Note: Descriptions are shown in the official language in which they were submitted.
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ROOF TRUSS
DESCRIPTION
Background Art
This invention relates generally to a metal structural member for use in
building
construction, and more particularly to a metal roof truss for construction of
roof framing
for supporting roofs.
A roof truss generally comprises two or more top chord members and one or more
bottom chord members. The ends of the top chords are secured together, and the
ends of
the bottom chords) are connected to the lower, free ends of the top chords for
forming the
perimeter of the roof truss. One or more web members span between and
interconnect the
top and bottom chords. The web members are secured at their ends to the top
chords) and
to the bottom chord(s).
In building construction, the roof structure is formed from a plurality of
trusses set
out across a building frame on anywhere from about 12 to about 60 inch
centers. When
erected upon the building frame, the truss spans the wall frames of the
building and is
fixed to the top of wall support frames. The sub-roof material is then
fastened to the top
chords, and ceiling material may be fastened to the bottom chords. The
reactions resulting
from the combined roof live, dead, and wind loads, plus the dead loads of the
roof trusses
and the roof and ceiling assemblies, are transferred by the trusses to the top
of wall support
frames.
Historically, roof trusses have generally been constructed of wooden chords
and
web members. More recently, various types of metal trusses have become
available.
While the unit raw materials costs for metal trusses may be competitive with
other
building materials, metal trusses typically have not been competitive against
wooden
trusses. But using metal as the material of construction has a number of
advantages,
including relatively stable price, increased unit strength, design
flexibility, durability, light
weight, reliability, minimum waste in use, recyclability and
noncombustability.
For the foregoing reasons, there is a need to provide a cost competitive light
weight metal roof truss for use in applications for which wood trusses would
be
structurally sufficient. The new metal truss should be easy to assemble while
providing
the aforementioned benefits compared with trusses made from other building
materials.
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The new metal roof truss should also require low capital investment to
produce, be able
to be adapted to mass production, and be able to be manufactured in a
manufacturing
facility or on a jobsite.
Disclosure of Invention
According to the present invention, a metal roof truss assembly is provided
comprising a plurality of elongated structural members, including a top chord,
a bottom
chord, and a web member. Each structural member comprises a planar base
terminating in
longitudinal edges and planar legs extending from the longitudinal edges of
the base and
terminating in longitudinal edges. The legs extend the length of the base such
that the
base and the legs define an open longitudinal channel. A flange is integral
with the
longitudinal edges of each leg. Each flange has a planar first portion
extending outwardly
from the legs and terminating in longitudinal edges, and a planar second
portion extending
from the longitudinal edges of the first portion of the flanges and
terminating in
longitudinal edges. The flanges selectively extend the length of the legs. The
structural
members are joined. The end of a first structural member at each junction is
inserted into
the channel defined by the legs and the base of a second structural member.
The inserted
end of the first structural member has no flanges for a length equal to at
least the depth to
which the first structural member is received in the channel of the second
structural
member so that the outer surface of the legs of the first structural member
are adjacent the
inner surface of the legs of the second structural member.
Also according to the present invention, a method of forming a roof truss
assembly
is provided. The method comprises the steps of providing a coil of
substantially flat sheet
metal, cutting a plurality of lengths of the sheet metal, and forming
structural members
from each of the lengths of metal. The structural members include a top chord,
a bottom
chord, and a web member. Each structural member comprises a planar base
terminating in
longitudinal edges and planar legs extending from the longitudinal edges of
the base and
terminating in longitudinal edges. The legs extend the length of the base such
that the
base and the legs define an open longitudinal channel. A flange integral with
the
longitudinal edges of each leg has a planar first portion extending outwardly
from the legs
and terminating in longitudinal edges, and a planar second portion extending
from the
longitudinal edges of the first portion of the flanges and terminating in
longitudinal edges.
The flanges selectively extend the length of the legs. The method further
comprises the
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steps of removing a portion of the flanges from an end of one of a first
structural and
inserting the end of the first structural member into the channel defined by
the legs and the
base of a second structural member so that the outer surface of the legs of
the first
structural member are adjacent the inner surface of the legs of the second
structural
member.
Brief Description of the Drawings
For a more complete understanding of the present invention, reference should
now
be made to the embodiments shown in the accompanying figures and described
below. In
the figures:
FIG. 1 is a front elevational view of a gable roof truss assembly according to
the
present invention;
FIG. 2 is a front elevational view of a second embodiment of a roof truss
assembly
according to the present invention;
FIG. 3 is a front elevational view of a third embodiment of a roof truss
assembly
according to the present invention;
FIG. 4 is a front elevational view of a fourth embodiment of a roof truss
assembly
according to the present invention;
FIG. S is a profile section of a truss member for use in the truss assembly
according to the present invention;
FIG. 6 is a profile section of another embodiment of a truss member for use in
the
truss assembly according to the present invention;
FIG. 7 is a perspective view of one half of the embodiment of the truss
assembly
shown in FIG. 3;
FIG. 8 is a perspective view of a notched truss member for use in a truss
assembly
according to the present invention;
FIG. 9 is a front elevation close-up view of a portion of the embodiment of
the
truss assembly shown in FIG. 3 showing a joint formed at the connection of the
ends of
two web members to a top chord member and the end of one of the web members to
a
bottom chord member;
FIG. 10 is an exploded view of the portion of the truss assembly shown in FIG.
9;
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FIG. 11 is a cross-section view taken along line 11-11 of FIG. 9 showing the
joint
formed at the connection of the end of the vertical web member to the bottom
chord
member;
FIG. 12 is a front elevation view of an apex joint at the peak of the
embodiment of
the truss assembly shown in FIG. 3;
FIG. 13 is an exploded view of the apex joint shown in FIG. 13;
FIG. 14 is a front elevation view of another embodiment of an apex joint at
the
peak of a roof truss assembly;
FIG. 15 is a close-up elevational view of a load bearing joint formed where
the
bottom chord and the top chord are joined at the lower right end of the
embodiment of the
truss assembly shown in FIG. 2;
FIG. 16 is an exploded of the load bearing joint shown in FIG. 15.
FIG. 17 is a cross-section view taken along line 17-17 of FIG. 15 showing the
joint
formed at the connection of the top chord member and bottom chord member;
FIG 18 is a profile section of a truss member as shown in FIG. 5 with a
section of
wood in the truss member.
FIG. 19 is a front elevation view of one end of the truss assembly shown in
FIG. 3
with a wood rafter tail in the end of the top chord;
FIG. 20 is a top plan view of a portion of a mufti-truss assembly;
FIG. 21 is an exploded view of the mufti-truss assembly shown in FIG. 20.
Best Models) for Carrying Out the Invention
Certain terminology is used herein for convenience only and is not to be taken
as a
limitation on the present invention. For example, words such as "upper,"
"lower," "left,"
"right," "horizontal," "vertical," "upward," and "downward" merely describe
the
configuration shown in the Figures. Indeed, the components may be oriented in
any
direction and the terminology, therefore, should be understood as encompassing
such
variations unless specified otherwise.
Refernng now to the drawings, wherein like reference numerals designate
corresponding or similar elements throughout the several views, FIG. 1 shows
an
embodiment of a roof truss assembly according to the present invention,
generally
designated at 30. The roof truss assembly 30 comprises several structural
truss members,
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including a pair of top, or upper, chord members 32, a bottom, or lower, chord
member
34 and web members 36. Adjacent upper ends of the top chord members 32 are
secured
together to form an apex joint 38. In this embodiment of the truss assembly
30, a
vertically-positioned heel element 40 is fastened between each end of the
bottom chord
member 34 and the free ends of the top chord members 32.
The top chord members 32 and the bottom chord member 34 form a triangle, with
the bottom chord member 34 as the base and the top chord members 32 forming
the sides
of the triangle. It is well known in the art that there are a number of roof
truss profiles in
addition to the triangular truss assembly 30 depicted in the FIGs. We do not
intend to
limit the application of the present invention to a single truss profile.
Rather, the present
invention is applicable to all known truss profiles.
The web members 36 extend between the top chord members 32 and the bottom
chord member 34. The opposite ends of the web members 36 are secured to the
top chord
members 32 and the bottom chord member 34 for rigidifying the roof truss
assembly 30.
It is understood that we do not intend to limit the application of the present
invention to a
roof truss assembly 30 having a predetermined position and number of web
members 36
as shown in the FIGS. The number and the position of the web members 36 and
the length
of the top chord members 32 and bottom chord member 34 will vary as necessary
depending upon the size of a building and the lengths of the.chord members 32,
34, in
order to provide the required structural strength. For example, a second
embodiment of a
truss assembly according to the present invention is shown in FIG. 2 and
generally
designated at 50. This truss assembly 50 does not include as many web members
36 as the
truss assembly 30 shown in FIG. 1. A third embodiment of a truss assembly
according to
the present invention is shown in FIG. 3 and generally designated at 60. This
truss
assembly 60 includes more web members 36 than the truss assembly 30 shown in
FIG. 1.
A fourth embodiment of a truss assembly according to the present invention is
shown in
FIG. 4 and generally designated at 70. In the embodiments of the truss
assembly 50, 60,
70 shown in FIGS. 2-4, the ends of the bottom chord member 34 are secured to
the top
chord members 32 adjacent the lower ends of the top chord members 32. Where a
truss
assembly will span a large distance, it may also be necessary to have a bottom
chord
member 34 comprising a plurality of sections which have been spliced.
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Each of the structural truss members of the truss assemblies according to the
present invention is formed from a strip or sheet of metal. The preferred
material of
construction is steel. However, the present invention is not limited to steel,
and other
metals such as aluminum, copper, magnesium, or other suitable metal may be
appropriate.
Further, it is desirable that the metal be light gauge metal, which is
generally less than
about 2.7 mm in thickness, for example, from about 12 to about 24 gauge. It is
understood, however, that the scope of the invention is not intended to be
limited by the
materials listed here, but may be carried out using any material which allows
the
construction and use of the metal roof truss assembly described herein.
According to the present invention, all of the structural truss members, the
top
chord 32 and bottom chord 34 and the web members 36, have the same cross-
sectional
shape, which simplifies the supply and handling of the material forming the
truss members
32, 34, 36. FIG. 5 illustrates one embodiment of a structural truss member,
generally
designated at 80, which is used to make up all of the truss members 32, 34, 36
of the roof
truss assemblies according to the present invention. The truss member 80 is an
elongated
member having a substantially C-shaped or U-shaped cross-section and comprises
a
substantially flat flange portion 82 along a longitudinal axis and spanning
between
parallel, substantially flat side webs 84 which extend substantially
perpendicularly from
the edges of the flange portion 82. The flange portion 82 and the side webs 84
define an
open longitudinal channel 86. The side webs 84 are bent outwardly at their
distal ends
forming substantially flat stiffening flanges 88 which are substantially
normal to the plane
of the side webs 84. The terminal edges of the stiffening flanges 88 are bent
upwardly
forming upturned lips 90 which are disposed substantially parallel with
respect to the side
webs 84. A steel roof truss including a top chord having the cross-section
shown in FIG. 5
is described in U.S. Patent No. 4,982,545, which issued January 8, 1991 and is
entitled
"Economical Steel Roof Truss", the contents of which are hereby incorporated
herein by
reference in their entirety.
FIG. 6 shows another embodiment of a structural truss member, generally
designated
at 100, which may be used for all of the structural truss members 32, 34, 36
according to
the present invention. In this embodiment, the terminal edges of the
stiffening flanges 88
are bent over the stiffening flanges so that the lips 90 extend inwardly and
substantially
parallel to the stiffening flanges 88.
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The dimensions of each portion of the structural truss members 80, 100 shown
in
FIGS. S and 6 may differ depending upon the length of the truss member as well
as the
load forces which the truss member will incur. In the embodiment of the truss
member 80
shown in FIG. 5, the width of the flange portion 82 between the side webs 84
may be from
about 1.5 inches to about 1.75 inches and the side webs 84 may be at least
about 2 inches
long. Each of the stiffening flanges 88 may be from about 0.5 inches to about
0.6 inches
wide and the lips 90 may be from about 0.25 to about 0.4 inches wide. In the
second
embodiment of the truss member 100 shown in FIG. 6, the parallelly disposed
lips 90 may
extend about 0.25 inches along the stiffening flanges 88. In keeping with the
present
invention, an important consideration is the length, or height, of the side
webs 84, which
translates to the depth of the truss member 80, 100. The truss member 80, 100
may be
manufactured in varying depths and widths depending on the required strength
to weight
ratio necessary to meet load bearing requirements and the gauge of metal used
to form the
truss member 80, 100.
Refernng now to FIG. 7, which is a perspective view of one half of the roof
truss
assembly 60 shown in FIG. 3, when the truss assembly 60 is assembled, the open
longitudinal channel 86 of the bottom chord member 34 faces upwardly and the
open
longitudinal channels 86 of the top chord members 32, which are not visible in
FIG. 7,
face downwardly. Structural joints are created where the top chord member 32
and the
bottom chord member 34 and the web members 36 intersect one another. The
joints
between the truss members can be secured using fasteners 42, such as bolts and
nuts, metal
screws, rivets, or any combination thereof. Alternatively, the truss members
may be
joined by welding, soldering, and the like.
In joining the structural truss members 32, 34, 36 according to the present
invention, a
portion of one end of a truss member is inserted into the open channel 86 of
another truss
member. The inserted end of the truss member is re-shaped, such as by bending,
notching,
and the like, to allow insertion into the open channel 86 of the other truss
member. The
inserted ends of the truss member may also be butt cut to simplify assembly as
well as to
minimize fabrication time and the chance for error, which may exist when
precise
geometric cuts are used. Referring to FIG. 8, an end of a re-shaped truss
member 80 is
shown with a length of the stiffening flanges 88 and upturned lips 90 of the
truss member
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80 cut away from the side webs 84 in an area where the truss member 80 is to
be inserted
into and joined with another truss member.
FIGs. 9 and 10 show a portion of the truss assembly 60 shown in FIGs. 3 and 7.
As
seen in the FIGs., a joint is formed at the connection of the ends of the two
web members
36 to the top chord member 32 and the opposite end of the vertical web member
36 to the
bottom chord member 34. The ends of the web members 36 have a portion of the
stiffening flanges 88 and lips 90 removed which allow the ends of the web
members 36 to
fit within the open channels 86 in the top chord member 32 and bottom chord
member 34.
The side webs 84 of the top chord member 32 and the bottom chord member 34 may
be
deformed slightly outwardly to fit over the ends of the web members 36.
Each of the top chord member 32 and the bottom chord member 34 and the web
members 36 define holes 48 for receiving fasteners 42, such as bolts as shown
in FIG. 10.
The pattern of holes 48 near the ends of the web members 36 is juxtaposed with
the
pattern of holes 48 of the connecting top chord member 32 and the bottom chord
member
34. The bolts 42 are received through the juxtaposed holes 48 so as to fixedly
connect the
truss members with associated nuts 43. It is understood that we do not intend
to limit the
application of the present invention to a roof truss assembly having a single
juxtaposed
bolt hole 48 at each joint. The number and the position of the bolt holes 48
will vary as
necessary depending upon the size of the truss members 32, 34, 36 in order to
provide the
required structural strength. A nylon patch, which is not visible in the
FIGs., may be
provided at the end of the bolts 42, which resists against loosening of the
nuts 43 from the
bolts 42 due to vibration, cyclic loading or during transportation.
The connection between the top and bottom chord members 32, 34 and the web
members 36 may also include a stiffener 102. As best shown in FIG. 11, the
stiffener 102
is a rigid element having a bore which slips over the bolt 42 between the side
webs 84 of
the web member 36. The length of the stiffener 102 is substantially the same
as the
distance between the side webs 84 of the web member 36 when inserted into the
top chord
member 32 or bottom chord member 34. The stiffener 102 supports the web member
36
and prevents the web member 36 from moving during load thereby strengthening
the
connection point between the web member 36 and the top or bottom chord members
32,
34. The stiffener 102 may be formed from any rigid material, including plastic
such as
nylon, metal, and the like.
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FIGs. 12 and 13 show the apex joint 38 formed at the peak of the third
embodiment
of the truss assembly 60 shown in FIGS. 3 and 7. The end of the left top chord
member 32
has a portion of the stiffening flanges 88 and lips 90 removed which allows
the end of the
left top chord member 32 to fit within the open channel 86 of the right top
chord member
32 so that the ends of the top chord members 32 overlap. It is understood that
the length
of the portion cut away from the stiffening flanges 88 and lips 90 depends
upon the angle
at which the top chord members 32 are joined. Bolt fasteners 42 secure the top
chord
members 32 to one another and to the upper ends of the web members 36, which
have a
portion of the stiffening flanges 88 and lips 90 removed, as described above.
Another embodiment of an apex joint 38 according to the present invention is
shown
in FIG. 14. In this embodiment, a horizontal web member 52 is provided between
the top
chord members 32 and a vertical web member 36. The ends of the horizontal web
member 52 are received within the open channels 86 of the top chord members 32
and
secured with bolt fasteners 42. The upper end of the vertical web member 36 is
similarly
secured to the horizontal web member 52 at substantially the mid-point of
horizontal web
member 52.
As shown in FIGs. 15 - 17, a load bearing joint is provided at the lower ends
of the top
chord member 32 and the ends of the bottom chord member 34. Specifically, a
portion of
the stiffening flanges 88 and lips 90 at the end of the bottom cord member 34
is removed
and the end of the bottom chord member 34 is fit into the open channel 86
adjacent the
end of the top chord member 32. As best seen in FIGS. 16 and 17, the chord-to-
chord
connection also includes a top heel stiffener 44 and a bottom heel stiffener
46. The heel
stiffeners 44, 46 are generally U-shaped in cross-section and are sized to be
inserted within
the channels 86 of the top and bottom chord members 32, 34 adjacent their
ends. The heel
stiffeners 44, 46 function as a load transfer element, facilitating the
transfer of load forces
between the chords 32, 34 and into the support wall (not shown) at the bearing
point of the
truss assembly. In addition, the bottom heel stiffener 46 strengthens the
bottom chord
member 34 at the bearing point. The ends of the top chord member 32 and the
bottom
chord member 34 and the heel-stiffeners 44, 46 are fastened together with one
or more
bolt fasteners 42. Alternatively, as shown in FIG. 1, a heel element 40 is
fastened between
the free ends of the top chord members 32 and each end of the bottom chord
member 34 in
the same manner as a vertical web member 36 as shown in the FIGs. and
described above.
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When assembled, the truss members of the truss assembly are all in essentially
the
same plane. It is understood that the term "planar" is riot limited to having
the truss
members all lying within the same plane, but includes structures wherein the
truss
members do not lie within the same plane so long as the general extent of the
truss
5 assemblies is substantially two-dimensional.
Also in keeping with the present invention, the open longitudinal channel 86
defined
by the flange portion 82 and the side webs 84 of the truss member 80, 100 may
be sized to
receive a wooden insert 104, as shown in FIG. 18. Preferably, the dimensions
of the
longitudinal channel 86 are compatible with dimensional lumber, for example,
the width
10 of the flange portion 82 being 1 %i" for receiving 2x2's, 2x4's, etc.,
depending on the depth
of the channel 86. The wooden insert 104 may be fixed in position by fasteners
(not
shown) which extend through the flange portion 82 or the side webs 84 of the
truss
member 80, 100 to engage the wooden insert 104 for securing the wooden insert
104 in the
truss member 80, 100. Alternatively, the inner surfaces of the side webs 84
may be
1 S provided with serrations to inhibit movement of the wooden insert 104.
Portions of the
side webs 84 could also be punched inwardly when the wooden insert 104 is
within the
channel 86 to form tangs (not shown) which bite into the surface of the wooden
insert 104.
The wooden insert 104 may be used as a structural component providing
additional
strength to a truss member 80, 100 which would eliminate the need for bracing.
The
wooden insert 104 also allows for a repair alternative in the field if the
truss member 80,
100 is damaged. As shown in FIG. 19, the wooden insert 104 may be inserted in
the
channel 86 at the lower end of the top chord member 32 to form a rafter tail
to
accommodate wood extensions for fascia.
Two truss assemblies may be connected together where added strength is needed.
FIGS. 20 and 21 show this connection, which is accomplished using two bolts 42
and a
threaded ply nut 110 positioned between the truss members for securing the
truss members
together at a plurality of locations. Preferably, the truss assemblies are
connected together
at each node point to ensure even distribution of load throughout the truss
assemblies. The
space between the truss members provided by eliminates any chance for
squeaking during
cyclic loading.
In a method for producing a truss assembly according to the present invention,
truss members can be produced from flat coils of sheet metal using an
automated roll
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forming machine. A suitable roll forming machine may include a processor, such
as a
computer, programmed and controlled to produce the structural truss members
for the
truss assembly according to a predetermined plan. The roll forming machine is
provided
with the plan for the truss assembly to be produced, including the positioning
of each of
the truss members. The various truss members are generated to an appropriate
length and
having the necessary features for joining the truss members, including holes
for fasteners
and flanges and lips removed from the side webs at the ends to accommodate
intersecting
truss members. The notches and holes are positioned to align with holes on
mating
structural truss members so the parts of the truss assembly may be easily and
quickly
assembled. There is no need for boring or punching holes during the assembly
of the truss
assembly. Additionally, service holes may be provided in the structural truss
members to
accommodate electrical wiring or other utilities. Using the method according
to the
present invention, a finished truss assembly is built from a single strip of
flat coil metal
stock, which significantly reduces the need to maintain inventory because
there is no need
for pre-manufactured stock length material.
The computer-controlled roll forming machine will produce the truss members
precisely according to the specifications determined by the processor. Thus,
the design
and production process for the truss assemblies for buildings is substantially
automated.
Moreover, since all of the truss members are formed with a common cross-
section,
production is simplified. The truss members are produced in a convenient
order, enabling
each truss member after the first to be immediately assembled with the
previous truss
members as the truss member is produced and without any subsequent forming
operations.
Furthermore, because the holes and intersecting ends of truss members are
automatically
formed by the roll forming machine, the truss members can be simply fitted and
secured
together without the need for special framing jigs to hold the truss members
in position
while holes are drilled, which eliminates the need for setup tables and the
time required to
layout the trusses prior to fabrication. The truss assemblies may be assembled
with the
use of simple free standing rests which are moveable, as required, to a
convenient location
to hold the truss members at a convenient height.
Software for the design of the truss assemblies and operation of the roll
forming
machine as described above, is available. For example, a suitable design and
fabrication
methodology has been described in U.S. Patent No. 6,253,521, which issued July
3, 2001,
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and is entitled "Steel-Framed Building Construction"; U.S. Patent No.
6,272,447, which
issued August 7, 2001, and is entitled "Fabrication And Design Of Structural
Members";
and U.S. Patent No. 6,757,643, which issued June 29, 2004, and is entitled
"Fabrication
And Design Of Structural Members", the contents of all of which are
incorporated herein
by reference in their entirety. The software provides a "real time" drawing
during
production, including the location within the final assembly of the each truss
member
being produced, to simplify the fabrication process.
Additionally, the truss members may be produced on a building site using a
portable roll forming machine, as is known in the art. On-site production from
metal coils
eliminates the need to bundle and carry lengths of metal section and to sort
the structural
truss members. On-site production also avoids any confusion as to the precise
location of
each structural truss member.
While the invention is illustrated and described herein in terms of a domestic
dwelling, it is understood that the invention is not limited to the
construction of domestic
1 S buildings and will have application in commercial and industrial
construction.
Although the present invention has been shown and described in considerable
detail with respect to a particular exemplary embodiments thereof, it should
be understood
by those skilled in the art that we do not intend to limit the invention to
the embodiment
since various modifications, omissions and additions may be made to the
disclosed
embodiments without materially departing from the novel teachings and
advantages of the
invention, particularly in light of the foregoing teachings. For example, the
truss profile
and the number and position of the truss members may be any of a number of
such truss
arrangements known in the art. Accordingly, we intend to cover all such
modifications,
omissions, additions and equivalents as may be included within the spirit and
scope of the
invention as defined by the following claims. In the claims, means-plus-
function clauses
are intended to cover the structures described herein as performing the
recited function and
not only structural equivalents but also equivalent structures. Thus, although
a nail and a
screw may not be structural equivalents in that a nail employs a cylindrical
surface to
secure wooden parts together, whereas a screw employs a helical surface, in
the
environment of fastening wooden parts, a nail and a screw may be equivalent
structures.
