Note: Descriptions are shown in the official language in which they were submitted.
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WA~L _~P_ORT BRACE
Backqround of the Invention
I. Fiel of the Invention
The present inVentiOn relates generally to elongated
support braces which are secured across a plurality of parallel
joists in a wall structure to resist the tendency of t~e wall
structure to rack under load, and more particularly, to such
a brace which is ernbedded in aligned narrow channels cut trans-
versely into the front surface of each of the plurality of par-
allel trusses.
II Description of the Prior Art
Wall frames are typically constructed by securing
a plurality of spaced and parallel vertically extending joists ~`
or trusses between horizontally extending beams called plates.
Although the joists are secured to the~ plates, addl~tional~str~eng
thening of the Structure is necessary in order to resist the
tendency of the structure to rack under load such as wind or
seismic forces and to increase the load carrying capacity~ o~ -
the structure. Thus, a diagonally extending bracing member
is often secured across the parallel joists in order to provide
such additional support.
One previously known type of wall construction~employed
wooden brace members having a let-in construction. This lst-in
construction is formed by providing a plurality of aligned reces-
ses within the parallel truss members and providing correspond-
ingly spaced recesses in a wooden brace member. In this manner,
the wooden brace extends across and between the parallel joists
and is secured by fasteners such as nails to each of the joists.
Such a construction is not only time consuming to cut and con-
struct, but it also requires that the recesses be sufficiently
deep to permit paneling or other surface material to be layed
flat against the trusses of the wall structure. Moreover, the
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removal of sections of the trusses il~ order to form the appro-
priate recesses incre~ses the infirmity of the completed struc-
ture. In addition, testing of these braces and wall construction
indicate that when the wall begins to fail because of racking
caused by application of an excessive load, the fasteners pull
out of the frame merr~ers. Conse~uently, the brace is pulled
apart from the wall structure, whereby the strength of the wall
structure is decreased.
One previously known device used to overcome the dis-
advantages of let-in bracing is the T-shaped metal brace such ~ .
as the braces disclosed in U. S. Patent No. 3,875,719. The
metal support strip is generally T-shaped with a narrow U-shaped
portion forming the base leg of the T. The brace is secured
across parallel wooden trusses or joists by embedding the base
portion of the strip in aligned saw kerfs extending across the
joists. The strips are commonly secured by fasteners such as
nails to each of the joists which it crosses. While these
previously known metal braces have been found to be advantageous
over wood let-in construction, it has also been found that a
large number of nails is required to secure the Strip to the
trusses and to insure that the base remains embedded in the
saw kerfs. In a~dition, these previously known strips and wall
constructiOnS have not been designed with regard to the inertial
characteriStics f the strip about the ma~or and minor axes of
the T-shaped configuration. Consequently, the maximum strength
and maximum strength per dimension have not previously been
realized or utilized in T-shaped metal supports for wood struc-
tural elements. Moreover, they are inefficient because they do
nOt make full use of the effec's resulting from the connection
to ~e joists.
Summary of the Present Invention
The present invention overcomes the above mentioned
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d;sadvantages by providing a brace and a braced wall
constr~ction in which the brace is designed as an
elongated T-shaped metal brace wherein the
cros~-sectional properties of the strip are defined by
the relationship that the moment of inertia about the
major axis (Ix) is less that the moment of inertia
about the minor axis (Iy)~ The base of the strip is
fr~ictionally engaged within each kerf. In additionr
the strip is secured to a single wall frame member at
each~ngitudinal end~by means secured through the
centroid of the metal brace. This additional
connection means prevents iongitudinal dispiacement of
the strip through the saw kerfs. At the sam~ time, it
decreases the effective buckling iength of the strip
but it also effects the performance of the strip as
expected from the cross~sectional properties.
Nevertheless, the adverse effect is compensated for by
further decreasing the ratio IX/Iy in the design of the
strip. Consequently, the strip can be made of a
minimum amount of materia} and will fail in the desired
mode, i.e. flexural buckling, whi~e the connection
increases the ioad capacity and fiexural buckling
strength of the brace.
In brief, the invention provides a wooden
structure of a buildin~ construction comprising: at
least one elongated top plate and at least one
elongated bottom plate; a plurality of spaced wooden
truss elements secured to said top and bottom plates; a
narrow, transversely inclined channel, and said
channels are aligned in a manner to receive a straight
metal strip inserted therein, said metal support strip
comprising a base portion generaliy U-shaped in cross
section wherein the opposin~ sides of said base portion
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extend generaily along a first axis, said U-shaped
portion being positioned in said channels, and further
comprising two flanges extending outwardiy from said
U-shaped portion and aligned generally along a second
axis normal to said first axis wherein the strip is
dimensioned in accordance with the relationship: Ix is
less than Iy~ wherein Ix is the moment of inertia about
said first axis and ~ is the moment of inertia about
said second axis; and first means for fixedly secur;ng
said strip to the wooden structure.
The invention urther provides a metal support
brace for building construction comprising an elongated
strip return-bent about its longitudinai axis to form a
base portion having two walls defining a channei
therebetween and further comprising two flanges
extending substantially normal from said base walls
whereby the strip is substantially T-shaped in
cross-section, said strip further comprising at least
one guide channel formed in said base walls near each
end of said strip by forcing a punch into said channel.
The actual shape of the brace of the present
invention is similar to previously known T-shaped metal
braces although the actual dimensions of particular
portions of the strip of the present invention are not
suggested by the previously known T-shaped metal
braces. Ihe brace generally comprises a strip of metal
having a thickness generally less than one-tenth of an
inch (2.54 millimeters) which is cold formed into a
returnbent substantially U-shaped base p~rtion and a
pair of side fianges extending from the free ends of
walls of the base and substantiaily normal thereto.
Unlike previously known T-shaped metal bracing which
was not designed to prevent buckling out of the plane
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of the wall during racking, whereby the nails hoiding
the brace are puiied from the studs, the brace of the
present invention is formed so that the cross-sectionai
properties provide a moment of inertia about
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an axis normal to the wall structure which is less than the mornent
of inertia about an axis parallel to the ~all. In accordance with
the cross-sectional propelties relationship described, the side
flanges are substantially narrower than previously known T-shaped
metal braces.
By securing the strip to the wall mem~ers through its
centroid, App]icant further avoids eccentric forces about the
centroid of the strip which tend to urge the base of the strip
out of the saw kerfs when a racking load is applied to the wall
structure. By avoiding the introduction of the5e forces which
are especially likely to occur when a T-shaped metal brace is
mounted by nails punched through the laterally extending flanges
of the brace, the resistance to racking and failure of the wall
structure becOme highly predictable and the ability of the wall
structure to resist racking becomes substantially dependent only
upon the cross-sectional characteristics of the T-shaped metal
brace. Accordingly, the brace of the present invention avoids
the tendency of the brace to buckle out of the plane of the wall
even when the use of warped joists predisposes the brace slightly
normal to the plane of the wall.
Testing has determined that the connection through the
centroid of the strip affects the performance of the cross-sec-
tional properties about the axis normal to the plane of the wall
more than about the axis parallel to the plane of the wall, the
effect most directly influences the effective buckling length of
the strip, but is better described in the context of the present
disclosure as producing the effective Iy. Nevertheless, appropri-
ate reduction of the Iy/Ix ratio results in a combination strip
and connection wherein the flanges of the strip can be reduced
without a loss of load capacity as might be expected. Conse-
quently, the brace can be proportioned so that buckling will occur
within the plane of the wall, but at hiaher loads than the previ-
ously known and wider wind braces.
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A steel brace of the present invention fails in a
desired manner, i. e. elastic flexural buckling, under a stress -
at load:
KL
Fal = .522 QFy _ QFy R 2
1494
Wherein the slenderness ratio KL is
O < KL ~ Cc/4
R
or inelastic flexural buckling at load:
~; : Fal = 151,900
( R )
Wherein KL ~ Cc/~ -, and
R
K is the ratio of the effective column length to the
actual unbraced length,
L is the length of the brace member extendlng between
two adjacent wall structure joists,
R is the radlus of gyration = ~I/Area,
is the yield strength of the brace material, and
Q is a form factor which reduces the effective yield
strength due to change in the effecti~e area of the strip due
to stress and the use of stiffened and unstiffened elements in
the bracei and the width to thickness ratio of the brace. ~ -
Thus, it can be seen that as the ratio Ix to Iy in-
creases the allowable a~ial stress in the brace for buckling
outside the wall becomes significantly greater than the a}low-
able axial stress required to induce buckling within the plane
of the wall.
In order to assure that the actual performance of the
brace formed from a minimum of material is closely approxi-
~ mated by the above analysis, it is essential that the bracebe fastened through its centloid to the wall structure. Actual
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testing has disclosed that an adequate degree of fixation is
provided throuyh the cent~oid of the brace when the base meJ~er
is provided with a pair of prepunched nail holes through the
central channel of the brace at each end of the brace. Prefer-
ably, the two holes at each end of the brace are spaced apart
from each other a predetermined distance which enables the en-
larged head of one nail to overlap a portion of the enlarged
head of the other nail- In addition, the holes are aligned
to be parallel to each other and perpendicular to the surface
of the joist into which this fastener is embedded.
Prepunching such holes is advantageous since it accur-
ately locateS the nails in relation to the member in which it
is embedded and thereby eliminates guesswork and improper place-
ment of the nails with respect to the wall plate in which it
is embedded. Preferably, the guide holes are located substan-
tially in the center of the wall plate to reduce splitting of
the wood or pulling out of the nail. Prepunching also causes
a pronounced rib in the base portion of the brace to provide
a more positive hold in the saw kerf and to maintain the brace
in position while the fasteners are installed.
In addition to reducing the likelihood of improper
installatiOn, the rib in the base portion of the brace caused
by prepunching also increases the column strength of the base
and thereby reduces the likelihood of deformation of the brace
when it is being driven into the saw kerf. In addition, a
greater portion of the shank of the nail is gripped by the brace
member than is provided by merely nailing through an unpunched
channel in the base.
Moreover, it has been found that when the holes are
prepunched only slightly past the lower corner of the U-shaped
channel, installation of the nail within the prepunched hole
causes the lower corner of the U-shaped channel to flare out
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more than would occur by merely nailing the nail through the
channel of the wall hr.ace. In addition, the small prepunched
opening formed in the bottom of the channel induces a unifor~ --
and predictable tearin~ at the base of the U-shaped channel
where the fastener is driven in. This uniformity reduces the
likelihood of stress concentrations at the tear lines and thereby
reduces premature failure of the wall brace.
In order to maximize the strength of the wall struc
ture, failure of the brace during racking of the wall structure
should occur within the plane of the wall, whereby the base
of the brace remains embedded within the saw kerfs and continues
to support the truss members of the wall construction during rack-
ing. The brace Of the present invention is especially advantage
ous in that its design characteristics produce such an effect.
At the same time, it is formed from less material than previously
known T-shaped metal braces and is thus more economical to pro- -
duce. Moreover, the wall structure construction has greater
load capacity than previously known T-shaped metal braces.
Since substantially fewer fasteners are required to secure the
brace to the truss wall structure, than in previously known
wall structures, installation of the strip of the present inven-
tion is easier and faster.
Thus, additional savings in material costs as well
as labor costs will b~ realized by those using the brace member
of the present invention.
Brief Description of the Drawing
The present invention will be better understood by
reference to the ~ollowing detailed description when read in
conjunctin with the accompanyiny drawinc in which like reference
characters refer to like parts throughout the several views,
and in which:
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FIG. 1 is an elevational view of a wall structure
employng two ~race members. of -~ e present invention;
FIG. 2 is a fragmentary perspective view of one end
of the brace member of the present invention;
FIG. 3 is an enlarged fragmentary front elevational
view of a portion of the wall structure shown in F'IG. 1 and
enclosed within the circle 2;
FIG. 4 is a fragmentary bottom plan view of one end
of the brace me~ber of the present invention;
FIG. 5 is a cross-sectional view of the hrace member
shown in FIGS. 1 through 4; and
FIG. 6 is a fragmentary cross-sectional ~iew of the
brace member similar to FIG. 5 but showing the fasteners installed
in the base of the brace.
Detailed Description of a Preferred
Embodiment of the Present Invention
Referring now to FIG. 1, the present invention 10
is thereshown comprising brace members 12 secured to the~wall
structure 14. ~he wall structure 14 comprises two top plates
16 and 18 supported above a bottom plate 20 by a plurality of
joists 22. Each brace 12 lS secured at its upper end by appro-
priate fasteners such as nails 30 to the top plate 16, and the
lower end of each brace 12 is secured in like manner to the
bottom plate 20. The brace 12 has a base embedded in saw kerfs
21 ~FIGS. 5 and 6) within the plates 16, 18, 20 and the joists
22, and are aligned with the axis of the brace 12.
Referring to FIG. 2, an end portion of the brace 12
is enlarged for clarity. The brace is formed from a metal strip
approximately .038 inches thick or approximately 20 guage.
The strip is return-bent at its center to form the substantially
U-shaped channel defined by a pair of base walls 32 and 34 inter-
connected at the bottom of '_he channel by the U-shaped corner 36.
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In practice, the corner 36 is slightly wider than the upper por-
tion of the channel so that the corner is compressed when embed-
ded in a saw kerf. The free ends of the base walls are bent
substantially normal to the base legs 32 and 34 to form a pair
of side flanges 38 and 40- The cross-sectional properties of
the brace about the Y and X axes are determined in accordance
with the relationship Iy < Ix when the effect of the connection
by fa~teners 30 is taken into account. By way of e~ample, a 20
guage metal support strip 2.3 inches wide has been formed to pro-
vide symmetrical flanges .404 inches wide and a base extending
.038 .752 inches beneath ~he flange to produce a brace which
exhibits the desired performance and load capacity in actual
testing.
When the s~rip has been so configured to form the
brace, a pair of guide channels or holes 42 and 44 are formed
between the legs 32 and 34 of the base of the strip. The guide ;
holes 42 and 44 are spaced from the end of the brace 12 so that
they are substantially centered at the middle of the top or
bottom plate into which the fasteners are to be embedded. In
addition, the guide holes 42 and 44 are preferably spaced from
each other only a slight distance so that the head of one fasten-
er 30 disposed in one of the guide holes will overlap a portion
of the head of the second fastener 30 disposed within the other
guide hole. As best shown in FIG. 3, the guide holes 42 and
44, and thus the fasteners 30 disposed in the guide holes 42
and 44 are aligned to intersect the centroid of the metal strip
by alignment with the axis of the channel between the base walls
32 and 34
Referring now to FIG. 4, the bottom of the end portion
of brace 12 shown in FIG. 2 is illustrated~ The guide hole
44 is thereshown as it is formed prior to installation of the
brace in the wall structure. The base legs 32 and 34 are bulged
slightly at 45 and a small ape-ture l~ss than the diameter of
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the fastener extends through the bottom 36 of the hase of the
brace 12. The guide hole 42 shown in ~IG. 4 illustrates the
condition of the guide hole after a fastener has been inserted
throuyh the guide hole. The bulges in the side legs 32 and
34 are slightly more pronounced and the aperture in the bottom
corner 36 of the base coincides with the diameter of the fas-
tener which has been inserted through the guide hole 42.
The additional expansion of the guide holes 4Z and
44 is best shown in FIGS. 5 and 6. FIG. 5 is a cross~sectiona
view of the brace showing a prepunched hole in hidden lines
which corresponds to illustration of guide hole 44 in FIG 4.
The line 5V indicates the extension or enlargement 45 of the
walls 32 and 34 formed when the guide holes are prepunched.
In addition, the line 50 indicates the additional depth to which
the brace becomes embedded in the plate beyond the wall of the
saw kerf in the joist.
The enlargements 45 become further pronounced when,
as shown in FIG. 6, the fasteners are inserted into the guide
holeS to expand the boundary line SO even further into the plate
surface adjacent the saw kerf. Moreover, engagement of the
fastener with the edges of the aperture originally formed in
the bottom corner 36 of the base by prepunching the guide holes,
spreads the bottom of the base in a bulbous manner as shown
at 52 and thus further increases the engagement between the
brace and the plate in which it is embedded.
By prepunching the holes 42 and 44 at each end of
a brace 12, guides are provided for the fasteners 30 which not
only increases the grip between the brace and the fastener,
but also increases the fixation of the brace with respect to
the wall structure members. The guides act to direct the fas-
teners through the centroid of the brace and thus eliminate
torsional moments about the centroid which tend to rotate the
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strip within the saw kerf which causes the brace to pull out
of the saw kerf under stress. Moreover, preforming of the guide
holes enables the use of lar~er nails than would otherwise be
easily insertable within the channel of the brace and, thus,
~urther increases the fixation of the brace wi*h respect to
the wall structure. In this manner, the need for inserting
fasteners throuyh the brace at each joist of the wall Structure
has been eliminated.
Due to the fact that the braces are rigidly secured
to the wall structure without inducing torsional moments about
the centroid of the brace, the side flanges 38 and 40 of the
brace are subs*antially smaller than the side flanges of previ-
ously known T-shaped wall braces. Such narrowing of the flanges
38 and 40 is advantageous in that it reduces the amount of mater-
ial necessary to form a brace of the present invention. In
addition, the narrow flanges discourage installers from driving
fasteners through the side flanges to secure the brace to the
wall structure. By eliminating fastening through the side flang-
es, torsional moments about the centroid of the brace are elimi-
nated. Consequently, these moments, which tend to force the
brace out of the saw kerfs when the wall construction is under
stress, are reduced significantly enough to permit the brace to
fail within the plane of the wall before the brace can be pulled
out of the saw kerfs. Therefore, the brace remains effective
against greater wall s*resses than previously known T-shaped
metal braces.
It has been found that the use of sixteen penny nails
to fasten a strip 12 to wall structures provides sufficient
fixation of the brace to the wall struciure. Although such nails
are larger and more expensive than nails commonly used to secure
metal braces to wall structures at each jois- intersection,
only four of these nails are required to secure each brace
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member to a wall structure. Consequently, material costs as
well as labor costs are substantially decreased fox installa-
tion of the brace member of the present invention.
Having thus described my invention, many modifications
thereto will become apparent to those skilled in the art to
which it pertains without departing from the scope and spirit
of the present invention as defined in the appended claims.
For instance, it is conceived that prepunched guide holes can
be formed along the length of the brace to increase the grip
of the brace within the saw kerf in each joist.
What is claimed is:
:
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