WO2009074777A1

WO2009074777A1 - Damper

Info

Publication number: WO2009074777A1
Application number: PCT/GB2008/004037
Authority: WO
Inventors: Mehrdad Asadi
Original assignee: Cellbond Limited
Priority date: 2007-12-12
Filing date: 2008-12-08
Publication date: 2009-06-18
Also published as: GB0724225D0

Abstract

A passive damper (10) comprises a first arrangement (20) configured to absorb energy when the damper (10) experiences a compressive strain and a second arrangement (30) configured to absorb energy when the damper (10) experiences a tensile strain. The first arrangement (20) comprises a cylinder (22), a piston (24) slidably mounted in the cylinder (22), an energy absorber (26) disposed in the cylinder (22) to absorb energy when the damper experiences compressive strains, and a ratchet mechanism (28) configured to allow movement of the piston (24) in the cylinder (22) in one direction only (from right to left as illustrated). The second arrangement (30) comprises a cylinder (32), a piston (34) slidably mounted in the cylinder (32), an energy absorber (36) disposed in the cylinder (32) to absorb energy when the damper experiences tensile strains, and a ratchet mechanism (38) configured to allow movement of the piston (34) in the cylinder (32) in one direction only (also from right to left as illustrated).

Description

DAMPER

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a damper for damping unwanted dynamic forces in a structure such as a building. BACKGROUND ART

Many structures such as multi-storey buildings and bridges are susceptible to resonance created by high winds or seismic activity. In order to mitigate the resonance effect, dampers are incorporated into such structures to suppress resonant waves. For example, dampers can be installed in the structural frame of a building to absorb some of the energy imparted to the building by ground movements during an earthquake . The dampers reduce the movement induced by dynamic loads applied to the building, reducing the chances of serious damage. There are many different kinds of damper known in the art, including both passive dampers (which require no input power to operate) and active dampers (which are force generators that actively push on surrounding structure to counteract a disturbance) . The passive dampers frequently used in structures include: metallic dampers which are designed to deform plastically when a building vibrates during an earthquake, with energy being absorbed during the plastic deformation; friction dampers which are designed to have moving parts that will slide over and rub against each other when a building vibrates during an earthquake, with energy being absorbed in overcoming friction between surfaces in contact ; and viscous fluid dampers which use a viscous fluid in a closed cylinder, with flow of the viscous fluid controlling reciprocal movement of a piston in the closed cylinder. DISCLOSURE OF INVENTION

In accordance with the present invention, there is provided a passive damper for absorbing energy imparted to a structure by dynamic lateral loads, comprising: a first arrangement configured to absorb energy when the damper experiences a compressive strain; and a second arrangement configured to absorb energy when the damper experiences a tensile strain; wherein each arrangement comprises a cylinder, a piston slidably mounted in the cylinder, an energy absorber disposed in the cylinder to absorb energy when the damper experiences strain, and a ratchet mechanism configured to allow movement of the piston in the cylinder in one direction only.

The ratchet mechanism of the first arrangement is configured to resist movement of the piston in the cylinder of the first arrangement when the damper is exposed to a tensile strain. Likewise, the ratchet mechanism of the second arrangement is configured to resist movement of the piston in the cylinder of the second arrangement when the damper is exposed to a compressive strain. The cylinder of the first arrangement may be coupled to the cylinder of the second arrangement. The two cylinders may be mounted back-to-back, preferably with the pistons being configured to move along a common axis . The two cylinders may be formed at least in part by a single member.

In one form of the first arrangement, the cylinder has a first end and a second end opposite the first end, the second end having an aperture through which a piston rod extends from the piston, with the energy absorber disposed between the piston and the first end. Thus, in use the piston moves in a direction from the second end to the first end of the cylinder of the first arrangement, as the energy absorber absorbs energy. In this way, the energy absorber of the first arrangement is exposed to a compressive strain when the damper experiences a compressive strain. The piston rod may be configured to attach the passive damper to the structure (e.g. building) to be damped. In one form of the second arrangement, the cylinder has a first end and a second end opposite the first end, the second end having an aperture through which a piston rod extends from the piston, with the energy absorber disposed between the piston and the second end. Thus, in use, the piston moves in a direction from the first end to the second end of the cylinder of the second arrangement, as the energy absorber absorbs energy. In this way, the energy absorber of the second arrangement is exposed to a compressive strain when the damper experiences a tensile strain. The piston rod may extend through the energy * absorber, and may be configured to attach the passive damper to the structure (e.g. building) to be damped.

The ratchet mechanism of at least one of the first and second arrangements may comprise a piston ring having one or more teeth on its radially outermost periphery for engaging with a plurality of complementary teeth on the inner periphery of the cylinder. The or each tooth of the piston ring may have a leading and trailing surface (with the leading and trailing surfaces being determined with reference to the direction of movement of the piston in the cylinder permitted by the respective ratchet mechanism) , with the trailing surface extending in a plane substantially perpendicular to the direction of allowed movement of the piston in the cylinder. In this way, and with flexure of the piston ring, the or each leading surface is able to slide over respective corresponding surfaces of the complementary teeth on the inner periphery of the cylinder when moved in one direction, whilst the or each trailing surface abuts firmly against respective corresponding surfaces of the complementary teeth on the inner periphery of the cylinder when movement in an opposite direction is attempted.

The energy absorber disposed in the cylinder of at least one of the first and second arrangements may comprise a sacrificial energy absorber. The sacrificial member may comprise a honeycomb member e.g. made of aluminium, possibly a honeycomb member as described in International application WO98/06553, the entire contents of which are incorporated herein by reference. Alternatively, or additionally, the energy absorber may comprise a metal foam material in appropriate configuration and crush direction. Alternatively, or additionally, the sacrificial member may comprise a press load (or egg box) member, possibly as described in International application WO00/31434, the entire contents of which are incorporated hereby by reference. The cylinder of the first and second arrangements may be arranged back to back. The directions of movement of pistons of the first and second arrangements may be co- linear. In this way, the damper may be incorporated into a bracing system of a building, e.g. along a diagonal of a rectangular or square structural frame of a building. BRIEF DESCRIPTION OF DRAWINGS

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a cut-away, schematic perspective view of a damper embodying the present invention;

Figures 2A, 2B, 2C and 2D illustrate details of the damper of Figure 1;

Figure 3 is a graph of stress vs strain illustrating performance of the damper of Figure 1 under compression. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT

Figure 1 illustrates schematically a passive damper 10 comprising a first arrangement 20 configured to absorb energy when the damper 10 experiences a compressive strain and a second arrangement 30 configured to absorb energy when the damper 10 experiences a tensile strain. The first arrangement 20 comprises a cylinder 22, a piston 24 slidably mounted in the cylinder 22, an energy absorber 26 disposed in the cylinder 22 to absorb energy when the damper experiences compressive strains, and a ratchet mechanism 28 configured to allow movement of the piston 24 in the cylinder 22 in one direction only (from right to left as illustrated) . The second arrangement 30 comprises a cylinder 32, a piston 34 slidably mounted in the cylinder

32, an energy absorber 36 disposed in the cylinder 32 to absorb energy when the damper experiences tensile strains, and a ratchet mechanism 38 configured to allow movement of the piston 34 in the cylinder 32 in one direction only

(also from right to left as illustrated) .

The damper 10 has a tubular body 40, with a plate 42 disposed in the body 40 to partition its bore and thereby define the cylinders 22 and 32 of the first and second arrangements 20 and 30. The cylinder 22 has a first end 50 adjacent the plate 42, and a second end 52 opposite the first end 50. The second end 52 has an aperture 54 through which a piston rod 56 extends from the piston 24. The energy absorber 26 is disposed between the first end 50 and the piston 24 so that it is compressed against the plate 42 as the piston 24 moves in a direction from the second end 52 to the first end 50. The cylinder 32 has a first end 60 adjacent the plate 42, and a second end 62 opposite the first end 60. The second end 62 has an aperture 64 in end wall 66 through which a piston rod 68 extends from the piston 34. The energy absorber 36 is disposed between the second end 62 and the piston 34 so that it is compressed against end wall 66 as the piston moves in a direction from the first end 60 to the second end 62.

The ratchet mechanisms 28,38 of the first and second arrangements 20,30 work in the same way as each other, so for simplicity only the ratchet mechanism 28 will be described in detail. The ratchet mechanism 28 comprises a split piston ring 70 having a plurality of teeth 72 on its radially outermost periphery 74, and a .plurality of complementary teeth 76 on the radially inner periphery 78 of the cylinder 22. The piston ring 70 is seated in a circumferential groove 80 in the piston 24 and is configured to urge teeth 72 against teeth 76, whilst being able to constrict sufficiently under reaction forces from tooth interengagement to allow 72 to slide over teeth 76. As shown in Figures 2C and 2D, the teeth 72 are each annular and have a leading surface or flank 82 and a trailing surface or flank 84. The leading flank 82 is inclined to the direction of movement M of the piston 24 in 5.cylinder 22, whereas the trailing flank is substantially- perpendicular to the direction of movement M. In this way, a compressive strain on the damper 10 will cause the leading flank 82 of teeth 72 to bear against the corresponding surfaces of the teeth 76. As such surfaces0 are inclined to the direction M, the piston ring 70 experiences a radially inward force causing it to constrict and allow the piston 24 to advance into cylinder 22. However, a tensile strain on the damper 10 will cause the trailing flanks 84 to bear squarely against the5 corresponding surfaces of the teeth 76. As such latter surfaces are perpendicular to the direction M, the piston ring 70 is able to resist piston 24 pull-out from cylinder 22.

Figure 3 illustrates the energy absorption of the0 damper 10 during a stress v deflection test.

Claims

1. A passive damper for absorbing energy imparted to a structure by dynamic lateral loads, comprising: a first arrangement configured to absorb energy when the damper experiences a compressive strain; and a second arrangement configured to absorb energy when the damper experiences a tensile strain; wherein each arrangement comprises a cylinder, a piston slidably mounted in the cylinder, an energy absorber disposed in the cylinder to absorb energy when the damper experiences strain, and a ratchet mechanism configured to allow movement of the piston in the cylinder in one direction only.

2. A passive damper according to claim 1, in which the ratchet mechanism of the first arrangement is configured to resist movement of the piston in the cylinder of the first arrangement when the passive damper is exposed to a tensile strain.

3. A passive damper according to claim 1 or claim 2, in which the ratchet mechanism of the second arrangement is configured to resist movement of the piston in the cylinder of the second arrangement when the passive damper is exposed to a compressive strain.

4. A passive damper according to any one of the preceding claims, in which the cylinder of the first arrangement is coupled to the cylinder of the second arrangement.

5. A passive damper according to claim 4, in which the cylinders of the first and second arrangements are mounted back-to-back with their respective pistons configured to move along a common axis.

6. A passive damper according to any preceding claim, in which the cylinder of the first arrangement has a first end and a second end opposite thereto, the second end having an aperture through which a piston rod extends from the piston, with the energy absorber disposed between the piston and the first end.

7. A passive damper according to any preceding claim, in which the cylinder of the second arrangement has a first end and a second end opposite thereto, the second end having an aperture through which a piston rod extends from the piston, with the energy absorber disposed between the piston and the second end.

8. A passive damper according to any one of the preceding claims, in which the ratchet mechanism of at least one of the first and second arrangements comprises a piston ring having one or more teeth on its radially outermost periphery for engaging with a plurality of complementary teeth on the inner periphery of the respective cylinder.

9. A passive damper according to claim 8, in which the or each tooth of the piston ring may have a leading and trailing surface, with the leading and trailing surfaces being determined with reference to the direction of movement of the piston in the cylinder permitted by the respective ratchet mechanism, with the trailing surface extending in a plane substantially perpendicular to the direction of allowed movement of the piston in the cylinder.

10. A passive damper according to any preceding claim, in which the energy absorber in at least one of the first and second arrangements comprises a sacrificial energy absorber.