CA1080936A

CA1080936A - Thermally insulated constructional panels for buildings and the like

Info

Publication number: CA1080936A
Application number: CA319,089A
Authority: CA
Inventors: Casey P. August
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-01-04
Filing date: 1979-01-04
Publication date: 1980-07-08

Abstract

ABSTRACT OF THE DISCLOSURE
Walls, floors and ceilings are constructed on site using pairs of correspondingly corrugated steel sheets having ridges and grooves.
Slabs of polystyrene foam are inserted into all grooves of one sheet leaving half of each slab projecting above the ridges of the first sheet. The second sheet is placed with its grooves fitted over the projecting slab portions and its ridges facing the ridges of the first sheet. The second sheet is forced into contact of its ridges with the ridges of the first sheet and the corresponding pairs of ridges are fastened together to firmly embrace each slab between the pair of sheets.

Description

2 FOR BUILDINGS AND THE LIKE

3 BACKGROUND OF THE INVENTION

4 The present invention relates to panel-like constructional members for use in the construction of walls, floors, ceilings, partitions, 6 and roofs of buildings, ships, and other structures, as well as to methods 7 of assembling such constructional members.
8 Conventional techniques for constructing building elements such 9 as walls, floors, ceilings, partitions and roofs require highly-paid skilled workmen using many specialized tools to fasten together small 11 components to form each element of a building. For example, bricklayers ! ;
12 may assemble basement walls from individual concrete blocks using mortar.
13 Once the foundation or basement wall is completed, skilled carpenters 14 assemble the building framework by fastening together hundreds of wood studs plates, lintels, joists and rafters with thousands of nails and 16 other fasteners. The outer surfaces of the walls and roof are then sheathed 17 by cutting and nailing sheets of plywood and other mater;als to the wooden 18 frame. Prior to interior finishing, the interior walls and ceilings of 19 the frame are typically covered with sheets of drywall or wood, while the floors are covered with plywood or wood planking. The entire process is 21 highly time-consumlng ands due to the skilled labour costs, extremely ;
22 expensive. The resulting cost of buildings, whether industrial, commercial, 23 or residential is correspondingly high.
. -~ 24 Moreover, the thermal insulation of such buildings entails a ~ . .
distinct intermediate step of insetting glass wool or other insulating 26 material into all the crevices of the wall and ce;ling framework and to -27 cover the interior surface of the insulated framework with a vapour barrier 28 of polyethylene film or the like before applying the drywall panelling. ~-29 An object of the present invention is to provide a panel-like constructional member having excellent thermal insulation propertles which 31 can be assembled rapidly without the benefit of high-paid highly skilled 32 craftsmen--2- i ~;' . . ' , , 1 Another object of the invention is to provide an inexpensive 2 panel-like constructional member which is thermally insulating and which 3 has sufficient vertical load-bearing strength to be used in forming a 4 wall of bu;lding.
Another object is to provide a method of assembling panel-like 6 constructional members which can be carried out rapidly and reliably by 7 a small number of relatively unskilled workmen.

9 To overcome the disadvantages of conventional construction techniques outlined above and to achieve the foregoing and other unstated 11 objects (which will become apparent upon appreciation of the disclosures 12 herein) the present invention provides a panel-like constructional member 13 comprising:
14 a) at least two sheets, at least one of the sheets being corrugated, said corrugated sheet having a front surface 16 thereof formed into parallel alternate ridges and grooves; -~
7 b) a slab of thermally insulating material disposed within 18 and substantially filling each groove while leaving at 19 least a minor portion of said slab projecting out of said I`
groove;
21 c) at least one other sheet being fastened to the ridges of 22 said corrugated sheet to thereby maintain each slab in a ~ ~ -23 firm embrace between the two sheets.
24 According to a preferred embodiment, the invention provides a 25 panel-like constructional member comprising:
26 a) a pair of correspondingly corrugated sheets, each corrugated ;~
27 sheet having a front surface thereof formed into parallel 28 alternate ridges and grooves, said sheets being positioned 29 to at least partially overlap each other, the overlapping ridges of one sheet being in contact with and fastened to 31 corresponding ridges of the other sheet to thereby form a 32 tubular cavity between each pair of corresponding grooves .. .....

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1 of the juxtaposed front surfaces of said corrugated sheets;
2 and 3 b) a slab of thermally insulating material disposed within 4 each said tubular cavity and being firmly embraced between each said pair of corresponding grooves.
6 Preferably, each ridge of the front surface of one corrugated 7 sheet is fastened to a corresponding ridge of the front surface of the 8 other corrugated sheet to thereby form a tubular cavity between each pair 9 of corresponding grooves of the juxtaposed front surfaces of the corrugated sheets.
11 It is preferable that each slab be pre-molded from expanded beads 12 of expandable polystyrene and that both sheets be identically corrugated 13 with ridges and grooves of rectangular cross-section, each groove being 14 wider than each ridge.
The invention also provides a method of assembling a panel-like ~ -16 constructional member from a pair of sheets of material and a plurality of 7 slabs of thermally insulating material, at least a first sheet having a 18 front surface thereof formed into parallel alternate ridges and grooves, 19 comprising the steps of:
a) placing said first sheet on a working surface with the front 21 surface thereof facing upwardly away from said working 22 surface;
23 b) positioning one of said slabs in each groove of said first 24 sheet, the lower portion of the slab being formed to substantially fill said groove of said first sheet while 26 leaving at least a minor portion of said slab projecting l;
above said groove;
28 c) positioning a second of said sheets over said first sheet 29 and over any projecting portions of said slabs; and d) compressing each slab by forcing said second sheet into ;
31 contact with each ridge of the first sheet and fastening 32 the sheets together to maintain each slab in a firm embrace :, .
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1 between the two sheets.
2 According to a preferred embodiment, the invention provides a 3 method of assembling a panel-like constructional member from a pair of 4 correspondingly corrugated sheets of material and a plurality of slabs ofheat insulating material, each sheet having a front surface thereof formed 6 into parallel alternate ridges and grooves, comprising the steps of: ::
7 a) placing a first of said sheets on a working surface with the front surface of the first sheet facing upwardly away ::
9 from said working surface;
b) positioning one of said slabs in each groove of the first ~
11 sheet, the lower portion of the slab being formed to : :
12 substantially f;ll said groove of said first sheet while -H: : .
13 leaving an upper portion of said slab projecting above ¦;i 14 said groove; ~.
c) positioning the front surface of a second of said sheets ¦
16 with each groove thereof fitted over and-in mating contact t~
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17- with a projecting upper portion of a corresponding one of , ~
18 said slabsi and ~ :-19 d) compressing each slab by forcing each ridge of the second sheet into contact with a corresponding ridge of the first 21 sheet and fastening these ridges together to maintain each 22 slab in a firm embrace between the pair of corrugated sheetS. ~

24 For a better understanding of the present invention, its advantages :
and applications, reference may be had to the following detailed description 26 of preferred embodiments thereof, taken together w;th the appended drawings, 27 wherein:
28 Figures la, lb, lc, ld, le, lf, and lg are perspective views of `~
29 the assembly of components into an embodiment of the novel constructional member which is preferred for use in walls of bu;ld;ngs;
31 Figure 2 is a perspective view of a completed discrete construc-.
32 tional member assembled by the method illustrated in Figures la to lg, : 5 -; ''' - -- . . . , . .. . ~,. ...
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1 Figure 3 is a cross-sectional view of an embodiment of the nove1 2 constructional member which is preferred for use in floors, roofs9 and 3 ceilings of buildings;
4 Figure 4 is a perspective view of a partially completed building constructed from constructional wall members illustrated in Fig. 2 and 6 from members illustrated in Fig. 3;
7 Figure 6 is a cross-sectional view of the wall corner construc-8 tion used in the building of Fig. 4i and 9 Figure 5 is a cross-sectional view of another embodiment of a constructional wall member in accordance with the invention.

12 Figures la to 19 are useful in illustrating the method of 3 assembling a constructional member in accordance with the invention.
4 Figure la shows a corrugated sheet 1 having its front surface formed into parallel alternate ridges lr and grooves 19. It is preferred 16 that the corrugated sheet 1 be formed from galvanized steel sheet, which 17 may, for example be about 18 or 20 gauge in thickness, although plastic 18 or other sheet material may be used. In order to permit insertion of 19 fewer but wider discrete slabs, which will be discussed in reference to Fig. lb, grooves 19 are preferably wider than ridges lr, and both are 21 substantially rectangular in cross-section. For example, the grooves lg 22 may be ten inches wide while the ridges lr may be only about two inches 23 wide.
24 In any event, the first step of the method is to place sheet 1 --on a working surface which may, for example, be the level concrete floor 26 of a warehouse or a flat area of the ground near the building site. As 27 can be seen in Fig. la, corrugated sheet 1 is placed with its front surface 28 (and thus ridges lr and grooves lg thereof) facing upwardly away from the 29 working surface (not shown).
Figure lb shows the step of inserting slabs 2 into grooves lg.
31 Each discrete slab 2 is composed of thermally insulating material which 32 is preferably resilient and is of a size and shape that, upon insertion . . . - . . .. . . ... . . . :

1 into a groove lg, slab 2 substantially fills groove lg while leaving a 2 portion of slab 2 projecting above groove lg. In order to ensure 3 desirable compression of slab 2 by the other sheet (as shown in Fig. lc), ~
4 the projecting portion of slab 2 should be slightly thicker than the ~ -groove of the other sheet 3 which will fit over slab 2. While slabs 2 6 are preferably pre-molded from expanded beads of expandable polystyrene, 7 they may also be composed of polyurethane foam or of any other suitable 8 insulating material.
9 Figure lc shows the step of positioning the second sheet 3 so that grooves 39 and ridges 3r of its front surface face downwardly to 11 thereby fit each groove 39 over and in mating contact with a corresponding 12 projecting portion 2p of a slab 2. The next step is to compress slabs 2 13 by forcing each ridge 3r into contact with a corresponding ridge lr and ¦ , ~
14 fastening these ridges together (as by self-tapping screws or by spot- ~ -15 weld;ng ridges 3r and lr to each other) to maintain slabs 2 in a firm embrace ¦~
16 between grooves 19, 39 of sheets 1, 2.
17 The configuration of sheet 3 should be such as to ensure a firm l-18 embrace, and preferably compression, of slabs 2, when ridges 3r are 19 fastened to corresponding ridges lr, thereby causing slabs 2 to lend their structural strength to sheets 1 and 3. As a result the panel-like 21 constructional member composed of sheet 1, slabs 2, and sheet 3 can provide ~
22 significant structural strength and, by suitable choice of the material `
23 composing slabs 2, good thermal insulation characteristics as well.
24 Where the panel-like constructional member is to be used as a wall of a bu;lding, it is preferably positioned so that ridges lr, 3r and 26 grooves lg, 39 are oriented vertically. This orientation of the construc-27 tional member maximizes its vertical load-bearing strength, with the 28 paired ridges lr, 3r functioning somewhat like the vertical wooden studs 29 used in conventional construction methods.
For use in exterior buildiny walls, the thermal insulation-31 rating of the novel panel-like constructional member may be further improved 32 by inserting an elongated member 4 of thermally insulating material (such -7- :
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1 as foam polystyrene) into each outer groove 309 formed on the opposite 2 side of sheet 3 from each ridge 3r, as shown in Figure ld. To cover each ~-3 outer groove 309, a Flat strip member 5 (for example, of steel sheet 4 material) may be fastened to the outer surface of sheet 3 adiacent each S outer groove 30g by screws or other means. As shown in Figure le, each 6 flat strip member 5 may have parallel inward flanges 5f projecting from 7 one surface thereof which serve to centre member 5 over outer groove 30g.
8 It will be understood that flat strip members 5 may be used alone, that 9 is, even where elongated insulating members 4 are not used.
As shown in Figure lf, side members 6, each of which has a 1l L-shaped cross-section with a bight portion between a pair of parallel 12 flange portions, are fitted over the side edges of the panel-like 13 constructional member. One flange portion of each side member 6 is 14 fastened to sheet 1 by screws or other means, while the other flange portlon is similarly fastened to sheet 3. Side members 6 serve not only 16 to cover and protect the exposed side edges of slabs 2, but also may be ¦ -` 17 used to attach the panel-like constructional member to an adiacent building 18 element, such as a second panel-like constructional member.
19 As shown in Figure lg, top and bottom plate members 7, each of ; which has a U-shaped cross-section with a bight portion between a pair ¦~
21 of para`llel flange portions, are fitted over the top and bottom edges 22 of the panel-like constructional members. When so fitted, the bight portion 23 of each plate member 7 covers the ends of a member of ridges, grooves, and 24 slabs, one flange portion is fastened to the outer surface of sheet 1, while the other flange portion is fastened to the outer surface of sheet 27 In addition to enclosing the bottom and top edges of the panel-28 like construct~onal member, plate members 7 may be used to attach it to 29 other portions of a building. For example, where the panel-like construc-30 tional member is to be used as part of a ground floor wall of a building, ~ ~ -31 the bottom plate member 7 is first bolted to the foundation wall with the 32 flange portions of plate member 7 projecting upwardly. The bottom edge of ' ' ' .. . .

1 the panel-like constructional member, which is normally lightweight enough 2 to be lifted by two unskilled workmen, is inserted between the upstanding 3 flange portions of bottom plate member 7. The flange portions of plate 4 member 7 are then fastened to sheets 1 and 3 by self-tapping screws or other means.
6 Figure 2 shows a completed, panel-like constructional member 7 assembled according to the method illustrated in Figures la to lg. As 8 will now be evident, the entire assembly can be done rapidly from a small 9 number of standardized prefabricated parts without measurement, cutting or other skilled operations. The only tool needed is typically a common 11 electric drill fitted with a screwdriver bit to drive self-tapping screws 12 to fasten together sheets 1, 3, side members 6, plate members 7, and ;
13 optionally flat strip members 5. Clearly the entire assembly can be 14 carried out rapidly at the bu;lding site by a few unskilled workmen after only a brief training period.
16 While the panel-like constructional member illustrated in 17 Figures 1 and 2 may be used not only for walls but also for ceilings, 18 roofs, and floors of buildings, the modified structure shown in Figure 19 3 is preferred for the latter applications. In the embodiment shown in Figure 3, sheet 1 is formed with deep inner ridges and inner grooves, 21 with a deep outer groove formed on the opposite side of each ridge.
22 After slabs 2 are inserted into the inner grooves, a substantially flat 23 sheet 3a is fastened to the inner ridges of sheet 1 by self-tapping screws 24 or other means. The entire panel-like constructional member of Figure 3 is then turned over so that the deep outer grooves of sheet 1 open upwardly.
26 Elongated members 4a, which may be formed of wood, high density foamed 27 polyurethane, or other material having appreciab1e compressive strengthj :
28 are inserted into, and substantially fill, the deep outer grooves of ~ -29 sheet 1. When the panel-like constructional member shown in Figure 3 is used for a floor or other non-vertical application, elongated members 4a 31 absorb the compressive stresses in the upper surface of the floor, while 32 flat sheet 3a absorbs the tensile stresses in the iower surface of the I ~ -.~ , .

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1 floor. Moreover, the exposed upper edges of elongated members 4a can 2 conveniently be screwed or nailed for attaching a desired floor covering.
3 Figure 4 shows a partia11y completed building using the construc-4 tional members of Figures 1 and 2 for walls, and the constructional members of Figure 3 for the floor and rooftceiling. As will be seen by reference 6 to Figures ld and 4, the inner wall surfaces of the building have vert;cal 7 inner grooves lig formed on the opposite surface of sheet 1 from ridges 8 lr. These inner grooves lig can conveniently be used for installation of 9 plumbing pipes 8, electrical wiring 9, and electrical outlet and switch boxes, as shown in Figure 6. As will be apparent, the rigidity of the 11 walls of the building may be increased by fastening steel strips 10 12 obliquely to the inner or outer surfaces of the walls if desired.
3 The building shown in Figure 4 will be seen to provide good 14 sound insulation and thermal insulation, both of which may be increased for cold climates by increasing the thickness of slabs 2 and the depth 16 of grooves lg and, in the case of walls, 39. For example, a slab 2 of 7 foam polystyrene (such as that sold by the Dow Chemical Company under 18 its trademark STYROFOAM SM) which is three inches thick provides a 19 thermal insulation value of about R-18. The thermal insulation of the assembled walls of Figure 4 would therefore be nearly as high.
21 Moreover, the building shown in Figure 4 is better adapted to 22 withstand earthquake tremors than masonry buildings and can therefore be used in earthquake-prone regions of the world. Because it can be 24 constructed on site from less expensive materials than are conventionally used, and because it can be assembled rapidly by a few relatively 26 unskilled workmen, it is well suited for use in developing countries 27 while providing better insulation proper~ies than those of more expensive 28 conventional buildings.
29 Where desired, the outer and inner surfaces of the novel build;ng may be finished in a convent;onal manner. For example, sheets 1 may be 31 perforated to afford purchase for an exterior decorative coating of stucco.
32 Alternatively, the outside walls may be faced with bricks, wood siding, or - 1 0- ,:
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1 the like. Similarly, the inner surface of walls and ceiling may be covered 2 by plasteror drywall sheets in a conventional manner, although the conven-3 tional vapour barrier sheet need not be applied as the sheets 1, 3 and 4 slabs 2 of the building shown in Figure 4 provide an effective vapour ~ -barrier.
Figure 6 shows a corner construction which may be used in the building 7 illustrated in Figure 4. As will be understood, side member 6a may be fastened 8 to the left-hand wall and side member 6b before the left-hand edge of the 9 right-hand wall is inserted into, and fastened to, edge member 6a.
Moreover, the wall structure of Figure 6 differs from that shown 1l in Figures 1 and 2 by the presence of a thermally insulating strip 11 which 12 may be inserted between adjacent slabs 2 immediately before the assembly l-13 step shown in Figure lc. Strips 11 serve to decrease the heat conductivity ,-14 of the structure by breaking the metal-to-metal conductivity between pairs of adjacent ridges lr, 3r.
16 As will be understood, many other cross-sectional configurations 17 may be chosen for sheets 1 and 3 and slabs 2 depending on decorative and 18 other considerations such as desired insulation thickness. One such 19 configuration is shown in Figure 5, which shows how narrower sheets 3 may be combined with wider sheets 1 for convenient fastening during 21 assemblY
22 It will also be understood that the novel constructional panels of 23 the subject invention may also be used in the construction of below-ground 24 walls for buildings, for the decks and cabins of ocean ships, and many other ~5 structural applications.
26 The present invention will thus be seen to accomplish the objects l -27 stated hereinbefore. It will be realized, however, that various changes ?8 and substitutions may be made to the specific embodiments described herein 29 for the purpose of illustrating the principles of the invention. For example, numerous choices of configurations, thickness, and material composition for ,-31 the sheets and slabs will become obvious to those skilled in the construction 32 Of buildings, ships, and other structures. Accordingly, it is intended that , ,, . . . : . ................................ , :
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1 thls invention be limited only by the scope of the appended claims. ~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A panel-like constructional member comprising:
a) at least two sheets, at least one of the sheets being corrugated, said corrugated sheet having a front surface thereof formed into parallel alternate ridges and grooves;
b) a slab of thermally insulating material disposed within and substantially filling each groove while leaving at least a minor portion of said slab projecting out of said groove;
c) at least one other sheet being fastened to the ridges of said corrugated sheet to thereby maintain each slab in a firm embrace between said two sheets.

2. A panel-like constructional member comprising:
a) a pair of correspondingly corrugated sheets, each corrugated sheet having a front surface thereof formed into prallel alternate ridges and grooves, each ridge of the front surface of one sheet being fastened to a corresponding ridge of the front surface of the other sheet to thereby form a tubular cavity between each pair of corresponding grooves of the juxtaposed front surfaces of said corrugated sheets; and b) a slab of thermally insulating material disposed within each said tubular cavity and being firmly embraced between each said pair of corresponding grooves.

3. A panel-like constructional member as set forth in claim 1, wherein each slab is pre-molded from expanded beads of expandable polystyrene.

4. A panel-like constructional member as set forth in claim 2, wherein each slab is pre-molded from expanded beads of expandable polystyrene.

5. A panel-like constructional member as set forth in claim 2, wherein each slab is pre-molded from expanded beads of expandable polystyrene and wherein each groove is wider than each ridge.

6. A panel-like constructional member as set forth in claim 5, wherein both sheets are identically corrugated and wherein said ridges and grooves are of substantially rectangular cross-section.

7. A panel-like constructional member as set forth in claim 5, an outer groove being formed on the opposite surface of each sheet from each said ridge, and comprising a flat strip member fastened to said opposite surface to thereby cover said outer groove.

8. A panel-like constructional member as set forth in claim 1, wherein each groove is wider than each ridge.

9. A panel-like constructional member as set forth in claim 8, an outer groove being formed on the opposite surface of said corrugated sheet from each said ridge, and comprising a flat strip member fastened to said opposite surface to thereby cover said outer groove.

10. A panel-like constructional member as set forth in claim 7 or 9, and further comprising an elongated member of thermally insulating material disposed within said outer groove.

11. A panel-like constructional member comprising:
a) a pair of correspondingly corrugated sheets, each corrugated sheet having a front surface thereof formed into parallel alternate ridges and grooves, said sheets being positioned to at least partially overlap each other, the overlapping ridges of one sheet being fastened to corresponding ridges of the other sheet to thereby form a tubular cavity between each pair of corresponding grooves of the juxtaposed front surfaces of said corrugated sheets; and b) a slab of thermally insulating material disposed within each said tubular cavity and being embraced between each said pair of corresponding grooves.

12. A method of assembling a panel-like constructional member from a pair of sheets of material and a plurality of slabs of thermally insulat-ing material, at least a first sheet having a front surface thereof formed into parallel alternate ridges and grooves, comprising the steps of:
a) placing said first sheet on a working surface with the front surface thereof facing upwardly away from said working surface;

b) positioning one of said slabs in each groove of said first sheet, the lower portion of the slab being formed to substantially fill said groove of said first sheet while leaving at least a minor portion of said slab projecting above said groove;
c) positioning a second of said sheets over said first sheet and over any projecting portions of said slabs; and d) compressing each slab by forcing said second sheet into contact with each ridge of the first sheet and fastening the sheets together to maintain each slab in a firm embrace between the two sheets.

13. A method as set forth in claim 12, each slab being pre-molded from expanded beads of expandable polystyrene, each groove being wider than each ridge.

14. A method as set forth in claim 12, an outer groove being formed on the opposite surface of said first sheet from each said ridge, comprising the further steps of:
e) positioning an elongated member of thermally insulating material in each outer groove of said first sheet, said elongated member substantially filling said outer groove;
and f) fastening a flat strip member to said opposite surface adjacent each outer groove to thereby cover each outer groove of said first sheet.

15. A method of assembling a panel-like constructional member from a pair of correspondingly corrugated sheets of material and a plurality of slabs of thermally insulating material, each sheet having a front surface thereof formed into parallel alternate ridges and grooves, comprising the steps of:
a) placing a first of said sheets on a working surface with the front surface of the first sheet facing upwardly away from said working surface;

b) positioning one of said slabs in each groove of the first sheet, the lower portion of the slab being formed to substantially fill said groove of said first sheet while leaving an upper portion of said slab projecting above said groove;
c) positioning the front surface of a second of said sheets with each groove thereof fitted over and in mating contact with a projecting upper portion of a corresponding one of said slabs; and d) compressing each slab by forcing each ridge of the second sheet into contact with a corresponding ridge of the first sheet and fastening these ridges together to maintain each slab in a firm embrace between the pair of corrugated sheets.

16. A method as set forth in claim 15, each slab being pre-molded from expanded beads of expandable polystyrene, each groove being wider than each ridge.

17. A method as set forth in claim 15, an outer groove being formed on the opposite surface of each sheet from each said ridge, comprising the further steps of:
e) positioning an elongated member of thermally insulating material in each outer groove of said second sheet, said elongated member substantially filling said outer groove;
and f) fastening a flat strip member to said opposite surface adjacent each outer groove to thereby cover each outer groove of each sheet.

18. A method as set forth in claim 14 or 17, wherein said elongated member is formed of a resilient material.

19. A panel-like constructional member as set forth in claim 8, wherein said other sheet is substantially flat.

20. A panel-like constructional member as set forth in claim 19, an outer groove being formed on the opposite surface of said corrugated sheet from each said ridge, and further comprising an elongated member disposed within said outer groove.

21. A panel-like constructional member as set forth in claim 20, said elongated member being wooden.

22. A panel-like constructional member as set forth in claim 1 or 2 and further comprising at least one plate member having a U-shaped cross-section with a bight portion between a pair of parallel flange portions, said plate member being disposed with said bight portion covering the ends of a plurality of ridges, grooves, and slabs and with one flange portion fastened to the outer surface of said one sheet and the other flange portion being fastened to the outer surface of said other sheet.