Note: Descriptions are shown in the official language in which they were submitted.
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The field of this invention is building materials, particularly
wooden beams, trusses, joists and girders. The current invention is
intended to be used primarily in residential or light commercial construc-
tion and other applications where a wooden joist is appropriate.
Increasing costs of lumber and potential lumber shortages have
precipitated the need for increased efficiency in the design and use of
wooden beams, trusses, joists and girders. Wooden trusses have been used
extensively. Chandler discloses a wood truss structure in United States
Patent 4,001,999, and a wood deck structure utilizing a wood truss in
United States Patent 3,345,792. Ilunt et al. discloses a continuous shear
resistant timber girder in United States Patent 3,861,109 which uses a
truss design including some attached side panels. Price uses a lattice
web in his wood truss shown in United States Patent 3,702,050. Snider
uses discontinuous side panels in his wooden joist shown web glued to the
flanges in United States Patent 4,074,498.
Construction of steel beams has been made more efficient by cut-
ting an I-beam web along a serrated line and fabricating the beam by
welding along the points of the serrations. This is demonstrated by Moyer
in United States Patent 1,644,940. A fabricated non-symmetrical steel
beam is shown by Simpson in United States Patent 3,263,387 Mar~is.
describes a hollow rectangular sectional metal beam using discontinuous
rectangular panel sidewalls in United States Patent 2,941,635.
The prior art has problems in several respects. Prior wood truss
devices have an overall depth so great in many cases they require an
increase to the height of the structure. This in turn increases building
costs associated with the increased height which offset or exceed the
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savings associated with the truss. This problem is especially applicable
to floor joists in most light construction. Wood trusses are difficult
and relatively costly to fabricate in many i~stances unless the time and
costs associated with a shop production layout are incurred. Special jigs
or patterns may be necessary to aid in the cutting, fitting and connecting
of truss components. The prior art has also not appropriately optimized
the amount of glue surface area required between the tension and compres-
sion chords and the truss members. Wooden beams cannot be fabricated by
gluing the points of serrated or dentated core halves together because of
insufficient glue area. The prior art has also failed to develop optimum
means for dissipating the effects of concentrated stresses at the support
points in wooden beams. True box type wooden beams heretofore disclosed
do not provide usable spaces for running transverse conduit at any point
along the entire length of the beam. Staggered placement of the side
panel elements has prevented convenient location of transverse runs of
conduit or other utility ducts. True box beams also use side panels which
are continuous for the length of the beam, requiring excessive amounts
of material. Current wooden box beams do not allow passage of conduit,
pipes, wires, etc. along the length of the beam because of the occasional
placement of vertical spacers. Box beams incorporating relatively large
distances between adjacent side panels at one point so that transverse
conduits may pass through the Qpening have reduced strength to resist
lateral loading.
SUMMARY OF THE INVENTION
One object of this invention is to provide a wooden joist which
requires less wood than solid joists while being relatively inexpensive
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and easy to make from readily available building materials without the
extensive production facilities. The joist allows pipes, heating ducts,
conduits and similar equipment to pass transversely and longitudinally
through the joist thus eliminating the need for a dropped ceiling. Pre-
ferably the joists are strong enough to allow spacing at greater center-
line-to-centerline di~tances and also greater clear space capabilities
than the conventional solid joists while providing increased resistance
to beam deflection.
The invention provides
a structural joist-like member comprising:
a) an elongated substantially rectangular tension chord;
b) an elongated substantially rectangular compression chord in
a spaced apart generally parallel opposed relation to said tension chord;
c) a number of planar dentations connecting the tension chord to
the compression chord, said dentations having two non-parallel side edges
resulting in each dentation having a broad end and a narrow end; a planar
face of the broad end being connected with the side edge of the compres-
sion chord; the narrow end of the said connected planar face being connec-
ted with the side edge of the tension chords; and tension and compression
chords being so connected by dentations disposed on both side edges along
the length of the ~oist thereby creating a joist having a substantially
hollow rectangular cross-sectional shape; said dentations forming one
side of the joist being coordinately disposed with dentations forming the
opposite side of the joist providing through passages permitting wiring,
pipes, conduit, ducts or other apparatus to extend transversely through
tï~e resulting joist openings;
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d) end reinforcements connected face-to-face with said tension
chord at each end thereof; said end reinforcements being between -the ten-
sion chord and the compression chord, said end reinforcements being at
each end of the joist extending inward from the end of the joist so that
each side edge of each end reinforcement is connected to the said connec-
ted planar face of at least two of the dentations; and
e) upright spacers at each end of the joist, said spacers being
connected to the adjoining faces of the said compression chord, said end
reinforcements, and planar faces of both dentations located at the joist
ends on opposite sides of the joist.
Preferably the connections are formed by gluing. Having a
sufficient glue area at these dentation-to-chord connections is a feature
which has been optimized by the current invention. The dentations may
also be attached to the tension and compression chords by using nails,
screws or other fasteners. Dentations are disposed along both side edges
of the tenslon and compression chords so that they form a joist having a
hollow rectangular cross sectional shape with discontinuous sides. The
dentations may be spaced at varying distances along the joist or abutting
one another.
The end reinforcements extend inwardly from the end of the
tension chord for a distance dictated by load requirements. Generally the
side edges of the end reinforcement contact at least two dentations. The
beam can be supported from either the tension chord or the compression
chord. From another aspect, the invention provides
a method of manufacturing structural members or joists comprising
*he s~eps of:
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a) connecting two elongated substantially rectangular end
reinforcements to an elongated substantially rectangular tension chord in
face-to-face orientation both of said end reinforcements being connected
to the same face of said tension chord, one at each end extending inward;
b) positioning an elongated substantially rectangular compres-
sion chord approximately parallel to and spaced apart from said connected
tenSion chord and end reinforcements being positioned between said tension
and compression chord;
c) connecting two vertical spacers to said compression and to
said end reinforcements, one vertical spacer being connected at each end
of said compression chord and end reinforcement combination to said com-
pression chord;
d) partitioning a rectangular sheet of wood or plywood into
interchangeable dentated panels; said dentated panels being shaped where-
upon severance along a single dentated partitioning line creates two
interchangeable panels without significant wastabo; each of said denta-
ted panels having:
i) an interior face;
ii) an exterior face;
iii) a continuous approximately straight compression edge;
iv) a continuous approximately straight end edge perpendicu-
lar to said compression edge;
v) a continuous approximately straight interior edge perpen-
dicular to said compression edge;
vi) a discontinuous approximately straight tension edge paral-
lel to said compression edge and perpendicular to said end edge;
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said dentated panels being further defined by removing certain
portions, said removed portions being shaped substantially like the
isosceles triangle with a truncated apex, the nonequal side of said tri-
angular portion being coincident with said tension edge;
said dentated panels being further defined by locating said
removed triangular portion nearest the end edge so that a portion of said
tension edge adjacent to said end edge is unremoved; the length of said
portion of tension edge which is unremoved is approximately equal to the
perpendicular distance from said interior edge to and including the trun-
cated apex of the triangular portion nearest to said interior edge; theshape of said dentated panels following the said line drawn perpendicular
to said interior end connecting said truncated apex of the removed triangu-
lar portion nearest the interior end; the width of said truncated apexes
being equal to the length of individual segments of said tension edge which
are unremoved other than the above described tension edge segment adjacent
to the end edge;
e) connecting an appropriate number of said dentated panels
to the side edges of said tension chord, compression chord, end reinforce-
ments and vertical spacers thereby forming a substantially hollow rectangu-
lar cross-sectional beam having a length approximately the same as said
tension and compression chords.
The joist can be used anywhere a solid wood joist would normally
be used, for either roofs, floors or both, in a home, commercial building
or apartment construction. The joist may also be used in other applications
where a wood or steel beam having equivalent strength is used. The joist
is oriented with respect to the load so that the one chord member receives
compressive forces and the other chord member receives tension forces.
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Where there is a single concentrated load applied to the beam, additional
reinforcement or varying dentation panel designs may be necessary to
optimally distribute the load. The joist can also be constructed with a
predetermined camber to compensate for flexing of the joist under its load
where the application so requires.
The current invention provides several advantages over the prior
art the first of which is a relatively low profile compared to prior wood
truss devices thus decreasing the overall structure height. The openness
of this joist also greatly reduces the amount of solid wood necessary to
support an equivalent load. The dentated side panel design reduces the
materials necessary for side panels by almost one half, compared to the
true box beams. The current invention can be constructed without metallic
fasteners or gusset plates since the chord-to-side panel connection may be
formed exclusively by adhesives. The joist can also be economically con-
structed with nominal setup or layout costs with readily available building
materials such as nominal tuo inch by four inch lumber for the chords and
structural grade plywood for the dentations. This simplified wooden con-
struction substantially reduces labor costs. The hollow rectangular cross-
sectional shape generally will evidence, it is believed, greater strength
against lateral loads than equivalent wood I-beams. The beam has the
definite advantage of allowing conduit, pipes and other equipment to be run
both transversely and longitudinally through the beam.
The joist of this invention may be assembled using any of the
~ell known glue systems. ~rcferahly a rapid curing glue such as a resor-
cinol phenol resin glue which may be cured by the use of radio frequency
energr is the most desirable glue for usage herein to optimize production.
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BRIEF DESCRIPTION OF Ti{E DRAWINGS
Figure 1 is a side view of one embodiment of the non-symmetrical
joist of this invention with portions broken away for convenience of illus-
tration;
Figure 2 is an end view of the joist shown in Figure 1 with the
compression chord at top and the tension chord and end reinforcement at
the bottom;
Figure 3 shows a partial bottom view of the joist shown in
Figure l;
Figure 4 is a cross-sectional view of the joist taken at line
4-4 of Figure l;
Figure 5 is a cross-sectional view of the joist taken at line
5-5 of Figure l;
Figure 6 is a cross-sectional view of the joist taken at line
6-6 of Figure l;
Figure 7 is a partial isometric view of an end portion of the
oist shown in Figure l;
Figure 8 shows the use of the mechanical fasteners to prelimi-
nary attach the dentated panels to the compression and tension chords;
Figure 9 shows an alternative embodiment of the invention;
Figure 10 shows a plan view of a rectangular panel marked for
sawing or otherwise severing so that eight interchangeable dentation panels
are produced;
Figure 11 shows a further alternative embodiment in which the
joist is supported upon the ends of the compression chord; and
Figure 12 is a cross-section of a third embodiment of the joist
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according to this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figures 1-8 show a preferred form of the invention as embodied
in a joist comprising tension chord 12, compression chord 14, and in
opposed relation on each side, two series of vertically disposed dentations
16. End reinforcements 18 and vertical spacers 20 are normally employed
in the preferred joist form. As shown in Figure 1 the end dentations 22
are about one-half the size of dentations 16. The dentations 16 and 22 of
the joist shown in Figure 1 are produced as shown in Figure 10 from a ply-
wood or other reconstituted structural grade wooden panel, shown generally
at 30. The panel is laid out in four parallel units about 12 inches wide,
each of which is subdivided into an interfitted pair of elongated dentated
panels 32,34. In this form of construction the dentations 16 and 22 of
panels 32,34 are cut apart along the line 36 and from the other pairs by
cutting along line 38. The dentated panels 32 and 34 are shown as used in
Figure 1 in tandem with end dentations 22 placed at the ends of the joist
and the tongues or tabs 40, abutting in the mid portion of the joist. Of
course, if different dimension beams are being produced, different size,
smaller or larger, dentated panels will be used.
It is to be noted that dentated panels 32,34 are placed on both
edges of the support and spaced apart chords 14 and 12 in alignment. This
arrangement provides passages 42 and 44 through the beam to permit various
forms of conduit as for electrical service, water, heating and ventilation
purposes to be passed both transversely and longitudinally through the
j oistS .
In the dentated panels 32 and 34, the various dentations 16 of
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the series are joined by bridge portions 46 as can be seen in both Figures1 and 10. When the joist is being assembled, bridge portions 46 are placed
against the edges of compression chord 14 and they are secured by an inter-
posed layer of adhesive 48, preferably a waterproof polymeric resin adhesive
such as a resorcinol phenol resin. In similar fashion) the blunt ends 17
of the tapered dentations 16 and 20 are adhesively joined at 49 to the
edges of the tension chord 12. In the preferred practice of producing
joists as shown and described in Figure 1, the parts are assembled and
securely clamped together for a time permitting the adhesive to set. Under
such circumstances no fasteners are required. Absent the availability of
suitable clamping equipment, the joist may be assembled as shown in Figure
8 wherein the glue joints are secured together temporarily by fasteners 50
which may be nails or screws. When the adhesive bonds have developed, the
strength of the joist will depend predominantly upon the glue joint.
In Figure 9 an alternative construction is shown in which the
dentations 52,54 are individual, truncated triangular shaped elements as
contrasted with the dentated panels 32,34 previously described. Preferably
dentations 52 and 54 in aligned opposite pairs are joined to the chords 12
and 14 by an adhesive as described above for the embodiment shown in
Figures 1-8.
In Figure 11 is illustrated a joist construction 62 for installa-
tion in a mode somewhat at variance with an installation of joists as shown
in Figures 1-8. In this case the compression chord 64 has been extended
and provided with end reinforcement 66 to form protrusions by which the
joist may be hung at its end from a transverse support means 68. This
distinguishes from the mode of installation of Figure 1 joist which is in-
stalled so that the ends of the tension chord 12 rest on transverse beams
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35 as suggested in Figure 8.
A further variation is illustrated in Figure 12. In this instance
the chordal members, being about twice as wide as they are thick, are dis-
posed on edge. The tension chord 72 and the compression 74 are joined in
spaced apart relation by opposed dentation panels 76,76. Advantages in
this variation are greater contacting glue surfaces and greater stiffness
in the joist. In some cases the height of the joist may be somewhat greater
if the pass through passages 78 are kept to size comparable to passages 42
of Figure 1 joist.
Usually the dentation panels 32,34 are cut from sheets of plywood
in thickness of 1/4 inch to 3/4 inch or thicker as various strengths are
specified. The chordal members are preferably dimension lumber, such as
lumber commonly known as two-by-fours which today have actual dimensions of
about 1-~ inches by 3-~ inches. This joist construction also allows for the
use of fabricated chordal members in which numerous pieces are finger-jointed
or spliced together at their ends. The full length gluing of the dentation
panels along the length of compression chord 14 effectively increases the
thickness, hence the strength of chords 14. End reinforcements 18 provide
greater gluing surfaces and strengthen the glue joints of dentation 16
and 22 to the tension chord, thus very effectively increasing the overall
joist strength and ruggedness at the load bearing points indicated by arrows
in Figure 1.
The structural members or joists described above are manufactured
by a method wherein a minimum of waste of the raw materials utilized occurs.
Initially a pair of elongated substantially rectangular end reinforcement
are connected to an elongated substantially rectangular tension chord
in face-to-face orientation. The tension chord is preferably a
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nominal two-by-four inch dimension lumber. Bo-th end reinforcement
elements are connected to the same face of the tension chord, one being
positioned at each end of the tension chord and extending inwardly. Pre-
ferably the joint between the end reinforcement elements and the tension
chord ~ill be formed by a suitable glue joint. An elongated substantially
rectangular compression chord is then positioned approximately parallel to
and in spaced apart relationship to the tension chord and end reinforcement
elements. Spacers are employed spanning the distance between the compres-
sion chord and the tension chord so that one spanner element is connected
at each end of the compression chord and end reinforcement combination
and to the tension chord. This configuration results in the tension chord
and compression chord lying in a substantially parallel relationship but
spaced apart a distance dictated by the ultimate dimensions of the
structural member being formed.
A rectangular sheet of wood, such as plywood or other reconsti-
tuted wood panel, is then partitioned into interchangeable dentated panels
by severing the sheet along a single dentated partitioning line to form
two interchangeable panels without wastage of the material. In Figure lO
a suitable pattern for partitioning the rectangular sheet of wood is shown.
The cuts along lines 38 are made to sever the sheet into four sections. The
four sections are then cut along a zigzag line 36 which forms a series of
toothlike projections or dentations. One of the two dentated panels thus
formed may be inverted and rotated 180 so that identical panels are formed.
Each of tlle dentated panels may be described as having an interior face
16a a~d exterior face 16b, a continuous approximately straight compression
edge 33, a continuous approximately straight end edge 35, substantially
perpendicular to the compression edge, an approximately straight interior
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edge 37, also substantially perpendicular to the compression edge and a
discontinuous approximately straight tension edge 39, substantially
parallel to the compression edge and perpendicular to the end edge. The
dentated panels can be further described as having a series of truncated
isosceles triangles removed from the tension edge 39 formed by severing
the sheet along the aforementioned dentated partitioning line.
Referring specifically to Figures 7 and 10, it will be seen that
four of the dentated panels are utiliæed in preparing the structural joist-
like member shown. Each of the dentated panels is positioned with its
end edge 35 at the end 41 of compression chord 14 and with compression
edge 33 co-planar with the outer surface of compression chord 14. In
this manner the dentations project downwardly as shown in Figure 7 and
the discontinuous tension edge 39 engages the sides of tension chord 12.
Glue joints or other suitable fastening means are utilized to attach the
panels 16 to the chord members 14 and 12 as well as to the above noted
end reinforcement 18 and vertical spacers 20.
Thus, by the method of this invention, it is possible to manu-
facture a surprisingly strong joist member of any length from two dimen-
sion lumber pieces of nominal size of two inches by four inches and a
sheet of plywood having the dimension of two feet by eight feet without
wastage of any material.
In some installations the joist may be installed in an overtur-
ned aspect whereupon the chord functions are reversed and a substantial
tension loading is imposed upon the lowermost member.
It will be noted that the joist as disclosed herein may be used
at center-to-center s~acings greater than customary with solid wooden
joists and in greater spans than have been customary ~or jois~s of
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comparable dimensions.
While the invention has been described in detail with reference
to the appended drawings, it is to be understood that changes and varia-
tions may be made without departing from the spirit and scope of the
invention as set forth in the appended claims.
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