US3616153A

US3616153A - Hollow structure of stacked sheets

Info

Publication number: US3616153A
Application number: US805646A
Authority: US
Inventors: Martin L Downs
Original assignee: Thilmany Pulp and Paper Co
Current assignee: Thilmany Pulp and Paper Co
Priority date: 1969-03-10
Filing date: 1969-03-10
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26

Abstract

A hollow structure is formed of thin sheets of material such as, for example, paper, paperboard or Gypsum with preformed openings in the sheets. The sheets are stacked in a programmed sequence to define a cavity of a predetermined shape within the interior of the article. The exterior edges of the sheets are also programmed in sequence to define the desired exterior surface for the article such as, for example, a simulated brick wall surface. By appropriately programming the sheets with interiorly disposed portions, it is possible to form and shape internal elements within the hollow cavity. The method of forming the article includes the bonding of the sheets such as, for example, by flooding the hollow cavity with the bonding agent and permitting penetration of the bonding agent into the stacked sheets.

Description

[72] Inventor Martin L. Downs Appleton, Wis.

[21] Appl. No. 805,646

[22] Filed Mar. 10, 1969 [45] Patented Oct. 26, 1971 [73] Assignee Thilmany Pulp and Paper Company Kaukauna, Wis.

[54] HOLLOW STRUCTURE 01F STACKED SHEETS 2 Claims, 9 Drawing lFigs.

2,055,296 9/1936 Lane Primary Examiner-John E. Murtagh Attorney-Fitch, Even, Tabin & Luedeka ABSTRACT: A hollow structure is formed of thin sheets of material such as, for example, paper, paperboard or Gypsum with preformed openings in the sheets. The sheets are stacked in a programmed sequence to define a cavity of a predetermined shape within the interior of the article. The exterior edges of the sheets are also programmed in sequence to define the desired exterior surface for the article such as, for example, a simulated brick wall surface. B y appropriately programming the sheets with interiorly disposed portions, it is possible to form and shape internal elements within the hollow cavity. The method of forming the article: includes the bonding of the sheets such as, for example, by flooding the hollow cavity with the bonding agent and permitting penetration of the bonding agent into the stacked sheets.

PATENIEMBI 26 Ian SHEET 10F d INVENTOR MARTIN L DOWNS PMEIEBBU 26 mm SHEET 2 BF 4 ATTYS PATENTE B 26 197i 3,61 6. 153

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HNVENTOR MRTIN L. DOWINS HOLLOW STRUCTURE OF STACKED SHEETS This invention relates to laminated hollow structures or articles suitable for various ends and uses and to methods of making the same.

Traditional methods of fabricating hollow structures such as, for example, platform skids, hollow core doors, aircraft foils, partitions onbuilding walls, involve the making of many separate pieces such as facing walls, braces, headers, stops, spacers, studs, etc., each having different shapes and often made from different materials. These respective pieces must be collected at an assembly area, properly positioned relative to one another and then fastened together in a series of operations. For example, when fabricating an interior or exterior building wall, the various component pieces are collected at the assembly site, studs or framing members are fastened together and in place, stops, headers or the like are positioned and fastened in place, and then interior and facing walls are attached to the oppositesides of the framing to enclose the in teriorly disposed members. The costs of collecting the component members and assembling thereof in this manner is overcome with the present invention.

A shortcoming of many hollow structures, particularly those having internal supporting members, isthat the structures are made from a number of diverse materials each having a different rate of expansion or contraction. n the other hand, structures made from the same or similar materials, such as wood, often have the grains of the respective pieces misaligned. Such structures are subject to splitting, cracking, or separating from each other under temperature or moisture cycling due to the differential rates or directions of expansion or contraction.

With the.present invention, many hollow structures made typically with wood, metal and plastic or combinations thereof, and, in the abovedescribed manner, may be made from thin sheet materials of paper, paperboard, paper waste, gypsumboard or other mineral materials with laminar stacking and plying techniques which not only form the exterior of the structure but also form, at the same time, interior elements, such as stops, braces, studs or the like within the hollow interior of the structure. By suitably sequentially programming the outer facing edges of the sheets used to make the structure, its

facing surfaces may be decoratively configured or textured, e.g., wall structures having brick, clapboard, or stone appearing surfaces. By additions of suitable bonding agents, fire proofing or other agents, the laminated paper or mineral sheet structure may be made .with unexpected hardness, strength, rigidity, and unity desirable for outdoor use or in loading bearing situations.

Accordingly, a general object of the invention is to provide a new and improved structure and methods of making the same.

Other objects and advantages will become readily apparent from the following detailed description and the accompanying drawings in which:

FIG. 1 is a fragmentary, perspective view with a portion of a sidewall broken away to expose an interior of a hollow structure embodying the features of the invention;

FIG. 2 is a reduced-in-size perspective view of a sheet used in forming the structure of FIG. I;

FIG. 3 is a reduced-in-size perspective view of another sheet used in forming the structure of FIG. ll;

FIG. 4 is an enlarged, exploded perspective view of several sheets used in forming the structure of FIG. 1;

FIG. 5 is a diagrammatic illustration of a manner of making the structure of FIG. 11;

FIG. 6 is a fragmentary, cross-sectional view of a manner of interlocking several wall structures made in accordance with another embodiment of the invention;

FIG. 7 is a fragmentary, cross-sectional view of another embodiment of the invention showing an interlocking pair of abutted wall structures;

FIG. 8 is a fragmentary, cross-sectional view of several wall members shown in FIG. 7 joined to a corner member; and

FIG. 9 is an enlarged, fragmentary view illustrating a manner of forming a clapboard surface: for a wall structure.

As shown in the drawings for purposes of illustration, the invention is embodied in a hollow structure which is formed with a large number of thin, flat, laminated sheets 11 at least some of which have preformed openings 112 programmed in sequence (vertically in this instance) to form and shape internal hollows or cavities M and to form and shape internal elements 15 disposed in the interior of the structure between facing walls 117 and I9. By sequentially programming the widths, lengths and the shapes of the exterior edges of the sheets, the appearance of the structure is defined. For instance, a decorative surface 211 of simulated brick is provided for the illustrative wall structure. Thus, by suitably shaping the sheets and programming the stacking of the shaped sheets, it is possible to produce various hollow structures without, as in the prior art, machining cavities thereinor without costly assembling of and fastening of many internal and external diverse elements.

As will be explained in greater detail hereinafter, hollow structures may be made primarily of relatively inexpensive materials such as paper, paperboard, paper waste, gypsumboard or the like which are made on mass scale basis with papermaking techniques, casting, molding or similar techniques. Papermaking or other continuous sheet forming machines offer the advantage of producing extremely long sheets for assembly into very long structures. For example, the

illustrated wall structurelmay be as much as 50 feet in length and formed with literally hundreds of plies of thin, flat sheets of paper or paperboard stacked one upon the other to desired height, say 8 or 10 feet. It will be appreciated that the longitudinal dimension of the structure will usually be aligned with the machine direction of the sheets and that the grain or machine directional strengths, if any, will be aligned in this longitudinal direction. This is helpful in reducing splitting or cracking due to temperature or moisture cycling. By incorporating into the sheets or by selection of a suitable bonding agent such as, for example, sodium silicate, the assembled sheets may lose their individual characteristic softness of paper and be transformed into a hard, rigid, and strongstructure capable of use as a building wall, either of a load or nonload bearing kind.

Before proceeding with a detailed description of the invention, the method of making the illustrated wall structure of FIG. 1 will be briefly described in connection with FIG. 5. A continuous web 29 of paperboard is fed forward, and, at a diecutting station 31, the preformed openings 12 are formed in the interior of the web and notches 33 are formed along the edges of the web. If desired, suitable control equipment at the diecutting station may render certain dies operative and other dies inoperative to provide a manner by which successive cuts may be changed in accordance with a desired sequence. At a severing station the web is severed transversely into sheets ll of the desired length. The sheets H are stacked in a predetermined sequence, such as the sequence in which the sheets were formed, at an assembling station 35. After the sheets are registered and stacked the stack may be moved forwardly to a bonding station 37 at which a suitable bonding agent such as sodium silicate adhesive is added as by flooding the hollow cavity with the structure. The bonding agent is allowed to penetrate toward the outer edges of the sheets and along inter faces between the sheets and by capillary action into the fibers of the sheet. The penetration, i.e., depth, of the bonding may be limited by controlling various factors such as the viscosity of the bonding agent, the time allowed for penetration, and the amount of compressive forces being applied to the stacked sheets. After adhesive penetration has proceeded as far as desirable, the excess of the adhesive is removed, as by tipping the stack. The adhesive retained by and on the sheets is allowed to dry with the adhesive becoming hard and forming the rigid hollow structure.

Referring now in greater detail to the individual elements comprising the hollow structure, the preferred sheets R11 are relatively flat with spaced faces 39 and. All which are substantially parallel to one another and adapted to be abutted against faces of other adjacent sheets when forming the structure. The preferred sheets are thin in cross section or depth between the

faces

39 and 41 as compared to the width or length dimensions of the sheets; and are typically i-inch or less thick paperboard, paper, asbestos, gypsum or other mineral board or the like. The thickness of the sheet may be varied depending upon the process used to form the sheet, the composition of the sheet, and the ultimate properties desired for the finished structure. The width of the sheet, i.e., the distance between

longitudinal edges

43 and 45 of the sheet, may be also varied considerably. It may be relatively narrow, such as onlyseveral inches for a door structure or in the range of 4 to 12 inches for a building wall or panel structure. The longitudinal length of the sheet may be, if desired, very long as this usually is in the machine direction for the paperboard. Hence, structures having lengths of 50 feet or more may be made. Thus, it will be seen that unlike many typical wall boards or other types of sheets, which are commonly limited to 4-feet by 8-feet sheets, because this is maximum width possible with machine on which they are formed, that structures of this invention may be made with heights and lengths considerably in excess of such dimensions.

Of particular importance in making inexpensive hollow structures is the ability to use relatively inexpensive materials such as a low-grade or scrap paper or paper formed such as on papermaking equipment utilizing low-grade furnishes. Blemishes, pinholes or the like in a given sheet of paper, which render the same waste for many uses, make relatively little difference in the quality of the final article or structure in this instance. It is to be understood that sheets 11 are not limited to any given material; but sheets of cellulosic materials and sheets made of inorganic materials such as asbestos, mica or the like are preferred because of low material and sheets formation costs. Also, continuous or large sheets may be handled and/or converted with conventional lines of equipment. Because the laminating techniques are used to make the ultimate structure, it is possible with the present invention to use asbestos or silicate fiberboard which would be too brittle and subject to cracking if attempted to be bent, scored or otherwise used in commercial building techniques.

Referring now in greater detail to the forming of the cavities 14 by the sequential programming of the performed openings 12 in the sheets 11. In this instance, the preformed openings in each of the sheets 11 in the center section of the wall structure are formed with identically shaped openings 12 which have internal edges 47 arranged vertically relative to one another to define, collectively, vertical walls forming large rectangular cross-sectioned cavities or circular cavities, such as seen in FIG. 4. More specifically, each of four planar vertical walls 49 defining a large hollow cavity is formed and shaped by the alignment in vertical planes of the edges 47 of many individual sheets shown in FIGS. 2, 3 and 4. Adjacent cavities are separated by narrow webs 51 in the sheets which are sequentially programmed to be vertically aligned and stacked to form vertically disposed cross walls 52 which are in the form of internal members which take the place of the conventional studs or cross frame members in conventional walls.

At various locations, the cavities 14 may be divided by a transverse wall such as a stop 53 into upper and lower portions and thereby prevent unrestricted air movement in the vertical direction throughout the height of the wall. If desired, each of the stops 53 may be provided with small vertically extending bores 54 of circular cross section to receive electrical conduits or to facilitate the fishing of electrical wires vertically through the interior of the wall. The stops 53 are formed by several of the abutted sheets having circular, performed openings within a central portion 55 of the sheets. As best seen in FIG. 4, these central portions 55 are much wider than the webs 51 and are aligned in a vertical plane with the latter to constitute a part of the cross walls 52 as well as the header walls 53. To obtain the necessary thickness, i.e., the vertical dimension, for the stop 53, the desired number of sheets having central portions 55 are sequentially programmed and stacked. As the sheets having the central portions 55 are substantially solid relative to the sheets having the large rectangular openings, the former adds rigidity to the wall structure. Sheets similar to those used to make the stops 53 may be used to define a bottom wall for the structure and/or a top wall therefor with the illustrated bores 54 therein.

If desired, the sequential programming of several sheets having the proper openings 12 therein may provide internal, diagonally extending braces 59 like that illustrated in FIG. 1. In this instance, the brace 59 is formed by providing the sheets comprising it with narrow webs 61 and having the edges 60 of the respective webs laterally displaced to each other. In this instance, each of the webs 60 has the same width and its edges 61 are offset laterally to define substantially parallel, opposite sides of the diagonal brace 59.

In the illustrated wall structure, the exterior facing walls are formed with a simulated brick surface which is made by controlling the shape or width dimensions of the sheet and sequentially stacking the sheets having the various shaped outer edges to achieve the desired bricklike pattern. More specifically, the illustrated facing walls 17 and 19 are formed with a bricklike appearance having horizontal channels simulating horizontal mortar lines 67 and vertically disposed channels simulating vertically disposed mortar lines 69. As can be best understood from FIGS. 2 and 4, the sheets used to form the bricklike areas are formed with spaced notches 71 at the location of each vertical mortar line 69, in this instance at both ends and at the center of the sheet. The marginal portions 73 of the 'sheets between the notches 71 will project from the plane of the mortar lines 69 to appear as the brick surfaces. The horizontal mortar lines 67 are formed by stacking the narrower width sheets (FIG. 4) having straight, longitudinally extending edges 72 one upon another. The narrowwidth sheets have a width equal to the distance between rear walls 74 of the respective notches 71 in the brick-forming sheets. Thus, a simulated brick surface is formed by stacking a series of wide sheets to provide the appearance of bricks spaced by horizontal mortar lines and stacking a series of narrow sheets providing the horizontal mortar lines between bricks. The painting of the mortar lines 67 and 69 with a grey or white color and the brick areas of a contrasting yellow or red color will enhance the appearance.

Many other simulated surfaces may be made by controlling the width of the sheet and sequentially programming the different widths of the sheets. For instance, a simulated clapboard surface 75 (FIG. 9) may be obtained by forming a series of vertically inclined surfaces 76. The sheets 11 illustrated in FIG. 9 have a progressively increasing width dimension from a minimum width for a sheet 110 to a maximum width for a sheet 11b which is stacked on a minimum width sheet 11a. The process is repeated to form a series of vertically tapered outer, clapboard appearing surfaces. A striated surface (not shown) for the walls may be formed by forming shallow recesses or grooves in edges of adjacent sheets which are all of substantially the same width.

To interlock several wall sections or structures together, the respective end walls 78 thereof may be formed with means including grooves, splines, or other configurations which would be difficult and costly to machine or cut at the ends of a conventional wall. For example, the end walls 78 may be made with centrally disposed, vertically extending grooves 79 (FIG. 4) to receive narrow, vertically extending keylike projections 80 formed on other wall section or structure, as best seen in FIG. 1. In the embodiment of the invention illustrated in FIGS. 1 and 4, another wider channel 81 is defined by inner, longitudinally extending walls 82 which intersect a transverse wall 83 in which is formed the key-receiving groove 79. A complementary shaped projection 85, as best seen in FIG. 1, is inserted into the wide groove 81 and abuts the respective

groove defining walls

82 and 83. In this manner, the wall sections are interlocked against sliding or shifting transversely to one another.

Another form of interlocking means used to join adjacent wall structures is shown in FIG. 6 with a vertical key 86 inserted into a pair of keyways 87 which are formed with reversely tapered sidewalls 88. The latter would be expensive and difficult to machine if formed in wood studs of conventional walls. Suitable semicylindrical, mastic slots 89 may be formed in the end walls of adjacent wall structures to receive a suitablesealing or mastic materiallat the vertically disposed joint. In this embodiment, end walls 90 of the structure are flat and abutted in a common plane.

Another form of interlocking means between wall structures, which would be difficult or expensive to machine in commercial. wall structures, is illustrated in FIG. 7. More specifically, the end walls of the structures are formed with a sinusoidal shape including an arcuately cross section projection9l and an arcuately shaped groove 93. The projections 91 and grooves 93 are complementary in size and the projection of one wall section fitsinto the groove of the other wall section. The interlocking projections on the respective wall sections prevent separation or sliding in a direction transverse to the plane of the facing walls. If desired, vertically disposed holes 95 may be formed at the endsof each of the wall sections to receive a rod, cable, strap or other member for registering of the sheets 11 during stacking and to facilitate the attachment of the wall structure to top or bottom plates. Also, mastic receiving slots 89 may be provided in the wall sections of FIG. 7.

- The sheets 11 may be provided with other openings 96, as illustrated in FIG. 7, in the opposite sidewalls forming portions thereof. When forming the wall section, vertical rods 97 may be positioned and then each sheet 11 may be sequentially placed in position above the rods 97 and then loweredon the rods to abut the next lower sheet of the wall section. The rods 97 in the holes 96 register the sheets prior to bonding the sheets together and the rods 97 may be left in the wall section to facilitate carrying and handling the wall sections. Also, by having the ends of the rods project above and below the wall section, the rods may be fastened to top and bottom plates at the site location to lock the wall section in position.

Also, wall structures may be quickly and rigidly joined ,together or to a post 99, as best seen inFlG. 9, by use of interlocking means in the form of the sinusoidally shaped ends which are interfitted. More particularly, the post 99 is formed of plied sheets each having a pair of sinusoidally shaped sides in the form of projections 101 and grooves 103. The grooves 103 receive the end wall projections 91 and likewise the wall section grooves 93 receive the post projections 101 with the end walls of the respective sections tightly abutted against the post walls. The sheets forming the post 99 may also be provided with preformed openings which are aligned to form vertically disposed holes 105 which are adapted to receive rods, straps or other members used to secure the post in place. Also, the post may be provided with semicircular, mastic receiving grooves 107 for alignment withthe similar grooves 89 in the wall structures. Thus, a convenient strong interlocking connection may be made with complex shapes which are too expensive or difficult to cut or machine in conventional walls.

Referring now in greater detail to the illustrated method of making the structures illustrated herein, the sheets ll may be secured or bonded together in a number of ways, such as, for example, by applying adhesive to the upper and lower faces 39 and 41 of the sheets during stacking or by impregnating the sheets with a suitable adhesive which can be activated after the sheets are stacked. While these methods may provide a satisfactory product, improved results have been obtained by simultaneous bonding of the sheets by slushing or flooding the large rectangular, cross-sectionedcavities 14 with a liquid adhesive for a predetermined period of time while the sheets are held with a predetermined compression which limits the rate of penetration of the adhesive along the abutted faces 39 and 41 of the sheets. Also, the viscosity of the adhesive is controlled to limit penetration of the adhesive by capillary action through the body of the sheets. It is preferred that the adhesive penetration proceed substantially to the outer edges of the sheets so that the edges are also bonded together while they still remain relatively dry. After a predetermined period, the adhesive is allowed to drain from the cavities M and the retained adhesive is allowed to dry or cure. To assist the penetration of the bonding material between the stacked piles, the sheets 111 may be formed with superficial indentations or grooves 1108, as best seen in FIG. d, in one or both faces extending from a preformed opening 112 which will be filled with the bonding material. The grooves 108 serve as irrigation channels providing a more positive liquid flow along the faces of the sheets toward the edges thereof. The grooves may be formed in the sheets at the time of manufacture or embossed therein by suitable embossing dies.

Sodium silicate adhesive has been used to bond paper based sheets into a strong, hard, rigid structure. A suitable sodium silicate adhesive is made by Philadelphia Quartz Company andv sold as N grade. A suitable pigment may be also added to the adhesive so that the final coloring and finish is made'simultaneously with the impregnation. In addition'to the slushing technique, the exterior facing walls and the interior walls of the cavity may be brushed or spread with the bonding agent, particularly when containing a pigment. Various bonding agents other than sodium silicate may be used to bond the respective plies or sheets together, the particular selection of a known adhesive being a matter of the use of the structure, cost and other considerations.

Referring now to FIG. 4, a manner of making the wall structure will be now described in greater detail. A suitable furnish containing cellulosic fibers and inorganic filler, such as clay, and also including fire retardants and mold resisting material is formed into a continuous web of paperboard on a cylindrical papermaking machine (not shown). While areas of the screen of the cylinder of this kind of papermaking machine may be selectively covered with a resist to prevent paper formation at the area of the preformed openings 12, it is preferred that the web 29 be continuous and uninterrupted and that the openings 12 be formed at the diecutting station 31. In some instances, the web 29 may be fed directly from the papermaking machine, but usually the web will be wound in suitable supply rolls lllll which can be stored and transported to the location at which the structure will be built. In either event, web 29 is fed forwardly to the diecutting station 311 at which the web is die cut to form the preformed openings 1'2, notches 33 and end wall configurations. The diecutting apparatus may take many forms such as the vertically reciprocating rams U3 and 115 which carry suitable paper-cutting dies for cooperating with suitably shaped openings in a dieblock lll6 disposed beneath the web. The material punched from the webs may be ejected down through the die block as the rams 1113 and 115 return upwardly, all in a conventional manner. It is preferred that the diecutting apparatus have the capability of allowing a change in the size and shape of the preformed openings 12 and cut the edges of the web in the desired sequence to form the simulated brick wall surface. For instance, the diecutting machine may be controlled by a program tape on which are encoded the location of the dies to be rendered 'etfective to make the desired cuts on the web. As an alternative, rotary cutting dies (not shown) may be used.

The web 29 may be cut into sheets at various locations either before or after diecutting the openings l2 and notches 33; and the web is illustrated as being severed into sheets by a reciprocating blade 119 after the openings have been formed. In the illustration of FIG. 5, the severing of the sheets forms the ends thereof with edges which will, when stacked and aligned, form the

grooves

79 and 81 at the end of "the wall sec tion. Also, another diecutter (not shown) may be used to trim the edges of the web when forming the narrow-width sheet for the horizontal mortar lines. The length of the severed sheets will usually be quite greater than illustrated herein as one of the advantages in forming walls with the present invention is obtaining a long wall length. The sheets are illustrated as being short to facilitate illustration and description of the invention.

On the other hand, when forming other articles, the length to width ratio of the sheets may be less than that illustrated for the wall structure.

At the assembling station 35, the sheets are registered and stacked by means such as a form 121 which has vertically disposed, registering bars 123 for abutting the ends of the respective sheets at each of the corners thereof. Centrally disposed, registering bars 125 are inserted into notches 71 at the center of the sheets and abut the edges 72 of the narrowwidth sheets to assure that the rear walls of the centrally notch sheets and the narrow sheet edges are aligned in vertical planes for forming the vertical mortar lines. Alternatively, the form may include or consist only of the vertical rods 97, such as illustrated in FlG. 7, with each sheet 11 having holes 96 to receive the rods as the sheets are stacked sequentially on the rods 97. in this instance, the sheets leaving the diecutting station are in the proper sequence for stacking and are thus sequentially programmed. On the other hand, the sheets need not be in the proper sequence for stacking as the sheets leave the cutting station as the proper sequencing and programming may be done at the assembly station by an operator having access to the various shapes needed.

ln this preferred embodiment of the invention, the stacked sheets are placed in compression between an upper plate 127 and a lower plate 129 with a hydraulic ram 131 exerting a predetermined pressure on the sheets at the bonding station 37 at which the internal cavities 14 are also filled from dispensers 133 with the bonding agent, sodium silicate in this instance. The sodium silicate penetrates along the interface between a lower face 39 of one sheet and the upper face 41 of an adjacent sheet, and capillary action of the fibrous sheets draws the bonding agent into the sheet, per se, to wet the fibers thereof. When the bonding agent penetrates to the outer walls of the structure defined by the edges of the sheets, the remaining pool of bonding agent in the cavities is drained therefrom as by removing the bottom plate 129 or inverting the stack to allow the adhesive to flow from the top of the cavities. After this, the wall structure is sent forward to the drying or curing station at which the sodium silicate hardens and the sheets become rigid. [t is preferred to hold the sheets in the form and under compression during the drying and curing of the adhesive to limit warpage. Any tendency of expansion of the cellulosic fibers during the cure results merely in densification of the sheets. If desired, suitable pigment may be added to the sodium silicate adhesive so that the finished coat is applied simultaneously with the bonding agent. After curing, the

compression plates

127 and 129 may be unclamped and the structure is completed and ready for use.

As stated at the outset, various kinds of hollow articles or structures (these terms having been used interchangeably herein) such as, but not limited to walls, air foils, doors, etc., may be formed by bonding superimposed sheets of relatively thin material such as paper, paperboard, asbestos board or the like. By sequentially programming preformed openings in the sheets, the internal elements and hollow cavities may be formed without machining or the fastening of numerous parts. In a like manner, the edges of the individual sheets also may be sequentially programmed to form the outer facing walls with a desired shape and to form the end walls with suitable interlocking shapes. In some instances, such as when forming the dovetail keyway slots illustrated in FIG. 6, the openings in the plies defining the sidewalls of the keyway slots are in one sense preformed openings 12 in that they define a hollow cavity and are in another sense part of the facing or end walls of the structure. Hence, the terms preformed openings and internal hollow cavities do not necessarily exclude a connection with the outer or surrounding walls.

While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A low-cost, hollow structure having structural integrity and rigidity for supporting loads, comprising a plurality of sheets stacked in face-to-face relationship, said sheets being thin in that the sheets have a thickness substantially les than the width or length dimensions of said sheets, said sheets being formed of a fibrous material, at least some of said sheets having preformed openings with such sheets being stacked in a programmed sequence to define a cavity of predetennined shape within the interior of said structure, certain of said sheets having interiorly disposed portions abutted to fonn and shape an internal reinforcing element within said cavity, the exterior of said sheets defining an exterior surface for said structure, and means including a bonding agent for bonding said sheets together along the faces thereof to provide said hollow structure, said bonding agent impregnating said fibrous sheets and providing said fibrous sheets with a rigidity and hardness substantially greater than the rigidity and hardness of said fibrous sheets prior to the impregnation thereof, said internal element extending diagonally relative to vertical and horizontal directions with said cavity.

2. A hollow structure comprising substantially flat sheets stacked face-to-face, said sheets having a depth dimension substantially less than a width or length dimension, exterior edges of said sheets being assembled to define facing walls for said wall structure, at least some of said sheets having performed openings, said preformed openings of adjacent sheets being programmed and assembled in sequence to define a predetermined contour for a cavity in said structure, said sheets being assembled to a height exceeding that of the width dimension of said sheets, and means bonding said sheets together to form said hollow structural wall, at least some of said sheets having grooves in the face of said sheet for conveying a liquid bonding agent outwardly from said preformed openings toward said facing walls for said wall structure.