U.S. patent application number 13/204470 was filed with the patent office on 2012-03-15 for force-resisting devices and methods for structures.
This patent application is currently assigned to EI-LAND CORPORATION. Invention is credited to Rory R. Davis, John Hulls.
Application Number | 20120060432 13/204470 |
Document ID | / |
Family ID | 27659934 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120060432 |
Kind Code |
A1 |
Hulls; John ; et
al. |
March 15, 2012 |
FORCE-RESISTING DEVICES AND METHODS FOR STRUCTURES
Abstract
In accordance with the present invention there is provided a
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure. The device includes at least one active element, the
active element having defined force versus deflection properties
and able to transmit force and dissipate and absorb energy, one end
of the active element configured to be connected to a structure,
and at least one frame element disposed about a discontinuous
structural element, wherein the frame is configured to be connected
to a second end of the active element, wherein the active element
and the frame element configured to resist forces applied to the
structure by transmitting forces across the discontinuous
structural element.
Inventors: |
Hulls; John; (Point Reyes,
CA) ; Davis; Rory R.; (Gardnerville, NV) |
Assignee: |
EI-LAND CORPORATION
|
Family ID: |
27659934 |
Appl. No.: |
13/204470 |
Filed: |
August 5, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11267323 |
Nov 7, 2005 |
7997042 |
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13204470 |
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10074684 |
Feb 11, 2002 |
7043879 |
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11267323 |
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Current U.S.
Class: |
52/167.3 ;
188/371 |
Current CPC
Class: |
E04H 9/02 20130101; F16F
7/003 20130101 |
Class at
Publication: |
52/167.3 ;
188/371 |
International
Class: |
E04H 9/14 20060101
E04H009/14; E04H 9/02 20060101 E04H009/02; F16F 7/12 20060101
F16F007/12 |
Claims
1. A shear membrane for absorbing forces and dissipating energy in
a shear structure under a shear force applied to the shear membrane
in a plane of the shear membrane, the shear membrane comprising:
two non-contacting structural elements; and an
elastoplastically-deforming element with a non-planar portion, the
non-planar portion absorbing a portion of the shear force applied
to the shear membrane and absorbing a portion of the energy of the
shear force by elastoplastic deformation of the
elastoplastically-deforming element under the shear force, wherein
the elastoplastically-deforming element connects the two
non-contacting structural elements with the non-planar portion
located between the two non-contacting structural elements.
2. The shear membrane of claim 1, wherein the
elastoplastically-deforming element exhibits reversible behavior
under one or more shear force cycles.
3. The shear membrane of claim 2, wherein the one or more shear
force cycles is at least 2 cycles.
4. The shear membrane of claim 3, wherein the one or more shear
force cycles is at least 3 cycles.
5. The shear membrane of claim 1, wherein a positive portion of the
shear force cycle is from a neutral force to a maximum positive
force and a negative portion of the cyclic load is from the maximum
positive force to the neutral force.
6. The shear membrane of claim 5, wherein regions of elastoplastic
deformation during the positive portion include, in order with
increasing force, a first elastic region, a first plastic region
and a second elastic region and wherein the regions or
elastoplastic deformation during the negative portion include the
regions of the positive portion, in order with decreasing force,
the second elastic region, the first plastic region and the first
elastic region.
7. The shear membrane of claim 1, comprising an opening in the
shear membrane framed by a plurality of framing elements, wherein
one of the two non-contacting structural elements is one of the
plurality of framing elements, wherein a shear force as a function
of deflection curve is substantially the same for the shear
membrane with the opening and for the shear membrane without the
opening.
8. The shear membrane of claim 7, wherein the opening is sized for
a window or a door.
9. The shear membrane of claim 1, wherein the non-planar portion
has a substantially v-shaped cross-section.
10. The shear membrane of claim 9, wherein the substantially
v-shaped cross-section is a v-shape with a non-symmetric bisector
of an apex of the v-shape.
11. The shear membrane of claim 1, wherein the shear membrane is a
portion of a building panel, a portion of a building wall, or a
portion of a roof panel.
12. The shear membrane of claim 1, wherein the
elastoplastically-deforming element transmits, absorbs and
dissipates all resultant forces in the shear membrane from the
applied shear force.
13. The shear membrane of claim 1, comprising means for attaching
at least one of the two non-contacting structural elements to an
adjacent structure.
14. The shear membrane of claim 13, wherein the adjacent structure
is a foundation.
15. A prefabricated shear membrane for absorbing forces and
dissipating energy in a shear structure under a shear force applied
to the prefabricated shear membrane in a plane of the prefabricated
shear membrane, the prefabricated shear membrane comprising: two
non-contacting structural elements; and an
elastoplastically-deforming element with a non-planar portion, the
non-planar portion absorbing a portion of the shear force applied
to the shear membrane and absorbing a portion of the energy of the
shear force by elastoplastic deformation of the
elastoplastically-deforming element under the shear force, wherein
the elastoplastically-deforming element connects the two
non-contacting structural elements with the non-planar portion
located between the two non-contacting structural elements.
16. The prefabricated shear membrane of claim 15, wherein the
elastoplastically-deforming element exhibits reversible behavior
under one or more shear force cycles.
17. The prefabricated shear membrane of claim 16, wherein the one
or more shear force cycles is at least 2 cycles.
18. The prefabricated shear membrane of claim 17, wherein the one
or more shear force cycles is at least 3 cycles.
19. The prefabricated shear membrane of claim 16, wherein a
positive portion of the shear force cycle is from a neutral force
to a maximum positive force and a negative portion of the cyclic
load is from the maximum positive force to the neutral force.
20. The prefabricated shear membrane of claim 19, wherein regions
of elastoplastic deformation during the positive portion include,
in order with increasing force, a first elastic region, a first
plastic region and a second elastic region and wherein the regions
or elastoplastic deformation during the negative portion include
the regions of the positive portion, in order with decreasing
force, the second elastic region, the first plastic region and the
first elastic region.
21. The prefabricated shear membrane of claim 20, comprising an
opening in the shear membrane framed by a plurality of framing
elements, wherein one of the two non-contacting structural elements
is one of the plurality of framing elements, wherein a shear force
as a function of deflection curve is substantially the same for the
prefabricated shear membrane with the opening and for the
prefabricated shear membrane without the opening.
22. The prefabricated shear membrane of claim 20, wherein the
opening is sized for a window or a door.
23. The prefabricated shear membrane of claim 15, wherein the
non-planar portion has a substantially v-shaped cross-section.
24. The prefabricated shear membrane of claim 15, wherein the
prefabricated shear membrane is a portion of a building panel, a
portion of a building wall, or a portion of a roof panel.
25. A building comprising the prefabricated shear panel of claim 15
and means for attaching the prefabricated shear panel to an
adjacent shear panel or to a foundation.
Description
RELATED APPLICATION DATA
[0001] This application is a divisional of application Ser. No.
10/074,684, filed on Feb. 11, 2002, the entire disclosure of the
prior application is considered as being part of the disclosure of
the present application and is hereby incorporated by reference
therein.
FIELD OF THE INVENTION
[0002] The present invention relates to devices and methods for
transmitting forces and dissipating and absorbing energy across
discontinuous structural elements. More particularly, the present
invention relates to a force-resisting device for transmitting
forces and dissipating and absorbing energy. The device includes at
least one active element; the active element configured to affect
the transmission, dissipation, and absorption functions by means of
controlled deformation.
BACKGROUND OF THE INVENTION
[0003] Building structures must be designed to safely withstand
forces that may be applied thereto. As construction techniques
improve, buildings are more capable of resisting loads that are
applied thereto. Examples of loads that may be applied to buildings
are those that result from earthquakes and windstorms. These forces
may resolve within a structure as tension, compression, shear,
torsion, or bending forces. Of the forces produced by such events
on a building, horizontal (or shear) loads are significant. These
horizontal forces attempt to shear (slide) the building off its
foundation. Additionally, horizontal forces that develop in an
upper story of a multiple story structure are transmitted to the
lowest story primarily as in-plane shear loads on the lower story
walls. In conjunction with shear forces, "uplift" or "overturning"
forces also result on the structure. These uplift/overturning
forces, generated in reaction to the moment of the shear force,
attempt to lift and rotate the walls of the structure about a lower
corner of the wall. In fabricating the structure, the structure
must be designed with sufficient "shear resistance" so that the
structure does not sustain excessive non-structural and/or
structural damage or collapse due to applied forces, potentially
resulting in extensive economic cost, serious injury or loss of
life. Shear resistance can be further defined as the ability of a
structure to absorb, dissipate, and transfer forces. To address the
need to build a structure having sufficient strength, uniform
building codes ("UBC's") provide required building practices
wherein the prescribed goal is life safety, but not necessarily to
retain the building as habitable after a natural disaster.
[0004] Damage caused by forces resulting from seismic and hurricane
events has exposed the need for improved force-resisting structures
and/or structural elements for both new building structures and for
retrofit into existing building structures.
[0005] Prior to the creation of the UBC's, early buildings were
constructed having little or no capability to resist shear forces,
uplift from foundations, and other loads. Walls of the structure
were generally constructed only of vertical frame members with
horizontal planks nailed across them. Later improvements included
the use of diagonal wood braces, or diagonal sub-planking in the
walls, with either shingles or some other outer layer to exclude
weather and provide a finished exterior. However, as understanding
of building performance in earthquakes and hurricanes continues to
improve, the necessity for better structural properties has become
more apparent and is being mandated by the UBC.
[0006] In general construction, the most common way of producing a
shear wall is to use plywood sheathing attached to a plurality of
vertical 2.times.4 or 2.times.6 inch wooden or metal framing
members. The plywood sheathing is attached to the framing members
with closely spaced nails/screws on the edges of the plywood panel.
The use of the plywood sheathing and specified fastening patterns
that are incorporated into all modern building codes has proven to
be a very successful method of producing a wall having shear
resistance. Analysis of damage caused in recent earthquakes, such
as the 1994 Northridge earthquake in California, illustrated that
in some cases, buildings built to the standards specified in the
California UBC survived rather well. However, there were a
substantial number of structural failures generally associated with
openings formed in shear walls and stress concentrations on
steel-frame building connections. Although, a building may remain
standing after an earthquake, it still may be rendered
uninhabitable due to non-structural and/or structural damage.
[0007] Problems caused by openings are twofold: stiffness reduction
and stress concentrations. First, openings dramatically reduce the
shear stiffness of the wall. For example, even comparatively small
window openings will reduce the shear stiffness sufficiently that
the wall can no longer be considered a continuous shear wall,
thereby increasing the effective aspect ratio of the wall, wherein
the aspect ratio is defined as the ratio of the height of the wall
H to the width of the wall W. When the aspect ratio of the wall is
increased, the overturning forces on the wall for the constant
overturning moment (where the moment is determined by story height
and shear force only) become higher and more localized.
[0008] Referring now to FIG. 1, there is illustrated an exemplary
embodiment of an isolated shear wall 10 illustrating the balance of
forces applied thereto. The force F is the shear force carried by
the shear wall at the top edge due to a loading event such as an
earthquake. The force must be reacted in shear at the foundation,
shown by the opposing force F at the bottom. The moment of F
relative to the foundation, equal to F multiplied by the story
height H, must be reacted by foundation vertical or overturning
forces A1, A2 (shown as discrete, but may be distributed near the
corners). The force A2 is particularly troublesome, as it is
tensile against the foundation, and is equal to (H/W).times.F. In a
case where there are adjacent additional structures, some of the
overturning moment may be carried by shear on the sides of the
shear wall 10, but eventually the entire overturning moment must be
reacted at the foundation by vertical forces, and those forces are
proportional to the panel aspect ratio H/W.
[0009] Referring now to FIG. 2A, there is shown an exemplary
embodiment of a shear wall 10 wherein an opening O has been formed
within the shear wall. As shown in FIG. 2A, the opening creates a
discontinuity in the force transmitting characteristics of the
shear wall, wherein forces that are normally carried across the
entire wall width W now must be carried across the reduced width
W'. The reduced width is less stiff and less strong, and the
opening corners also introduce panel stress concentrations that did
not previously exist. The corners A tend to crack open, and the
corners B tend to crush and buckle closed, under the direction of
force F' shown, as FIG. 2B shows. Therefore, the load carrying
stiffness and overall strength of this shear wall is substantially
reduced. In addition, if adjacent structures exist, they will be
caused to carry more forces because this panel is less stiff and as
a result takes up a smaller proportion of the forces.
[0010] To address the weakness created in shear walls due to
openings formed therein, there have been recent changes in the UBC.
The recent changes to the UBC have halved the maximum aspect ratio
of shear walls and shear wall segments so that the minimum width of
an 8 ft high shear wall has been increased from 2 ft. to 4 ft, for
a maximum aspect ratio of two.
[0011] Another problematic variable in the construction of a
building is the variations in construction quality, foundation
quality, and soil variability. Following the 1994 Northridge
earthquake, it was discovered that a large percentage of building
failures occurred as a result of poor field construction practice.
One study indicated that one third of the seismic safety items
installed were missing and/or improperly installed or poorly
implemented in over 40% of the structures surveyed.
[0012] Further still, it is important that structural elements
within the building structure have generally similar strength and
stiffness properties in order to share the applied loads. If every
structural element does not work together, this may lead to
excessive damage or failure of a structural element due to force
over-loading of the structural element, as opposed to load sharing.
There may be locations within a building structure wherein walls
having different stiffness/strength are joined together. For
example, a structure may be built with a concrete retaining wall,
wherein timber-framed shear walls may be joined to the poured
concrete retaining wall. Many times, during seismic events the
connection point of the two walls having different stiffness will
separate due to the difference in stiffness of the walls in
relation to the movement of the wall in response to the seismic
event. In addition, irregular placement of structural elements with
varying stiffness/strength characteristics can result in twisting
of the structure leading to additional torsional stresses and other
stress amplifications. Thus, there is a need for a device that will
transmit forces and dissipate and absorb energy across
discontinuous structural elements.
[0013] In addition to that above, another aspect to be considered
is the manner in which the UBC is interpreted by local building
inspectors. Often, building inspectors will make highly restrictive
interpretations of the building codes in an effort to promote
increased safety in building practices.
[0014] There have been numerous attempts to address increasing the
shear resistance of a structure where the structure includes a
number of discontinuities/openings formed in shear wall(s). One of
the most common methods of addressing the need to increase the
shear resistance of a structure has been to include a moment frame
in the design of the structure, whereby steel beams are rigidly
connected together such that any force applied to the structure
will be carried through the moment frame. A moment frame is
typically embodied as a large heavy steel structure designed to
transmit shear forces of the structure into the foundation or into
special footings formed in the foundation, via bending (or moment)
resistance of large steel members. However, a moment frame must be
specifically engineered for each application, thus adding
significant cost and complexity to the structure. In residential
construction, even a modest opening in a shear wall can require 6''
or 8'' steel girders weighing hundreds of pounds and the attendant
foundation reinforcement required to absorb the loads transmitted
thereto by the moment frame. The architect/builder must also
account for shipping and handling costs associated with the
installation of these heavy steel beams on the building site.
Further still, the use of a moment frame causes significant
problems with the insulating properties of the building, as the
metal beams act to conduct heat through the walls of the structure
to the interior of the structure, thus causing degradation of
insulation properties.
[0015] Although moment frames appear to be a solution, albeit
inefficient, to increase the shear resistance of a structure, there
are still shortcomings of the popular field welded-field bolted
beam-to-column moment frame connection. Observation of damage
sustained in buildings during the 1994 Northridge earthquake showed
that, at many sites, brittle fractures occurred within the
connections at very low levels of loading, even while the structure
itself remained essentially elastic (Federal Emergency Management
Administration Report 350). This type of connection is now not to
be used in the construction of new seismic moment frames. For
example, tests conducted by the Seismic Structural Design
Associates, Inc. (SSDA) have shown large stress and strain
gradients in moment frame joints/connections that exacerbate
fracture. To address these large concentrations of stress in the
corners, there has been much work attempting to improve the ability
of the corners of a moment frame to resist loads. One such
improvement to a corner connection is embodied in U.S. Pat. No.
6,237,303.
[0016] Another approach to structural reinforcement is to utilize a
pre-built shear wall such as the Simpson StrongWall.RTM.. The
StrongWall.RTM. is a pre-built shear wall that may be integrated
into a building structure. The StrongWall.RTM. is constructed of
standard framing materials and metal connectors. The
StrongWall.RTM. further includes a plurality of devices configured
to anchor the StrongWall.RTM. to a building foundation. The
StrongWall.RTM. must be connected to the framing of the structure
as well as to the foundation. Because the StrongWall.RTM. must be
connected to the structure's foundation, this requires special work
on the foundation prior to installation, thus rendering retrofit
application of the StrongWall.RTM. not cost effective. In addition,
the StrongWall.RTM. is delivered to a job site as a pre-built
panel, thus the architect/builder must account for shipping and
handling costs associated with the installation of these heavy
panels on the building site.
[0017] Shortcomings of both moment frames and StrongWalls.RTM. are
that both devices do not attempt to match the shear stiffness and
strength characteristics of the surrounding structure. Instead,
each device is designed without regard for the structure it will be
used within, and is generally designed to carry the entire shear
load of a wall or wall segment. As described above, a moment frame
is typically constructed of steel beams, wherein the beams are
rigidly connected together such that any force applied to the
structure will be carried through the moment frame and into the
foundation. The StrongWall.RTM. is designed in a similar manner,
wherein the StrongWall.RTM. attempts to be stronger than the
surrounding structure. Moment frames and larger StrongWalls.RTM.,
due to their size and weight, can be difficult to move around the
job site and install without the use of costly heavy equipment.
Both the moment frame and the StrongWall.RTM. significantly
increase the overall cost of the structure. Therefore there is a
need for a lightweight device that may be installed within or about
openings of a structure to maintain the properties of that
structure as a generally continuous element.
[0018] While the two devices described above may be readily
utilized in new construction there is still a need for devices that
may be utilized during structural retrofits, seismic or hurricane
upgrades, and/or remodels. For example, a homeowner may cut an
opening in a shear wall to place a new window or doorway. Many
times, these home retrofits are done without any consideration to
shear strength of the wall or obtaining a permit. Thus, when the
homeowner wishes to sell their house that includes these
"improvements", many times their homes will not meet code and
cannot be sold as is. What is therefore needed is a device that can
be readily adapted to retrofits to maintain the properties of the
structure as a generally continuous element after an opening has
been formed in the shear wall. There is also a need for an easily
manufactured, lighter, less complicated, more versatile,
adjustable, easier to install device for new construction.
SUMMARY OF THE INVENTION
[0019] The purpose of the present invention is to provide devices
and methods for structurally reinforcing a building element such as
a shear wall, while eliminating the high cost, complexity, weight
and handling problems of the prior art, while further allowing a
builder and/or architect to consider the entire wall as a generally
continuous shear wall, and to allow a structure to be designed
without having to consider any of the discontinuity problems
previously described. A further purpose is to eliminate the need to
repeatedly engineer solutions specific to particular
shear-resisting elements, openings and discontinuities in specific
buildings, and to allow the safe installation of windows and doors
in existing buildings without the need for extensive design,
structural reinforcement or engineered modifications.
[0020] To accomplish these purposes there is provided a
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure. The device includes at least one active element, the
active element having defined force versus deflection properties,
wherein the active element is configured to provide a load path
across a discontinuous structural element.
[0021] In one embodiment there is provided another force-resisting
device for transmitting forces and dissipating and absorbing energy
across a discontinuous structural element of a structure, the
device including at least one active element having at least a
first end and a second end, the active element having defined force
versus deflection properties and configured to transmit force and
dissipate and absorb energy, wherein the first end of the active
element is configured to be connected to a structure; and at least
one frame element disposed about a discontinuous structural
element, wherein the frame element is configured to be connected to
the second end of the active element, the active element and the
frame element configured to resist forces and reduce stresses and
replace stiffness, dissipation, and strength to the structure.
[0022] In a further embodiment there is provided yet another
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure, the device including at least one active element having
at least a first end and a second end, the active element having
defined force versus deflection properties and configured to
transmit force and dissipate and absorb energy, wherein the first
end of the active element is configured to be connected to a
structure. The force-resisting device further includes at least one
frame element configured to be connected to a discontinuous
structural element, the frame element is configured to be connected
to the second end of the active element, wherein the active element
and the frame element configured to resist forces applied to the
structure by transmitting forces across the discontinuous
structural element.
[0023] In a further embodiment there is provided yet another
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure, the device including at least one active element having
at least a first end and a second end, the active element having
defined force versus deflection properties and configured to
transmit force and dissipate and absorb energy, wherein the first
end of the active element is configured to be connected to a
structure, and at least one reinforcement element, the
reinforcement element configured to be connected to a structure.
The force-resisting device further includes at least one frame
element configured to be disposed about a discontinuous structural
element, wherein the frame element is configured to be connected to
the second end of the active element, the active element, the frame
element, and the reinforcement element configured to resist forces
applied to the structure by transmitting forces across the
discontinuous structural element and further configured to reduce
stresses and replace stiffness, dissipation, and strength to the
structure.
[0024] In still another embodiment there is provided a method of
restoring the stiffness, energy dissipation capacity, and strength
of a structure containing a discontinuous structural element, the
method including the step of: transmitting forces across the
discontinuous structural element, thereby providing load sharing
across the discontinuity.
[0025] In a further embodiment there is provided a method for
selecting a force-resisting device, the device configured to
transmit loads and to dissipate and absorb energy, the method
including the steps of; selecting a structural element to be
reinforced; selecting a design configuration of a force-resisting
device containing at least one active element; selecting a design
configuration for the active element; building a computer generated
finite element model of the force-resisting device with at least
one degree of freedom for transmitting force and dissipating and
absorbing energy; and using the computer generated finite element
model in a finite element analysis program to iterate the design of
the active element to produce defined force versus deflection
properties.
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] Features and advantages will become apparent from the
following and more particular description of the preferred
embodiments of the invention, as illustrated in the accompanying
drawings, and in which like reference numerals generally refer to
the same parts or elements through-out the view, and in which:
[0027] FIG. 1 is an elevational view of an exemplary shear wall
illustrating the balance of forces applied thereto.
[0028] FIG. 2A is an elevational view of an exemplary shear wall
including an opening formed therein illustrating the reduction of
load bearing width.
[0029] FIG. 2B is an elevational view of an exemplary shear wall
including an opening formed therein illustrating the concentration
of stresses in the corners of the opening;
[0030] FIG. 3 is an elevational view of the backside of an
exemplary shear wall illustrating the stud framing and sheathing
attached thereto.
[0031] FIG. 4A is an elevational view of an exemplary embodiment of
the force-resisting device in accordance with the present
invention.
[0032] FIG. 4B is an elevational view of an exemplary embodiment of
the force-resisting device according to the present invention.
[0033] FIG. 5 is a sectional perspective view of an exemplary
embodiment of a force-resisting member of the force-resisting
device, taken about line A-A of FIG. 4B, which contains an active
element according to the present invention.
[0034] FIG. 6 is an exaggerated deformation and color-coded
sheathing shear stress display of a computer simulation of an
exemplary shear wall undergoing deflection due to a shear force
applied thereto.
[0035] FIG. 7 is an exaggerated deformation and color coded
sheathing shear stress display of a computer simulation of an
exemplary shear wall having an opening formed therein, wherein the
shear wall is undergoing deflection due to a shear force applied
thereto.
[0036] FIG. 8 is a display of a computer model of an exemplary
shear wall illustrating schematically the force-resisting device
according to the present invention as disposed about the periphery
of an opening formed within the shear wall.
[0037] FIG. 9 is an exaggerated deformation and color-coded
sheathing shear stress display of an exemplary shear wall having an
opening formed therein and the force-resisting device disposed
thereabout, wherein the shear wall is undergoing deformation due to
an applied force.
[0038] FIG. 10 is a graph illustrating the shear load versus
deflection properties of an exemplary shear wall, an exemplary
shear wall having an opening, and an exemplary shear wall including
the force-resisting device according to the present invention.
[0039] FIG. 11 is a sectional perspective view of a computer model
of a portion of an exemplary embodiment of a force-resisting member
of the force-resisting device, taken about line A-A of FIG. 4B,
including an active element according to the present invention.
[0040] FIG. 12 is a true scale deformation and color coded stress
display of a computer simulation of an exemplary embodiment of a
force-resisting member of the force-resisting device including the
active element undergoing progressively plastic compression due to
an applied force.
[0041] FIG. 13 is a true scale deformation and color-coded stress
display of a computer simulation of an exemplary embodiment of a
force-resisting member of the force-resisting device including the
active element undergoing progressively plastic deformation in
tension.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Definitions
[0042] As used herein the following terms are to be understood to
be defined as described below. "Load sharing" shall be understood
to define the carrying of a total load by some division among more
than one load-bearing element. For example, parallel load bearing
elements carry load in proportion to their stiffness, while series
load bearing elements carry full load (i.e., do not share
load).
[0043] "Transmit" shall be understood to define the capacity of an
element to withstand applied forces and to react them from one
location to another, according to the laws of mechanics,
specifically force equilibrium. Transmission of forces of an
element within a system always depends on its geometric
configuration and its strength capacity relative to the force
magnitude to be transmitted, and in some instances on its
stiffness.
[0044] "Load path" shall be understood to define a route for load
to be transmitted.
[0045] "Dissipation" shall be understood to define a process of
conversion of energy from an undesirable motion form permanently
and irreversibly to a benign form, which as one example involves
converting mechanical work energy (force acting over a distance)
into plastic strain energy of a material, and subsequently heat
energy. Dissipation is effected by mechanical damping and
plasticity, and can be used to reduce maximum deflection of
structures subjected to external forces.
[0046] "Absorption" shall be understood to define a process of
conversion of energy from an undesirable motion form reversibly and
temporarily to a benign form, which as one example involves
converting mechanical work energy (force acting over a distance)
into elastic strain energy of a material, which can be later
restored. Such absorption is affected by mechanical stiffness or
springs, and can be used to reduce maximum deflection of structures
subjected to external forces.
[0047] "Force resisting" shall be understood to define the ability
of a device to transmit structural forces, to dissipate energy by
some means, and to absorb energy by some means, in some absolute
magnitude and relative proportion.
[0048] "Shear wall" shall be understood to define a structure
capable of resisting shear forces, the shear wall being constructed
of framing members having a sheathing material disposed thereon.
The framing members may be constructed of wood, metal or similar
materials.
[0049] "Active element" shall be understood to define a
load-bearing element with defined load versus deflection properties
that may be designed by engineering analysis in one or more
directions or degrees of freedom. The active element is a device
configured to deflect or distort in a controlled manner under
load.
[0050] "Finite element analysis" shall be understood to include the
use of a computer model based on the finite element mathematical
method to predict reaction forces, deformations, stresses, and
strains of a structure in response to applied forces or enforced
displacements.
[0051] "Discontinuous structural element" is herein defined as any
load bearing structure or portion of load bearing structure that
has some feature within it that makes the structure's force
transmitting, stiffness (absorbing), dissipating, absorbing, or
strength characteristics non-uniform, and results in a change of
load sharing within the structure, influences the proportion of
load shared by the structure relative to adjacent structures, or
causes stress concentrations in the structure. Examples of features
that cause discontinuous structural elements are door and window
openings, localized overly stiffened structural elements, coupled
structural elements with different stiffness properties,
asymmetrical building configurations, locations in a structure
where relative movement of adjacent parts may occur during a
loading event, or other similar features.
[0052] "Generally continuous shear wall" shall be defined as a
shear wall that behaves substantially the same as a continuous
shear wall at its edges, i.e., load versus deflection, stiffness,
and dissipation characteristics are similar, despite the presence
of discontinuities within it.
[0053] "Drift" shall be understood to define the amount of
deflection or movement of a shear wall or structural element due to
a load applied thereto.
[0054] "Retrofit" shall be understood to include remodeling,
reconstruction, structural upgrading, strengthening, fabrication of
shear walls, or similar constructions processes.
[0055] The present invention provides devices and methods for
maintaining the strength, stiffness (absorption), and dissipation
properties of a structure, wherein said properties have been lost
due to an opening or other discontinuity formed within the
structure. In the case of an opening, the force-resisting device of
the invention transmits the forces and dissipates and absorbs
energy at the edge of the opening in such a manner that the
exterior edges of the structure into which the opening is cut
behave under shear load substantially as if there were no opening
formed in the structure. As utilized herein, it shall be understood
that the term structure is intended to refer to the entire building
structure or to a portion of the entire building structure, such as
a shear wall.
[0056] The device in accordance with one exemplary embodiment
includes a lightweight force transmitting and energy dissipating
and absorbing force-resisting device that may be disposed about an
opening formed in a shear wall. The force-resisting device contains
active elements that have defined force versus deflection
properties, which may be designed by engineering analysis, such
that the forces developed about the opening due to shear on the
wall are transmitted around the opening. By designing the proper
force-resisting device and active elements, the stress
concentrations at the periphery of the opening are mitigated so
that the strength of the structure is substantially the same as if
an opening had not been formed within the wall, thereby enabling a
shear wall having an opening formed therein to behave as a
generally continuous shear wall.
[0057] Referring now to FIG. 3, there is shown a shear wall 10. The
shear wall 10 as shown FIG. 3 includes, a four-foot by eight-foot
plywood sheathing panel 12, and a plurality of two inch by
four-inch studs 14 disposed about the periphery of the panel. The
shear wall 10 as shown in FIG. 3 mimics a typically constructed
shear wall in a structure such as a private home. It shall be
understood that the shear wall 10 illustrated in FIG. 3 shall be
understood as being exemplary; the shear wall may be constructed of
metal framing having a plywood panel disposed thereon. Furthermore,
it is contemplated that other engineered materials may be utilized
for both the framing elements as well as the sheathing
material.
[0058] Referring now to FIG. 4A there is shown an exemplary
embodiment of the force-resisting device 100 in accordance with the
present invention. As shown in FIG. 4A, the force-resisting device
100 includes an active element 130 disposed within a
force-resisting member 120. The force-resisting member 120 may
further include a plurality of apertures 129 disposed adjacent to
the active element 130, wherein the apertures are configured to
receive connection means for connecting the active element to a
structure. Still further, the force-resisting device may include a
frame element 90, wherein the frame element 90 may be coupled to
the force-resisting member 120. As shown in FIG. 4A, the active
element has defined force versus deflection properties, wherein the
active element is configured to provide a load path across a
discontinuous structural element.
[0059] Referring now to FIG. 4B, there is shown an alternative
exemplary embodiment of the force-resisting device 100 in
accordance with the present invention. As shown in FIG. 4B, the
force-resisting device includes at least one active element 130;
the active element disposed within a force-resisting member 120, at
least one frame element 90, and at least one reinforcement element
110. As shown in FIG. 4B, the force-resisting device 100 is shown
as being configured to be disposed about a discontinuous structure,
such as an opening formed in a structure. It shall be understood
that the reinforcement element 110 may be fixedly attached to the
opening periphery utilizing suitable known means such as screws,
bolts, glues, or nails. Additionally, the reinforcement element 110
may be fixedly connected to an end of the force-resisting members
120 through the use of fastening means such as those above. Further
still, it is contemplated that the reinforcement element 110 and
the force-resisting member 120 may be formed as a unitary member.
It is also contemplated that the reinforcement element 110 and the
force-resisting member 120 may not be connected directly, but may
be individually connected to the shear wall adjacent to the
opening, or to some intermediate members, or to a mounting frame
disposed about the periphery of the opening. The force-resisting
device 100 as shown in FIG. 4B and described above is shown as
being configured to be disposed about an opening, therefore the
force-resisting device includes at least four force-resisting
members 120 and at least four reinforcement elements 110.
Additionally, as shown in FIG. 4B, the frame elements 90 are
configured to be disposed about the periphery of the opening
thereby forming a frame 99. The force-resisting members 120 and/or
the reinforcement elements 110 are attached at one side, to the
opening periphery either directly or indirectly, and at the other
side to the frame 99 or a structure disposed about the opening, so
that forces can be transmitted across the opening.
[0060] Frame elements 90 or frame 99 may be configured having a
variety of structural properties. For example, the frame 99 or the
frame elements 90 may be made sufficiently rigid such that any
forces applied to the frame will be transmitted with little
deflection. Alternatively, the frame 99 may be configured to be
"soft" or flexible, thus, the frame 99 can be configured to
function as an additional active element in conjunction with the
other active element(s) embodied in the force-resisting device 100
in accordance with the present invention. It is further
contemplated that the geometry of the frame 99 may be adjusted such
that the frame 99 includes a plurality of active elements formed
therein. For example, the frame may be constructed including
multiple "active folds." It shall be understood that the reference
to active folds above should not be considered limiting and that
other geometries and embodiments of the active element as described
herein may be embodied in the frame 99 or frame elements 90.
[0061] The frame 99 may be further configured to include mounting
area(s) to receive and retain elements, such as windows and doors.
The frame 99 may be configured to receive windows or doors in
different manners. For example, the mounting area may include a
soft and resilient interface to allow the force-resisting device,
including window or doorframe, to flex as needed, and allow the
window or door to float within the frame. Second, the mounting
frame may be rigid to keep deflections so low that the window or
door are not loaded even if fixedly connected to the frame, while
the active element(s) sustains all the deflection. Still further,
these mounting areas can be used to provide accurate openings into
which the doors and windows could be fitted without the
conventional use of shims, thus cutting down installation time and
adjustment and reducing the risk of distortion of window and door
frames by improper installation or subsequent settling of the
building. This aspect of the invention is especially valuable in
the case of vinyl-framed doors and windows, which are comparatively
soft, and easily distort. Incorporating a mounting frame within the
force-resisting device 100 provides an additional benefit of
reducing air gaps around the window or door openings that may lead
to energy loss. Yet another benefit of forming a door or window
frame within the force-resisting device 100 is that this not only
provides the advantages previously mentioned, but also distributes
any loads from attempted forced entry directly into the structure
of the wall containing the opening, thus providing greatly enhanced
security for openings, as opposed to conventional door/window
frames, which are simply nailed into the rough framing of the
building. An additional safety function is also introduced by
providing a proper mounting for doors and windows, therefore the
likelihood of a window shattering or a door becoming stuck or
jammed due to forces applied during an earthquake is reduced
because the device according to the present invention transmits
force about the opening thereby reducing the amount of force
applied to the windowpanes and/or door.
[0062] The function of the invention may be achieved with less
hardware than shown in the exemplary embodiments of FIGS. 4A and
4B. It is contemplated that the force-resisting device according to
the present invention may function with a single active element,
provided the active element is attached at a first end to the
opening periphery and at a second end to some structure that reacts
the forces transmitted through the active element to some other
location about the opening. For example, the device of FIG. 4B
could be reduced to a single force-resisting member at the left
side which is attached at one end to the left side of the opening
and at the other end to an "L" shaped frame along the left and top
of the opening, which is in turn rigidly fixed by some means to the
opening periphery along the top. In this case, load is transmitted
from the left side of the opening, through the active element,
through the frame, to the top edge of the opening (not through a
second active element). However, for best load distribution, stress
control, and simplicity, symmetrical configurations using two
opposing or all four opening sides of a rectangular opening (or
configured similarly about a non-rectangular opening) are
preferred.
[0063] The reinforcement element 110 and the force-resisting member
120 as shown in FIGS. 4A and 4B may be constructed of materials
such as steel, stainless steel, aluminum, copper, brass, titanium,
or other metals. It is further contemplated that the reinforcement
element 110 and the force-resisting member 120 may be constructed
of engineered composite materials such as fiberglass, carbon fiber,
graphite, Spectra.RTM., or similar composite materials. Still
further, it is contemplated that the reinforcement element and the
force-resisting member may be constructed of a combination of any
of the materials listed above and other materials not listed. It
shall be understood that the list of materials above is merely
exemplary and should not be considered limiting in any manner; it
is contemplated that other materials not listed may be utilized in
the construction of the reinforcement element or the
force-resisting member in accordance with the present
invention.
[0064] Although the force-resisting device 100 is illustrated in
FIG. 4B as being formed of multiple reinforcement elements and
force-resisting members, which are then assembled, it is
contemplated that the force-resisting device according to the
present invention may be constructed as a unitary member.
Furthermore, although the present invention has been illustrated as
being disposed about a window opening formed within a shear wall,
it is contemplated that the force-resisting device 100 according to
the present invention may be utilized around any type of opening or
structural discontinuity. For example, in a door or hallway opening
where there is no remaining shear panel along the lower edge of the
opening, loads may be transferred across the bottom of the opening
through the use of a structural sill plate or by utilizing an
existing sill plate, if the existing sill plate is capable of
transmitting the applied loads. In some cases, with proper design
of the side and top of the force-resisting device, it will also be
feasible to eliminate the bottom element altogether. Further still,
if the foundation has mechanical properties sufficient to carry the
appropriate forces, the vertical elements of the force-resisting
device 100 may be attached to the foundation.
[0065] Referring now to FIG. 5 there is shown a sectional
perspective view of an exemplary embodiment of the force-resisting
member 120 in accordance with the present invention. As shown in
FIG. 5, force-resisting member 120 includes the active element 130
formed within an elongated member 122, the elongated member 122
having a first end 123, a second end 124, the active element 130
having defined force versus deflection properties in the X and Y
directions, such that the active element is configured to provide
load sharing across a discontinuous structural element. The active
element 130 as shown in FIG. 5 is shown as being embodied as an
"active fold" formed within the elongated member 122 and disposed
between the first end 123 and the second end 124, and formed
between the edges of the elongated member 122. As shown in FIG. 5,
the first surface 125 and second surface 126 adjacent to either
side of the active element 130 are substantially parallel to each
other, but they need not be. Further still, it is contemplated that
the force-resisting member 120 may further include apertures 129
disposed through the substantially horizontal portions 128 of the
elongated member adjacent to the active element 130.
[0066] Although the active element is described and shown as being
an "active fold" it is contemplated that other geometries and
mechanical structures could be utilized. For example, the active
element may comprise any one of the following devices individually
or in any combination thereof. Examples of such active elements
are: at least one cutout, a single slot, a plurality of slots
(where in all cases the remaining material is the active element),
a plurality of folds, a plurality of pins and engaging members
(where the pins or engaging members deflect/distort), or an
aperture having a web disposed thereacross (where the web
deflects/distorts). It shall be further understood that the
examples above are merely exemplary and should not be considered
limiting in any manner. Any geometry and combination(s) of
materials can be used for the active element that generates a
useful force versus deflection property when loaded in one or more
directions.
[0067] The active element 130 may be formed within the elongated
member 122 utilizing known manufacturing processes such as
pressing, bending, casting, cutting, or other methods suitable for
the material used. The force-resisting member 120 and active
element 130 in accordance with the present invention may be
constructed of materials such as those listed above with regard to
the reinforcement element 110, or combinations of more than one
material. Under certain conditions, it may desirable to further
tune the force versus deflection properties of the active element
130. The force versus deflection properties of the active element
130 can be tuned by increasing/decreasing the height of the active
element, providing multiple active elements within the elongated
member 122, adjusting the geometry of the active element(s),
varying the material thickness of the active element and/or of the
elongated member 122, or other variations. For example, it may be
desirable to provide more energy dissipation or absorption under
greater earthquake forces that result in overall building
deflections greater than the two inches required by the code. The
active element 130 may produce force versus deflection properties
under tension and compression in direction X and opposing senses of
shear in direction Y as the building will sway back and forth under
earthquake loads producing an oscillating response.
[0068] It shall be understood that the principle of the active
element 130 may be incorporated into any other type of structural
building connector wherein the connector is designed to transmit
forces and dissipate/absorb energy. For example, at least one
active element may be incorporated into building connectors adapted
to attach two portions of a structure having dissimilar modulus or
stiffness, such as a concrete wall to a timber framed structure.
Alternatively, active element 130 may be embodied within a corner
force-resisting device (not shown) on a shear wall. The corner
force-resisting device may be connected to the framing members and
the top or bottom plate of the shear wall. The corner
force-resisting device may be designed so that as forces are
imposed at a joint during a loading event, the corner
force-resisting device transmits force and dissipates/absorbs
energy via a defined force versus deflection property, which may be
designed by engineering analysis. Depending on the structural
location of the application in a building or structure, the force
versus deflection property may be designed for differing absolute
and relative levels of stiffness and dissipation. It shall be
understood that the building connectors above are merely exemplary
and should not be considered limiting in any manner; it is
contemplated that other building connectors not listed may be
utilized wherein the connector is designed to transmit forces and
dissipate/absorb energy. Such benefits can be obtained at any
location in a structure where relative movement of adjacent parts
may occur during a loading event.
[0069] Referring now to FIGS. 6-9, there are shown computer models
and color coded results of computer simulations of an exemplary
shear wall with and without the force-resisting device according to
the present invention undergoing "drift" (deflection) in response
to in-plane shear forces as in an earthquake. FIGS. 11-13 show
computer models and color coded results of computer simulations of
the active element 130 undergoing deformation due to force
application. The analysis results presented in FIGS. 6-13 are
provided to aid in understanding of the function of the invention,
and are not to be considered limiting in any way.
[0070] Referring now to FIG. 6 there is shown an exemplary shear
wall 200 undergoing drift due to an applied shear force. In each of
the displays illustrated in FIGS. 6, 7, and 9, the drift was
restricted to two inches maximum because two inches of drift is a
requirement generally accepted by present building codes for an
eight-foot high wall, and the deflection is exaggerated for viewing
clarity. As shown in FIG. 6, for a solid plywood shear wall, loaded
to produce the maximum code allowable two inches of drift requires
a force of approximately 9855 pounds to be applied to the shear
wall. Additionally, as shown in FIG. 6, the stresses within the
solid shear wall sheathing are distributed smoothly throughout the
panel and around the periphery of the shear wall.
[0071] Referring now to FIG. 7, there is shown the shear wall 200
wherein an opening or discontinuity has been formed therein. The
opening formed within the shear wall models a typical window
opening of about 30 inches.times.30 inches. As shown in FIG. 7, the
center portion 250 adjacent to the opening 240 deflects greatly due
to the applied load. As shown, the shear wall deflects the allowed
two inches when only 2807 pounds have been applied to the shear
wall. Thus the load resisting capacity of the shear wall 200 is
reduced by a factor of almost four. Furthermore, as shown in FIG.
7, the opening also produces extreme concentration of stresses in
the corners of the opening as can be evidenced by the red stress
pattern indicators 280.
[0072] Referring now to FIG. 8, there is shown the backside of the
model of the shear wall 200. As shown in FIG. 8, the
force-resisting device 100 of the present invention has been
disposed about the periphery of the opening 240 formed within the
shear wall 200. The force-resisting device 100 includes, in this
case, four force-resisting members 120 in communication with the
periphery of the opening, wherein each of the force-resisting
members are configured to restore stiffness and dissipation
capacity to the shear wall by transferring forces about the
periphery of the opening/discontinuity through controlled
deformation of the active elements. It shall be understood that the
active element may be configured to deform plastically,
elastically, or in any combination thereof. For example, the active
element may initially deform elastically, then as loads increase
deform plastically until a predetermined amount of deformation has
occurred, then deform elastically again, or the active element may
act in a progressive elastic or plastic manner.
[0073] As shown in FIG. 8, the force-resisting device 100 includes
two horizontal force-resisting members 120 and two vertical
force-resisting members 120. The force-resisting members 120 each
include an active element as described in detail above with
reference to FIGS. 4A, 4B and 5. Further still, the horizontal
and/or vertical force-resisting members 120 are attached to the
plywood panel 12 utilizing fasteners such as screws, bolts, glues,
rivets or similar products disposed through the apertures formed in
one end portion of the elongated member(s) 122. In addition to
being attached on one end to the shear wall, a second end of the
force-resisting members 120 may be attached to the frame 99,
wherein the frame 99 may be configured as described above. It is
further contemplated that the force-resisting device 100 in
accordance with the present invention may comprise a mounting
device configured to be disposed peripherally about an opening. In
a preferred embodiment the mounting device is formed as a unitary
member including at least four corner elements and elongated plate
members extending therebetween. The mounting device configured to
be affixed to the shear wall and to receive at least one
force-resisting member 120 thereon. It is further contemplated that
the mounting device may be integrally formed with the frame 99 and
the force-resisting member 120.
[0074] The force-resisting member including the active element is
designed to implement the desired known force versus deflection
properties of the active element. This allows the engineer to
select and design the proper active element that will provide load
sharing across a discontinuity formed in the shear wall such that
the shear wall including the force-resisting member performs
substantially as if no opening existed in the shear wall. This
allows an engineer to "tune" the building such that all of the
shear walls behave in a similar manner so that a force
concentration is not created in any portion of the building that
could lead to failure of the building.
[0075] As embodied in the present invention and illustrated in the
sample computer simulation figures, the active element is
configured to undergo deformation, thus carrying the loads from the
edge of the plywood panel opening in tension and compression across
the active element and at the same time absorbing and dissipating
energy. This particular modeled design uses steel of the requisite
shape and thickness, but it is obvious to one skilled in the art
that a wide range of materials and configurations in many
combinations can be employed to produce suitable force/deflection
properties.
[0076] Referring now to FIG. 9, there is shown the modeled shear
wall undergoing drift due to a shear force applied thereto. As
shown in FIG. 9, to achieve two inches of drift in the shear wall
200 including the force-resisting device 100 designed for this size
opening, in this size and configuration shear panel, requires
10,705 lb for force. Comparing this to FIGS. 6 and 7 it can be seen
that the shear wall including the opening 240 and the
force-resisting device 100 behaves substantially like the shear
wall 200 as shown in FIG. 6 with no opening. That is, with the
force-resisting device 100 disposed about the periphery of the
opening the shear wall including the opening functions in nearly
the same manner as that of a solid shear wall, i.e., it transmits
substantially similar shear force for a given deflection, and the
stresses in the panel are not concentrated and do not result in
premature failure. This can be better understood with reference to
the graph shown in FIG. 10.
[0077] Referring now to FIG. 10 there is shown a graph illustrating
the performance of the shear wall 200 shown in FIGS. 6-9. As shown
in the graph in FIG. 10, the present invention when disposed about
an opening formed in a solid shear wall replaces all of the lost
stiffness and dissipation capacity of the solid panel. It will be
appreciated that the force versus deflection properties of the
invention can be adapted to suit a wide range of plywood thickness
and other shear panel and sheathing material characteristics. The
exemplary shear wall modeled in FIGS. 6-9 was modeled to replicate
1/2'' Douglas fir plywood shear wall sheathing as this is typical
of materials used in conventional building practice. Referring now
to the graph illustrated in FIG. 10, there is shown three separate
load versus deflection characteristic lines. The first line 400
illustrates the load versus deflection characteristics of the solid
shear wall of FIG. 6, and the second line 500 illustrates the load
versus deflection characteristics of the shear wall including a 30
inch by 30 inch window opening as illustrated in FIG. 7. As can be
seen by the difference between line 400 and line 500 the creation
of the opening within the solid shear wall drastically reduces the
load bearing capacity of the shear wall. Referring now to line 600,
there is shown the load versus deflection characteristics of the
shear wall including the 30.times.30 inch opening and the
force-resisting device 100 in accordance with the present invention
disposed about the periphery of the opening. As shown in the graph
of FIG. 10, the present invention restores the shear capacity of
the shear wall such that the shear wall including the present
invention and a 30.times.30 inch opening formed therein performs
substantially similar to a solid shear wall. Thus, it can be seen
that the force-resisting device is configured to resist forces and
reduce stresses and replace stiffness, dissipation, and strength to
the structure such that the structure behaves substantially as if a
discontinuous structural element has not been formed therein.
[0078] Thus it can be seen with reference to FIGS. 4B, 6-10 in
accordance with the present invention there is provided a
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure by providing at least one active element having at least
a first end and a second end, the active element having defined
force versus deflection properties and configured to transmit
forces and dissipate and absorb energy, wherein the first end of
the active element is configured to be connected to a structure.
The force-resisting device further includes at least one frame
element disposed about a discontinuous structural element, wherein
the frame element is configured to be connected to a second end of
the active element, the active element and the frame element
configured to resist forces and reduce stresses and replace
stiffness, dissipation, and strength to the structure.
[0079] Thus it can be seen with reference to FIGS. 4B, 6-10 in
accordance with the present invention there is provided a
force-resisting device for transmitting forces and dissipating and
absorbing energy across a discontinuous structural element of a
structure by providing at least one active element having at least
a first end and a second end, the active element having defined
force versus deflection properties and configured to transmit
forces and dissipate and absorb energy, wherein the first end of
the active element is configured to be connected to a structure.
The force-resisting device further includes at least one frame
element connected to a discontinuous structural element, the frame
element is configured to be connected to a second end of the active
element, wherein the active element and the frame element
configured to resist forces applied to the structure by
transmitting forces across the discontinuous structural
element.
[0080] Additionally, it can be further seen with reference to FIGS.
4B, 6-10 in accordance with the present invention there is provided
a force-resisting device for transmitting forces and dissipating
and absorbing energy across a discontinuous structural element of a
structure by providing at least one active element having at least
a first end and a second end, the active element having defined
force versus deflection properties and configured to transmit
forces and dissipate and absorb energy, wherein the first end of
the active element is configured to be connected to a structure,
and at least one reinforcement element, the reinforcement element
configured to be connected to the structure. The force-resisting
device further includes at least one frame element disposed about a
discontinuous structural element, wherein the frame element is
configured to be connected to a second end of the active element,
the active element, frame element, and reinforcement element
configured to resist forces applied to the structure by
transmitting forces across the discontinuous structural element and
are further configured to reduce the stresses and replace
stiffness, dissipation, and strength to the structure.
[0081] Thus it can be seen with reference to FIGS. 4B, 8, 9, and 10
in accordance with the present invention that there is provided a
method for restoring stiffness, energy dissipation capacity, and
strength of a structure containing a discontinuous structural
element by transmitting forces across the discontinuous structural
element, thereby providing load sharing across the
discontinuity.
[0082] It will be appreciated by one skilled in the art that the
large number of calculations required to produce an active element
having accurately known force versus deflection properties over the
entire working deflection range requires the use of a finite
element analysis (FEA) computer program capable of iterative
calculations to optimize the performance of the active element. An
example of such a program is ANSYS, available from ANSYS, Inc. in
Houston, Pa. While it is true that the active element can be
designed without the use of a computer, to properly optimize the
design would require an overly excessive number of calculations and
would not be accurate. Therefore, the use of a computer model in a
finite element analysis program is the preferred embodiment.
[0083] Thus it can be seen with regard to FIG. 10 there is provided
a method for selecting a force-resisting device, the
force-resisting device being configured to transmit loads and to
dissipate and absorb energy by selecting a structural element to be
reinforced and selecting a design configuration of a
force-resisting device, the force-resisting device including at
least one active element and selecting a design configuration for
the active element, then building a computer generate finite
element model of the force-resisting device with at least one
active element having at least one degree of freedom for
transmitting force and dissipating and absorbing energy, and using
the computer generated finite element model in a finite element
analysis program to iterate the design of the active element to
produce defined force versus deflection properties.
[0084] Referring now to FIGS. 11-13 there is illustrated a color
computer simulation simulating the forced response of the modeled
sample active element in accordance with the present invention.
[0085] Referring now to FIG. 11, there is shown a perspective view
of a section of an exemplary force-resisting member 120 including
the active element 130, wherein no force has been applied. The
active element 130 being defined by three bend points 141, 142, and
143.
[0086] Referring now to FIG. 12, there is shown a sectional view of
an exemplary model of a force-resisting member 120 and the active
element 130 wherein a force has been applied to the force-resisting
member 120 in the X direction of FIG. 5. As shown in FIG. 12, the
active element undergoes compression resulting in localized elastic
and plastic bending primarily at the three pre-bent points 141,
142, and 143. The elastic bending effects energy absorption and the
plastic bending effects energy dissipation, while the geometry and
size of the active member provides for the ability to transmit
sufficient load to be effective without material failure. Also, to
avoid failure, a ductile metal is used for this case.
[0087] Referring now to FIG. 13, there is illustrated a
cross-sectional view of an exemplary model of a force-resisting
member 120 wherein a tension force has been applied thereby causing
the active element 130 to elongate. By elongating as shown in FIG.
13, the active element is subjected again to localized elastic and
plastic bending primarily at the three pre-bent points 141, 142,
and 143, resulting in absorption, dissipation, and load
transmitting effects similar to the compression case.
[0088] As the active element undergoes compression or tension as
illustrated in FIGS. 12-13, the active element behaves in a general
manner similar to that of the materials of which the shear wall has
been constructed. That is, the force-resisting device 100 according
to the present invention is not intended to create a rigid
non-yielding structure within the shear wall; instead the active
element is configured to behave in a progressively plastic manner
similar to the natural behavior of the surrounding plywood panel
structure and to not create an overly stiff portion which would
cause the forces to become concentrated therein.
[0089] It will be appreciated that different elements of the
invention can be manufactured in many ways, either stamped, rolled
or bent from one or more pieces of steel or other material,
produced with separate reinforcement elements as in the embodiment
shown. It can be made of non-metal materials such as engineered
plastics and engineered wood-based products or other engineered
materials either alone or in combination with any of the materials
listed above in conjunction with steel and other materials as long
as the force versus deflection properties are as desired. Use of
different materials can also allow reduced heat transmission; it is
often desirable to reduce heat loss through doors and windows to
increase the energy efficiency of the structure. Use of different
materials and combination of materials can also facilitate
installation, by mechanical fasteners, gluing or bonding,
interlocking or capture between studs and shear panels or other
elements of the adjacent structure or other fastening means. It
shall be appreciated that the force-resisting device in accordance
with the present invention may be utilized for new building
construction or for retrofits by providing a lightweight device
that may be easily adapted for use within different areas or
portions of a structure.
[0090] The implementation of force-resisting devices for different
size openings or different discontinuity features in different
configurations of shear walls may be done without changing the
design or geometry of the active element by using tailored specific
lengths of the same force-resisting elements on one or more sides
of the opening or discontinuity.
[0091] The implementation of force-resisting devices for different
size openings or different discontinuity features in different
configurations of shear walls may be done by varying the active
element design, by using tailored specific X and Y directional
force-resisting behavior on one or more sides of the opening or
discontinuity. For example, in some cases, suitable force-resisting
devices can be developed using only vertical side force-resisting
members with no horizontal top and bottom force-resisting members,
provided the Y or vertical direction stiffness of the remaining
vertical members is high in proportion to the X or horizontal
direction stiffness, such that the assembly does not rotate
appreciably under load.
[0092] The implementation of force-resisting devices for different
size openings or different discontinuity features in different
configurations of shear walls may be augmented by using the frame
99 or frame elements as an additional active element. For example,
the frame itself may be designed to dissipate energy by plastic
deformation in addition to stiffness and ability to transmit
forces. This would in most cases require the window or door in the
frame to be mounted resiliently to avoid damage.
[0093] Although the present invention has been described in detail
with regard to resisting lateral or in-plane forces, as will be
appreciated by one having ordinary skill in the art, the
force-resisting device according to the present invention is also
applicable to substantially horizontal perpendicular loads and/or
rotational loads which may be applied to a structure.
[0094] Although the present invention has been described with
reference to specific embodiments, it shall be understood that this
should not be considered limiting in any manner. Without departing
from the spirit and scope of this invention, one of ordinary skill
in the art can undertake various changes and modifications to the
present invention to adapt it to various usages and conditions. As
such, these changes and modifications are intended to be within the
full range of equivalence of the following claims.
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