U.S. patent application number 15/419741 was filed with the patent office on 2017-05-18 for moment frame links wall.
The applicant listed for this patent is Simpson Strong-Tie Company, Inc.. Invention is credited to Guy T. Anderson, Steven E. Pryor.
Application Number | 20170138043 15/419741 |
Document ID | / |
Family ID | 35373822 |
Filed Date | 2017-05-18 |
United States Patent
Application |
20170138043 |
Kind Code |
A1 |
Pryor; Steven E. ; et
al. |
May 18, 2017 |
MOMENT FRAME LINKS WALL
Abstract
A lateral bracing system having high initial stiffness and
including yield links capable of effectively dissipating stresses
generated within the lateral bracing system under lateral
loads.
Inventors: |
Pryor; Steven E.; (Dublin,
CA) ; Anderson; Guy T.; (Valley Springs, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Simpson Strong-Tie Company, Inc. |
Pleasanton |
CA |
US |
|
|
Family ID: |
35373822 |
Appl. No.: |
15/419741 |
Filed: |
January 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14319983 |
Jun 30, 2014 |
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15419741 |
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13214000 |
Aug 19, 2011 |
8763319 |
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14319983 |
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10847851 |
May 18, 2004 |
8001734 |
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13214000 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E04B 1/98 20130101; Y02A
50/00 20180101; E04B 2/56 20130101; E04H 9/14 20130101; E04B 1/36
20130101; E04B 2001/2415 20130101; E04H 9/028 20130101; E04B 1/2403
20130101; E04B 2001/2463 20130101; Y02A 50/14 20180101; E04B
2001/2448 20130101; E04H 9/021 20130101; E04B 2001/2496 20130101;
E04B 2001/2442 20130101; E04H 9/0237 20200501 |
International
Class: |
E04B 1/98 20060101
E04B001/98; E04B 1/24 20060101 E04B001/24; E04H 9/02 20060101
E04H009/02; E04B 1/36 20060101 E04B001/36; E04B 2/56 20060101
E04B002/56 |
Claims
1. A bracing system for use in constructions, the bracing system
comprising: a structural frame having a first structural support
member and a second structural support member; a mounting element
having a first portion fixedly attached to the first structural
support member, and having a second portion comprising a single
pivot coupling pivotally coupling the second structural support
member to the second portion of the mounting element, the second
structural support member pivoting clockwise about a pivot point at
the pivot coupling upon a first load exerted on the structural
frame, and the second structural support member pivoting
counterclockwise about the pivot point at the pivot coupling upon a
second load exerted on the structural frame, the second load being
opposite to the first lateral load, the first structural support
member being spaced from the second structural support member, the
space and the pivot coupling enabling rotation of the first
structural support member relative to the second structural support
member without damaging the first or second structural support
members; and a yield link affixed at a first end to the first
structural support member and at a second end, opposite the first
end, to the second structural support member, the yield link having
a section between the first and second ends capable of yielding in
tension and compression to dissipate stress within the frame upon a
lateral load applied to the structural frame.
2. A bracing system as recited in claim 1, further comprising a
buckling restraint block affixed to the second structural support
member, the buckling restraint block limiting buckling of the yield
link.
3. A bracing system as recited in claim 1, wherein the section has
a smaller width than the yield link at the first and second
ends.
4. A construction, comprising: a first structural support member; a
second structural support member; a mounting element having a first
portion fixedly attached to the first structural support member,
and having a second portion comprising a single pin joint pivotally
coupling the second structural support member to the second portion
of the mounting element, the mounting element allowing rotation of
the first structural support element relative to the second
structural support element without damage to the first or second
structural support elements; and a lateral bracing system affixed
between the first and second structural support members, including:
a pair of yield links, each yield link including a first end
affixed to the first structural support member, and a second end
affixed to the second structural support member, a yield link of
the pair of yield links having a middle section of smaller width
than at the first and second ends, the middle section capable of
yielding in tension and compression to dissipate stress within at
least one of the first and second structural support members upon a
lateral load applied to at least one of the first and second
structural support members.
5. A construction as recited in claim 4, wherein the mounting
element comprises a pair of brackets.
6. A construction as recited in claim 4, wherein the mounting
element comprises a pair of plates.
7. A lateral bracing system for use in constructions, the lateral
bracing system comprising: a structural frame having a column and a
beam; a pivot coupling for coupling the column to the beam, the
pivot coupling comprising a single pin, the structural frame
pivoting clockwise about a pivot point at the pivot coupling upon a
first lateral load exerted on the structural frame, and the
structural frame pivoting counterclockwise about the pivot point at
the pivot coupling upon a second lateral load exerted on the
structural frame, the second lateral load being opposite to the
first lateral load; and a pair of links, each link having a first
end affixed to the column and a second end affixed to the beam,
each link preventing pivoting of the beam relative to the column
for lateral loads which do not cause yielding of the links, and
each link capable of yielding in tension and compression to
dissipate stress within the frame upon the first or second lateral
loads applied to the structural frame. A lateral bracing system as
recited in claim 2, the framing member formed of a substantially
rigid material including at least one of steel, wood and a
polymer.
8. A lateral bracing system as recited in claim 7, the links
including a portion capable of yielding under a stress at which the
structural frame does not yield.
9. A lateral bracing system as recited in claim 7, the links
comprising a first link, and a second link, the first and second
links mounted to the structural frame on opposite sides of the
beam.
Description
CLAIM OF PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/319,983 filed Jun. 30, 2014 entitled MOMENT
FRAME LINKS WALL, which is a continuation of U.S. patent
application Ser. No. 13/214,000 filed Aug. 19, 2011 entitled MOMENT
FRAME LINKS WALL, now U.S. Pat. No. 8,763,319, which is a
continuation of U.S. patent application Ser. No. 10/847,851 filed
on May 18, 2004 entitled MOMENT FRAME LINKS WALL, now U.S. Pat. No.
8,001,734, which applications are incorporated herein by reference
in their entirety.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to hysteretic damping for
structures used in light-framed constructions, and in particular to
a lateral bracing system constructed to provide a high degree of
energy dissipation through hysteretic damping along with high
initial stiffness so that energy is dissipated at low force
thresholds within a light-framed construction.
[0004] Description of the Related Art
[0005] Shear stresses due to natural phenomena such as seismic
activity and high winds can have devastating effects on the
structural integrity of light-framed constructions. Lateral forces
generated during such natural phenomena may cause the top portion
of a wall to move laterally with respect to the bottom portion of
the wall, which movement can result in damage or structural failure
of the wall and, in some instances, collapse of the building.
[0006] In constructions such as residences and small buildings,
lateral bracing systems were developed to counteract the
potentially devastating effects of shear stress on the structural
integrity of light-framed constructions. Although various designs
are known, typical lateral bracing systems include vertical studs
spaced from each other and affixed to horizontal top and bottom
plates. The bottom plate is typically anchored to the floor
diaphragm or foundation. The bracing system typically further
includes sheathing affixed to the studs, upper plate and/or lower
plate to increase structural performance under lateral forces. The
sheathing used may be oriented strand board (OSB) or plywood, but
fiberboard, particleboard and drywall (gypsum board) are also
used.
[0007] Alternatively or additionally, light-framed construction
wall sections may include lateral bracing systems in the form of
prefabricated shearwalls. Shearwalls within wall sections of
light-framed constructions provide lateral stability and allow the
lateral forces in the wall sections to be transmitted from the
upper portions of the wall through the shearwalls to the floor
diaphragm or foundation of the building where they are dissipated
without structural effect on the wall or building.
[0008] Many conventional lateral bracing systems perform well
initially under lateral loads, but yield and fail upon the
repetitive lateral loads which often occur during significant
seismic activity and high winds. Upon appreciable yield or failure
of the lateral bracing system, the entire system must be
replaced.
[0009] It is known to provide conventional high strength walls that
are capable of withstanding significant lateral loads that occur
during seismic and other events. However, such walls place high
demands on foundation anchorage and the foundation itself. Namely,
the holdown bolts and foundation must also be made strong enough to
withstand the large forces transmitted from the wall as they are
dissipated through the holdown bolts and into the foundation.
Therefore, while stronger walls conventionally perform better under
the seismic activity and other loads, conventional design
requirements attendant stronger walls cascade throughout the entire
structure, requiring stronger foundation anchorage and stronger
foundations.
[0010] A further difficulty with conventional lateral bracing walls
is that the corners of such walls tend to bind against their
support surfaces under lateral loads. FIG. 1 shows a conventional
shearwall 20 mounted at its bottom on a support surface 22 and at
its top to a pair of top plates 24. A lateral force F as shown will
result in a downward force F1 at point A and an upward force F2 at
point B. Under high lateral loads, these upward and downward loads
can damage the wall 20 and/or the support structures above and
below the wall.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an advantage of the present invention to
provide a lateral bracing structure having high initial
stiffness.
[0012] It is another advantage of the present invention to provide
a lateral bracing system including controlled and predictable
deflection and load bearing characteristics of the wall member and
controlled and predictable yield of the yield links.
[0013] It is a still further advantage of the present invention to
provide a lateral bracing system where failure is limited to the
yield links, which are easily replaced, thereby restoring the
lateral bracing system to its full load bearing capacity.
[0014] It is another advantage of the present invention to provide
a lateral bracing system capable of fitting between conventionally
located wall studs, and which can be isolated from gravity
loads.
[0015] These and other advantages are provided by the present
invention, which in embodiments relates to a lateral bracing system
for use in constructions such as light framed constructions. The
lateral bracing includes a structural moment frame supported
between an underlying support surface such as a building foundation
and an upper support surface such as a top plate. The moment frame
may be pivotally affixed to the underlying support surface by a
pivot coupling, such as for example a pin joint. The moment frame
may similarly be affixed to the upper support surface by a second
pivot coupling.
[0016] The lateral bracing system may further include a pair of
yield links affixed between the frame and the underlying surface,
one such yield link on each side of the moment frame. The yield
link is provided to yield under a lateral load applied to the
structural frame. Upon such yielding, the pivot couplings allow the
structural frame to pivot to dissipate stress from within the
structural frame. The yield links have a yield point below that of
the moment frame, and will yield under lateral forces exerted on
the lateral bracing system before the moment frame. Thus, damage to
the moment frame is prevented by allowing the moment frame to pivot
and dissipate the energy within the moment frame which could
otherwise damage the moment frame if it were allowed to build up
beyond the yield point of the moment frame.
[0017] In an alternative embodiment of the present invention, a
second pair of yield links may be provided between the moment frame
and the upper support surface to improve the rigidity of the
structure while still allowing the links to yield prior to damage
to the structural moment frame. In embodiments including one or two
pairs of yield links, in the event the links are damaged upon
yielding, the lateral bracing system may be restored to its virgin
integrity and load bearing capabilities simply by removing and
replacing the yield links. The structural frame need not be
replaced.
[0018] In another alternative embodiment of the present invention,
the lateral bracing system may consist of a vertical column element
coupled to a horizontal beam element with a moment resisting joint.
This moment resisting joint could consist of a central hinge, for
example defined by a mounting element, with a pair of exterior
yielding links, one on either side of the central hinge. The
bending strength of the column and beam could be designed to exceed
the moment capacity of the yielding links, thus restricting damage
in a lateral event to the links only. Furthermore, the beam could
be configured to either run over the top of the column, or frame
into the side of the column, without impacting the performance of
the connection via the yielding links.
[0019] Additionally, the moment resisting joint between the beam
and column alleviates the need for a similar connection at the
column base, at, for example, the foundation or lower floor. This
means that forces that would otherwise be transmitted to the
foundation or floor are drastically reduced, and energy dissipation
of a lateral event would be contained within the frame and not rely
on a yielding connection to the surrounding structure. Such a
beam/column configuration may be used in a variety of applications,
such as for example at the structural opening at garage fronts in
light frame constructions, or around windows in light frame
constructions. In such an installation a column element could also
be placed on either side of the beam element allowing for two
energy dissipating joints in the assembly, each containing a pair
of yielding links.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will now be described with reference
to the figures, in which:
[0021] FIG. 1 is a prior art front view of a conventional wall
under a lateral load;
[0022] FIG. 2 is a perspective view of a lateral bracing system
according to a first embodiment of the present invention;
[0023] FIG. 3 is a front view of the lateral bracing system shown
in FIG. 1;
[0024] FIG. 4 is a side view of the lateral bracing system shown in
FIG. 2;
[0025] FIG. 5 is an enlarged partial perspective view of a bottom
portion of the lateral bracing system according to the present
invention;
[0026] FIG. 5A is an enlarged partial perspective view of a bottom
portion of the lateral bracing system including yield links
according to an alternative embodiment of the present
invention;
[0027] FIG. 5B is an enlarged partial perspective view of a bottom
portion of the lateral bracing system according to an alternative
embodiment of the present invention;
[0028] FIG. 6 is a perspective view of a lateral bracing system
according to a second embodiment of the present invention;
[0029] FIG. 7 is a front view of a lateral bracing system shown in
FIG. 6;
[0030] FIG. 8 is a perspective view of the lateral bracing system
according to a third embodiment of the present invention;
[0031] FIG. 9 is a front view of the lateral bracing system shown
in FIG. 8;
[0032] FIG. 10 is a perspective view of a lateral bracing system
according to an alternative embodiment of the present
invention;
[0033] FIG. 11 is a front view of the lateral bracing system
according to FIG. 10;
[0034] FIG. 12 is a top view of the lateral bracing system
according to FIG. 10; and
[0035] FIGS. 13 through 15 are alternative embodiments of the
lateral bracing system shown in FIGS. 10-12.
DETAILED DESCRIPTION
[0036] The present invention will now be described with reference
to FIGS. 2 through 15, which in embodiments of the invention relate
to a lateral bracing system having high initial stiffness and
including yield links capable of effectively dissipating shear
stresses generated within the lateral bracing system under lateral
loads. It is understood that the present invention may be embodied
in many different forms and should not be construed as being
limited to the embodiments set forth herein. Rather these
embodiments are provided so that this disclosure will be thorough
and complete and will fully convey the invention to those skilled
in the art. Indeed, the invention is intended to cover
alternatives, modifications and equivalents of these embodiments,
which are included within the scope and spirit of the invention as
defined by the appended claims. Furthermore, in the following
detailed description of the present invention, numerous specific
details are set forth in order to provide a thorough understanding
of the present invention. However, it will be clear to those of
ordinary skill in the art that the present invention may be
practiced without such specific details.
[0037] Referring now to FIGS. 2-4, there is shown a lateral bracing
system 100 including a moment frame 101 and yield links 110. Moment
frame 101 is a structural frame including a substantially flat
planar diaphragm 102 bounded along each of its longitudinal edges
by framing members 104. Diaphragm 102 and framing members 104 may
each be formed of 7-gauge sheet steel (0.1875 inches). Other
gauges, such as for example 10-gauge sheet steel, and other
materials, such as for example sawn and/or engineered lumber may be
used in alternative embodiments. Additionally, instead of the
diaphragm and framing members being separate pieces, the moment
frame 101 may instead by formed of a single rolled steel section
having a C-shape or Z-shape in a horizontal cross-section. While
framing members are shown only along the two vertical edges of
diaphragm 102, it is understood that the framing members may
additionally extend around the top and/or bottom edges of the
diaphragm 102 in alternative embodiments.
[0038] Diaphragm 102 is mounted to a sill plate 106 by a pair of
right angle brackets 108, formed for example of 1/2 inch thick
steel plate. Each of the right angle brackets 108 includes a first
section mounted on sill plate 106 as by welding, bolting, gluing
and/or other affixation mechanisms, and each bracket 108 includes a
second portion extending up from the sill plate which is juxtaposed
to each other in a spaced and parallel relation. The second
portions of each of brackets 108 are spaced so as to receive a
lower portion of diaphragm 102 therebetween. The diaphragm 102 may
be fixed to the brackets 108 by a pivot coupling such as a pin
joint formed by pin 109 (FIG. 5) fixed within a hole formed in each
of the second portions of bracket 108 and the lower portion of
diaphragm 102. The pin joint allows pivoting of the moment frame
under an applied lateral load. As explained hereinafter, the top of
the moment frame may also be mounted to its support surface by a
pivot coupling allowing pivoting of the moment frame under lateral
loads. As is also explained hereinafter, the top and/or bottom of
the moment frame may be affixed with a fixed coupling instead of a
pivot coupling.
[0039] The pin joint fixedly mounts the diaphragm 102 to the
brackets 108 and sill plate 106, but prevents stress between the
diaphragm and the brackets by allowing the diaphragm to pivot with
respect to the brackets. Thus, together with the yield links
(explained hereinafter), the pin joint prevents damage to the
moment frame 101, by allowing the moment frame to pivot, thereby
preventing the build-up of large sheer stresses within the moment
frame 101 that would otherwise occur if the moment frame were
constrained from pivoting.
[0040] The bottom portion of diaphragm 102 has edges which slope
upward from a neutral longitudinal axis of diaphragm 102 to framing
members 104 as shown in FIGS. 2, 3, 5 and 5A. The slope prevents
contact or binding of portions of lateral bracing system 100
against the sill plate upon pivoting of the lateral bracing system
under lateral loads. Such contact could otherwise damage the moment
frame, sill plate and/or the underlying surface. The angle of the
slope may vary in alternative embodiments, from greater than zero
degrees and higher from the horizontal, and from about 2.degree. to
about 5.degree. in further embodiments. It is also contemplated
that the bottom portion of the diaphragm 102 have no slope, but
rather be horizontal to sill plate 106. Such an embodiment is shown
for example in FIG. 5B. In such an embodiment, the bottom edge of
the diaphragm may be flush against or slightly spaced from the sill
plate.
[0041] Sill plate 106 is in turn affixed to an underlying surface
by anchors 130 as explained hereinafter. In embodiments of the
invention, sill plate 106 may be formed of 1/2-inch thick steel. It
is understood that both sill plate 106 and right angle brackets 108
may be formed of thicknesses other than 1/2-inch, and/or materials
other than steel, in alternative embodiments of the invention.
[0042] Yield links 110 are provided to dissipate shear stresses
within lateral bracing system 100 generated by lateral loads, and
to prevent the moment frame 101 from being damaged due to such
sheer stresses. The lateral bracing system 100 exhibits high
stiffness and rigidity for sheer stresses within the system below a
threshold level. However, yield links 110 have a yield capacity
below bending strength of moment frame 101, and will yield under
lateral forces exerted on the lateral bracing system before moment
frame 101.
[0043] A lateral force on bracing system 100 will result in upward
and downward forces in the framing members 104 and along the
longitudinal edges of the moment frame 101, as well as shear
stresses within the moment frame around the neutral longitudinal
axis of the moment frame. The upward and downward forces are
transmitted to and borne by the yield links 110. However, at
lateral forces above a predetermined threshold, the yield links
will yield, allowing the moment frame to pivot around the pin
joint(s) and dissipating the shear stresses from within the moment
frame. The pivoting allowed by the pin joint(s) and the yielding of
the yield links thus prevents damage to the moment frame which may
have occurred if the shear stresses within the moment frame were
allowed to exceed the yield point of the moment frame. As explained
hereinafter, the yield links 110 have a design allowing them to
yield stably under both tension yield and compression yield.
[0044] Embodiments of the present invention preferably include a
pair of yield links 110, one on either side of moment frame 101.
For ease of description, only one of the yield links 110 will be
described hereinafter. However, it is understood that the yield
links are identical to each other in embodiments of the present
invention, and the following description applies to both yield
links. It is understood that the yield links may not be identical
to each other in alternative embodiments of the present invention.
Moreover, it is contemplated that lateral bracing system 100
includes only one yield link 110 on either side of moment frame 101
in alternative embodiments of the invention.
[0045] A yield link 110 is preferably formed of a yield member 114
mounted to the lateral bracing system by an upper mount 112 and a
lower mount 116. The yield member 114 may have ends which are
threaded, so as to mate with threads within the upper and lower
mounts 112, 116 to affix the yield member to the mounts. In such an
embodiment, the threads at opposite ends of yield member 114 may be
oppositely facing so that the distance between mounts 112 and 116,
and the forces within yield link 110, may be adjusted by rotating
yield member 114. It is understood alternatively that yield member
114 may be affixed to upper and lower mounts 112, 116 as by
welding, bolting, gluing and/or other affixation mechanisms.
[0046] Upper and lower mounts 112, 116 are preferably formed of
steel. Yield member 114 may be formed of mild steel, such as for
example ASTM A36 steel. Other materials exhibiting stable yielding
qualities and good energy absorption may alternatively be used for
yield member 114, including other metals such as for example copper
and bronze, and various polymers.
[0047] In embodiments of the present invention, a casing (not
shown) may be provided around yield member 114 so that yield member
114 and the casing together form an element with not only stable
tension yielding behavior, but also stable compression yielding
behavior because of the prevention of buckling by the casing. The
casing in such an embodiment may be formed of various materials,
such as concrete, a variety of polymers, or wood.
[0048] Whether formed of yield member 114 by itself, or as part of
a buckling restrained element, the yield member 114 will yield
stably, controllably and predictably in tensile yields and/or
compression yields upon application of lateral loads above a
threshold level. The threshold level at which the yield member will
yield may also be controlled and predictable based on the
configuration of the yield link. The thickness of the steel from
which the yield member 114 is formed, as well as the length of the
yield member, may be optimized by computer modeling to provide the
desired performance and yield characteristics for yield links
110.
[0049] If the moment capacity of the joints is known by virtue of
the link yield capacity and the physical geometry of the section,
then the moment frame can be sized to exhibit elastic behavior even
while the full inelastic strength of the links are being taxed. In
one embodiment, yield member 114 may be formed of 1 inch diameter
steel, and the upper and lower mounts may be separated a distance
of 6 inches. However, it is understood that the desired
configuration of the yield links may vary in alternative
embodiment.
[0050] Moreover, although yield link 110 is shown including a
straight length of circular steel in the figures, it is understood
that yield link 110 may have various configurations in different
embodiments of the present invention, with a provision that the
yield link stably under lateral loads applied to lateral bracing
system 100. For example, in one embodiment, the straight yield
member 114 may be replaced by a length of steel having a variety of
configurations that will allow yield link 110 to stably yield under
lateral loads above predictable levels. The yield member 114 may
include bends or a helix. It may also have cross-sectional shapes
other than round in alternative embodiments, such as for example
that shown in FIG. 5A, discussed hereinafter.
[0051] Upper mount 112 may be affixed to frame member 104 as by
welding, bolting, gluing and/or other affixation mechanisms. Lower
mount 116 may be affixed to sill plate 106 by mounting plates 118,
which may be steel plates affixed to opposed sides of lower mount
116. Mounting plates 118 may in turn be bolted to a U-shaped
channel 120 by a pin joint including pin 122 fixed within holes
formed in opposed mounting plates 118 and opposed sidewalls of
U-shaped channel 120. The pin joint allows pivoting of yield link
110 with respect to the U-shaped channel 120 and sill plate 106 to
prevent generation of sheer stresses between yield link 110 and
U-shaped channel 120.
[0052] It is understood that lower mount 116 may be affixed to sill
plate 106, either directly or indirectly, by other mechanisms in
alternative embodiments of the present invention. For example, in
one such alternative embodiment, the mounting plates 118 may be
omitted, and a hole formed through the lower mount so as to allow
the lower mount to be affixed to the U-shaped channel 120 by pin
122. Moreover, it is understood that the pin joint may be omitted
in an alternative embodiment, so that the lower mount 116 is
affixed to the sill plate 106 without the ability to freely pivot
with respect to the sill plate. It is further understood that the
upper mount 112 may be affixed to the frame member 104 by a pin
joint between the upper mount and the frame member instead of or in
addition to the pin joint mounting the lower mount 116 to the sill
plate 106.
[0053] An alternative embodiment of a yield link in accordance with
the present invention is shown in FIG. 5A. The yield link 160
according to this embodiment may be formed from one or more flat
plate elements 162 that are affixed at one end to the frame member
104 by bolts, welding, gluing and/or other affixation means, and at
the opposite end to the sill plate 106 by bolts, welding, gluing
and/or other affixation means. The flat plate element(s) may have a
constant cross-sectional shape, or the element(s) may have a
central tapered midsection 164 similar to a milled steel coupon
sample. A buckling restraint stiffener 166 as shown may further be
provided. The buckling restraint stiffener 166 may be affixed to
the frame member 104 as by bolting, welding, gluing and/or other
affixation means. The buckling restraint stiffener shown has a
corrugated cross-section, but it is understood that other
cross-sections may be provided to effectively restrain the flat
plate element 162 from buckling under compressive loads.
[0054] Sill plate 106 is mounted on an underlying support surface
126 by means of anchors 130. In the embodiment shown, the
underlying support surface 126 comprises a concrete foundation, but
it is understood that underlying support surface 126 may be any
surface on which a conventional lateral bracing system may be
located, for example, a floor diaphragm on the building foundation
or a floor diaphragm on a top plate of a lower floor. Anchors 130
may be conventional anchors for mounting a wall section to
underlying support surface 126, and depending on the nature of
support surface 126, anchors 130 may be for example strap anchors,
mud sill anchors, retrofit bolts, foundation plate hold downs,
straps, ties, nails, screws, framing anchors, plates or a
combination thereof.
[0055] The bracing system 100 may be attached to one or more top
plates 128, as by bolts fitting through the top plates and into
moment frame 101. It is understood that the bracing system 100 may
be affixed to top plates 128 by other mechanisms in alternative
embodiments.
[0056] One such alternative embodiment for affixing bracing system
100 to top plates 128 is shown in FIGS. 6 and 7. The embodiment
shown in FIGS. 6 and 7 is substantially similar to the embodiments
disclosed with respect to FIGS. 2-5, with the exception that moment
frame 101 is affixed to top plates 128 via a pivot coupling such as
a pin joint. In particular, the moment frame may be affixed to the
top plates by a pair of right angle brackets 140 similar in
structure and operation to right angle brackets 108. A pin 142 is
received within aligned holes formed through brackets 140 and a top
portion of diaphragm 102 to affix the moment frame 101 to top
plates 128. The pin joint allows pivoting of lateral bracing system
100 with respect to top plates 128 without generating sheer
stresses in the diaphragm 102 or top plates 128. Thus, upon
yielding of the yield links as previously explained, damage to the
moment frame is prevented by allowing the moment frame to pivot and
dissipate the energy within the moment frame which could otherwise
damage the moment frame if it were allowed to build up beyond the
yield point of the moment frame.
[0057] In embodiments, the top portion of diaphragm 102 has edges
which slope downward from a neutral longitudinal axis of diaphragm
102 to framing members 104 as shown in FIGS. 6 and 7. The slope
prevents contact or binding of portions of lateral bracing system
100 against top plates 128 upon pivoting of the lateral bracing
system under lateral loads.
[0058] As is further shown in FIGS. 6 and 7, the aligned holes
formed in respective brackets 140 for receiving pin 142 have an
oblong shape. This shape significantly or entirely prevents
vertical loads from top plates 128 from being transmitted to
lateral bracing system 100. Thus, only lateral loads are
transmitted. As explained hereinafter, the decoupling of vertical
loads allows for easier control and predictability of the yield
links performance.
[0059] As seen in FIGS. 6 and 7, the diaphragm 102 has longitudinal
edges and framing members 104 which slope inward from bottom to
top, for example, 2 to 10 degrees from vertical. It is understood
that the edge may be vertical (i.e. 0 degree slope) in alternative
embodiments. It is understood that the embodiments described with
respect to FIGS. 2-5 above, and FIGS. 8-9 below may have similarly
sloped edges.
[0060] A further alternative embodiment of the present invention is
shown in FIGS. 8 and 9. The embodiment shown in FIGS. 8 and 9 is
similar to the embodiments described above with respect to FIGS. 6
and 7, with the exception that a second pair of yield links 150 are
provided. Yield links 150 are mounted between moment frame 101 and
top plates 128, and are structurally and operationally similar to
yield links 110. Yield links 110 and 150 together with framing
members 104 define a structural frame providing high initial
stiffness and stable, controlled and predictable yielding under
lateral forces above a predetermined threshold level. The addition
of the second pair of yield links improves the rigidity of the
structure while still allowing the links to yield prior to damage
to the structural moment frame. It is understood that yield links
110 may be omitted in alternative embodiments leaving only yield
links 150 at the top of the moment frame.
[0061] The width of the lateral bracing system 100 may be such that
it fits in between support studs formed in a wall. Thus, a
plurality of lateral bracing systems according to the present
invention may be provided within a wall to greatly enhance the
ability of the wall to withstand lateral loads and sheer stresses.
In one embodiment, the width of the lateral bracing system may be
approximately 14 inches. However, the width may be greater than or
less than 14 inches in alternative embodiments. Moreover, the
lateral bracing system 100 need not fit between support studs in
alternative embodiments.
[0062] In accordance with the embodiments of the present invention
described above with respect to FIGS. 2-9, lateral bracing system
100 has sufficient stiffness and rigidity to provide a high degree
of resistance to deflection under applied lateral loads. However,
at lateral loads above a controllable and predictable level, the
structure of the present invention provides for stable yielding of
the yield links and deflection of the moment frame. In this way,
the applied lateral loads are hysteretically dampened from the
system, and a high degree of energy is dissipated, thereby
preventing damage to the moment frame 101.
[0063] Moreover, the energy dissipation provided by the yield links
described above allows the lateral bracing system 100 to be
designed to withstand lower sheer forces in comparison to
conventional systems of similar dimensions. This translates into
lower design forces for the anchors and underlying support surface
as well. Thus, the reduction in design forces within lateral
bracing system due to the yield links 110/150/160 cascades
throughout the entire design.
[0064] Furthermore, isolating the vertical loads with the pin
joints at the top and/or bottom of the lateral bracing system
allows for easy and predictable control of various parameters of
the lateral bracing system, including for example the initial
stiffness of the lateral bracing system, the amount of deflection
the top of the wall may undergo, the amount of force required
before the yield links will yield, and peak anchor bolt demands.
Moreover, the energy dissipation and stable yielding of the yield
links allow the system 100 to withstand repeated deflection under
lateral loads without failure.
[0065] In the event the links are damaged upon yielding, the
lateral bracing system may be restored to its virgin integrity and
load bearing capabilities simply by removing and replacing the
yield links. The structural frame remains intact and need not be
replaced.
[0066] In embodiments of the present invention discussed thus far,
the lateral bracing system 100 has been comprised of a moment frame
having yield links affixed to either side. In further embodiments
of the present invention, the lateral bracing system 100 may be
formed of a vertical column affixed to a horizontal beam by a
moment resisting joint comprised of a central mounting element and
yield links on either side of the mounting element. The moment
resisting joint provides moment and displacement resistance between
the beam and column, while allowing stable yield upon high lateral
forces. Such embodiments are shown and described hereinafter with
reference to FIGS. 10 through 15.
[0067] Referring to FIGS. 10-12, there is shown a lateral bracing
system 100 including a vertical column 180 affixed to a horizontal
beam 182 by a moment resisting joint 184 comprised of a central
mounting element 188 and yield links 160. Although referred to as a
vertical column and a horizontal beam, it is understood that the
column and beam may be affixed to each other by a moment resisting
joint at angles other than 90.degree. in alternative embodiments.
The moment resisting joint includes yield links 160, for example as
shown and described above with reference to FIG. 5A. In the
embodiment shown, an end of the beam is mounted onto the side of
the column via an end plate 186. In such an embodiment, the pair of
yield links 160 may be provided on top and bottom horizontal
flanges of the beam 182 between the beam and the end plate.
However, as explained hereinafter, the beam may alternatively be on
top of the column so that an end of the column is mounted to a
flange of the beam via an end plate. In such embodiments, the yield
links 160 would be provided on respective vertical flanges between
the column and the end plate.
[0068] As seen in FIGS. 10 and 11, the beam 182 may include a
central diaphragm with sloping edges as shown and as described
above. A central point of the diaphragm may be affixed to end plate
186 via a mounting element 188. The mounting element 188 may be no
more than a welded seam, such as shown in FIGS. 10 and 11. However,
it is understood that the central diaphragm of the beam may be
affixed to the end plate by other types of mounting elements, such
as for example a pair of brackets having a pin joint (FIGS. 5 and
5A) or a pair of brackets or plates not having a pin joint, but
instead simply affixing the diaphragm to the end plate as by bolts,
welds, gluing and/or other affixation means (FIGS. 14 and 15). The
end plate 186 is in turn affixed to a vertical flange of the column
180 via bolts 192, welding, gluing and/or other affixation means.
The yield links shown in FIGS. 10-15 are those described above with
respect to FIG. 5A. However, it is understood that any
configuration of yield link described herein may be used in the
embodiments described with reference to FIGS. 10-15.
[0069] In order to provide greater load-bearing capabilities at the
joint between the column and beam, stiffeners 194 may be welded,
bolted, glued and/or otherwise affixed to the central diaphragm and
flange of the column 180. As seen in FIGS. 10-12, the stiffeners
194 are structural pieces that extend perpendicularly from the
opposed surfaces of the central diaphragm and flange on both the
front and back surfaces of the diaphragm. Four such stiffeners are
shown in FIGS. 10-12. The stiffeners may extend partly across the
column diaphragm as shown, or entirely across the diaphragm. FIG.
13 shows an alternative system to improve the load-bearing
capabilities at the joint between the column and beam. As shown
therein, the portion 196 of the vertical flange in contact with the
end plate 186 may be made thicker. This may be done by removing the
top portion of the flange and replacing it with a thicker member,
or otherwise fortifying the top portion of the flange. The portion
196 may be used instead of or in addition to the stiffeners 194. It
is further understood that the stiffeners 194 and/or thicker
portion 196 may be omitted in embodiments of the present
invention.
[0070] The moment resisting joint shown in FIGS. 10-13 provides
high initial stiffness and resistance to relative movement between
the column 180 and the beam 182 under lateral loads, but provides
stable yielding under lateral loads above a controllable level. In
particular, bending strength of the column and beam could be
designed to exceed the moment capacity of the yield links. Thus,
the yield links 160 yield under lateral loads before bending or
deformation of the column or beam, and any damage is limited to the
yield links which may be easily removed and replaced. Furthermore,
the beam could be configured to either run over the top of the
column, or frame into the side of the column, without impacting the
performance of the connection via the yielding links.
[0071] Additionally, the moment resisting joint between the beam
and column alleviates the need for a similar connection at the
column base, at, for example, the foundation or lower floor. This
means that forces that would otherwise be transmitted to the
foundation or floor are drastically reduced, and energy dissipation
of a lateral event would be contained within the frame and not rely
on a yielding connection to the surrounding structure. Such a
beam/column configuration may be used in a variety of applications,
such as for example at the structural opening at garage fronts in
light frame constructions, or around windows in light frame
constructions. In such an installation a column element could also
be placed on either side of the beam element allowing for two
energy dissipating joints in the assembly, each containing of a
pair of yielding links.
[0072] In embodiments of the invention, it is understood that the
portion of the central diaphragm which affixes to the sill plate
(FIGS. 2-9) or endplate (FIGS. 10-15) need not have sloping edges.
Such an embodiment is shown in FIGS. 14 and 15. In this embodiment,
the central diaphragm of the beam may affix to the endplate as by a
mounting element 188 in the form of a plate which is bolted to the
central diaphragm and welded to the endplate. It is understood that
the mounting element 188 may be affixed to both the central
diaphragm and endplate by bolting, welding, gluing and/or other
mounting means in alternative embodiments. As best seen in FIG. 15,
a slight space may be left between the end of the beam 182 and
endplate 186 to allow rotation between the beam and column upon
high lateral loads and yielding of the yield links without binding
between the column and beam. It is understood that the moment frame
101 of FIGS. 2-9 may also be affixed at its top or bottom with a
configuration as shown and described with respect to FIGS. 14 and
15.
[0073] Although the invention has been described in detail herein,
it should be understood that the invention is not limited to the
embodiments herein disclosed. Various changes, substitutions and
modifications may be made thereto by those skilled in the art
without departing from the spirit or scope of the invention as
described and defined by the appended claims.
* * * * *