Spring devices – Resilient shock or vibration absorber – Variably preloaded
Patent
1995-08-21
1997-08-12
Young, Lee W.
Spring devices
Resilient shock or vibration absorber
Variably preloaded
267152, F16M 500, F16F 308
Patent
active
056557566
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to energy absorbers used for reducing the effects of induced motion or displacement in variety of structures and equipment and methods for their manufacture.
The energy absorbers of the invention may be used in large structures such as buildings or bridges to reduce the effects of motion induced during earthquakes or from strong winds. They may also be used as shock absorbers or energy absorbing stops for halting railway wagons or other moving objects. They may also be used to damp vibration from industrial machinery or engines or the like or from domestic appliances such as washing machines for example, or in any other application where it is desired to isolate from or damp any motion, vibrations or similar. The energy absorbers of the invention have various applications.
BACKGROUND OF THE INVENTION
Energy absorbers which employ elastic or plastic deformation of certain materials to absorb energy are well known. U.S. Pat. Nos. 4,117,637, 4,499,694 and 4,593,502 describe forms of cyclic shear energy absorbers which in seismic isolation applications are typically interposed between two vertically contiguous weight holding members of a structure, such as between the piles and a base floor of a medium size building or between the foundation blocks and upright supports in a bridge. Typically around fifty to one hundred such energy absorbers are used in a building in the form of bearings in the building foundations to seismically isolate the building. A general discussion of these and related devices is given in "An Introduction to Seismic Isolation", R. I. Skinner, W. H. Robinson and G. H. McVerry, Wiley, 1993.
Such bearings used for seismic isolation for example typically comprise a resilient support pad which takes a portion of the weight of the structure and an energy absorbing core comprising a material which deforms plastically as the structure sways relative to the ground. The support pad typically comprises alternating layers of an elastic material such as rubber and plates of a relatively stiff material such as steel bonded together. The energy absorbing core is typically formed of lead. The bearing may be fixed between connector plates which are in turn connected to the building structure members above and below. Alternatively the bearing may simply be fitted into a recess or equivalent on each building structure member. Such energy absorbers are commonly known as lead-rubber bearings.
Lead is the preferred material for forming the energy absorbing core for several reasons. First it yields at a room temperature shear stress of around 10.5 MPa which is low compared with other metals and equivalent plastic materials. Second it restores its mechanical properties through recrystallisation and associated processes relatively rapidly following yield deformations, which provides outstanding resistance to work hardening under cyclic shear at ordinary temperatures. Third lead is readily available at the purity required to exhibit these properties.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide for improved performance of such energy absorbers for seismic isolation and other applications.
The invention broadly comprises an energy absorber for interposing between two members to absorb energy of motion which may be induced between the two, comprising a core of a plastically deformable energy absorbing material and means surrounding the core which applies approximately hydrostatic pressure at least approaching the shear yield stress of the energy absorbing material to the core and transfers motion between said members as shear forces across the core.
Preferably the hydrostatic pressure applied to the core exceeds the shear yield stress of the energy absorbing material. Preferably the hydrostatic pressure is 10 MPa or more and most preferably in the range 20-100 MPa.
Preferably the energy absorbing material of the energy absorber core is lead, but other energy absorbing materials which may be used include alloys of lead, aluminium at
REFERENCES:
patent: 3134585 (1964-05-01), Trask
patent: 4593502 (1986-06-01), Buckle
patent: 4633628 (1987-01-01), Mostaghel
patent: 5201155 (1993-04-01), Shimoda et al.
patent: 5372156 (1994-12-01), Luz et al.
Damping Systems Limited
Young Lee W.
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