US2287081A - Structural element - Google Patents

Description

P. B. AT1-WELL 2,287,081

STRUCTURAL ELEMENT Filed May 2o, 1940. 2 sheets-sheet 1 June 23, 1942.

Patented Jne 23, 1942 STRUCTURAL ELEMENT P. Bobbin Attwell, Seattle, Wash., assignor to I. F. Laucks, Inc., Seattle, Wash. a

Application May zo, 1940, serial No. 336,272

(ci. zii-0.5)

Claims.

The present invention relates to structural elek ments, such as beams, timbers, girders, spars and the like, and to novel structures in which such elements may be incorporated.

It is an object of the present invention to provide anovel form of beam, fabricated from a plurality of smaller elements and assembled in such manner as to provide a beam having characteristics as to uniformity, strength and rigidity as good or better than the best natural wooden beams of corresponding size.

It is a further object of the invention to fabricate, from a plurality of individual elements, wooden beams and the like of greater size than can be readily found in a single piecein the forests at the present time. Moreover, the invention provides smaller beams or spars of greater uniformity as to weight and strength than can be secured in large quantities from standard lumber. Such uniform beams or timbers are of special utility as spars for aircraft wings.

It is a further object of the invention to provide a novel form of large beam for supporting roof structures of unusually wide span. In accordance with one phase of the invention, wide roof structures are supported from a central supporting area, with the ends of the beams unsup- It is a further object of 'the invention to provide a supporting beam fabricated from inexpensive materials and having a novel internal structure which imparts great strength and rigidity to the beam and enables the same to support heavy loads over unusually great spans.

It is a further object of the invention to provide a beam which may be constructed by ordinary carpenters from readily available lumber at the place where the beam is to be ursed, or on the job, problems. To this end, the invention provides a beam which may be fabricated from standard boards or planks, such as 2 x 8 or 2 x 12 slabs, glued together in a novel manner, at the place where the beam is to be used, so that bridges,

buildings, such as airplanehangars, etc., can be f constructed in relatively inaccessible locations.

It is a further object of the invention to provide beams, girders, trusses and the'like which are of particular utility for military purposes,

in that they may bereadily and quickly made up thereby simplifying transportationk at the location where they are to be used, from a plurality of easily transportable units. More particularly, the invention provides methods and means whereby an advancing army can quickly fabricate beams and truss members 'of practically any desired size, on the site, to build or re-build bridges or the like which, for instance, may have been destroyed by a retreating army. The constituent parts of beams, girdersv or truss members, consisting essentially of standard relatively smallv wooden planksand glue, such as dry, powjected to tensional strainswhile other portions are subjected to compression forces. The beam of the` present invention has been constructed in recognition of these factors, and special features have been combined in a novel and improved manner to make certain portions of the beam effectively resistant to tensional strains and other portions similarly resistant to compression forces.

In the accompanying drawings and in the fol'- lowing descriptioma plurality of specific embodiments of the invention are shown and described with considerable particularity, but it must be understood that the invention is not limited to the specific details disclosed, sincemany modiart.

In the drawings:

Figure 1 is a side elevation of one form of beam, adapted to be supported at its ends and to support a load intermediate thereof.

Figure 2 is a somewhat diagrammatic side elevation of a second form of beam, adapted to be supported at a central supporting area. and to ent invention is preferably made up of boards or planks of common sizes, readily availablel from cations will readily occur to one lskilled in the lumber yards. The members are arranged horizontally in endto end relation in superimposed layers. and all contacting faces thereof are firmly united by a glue bond, such as 'a water-resistant and laid up ina suitable manner and spiked together to hold the layers and individual slabs in firm contact under suiiicient pressure to enable the adhesive to set and provide a firm bond. If a water-resistant casein glue of the self-bonding type is used, the bond will be formed in four to eight hours under a minimum pressure, such a's can be readily applied by nails or spikes. These glues are well known and are commonly used where the bonding pressure is applied by nailing instead of by clamps.

'I'he beam Il is adapted to be supported at its ends, as indicated at Il, I2 and the load is normally applied at I3. Hence, the bottom layer or layers, extending substantially one-third of the height of the beam, are subjected to tensional strains. while the layers at the top one-third are subjected to compression forces. Throughout the central zone, the forces are substantially neutral.

In accordance with the present invention, the lower,tensionreceiving layers are made up of -boards or planks I4 having their ends cut on anguiar planes to-provide a scarfed joint l5, characterized by a substantial overlap of the adjacent boards and a greatly increased gluing area.

The amount of overlap or scarf may vary from about six to twelve times the thickness of the slab, a longer overlap being preferable as producing a stronger joint. It is known that a wellglued scarf having a length to thickness ratio of 10 or 12 to 1 of thickness approximates the strength of an unbroken member. Such a joint effectively resists the tensional strains to which the layers are subjected.

Although theangle of pitch of the end faces of the lower planks I4, providingy the scarfed joints I5 may be varied, it thus preferably is at least 8 or 10 to 1. That is, for every unit of vertical thickness of each plank, the scarred end extends longitudinally 8 or 10 units.

The upper, compression-resisting layers I6 are provided with square-cut'butt joints I1, glued together as previously described, with the result that compression forces are transmitted squarely from end to end of the individual planks in the compression-receiving layers. For the sake of simplicity, the intermediate layers I8 also may be provided with square-cut, butt joints.

A second form of beam made in accordance y with the present invention is shown in Figure 2.

This beam preferably functions on the cantilever principle, is supported at a central area andvpro-l jects laterally in Vopposite directions to support the load of a roof or the like, the ends of the beam being unsupported. The beam 26 in Figure 2 is shown as a support for the roof of a novel provided with square-cut ends, providing square,-

amazon the side edge of the roof and enclosing the ends of the beams.`

'I'he beams-20 are supported upon pairs of columns 25, 26, as indicated in Figure 4, in parallel relation, spaced on suitable centers, e. g., 10 ft. centers. -Preferably, the ends of the building are closed by suitable walls 31. f The sliding door arrangement may be such that substantially the entire sides of the building may be opened, to facilitate the entrance and exit of airplanes or the like.

The central supporting area of the beams may conveniently be used as a base for a monitor building 40, provided with windows 4I and a iioor represented diagrammatlcally at 42, which building may house oilices, shops or the likel Moreover, the space between the various supporting columns 25, 26 mayf-'be utilized for storage, ma-

' chine slops or for other purposes.

The beam 20 may be made up of wooden slabs, such as 2" x 10" or 2" x 12" planks, which may be readily obtained from any mill or lumber yard.

Douglas nr or'long leaf Southern pine combine the qualities of uniformity and strength and are lbond, and to prevent.l relative sliding movement between the laminations. With a beam of this. type, used in a building of the kind shown in Figures 3 and 4, the top layers 45, 46, 41 are placed under tension when the load is applied and the lower layers are placed under compression. Hence, the upper layers are made up of planks having their ends cut on angles sharply disposed to the horizontal, thereby greatly increasing the area of the glue bond between the ends of the planks and providing a scarfed joint, as described above. `The angle of pitch of the end faces, again, is preferably 8 or 10 to 1 or greater.

Certain of the lower layers, such as those indicated at--55, which are subjected to compression forces when the load is applied, are made up of planks adhesively united as aforesaid, but

butt joints 56, whereby compression forces in the layers are transmitted squarely from one plank to the next. convenience, be made from planks also having square, butt joints.

As suggested in Figure 2, in order to increase the strength of the beam and to resist bending thereof, it is sometimes found desirable to apply a plurality of additional tension-resisting layers 51, 58, 59 to the upper faces of the end portions of the beam, between the central supporting area and the extremities thereof. As shown in Figure 1,` three layers of progressively decreas- Sliding doors 35 may be supported by any approprlate hanger means secured tothe ends of the beams or a finishing strip 36 disposed along cases, however, the extra layers 51-59 appliedv to the upper surface of the end portions of the beams are unnecessary.

a In actual practice. cantilever beams in accordance with the present invention have been constructed having overall lengths of feet. These beams were built up of dressed, 2" x 10" The intermediate layers may, for i l 2,287,081 I planks of suitable length, adhesively secured together with the top three'layers,`- aswell as the extra layers 51, 58, 59, provided with scarfed joints and theremaining layers with square, butt joints. At the center, there were thirty-sixlayers of planks, providing a vertical thickness of .substantially feet, 2 inches. The beam tapered toward its ends, as indicated diagrammatic'ally in Figure 2, to a thickness of inches at its extremities. n sion, the two supporting points were spaced feet apart, thereby providing a span of '45 feet from each point to the adjacent end of the beam.

For the sake of clarity, in the accompanyingv In the installation under discus pletely through the beam. Hence, the invention I is ofvparticular utility where the high uniformity characteristics are desired, suchsas in aircraft construction. The invention is not limited to the specific i details of construction described above, but cov' ers all constructions coming within the scope of with suitable scarfed or butt joints are equiv-V In making the beam, ,the slabs or planks may be adhesively coated, as stated above, with a suitable glue, for example, water-resistant casein'Vl glue, desirably of the self-bonding type; After being coated with such a glue, the planks are secured together by conventional nails or spikes,

' to hold the layers in firm contact under reasonable pressure, while the adhesive is setting and to obviate the necessity of using large pressure applying clamps, forms or the like. The planks are preferably laid up in a rough form, so as to give the desired pitch or camber to the laterally projecting portions of the beam, beyond the central supporting zone, which facilitates drainage of rainwater on the roof toward the center where it may be carried away by appropriate drainage' spouts, not shown. This is of especial advantage in constructing airplane hangars for military purposes in cold climates, so as to obviate any icing-up of the doors.

Beams and girders made in accordance `with the present invention have many advantages as compared with steel girders and single-piece, solid wooden timbers. Steel girders are far more expensive andmust be fabricated at a steel mill and transported to the place of installation. The transportation costs and difculties alone, in many cases, make'the beam of the present invention more economical and convenient than steel beams. Extremely large wooden timbers, on the other hand, are practically unavailable today, because of the scarsity of large trees. Moreover, trees large enough to provide beams of the size contemplated by this invention, if existent, are usually inaccessible, and transportation problems, agaiinare encountered.

In the manufacture of certain types of aircraft wings and the like, wooden spars characterized by high strength and great uniformity are essential, but considerable trouble has been encounthe appended claims and their equivalents. For

instance, it is, of course, understood that in the case of members of small section such as the laminated airplane wing Aspars previously described, relatively thin wood veneers provided aient to the slabs or planks of dimension lumber used in constructing large structural beams.

.I claim:

1. A structural unit, such as a beam, girder or timber, of the type adapted to have portions subjected t6 tensional strains and other portions subjected to compression forces when in load supporting condition, said unit comprising a plurality of elongated boards or planks horizontally aligned in end to end relation and superimposed jin layers with the contacting surfaces `thereof?adliesively united by a glue bond, the

-boards or'planks in the layers in the portion subjected to tensional' strains being connected at their ends by angularly cut, glue-bonded scarfed joints and the boards or planks in the layers in the portion subjected to compression forces being connected at their ends by substantially squarecut butt joints.

' 2. A beam adapted under load to have a portion thereof subjected. to tensional strain and another portion subjected to compression forces, said beam comprising a plurality of'wood slabs arranged end to end and superimposed in face to face relation in a plurality of layers, and'glue bonds between the adjacent faces and ends of the slabs, the adjacent ends ofthe individual slabs in a layer in the tension-receiving portion being cut on planes disposed on oblique angles to the top and bottom faces of the slabs and providing glue-bonded scarfed joints to resist the tension in said layer, the adjacent ends oi the individual slabs. in a layer in the compressionreceiving portion being cut on planes disposed substantially at right angles to the top'and bottom faces of the slabs and providing square, butt joints, whereby the compression forces in said layer `are resisted.

3. An elongated beam of substantial height j adapted underload to have substantially onetered in securing such spars from natural wood K and the supply is constantly diminishing. The

present invention is of particular utility in this field, since the laminations. built up and glued together, as described above, provide a spar structure of maximum uniformity. Any flaws or weaknesses in one ply are counteracted and olfset by the adjacent plies and the glue bond. Be-l cause ofthe manner in which the beam is constructed from a plurality of layers, it is impossible for a vflaw or weak spot, such as might result from a knot in the wood, to extend comthird of its height subjected to tensional strain and the opposite one-third subjected to compression forces, said beam -comprising a plurality of wood boards or planks arranged end to end and superimposed in face to face relation in a plurality ofL layers, and glue-bonds between the adjacent faces and ends thereof, the adjacent ends of the boards or planks in the layers in the first-mentioned one-third of the height of the beam being cut on planes disposed on oblique angles and providing a glue-bonded scarfed joint to resist said tensional strains, the adjacent ends of the individual boards or planks in the layers in the lastmentioned one-third of the beam being substantially square-cut and providing square, butt joints to resist said compression forces.

4. A beam adapted to resist bending stresses j.

' sion-receiving layers 4theadjacent planks are cut on angularly dissupported glue-bonded together, thereby providing an elonthereof subjected to tension under said bendingstresses and strains, the ends of the planks are joined with 'angularly out, scarfed joints, while, in the portions of the beam subjected to compression, the ends'of theplanks are joined in square-cut butt joints.

5. An elongated beam adapted to be supported at its ends and to support a loadintermediate its ends, comprising a plurality of wood planks arranged end to end and superimposed in face to face relation in a plurality of layers, and gluebonds between the adjacent faces and ends of the slabs, characterized in that in the lower, tenoi the beam, the ends of posed planes providing scarfed joints and that in the upper, compression-receiving layers, the ends of the planksare cut substantially square, providing butt joints.

6. An elongated beam comprising a plurality of wood planks arranged end to end and superimposed in face to face relation in a plurality of layers, and glue-bonds between the adjacent faces and ends of the slabs, characterized `in that in the upper, tension-receiving layers of the beam, the ends of the adjacentiplanks are cut on angularly disposed planes providing scarfed joints and that in the lower, compression-receiving layers, the ends of the planks are out substantially square, providing butt joints.

'7. A beam for roofs' or the like adapted to be supported from a central portion and to be unlaterally therefrom to its edges, said beam comprising a plurality of elongated wooden slabs horizontally arranged in end to end relation in layers superimposed upon eachother, and securing means rigidly connecting all of the adjacent faces of all of ing of progressively increasing bottom of the beam toward the top, at the bottom being relatively short and only of sullicient length to span the central supporting area.

8. A beam for roofs or the like adapted to be supported from a central portion and to be unsupported laterally therefrom to its edges, said beam comprising a plurality of elongated wooden slabs horizontally arranged in end to end relation in layers superimposed upon each other, and glue-bonds between the adjacent faces of the slabs, said layers being of progressively increasing length from the bottom of the beam toward the top, the layers at the bottom being relatively short and only of sufiicient length to span the central supporting area while the slabs in certain of the upper layers extend continuously from end to end of the beam.

9. A beam for roofs or the like adapted to be length` from the elongated wooden slabs arranged horizontally in joined together at their ends by glue-bonded scarfed joints, while the slabs in the lower, pressure-receiving layers are joined at their ends by substantially square-cut butt joints.

10. A beam comprising a plurality of gluebonded wooden planks arranged end to end in superimposed layers, 'the planks in the tensionreceiving layers being joined at their ends by glue-bonded scarfed joints to resist endwise separation under tensional strains, and the planks in the compression-receiving layers being joined by substantially square-cut endabutted joints to prevent relative endwise movement thereof under compression forces.

` 11. A beam comprising a plurality of elongated wooden slabs arranged in end to end relation and superimposed in a plurality of layers and all secured together by glue-bonds between the adjacent faces thereof, said beam, on the face thereof which is subjected to tensional strains when bending forces are applied, being provided with a plurality `of additional layers ot wood slabs adhesively united thereto, the individual slabs in the last-mentioned layers being secured together in end to end relationby angularly cut, gluebonded scarfed joints.

l2. A cantilever beam for roofs or the like adapted to be supported from a central area and to be unsupported from that area outwardly to 1ts ends, said beam comprising a plurality of end to end relation and superimposed in a pluralityof layers all secured together by a gluethe slabs, said layers bethe layers supported from a central portion and to be unprojecting from said area in opposite directions toward the open sides of -the building, said and glue-bonds between the adjacent faces of the slabs, said layers being of progressively increasing length from the bottom of the beam toward the top, the layers at the bottom being relatively short and only of suillcient length to span the central supporting area while the slabs in certain of the upper 'layers extend continuously from end to end of the beam, the slabs in the last-mentioned tension-receiving layers being bond between the adjacent faces, whereby, when loads are applied to the ends of the beam, the slabs in the upper layers are subjected to tensional strains, and a plurality of additional, tension-resisting slabs applied to the upper face of the beam, adhesively united thereto and extendlng from the margins of said central supporting area outwardly to the ends of the beam, the individual slabs in the last-mentionel layers being joined together at their ends lby angularly cut scarfed joints.

13. In a building, such as an airplane hangar or the like having end walls and unobstructed open sides, a roof and means for supporting the same from a central supporting area, said means comprising 'a plurality of spaced parallel beams projecting from said area in opposite directions toward the open sides of the building, said beams each comprising a plurality of elongated wood planks arranged in end to end relation in a plurality of superimposed layers and all secured together by glue-bonds between the adjacent faces thereof, the planks in the upper, tension-receiving layers of the beam being joined at their ends by angularly cut, glue-bonded, scarred joints.

14. In a building, such as an airplane hangar. `or the like having end walls and unobstructed open sides, a roof and means for supporting the same from a central supporting area, said means comprising a plurality of spaced parallel beams beams each comprising a plurality of elongated wood planks arranged in end to end relation 1n a plurality of superimposed layers and. all secured together by glue-bonds between the adjacent faces thereof, the planks in the upper tension-receiving layers being joined at their ends by angularly cut, glue-bonded, scarfed' joints while the planks in the lower, compression-receiving ends by square-cut butt joints.

layers.. are joined at their 'I `l 15. A roof for a building. such as an airplane hangar or the like which has substantially -unobstructed-'open sides and a centrally positioned,

longitudinally extending roof-supporting structure, said roof comprising a plurality of spaced parallel beams projecting from said supporting structure in opposite directions toward the open sides of the building and a continuous roof oovering carried' bysaid beams. said. beams each Y comprising a plurality of elongated wood planks arranged in end to end relation inA a" plurality of' superimposed layers and all secured together by glue-bonds between the adjacent faces there# of. theplanks'in the upper, tension-receiving layers of the beam being joined at theirends by angularlyycut, glue-bonded, scarfed joints.

P. BoBBIN ATTWELL.

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