HK1222896B - Device for damping vibrations in a cable - Google Patents

Description

The present invention relates to techniques for dampening vibrations of cables used to suspend works of art.

The main reason for this is that the use of the 'cross-linking' method is not always possible, and that the use of the 'cross-linking' method is not always possible.

In a first type of shock absorber (see for example EP 0 343 054 A1, DE 295 17 250 U1 or WO 98/04780 A1), vibration energy is dissipated around the cable in an area radially bounded by an element attached to the suspended structure.

Other devices use linear shock absorbers such as hydraulic pistons, which can be arranged on arms extending between the cables and the suspended structure (see e.g. JP 09-59921 A) or between the cable and a tube attached to the suspended structure and containing the lower part of the cable (see e.g. FR 2 859 260 A1 or JP 06-58370 A).

A pendulum cushioning device has an oscillating arm connected to the cable, the oscillations of which are cushioned by viscous friction.

In an embodiment of the pendulum damping device, shown in Figure 1, arm 10 oscillates around a pivot 11 mounted on a support 12 itself pivoting on a chassis 13 attached to the bridge deck 14. Two hydraulic pistons 15 arranged in an X-shape are mounted between the bottom of arm 10 and the chassis 13 or deck 14. The vertical movements of the crank 16, held in a coupler 17 to the top of arm 10, are damping by the pistons 15 as the arm 10 goes up and down, the vertical movements of the crank 11 being accepted by the tilt of the support 12.

The pendulum device provides strong cushioning on cables, especially long cables. It is typically located in the lower part of the cable, about 2-3% of its total length from the low anchorage. The design of this device allows for both vertical and transverse cable movements, over large runs, to be cushioned, typically within ±100 to ±150 mm.

The cable deviations are sometimes even greater, especially when the structure is flexible, and the required gaps are even greater, for example up to ± 700 mm.

The concept of the pendulum system is then limited: the cylinders have very long strokes, the system becomes excessively bulky, as shown in Figure 1. A shock piston is typically three times its stroke length, so that pistons over 2 metres in length may be needed.

The purpose of the present invention is to improve the pendulum device and to facilitate its insertion into the work, particularly if the amplitudes of the vibrations to be damped are large.

A vibration damper is proposed for a cable, in particular a bridge hood, which includes: a swinging arm around a pivot; a first shock absorber to absorb at least some of the swinging arm; a coupling attached to the cable; a second linear stroke shock absorber with an upper end connected to the coupling and a lower end connected to the arm; and a guide to slide the coupling relative to the arm parallel to the stroke of the second shock absorber so that the transverse cable movements at the stroke of the second shock absorber are communicated to the arm independently of the second shock absorber.

The guide is a kind of slide that disconnects the movement of the cable perpendicular to the arm, which is damped by the first shock absorber, from the parallel movement of the arm, which is damped by the second shock absorber.

In a configuration of the device, the first shock comprises at least one piston arranged transversely to the arm and connected to the arm below the pivot. The piston may be placed under an upper face of the structure suspended by the cable, particularly if the pivot is positioned relative to the arm so that the distance between the pivot and the coupler attachment point on the cable is greater than the lever arm, relative to the pivot, of the force exerted by the piston on the arm. The difference in lever arm, relative to the first pivot, between the transverse forces applied by the vibrating cable and the resistance opposed by the shock piston to this piston has a running speed.

The pivot, when placed within the thickness of the structure suspended by the cable, can be made invisible to persons travelling on the structure. It provides an advantageous ball or gimbal joint, which allows the device to accept movements of the coupler parallel to the cable axis, for example due to thermal expansion of the cable.

Another aspect of the present invention relates to a drawbridge, comprising at least one pylon, a apron, drawbars consisting of cables extending obliquely between the pylon and the apron to suspend the apron and, mounted between at least one cable and the apron, a cushioning device as defined above.

Other features and advantages of the present invention will be described in the following description of a non-limiting example of implementation, with reference to the attached drawings, in which: Figure 1 is a diagram of a previously known pendulum damper; Figure 2 is a schematic view of the profile of a drawbridge; Figure 3 is a diagram illustrating the kinematics of an example of a damper according to the invention; Figure 4 is a side view of the lower part of a harness fitted with a damper according to an embodiment of the invention; Figure 5 is a cut-out view of the damper in Figure 4, the V-V plane shown in Figure 4; and the following Figures 6 to 8 are diagrams illustrating possible variants of the damper.

The invention is described below in its application not limited to drawbridge, where the vibration-damping cables are the drawbridges 16 which extend between a pylon 20 of the bridge and its apron 14 to suspend the apron 14.

One or more of the 16 hoods are fitted with a cushioning device 22 with an arm that extends transversely to the 16 hood between a P-attachment point near its low anchorage (e.g. a few per cent of the total length of the hood) and the apron 14.

Figure 3 shows schematically the kinematics of a cushioning device 22 as shown in Figure 2. The arm 25 of the device 22 is oriented in an X-direction and articulated to the bridge deck by means of a pivot 26, e.g. a ball, so that it can swing around pivot 26, and its oscillation movement (F-arrows in Figure 3) is cushioned by means of a first cushioning device 30.

In the example shown in Figure 3, the first shock absorber 30 is a hydraulic piston with a first end connected to a fixed point on the front 14 and a second end connected to the arm 25 at a point Q adjacent to its lower end. The first shock absorber 30 extends considerably perpendicular to the arm 25. Other arrangements are possible for the first oscillator 30: it can be predicted that there are several hydraulic pistons, or that the hydraulic piston (or one of them) is located above the pivot 26, or that the damping effect is obtained by the blending of a screw in the middle into which the lower end of the arm 25 fits (similarly in FR 664 to A 9201)... when the first shock absorber 30 is of a linear type, it is preferable that its connections to arm 25 and to the fixed point of the apron 14 be articulated connections, e.g. to the ball. Thus, the linear shock absorber 30 is not subjected to undesirable bending moments when the X direction oscillates around the pivot 26 due to transverse or axial movements of the harness 16.

Between arm 25 and coupler 27 mounted on the bonnet 16 at a P-attachment point, a slide guide 28 is placed to ensure that the coupler 27 remains in arm 25 alignment. A second linear-swing shock absorber 31, such as a hydraulic piston, is mounted between coupler 27 and arm 25. This shock absorber 31 dampens the movements of bonnet 16's P-attachment point parallel to arm 25.

In the configuration shown in Figure 2, the arms of the dampers 22 are oriented perpendicular to the respective hoods 16 whose movements they dampen. This provides maximum efficiency for the damper. Other arrangements are possible, however, for example by arranging the arms 25 vertically (i.e. at an angle not perpendicular to their respective hoods). To dampen the vibrations of a hood 16, the device 22 may also have two arms arranged on either side of the vertical plane containing the hood 16.

The guide 28 avoids the communication to piston 31 of undesirable bending forces resulting from movements of the hood 16 perpendicular to the arm 25. It allows a decoupling between the cushioning of parallel movements to the arm, provided by the shock absorber 31, and the cushioning of perpendicular movements to the arm, provided by the shock absorber 30. The two shock absorbers 30, 31 can then be independently designed and optimized to achieve the desired damping effects.

Figures 4 and 5 show the deck 14 of a bridge held by a harnessed suspension, and the anchorage area of one of the 16 decks on this deck 14. Each deck is a cable typically made up of a beam of metal rods possibly of the curved-wire or greased-wire type.

At this point P, a collar 40 is tightened around the torsion beam of the hood 16 to attach it to the coupling 27.

In the example shown in Figures 4 and 5, the slide guide 28 is made as a hollow metal profile in which the piston 31 is housed. In this example, a threaded rod 41 and nuts 42 ensure the fixing of the upper ends of the piston 31 and the guide 28 to the coupling 27. This fixation can be articulated, for example, with a ball joint. Another connection 43, for example, a screw or pin, connects the lower end of the piston 31 to the upper end of the arm.

The 25th arm of the damping device comes out of the guide 28 at its lower end. The guide 28 has, relative to the 25th arm, a telescopic motion damping by the piston 31, and it does not communicate bending moments to the piston 31. Slip skates or bearings 45 are arranged between the arm 25 and the inner face of the guide 28 to guide the telescopic motion and minimize the coefficient of friction between these two parts, so as not to disrupt the operation of the damping device 22.

It should be noted that the second shock absorber 31 and the slide guide 28 can be arranged in very different ways.

For example, rather than having a hydraulic piston 31 in a central position surrounded by the guide 28 as in Figures 4 and 5, the guidance of the telescopic movement in relation to the arm 25 can be provided by a central guide with a second linear shock absorber 31 comprising one or more parallel pistons in an eccentric position, connected to respectively solidary plates of the coupler 27 and arm 25.

In the case of Figures 4 and 5, the sliding contact (slides 45) by which guide 28 allows the coupling 27 to slide relative to arm 25 is located below the lower end of the linear shock absorber 31. Alternatively, this sliding contact may be located above the linear shock absorber 31. For example, the coupling 27 may be mounted sliding along rails parallel to the X-axis and rigidly connected to the arm 25 swinging around the axis 26.

In this example, the arm 25 is in the form of a hollow profile in which the shock piston 31 is housed, which is connected, preferably in an articulated manner, between the coupling 27 attached to the bonnet 16 and a point 62 fixed to the arm 25 and located towards the bottom of it. The arm 25 is extended at its upper end by a frame 60 surrounding the bonnet 16 and the collar 27. This frame 60 here plays the role of a guide. Its flanks have two inward-facing sliding surfaces 61 which cooperate with the torque 27 to coil the latter in its flow relative to the arm 25. The sliding surfaces 61 are facilitated by two mat matches to the arm 25 X and a relatively low coiling efficiency allows the arm 31 to achieve a relatively high friction flow.

In the example shown in Figure 6, the arm 25 has, under pivot 26, a 63-cubic-inch extension whose end is articulated to the first shock piston 30 at point Q. This cubic extension allows for different possible positions of shock 30 depending on the load stresses near the edges of the apron 14.

The design illustrated in Figures 4 and 5 is aesthetically advantageous since only the swing arm 25 emerges from the top of the deck 14 to penetrate the guide 28. The pivot 26 is located within the thickness of the deck 14, and the piston of the first shock absorber 30 is located below the deck 14. The lower part of the swing arm 15 can move in a reservoir 48 of appropriate shape arranged on the lower side of the deck 14. Similar advantages are obtained with a design of the type in Figure 6.

The pivot 26 is positioned along the arm 25 to obtain a leverage effect for the action of the first shock absorber 30, which allows it to have a compact configuration. For this, the distance D between the pivot and the attachment point P of the coupler 27 is greater than the lever arm of the piston 30, which is equal to the distance d between the pivot and the connection point Q of the piston 30 on arm 25 in the particular configuration schematized in Figure 5 (or approximately equal to the length of the elongated extension 63 in the particular configuration schematized in Figure 6). The distance D above is of course variable according to the elongation of the piston 31. When D ≥ 31 is indicated, it is always understood that D ≥ 31 is greater when the piston has to be increased in the minimum way.

The fact that the pivot 26 is a ball allows the device 22 to allow movements of the P-attachment point of the hood in a direction perpendicular to arm 25 in the plane containing hood 16 and arm 25. These movements can be due either to vibrations of the hood if the arm 25 is not strictly perpendicular to it or to its elongation due to thermal expansion.

One variant is to make pivot 26 by means of a cardan-type joint between the apron 14 and the arm 15, i.e. with two axes of joint perpendicular to each other. One such variant is illustrated very schematically in Figure 7. One of the two axes supplies the pivot 26 proper by being fixed in relation to apron 14 and essentially parallel to the vertical plane containing the hood 16, so that the oscillations of the arm 25 it allows are allowed to the first piston 30 to cushion them. The second 71 of the cardan joint is fixed in relation to the first arm 25 and essentially perpendicular to the vertical plane containing the hood 16, so that the oscillations of the arms 25 it allows to be absorbed without being communicated to the axis 30. Q 25 is connected to the lower part of the arm 70 which is perpendicular to the axis 70 and the lower part of the arm 70 is connected to the same point.

Another possible arrangement of the first shock absorber 30 is shown schematically in Figure 8. In this example, the first shock absorber 30 is connected to arm 25 in arm 14 under pivot 26 by means of two beams 80, 81. The beam 80 has one articulated end at the foot of arm 25 and another articulated end at one end of arm 81. The second end of arm 81 shows the articulated connection with the first shock absorber 30.In the example shown in Figure 8, the bearing 80 extends perpendicularly to the arm 25 when it is at rest, while the bearing 81 extends significantly parallel to the arm 25. The bearing 80, 81 forms a mechanism for multiplying the damping force when necessary.

The embodiments described and discussed above are illustrations of the present invention, and may be modified in various ways without going beyond the scope of the invention as shown in the claims attached.

Claims (14)

1. A device for damping vibrations of a cable, the device (22) comprising:

   - an arm (25) oscillating about a pivot (26) ;

   - a first damper (30) for damping at least some of the oscillations of the arm; and

   - a coupler (27) attached to the cable (16),

   and being characterized by:

   - a second damper (31) having a linear-stroke, an upper end connected to the coupler and a lower end connected to the arm; and

   - a guide (28, 60) for letting the coupler slide with respect to the arm parallel to the stroke of the second damper so that movements of the cable transverse to the stroke of the second damper are communicated to the arm independently of the second damper.
2. The damping device as claimed in claim 1, wherein the first damper comprises at least one piston (30) disposed transversely to the arm (25).
3. The damping device as claimed in claim 2, wherein said piston (30) is connected to the arm (25) below the pivot (26).
4. The damping device as claimed in claim 2 or claim 3, wherein said piston (30) is placed under an upper face of a structure (14) suspended by means of the cable (16).
5. The damping device as claimed in claim 4, wherein the pivot (26) is positioned relative to the arm (25) so that a distance (D) between the pivot and the point (P) of attachment of the coupler (27) to the cable (16) is greater than a lever arm, relative to the pivot, of a force exerted by the piston (30) on the arm, and preferably at least three times greater than said lever arm.
6. The damping device as claimed in any one of the preceding claims, wherein the pivot (26) is placed within a thickness of a structure (14) suspended by means of the cable (16).
7. The damping device as claimed in any one of the preceding claims, wherein the pivot (26) provides a ball joint or gimbal type of articulation.
8. The damping device as claimed in any one of the preceding claims, wherein the pivot (26) is substantially fixed with respect to a structure (14) suspended by means of the cable (16).
9. The damping device as claimed in any one of the preceding claims, comprising sliding shoes (45) between the arm (25) and the guide (28).
10. The damping device as claimed in any one of the preceding claims, wherein the guide (28) lets the coupler (27) slide with respect to the arm (25) by at least one sliding contact (45) situated under a lower end of the second damper (31).
11. The damping device as claimed in any one of claims 1 to 9, wherein the guide (60) lets the coupler (27) slide with respect to the arm (25) by at least one sliding contact (61) situated above the second damper (31).
12. The damping device as claimed in claim 11, wherein the arm (25) is hollow and the second linear-stroke damper (31) is housed in the arm while being connected between the coupler (27) and a point (62) fixed with respect to the arm.
13. The damping device as claimed in any one of the preceding claims, wherein the first damper (30) is connected to the arm (25) via a force gearing-down mechanism (80, 81).
14. A cable-stayed bridge, comprising at least one tower (20), a deck (14), stays (16) consisting of cables extending obliquely between the tower and the deck in order to suspend the deck, and at least one damping device (22) as claimed in any one of the preceding claims mounted between a cable and the deck.