US2207952A

US2207952A - Structural unit and method of making it

Info

Publication number: US2207952A
Application number: US129391A
Authority: US
Inventors: Walter H Stulen
Original assignee: LIDA FOSTER STULEN
Current assignee: LIDA FOSTER STULEN
Priority date: 1937-03-06
Filing date: 1937-03-06
Publication date: 1940-07-16
Anticipated expiration: 1957-07-16

Description

July 16, 1940. W H, STULEN 2,207,952

bTRUCTURAL UNIT AND METHOD OF MAKING IT Filed March 6, 1957 5 Sheets-Sheet 2 INVENTOQ. m /f July 16, 1940. w. H. sTuLEN 2,207,952

STRUCTURAL UNIT AND METHOD 0F MAKING IT Filed March 6, 1937 3 Sheets-Sheet 5 Patented July 16, i940 i y i l UNITED STATES PATENT lori-ics I STRUCTURAL UNIT AND vMETHOD OF MAKING IT `Walter H. Stulen, Pittsburgh, Pa., assignor to Lida, Foster Stulen, Bellevue, Pa.

Application March 6, 1937, Serial No. v12.9,391

` 22 Claims. (C1. iss- 34) This invention relates to structural building pieces of sheet metal are secured in any of sevunits made from metal sheets or plates and loneral particular relations with longitudinally ex gitudinally extending shaped metal sections and y tending load carrying shaped metal sections ,and is particularly concerned with building units of in which the particular relation of the sheet the indicated character adapted to be built into metal areas is determined by the particular use 5 panels and embodied in the fabrication ofv frameto which the building unit is to be put. n, l less buil-dings. The foregoing and other objects of my inven-vv In my Patent No. 2,075,874, entitled Frameless tion are achieved by the provision of a strucbuilding, I disclosed and claimed one type of tural building` unit comprising three longitudinalbuilding unitconstructed from sheet metal and ly extending shaped metal sections positioned 10- shaped metal load carryingvmembers, such as relative to `each other to define in transverse channels and angle irons. Likewise,.in the resection the corners of a triangle. Individual ferred-to patent, I disclosed and claimed the use sheet metal sections o f similar polygonal shaper of my building unit in the fabrication of frameare welded to the sections at longitudinally reless buildings in which the usual isolated joists, Current points and` provide longitudinally rei5. 4 beams and other structural members forming a peated triangular sheet metal areas between the skeleton framework for a building are-replaced sections. by individual structural unitsy built into panels In the method of my invention individual sheet which form the walls, floors, ceilings and roof of metal Yareas of the desired polygonal shape, as

the building and in and of themselves'serve'to fOrexample, triangular or rhombic, are cut from 20 carry the strains and loads imparted lto the a relatively narrow strip of sheet metal so that building in use. there is no waste metal and these areas are then My present invention is concerned with a struc- Welded with or Without an intermittent bending tural building unit of the same general character Operation to longitudinally extending shaped met- 'as that disclosed and claimed in my identified al :.sectons, as for example, channel Shaped 25 patent and hence the fabrication of the building Sections 0r angles positioned to define in trans-v unit `of my present invention into` panels for a Verse section the-corners of a triangle. frameless building will not be discussed here. For a better understanding of my invention ref- However, it should be ,understood that the strueerence should be had to the accompanying drawtural unit of my present invention is particularings wherein Fig. 1 is a plan View (if used hori- 30 lyv adapted to the formation of panels made from ZOIltally) 0r an elevation (if used vertically) of a a plurality of units with the panels then being Sirlltlliel building unit embodying the Driniples used in the construction of a frameless building. Of my invention; Fig. 2 isa side elevation of the v It is the general object of my invention to probuilding unit ShOWn in Fig. 1; Fig. 3 is a transvide an improved structural building unit made verse cross sectional view taken on line III- III 35A from sheet metal and shaped metal secti0ns,.and of Fig. 1; Fig. 3a is a cross sectional View through adapted for the fabrication of panels and framea panel constructed from the units of Figs. 1 t0 3; less buildings, n Fig. 4 is a plan or elevation of another embodi- Another object 0f my invention is to provide ment Of my lllVelll'JiOll.; Fig. 5 iS 9. Side' eleVatlOll.

40 a building unit wherein sheetmetai in the form. 0f the building unit Shown in Fig..4; Fig. 6 is a 4o of individual sections of polygonal shape is Welded transverse cross sectional View taken on line to three longitudinally extending shaped metal VI-VI of Fig. 4,; Fig. 7 is a plan View of a strip sections so that the sheet metal forms triangu- 0f Sheetvmetel marked fOr Cutting into individual lar areas repeated longitudinally of the unit. and areas in accordance with the principles 0f. my

substantially in end to end contact. invention; Fig. 8 is a plan view of another strip 45,.

Another object of my invention is the provision of sheet Ametal illustrating a modied manner of of improved methodstfor manufacturing struc- Cutting the strip; Fig. 9 is a plan or elevation tural building units of sheet metal by which the of another structural unit constructed in accordsheet metaly parts of a unit can be rapidly cut ance with my invention; Fig. 10 is a side elevafrom relatively narrow strips of sheet metal to tion ofthe unit illustrated in Fig. 9; Fig. 11 is a 50' form individual areas which are secured in lontransverse cross -sectional View taken on line gitudinally spaced relation to shaped metal sec- XI-XI of Fig. 10; Fig. 12 is a plan View of a. tions... l y l i strip of sheet metal marked for cutting to form Another object of my invention is to provide the sheet metal `areas ,o f the building units of.`

51.5 an improved structural unit-in which individual Figs. 1 to3 and 9 to l1; Fig,-l3 is a plan or. 55

elevation of a structural building unit similar to that shown in Figs. 9 to 11 but wherein the individual sheet metal areas of similar shape are arranged to form a building unit of a modified form; and Fig. 14 is a transverse cross sectional View taken on line XIV-)UV of Fig. 13. i

In the embodiment of my invention illustrated in Figs. 1 to 3, the numeral I0 indicates a longitudinally extending shaped metal section, ordinarily in the form of a rolled or pressed channel, having side anges forming an angle of between about 120 and 150 with the latbaseV of the channel. Positioned paralleltvith the channel I0 and in alignment with the flanges are shaped metal sections I2 and I4, ordinarily formed angles, and together with the channel defining in transverse section the corners of a triangle, as best seen in Fig. 3. Completing the building unit are longitudinally spaced individual sheet metal members I6 of polygonal shape, as for eX- ample triangular, Which are Welded or otherwise secured to the longitudinally extending metal sections I0, I2 and I4, as illustrated in the several gures, so that a girder or truss member I 5 is provided in which the sheet metal members form diagonally extending load carrying Webs. i i

In the embodimentv of the invention illustrated the sheet metal members II5 of triangular shape are secured to the angles I2 and I4 at their bases and the vertexes of the sheet metal members I6 are secure-d to the channel I0, preferablyv at the inside as shown in Fig. 3 so that the channel flanges lieto the outside of the ends ofthe sheet metal members I6. Bly-aligning the flanges of the channel I0 with the plane of the sheet metal members the fastening of these parts together is facilitated and loads are transmitted directly therebetween. In use the building unit is employed with the channel I0 away from the load as shown in Fig. 3 but it can be used with the angles I2 and I4 positioned away from the load. In actual construction the individual building units I5 of this embodiment of my invention are adapted to be positioned side by side and welded into panels as fully described in myy ycopending `application Serial No. 13,868 heretofore mentioned. The fabricated panels are then adapted to be constructed into a frameless build-` ing, i. e., one in which the skeleton framework is entirely omitted.

Fig. 3a illustrates a cross section through a panel so constructed and wherein the individual vunits I5 of Figs. 1 to 3 are arranged in a giveand-take relation with eachl other. More particularly, Where the total Width of the Wall, floor or other member to beformed by the panel is some-What greater than the sum of the widths of the several units I space one or more of the units equal distances Il' apart so that together they provide a panel of the desired width. The units are then secured together as by transversely or obliquely extending tie straps I8 and` boundary plates or channels I9 as fully described in my copending application Serial No. 13,868.

In the form of my invention illustrated in Figs. 4 to 6, the

numerals

2G, 22 and 24 indicate longitudinally extending shaped metal sections positioned relative to each other so that in transverse section they denne the corners of a triangle. Ordinarily, the section 20 is a channel having .side flanges making an angle from between about 120 to about 150 with the base, and the

sections

22 and 24 are formed angles. Secured toY the longitudinally 'extending

metal sections

2B, 22 and 24 are sheet metal members 26 which,

as best seen in Figs. 7 and 8, may take the form of rectangles or rhomboids which are bent along a diagonal with the sheet metal member being Welded or otherwise secured along the bent diagonal to the channel 20 preferably on the inside and welded or otherwise secured at its laterally projecting corners to the longitudinally extending metal sections 22 and '24. Thus the sheet metal provides triangular areas extending between the

metal sections

20, 22 and 24 so that l a load carrying member is provided.

The individual building units of Figs. 4 to 6 are adapted to be assembled into panels and the panels into a frameless building structure as heretofore described. When the individual units are built up into panels, the panels preferably include diagonally extending metal ties or straps 2B spanning the

metal sections

22 and 24, preferably at the points Where the sheet metal members 2:6 are secured to. the shaped metal sections. To further strengthen each building unit I may provide upturned flanges or pressed beads 3B upon the edges of thesheet metal members.

As will be seen from 5, the .use of individual sheet metal members for fabricating a building unit as described provides a plurality of longitudinally overlapping triangular areas for carrying strains between the

metalsections

20, 22 and 24. It should be understood that the exact shape of the sheet metal members 26 may be varied within rather Wide limits so that exact angles formed by the nanges 30 of the sheet metal members and the longitudinally extending metal sections, can be adapted to.y best transmit the strains imparted thereto in use.

An important. part of my inventive concept is the provision of an improved method for making structural building units including individual sheet metal members and my method is clearly illustrated in Figs. 7 and 8. In Fig. '7, the letter S indicates a stripv of sheet metal of relatively narrow width and of a thickness suitable for use in the construction of a unit. The dot and dash lines 34 indicate how` the strip is cut. to provide a plurality oi' sheet metal members, as, for example, the members 26. In Fig. 8, the letter S1 indicates a narrower strip of sheet metal likewise marked with dot and dash lines 36 which indicate the position of cuts.

v to be made-in order to produce a plurality of sheet metal sections therefrom. From the foregoing it will be recognized that in the fabrication of building units including sheet metal mem,- bers, the members canv be cut `from av strip of she-et metal Without wastefand this operation adapts itself to modern machineryy and production methods so that individual sheet metal sections of the desired shape and size can be rapidly and eiciently produced.

In the form of my invention shown in Figs. 9 to 11, the numerals 4I), 42 and 44 indicate longitudinally extending shaped metal sections positicned in parallel relation to each other so that in transverse section they formthe corners of a triangle, as is evidentfrorn Fig. 11. Completing the building unit are sheet metal membersk 46 of substanitally triangular shape which are welded or otherwise secured by their bases to the metal 'section 40 and .byy their vertexes to

themetal sections

42 and 44. lIn otherv words, this embodiment of my invention is substantially the same as that shown in Fig. 1 except that the sheet metal members of Fig. 1 are welded by particularA building v (ifiV their bases to the outside of the shaped metal sections instead of to theinside of the metal sections. Moreover, in the 'embodiment of my invention shown in Figs. 9 to 11 the centrally positioned hapedfmetal section 40, ordinarily in the fornrof a channel, as will be seen from Fig. 11, is in the horizontal use of the unit positioned at the top thereof. A pressed bead 48 may be included along one or more edges of the individual sheet metal members 46 whereby the strength of the sheet metal to resist buckling under compressive strains is improved.

As shown in Fig.` 12 I contemplate cutting the individual sheet metal members 46 from a relatively narrow strip S2 on lines 50 by modern production methods and apparatus as heretofore described. This operation can be performed without waste and the individual members produced -can be rapidly welded or otherwise secured to the longitudinally extending shaped metal secttions to form a structural building unit having rthe desired load carrying characteristics. If it iis found desirable to provide additional space Afor fastening surfacing or like materials to the building unit or if additional venting of the unit is desired, the individual sheet metal members 46 may be cut with notches -as indicated by the lines 52 in Fig. 12. I may also form the sheet 'metal areas with cut out portions as shown, for example, by the dotted lines A3 in Rodgers Patent No. 1,324,982, if this be desirable.

The embodiment of my invention shown in Figs. 13 and 14 is identicalwith that shown in Figs. 9 to `11 and just described with the exception that the individual sheet metal members are longitudinally offset on the two sides of the iunit, More particularly, in Fig. 13 the

numerals

60, 62 and 64 indicate longitudinally extending shaped metal sections positioned parallel to each other but in transverse section defining the cor- Aners of a triangle, as `seen in Fig. 14. The individual

sheet metal members

66 and 68 are of substantially triangular shape and are formed, in the embodiment of the invention illustrated, with notches 'l0 and 12.

The sheet metal members 66 are longitudinally offset lrelative to the members 68 so that in plan 'View the members form a Z-sh-aped or zigzag 'strengthening member of sheet metal which is particularly adapted to transmit strains and loads between the shaped metal sections and provide -a structural building unit having'a large number of places for fastening surfacing materials to the 'unit and employing a minimum of sheet metal.

The individual buildingunits of the `embodiment of my invention shown in Figs. 13r and 14 4can be formed into panels land the panels'into frameless building structures as heretofore described. In connecting the individual building 'units together into panels I have found it advisable to employ diagonally extending metal ties or straps, identified byy thenumeral 16, which are connected to the rolled metal sections 6,2 and 64 adjacent the points where the

sheet metal members

66 and 68 are likewise secured thereto.

The individual sheet metal members 66 and `lill can be made from the same strip S2 ofsheetmetal shown in Fig. 12 and cut as described in conjunction therewith. l

From the foregoing description it will bek appreciated that the objectsof my invention have been achieved by fthe provision of an improved type of structural building unit'fadapted to-be made from individual sheet metal` members or "areas and longitudinally extending shaped metal sections. The building units can take several different forms dependent upon the particular use to which the unit is to be placed. The sheet metal members can be cut without waste and by rapid commercial production methods and apparatus, and the sheet metal membersy can be positioned in fabrication at any desired longitudinally repeated positions to provide a building unit ofthe character desired.

A unit constructed in accordance with the principles of my invention can be made of any 'width and height and in any desired length, as will be recognized. Ordinarily the units are from between 3 and 10 inches in height and are from 6 inches to 3 feet in width but are usually about '7l/2 inches high and 18 inches Wide. All of the units herein described are adapted to be readily fabricated into panels which in turn can be made into a frameless building. The individual units, the fabricated panels and the constructed frameless building are all adapted to be readily cov'L ered or surfaced in any desired way, as for example with metal, wood, brick or other building or surfacing materials, since the surfacing materials can be readily fastened to the building units lat any of a plurality of spaced points thereon.

Although the expression` sheet metal has been employed in the specification and claims, I contemplate using metal in sheet form of any necessary thickness to carry required loads. Particularly, metal plates can be employed and the expression sheet metal is intended to broadly cover plates or sheets.

While in accordance with the patent statutes several embodiments of my invention have been illustrated and described, it should be understood that my invention is not limited thereto or thereby but is defined in the appended claims.

I claim:

1. A structural building unit comprising a longitudinally extending channel, two longitudinally extending angles positioned relative to the channel to define in transverse section the corners of an isosceles triangle, individual sheet metal members of similar polygonal shape welded to the channel and to the angles at longitudinally re-y current points .and providing longitudinally repeated. polygonal sheet metal areas between the Tchannel and each angle.

2. A structural building assembly comprising a plurality of units each comprising three longitudinally extending metal sections positioned irel- 'ative to each other to define together in trans l verse section the corners of an isosceles triangle, individual sheet metal members of similar polygonal shape weldedr to the sections at longitudinalily recurrent points and providing spaced apart longitudinally repeated polygonal sheet metal areas between the sections and means securing the units side by side into a fiat panel assembly.`

3. A structural building unit comprising a chan nel having anges forming an angle of between about and about 150 degrees with the base of the channel, angles parallel to the channel and positioned in alignment with the flanges of the channel, a sheet metal member of'substantially` triangular shape secured at its base to an angle and at its vertex to the inside of the ange of ithe channel, a sheet metal member similar to the first-named member and secured to the other anfgle and to the channel in opposed relation to the first-named member, and a` plurality vof opposed sheet metal members secured to the channel and the angles at longitudinally spaced points.

Li.' A structural building unit comprising ya so; y

Coi

channel having flanges forming an angle of between about 120 and about 150 degrees with the base of the channel, angles parallel tothe channel and positioned in alignment with the ianges of the channel, a sheet metal member of substantially triangular shape secured to an angle and to the inside of the ange of the channel, a sheet metal member similar tothe rst-named member and secured to the other angle and to the channel in opposed relation to the first-named member, and a plurality of opposed sheet metal members secured to the channel and the angles at longitudinally spaced points.

5. A structural building unit comprising a channel having anges forming an angle of between. about 120 and about 150 degrees with the base of the channel, angles parallel to the channel and positioned in alignment with the flanges of the channel, a sheet metal member of substantially triangularl shape secured at .its base to a` iiange of the channel and at its vertex to an angle, a sheet metal member similar to nist-named member and secured to the other angle and to the channel. in opposed relation'to the rstnamed. member, and a plurality of opposed sheet metal members secured to the channel and the angles at longitudinally spaced points.

6i. A structural building unit comprising three longitudinally extending metal sections positioned parallel to each other and inV transverse section defining the corners of an isosceles triangle, the section at the vertex of the trianglebeing a channel and the sections at the base corners of the triangle being angle irons, a .plurality oi sheet metal members of .substantially rectangular shape, each of said members being bent along substantially a diagonal and welded in the region of its bend to the section positioned at the vertex of the triangle and at each of its extending corners to one section positioned at the base corners of the triangle, the members being secured to the rolled metal sections at longitudinally repeated points and having their ends extending longitudinally past each other, strengthening anges formed on at least some edges: of the members, andl straps extending between the metal sections at the points of joinder of the members thereto.

7. A structural building unit comprising three longitudinally extending metal sections positioned parallel to each other and in transverse section defining the corners of an isosceles triangle, a plurality of sheet metal members of substantially rectangular shape, each of said members being bent along substantially a diagonal and welded in the region of its bend to the section positioned at the vertex of the triangle and. at. each of its extending corners to one section positioned at the base corners of the triangle,

the members being secured to the rolled metall.-

sections at longitudinally repeated points and having their ends extending longitudinally past' each other, strengthening anges formed on at least some edges of the members, and straps extending between the metal sections at the points of joinder of the members thereto.

8. A structural building unit comprising three longitudinally extending. meta-l sections positioned parallel to eachother and in transverse section defining the corners of an isosceles triangle, a plurality of sheet metal members of substantially rectangular shape, each of said members being ben-t along substantially a diagonal and welded in the region of itsI bend to the section Apositioned at the vertex of the triangle and at each of its extending corners to one sec.- ton positioned at the base corners of the triangle, the membersY being secured to the sections at longitudinally repeated points and havingtheir ends extending longitudinally past each other, and strengthening flanges formed on .aty

bers being bent along substantially a diagonalI- and welded in the region of its bend to the sec-- tion positionedat the vertex of the triangle'an'dA at each of Iits extending corners to one section positioned at the base corners of the triangle,- the members Vbeing secured to the metal sections at longitudinally `repeated points andv having;

their ends extending longitudinally Vpast each. other, and strapsy extending betweenthe metal.

sections at the pointsof joinder of the members;

thereto.

l0. A structural building unit comprising three longitudinally extending metal sections positioned parallel to each. other and in transverse section defining the corners off an isoscelestrig.- angle, and a plurali-ty of sheet metal memberst of substantially rectangular shape, each of saidmembers being bent along substantially a diagonal and welded in the region of its bend to the section positioned at the vertex of the triangle and at each of its extending corners to one section positioned at the base corners ofthe tri.-l

angle, the members. being secured tothe metal sections at longitudinally repeated points and having their ends extending longitudinally past each other.

11. A structural build-ing unit comprising. three longitudinally extending metal sections. positioned parallel to eachother an-cl. in transverse section dening. the corners of angle, and a plurality of sheet of substantially rectangular shape, eachl of said members being bent along substantially'a dia-gonal and welded in the region of. its bend to the section' positioned at the vertex of the triangle and at each of its extending corners tov onesection positioned at the base corners of the. triangle, the membersbeing secured to the metal' sections at longitudinally repeated poi-nts.

12. A structural v longitudinally extending metal in transverse section the cornersofv anisosceles triangle, the section atthe vertex of the triangle being a channel having flanges in alignment with the sections at the base corners of the tri-,i angle which are angle irons,

their bases to the metal section at the vertex of' the triangle and secured at their vertexes to the metal sections at the base corners of the triangle, each of said sheet metal members having a notch cut in. its base so as toy form: a V-shaped area, said members beingsecured to the metal. sections so that a sheet metal area of repeated zigzag or Z-shape isprovided, and strengthen-ing` ank isosceles trimetal members building unit comprising three.

sections defining.

individual ksheet-y metal mem-bers of triangular shape securedV ati 'section at the vertex of the triangle and secured at their vertexes to the metal sections at the base corners or' the triangle, each oi said sheet metal members having a notch cut in its base so as to form a V-shaped area, said members beingl secured to the metal sections so that a sheet metal area of repeated zigzag or Z-shape is provided, and strengthening means formed on at least some of the edges of the members.

14. A structural building unit comprising three longitudinally extending metal sections defining in transverse section the corners of an isosceles triangle, and individual sheet metal members of triangular shape secured at their bases to the metal section at the vertex of the triangle and secured at their vertexes to the metal sections at the base corners of the triangle, each of said sheet metal members having a notch cut in its base so as to form a V-shaped area, said members being secured to the metal sections so that asheet metal area of repeated zigzag or Z-shape is provided.

15. That method of making structural building units from sheet metal and formed metal sections which comprises without waste continuously cutting from a strip of sheet metal individual sheet metal members, securing the individual members to longitudinally extending shaped metal sections positioned in transverse section to define the corners of a triangle, said securing operation being such that the members provide longitudinally repeated substantially triangular areas on each side of the section positioned at the vertex of the triangle.

16. That method of making structural building units from sheet metal and formed metal sections which comprises without waste continuously cutting from a strip of sheet metal individual sheet metal members substantially in the form of isosceles triangles, forming the edges of the members to better resist compressiveforces, securing the individual members to longitudinally extending shaped metal sections positioned in transverse section to define the corners of a triangle, said securing operation being such that the members provide longitudinally repeated substantially triangular areas on each side of the section positioned at the vertex of the triangle.

17. That method of making structural building units from sheet metal and formed metal sections which comprises Without waste continuously cutting from a strip of sheet metal individual sheet metal members substantially in the form of rectangles, bending each member substantially along a diagonal, securing the individual members to longitudinally extending metal sections positioned in transverse section to define the corners of a triangle, said securing operation being such that the members provide longitudinally repeated substantially triangular areas on each side of the section positioned at the vertex of the triangle.

18. A structural building unit comprising three longitudinally extending metal sections each of substantially angular shape in cross section and positioned relative to each other to define together in transverse section the corners of an isosceles triangle, individual sheet metal members of similar polygonal shape welded to the sections at longitudinally recurrent points and providingy spaced apart longitudinally repeated polygonal sheet metal areas between the sections.

19. A substantially rectangular panel for use in constructing frameless metallic buildings, said panel comprising a plurality of elongated units which are joined together side by side by means of transverse members, each unit including a pair of spaced longitudinal base members, and a raised centrally disposed member, a plurality of plates having a central ridge portion and opposed triangular outwardly and downwardly depending side portions, the plates being joined to the central member along said central ridge portion, the opposed transverse corners of the plates being joined to the base angle, the several plates being disposed along the members in end to end relationship.

20. A structural building unit comprising three longitudinally extending metal sections positioned parallel to each other and in transverse section defining the vertex and base corners of an isosceles triangle, a plurality of sheet metal members of substantially rectangular shape, each of said members being bent along substantially a diag- 'onal and welded along the region of its diagonal bend to the section positioned at the vertex of the triangle and at each of its base corners to one section positioned at the base corners of the triangle, .the members being secured to the metal sections at longitudinally repeated points and having strengthening flanges formed on the compression edges of at least some of the members.vk

21. A structural building unit comprising three longitudinally extending metal sections positioned parallel to each other and in transverse section defining the vertex and base corners of an isosceles triangle, a plurality of sheet metal members of substantially rectangular shape, each of said members being bent along substantially a diagonal and welded along the region of its diagonal bend to the section positioned at the vertex of the triangle and at each of its base corners to one section positioned at the base corners of the triangle, the members being secured to the sections at longitudinally repeated points` and strengthening ilanges formed on at least soma edges of the members.

22. A structural building unit comprising three longitudinally extending metal sections positioned relatively to each other to dene together in transverse section the corners of an isosceles triangle, a sheet metal member of substantially triangular shape secured at its base to one metal section deiining a base corner of the isosceles triangle and at its vertex to the metal section defining the topof the isosceles triangle, a sheet metal member similar to the rst-named member and secured at its base to the other metal section deiining the base corner of the isosceles triangle and at its vertex to the metal section defining the top of the isosceles triangle and in substantially opposed relation to the iirst-named sheet metal member, and a plurality of opposed sheet metal members secured to the longitudinally extending metal sections at longitudinally spaced points and in a similar manner.

' WALTER I-I. S'I'ULEN,