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This Application is a 35 U.S.C. §371 National Stage Entry of International Application No. PCT/FR2011/052897, filed Dec. 7, 2011 and claims the benefit of priority to French Application No. 10 60270, filed Dec. 8, 2010, each of which are incorporated by reference in their entirety herein. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns devices for deviating structural cables, especially stays. 
     At present it is common to make structural cables as a bundle of individual stretched tendons anchored at their ends. The design of an construction work may involve diverting the cable in one or more areas of its path. 
     In stayed structures, the cables have an upper part situated near a tower and lower extremities anchored to the suspended structure, for example, the deck of a bridge. In a conventional design, the upper extremity of each cable is anchored to the tower. In other stayed structures, the cables follow paths whose general shape is that of an inverted V, and they are diverted to the tower by means of a device commonly referred to as a saddle. 
     At the saddle, the cable strands follow curved paths, typically with a substantially constant radius of curvature. Preferably, the tendons extend uninterruptedly along the saddle. Sufficient friction must be provided between the tendons and the saddle to avoid unwanted slippage. 
     WO 2007/121782 A1 discloses a saddle wherein each strand forming a tendon of the cable is received in an individual conduit whose wall presents, on either side of the plane containing the curved path of the strand, two inclined faces, giving the conduit a generally V-shaped cross-section. The V shape of the conduit&#39;s cross-section immobilizes the strand through a wedge effect whenever tension is applied to it by the load on the structure. This saddle design is not without its drawbacks. In particular, the contacts between the strand and the wall of its conduit are local, which is not favorable to good distribution of local stresses. Moreover, the saddle is not compatible with the use of individually sheathed strands because the individual sheath of a strand would be damaged by the pinching force brought about by the V shape of the conduit. Nonetheless, individually sheathed strands are frequently preferred for making structural cables because their corrosion resistance is enhanced by the insulation conferred by the sheath. If, however, use such strands with the saddle of WO 2007/121782 A1 is desired, the sheaths must be removed on the length of the strands placed inside the saddle, which requires the use of special measures to sufficiently insulate the metal of the strands. In spite of these measures, which can be complex and costly, stripping the tendons near the saddle risks introducing weakness into the anticorrosion protection of the stays. 
     An object of the present invention is to propose a different saddle design, which reduces the incidence of the aforementioned problems, in particular by ensuring adequate transmission of stresses within the curved path followed by the tendons. 
     SUMMARY OF THE INVENTION 
     The invention thus proposes a device for deviating a structural cable having a plurality of stretched tendons. The device comprises a body traversed by conduits. Each conduit has a wall to guide one of the tendons along a curved path. The conduit wall having a support area for supporting that tendon, located on an interior side of the curvature of the path, which support area presents, at least in a central portion of the conduit and transverse to the curved path, a cross-section in the shape of a circular arc having a radius substantially equal to half the external diameter of the tendon, the central portion of the conduit having a widened cross-section outside the support area 
     The tendons are held in the conduit, preventing them from sliding along the curved path, by the friction on the tendon in the support area of the wall of the conduit, whose roughness may be more or less significant. The tendon is in contact with this support area over a surface having a certain extent, depending on the shape of the circular arc, whose radius is adapted to the tendon. It is pressed against this support area by the tension applied to the cable. 
     Because of the good distribution of stresses transmitted between the tendons and the wall of their conduits, the deviation device enables the use of tendons each of which has a metal strand and a plastic sheath surrounding the strand. The sheath can thus pass uninterrupted through the saddle and up to the cable anchors by being applied to the support area of the wall of the conduit. 
     It has been determined that an angular sector of at least 60° for the shape of the arc of circle of the section of the support area provides sufficient frictional blocking in a number of configurations. This angular sector may, in particular, be in a range between 90 and 120°. 
     It is generally appropriate for the conduits to present a cross-section that is sufficient to allow the tendons to be threaded without difficulty. This property can be obtained by providing a cross-section that is large enough to contain a circle whose diameter is at least 2 mm greater than the external diameter of the tendon. 
     The shape of the cross-section of the central portion of the conduit outside the support area may be that of an arch whose diameter is greater than the external diameter of the tendon. An arched shape, circular, for example, avoids undesirable concentrations of stresses in the material situated between the individual conduits of the device. 
     In order to accommodate a margin of angular variation of the cable on either of the sides of the device, the conduit can be shaped in such a way that its cross-section widens outwardly on at least one side of its central portion. The widening can in particular follow, on the interior side of the curvature of the path, a substantially circular generatrix whose radius is less than the radius of curvature of the path in the central portion of the conduit. 
     In an embodiment, the deviation device further comprises a curved tube to receive the structural cable, the body provided with conduits being housed inside the curved tube. 
     Another aspect of the invention relates to an construction work such as, for example, a cable-stayed bridge, comprising at least one structural cable having a plurality of stretched tendons, anchors for the tendons at the extremities of the cable, and at least one cable deviation device between the two anchors, this device being as defined above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and benefits of the present invention shall appear from the following description of a non-limiting embodiment by referring to the attached drawings, in which: 
         FIG. 1  is a diagram of a cable-stayed bridge to which the invention may apply; 
         FIG. 2  is a very schematic view of a stay equipped with an embodiment of the diverting device; 
         FIG. 3  is an axial cutaway of a conduit belonging to the diverting device; 
         FIG. 4  is a cross-section of the diverting device, along plane IV-IV, as indicated in  FIG. 3 ; 
         FIG. 5  is a cross-section of a conduit in which a cable tendon is housed; and 
         FIG. 6  is a view similar to that of  FIG. 5 , illustrating the conduit and the tendon during installation of the cable. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiment of the construction work shown in  FIG. 1  consists of a cable-stayed bridge. The deck  1  of such a bridge is conventionally supported by one or more towers  2  by means of stays  3  that follow inclined paths between the tower and the deck. At tower  2 , each stay  3  extends through a deviation device  5  realized in accordance with the invention, hereinafter referred to as a saddle. 
     In the embodiment shown in  FIG. 2 , the saddle  5  has a curved metal tube  6  buried in the concrete used to make the tower  2 . The curved tube  6  has, for example, been shaped by bending a steel tube, then placed in the appropriate geometric configuration before the concrete of the tower  2  is poured. Here, the structural cable is formed by a stay  3 , composed of a plurality of stretched tendons  4  which extend through saddle  5  without interruption. The tendons  4  preferably consist of individually sheathed strands, wherein the metal strand and its plastic sheath are both uninterrupted within the saddle  5 . Through the saddle, each tendon  4  follows a curved path T ( FIG. 3 ) defined by an individual conduit  10 . The conduits  10  are formed in a body  7  made of molded material housed inside the curved tube  6 . 
     On the exterior of saddle  5 , the stay  3  freely extends to the two anchors  8  installed on deck  1 . These anchors  8  can, for example, be in accordance with that described in WO 00/75453 A1. 
     Each of the conduits  10  arranged in the saddle  5  receives a respective sheathed strand  4 . In their central portion, they preferably follow a curved path T of constant radius R. In this portion, the cross-section of the conduit  10  has, for example, the shape shown in  FIG. 4 , where the wall of the conduit has a support area  11  on the interior side of the curvature of the path T. The shape of the support area  11  is a circular arc of radius r. 
     As shown in  FIGS. 4 and 5 , the radius r of the circular arc shape of the support area  11  in the central portion of the conduit  10  corresponds to half the external diameter of the tendon  4 . Thus, the support area  11  provides a relatively extensive contact area between the wall of the conduit  10  and the periphery of the tendon  4 , which creates a frictional force suitable for holding the tendon in position whenever tension is applied by the load on the structure. The angular sector α over which the support area extends is preferably at least 60°. Optimally, this angular opening α is in the range of 90° to 120°. 
     The upper portion  12  of the wall of the conduit  10 , on the exterior side of its curvature, is wider than the support area to allow the unencumbered introduction of the tendon  4  when installing the stay. This widening of the central portion of the conduit outside the support area  11  can be realized by giving the upper portion  12  a cross-section in the shape of an arch whose diameter is greater than the exterior diameter of the tendon. It has been found that introduction of the tendon  4  in the conduit can be accomplished without difficulty when the cross-section of the conduit, in its central portion, is sufficient to contain a circle, C, whose diameter is at least 2 mm greater than the external diameter of the tendon  4 , as shown in  FIG. 6 . 
     Thus, the tendon  4  can be threaded through its conduit without rubbing against saddle  5 . To that end, a movable shim  15  can be used, for example, in the shape of a ribbon of plastic material, before threading. Once the tendon  4  has been installed, the shim  15  is removed, the tendon  4  then being laid in the support area  11 . 
     The arched shape of the upper portion  12  of the wall of the conduit  10  can, in particular, have a circular profile of radius r′&gt;r, with radial shoulders  13  connecting the support area  11  to the upper portion  12 . The rounded shape of the arch is favorable to the vertical flow of the compressive stress occurring in the molded matrix  7  of the saddle  5 . 
     In a preferred embodiment, the cross-section of the conduit  10  widens toward the exterior on either side of the central portion. This widening, visible in  FIG. 3 , can be used to guide the deflection of the tendons, which results from variations in the load on the cables. 
     On the interior side of the curvature of the path T, the widening of the cross-section of the conduit  10  can follow a generatrix whose shape is preferably circular, with a radius R′ that is less than the radius of curvature R of the path T in the central portion of the conduit  10 . The fact that the radius R′ is constant enables the bending stresses to which the tendons  4  are subject to be limited. 
     The widening of the cross-section of the conduit  10  at both ends may result from a homothetic transformation of the shape shown in  FIG. 4 . A variant consists in gradually enlarging outwardly the interior portion of the section of the conduit so that it tends toward the circle of radius r′ along the outer face of the saddle  5 . Another variant consists in putting, on either side of the central portion of constant section of the conduit  10 , a trumpet-shaped widening of circular cross-section whose smallest diameter is equal to r′. In this way, the widening can be simply realized with a machined guide piece placed in the opening of the conduit  10 . 
     The central portion of the conduits  10  can be realized by being molded in the material  7 , e.g. filler mortar, constituting the matrix of the saddle  5 . In this way, negative molds having the shape of the conduits  10  are disposed in the curved tube  6 . Their positions and transverse spacing are maintained by guides regularly spaced in the tube  6 . The tube  6  is then filled with a hardenable material such as a high-resistance mortar. Unmolding can then take place either by mechanical destruction of the molds, or by dissolution, or by shrinkage. This realization of the saddle by molding can take place in a factory. At the worksite, the saddle thus realized is lifted to the tower and placed in the predetermined position. Once the tower is complete, the tendons  4  of the stay are lifted, threaded through the saddle  5 , and anchored to the deck  1 . 
     One advantage of the above-described saddle  5  is that it is compatible with the use of tendons  4  consisting of individually sheathed strands. The section of such a tendon  4  is shown in  FIGS. 5 and 6 , where reference  16  denotes the twisted metal wires of the strand and reference  17  denotes the plastic sheath that surrounds those wires. The wires  16  are typically of galvanized steel, while the sheath  17  is of high-density polyethylene (HDPE). A flexible fill material fills the spaces between the metal wires  16  and those between the wires  16  and the sheath  17 . 
     The sheathed strand  4 , shown in  FIGS. 5 and 6  has a circular external section. The support area  11  of the conduits  10  is then designed to have the same radius, r, as the sheathed strand  4 . In practice, there can be a slight difference in radius between the support area  11  and the external section of the tendon  4 , to the extent that the flow of the plastic material of the sheath  17  pressed against the wall of the conduit remains acceptable. Similarly, it is possible that the external cross-section of the tendon  4  is not exactly circular but, for example, hexagonal with rounded corners, following extrusion of the sheath  17  on the metal strand. In this case, the “external diameter of the tendon” should be understood as being the diameter of the smallest circle in which the cross-section of the tendon can be inscribed. This definition of the “external diameter of the tendon” also holds for an unsheathed metal strand. Although not preferred, the latter case falls within the scope of the invention, the contacts between the stretched tendon and support area  11  of its conduit then following spiral lines instead of being point contacts. 
     The embodiments mentioned above are illustrations of the present invention. Various modifications can be made without falling outside the scope of the invention, which is based on the attached claims. In particular, the deviation device according to the invention can be used to d structural cables other than stays.

Summary:
The structural cable has several stretched tendons ( 4 ). It is diverted in a device comprising a body crossed by conduits ( 10 ). Each conduit has a wall to guide one of the tendons along a curved path. The wall of the conduit has a tendon support area ( 11 ) directed toward the interior of the curve of the path. This support area presents, in the center portion of the conduit and transverse to the curved path, a section in the shape of a circular arc whose radius is appreciably equal to half the external diameter of the tendon. The central portion of the conduit has a cross-section enlarged outside the support area.