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FIELD OF THE INVENTION 
     The present invention relates to anchoring devices for fixing structural cables to building elements. 
     In particular, the invention applies each time it is necessary to fix a cable, subjected to tensile loadings, to equip building elements such as cable-stayed bridges, suspension bridges or the like, by connecting the tops of the towers of these bridges to their decks and to their anchor blocks. 
     DESCRIPTION OF THE RELATED ART 
     The cables habitually encountered in such building elements comprise a number of strands each of which comprises metal wires themselves enveloped together in a protective sheath, each of these protective sheaths being interrupted at a terminal edge so that the strands each have a bared end portion. 
     The anchoring devices habitually encountered, particularly in EP-A-0 323 285, comprise: 
     a perforated block in which the bared end portions of the various strands are individually anchored, 
     a bearing surface which is secured to the building element and against which the periphery of the perforated block axially bears, 
     a tube to which the perforated block is attached on the bearing surface side, the tube transversely delimiting a chamber inside which the terminal edges of the strands are located and which is filled with a substance that protects the bared end portions present in the chamber, and 
     a packing box which seals the chamber, at the opposite end to the anchoring block, and which has the sheathed strands passing in a sealed manner through it, the packing box comprising: 
     at least two perforated plates of which one, known as the inner plate, is arranged on the same side as the chamber and of which the other, known as the outer plate, is arranged at the opposite end to the perforated block with respect to the inner plate, and 
     at least one piece of packing which is inserted between the inner plate and the outer plate. 
     In the known embodiments of the packing boxes encountered in the anchoring devices of the kind in question, the inner plate of the packing box is stationary while the outer plate can move and is driven toward the stationary plate by means of threaded rods passing through the perforated block and placed under tension. These rods are both screwed into the outer plate and into a nut butting against the perforated block. 
     To ensure good leaktightness of the anchoring device, it is possible for the packing of the packing box to be compressed again by exerting tension on the outer plate should that prove necessary. However, the ends of the threaded rods screwed into the outer plate are located on the same side as the cables and are therefore not accessible to the operator unless he dismantles the entire anchoring device. 
     An anchoring device such as this therefore involves significant and expensive maintenance operations because the mechanically stressed parts are located in places which are difficult to access. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the aforementioned drawbacks by providing an anchoring device that makes maintenance operations easier. 
     To this end, according to the invention, an anchoring device of the kind in question is essentially characterized in that the outer plate is stationary with respect to the chamber and in that the device comprises means for pressing on the inner plate. 
     Thus, by virtue of these arrangements, all the constituent elements of the packing box are protected against corrosion and the elements which allow the packing to be compressed are accessible from the opposite side of the anchoring device to the side from which the cables extend, and therefore do not entail costly disassembly. 
     In some preferred embodiments of the anchoring device according to the present invention, recourse is further had to one and/or other of the following arrangements: 
     the means for pressing on the inner plate comprise a compression rod, one end of which is in abutment against the inner plate and the other end of which passes through a hole made in the perforated block and which can be actuated from the opposite side of the perforated block to the bearing surface secured to the building element; 
     the compression rod is a threaded rod and the hole is tapped, the rod being operable by screwing; 
     the compression rod is in abutment against an insert plate fitted adjacent to the inner plate; 
     the pressing means comprise a stop which is integral with the tube and which is situated inside the tube at a distance from the outer face of the outer plate that is more or less equal to the thickness of the packing box, and in which said at least one piece of packing is perforated with passages of a diameter smaller than the diameter of the sheathed strands; 
     the packing box is placed in a groove formed inside the tube and the stop is defined by the step between the groove and the main part of the tube; 
     the outer plate is in abutment against a stop sleeve attached to the end of the tube by screwing; 
     the outer plate is in abutment against a perforated plate attached to the end of the tube; 
     the protective substance is compressed in the chamber; and 
     a cap is sealed onto the perforated block, delimiting a chamber into which the bared end portions of the strands project, the chamber being filled with said protective substance. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     Further features and advantages of the invention will become apparent in the course of the following detailed description of two of its embodiments which are given by way of nonlimiting examples with reference to the appended drawings in which: 
     FIG. 1 is an overall schematic view of a suspension bridge, the cables of which are immobilized using anchoring devices according to the present invention; 
     FIG. 2 is a view in cross section of a cable of FIG. 1; 
     FIG. 3 is an enlarged sectional view of one of the strands that make up the cable of FIG. 2; 
     FIG. 4 is a view in longitudinal section of a first embodiment of the anchoring device for the cable of FIGS. 2 and 3; 
     FIG. 5 is a view in longitudinal section of a second embodiment of the anchoring device for securing the cable of FIGS. 2 and 3; and 
     FIG. 6 is an enlarged sectional view of the packing box of the anchoring device of FIG.  5 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The building element  1  depicted in FIG. 1 is, for example, a suspension bridge. This bridge conventionally has a deck  2 , two posts or towers  3 , two parallel suspension cables  4 , just one being visible in the figure, and a number of hangers  4   a  which are attached to the cables  4  and which carry the deck  2 . 
     The suspension cables  4  are stretched between two anchoring blocks  9  in the ground, located at the two ends of the bridge, and are supported by the two towers  3 . 
     As shown more particularly in FIG. 2, the cable  4  in question is made up of a number of individual strands  5 . 
     Each strand  5  is itself formed, as shown in FIG. 3, of a number of elemental wires  6 , for example seven of these. These wires may be parallel or twisted and are made, for example, of galvanized steel. This collection of wires is surrounded by a protective sheath  7  capable of protecting them throughout their life against corrosion due to inclement weather or other external attack, particularly due to moisture and handling. This sheath is made, for example, of a plastic, such as polyethylene or a polyamide, or of a metal such as aluminum or stainless steel. The sheath is attached directly to the bundle of wires by extrusion. 
     The sheath in question may also be made of any other desirable coating of the bundle of wires  6 , for example of an epoxy paint coated onto it. 
     The spaces between the wires  6  and sheath  7 , if there are any, may or may not be filled with a protective substance  8  such as, for example, a resinous pitch of the epoxy type or a wax or polybutadiene. 
     The sheathed strands  5  thus defined, are all mutually identical, are autonomous, and remain so throughout the life of the cable  4  that they form. 
     The sheathed strands  5  of the cable  4  are tensioned individually, in a way known per se, on the bridge  1 . For example, they are fitted using extruded sleeves or alternatively, as depicted in FIGS. 4 and 5, by clamping the ends of the strands  5  in split jaws  10 . 
     For that, each of the protective sheaths  7  of the strands  5  is interrupted at a terminal edge T so that each strand  5  has a bared end portion  11 . 
     The bared end portions  11  are clamped in the split jaws  10  each of which has, on the one hand, a tapped cylindrical hole capable of contiguously surrounding the end of the strand that is to be anchored and, on the other hand, a frustoconical external surface capable of collaborating with a complementary housing formed in a perforated anchoring block  15 . 
     Each strand  5  is thus tensioned between, for example, a post  3  of the bridge  1  and the perforated block  15  secured, for example, to one of the anchoring blocks  9  for this bridge. 
     The perforated block  15  has two opposite faces: an outer face  16  and an inner face  17 . The outer face  16  faces away from the strands  5 . The ends  12  of the end portions  11  project from this face. The inner face  17  faces toward the strands  5 . 
     In order to protect the end portions  11  of the strands  5  against corrosion, the terminal edges T of each of these strands are located inside a chamber  20  delimited: 
     at a first axial end, by the inner face  17  of the perforated block  15 , 
     transversely by a rigid tube  22  which is, for example, of cylindrical shape on a circular base and which is screwed or welded at one of its ends so as to be adjustable or stationary with respect to the inner face  17  of the perforated block  15 ; 
     and at the opposite axial end to the block  15 , by a packing box  25  through which the sheathed strands  5  pass in a sealed way and which is pressed in a sealed way against the inner face  23  of the tube  22  under the effect of axial compression. 
     The packing box  25  consists, in a way known per se, of three perforated plates  26 ,  27  and  28 , between which two pieces of packing  29  and  30 , made: of an elastomeric material or the like, are inserted. 
     The perforated plates  26  to  28  are rigid plastic plates and all the plates and pieces of packing run transversely to the strands  5  so that the latter can pass through them. The plate  26  is an outer plate located at the end of the tube  22  facing toward the main length of cable, that is to say, toward the side from which the strands  5  run toward the tower  3 . This plate is held in a stationary position with respect to the chamber  20  by being in abutment against a return  32  formed at the end of the tube  22 . 
     The plates  26  to  28  hold the pieces of packing  29 ,  30  in compression to cause the edges of the pieces of packing to expand and produce the desired sealing. For this purpose, bearing means  35  collaborate with the plate  28  closest to the chamber  20 , also known as the inner plate. 
     In the first embodiment depicted in FIG. 4, the bearing means  35  consist in an insert plate  36  which is perforated and pressed against the inner plate  28  and in threaded rods  37  (just one being depicted in FIG.  4 ). The threaded rods adopt the shape of screws each equipped with a head  38 . 
     A first end of the threaded rod or screw  37  presses against the insert plate  36  while the second end of the rod  37  passes through a tapped hole  12  formed in the perforated block  15  so that the head  38  projects from the outer face  16  of this block. The threaded rod  37  can be operated by means of the head  38  to be screwed through the tapped hole. 
     The insert plate  36  is pushed back by the screwing of the threaded rods or screws  37 . During this compression, the insert plate  36  moves the inner plate  28  closer to the outer plate  26  which itself remains stationary. 
     In order to immobilize the perforated block  15  with respect to the anchoring block  9 , an adjusting tube  40  is mounted secured to the outer face of the tube  22 , near the end of this tube adjacent to the perforated block  15  while a ring  41  is attached by screwing onto a complementary screw thread formed on the adjusting tube  40 . This ring bears axially against an annular bearing surface  42  forming part of the anchoring block  9 . The adjusting tube  40  is, for example, welded or screwed onto the tube  22  while the perforated block  15  is screwed onto the adjusting tube using screws  43  which are accessible from the outside face  16  of this block. 
     Furthermore, a cap  45  is sealed onto the outer face  16  of the perforated block  15  and is held thereon using screws  46 . This cap delimits a chamber  47  in which the ends  12  of the bared end portions  11  of the strands  5  are situated, and which contains a flexible protective substance protecting these ends against corrosion. 
     The chamber  47  is filled with protective substance protecting against corrosion through an orifice which is then closed with a plug  48 . The chamber  47  communicates with the chamber  20  via passages formed in the perforated block  15  (and which have not been depicted). 
     Once the strands  5  have been tensioned and once compression has been exerted on the insert plate  36  using the threaded rods or screws  37 , the entirety of the two chambers  20  and  47  is filled with the substance that protects the bared portions of the strands  5  against corrosion. 
     By virtue of this arrangement, each strand S is autonomous throughout its length and may be tensioned or slackened independently of its neighbors. The ends  12  of these strands are readily accessible from the outer face  16  of the perforated block  15 . 
     Likewise, the pieces of packing  29  and  30  may easily be recompressed periodically to maintain a good seal by screwing the heads  38  of the screws which are easily accessible from the outer face  16  of the block  15 . The operator does not have to remove some of the constituent parts of the anchoring device described previously in order to access hidden parts. 
     The second embodiment depicted in FIGS. 5 and 6 differs from the previous embodiment only in the form of the bearing means  35 , the diameter of the passages formed in the pieces of packing  29  and  30 , and the opposite end of the tube to the anchoring block. 
     The strands  5  are inserted in the pieces of packing  29  and  30  through passages  50  which have a diameter slightly smaller than that of the sheath  7  of the strands  5 . In addition, a groove  51  is formed at the opposite end of the tube  22  to the anchoring block  15 . The tube  22  thus has, at its end, a portion of inside diameter greater than the inside diameter of the rest of the tube. A step  52  is defined by this change in diameter. The three perforated plates  26  to  28  and the pieces of packing  29  and  30  are inserted in this groove  51  via the end of the tube  22 . The plates and the pieces of packing are in abutment against the step  52  and are kept in compression against one another by means of a stop sleeve  53 . This sleeve is attached to the end of the tube  22  and held in place by means of a screw thread  54  which collaborates with a tapping formed inside the end portion of the tube. 
     As an alternative, a perforated plate replaces the stop sleeve and is screwed onto the end of the tube  22 . This plate contains as many perforations as there are strands to be inserted into the packing box. 
     When the strands  5  are inserted in the packing box, the additional material of the pieces of packing  29  and  30 , due to the smaller diameter of the passages  50  is compressed against the groove  51 , providing a very good seal. 
     Sealing is further improved when inserts are attached and inserted in the packing box in such a way that the material of the pieces of packing in even more pushed back. To this end, the perforated plate has a greater number of perforations than there are strands. 
     In yet another alternative form, the substance in the chamber  20  is compressed in such a way that the inner plate  25  of the packing box is pushed back toward the outer plate which itself remains stationary. The pieces of packing  29 ,  30  are thus compressed more strongly, enhancing the sealing.

Summary:
An anchoring device for fixing a structural cable to a building element, the cable comprising a plurality of strands each comprising wires which are themselves enclosed together in a protective sheath, each of the protective sheaths being interrupted at a terminal edge such that the strands have each an exposed end section. The exposed section is inserted in a sealed chamber with a packing box whereof on plate is fixed and the other plate is compressed by threaded rods.