, through the opening (12) of one end, each of the tendons (4), each of said tendons being made up of a traction rod having a first cross-sectional area (540) and an end portion (41) having a second cross-sectional area (541) larger than said first cross-sectional area (540), and
-filling the cavity (11) with an embedding material (50), this process being characterized in that,
the insertion of each tendon (4) consists in pushing said tendon (4) into the guide tube (30), then into the cavity (11), until its end piece (41) comes in contact with the bottom surface of the cavity (11) which presents a surface (511) corresponding to the largest cross-sectional area of the cavity (11),

the insertion of a tendon (4) is repeated until a number of tendons (4) have been installed in the same way, and
a new end piece (41) to be installed may not have room at the bottom of the cavity (11); in that case,
in order for the tendon in question to play its full part later on, it suffices if the end piece (41) is pushed down as far as possible in the cavity (11) until it comes up against one or more pieces (41) already installed or against the sidewall of the cavity
(11),
in order to anchor the guying or the prestressed element, a certain number N of tendons (4) must be inserted in the cavity (11), this insertion being preceded by a choice of tendons for which the following relations should exist:
(NxS41) to allow the end pieces (41) to be disposed properly on the bottom of the cavity (11), and
[(N-l)x S40] + S41 to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (SI2), and

(NxS41)*> S12
for enabling blockage of the tendons (4) in the cavity (11) by preventing the mutually blocked end pieces (41) from coming out through the opening (12), wherein (N x S41)* represents generally the surface generated by the casing of the bundle of the N assembled end pieces (41), each having a cross-sectional area (S41).
2. A method as claimed in claim 1, wherein the cavity is made
by installing a substantially oblong, tapering anchor member (1)
having two ends, the area of the cross section of a first end being
less than the area of the cross section of another portion of the
anchor member, said anchor member being made up substantially
of a wall (10) bounding a cavity (11) of a shape substantially similar
to that of said member and provided with an opening (12) having a
first cross-sectional area (SI2) at said first end of the anchor
member and comprising a bottom wall (14) at the second end,
another cross section of said cavity having another area (Sll)
greater than the first area (S12), said anchor member (1) then being
embedded or concreted in the surrounding structure (2), leaving
said opening (12) free.
3. A method as claimed in claim 1, wherein the cavity (11) is
made by installation of a template capable of being dismantled and
having a substantially oblong and tapering outside shape, the
surrounding structure (2) then being concreted about said
template, the template then being dismantled by one of its ends,

leaving a cavity (11) of substantially oblong and tapering shape in the concreted surrounding structure (2), as well as an opening (12) toward said cavity, the area (812) of the cross section of a portion of said cavity close to the opening (12) being less than the area (811) of the cross section of another portion of said cavity.
4. A method as claimed in claim 1, wherein the cavity (11) is
made by installing an inflatable flexible part which, once inflated,
has a substantially oblong and tapering shape, the surrounding
structure (2) then being concreted about said inflated part, the part
then being deflated, leaving a cavity (11) of substantially oblong
and tapering shape in the concreted surrounding structure (2), as
well as an opening (12) toward said cavity, the area (SI2) of the
cross section of a portion of said cavity close to the opening (12)
being less than the area (Sll) of the cross section of another
portion of said cavity.
5. A method as claimed in claim 1, wherein the cavity (11) is
made by boring a cavity of substantially oblong and tapering shape
in the surrounding structure (2), said cavity having an opening
(12), the area (S12) of the cross section of a portion of said cavity
close to the opening (12) being less than the area (Sll) of the cross
section of another portion of said cavity.
6. A method as claimed in one of the preceding claims, including
after the step of making the cavity (11) a step of installing or
concreting a structural element (3) to be prestressed, said
structural element (3) comprising a longitudinal conduit (30) for the

passage of the tendons (4), one end of said longitudinal conduit (30) communicating (13) with the opening (12) provided in the cavity (11) of the anchoring device.
7. A method as claimed in one of the preceding claims,
comprising after the step of filling the cavity (11) with an
embedding material (50) a step of tightening each of the tendons
(4).
8. A method as claimed in claim 7, comprising after the step of
tightening the tendons (4) a step of filling the longitudinal conduit
(30) of the prestressed structural element (3) with a sealant (60).
9. An anchor member (1) for constructing an anchoring device
having more than one tendon, said anchoring device being
accessible from only one side, wherein said member is of
substantially oblcng, tapering shape and has two ends, the area of
the cross section of a first end being less than the area of the cross
section of another portion of the anchor member, said anchor
member being made up substantially of a wall (10) bounding a
cavity (11) of a shape substantially similar to that of said member
and being provided with an opening (12) having a first cross-
sectional area (SI2) at said first end of the anchor member and
comprising a bottom wall (14) at the second end, another cross
section of said cavity having another area (Sll) greater than the
first area (SI2), this anchor member being intended to be used with
a predetermined number (N) of tension members (4) each having
one end intended to be inserted in an anchor cavity (11) of an

anchoring device accessible from only one side, said tendon being made up of a traction rod (40) provided at its end intended to be inserted in said cavity with an end portion (41) having a cross-sectional area (S41) greater than the area (S40) of the cross section of said traction rod (40), wherein the area (SI2) of the cross section of the opening (12) of the cavity (11) of the anchor member (1)
is greater than the area made up of the sum of the areas (S40) of the cross-sections of (N-l) traction rods (40) added to the maximum area (S41) of the cross section of an end portion or of an end piece (41) of the tendons (4), but
is smaller than [(N-1) x S40] + S41
to allow the insertion of the last tendon (4), i.e., to allow the last end piece (41) to pass into the guide tube (30) and into the opening (12) with a cross-sectional area (S12) of the cavity (11).
10. An anchor member as claimed in claim 9, wherein the area
(S11) of the maximum cross section of the cavity (11) is greater
than the sum of the maximum areas (S41) of the cross-sections of
the end portions or of the end pieces (41) inserted in said cavity.
11. An anchor member as claimed in one of the claims 9 or 10,
wherein the area (SI2) of the cross section of the opening (12) of
the cavity (11) is less than the area of the cross section made up of
the assembly of the areas (S41) of the cross-sections of the end
portions or of the end pieces (41) inserted in said cavity.

12. An anchor member as claimed in claim 9 having a
frustoconical shape.
13. An anchor member as claimed in claim 9 having a
frustopyramidal shape.
14. An anchor member as claimed in one of the claims 9 to 13
provided with an inlet (15) disposed in proximity to its bottom wall
(14), said inlet being connected or connectible to a tube (16) for
injecting a liquid or semi-liquid product (50).
15. An anchor member as claimed in claim 14 provided with an
outlet (17) disposed in proximity to its opening (12), said outlet
being connected or connectible to an exhaust tube (18).
16. An anchor member as claimed in one of the claims 9 to 15,
wherein the opening (12) is provided with means (13) for fastening
a guide tube (30) intended to contain tendons (4).
17. An anchor member as claimed in one of the claims 9 to 15
provided with at least one peripheral widening (19) on its outer
lateral surface.
18. An anchor member as claimed in one of the claims 9 to 16
made at least partially of metal.

19. An anchor member as claimed in one of the claims 9 to 17
made at least partially of synthetic material.
20. An anchor member as claimed in one of the claims 9 to 17
made at least partially of concrete.
21. A tendon (4) having one end intended to be inserted in an
anchor cavity (11) of an anchoring device accessible from only one
side, by a guide tube (30) said tendon being made up of a traction
rod (40) provided at its end intended to be inserted in said cavity
with an end portion (41) having a cross-sectional area (S41) greater
than the area (S40) of the cross section of said traction rod (40),
wherein the end portion or the end piece (41) has a convex lower
end portion (44).
22. A tendon as claimed in one of claim 21, wherein the end
portion or the end piece (41) has a convex upper end portion (43).
23. A tendon as claimed in one of the claims 21 or 22, wherein
the end portion or the end piece (41) has a tapering central portion
(42), the area of the smallest-area cross section being adjacent to
the upper end portion (43), while the area (S41) of the largest-area
cross section is adjacent to the lower end portion (44).
24. A tendon as claimed in one of the claims 21 or 22, wherein
the end portion or the end piece (41) has a right cylindrical central
portion (42) having a constant cross-sectional area (41), bounded
by an upper end portion (43) and a lower end portion (44).

25. A method of constructing an anchoring device substantially
as hereinbefore described with reference to the accompanying
drawings.
26. An anchor member substantially as hereinbefore described
with reference to the accompanying drawings.
27. A tendon substantially as hereinbefore described with
reference to the accompanying drawings.

Documents:

120-del-1999-abstract.pdf

120-del-1999-claims.pdf

120-del-1999-correspondence-others.pdf

120-del-1999-correspondence-po.pdf

120-del-1999-description (complete).pdf

120-del-1999-drawings.pdf

120-del-1999-form-1.pdf

120-del-1999-form-13.pdf

120-del-1999-form-19.pdf

120-DEL-1999-Form-2.pdf

120-del-1999-form-29.pdf

120-del-1999-form-3.pdf

120-del-1999-form-4.pdf

120-del-1999-form-6.pdf

120-del-1999-gpa.pdf

120-del-1999-petition-138.pdf

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Patent Number

231005

Indian Patent Application Number

120/DEL/1999

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

28-Feb-2009

Date of Filing

20-Jan-1999

Name of Patentee

VSL INTERNATIONAL AG.

Applicant Address

SCHEIBENSTRASSE 70, 3014 BERN, SWITZERLAND.

Inventors:

#	Inventor's Name	Inventor's Address
1	HERVE BELBEOC'H	18, RUE DE 1 'ORANGERIE, F-78000 VERSAILLES, FRANCE

PCT International Classification Number

E04C 1/40

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA