Note: Descriptions are shown in the official language in which they were submitted.
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Dkt. No. 92900/23
ENERGY ABSORBER AND METHOD OF FORMING THE SAME
FIELD OF THE INVENTION
[001] The present invention relates to energy absorbers, and in particular to
energy
absorbers for earthquake resistant buildings.
BACKGROUND OF THE INVENTION
[002] Earthquakes exert lateral and vertical forces on a building, and
fabricating a
structure that will withstand these random, often sudden forces is a complex
task. When
designing an earthquake-resistant building, engineers can choose various
structural
components, such as shear walls, braced frames, moment resisting frames,
diaphragms
and horizontal trusses. These building elements impart earthquake resistant
structures
with the ability to resist and sometimes to absorb and dissipate seismically
induced
motion through a combination of means, including damping means which absorbs
energy and decreases the amplitude of oscillations of a vibrating structure
and inelastic
deformation means which can withstand considerable inelastic deformation. The
structural elements can be used alone or in combination to achieve the
necessary energy
absorption and dissipation.
[003] There are many known supporting structures having ring-like or
cylindrical
elements that are used to make a building earthquake resistant. For example,
U.S.
Patent No. 981,824 to Veres shows diagonal braces connected between upright
columns
and a cylindrical post and secured to the cylindrical post with adjustable
nuts. U.S.
Patent No. 5,605,021 to Thomann describes an earthquake-proof building which
includes circular rings supporting circular dish elements. However, the
purpose of the
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known ring-like supporting structures discussed above is to enhance the
rigidity of a
building so that the building acts as a unit during an earthquake. U.S. No.
5,097,547 to
Tanaka et al. discloses a vibration absorption device which comprises outer
and inner
rings interconnected by radial spokes. The deformation of the radial spokes
due to
rotation of the outer ring relative to the inner ring during application of a
vibratory force
results in absorption of energy.
[004] Accordingly, there is a need for a deformable part of a supporting
structure
that can absorb energy and easily reverse its load-bearing capacity,
particularly for use in
imparting requisite earthquake resistance to a building.
SUMMARY OF THE INVENTION
[005] An energy absorber according to an exemplary embodiment of the invention
includes one or more ductile members and two or more bracing members that
support
the one or more ductile members. When a force is applied to the energy
absorber, the
one or more ductile members deform to absorb energy. In one embodiment of the
invention, the one or more ductile members are ductile rings.
[006] A particular application for the energy absorber of this invention is
incorporation in a building to impart earthquake resistance to the building.
The energy
absorber according to this exemplary embodiment of the invention includes at
least one
ductile ring adapted to be disposed within a panel member of a structural
element of the
building, and tension rods each of which includes a first end connected to the
at least
one ductile ring and another end adapted to be connected to the panel member,
wherein
the ductile ring is disposed at substantially the center of the panel member.
The
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structural element can be, for example, a shear wall or part of a truss and
the panel
member can be, for example, rectangular.
[007] An energy absorber according to another exemplary embodiment of the
invention includes a panel member that is attachable to a structural element
of a
building, at least one ductile ring disposed within the panel member, and at
least two
bracing members that connect the at least one ductile ring with the panel
member.
[008J In one embodiment of the invention, a plurality of ductile rings are
disposed
adjacent to one another.
[009] In another embodiment of the invention, a plurality of ductile rings are
nested
within one another, and energy absorbing material may be disposed between the
rings.
[010] The invention also encompasses a method of forming an energy absorber
for
an earthquake resistant building, including connecting respective first ends
of two or
more bracing members to one or more ductile members, disposing the one or more
ductile members within an opening of a structural element of the building, and
connecting respective second ends of the two or more bracing members to the
structural
element of the building.
BRIEF DESCRIPTION OF THE DRAWINGS
[011] Various exemplary embodiments of this invention will be described in
detail,
with reference to the following figures, wherein:
[012] FIG. 1 illustrates an energy absorber according to an exemplary
embodiment
of the invention within a panel member installed in a building;
[013] FIG. 2 is a detailed view of the energy absorber of FIG. 1 within a
panel
member;
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[014] FIGS. 3 and 4 illustrate the operation of an energy absorber according
to an
exemplary embodiment of the invention during application of shear forces to
the panel
member;
[015] FIG. 5 is a load-deformation curve for an energy absorber according to
an
exemplary embodiment of the invention during cyclic loading;
[016] FIG. 6 shows an energy absorber according to another exemplary
embodiment
of the invention;
[017] FIG. 7 shows a partially cut away view of an energy absorber according
to
another exemplary embodiment of the invention;
[018] FIG. 8 shows an energy absorber according to another exemplary
embodiment
of the invention;
[0191 FIG. 9 shows a partially cut away view of an energy absorber according
to
another exemplary embodiment of the invention;
[020] FIG. 10 shows an energy absorber according to an exemplary embodiment of
the invention in which a ductile ring is made of four portions; and
[021] FIG. 11 shows an energy absorber according to an exemplary embodiment of
the invention including a diamond-shaped ductile member.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[022] The various exemplary embodiments of the present invention are directed
to
an energy absorber that imparts buildings with the ability to withstand forces
caused by,
for example, earthquakes. It should be appreciated that the various concepts
of the
present invention are not necessarily limited to earthquake resistant
structures, but are
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also applicable to structures that are designed to withstand forces generated
by any other
factor, such as, for example, explosions or high winds.
[023] FIG. 1 illustrates an energy absorber 4 according to an exemplary
embodiment
of the invention used in a building 1. According to the present embodiment of
the
invention, the energy absorber 4 is located in an opening 3 in a structural
member of a
building, such as shear wall 2. However, it should be appreciated that the
present
concept is not limited to shear walls, and the energy absorber 4 can be
applied to any
other structural element of a building, such as, for example, a truss or a
joist. Further,
the energy absorber 4 need not be disposed vertically within the building 1,
but can be
disposed oriented in any direction which would maximize force-absorption.
(024] FIG. 2 is a more detailed view of an embodiment of the energy absorber 4
of
FIG. 1. As shown in FIG. 2, the energy absorber 4 includes a ductile member 6,
four
braces 8 and four frame members 10 which form structural panel 5. The braces 8
support the ductile member 6 at substantially the center of the structural
panel 5. The
ductile member 6 is formed of a ductile material, such as, for example, steel
or
aluminum. One of the ends of the braces 8 are connected to the ductile member
6 by
any suitable fastening elements, such as, for example, adjustable nuts 12. The
opposite
ends of the braces 8 are attached to respective corners of the structural
panel 5 by, for
example, pin joints, welding or bolts. The number of braces 8 is not limited
to four and
any number of braces 8 can be used in the various exemplary embodiments of the
invention. In the present embodiment of the invention, the braces 8 are
tension rods,
but can also be any other suitably rigid structural supports for the ductile
element 6.
Further, the ductile member 6 need not be ring-shaped, as shown in FIG. 2, but
could
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have other shapes as would be understood by workers skilled in the art.
Furthermore,
structural panel 5 is not limited to a rectangular shape and can take other
shapes, such
as, for example, circular. For convenience, the present invention will be
described below
with reference for the most part to a circular ductile ring.
[025] The energy absorber in accordance with FIG. 2 is modular in nature, that
is,
prefabricated, and the structural panel 5 is combined with a shear wall or
other
structural element during construction of the building. For example, the
entire energy
absorbing structural panel 5 shown in FIG. 2 may be prefabricated to include
the energy
absorber 4 before placement of the panel into the shear wall 2. Prefabrication
of the
structural panel 5 allows for more easy transport to the construction site and
placement
into structural elements of the building. However, the energy absorber 4 can
also be a
separate element that can be placed into an opening in the shear wall 2
without the
frame members 10.
[026] FIGS. 3 and 4 illustrate the operation of the energy absorber 4 during
application of shear forces to the structural panel 3. As shown in FIG. 3, the
application
of shear force F1 to the structural panel 3 causes a deformation y so that one
diagonal of
the panel 3 increases in length and another diagonal of the panel 3 decreases
in length.
The deformation of the structural panel 3 causes the ring 6 to deform into an
oval in a
ductile manner so that the braces 8 will tend to stay in tension. This causes
absorption
of energy, or, put another way, substantially reduces the transfer of such
energy through
the remainder of the building 1 to prevent or diminish structural damage to
the building
1 during an earthquake or other disaster. As shown in FIG. 4, when the shear
deformation is reversed by a shear force F2, the ovalization of the ring is
reversed, again
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tending to keep the braces 8 in tension. As can be seen in FIGS. 3 and 4, the
ring
structure of the energy absorber 4 minimizes or substantially eliminates
buckling and/or
slacking of the braces 8 upon shear reversal, which would normally occur if no
such ring
structure was present.
[027] FIG. 5 is a load-deformation diagram which generally illustrates the
deformation of the structural panel 3 during application of a shear force F
that causes a
deformation y. For each cycle of loading, the corresponding point in the load-
deformation curve A traces out a loop representing energy absorption. The
shaded
region B represents the total amount of energy absorbed during the load
cycling. When
the structural panel 3 is subjected to shear forces, the resulting shape of
the load-
deformation diagram takes on a near ideal form. As can be seen from the
hysteretic
load-deformation curve A, the energy absorber of the present invention can
maintain
nearly all of its strength and stiffness over a number of large cycles of
inelastic
deformation. The resulting force-deformation "loops" are quite wide and open,
showing
a large amount of energy dissipation capacity.
[028] FIG. 6 shows an energy absorber according to another exemplary
embodiment
of the present invention. The energy absorber 20 according to that embodiment
of the
present invention includes a first ductile ring 22, a second ductile ring 24
and four
braces 26. The first ductile ring 22 is disposed adjacent to, but spaced from,
the second
ductile ring 24, so that an opening 23 is formed between the first ductile
ring 22 and the
second ductile ring 24. As shown in FIG. 6, each of the braces 26 include a T-
shaped end
welded or otherwise bonded to the first and second ductile rings 22 and 24 so
that each
of the braces 26 protrude from the opening 23 between the first and second
ductile rings
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22 and 24. The opposite ends of the braces 26 are attached to respective
corners of a
structural panel by, for example, pin joints, welding or joints. As in other
embodiments
of the invention, the number of braces 26 is not limited to four. Further, the
number of
ductile rings is not limited to two, but can be any number of ductile rings
disposed
adjacent to one another. The plural ductile ring structure of the present
embodiment
allows for easier connection of the ductile rings to the diagonal braces and
provides
additional energy absorption compared to the single ductile ring structure.
[029] FIG. 7 shows a partially cut away view of an energy absorber according
to
another exemplary embodiment of the invention. The energy absorber 30
according to
that embodiment of the invention includes a first ductile ring 32, a second
ductile ring
34 and two braces 36. The first ductile ring 32 has a smaller diameter than
the second
ductile ring 34, and is placed inside, or "nested" with, the second ductile
ring 34. It
should be appreciated that the number of nested rings is not limited to two,
and any
number of such rings having different diameters can be nested together. The
first ductile
ring 32 and second ductile ring 34 are preferably nested in contact with one
another.
Two slotted openings 33 are formed on the side portions of the first ductile
ring 32, and
corresponding two slotted openings 35 are formed on the side portions of the
second
ductile ring 34. Each of the braces 36 extends through respective slotted
openings 33
and 35 in the first and second ductile rings 32 and 34, and are fastened to
the first and
second ductile rings 32 and 34 by, for example, adjustable nuts 38. When a
shear force
is applied to the energy absorber 30, the first and second ductile rings 32
and 34 deform
into an oval shape. The slotted openings 33 and 35 allow the first and second
ductile
rings 32 and 34 to rotate and slide over one another during their respective
deformation.
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Frictional forces caused by the relative motion of the first and second
ductile rings 32
and 34 result in additional energy absorption.
[030] FIG. 8 shows an energy absorber according to another exemplary
embodiment
of the invention. The energy absorber 40 of that embodiment of the invention
has
substantially the same structure as the previous embodiment except for the
shape and
connection of the braces. The energy absorber 40 includes a first ductile ring
42 nested
within a second ductile ring 44. Each of two braces 46 includes a T-shaped end
that is
welded or otherwise bonded to the second ductile ring 44. Frictional forces
between the
first and second ductile rings 42 and 44 during application of shear force to
the energy
absorber 40 results in increased energy absorption.
[031) FIG. 9 shows a partially cut away view of an energy absorber according
to yet
another exemplary embodiment of the invention. That embodiment is
substantially the
same as the embodiment shown in FIG. 7 except that the first and second
ductile rings
32 and 34 are separated by an energy absorbing material 50. That is, rather
than being
in contact with one another as in the previous embodiment, the first and
second ductile
rings 32 and 34 are spaced apart with an energy absorbing material SO disposed
between
them. The energy absorbing material 50 may be, fox example, any foam or gel-
like
substance that can be injected between the first and second ductile rings 32
and 34 or
preformed in a ring structure to fit between the first and second ductile
rings 32 and 34.
[032] The means of attaching the braces to the ductile ring described in the
previous
embodiments of the invention are merely exemplary, and any suitable fastening
configuration and structure can be used. For example, FIG. 10 shows an energy
absorber
60 according to an exemplary embodiment of the invention in which a ductile
ring 62 is
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made of four portions. A brace 64 extends between each of the portions and is
bolted to
the ductile ring 62 by, for example, adjustable nuts 66.
[033] As previously mentioned, the ductile member in various exemplary
embodiments of the invention is not limited to a circular shape. For example,
FIG. 11
shows an energy absorber 70 including a diamond-shaped ductile member 72. The
ductile member 72 can be formed of four portions. A brace 74 extends between
each of
the portions and is bolted to the ductile member 72 by, for example,
adjustable nuts 76.
It should be appreciated that the diamond-shaped ductile member can be
attached to the
braces by any other suitable means, such as by means described in previous
embodiments with reference to a circular ductile member. Further, multiple
diamond-
shaped ductile members can be nested together or disposed next to each other
to
enhance energy absorption.
[034] While this invention has been described in conjunction with the
exemplary
embodiments outlined above, it is evident that many alternatives,
modifications and
variations will be apparent to those skilled in the art. Accordingly, the
exemplary
embodiments of the invention, as set forth above, are intended to be
illustrative, not
limiting. Various changes may be made without departing from the spirit and
scope of
the invention.
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