The invention relates to a vibration damper. More particularly, it relates to a damper for damping vibrations in cables mounted on structures, such as bridges. It has other related applications.

Background Art

A vibration damping device for purposes similar to the one of this invention is described in WO 02/29276, the contents of which are hereby incorporated by reference. The assembly of the present invention is a refinement of the invention described in that specification.

Disclosure of Invention

In a first embodiment the invention consists in a vibration damping assembly for damping vibrations in a cable having a longitudinal axis and secured to a structure, the assembly comprising:

at least two sets of four pairs of shear dampers, each pair being mounted end to end with a common longitudinal axis,

a pair of idler plates, each having a hole therethrough through which, in use, the cable passes, in a loose fit, the distal ends of each of the pairs of shear dampers being mounted on faces of the idler plates,

a cable mounting device, secured to the cable, and secured to the common ends of one pair of each of the sets of shear dampers,

a structure mounting device secured to a part of the structure, and secured to the common ends of the other pair of each of the sets of shear dampers,

whereby in use the two sets of pairs of shear dampers are disposed radially about the longitudinal axis of the cable to damp vibrations in the cable.

In another embodiment the invention consists in a vibration damping assembly for damping vibrations in a cable having a longitudinal axis and secured to a structure, the assembly comprising:

at least two sets of four pairs of shear dampers, each pair being mounted end to end with a common longitudinal axis,

an idler plate having a hole therethrough, through which, in use, the cable passes in a loose fit, the common ends of each of the pairs of shear dampers being mounted on or forming a part of the idler plate,

a pair of cable mounting devices, each of which is secured to the cable and also secured to a distal end of one pair of each of the sets of shear dampers,

a pair of structure mounting devices, each of which is secured to a part of the structure, and also secured to a distal end of one pair of each of the sets of shear dampers,

whereby in use the two sets of pairs of shear dampers are disposed radially about longitudinal axis of the cable to damp vibrations in the cable.

In one embodiment the sets of pairs of shear dampers are radially disposed substantially symmetrically about the longitudinal axis of the cable.

In one embodiment there are three sets of pairs of shear dampers disposed radially about to the longitudinal axis of the cable.

In one embodiment there are four sets of pairs of shear dampers disposed radially about the longitudinal axis of the cable.

In one embodiment there are five or more sets of pairs of shear dampers disposed radially about the longitudinal axis of the cable.

In another embodiment the invention consists in a vibration damping assembly for damping vibrations in a cable having a longitudinal axis and secured to a structure, the assembly comprising:

at least two pairs of shear dampers, each pair being mounted end to end with a common longitudinal axis,

a pair of idler plates, each having a hole therethrough through which, in use, the cable passes, in a loose fit, the distal ends of each of the pairs of shear dampers being mounted on the faces of the idler plates,

a cable mounting device, secured to the cable, and secured to the common end of one pair of shear dampers,

a structure mounting device secured to a part of the structure, and secured to the common end of the other pair of shear dampers,

whereby in use the two pairs of shear dampers are disposed to one side of the longitudinal axis of the cable to damp vibrations in the cable.

In another embodiment the invention consists in a vibration damping assembly for damping vibrations in a cable having a longitudinal axis secured to a structure, the assembly comprising:

at least two pairs of shear dampers, each pair being mounted end to end with a common longitudinal axis,

an idler plate having a hole therethrough, through which, in use, the cable passes in a loose fit, the common ends of each of the pairs of shear dampers being mounted on or forming a part of the idler plate,

a pair of cable mounting devices, each of which is secured to the cable and also secured to the distal ends of one pair of shear dampers,

a pair of structure mounting devices, each of which is secured to a part of the structure, and also secured to the distal ends of the other pair of shear dampers,

whereby in use the pairs of shear dampers are disposed to one side of the longitudinal axis of the cable to damp vibrations in the cable.

In one embodiment the structure is a bridge.

In one embodiment a part of the structure to which the assembly is attached is a tube surrounding the cable.

In one embodiment the each shear damper is a laminate of layers of elastic material and stiffening plates secured together.

In another embodiment the elastic material is rubber and the stiffening plates are made of steel.

In another alternative embodiment each shear damper is a laminate of elastic material, stiffening plates and has a central bore filled with a plastic material.

In one embodiment the elastic material is rubber, the stiffening plates are of steel and the plastic material is lead.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or

collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The invention consists in the foregoing and also envisages constructions of which the following gives examples only.

The term "comprising" as used in this specification means "consisting at least in part of that is to say when interpreting the statements of invention including that term, the features prefaced by that term in each statement all need to be present but other features can also be present.

The term "shear damper" means a damper that dampens relative forces between a cable and a structure to which the cable is affixed. Suitable shear dampers are laminates of an elastic material, such as rubber, and stiffening plates, such as steel plates. Shear dampers consisting of laminates of elastic material and stiffening plates with a core filled with plastic material, such as lead, as described in WO 02/29276 and WO 97/25550, are particularly suitable for use in this invention.

Brief Description of the Drawings

Figure 1 is the sectional view I-I shown in Figure 2, of one embodiment of the invention in a neutral position.

Figure 2 is a plan view of the embodiment of the invention shown in Figure 1.

Figure 3 is a sectional view of the embodiment of the invention shown in Figures 1 and 2, where vibration in the cable has moved it in the direction of arrow A.

Figure 4 is a sectional view of the second embodiment of the invention.

Figures 5 is a sectional view of an embodiment of the invention where the damping is provided by two pairs of shear dampers.

Figure 6 is a sectional view of another embodiment of the invention where the damping is provided by two pairs of shear dampers.

Figure 7 is a sectional view of the embodiment shown in Figure 1 on which there has been provided an annular buffer.

Figure 8 is a sectional view of the embodiment shown in Figure 4 on which there has been provided a pair of annular buffers.

Modes of Carrying out the Invention

Construction

Referring particularly to Figures 1 and 2, there is generally shown the damping assembly 10 which is secured to a cable 12 on the inside and a tube 30 on the outside. The tube 30 is mounted on and forms a part of a structure to which cable 12 is secured. In a typical application of this invention the damping assembly may be used for damping rain and wind induced excitations in cables on cable-stayed bridges.

The damping assembly 10 consists of an upper idler plate 20 and a lower idler plate 22 which are substantially annular in shape, the central hole 21 having dimensions sufficient to accommodate vibrations in cable 12. Between each of the idler plates 20 and 22 are two sets 14 and 16, each having two pairs, of shear dampers 18. Each of the pairs of shear dampers 18 is assembled end to end with a common longitudinal axis. The common end of the radially inner pair of shear dampers 18 in each set 14 and 16 in Figure 1 is mounted on flange 26 of clamp 24 which in turn is clamped to cable 12. Each common end of the radially outer pair of dampers 18 in each set is attached to annular structure mount 28.

The distal ends of each of the shear dampers 18 shown in Figure 1 are attached to the inner faces of idler plates 20 and 22 respectively.

In the embodiment shown in Figures 1 to 3 the portion of the cable 12 below the damping assembly 10 is surrounded by a tube 30. This tube 30 has a flange 32 at its open end. Mount 28 is an annular ring which is welded or bolted to flange 32.

The cable 12 may be of solid steel or may be of wound wire rope.

The shear dampers 18 may be of either the steel and rubber laminated type or the steel and rubber with lead core type, depending on the strengths of the vibrations being damped and the diameter of the cable.

In the embodiment illustrated in Figures 1 to 3 the two sets 14 and 16 of pairs of dampers 18 are substantially symmetrically and diametrically opposite to one another.

In alternative embodiments there can be three, four, five or more sets of pairs of dampers mounted on idler plates 20 and 22, cable clamp flange 26 and structure mount 28 in the same way as the two sets as shown in Figures 1 to 3. The sets of dampers 18 will most commonly be radially disposed symmetrically around the longitudinal axis of the cable 12. However, there may be some applications where the forces being damped are asymmetrical and the sets of dampers 18 can be arranged to compensate for this.

A second embodiment of the invention is illustrated in Figure 4. In this embodiment, the damping assembly 34 also has two sets 14 and 16 of two pairs of shear dampers 18.

However, instead of having a pair of idler plates, a single cable clamp and a single structure mount, in this embodiment there is a single idler plate 36 and two cable clamps

38 and two structure mounts 40. In this embodiment tube 30 does not have a flange at its open end. Structure mounts 40 attach the distal ends of outer shear dampers 18 to the inner faces of tube 30. The structure mounts 40 are L-shaped in cross-section and circular in shape. They can be welded to the tube 30. The cable clamps 38 are similar

in shape and cross-section to mounts 40. They may be affixed to cable 12 by conventional clamping means.

The alternative embodiment of the invention illustrated in Figure 5 is the same as that in Figure 1 except that the damping assembly 42 has only two pairs of shear dampers 18.

The distal ends of dampers 18 are mounted on the inner faces of idler plates 20 and 22.

The common end of one pair is mounted on opposite faces of annular disc shaped structure mount 28. The common end of the other pair is affixed to flange 26 of cable clamp 24. The pairs of shear dampers 18 can be radially aligned with one another as are the two sets of pairs 18 in Figure 1, or they can be aligned on different radii to one side of the longitudinal axis of cable 12.

The embodiment of Figure 5 can be used to damp very small vibrations where two or more sets of pairs of shear dampers are not required.

The alternative embodiment shown in Figure 6 is the same as that in Figure 4 except that the damping assembly 44 has only two pairs of shear dampers 18. The distal ends of one pair are mounted on cable mounts 38 and the distal ends of the other pair are mounted on structure mounts 40 in the same way as in the embodiment of Figure 4. The common ends of both pairs of shear dampers are affixed to the top and bottom faces of idler plate 36.

The embodiment of Figure 6 can be used in the same applications as that in Figure 5.

Although not essential, it is advantageous that the vibration damping assembly be adapted so that the outer surface of cable 12 does not come into contact with the inner edges of idler plates 20 and 22 in Figures 1-3 and 5, and that the inner edge of idler plate 36 in the embodiment shown in Figures 4 and 6 does not come into contact with the outer surface of cable 12. This is so as to avoid wear of the outer surface of cable 12.

This can be achieved in three different ways. The first way is by selecting dampers 18 that are of sufficient stiffness. The stiffness would limit lateral travel during vibration so that the inner edges of the idler plates would not touch the outer surface of cable 12.

In the second alternative, the gap 27 between the structure mount 28 and the cable clamp 24 in each of Figures 1-3 and 5 is smaller than the gaps 13 and 15 between the inner edges of the idler plates 20 and 22 and the outer surface of cable 12. Similarly, the gap 37 between idler plate 36 and cable 12 is greater than the gaps 39 between the inner edges of mounting plates 40 and outer edges of cable clamps 38.

A third way of avoiding contact between idler plates 20 and 22 and cable 12 is to provide a buffering member 46 as illustrated in Figure 7. In the embodiment illustrated, buffer 40 is annular. Buffer 46 is preferably made of high damping rubber.

A further alternative of the third way is illustrated in Figure 8. In Figure 8 there is a pair of annular buffers 48 and 50 fitted to the outside edges of cable clamps 38. The buffers 48 and 50 are also preferably made of high damping rubber. The gap 39 between each structure mount 40 and its corresponding cable 12 when the annular buffers are fitted is less than the gap 37 between the inner edge of idler plate 36 and the outer surface of cable 12.

Operation

In the embodiment illustrated in Figure 3 vibration forces acting on cable 12 have moved it in the direction of arrow A. It will be seen that the force is being damped both by set 14 of the pairs of shear dampers 18 whose common end plates are displaced towards one another; and by the set 16 of the pairs of shear dampers whose common end plates are being displaced apart. The damping forces generated by the sets 14 and

16 of shear dampers 18 damp the vibration and return the cable 12 to the neutral position illustrated in Figure 1.

The clamping assemblies of each of the other embodiments shown in Figures 4 to 6 operate in much the same manner. Relative movement between the cable 12 and the tube 30 is accommodated by relative parallel movement between the distal ends and the common end of each pair of dampers 18. The dampers 18 gradually return to their neutral positions shown in Figures 1, 2 and 4 to 6 as they damp the relative movement.

Where an assembly has been adapted in the second way so as to avoid contact between the outer surface of the cable 12 and the inner edges of an idler plate 36 or plates 20 and 22 the limit of travel occurs when the inner edge of structure mount 28 in Figures 1, 2, 3, 5 and 7 and the inner edges of structure mounts 40 in each of Figures 4, 6 and 8 come into contact either with the outer edges of cable clamps 24 or 38 respectively.

Where an assembly has been altered in the third way to avoid contact with cable 12, the limit of travel occurs when the inner edge of structure mount 28 has contacted buffer 46 (Figure 7) or the inner edges of structure mounts 40 have contacted buffers 48 and 50 and the limits of compression of the buffers have been reached.

In each of these various ways, contact is avoided between the inner surfaces of the relevant idler plate 20, 22 or 36 and the outer surface of cable 12.

Advantages

There are several advantages of the damping assembly of the invention. The damper is activated at small vibration amplitudes caused by a combination of rain and wind. At high work loads there is no additional wear on the damper. One embodiment is designed to be easily retrofitted to existing cable-stay bridges where vibration damping is required. The damping forces are substantially constant and independent of the displacement of the cable to be damped. The damping characteristics are insensitive to the frequency of the vibrations. Damping of a stay cable is not affected by longitudinal movement of the cable due to load variations.

It is not the intention to limit the scope of the invention to the abovementioned examples only. As would be appreciated by a skilled person in the art, many variations are possible without departing from the scope of the invention as set out in the claims.