US3122223A

US3122223A - Prefabricated building construction

Info

Publication number: US3122223A
Application number: US46019A
Authority: US
Inventors: Glenn J Chell; Buderus Brooks; Palmer Robert
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-07-28
Filing date: 1960-07-28
Publication date: 1964-02-25
Anticipated expiration: 1981-02-25

Description

Feb. 25, 1964 G. J. CHELL ETAL 3,122,223

PREFABRICATED BUILDING CONSTRUCTION Filed July 28, 1960 4 Sheets-Sheet 2 Fla " INVENTOR5 lennJChclZ firoaks Buderus BY Eobari Palmer 775 W 400 J/j/M 1M fliiorneys 1954 G. J. CHELL ETAL 3,122,223

PREFABRICATED BUILDING CONSTRUCTION Filed July 28, 1960 4 Sheets-Sheet 4 N VE N T025 Glen n J. (he/I nooks zzderzzs aberz aimer United States Patent PREFABRHIATED BUILDENG CGNSTRUCTEQN Glenn 3. Cheil, Highland Paris, El. (5425 N. Kedzie Ave, Chicago, B1,}; brooks Bnderus, 233 N. I'Jortiiwest Highway, Park Ridge, Ill; mil Robert Palmer, 18.12%.

Hinman Ava, 'Evanston, 111.

Filed July 28, 19st Ser. No. 46,619 8 (Iiaims. (Cl. 189-34) This invention relates to the construction of schools, homes, commercial buildings and other structures and pertains particularly to building constructions of the type in which various components of the building are prefabricated at a factory or shop, for assembly at the building site.

One object of the present invention is to provide a new and improved building construction in which the walls of the building are assembled from standard or universal prefabricated frames or other units.

It is another object to provide a new and improved building construction of the foregoing character, having means for readily securing the prefabricated wall units to the foundation of the building.

A further object is to provide a new and improved construction in which the wall units are wchored to the sills of the footings by special base plates which have flanges imbedded in the floor slab of the building,

Another object is to provide a new and improved building construction in which the walls are made of prefabricated structural frames which include column members to bear the load imposed on the wall, panels being mounted in the frames to close the wall.

A further object is to provide a new and improved arrangement for securing beams or joists to the column members of the wall.

Still another object is to provide a highly flexible and advantageous building construction of the foregoing character which is easy to erect and extremely low in cost.

Further objects and advantages of the present invention will appear from the following description, taken with the accompanying drawings, in which:

FIG. 1 is an elevational View of a portion of a building wall, to be described as an illustrative embodiment of the present invention.

FIG.'2 is a fragmentary horizontal section, tanen generally along a line 22 in FIG. 1.

FIG. 3 is a fragmentary vertical section, taken along -a line 33 in Flu. 1.

FIG. 4 is a fragmentary exploded view in perspective, showing the marmer in which the prefabricated wall units are mounted on the foundation of the building, and the arrangement whereby horizontal joists or beams may be secured to the wall units.

FIG. 5 is a vertical section showing a modified arrangement for mounting the wall units on the foundations of the building.

FIG. 6 is a fragmentary elevational View showing the construction of FIG. 5..

FIG. 7 is an end view of the exterior stone sill employed in the construction of FIG. 5.

FIG. 8 is a perspective View of the sill of FIG. 7.

FIG. 9 is an end view of the interior sill shown in FIG. 5.

FIG. 10 is a perspective view of the sill of FIG. 9.

FIGS. 11, 12 and 13 are end, top and side views of the base plate shown in FIG. 5

This application is a continuation-in-part of the copending abandoned application of the same inventors, Serial No. 768,108, filed October 20, 1958, which disclosed the embodirnent of FIGS. 1-4 and claimed various features thereof.

In general, FIG. 1 illustrates a building Wall 10, which ice is made up of standard or universal

prefabricated frames

12 and 14. Actually, the

frames

12 and 14 are nearly identical, as will be fully apparent shortly. It will be seen that the frame 12 has a glass panel 16 mounted in its upper end, while an opaque closure panel 18 is mounted in the lower end of the frame. The frame 14 is similar to the frame 12, but is inverted in position, so that a doorway 2i is formed in the lower portion of the frame. A glass window panel 22 may be mounted in the upper portion of the frame 14.

The illustrated frame 12 has a pair of

vertical side members

24 and 26. Top and bottom members 23 and 3t; extend between the

side members

24 and 26 at the upper and lower ends thereof. It will be apparent that the frame 12 is rectangular in shape. Preferably, a cross member 32 also extends between the

side members

24 and 26 at a point between the upper and lower ends thereof. In this case, the cross member 32 is substantially nearer the lower end of the frame 12 than it is to the upper end thereof. Thus, the cross member 32 forms a relatively large opening 34 in the upper end of the frame 12, while forming a relatively small opening 36 in the lower end thereof. As shown, glass window panel 16 is mounted in the large opening 34 while the closure panel 18 is mounted in the small opening 36, The

members

24, 2e, 28, 3d and 32 of the frame 12 may be made of steel or other suitable material, and may be welded or otherwise secured together.

The frame 14 is nearly the same as the frame 12, but is inverted in position so that the large opening in the frame 14- will be at the lower end to form the doorway 29. Actually, the frame 14 could be identical with the frame 12, and merely inverted in position, but it is preferred to modify the frame 14 in certain respects. Thus, the frame 14 may have the

same side members

24 and 26 as the frame 12. The top member 28 may also be the same. However, it is preferred to omit the bottom member 3i from the frame 14, so that the doorway will extend to the bottom of the frame without obstruction. The frame 14 may have a cross member 32a which is the same as the cross member 32, but is located near the upper end of the frame so that the opening 20 will be of doorway height.

The building wall 19 may comprise any suitable numer of the frames 12, secured together edge to edge. Frames 14 may be inserted into the wml to form doorways as needed.

As shown in FIG. 2, each of the illustrated

side members

24 and 26 is hollow and generally rectangular in cross section. The side members 24 and may actually be identical, but reversed from left to right. Thus, each side member 24 or 25 has aflange 4i? thereon which projects into the

openings

34 and 36.

Similar flanges

42 and 44 are formed on the top and

bottom members

28 and 3%. Moreover, the cross member 32 has

similar flanges

46 and 48 which project upwardly and downwardly into the

openings

34 and 36. These flanges 419-48 form ledges 5i) and 52 which extend entirely around the boundaries of the

openings

34 and 36. In the case of the opening 34, the glass panel 16 is mounted against the ledge 56. A suitable sealing material or compound 54 may be interposed between the glass panel 16 and the ledge to form a weather-proof seal and to cushion the glass. The sealing member 54 may be made of rubber, putty or the like. Molding strips 55 may be mounted on the

members

24, 26, 28 and 32 to hold the glass panel 16 in place. As shown, the molding strips 56 are L-shaped or angular in cross section. They may be secured to the frame members by means of screws 58 or other suitable fasteners.

Inthe case of the opening '36, the closure panel 18 may be mounted against the ledge 5'2. The illustrated panel is constructed for exterior use, so as to withstand the weather. Thus, for example, the panel 18 may comprise a sheet of relatively thick building board 60 faced with a thin sheet 62 of weather-resistant material such as porcelain enamelled steel, aluminum or the like. The inner side of the board 60 may be lined with a thin sheet 64 made of heavy water-proof paper, aluminum foil, or some other suitable material. Of course, the panel 18 may be made of any other suitable material, such as precast concrete, asbestos-cement board or the like. Additional molding strips 56 may be employed to secure the panel '18 against the ledge 52.

For the sake of enhanced insulation and improved appearance, an interior panel 68 may be mounted against the inner side of the ledge 52. The panel 68 may be made of interior wall board or any other suitable material. Additional molding strips 56 may be utilized to hold the panel 68 against the ledge 52.

The

side members

24 and 26 are arranged so that tight, weather-proof joints may readily be formed between adjacent frames. Each of the

side members

24 and 26 has a flange 7 t which projects laterally therefrom so as to extend outwardly from the edge of the frame 12. The flange 70 is positioned near one side of the frame. Thus, the flange 70 on the lefthand side member 24 is near the interior side of the frame, while the flange 70 on the righthand side member 26 is near the exterior side. As already indicated, the

members

24 and 26 are actually identical, but reversed from left to right. "It is this reversal which positions the flanges 70 in spaced apart relation from front to rear on the adjacent side members.

From FIG. 2 it will be apparent that the outer edges of the flanges 70 engage the

opposite side members

24 and 26 so that the side members are spaced apart by a distance corresponding to the height of the flanges. The flanges 70 extend between the

adjacent side members

24 and 26 so as to provide tight joints therebetween. A vertical strip 74 of soft material, such as synthetic rubber or the like, may be compressed between the adjacent side members 24 and '26 to make the joint weather-proof. Preferably, the sealing strip 74 is located just behind the flange 70 near the exterior side of the

frames

12 and 14. Bolts 76 may be employed to secure the adjacent side frames 24 and 26 together. To facilitate assembly of the frames '12 and 14, plates 78 may be welded or otherwise secured inside the

side members

24 and 26. The plates 78 may be drilled and tapped to form threaded openings for receiving the bolts 76., The bolts 76 may be formed with flat heads 80 so that the heads may be countersunk so as to be flush with the faces of the

side members

24 and 26. Reinforcing plates 82 are preferably welded or otherwise secured inside the

members

24 and 26 so that countersunk bolt holes 84 may be formed therein.

The fabrication of the

side members

24 and 26 may be facilitated greatly by forming each side member from two sheet metal channels 86 and 88. From FIG. 2 it will be seen that the channels 86 and 88 are formed with

flange elements

90 and 92 which are welded or otherwise secured together face to face, to form the flange 40. Similarly, the channels 86 and 88 are formed with

flange elements

94 and 96 which are welded together face to face, to form the flange 70. As shown,

flange elements

90 and 92 are folded double so as to have a thickness twice that of the sheet metal employed in the channels =86 and 88. In this case, the

flange elements

94 and 96 are of single thickness.

From FIG. 3 it will be apparent that the upper member 28, the lower member 39 and the cross member 32 are also hollow and generally rectangular in cross section. Each of these members 28, 3t} and 32 is also preferably fabricated from two opposed channels. Thus, the upper member 23 comprises a pair of identical channels 100. Similarly, identical channels 102 are employed in the lower member 36, while identical channels 164 are utilized in the cross member 32. The channels of the upper member 28 are formed with double thickness flange elements 106 which are welded together to provide the flange 42. The flange 44 on the lower member 30 is formed by double thickness flange elements 108, welded together. Similarly, the

flanges

46 and 48 on the cross member 32 are formed by double

thickness flange elements

110 and 112.

FIGS. 3 and 4 illustrate advantageous means for mounting the

prefabricated frames

12 and 14 on the foundation of a building. In this case, the foundation comprises a concrete footing 116 with a sill 118 mounted thereon. The sill 118 may be made of pre-cast concrete, stoneor the like. It will be apparent that the illustrated sill 118 has an upper surface 12% adapted to support the

frames

12 and 14. The exterior side of the sill 118 has a surface 122 which slopes downwardly from the surface to drain off water. An upwardly projecting flange 124 is formed at the interior edge of the sill 118.

A bearing or base plate 126 may be provided to support each adjacent pair of

side members

24 and 26. In this case, the plate 126 has a horizontal portion '128 adapted to rest upon the horizontal surface of the sill. An inverted channel portion 130 is formed on the plate 126 and is adapted to be received over the flange 124 on the sill 118. When the inverted channel portion 130 is hooked over the flange :124, the plate 126 is prevented from shifting in a direction transverse to the length of the sill. Along its inner edge, the bearing plate 126 may be formed with a flange 132 which slants downwardly and inwardly. As shown in FIG. 3, the flange 132 may be imbedded in a concrete floor slab 134 formed on the inside of the building. This will securely anchor the bearing plate 126 against any shifting movement. Holes 136 may be formed in the anchoring flange 1-32 to receive the concrete while it is still plastic, so as to form a strong bond with the concrete slab 134 after it has hardened.

The lower ends of the

side members

24 and 26 are adapted to be supported upon the horizontal portion 128 of the bearing plate 126. To prevent the side members 24- and 26 from shifting, two pairs of

lugs

138 and 140 are arranged to project upwardly from the horizontal plate portion 128. The lugs 138 and 140' are adapted to be received within the lower ends of the

hollow side members

24 and 26, adjacent the inner and outer walls thereof, as shown in FIGS. 3 and 4. The

side members

24 and 26 may be secured to either or both of the corresponding lugs 13-8 and 140 by means of bolts 142 or other suitable fasteners. In this case, the bolts 142 are adapted to be inserted through holes 144 in the inner walls of the side members. Tapped holes 146 are provided in the lugs 138 to receive the bolts 142. As illustrated, the

lugs

138 and 140 are formed by welding or otherwise securing short lengths of angle stock to the horizontal plate portion 128.

A weather-proof joint may be formed between the sill 118 and the frames 12 by interposing a sealing strip or gasket 148 between the horizontal surface 120' of the sill 118 and the lower members 30 of the frames 12. The sealing strip 148 may be made of a suitable soft material such as synthetic rubber.

As shown in the upper portion of FIG. 4, it is an easy matter to mount joists or beams 152 on the upper ends of the

frames

12 and 14. In this case, each beam 152 has a flange or ledge 154 which projects beyond the end of the beam from the upper edge thereof. This flange 154 is adapted to rest upon the upper ends of the

side members

24 and 26. The beam 152 may be formed with vertical, laterally extending side flanges 156 which may be secured to the

side members

24 and 26 by means of bolts 158 or the like. Each bolt 158 extends through a hole 160- in the flange 156 and a pair of holes 162 formed in the front and rear walls of one of the side frames 24 and 26. The bolt may also extend through an additional hole 160 in a second beam 152. Thus each set of bolts may be employed to secure two aligned beams to the side frames.

As illustrated, each beam 152 is I-shaped in cross section, and thus has a vertical web 166, with upper and lower

horizontal flanges

168 and 170 formed thereon. The supporting flange 154 may constitute an extension of the upper flange 168. The flanges 156 may be formed by a vertical plate welded to the end of the beam 152.

It will be recognized that the frames 12 and 14- may advantageously be manufactured in a factory or shop. The frames may be of standard sizes and may be assembled in various combinations to provide the desired type and size of building wall.

In constructing the building, the footing 116 is poured and the sill 118 is mounted thereon. The bearing plates 126 are then placed on the sill 11 8, and the

side members

24 and 26 of the

frames

12 and 14 are slipped over the lugs 13% and 14% on the bearing plates 126. The

frames

12 and 14 are then secured together by the bolts 76, and are secured to the bearing plates 126 by the bolts 142. When the concrete floor 134 is poured the flanges 132 will be imbedded in the concrete so as to anchor the bearing plates 126.

The joists or beams 152 are secured to the upper ends of the side frames 24 and 26 by resting the flanges 154 thereon and installing the bolts 158. It will be understood that a suitable roof may be supported by the beams 152.

The building wall may be completed by installing the

glass panels

16 and 22 and the

closure panels

18 and 68, using the molding strips 56 to secure the panels in place. Both the panels and the molding strips may be precut to standard sizes so that the installation of the panels will be a simple matter.

It Will be understood that a variety of buildings may be constructed by employing the prefabricated units. The illustrated construction is especially well adapted for constructing schools or similar buildings. The horizontal dimensions of the rooms in the building will be multiples of the horizontal width of the prefabricated units. Since the units are of relatively small widths, the illustrated construction affords ample flexibility in the design of buildings having rooms of various sizes and shapes. Because of the standardized, low cost construction of the prefabricated units, and the ease with which the units may be assembled, the cost of the building is extremely low.

FIGS. -13 illustrate a modified arrangement for anchoring the prefabricated frames 12 to the foundations of the building. It will be understood that the doorway frames 14 may be substituted for the wall frames 12, as needed. As shown to advantage in FIG. 5, the frames 12 are secured to modified bearing or base plates 226 which are mounted on a modified exterior sill 218 made of cut stone, pre-cast concrete, or the like. As before, the sill 218 is suitably mounted on the footing or foundation wall 116, as by a bed .of mortar 217.

FIG. 5 also illustrates an interior sill 219 adapted to be mounted on an interior footing or foundation 216. The interior sill 219 is similar to the exterior sill 218, as will be described in detail shortly.

As before, the exterior sill 218 has an upper surface 220 adapted ot support the frames 12. The exterior side of the sill 218 has a surface 222 which slopes downwardly from the surface 220 to drain off water. An upwardly projecting flange or ridge 224 is formed at the interior edge of the sill 218.

However, in this case, the bearing or base plate 226 is mounted in a gap or notch formed in the flange 224. The base plate 226 has a horizontal portion 228 which rests upon the horizontal upper surface 220 of the sill 21 8 and extends through the gap 227. The modified base plate 226 is not provided with the inverted channel portion 130, as shown in FIGS. 3 and 4. Instead, the

base plate 226 has a downturned flange 229whichis engageable with the inwardly facing side surface 231 of the sill 218. The flange 229 is adapted to locate the base plate 226 on the sill 21 8 and to prevent the base plate from moving outwardly when the wall units 121are being erected. .A flange 23 2 slants inwardly and downwardly from the vertical flange 229 and is adapted to be imbedded in the concrete floor slab 134. To increase the security of the imbedment, an upturned flange 233 may be formed on the lower edge of the flange 232. The flange 233 acts in the manner of ahook when it is imbedded in the concrete.

As shown, the modified base plate 226 is provided with upwardly projecting

lugs

238 and 240 which are adapted to extend upwardly into the side members24 and 26 of the frames 12. The illustrated lugs 238 and 240 .take the form of flanges on a channel member 241 which is welded or otherwise secured to the base plate 226. As shown to advantage in FIGS. 12 and .13, two of the channel members 241 are mounted on each base plate 226. Thus, the lugs on each base plate project upwardly into the side members of adjacent frames in the wall. In each case, the lug 238 engages the inner 'wall of the

side members

24 or 26 while the lug 24% engages the outer wall of the side member. The side members .24 and 26 are secured to the lugs 23% by means of screws242 which may be of the self-tapping type and may be screwed into suitable openings 239 in the lugs 23%. Each screw 242 may have a flat head 243 which may be countersunk into a recess 245 formed in the

side member

24 or 26. A channel or recess 247 may be formed in each of the lugs 235 to receive the head 243 and the recessed portion 245.

As shown to advantage in FIGS. 5, 9 and 16, the interior sill 219 is the same as the exterior sill 213, except that the sloping portion 222 is omitted. The base plate 226 may be employed in connection with the interior sill 21?, in the same manner as in the case of the exterior sill 218.

In the erection of the building, the interior and

exterior sills

219 and 218 are mounted on the

foundations

216 and 116 in any suitable manner, as by the use of the beds or mortar 217. The base plates 226 are then placed on the sills, and the

frames

12 and 14 are mounted on the base plates, so that the lugs 23% and 241 will extend upwardly into the

side members

24 and 26 of the frames. The screws 242 may be inserted to secure the side members to the lugs 233.

It will be seen that the ridges 224 and the flanges 229 prevent the

frames

12 and 14 from shifting transversely on the sills 213 and 219. The ridges 22 i engage the lower portions of the frames and prevent them from sliding in one transverse direction, while the flanges 229 on the base plates 22-6 engage the sills and prevent the frames from sliding in the opposite transverse direction.

When the

frames

12 and 14 have been erected, the concrete floor slab 134 may be poured. The

flanges

232 and 233 will be inzbedded in the concrete slab 134, so that the base plates 226 and the

frames

12 and 14 will be securely anchored. In finishing the slab 134, the ridges 224 may be employed as leveling grounds for the upper surface of the slab.

The arrangements of the base plate are extremely low in cost. Nevertheless, such arrangements make it very easy and quick to erect the wall frames for the building.

Various other modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the invention, as exemplified in the foregoing description and defined in the following claims.

We claim:

1. In a building wall, the combination comprising a plurality of generally rectangular frames arranged edge to edge, each frame having two vertical side members and top and bottom members extending therebetween,

means for mounting panels in said frames, each side member of each frame being generally of hollow rectangular cross section, each side member having a vertical flange projecting laterally in an outward direction therefrom and engaging the adjacent side member 'of the ad.- jacent frame, said flange on one side member of each frame being oifset forwardly while said flange on the other side member of the frame is oflset rearwardly, said flanges on adjacent side members of adjacent frames thereby being spaced apart from front to rear, means securing together the adjacent side members of adjacent frames, each of said side members comprising front and rear channel components with flange elements thereon, said flange elements of said components being secured together face to face to define said flange on each side member.

2. A modular frame for use in a building Wall, said frame comprising two vertical side members, top and bottom members extending between said side members,

and means for mounting panels in said frame, said side members being generally of hollow rectangular cross section, each side member having a vertical flange projecting laterally in an outward direction therefrom for engaging the adjacent side member of the next frame in a building wall, said flange on one side member of said frame being offset forwardly while said flange on the other side member of the frame is offset rearwardly, the flanges on the opposite side members thereby being spaced apart from front to rear, each of said side members comprising front and rear channel components with flange elements thereon, said flange elements of said components being secured together face to face to define said flange on each side member.

3. In a building wall, the combination comprising a plurality of generally rectangular frames arranged edge to edge, each frame having two vertical side members and top and bottom members extending therebetween, means for mounting panels in said frames, each side member of each frame having a flat side surface with a vertical flange projecting laterally in an outward direction therefrom and engaging the flat side surface on the adjacent side member of the next frame in the wall, said flange on one side member of each frame being oflset forwardly while said flange on the other side member of the frame is offset rearwardly, the adjacent side members of adjacent frames thereby having two of said flanges extending therebetween and spaced apart from front to rear, each pair of adjacent frames having a vertical sealing strip of soft material compressed between the flat side surfaces of the adjacent side members and disposed between said two flanges, and means securing together the adjacent side members of adjacent frames.

4. In a building wall, the combination comprising a plurality of generally rectangular frames arranged edge to edge, each frame having two vertical side members and top and bottom members extending therebetween, means for mounting panels in said frames, each side member having a flat side surface with a vertical flange projecting laterally in an outward direction therefrom and engaging the flat side surface on the adjacent side member of the next frame, said flange on one side member of each frame being offset forwardly while said flange on the other side member of the frame is offset rearwardly, the adjacent side members of adjacent frames thereby having two of said flanges extending therebetween and spaced apart from front to rear, and means securing together the adjacent side members of adjacent frames.

5. A modular frame for use in a building wall, said frame comprising two vertical side members, and top and bottom members extending between said side members, each side member having a flat side surface with a vertical flange projecting laterally in an outward direction therefrom for engaging the flat side surface on the next frame in the Wall, said flange on one side. member being offset forwardly While said flange on the other side member is. offset rearwardly, said flanges on opposite side members thereby being spaced apart from front to rear.

6. In a building wall, the combination comprisinga plurality of generally rectangular upright frames, secured together edge to edge, and constituting the sole structural support for said wall, each frame having two vertical edge structural members and top and bottom horizontal structural members extending therebetween, means for mounting panels in said frames, each edge member being hollow and of closed generally rectangular cross section, each pair of adjacent frames having a generally horizontal base plate located under the adjacent edge members of said frames, said base plate having four spaced lugs thereon projecting upwardly therefrom into the adjacent hollow edge members of said frames, two of said lugs being snugly received in each of said hollow edge members and being engaged with opposite sides thereof, and means securing each of said hollow edge members to at least one of said lugs, said base plate havinga downwardly extending anchoring flange thereon adapted to be embedded in concrete or the like.

7. In a building wall, the combination comprising a plurality of upright generally rectangular frames arranged edge to edge and constituting the sole structural support for said wall, each frame having two vertical edge column members along opposite edges thereof and a top horizontal structural member extending between said column members'and secured rigidly thereto, the column members on adjacent frames being engaged with each other, a horizontal I-beam having a central vertical Web and top and bottom horizontal flanges connected to said web, a vertical end plate secured to said Web and said upper and lower flanges at one end of said beam, said end plate extending laterally on both sides of said web, said adjacent column members of said frames and said end plate having aligned openings therein, and a plurality of fasteners extending through said openings and securing said end plate to said column members of both of said adjacent frames, while also securely joining said column members.

8. The combination of claim 7, in which said upper flange of said I-beam is provided'with a horizontal extension which engages and is supported by the tops of the adjacent frames.- 7

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN A BUILDING WALL, THE COMBINATION COMPRISING A PLURALITY OF GENERALLY RECTANGULAR FRAMES ARRANGED EDGE TO EDGE, EACH FRAME HAVING TWO VERTICAL SIDE MEMBERS AND TOP AND BOTTOM MEMBERS EXTENDING THEREBETWEEN, MEANS FOR MOUNTING PANELS IN SAID FRAMES, EACH SIDE MEMBER OF EACH FRAME BEING GENERALLY OF HOLLOW RECTANGULAR CROSS SECTION, EACH SIDE MEMBER HAVING A VERTICAL FLANGE PROJECTING LATERALLY IN AN OUTWARD DIRECTION THEREFROM AND ENGAGING THE ADJACENT SIDE MEMBER OF THE ADJACENT FRAME, SAID FLANGE ON ONE SIDE MEMBER OF EACH FRAME BEING OFFSET FORWARDLY WHILE SAID FLANGE ON THE OTHER SIDE MEMBER OF THE FRAME IS OFFSET REARWARDLY, SAID FLANGES ON ADJACENT SIDE MEMBERS OF ADJACENT FRAMES THEREBY BEING SPACED APART FROM FRONT TO REAR, MEANS SECURING TOGETHER THE ADJACENT SIDE MEMBERS OF ADJACENT