Energy absorber

Details Energy absorber Energy absorber

2000-03-06

2001-11-27

Friedman, Carl D. (Department: 3635)

Static structures (e.g., buildings)

Means compensating earth-transmitted force

C052S167400, C052S167500, C052S167600

Reexamination Certificate

active

06321492

ABSTRACT:

TECHNICAL FIELD
This invention relates to a frictional braking device. More particularly it relates to a friction ball primarily intended to be used in seismic and vibration isolation.
BACKGROUND ART
Seismic isolation involves isolating structures and damping the isolated structures from incoming forces due to earthquakes. New Zealand Patent 178949 describes a very successful bearing which may be used to isolate structures in this way. The favoured embodiment of this invention is referred to as a lead rubber bearing. A more comprehensive discussion of seismic isolation and the lead rubber bearing can be found in “
An Introduction to Seismic Isolation
”, Skinner et, John Wylie and Sons (1993).
Another means of seismically isolating structures is a bearing sold under the trade mark “Frictional Pendulum” by Earthquake Protection Systems Inc, of Alameda, Calif., USA. Such a bearing consists of a pendulum member with a frictional surface at the distal end of the pendulum member which slides over a polished surface. This is described in U.S. Pat. No. 4,644,714.
Another device intended to provide seismic isolation is described in the U.S. Pat. No. 4,726,161. This apparatus includes a rollable bearing and a bowl. A spring urges the rollable bearing into contact with the bowl. The combination dampens seismic forces on a structure supported on said rollable bearing.
In U.S. Pat. No. 5,599,106 there is described a seismic isolating bearing. This consists in upper and lower load plates with downward and upward facing rigid surfaces, respectively, at least one of which is conical. A rigid ball is sandwiched between the plates. The ball rolls up a conical surface when one load plate is displaced laterally from the other by an external force, and returns to the centre of the core by gravitational forces when the external force ceases.
The invention described in WO97/48866 is a seismic isolator consisting of a ball interposed between a foundation and a building. The ball is retained in a cage like structure secured to the underside of the building. It rolls on a hemispherical surface secured to the foundation.
In all of the prior art devices described above the bearing element, or ball, and the surfaces on which it rolls are substantially incompressible. This means that when there is relative movement between the structure being supported and the surface upon which the bearing rests there is no braking force being applied apart from the weight of the structure itself. If the incoming forces causing relative movement are long lasting then it can take a considerable amount of time for the structure to come to rest.
It is an object of this invention to go some way towards overcoming this disadvantage or at least to offer the public a useful choice.
DISCLOSURE OF INVENTION
Accordingly the invention may be said broadly to consist in an external force damping bearing assembly comprising:
an upper surface which in use supports a structure,
a lower surface co-operable with said upper surface, and
a friction ball which in use is positioned between said upper surface and said lower surface to support said structure,
said friction ball comprising a core of particulate material and an outer layer enclosing said core, said ball, when supporting said structure, being deformed, said deformation generating frictional forces between particles of said particulate material which resists rolling motion within said ball to dampen an external force applied to said lower surface or to said upper surface.
In one alternative said external force is a seismic force acting on said lower surface.
In another alternative said external force is a wind force acting on said upper surface through said structure.
Preferably said particular material is a plurality of small friction balls of construction as defined herein and of diameters sufficiently small that a plurality of said friction balls fit within said core.
More particularly said particulate material is sand, quartz, glass, steel, metal balls or spherical or non-spherical balls.
Preferably said core is partly filled with material.
Alternatively said core is completely filled with material.
In a third alternative said core is filled to a hydrostatic pressure of 0-5 MPa.
Alternatively said core is filled to a hydrostatic pressure of up to 20 MPa.
Alternatively said core is filled to a hydrostatic pressure of up to the structural limit of said outer layer.
Preferably said outer layer comprises rubber.
More preferably said rubber outer layer is reinforced rubber.
Preferably said rubber is reinforced with fibre, metal wire, carbon fibre, cord, rubber thread or the like.
In another embodiment said friction ball has a laminated construction comprising two or more laminae surrounding a central core.
In one embodiment the outer surface of said friction ball is an elastomer with a high coefficient friction.
In another embodiment said outer layer is rubber with a tread.
In another embodiment said outer layer has a treadless but roughened surface.
Preferably the shape of said friction ball is any geometrical shape capable of rolling motion.
Preferably the undeformed shape of said friction ball is spherical.
Alternatively said undeformed shape is elliptical.
Alternatively said undeformed shape is ellipsoidal.
Preferably at least one of said upper and lower surfaces is concave or conical.
More preferably both said surfaces are concave.
Preferably said concave surface may be spherical, parabolic or defined by a polynomial, trigometrical or hyperbolic function or any other smooth curve or combination of curves.
Alternatively said surface is conical.
Preferably there is a rest in said concave or conical surface adapted to receive a said friction ball.
Preferably said rest is concave with a radius of curvature less than that of said concave surface.
Preferably a said lower surface mountable on a foundation member.
Preferably said foundation member is a pile.
More preferably said foundation member is an internal or external basement wall.
Preferably a said upper surface is mountable on the bottom of a structure to be supported thereby.
Alternatively said upper surface is an integral part of said structure.
In a further alternative there are a plurality of said friction balls resting on each said lower surface.
In one embodiment there are three said friction balls.
In another embodiment there are seven said friction balls.
Preferably there is a rest within said lower concave surface to receive said plurality of friction balls, the rest being shaped so that the upper surfaces of said balls contact said upper surface evenly over the contact area of each of said balls.
In another embodiment the invention may be said broadly to consist in a method of seismically isolating a structure which comprises interposing a plurality of bearing assemblies (as herein above defined) between a structure and a predetermined number of foundation points upon which said lower surfaces are positioned.
In one alternative said bearing assemblies are installed at the time of construction of said structure.
In another embodiment said bearing assemblies are retrofitted between an existing structure and its foundation.
Preferably said bearing assemblies are provided above all foundation members.
Preferably said foundation members are piles.
Alternatively said foundation members are perimeter or internal walls.
Preferably said structure is a house.
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 of 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.


REFERENCES:
patent: 2014643 (1935-09-01), Bakker
patent: 4496130 (1985-01-01), Toyama
pa

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