Abstract:
The device includes a first member surrounding and secured to a section of a cable, a second member connected to an element to which a portion of the cable is attached, and arranged around said first member, a resilient or viscoelastic ring engaging the first member and the second member, and a flexible container housed in a ring-shaped compartment between the two members and filled with a viscous substance.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns a device for damping vibration in a cable. It has particular but not exclusive application in the field of civil engineering works with a structure using such cables, for example suspension or cable-stayed bridges. 
     These cables or stays are subjected to vibration caused by the wind and/or the rain or else by vehicle traffic on the bridge. 
     The invention concerns more exactly a device including a first member surrounding and secured to a section of the cable, a second member, connected to an element to which a cable portion is attached, and arranged around the first member, and damping means arranged between the first and second members. 
     A device of this type, for damping vibration in a stay, is described in European patent 0 343 054. In the damping device presented in this document, the two members delimit a ring-shaped cavity filled with a viscous substance providing the required damping during relative motions of the two members. 
     This former device has good performance in terms of damping. It has the further advantage of being relatively compact and of not being detrimental to the aesthetic quality of the structure. However, ensuring a seal between the ring-shaped cavity and the exterior can be tricky. A set of joints has to be set in place, which limits the reliability of the device and complicates its installation. On the other hand, the development of a particular device requires a special design of the two members and appropriate sealing means, with this design having to be re-conceived each time, for example, that changes are made to the stay dimensions or to the required dynamic properties. 
     One object of the present invention is to propose a damping device for a tensioned cable, as a straightforward and reliable response to problems of sealing, the achievement of which is facilitated. 
     SUMMARY OF THE INVENTION 
     The invention thus proposes a damping device of the type mentioned in the introduction, in which damping means include on the one hand a resilient or visco-elastic ring engaging the first member and the second member, on the other hand a flexible container containing a viscous substance, this flexible container being housed in a ring-shaped compartment formed between the first and second members. 
     The flexible container constitutes a constant volume damping chamber which can be easily sealed. Cable vibration is effectively attenuated through the combined effect of the resilient or visco-elastic ring and the viscous damping provided by the substance contained in the flexible container. Dissipation of vibrational energy results from the movements of the viscous substance in the flexible container, prompted when the cable vibrates relative to the element to which it is attached. 
     In a preferred version, the flexible container consists of a hose coiled in the ring-shaped compartment. It is thus possible to adapt to different dimensions of the cable or stay to be damped, simply by adjusting the length of the hose. 
     To facilitate the installation of the device, the resilient or visco-elastic ring may be composed of two parts of generally semi-cylindrical shape which can be attached to each other by means of pins approximately parallel to the cable section, of assembly bolts or else of a tightening belt. 
     To advantage, each of these parts comprises several metal half-bushings sunk into a resilient or moulded visco-elastic material, the half-bushing ends protruding from the moulded material and being provided respectively with assembly means such as pinning apertures. 
     In a version of this latter type, each of the parts comprises two outer half-bushings of the same diameter, located on either side, an inner half-bushing of smaller diameter relative to the cable section direction. It is then the flexibility of the resilient or visco-elastic material between the inner half-bushing and the outer half-bushings which enables the relative motion of the cable section relative to the second member, while exerting return force towards the normal position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows diagrammatically how a device in accordance with the invention is placed near the anchored end of a stay; 
     FIG. 2 is an axial sectional view of a device in accordance with the invention; 
     FIG. 3 is a cross sectional view, along the plane III—III shown in FIG. 2, of an inner the of the device, and showing additionally the sectional plane II—II of FIG. 2; 
     FIG. 4 is a perspective view of a moulded part forming half of a resilient ring of the device shown in FIG. 2; and 
     FIG. 5 is an axial sectional view of another version example of a device in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows diagrammatically the place where a damping device may be placed in accordance with the invention on the stay  6  of a structure  8  such as a cable-stayed bridge. 
     In a known way, the stay is anchored at its two ends on respective blocks  10  integral with appropriate footings and structure elements  12 . In the example shown in FIG. 1, the damping device is placed near the lower end  14  of the stay  6 , anchored in the apron  12  of the bridge. It will be understood that a similar structure may be placed near the upper end of the stay  6 , anchored in a bridge tower. 
     The end  14  of the stay passes into a rigid tubular guide  16  fixed to the anchoring block  10 . 
     The damping device, which is shown very diagrammatically in FIG.  1  and in more detail in FIG. 2, comprises: 
     an inner tube  20  into which passes a stay section  6 , and fixed to this section; 
     an outer tube  22  placed around the inner tube  20 ; 
     a resilient or visco-elastic ring  24  one inner face of which is supported against the inner tube  20  and an outer face is supported against the outer tube  22 ; 
     a flexible container such as a hose  26  containing a viscous substance  28 . 
     In the example in FIG. 2, this container  26  is housed in a ring-shaped compartment  30  delimited on the one hand by a ring-shaped groove  32  with a V-shaped cross section present on one face of the resilient ring  24 , and on the other hand by one of the tubes  20 ,  22  (the outer tube  22  in the example shown). 
     FIGS. 2 and 3 show a possible assembly of the inner tube  20  on the stay  6  in the case where the latter is composed of strands collected into a bundle of hexagonal cross section. The tube  20  consists of two semi-cylindrical portions  20   a,    20   b  each belonging to a respective bush. Each of the bushes includes three plates  34  which are applied against the sides of the hexagonal section of the stay, with interposition of a strip of adhesive  36 . Longitudinal wedges  38  are welded between the semi-cylindrical portion  20   a  and the plates  34 , at the centre of the latter. As is shown in FIG. 1, the plates  34  have two axial ends which protrude from the tube  20 . At these ends, the two bushes comprise lateral edges  40  enabling their assembly by means of screws  42 . The tightening of the screws  42  enables the tube  20  to be locked on the stay  6  section. 
     The outer tube  22  is presented as a cylindrical casing which, in use, is attached to the tubular guide  16  anchored to the footing. In the assembly example shown in FIG. 1, the outer tube  22  has towards the lower end of the stay a flange  46  bolted on an additional flange  48  provided at the outlet of the tubular guide  16 . 
     In order to facilitate its installation on the stay, the resilient ring  24  is constituted in two halves of generally semi-cylindrical shape assembled after their installation on the inner tube  20 . 
     Such a half-ring  50  is shown in FIG.  4 . It is composed of three metal half-bushings  52 ,  54 ,  56  sunk by moulding into an elastomer material  58 , namely two outer half-bushings of the same diameter  52 ,  54  and an inner half-bushing of smaller diameter  56 . In a radial plane, the elastomer material  58  has a generally V-shaped cross section, the inner half-bushing  56  being located at the base of this V, and the two outer half-bushings  52 ,  54  being located at the ends of the branches of this V. The groove  32  is thus determined between the two branches of the V constituted of elastomer material capable of compression under the stress of transverse vibration of the stay  6 . 
     As is shown by the upper part of FIG.  2  and the partial stripping of the elastomer material  58  in FIG. 4, the metal half-bushings  52 ,  54 ,  56  each have, over most of their perimeter, a rectangular shaped cross section. To allow the assembly of the two halves  50 , the half-bushings  53 ,  54 ,  56  each have their two ends  62 ,  64 ,  66  which protrude from the moulded elastomer material  58 . One end  62 ,  64 ,  66  of each half-bushing  52 ,  54 ,  56  is in the shape of a clevis provided with a pinning aperture  72 ,  74 ,  76 , whereas the other end  63 ,  65 ,  67  has a complementary shape of the clevis and is provided with a corresponding pinning aperture  73 ,  75 ,  77 . The pinning apertures  72 - 77  allow the assembly of the two ring halves  50  by means of three pairs of pins  82 ,  84 ,  86  extending parallel to the direction of the stay section  6  (see the lower part of FIG.  2 ). 
     A ring half  50  is easily manufactured by injecting the elastomer material  58  into an appropriately shaped mould in which have previously been placed the three half-bushings  52 ,  54 ,  56 , then by vulcanising the elastomer material. The stiffness of the resilient ring  24  may be adjusted in accordance with the required dynamic properties by working on the elasticity parameters and levels of thickness of the resilient or moulded visco-elastic material. 
     In the device in FIG. 2, the flexible hose  26  is coiled in a helix in the compartment  30  delimited on the one hand by the groove  32  of the ring  24 , and on the other hand by the inner face of the outer tube  22 . The hose  26  has one of its ends closed, and its other end which communicates with the outside of the compartment  30  by means of a bore  90  arranged in a drift pin  84  of one of the pairs of outer half-bushings  54  of the resilient ring  24 . This end  92  of the hose  26  is thus accessible to fill the latter with the viscous damping substance. This substance  28  is typically an oil or another viscous fluid, or a viscous gel the viscosity of which is optimised as a function of the characteristics of the stay to be damped. 
     The installation of the damping device described above is carried out for example in the following way. The strands of the stay  6  are installed and anchored at their two ends, by passing them through the tubular guide  16  and the outer tube  22 . The tube  22  is then separated from the guide  16  so as to give access to the stay section receiving the device. The inner tube  20  is installed and locked on the stay section by assembling its two bushes and by tightening the screws  42 . The two halves of the ring  24  are then installed around the inner tube  20 , then pinned. After coiling the flexible hose  26  in the groove  32 , the outer tube  22  is engaged around the whole, the hose  26  is filed with oil  28 , and the outer tube  22  is attached to the flange  48  of the tubular guide  16 . When the strand  6  comprises an outer protective casing, the latter may be attached on the end of the outer tube  22  opposite the guide  16 . 
     FIG. 5 shows a version variant of the invention, in which the ring  24  and the ring-shaped compartment where the flexible container is housed are juxtaposed along the direction of the stay  6  section. The inner tube is divided into two juxtaposed sections  100 ,  101  attached to the stay in the manner described by reference to FIG.  3 . One of these sections  100  receives the ring  24  which has the same structure and the same mode of assembly as previously (FIG.  4 ), except that the groove  32  is not used for containing the viscous substance container. 
     The other section  101  of the inner tube is provided with two transverse flanges  103 ,  104  at its axial ends. The ring-shaped compartment  105 , receiving the flexible container  106  of viscous material  28 , is delimited internally by the inner tube section  101 , and axially by the two flanges  103 ,  104 . Outwards, this compartment  105  is delimited by a bushing  107  acting as a piston. This bushing  107  is presented in the form of two half-bushings assembled around the stay during the installation of the device. Outwards, the half-bushings have radial protrusions  108  by which they rest on the outer tube  22 . 
     In the version in FIG. 5, the flexible container  106  consists of a pocket occupying the axial length of the ring-shaped compartment  105  and encasing the perimeter of the tube section  101 . This pocket  106  is filled with viscous substance  28  after installation of the unit via conduits  109  passing through the bushing  107  and its protrusions  108  as shown in FIG.  5 . In use, vibration in the stay results in the piston-bushing  107  being moved radially relative to the tube section  101  and to the flanges  103 ,  104  so that the substance contained in the pocket  106  moves within a constant volume chamber and provides the damping required. 
     Although the invention has been described by reference to particular version examples, it will be understood that various variants may be provided to these examples without departing from the context of the present invention. Thus, a device in accordance with the invention may be used to damp vibration in a cable other than a stay, for example a track cable or a suspension bridge hanger or again a submarine cable etc. The cable portion attached to a footing or the like is not necessarily one of its ends. On the other hand the element to which this portion is attached may be a footing or any structure element, including a cable network.