CA1122378A - Hollow rectangular joist - Google Patents

Abstract

ABSTRACT
A wooden structural member or joist having a continuous tension chord and a continuous compression chord which are spaced apart and parallel. The tension chord and compression chord form the effective top and bottom of the joist, the actual orientation depending on the type of load imposed upon the joist. Dentations or dentated panels connect the side edges of the tension chord to the side edges of the compression chord, thus forming the two sides of the joist which has a hollow rectangular cross sectional shape. The dentations are planar with two parallel edges and two non-parallel edges tapering together forming a broad end and a narrow end. The face of the broad end is glued to the side edge of the compression chord, and the face of the narrow end is glued to the side edge of the tension chord. The sides of the joist are discontinuous because of the dentated shape. The dentations are coordinately spaced to allow pipes, conduits, ducts and other equipment to pass transversely through the joist. The hollow rectangular shape also allows such equipment to pass longitudinally along the joist between the ends.

Description

~,Z237~

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 ll~Z378 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 ~l~Z378 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;

`` :l.~ZZ378 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:

3l~8 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;

ll~Z37~3 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.

~l~Z378 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.

~l~Z37~

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 237~

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 ~Z378 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 Z3 ~'8 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 ll;~Z3~7~3 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 Z3.~8 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 Z371~

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.

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 compression chord; the narrow end of the said connected planar face being connected 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 joist 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 permit-ting wiring, pipes, conduit, ducts or other apparatus to extend transversely through the resulting joist openings;
d) end reinforcements connected face-to-face with said tension chord at each end thereof; said end reinforcements being between the tension 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 connected 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.

2. The inventions of Claim 1 wherein the dentations are spaced together so that a portion of the non-parallel side edges of the broad end of the dentations are in contact with at least a portion of any adjoin-ing non-parallel side edges of the broad end of the adjacent dentation(s).

3. The invention of Claim 1 wherein the joist is constructed entirely of wood.

4. The invention of Claim 1 wherein said tension chord, compres-sion chord, end reinforcements and vertical spacers are made from 2 inch by 4 inch nominal sized lumber, and said dentations are made from plywood.

5. The invention of Claim 1 having said connections effected by an interposed adhesive.

6. The invention of Claim 4 having all of said connections effec-ted by an interposed adhesive film.

7. The invention of Claim 5 having at least one of said connections effected by the use of mechanical fasteners.

8. The invention of Claim 6 having at least one of said connections effected by the use of mechanical fasteners.

9. A structural member comprising:
a) an elongated tension chord having a substantially rectangular cross-sectional shape;

b) an elongated compression chord having a substantially rectangular cross-sectional shape; said compression chord being spaced apart and substantially parallel to said tension chord;
c) planar dentated panels, each of said panels having:
i) an interior face;
ii) an exterior face;
iii) a continuous approximately straight compression edge;
iv) a continuous approximately straight end edge perpen-dicular to said compression edge;
v) a continuous approximately straight interior edge perpendicular to said compression edge;
vi) a discontinuous approximately straight tension edge parallel to said compression edge and perpendicular to said end edge;
said dentated panels being further defined by removing certain portions thereof, said removed portions being substantially in the form of isosceles triangles with a truncated apex, the unequal side of said triangular portion being coincident with said tension edges;
said dentated panels being further defined by locating said removed triangular portion nearest to 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 being approximately equal to the perpendicular distance from said interior edge to and including the truncated apex of the triangular portion nearest to said interior edge; the shape of said dentated panels following the said line drawn perpendicular to said interior end connecting said truncated apex of the removed triangular 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;
said dentated panels are connected to said tension chord and compression chord to form a structural member having substantially hollow rectangular cross-sectional shape;
said dentation panels being connected to said tension chord and compression chord so that half of said dentated panels form each side of the structural member with an edge of a dentated panel being adjacent to the ends of said tension and compression chords; said interior faces of said dentated panels being connected to both side edges of said tension chord and compression chord adjacent to said tension edge and compression edge of said dentated panels;
d) two elongated end reinforcements having a substantially rectangular cross-sectional shape; said end reinforcements being located between said tension and compression chords in contact with said tension chord, said end reinforcements each extending from one end of the struc-tural members inwardly both side edges of each end reinforcement being connected to and in contact with at least two dentations of each dentation panel located adjacent to the ends of said structural member; and e) upright spacers located between said compression chord and said end reinforcements at both ends of the structural member, each such vertical spacer being connected to adjoining surfaces of said compression chord, end reinforcements, and interior faces of two dentation panels.

10. The invention of Claim 9 wherein the joist is constructed of wood.

11. The invention of Claim 9 wherein said tension chord, compression chord, end reinforcement, and vertical spacers are made from 2 inch by 4 inch nominal sized dimension lumber, and said dentation panels are cut from plywood.

12. The invention of Claim 9 having said connections effected by an interposed adhesive film.

13. The invention of Claim 12 having at least one of said connec-tions effected by the use of mechanical fasteners.

14. The invention of Claim 9 having at least two identical but reversed dentation panels on each side of the structural member.

15. The invention of Claim 9 wherein said compression chord is longer than said tension chord, and further comprising two additional end reinforcements being located between said tension and compression chord, said additional end reinforcements each extending from one end of the compression chord inwardly, both side edges of each additional end reinforcement being connected to and in contact with at least two denta-tions of each dentated panel located adjacent to the end joist, said structural member being supported at each end by the overhanging compres-sion chord and additional end reinforcement.

16. A method of manufacturing structural members or joists compri-sing the steps of:
a) connecting two elongated substantially rectangular end rein-forcements 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 compres-sion 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 wastage; each of said dentated panels having:
i) an interior face;
ii) an exterior face;
iii) a continuous approximately straight compression edge;
iv) a continuous approximately straight end edge perpendi-cular to said compression edge;
v) a continuous approximately straight interior edge per-pendicular to said compression edge;
vi) a discontinuous approximately straight tension edge parallel to said compression edge and perpendicular to said end edge;
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 truncated apex of the triangular portion nearest to said interior edge;
the shape of said dentated panels following the said line drawn perpendi-cular to said interior end connecting said truncated apex of the removed triangular 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 rectan-gular cross-sectional beam having a length approximately the same as said tension and compression chords.

17. The method of manufacturing joists presented in Claim 16 having all of said connecting and connections accomplished by gluing or otherwise adhering the parts together.

18. The method of manufacturing joists presented in Claim 16 having said tension chord, compression chord, end reinforcements and vertical spacers manufactured from dimension lumber and said dentated panels being manufactured from 4 foot by 8 foot sheets of plywood cut longitudinally into quarters which are in turn each severed into two interchangeable dentated panels.

19. The method of manufacturing joists of Claim 17 having at least one of said connections further accomplished by using nails or other mechanical fasteners.

20. The method of manufacturing joists of Claim 16 being further comprised of the steps of connecting two additional end reinforcements to said compression chord; wherein said compression chord is longer than said tension chord and said joist is supported through said overhanging addition end reinforcements and compression chord.