WO2007071066A1

WO2007071066A1 - Long period pendulum arrangement

Info

Publication number: WO2007071066A1
Application number: PCT/CA2006/002120
Authority: WO
Inventors: Scott Gamble; Andrew Smith; Trevor Haskett
Original assignee: Motioneering Inc.
Priority date: 2005-12-22
Filing date: 2006-12-22
Publication date: 2007-06-28
Also published as: CA2531359A1

Abstract

A pendulum arrangement for a Tuned Mass Damper utilizes a pair of generally equal masses, the masses being arranged so that first surfaces thereof face each other and second surfaces thereof face away from each other. A hinge structure is affixed to the first surfaces of the masses so as to hingedly connect the two masses together. Spaced apart tension members are connected at one end thereof to a supporting frame and at the other end to the hinge structure. Each one of a pair of compression members is pivotally connected at one end thereof to an upper portion of an adjacent mass and pivotally rests on a lower support surface. The masses are supported by the tension and compression members for limited swinging movement thereof with a substantially lower period that could be achieved within the same space with a conventional pendulum.

Description

LONG PERIOD PENDULUM ARRANGEMENT

Background of the Invention

There are many structures that vibrate under the influence of external forces and it is very desirable to minimize the effects of such vibrations in order to maintain the integrity of such structures. Large (tall) buildings can be subjected to considerable forces due to prevailing winds, and turbulence which can set up vibrations within the building structure. Buildings in certain geographical areas can be subjected to ground-based displacement forces such as earthquakes and tremors, which can result in considerable damage, or even destruction if the induced vibrations are excessive. In the past it has been known to counteract vibrations in buildings by the use of suspended masses, in the form of a simple pendulum, which move in opposition to the induced vibrations and help to dampen those vibrations and thus help to keep the building more stable and less prone to damage. The same principle can be used to dampen vibrations in other large structures, including but not restricted to bridges and construction and production machinery.

Increasingly, high-rise buildings are being built with more aggressive slenderness ratios (the ratio of building height to width). While the structure may be strong from a design load perspective, it may also be quite flexible. In moderate to strong wind events, occupants of the uppermost floors will be subjected to vibrations that can range from annoying to worrisome or even dangerous.

Suspended mass vibration absorbers or dampers are most effective if located at the very top of the structure. However, it is the real estate at the top of such a high-rise building that has the greatest commercial or retail value, and therefore the space given over to such a vibration absorber or damper comes at a great price.

Additionally, for a vibration absorber or damper based on a pendulum configuration the required pendulum length may be difficult to contend with. Fundamental building periods are commonly in the range of 5 to 8 seconds, and therefore the pendulum length can approach 16m, a length which is much too great for common use.

A Tuned Mass Damper (TMD) is a machine or system that removes vibrational energy from a structure to which it is attached. The structure can be a building, bridge or another machine. A TMD can be configured as, but is not limited to, a mass suspended on tension members or other linkages. Usually, an energy dissipation device is attached to the mass to provide damping. Tuning of the TMD is required so that its eigenfrequency is almost equal to that of the structural system to which it is applied. On a TMD that is configured as a simple pendulum the length of the tension members, such as cables, is the means by which the frequency of the TMD is determined. By changing the effective length of the tension members, the eigenfrequency of the TMD system can be tuned to a desired level. Within a given available vertical space it is easy to increase the eigenfrequency of a pendulum by shortening its length. This has the effect of increasing the rate at which the restoring force (due to gravity) is generated per unit of lateral displacement. An alternate means of augmenting the rate of increase of the restoring force includes attaching a spring to the pendulum. On the other hand, within a fixed vertical space, noting that space is a premium at the top of a high-rise building, it is not possible to achieve a lower eigenfrequency without some type of additional works (e.g. an inclined gate pendulum) since a lengthening of the pendulum is generally not an viable option.

Summary of the Invention

The present invention provides a system for decreasing the period of a pendulum beyond that that can be achieved solely through adjusting the length of a simple pendulum.

The present invention utilizes two or more adjacent masses that are hinged together between the masses. The hinge passes between adjacent surfaces of the masses. The masses are supported by two or more tension members suspended from a suitable frame, and connected to the masses at or near the hinge, the tension members being capable of full articulation whenever the masses move. Additionally, towards the outer extremity of each mass, opposite the hinge, there is a generally vertical compression member that is closely adjacent the respective surface and that is in contact with a support flange or other suitable means. Thus the weight of each mass is supported vertically by the tension members between the masses and by the compression members. The compression members are mounted so that they are capable of full articulation at each end thereof. The present invention permits the creation of a compact dynamic vibration absorption system that is easily adapted to existing and/or new building construction and which improves on prior art damping systems. The present invention may be characterized as a'Tuned Mass Damper" (TMD), a machine or system that removes or reduces vibrational energy from a structure, such as a building, a bridge or a machine, to which it is mounted.

The principles of the present invention are, in fact, applicable to other structures, appliances or devices which utilize a pendulum and in which available vertical space may be a design constraint. Notwithstanding that the invention flowed from investigations into improving the vibration damping within high-rise buildings and the like, the use of pendulum masses supported from above and below can find application in simpler consumer goods such as metronomes and grandfather clocks, for example.

Generally speaking and in summary, the present invention may be considered as providing a pendulum arrangement comprising: a pair of generally equal masses each having a centre of mass, the masses being arranged so that first surfaces thereof face each other and second surfaces thereof face away from each other; hinge means affixed to the first surfaces of the masses so as to hingedly connect the two masses together; spaced apart tension means connected at one end thereof to frame means and at the other end to the hinge means; and compression means pivotally connected at one end thereof to an upper portion of each mass and pivotally resting on a lower support surface; whereby the masses are supported by the tension means and the compression means for limited swinging movement thereof.

Brief description of the Drawings

Figure 1 is a perspective view illustrating the arrangement of pendulum masses according to the present invention.

Figure 2 is a side elevational view illustrating the arrangement of the pendulum masses and the manner in which various portions thereof will react during swinging movement of the masses. Description of the Preferred Embodiment

The basic arrangement of masses that can be utilized as a Tuned Mass Damper (TMD) in accordance with the present invention is illustrated somewhat schematically in Figure 1. Therein it is seen that a pair of generally identical masses M are arranged side by side in generally close proximity to each other. Each mass M is illustrated as being generally parallelepiped in shape, although other three- dimensional shapes could be utilized (eg. spheres, etc). In the case of the masses M, each has a first or inner surface 12 with the respective inner surfaces 12 facing each other. Each mass M also exhibits a second or outer surface 14 opposite the inner surface 12 thereof. Extending outwardly from each mass, generally at the top thereof, is a strong support flange 16 the purpose of which will become apparent shortly.

Each mass will have a centre of mass. If the masses are generally symmetrical then the centre of mass will generally correspond with the centre of gravity. The masses M are connected together by hinge means 18, which means includes components affixed or secured to each of the masses. Preferably the hinge means will extend along the full length of the adjacent masses so that there can be no rotating of the masses lengthwise relative to each other about a vertical axis.

Tension means 20, such as suspension cable means, extend downwardly from suitable frame means (not shown) which will be integral with the structure (such as a building) that is to be influenced by the TMD of the present invention. The tension means 20 are spaced apart along or near the hinge means 18 and are secured thereto at the ends opposite the ends secured to the frame means. The tension means 20 are capable of full articulation, such they can move should the masses and the connecting hinge means start to move or swing from their normal stationary or rest position. Clearly the tension means 20 could comprise cables such as illustrated herein, or they could comprise other means, such as chains or extremely heavy ropes, or any other means which would not be subject to significant elongation under the weight of the masses M.

Positioned generally adjacent to each second or outer surface 14 of each mass M is compression means 22, shown as being in the form of a solid column. Each compression means 22 has its lower end resting on a support surface (not shown) that is part of the structure to be influenced by the TMD of the present invention. The upper end of each compression means 22 is in contact with the undersurface of the respective support flange 16 extending outwardly from the adjacent mass M. Each column is capable of pivotal movement at both the upper and lower ends thereof relative to the support surface and the support flange. As with the tension means, the compression means 22 need not take the form of a column per se, the only aspects of concern being that the compression means be capable of pivoting movement as the masses M swing on the tension means and not be subject to significant compression under the weight of the masses.

It will be noted that the tension means will compensate for any abnormal compression of the compression means and that the compression means will compensate for any abnormal extension of the tension means.

Figure 2 is a side elevational view further illustrating the masses M, the support flanges 16, the hinge means 18, the tension means 20 and the compression means 22. In Figure 2 the masses M are shown in an orientation that they assume during swinging movement thereof. As illustrated, the masses are shown at one instant of a swinging movement towards the right of the view.

As can be seen in Figure 2 the compression means 22 have pivoted towards the right, as permitted through the pivotal connection thereof to the respective support flange 16. Since the masses have swung to the right in the view and since the tension means are suspended from a specific point on the supporting frame, the tension means have also pivoted or swung to the right, under the influence of the moving hinge means 18. The effect of the constrained movements of the masses M is to raise the hinge line H, that being the arcuate line followed by the hinge means 18, upwards while at the same time the compression means will force their pivot points at the support flanges 16 lower (arcs P). This motion results in a rotation of the masses about the hinge line relative to each other. By manipulating the relative radii of these arcs it is possible to force the centre of mass of the system to follow a much larger radius than would be possible with a simple pendulum supported by a cable or other tension means of a length similar to the length of tension means 20.

The geometry of each mass block M can be changed to control the centre of mass of the system. For example, by shifting the centre of mass of each individual mass M towards the hinge means 16 a shorter period can be obtained. The opposite would occur if the centre of mass were to be moved outwardly towards the pivot point of the compression means.

Figures 1 and 2 also illustrate optional damping means 24 for dissipating energy generated during swinging movement of the masses. Each damping means comprises a piston/cylinder arrangement wherein a cylinder member 26 is pivotally connected to suitable mounting means at the support surface and the rod 28 extending from the cylinder member, and connected to a piston member within the cylinder member, is pivotally connected to the adjacent mass M, as at the flange member 16. The piston/cylinder arrangement can be a pneumatic or a hydraulic cylinder, depending on the degree of damping effect that is desired or required.

The pendulum system can also be tuned for different frequencies in the principal swinging directions by restricting the effective length of the tension means using a bi-tuning frame.

Should space permit or should additional damping be required it would be possible to "daisy chain" several of the pendulum arrangements with adjacent masses sharing compression means and/or tension means.

With the present invention it is possible to achieve a period that is significantly lower than a conventional pendulum of the same height/length would allow. The present invention is simple in its construction and has fewer moving parts, as well as fewer critical parts, than previously known Tuned Mass Dampers that attempt to fit within smaller confines.

Claims

CLAIMS:

1. A pendulum arrangement comprising: a pair of generally equal masses each having a centre of mass, the masses being arranged so that first surfaces thereof face each other and second surfaces thereof face away from each other; hinge means affixed to the first surfaces of the masses so as to hingedly connect the two masses together; spaced apart tension means connected at one end thereof to frame means and at the other end to the hinge means; and compression means pivotally connected at one end thereof to an upper portion of each mass and pivotally resting on a lower support surface; whereby the masses are supported by the tension means and the compression means for limited swinging movement thereof.

2. The arrangement of claim 1 wherein said tension means are connected to said frame means and to said hinge means for full articulation relative to said frame means and said hinge means.

3. The arrangement of claim 1 wherein said tension means comprises a cable, chain or rope connected to each end of said hinge means and to said frame means.

4. The arrangement of any one of claims 1 to 3 wherein said compression means comprises at least one column member positioned generally centrally of the second surface of each said mass, said one end of each column member being pivotally connected to a support flange extending outwardly of the mass adjacent to such column.

5. The arrangement of any one of claims 1 to 4 including damping means connected to each said mass to dissipate energy generated during swinging movement of said masses.

6. The arrangement of claim 5 wherein each said damping means comprises a piston and cylinder arrangement pivotally connected at one end to said upper portion of the adjacent mass and at the other end thereof to said support surface.