US3486729A

US3486729A - Pretensioned knockdown concrete wall form panel

Info

Publication number: US3486729A
Application number: US680796A
Authority: US
Inventors: Vernon R Schimmel
Original assignee: Symons Manufacturing Co
Current assignee: General Electric Co
Priority date: 1967-11-06
Filing date: 1967-11-06
Publication date: 1969-12-30
Anticipated expiration: 1986-12-30

Description

Dec. 30, 1969 v, S 7 3,486,729

PRETENSIONED KNOCKDOWN CONCRETE WALL FORM PANEL Filed Nov. 6, 1967 3 Sheets-Sheet 1 FIG. Ii FIG. 2

INVENTOR. VERNON R SCH/MMEL ATTORNEY v. R. SCHIMMEL 3,486,729

PRETENSIONED KNOCKDOWN CONCRETE WALL FORM PANEL Dec. 30, 1969 3 Sheets-Sheet 2 Filed NOV. 6, 1967 FIG. 4

INVENTOR. VERA/0N R. SCH/MMEL A TTOR/VE) Dec. 30,1969 v. R. SCHIMMEL PRETENSIONED KNOCKDOWN CONCRETE WALL FORM PANEL 3 Sheets-Sheet 5 Filed Nov. 6, 1967 FIG. 10

FIG. 9

' INVENTOR. VERNON R. SCH/MMEL FIG. I2-

ATTORNEY.

United States Patent 3,486,729 PRETENSIONED KNOCKDOWN CONCRETE WALL FORM PANEL Vernon R. Schimmel, Arlington Heights, 11]., assignor to Symons Mfg. Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. 6, 1967, Ser. No. 680,796 Int. Cl. E04g 9/08 US. Cl. 249-189 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to concrete wall forms and has particular reference to a prefabricated rectangular concrete wall form panel which comprises a rectangular plywood facing and a rectangular reinforcing frame in the form of steel studding, the panel being adapted to be arranged in an upstanding position and also in edge-to-edge relationship with similar prefabricated panels in order to form with such similar panels one side of a concrete wall form into which wet concrete may be poured for wall-forming purposes. Concrete wall form panels of the type under consideration also find use in connection with the formation of horizontal floor and ceiling slabs and, in such an instance, they are arranged in edge-to-edge relationship with the panel facings lying in a common horizontal plane so that the concrete may be poured on the continuous unbroken upwardly presented slab-supporting face that is formed by the upper surface of the facings.

Such concrete wall form panels are manufactured in sizes which vary both as to length and width. In the panels of large size, transverse intermediate reinforcing members or crossbars of steel extend between the marginal longitudinal frame members of the rectangular reinforcing studding at spaced regions therealong and serve to reinforce the medial regions of the plywood facings against outward bulging under the thrust of the hydrostatic head of the poured concrete. The marginal frame members, both longitudianl and transverse, are constructed and shaped so that they will cooperate with various articles of concrete hardware such as (l) clamping devices (bolt and wedge assemblies) for drawing the edges of adjacent panels together, (2) horizontal tie rods which extend transversely across the concrete wall form and have the ends thereof extending between adjacent panels and attached or connected to the aforementioned clamping devices, (3) waler clamping devices, and (4) other accessory hardware items. Insofar as the plywood facing of a concrete wall form panel of the type under consideration is concerned, the longitudinal and transverse steel frame members of the rectangular reinforcing studding are formed with inwardly extending ribs which define a marginal recess around the inside rim of the studding and the edge portions of the plywood facing seat within such marginal recess with the inside face or surface lying flush with the inner edges of the frame members to the end that the inner face of the panel as a whole 3,486,729 Patented Dec. 30, 1969 presents a smooth, continuous, unbroken planar surface. These structural features of a conventional or standard concrete wall form panel have been preserved in the improved panel of the present invention.

A panel of the general type briefly outlined above is possessed of certain limitations which are obviated by the present invention. Among these limitations is the tendency for the various steel crossbars to flex or bend outwards under the tremendous outward pressure of the poured concrete against the plywood facing. To increase the number of crossbars or to employ a heavier gauge steel in the construction of the crossbars would be to increase the weight of the panel beyond acceptable limits. According to the present invention, there is provided novel means whereby the individual crossbars are pretensioned against flexing when lateral thrust is applied thereto and the provision of such means in connection with a concrete wall form panel constitutes one of the principal objects of the present invention.

Another limitation that is attendant upon the construction and use of a conventional steel studded concrete wall form panel resides in the difficulty which is encountered in a plywood facing replacement operation. It is the current practice to provide flat diagonal braces at the corner regions of the permanently welded rectangular reinforcing studding and to rivet the plywood facing to these braces. This practice is not altogether satisfactory in that not only is it difficult to remove and replace the rivets when plywood facing substitution is required, but also after a period of use, particularly in inclement weather, repeated exposure of the plywood facing to moisture causes shrinkage thereof so that the rivets pull away from the plywood and the net result is that the rivet heads and their surrounding voids leave undesirable marks in the hardened concrete wall. This limitation also is obviated by the present invention in that a novel knockdown panel construction is provided wherein the longitudinal and transverse marginal .frame members of the rectangular reinforcing studding are capable of being easily separated to release the panel facing which is held to the crossbars by a comparatively small number of screws which extend into the plywood facing from the outside thereof. After the screws are removed, the panel facing is then released from the studding and a new plywood facing may be substituted by a reversal of the knockdown operation.

It is a further feature and object of the present invention that the pretensioning means by which the crossbars of the panel are rigidified, as described above, also constitutes the clamping means whereby the longitudinal and transverse frame members of the steel studding are releasably held together.

Other objects of the invention and the various advantages and characteristics of the herein disclosed concrete wall form panel will be readily apparent from a consideration of the following detailed description.

The invention consists in the several novel features hereinafter set forth and more particularly defined by the claims at the conclusion hereof.

In the accompanying three sheets of drawings forming a part of this specification, a concrete wall form panel embodying the invention, that is, the features briefly set forth above, is illustrated in detail.

In these drawings:

FIG. 1 is a fragmentary perspective view of a portion of a concerete wall form employing a multiplicity of the panels of the present invention and showing the same operatively connected together in edge-to-edge and opposed relationship;

FIG. 2 is an enlarged horizontal sectional view taken on the line 2-2 of FIG. 1;

FIG. 3 is an outside or rear plan view of one of the panels of FIG. 1;

FIG. 4 is an enlarged horizontal sectional view taken on the line 44of FIG. 3;

FIG. 5 is an enlarged vertical sectional view taken on the line 5-5 of FIG. 4;

FIG. 6 is an enlarged fragmentary exploded perspective view of a corner fastening nut and bolt clamping assembly that is employed in connection with the invention;

FIG. 7 is a sectional view similar to FIG. 2 but showing one of the two adjacent panels removed, the other panel being shown in its free unattached condition;

FIG. 8 is an enlarged fragmentary detail side elevational view of a portion of the panel of FIG. 3, the view being taken in the direction of the arrow and limited by the confines of the line 88 of FIG. 3;

FIG. 9 is an enlarged fragmentary end elevational view of a corner region of the panel of FIG. 3, the view being taken in the direction of the arrows that are associated with the line 99 of FIG. 3;

FIG. 10 is a perspective view of a captured wedge and an associated T-bolt that are employed in connection with the invention;

FIG. 11 is an enlarged horizontal sectional view taken on the line 11-11 of FIG. 3; and

FIG. 12 is a side elevational view of one of the tensioning rods that are employed in connection With the present invention.

Referring now to the drawings in detail and in particular to FIG. 1, a fragmentary portion of a composite concrete wall form is designated in its entirety by the reference numeral 10, the form embodying a number of the improved pretensioned knock-down panels 12 of the present invention. The wall form 10 is made up of two spaced apart series 14 and 16 of the rectangular Wall form panels 12, with the panels of each series being arranged in a vertical position and edge-to-edge relationship. The panels 12 of the two series are maintained in their parallel spaced apart relationship by means of fiat slotted tie rods 18 in a manner that will be made clear presently.

The various panels 12 of the concrete wall form 10 are of the prefabricated, steel-studded type in that they consist of rectangular plywood facings 20, together with marginal studding in the form of rectangular steel reinforcing frames 22 which extend around and enclose the plywood facings and consist of vertical and horizontal frame members 24 and 26 (see FIG. 3). At appropriate levels in each wall form panel, intermediate horizontal crossbars 28 which are of special construction and have associated therewith novel pretensioning means extend between the opposed vertical frame members 24 of the rectangular reinforcing studding and are releasably secured in position therebetween in a manner that will be set forth in detail presently. According to the present invention, the various crossbars 28 serve a five-fold purpose. Firstly, they serve as a means whereby the medial regions of the vertical frame members 24 are releasably held in position against the ends of the crossbars. Secondly, they serve as tensioning members whereby the entire panel as a whole is rigidly pretensioned. Thirdly, they have associated therewith tensioning means which serves to flex the crossbars in a direction which resists the outward thrust that is imparted to the crossbars at the time the wet concrete is poured against the inner surface of the plywood facing of the panel. Fourthly, they serve as clamping members which serve to draw the two vertical frame members inwardly toward each other and against the longitudinal edges of the plywood facing so as to capture these edges and assist in maintaining the plywood facing in position within the confines of the rectangular frame that constitutes the reinforcing studding. Fifthly, the crossbars serve as anchor members for the medial regions of the plywood facing and eliminate the need for using diagonal braces and rivets such as have heretofore been considered necessary in the construction of a conventional steel-studded plywood concrete wall form panel.

The vertical frame members 24 and the horizontal frame members 26 are of similar construction insofar as their cross-sectional shape is concerned. Therefore, a description of one of them will largely suflice for a description of the others, identical reference numerals being employed to assist in the comparison. Each frame member is in the form of an elongated length of rolled steel stock which, as best shown in FIGS. 9 and 11, comprises spaced apart outer and inner coplanar

side rail portions

30 and 32, and inwardly extending intermediate through section 33. The latter consists of outer and inner trough sides 34 and 36 and a slightly inclined trough bottom 38. The inner side rail portion 32 and its adjacent inner trough side 36 establishes a right angle recess 40 within which the adjacent edge portion of the plywood panel facing 20 seats. The outside edge portion of the outer side rail section 30 is provided with an inturned flange 42 which lends rigidity to the frame member as a whole. At the corner regions of the panel, as shown in FIGS. 1 and 9, the horizontal frame members 26 are recessed at their ends in conformity with the cross-sectional shape of the vertical frame members in order to attain proper interfitting between the longitudinal and transverse frame members at said corner regions of the panel. The trough bottom 38 is inclined outwards in the direction of the inturned flange 42 with the result that the inner trough side 36 is of greater depth than the outer trough side 34.

In order to secure the vertical and

horizontal frame members

24 and 26 together at the corner regions of the panel, the corner fastening or clamping assembly which is illustrated in FIGS. -6 and 9 and is designated in its entirety by the reference numeral 50 is employed, it being understood that there is an assembly 50 at each corner of the panel. Said assembly comprises a fastening bolt 52 having a block-like head portion 54 and a cylindrical shank 56. The latter is adapted to receive thereover a washer 58, the nut being received on an externally threaded end portion 62 of the shank 56. Said end portion 62 is turned laterally at a small angle to accommodate the angular inclination of the bottom 38 of the intermediate trough section 33 of the adjacent vertical frame member 24 (see FIG. 9). The block-like head portion 54 of the assembly 50 is fixedly connected by a bolt 64 to the bottom 38 of the intermediate trough section 33 of the adjacent horizontal frame member 26. The shank 56 of the corner clamping assembly 50 projects through a hole 68 in the bottom 38 of the intermediate trough section 33 of the adjacent vertical frame member 24 so that after application of the washer 58 and the nut 60 as shown in the drawings, the corner connections between

adjacent frame members

24 and 26 will be complete. It is to be noted at this point that the four fastening or clamping assemblies 50, in combination with certain additional fastening means that are associated with the various crossbars 28- and will be described subsequently, constitute substantially the sole means for maintaining the components of the panel 12 in its assembled relationship.

Referring now to FIGS. 1, 4, 5, 7 and 8 wherein the details of the various crossbars 28 are best illustrated, each crossbar, like each of the

frame members

24 and 26, is of rolled steel stock and is generally of U-shape in cross section so as to provide a channel consisting of spaced apart sides 70 and a bottom 72. The crossbars bridge the distance between the opposed vertical members 24 of the frame 22 of the panel 12 at the selected elevations and the channel sides 70 are provided with outturned flanges 74 which lie flush against the inside faces of the plywood facing 20 and are secured thereto by rivets 76 or other fastening devices. As shown in FIGS. 1 and 4, the ends of the crossbars 28 are cut to fit the irregular transverse cross sectional shape of the vertical frame members 24 thus providing tongue-like projections 78 which extend into the trough-like contour that is afforded by the outer trough sides 34, the side rail portions 30, and the inturned flanges 42.

As best shown in FIGS. 4, 5 and 8, each crossbar 28 has associated therewith a reaction pin 80 which projects across the medial region of the crossbar, extends through aligned holes in the channel sides 70, and is disposed a slight distance inwards of the channel bottom 72; and this pin 80 is traversed by an elongated steel pre-tensioning rod 82 which is of wide angle V-shape and has inwardly diverging legs 83 the ends of which are threaded as indicated at 84. The threaded ends 84 of the rods 82 project through holes 86 (see FIG. 5) in the bottoms 38 of the intermediate trough section 33 of the vertical frame members 24. Said threaded ends 84 receive thereover washers 87 and nuts 88 by means of which the rods 82, after tightening of the nuts in the direction of the adjacent trough bottoms 38, are placed under tension so that the apex regions of the rods are drawn hard against the rivets 80 and the rods are thus placed under an appreciable degree of tension. Reference to FIG. 12 will reveal the fact that the various rods 82 are preformed in their wide angle V-shape to facilitate their initial insertion into the interior of the crossbars 28 and also alignment of the threaded rod ends 84 with the holes 86 in the trough bottoms 38 of the trough sections 33 of the vertical frame members 24. It is to be noted that the angularity of the diverging legs 83 of the rods 82 is commensurate with or corresponds to the slope of the bottoms 38 of the intermediate trough sections 33 of the vertical frame members 24 so that, unlike the shank portions 56 of the bolts 52, it is not necessary to turn or bend the threaded ends of the rods laterally out of alignment with the legs 83.

The manner in which adjacent panels 12 in the concrete wall form are assembled upon one another in their edge-to-edge relationship is best illustrated in FIGS. 1, 2, 7 and 10 of the drawings. The assembly is made by means of conventional T-bolts 90 which cooperate with special wedge members 92, the latter being captured by the various crossbars 28 and held against removal from the associated panel 12. An assembly of such a T-bolt and such a wedge member in its free state is illustrated in FIG. 10 of the drawings. As clearly shown in FIGS. 1, 2 and 3, the vertical frame members 24 are provided with dados 94 in the vicinity of the crossbars 28, these dados being formed only in the inner side rail portions 32 (see FIGS. 1, 2 and 9) which serve as protective flanges for the edges of the plywood facing 20 of the concrete wall form panel 12. When a pair of adjacent panels are brought to their normal edge-to-edge relationship, the dados 94 in the vertical flame members 24 of the two panels register with each other (see FIG. 2) and provide voids for receving the adjacent end portions of the flat slotted tie rods 18. No dados are formed in the outer side rail portions 30 of the vertical frame members 24 and the adjacent tie rod end portions pass between these opposed outer side rail portions of the vertical frame members of the adjacent panels. Thus, as shown in FIG. 1, the tie rod end portions between adjacent panels 12 will fit within pairs of registering dados 94 near the inner sides of the panels in the vicinity of the plywood facings 20 but will only bear against the outer side rail portions 30 near the outer sides of the panels and establish gaps such a are shown at 100 in FIG. 1, such gaps being between the opposed side rail portions 30 of the vertical frame members 24. Said outer rail portions 30 of the vertical frame members 24 are provided with rectangular slots 102 (see FIGS. 2 and 9) in the vicinity of the crossbars 28, and these slots are designed for reception of the T-bolts 90. Each T-bolt 90 is of flat construction and has an enlarged T-head 104 (see FIG. 10) and an elongated further shown in FIG. 2 and the slot 108 in the shank moves into vertical register with a pair of vertically aligned, longitudinally extending slots 110 in the sides 70 of the adjacent channel-shaped crossbar 28 near the adjacent end thereof. The associated wedge member 92 of each T-bolt and wedge member assembly is generally of C-shape design and embodies upper and lower

horizontal foot portions

112 and 114 and a vertical connecting bight portion 116. The latter has an inclined outer edge 118 which, in combination with the

foot portions

112 and 114 of the wedge assembly 92 effects the wedging action whereby a pair of adjacent concrete wall form panels 12 are drawn hard against each other in their edge-to-edge relationship. The bight portion 116 of the wedge member 92 projects through the associated two aligned slots 110 in the channel sides 70 of the adjacent crossbars 28 and also through the slot 108 in the shank 106 of the associated T-bolt 90 with the inclined edge 118 of said bight portion opposing the outer end of the T-bolt shank and with the

foot portions

112 and 114 of the wedge member 92 opposing and bearing against the inner surface of the outer side rail portion 30 of the adjacent vertical frame member 24. Thus, when the wedge member is driven downwardly by striking the upper foot portion 112 thereof with an impact tool such as a sledge or a hammer, the wedge member will be driven to the wedging position wherein it is shown in FIG. 2 (also full lines in FIG. 7) and the associated T-bolt 90- will be placed under tension so as to draw the two opposed vertical frame members 24 of the two panels hard against each other.

The captured wedge member 92 is shown in its free state in FIG. 7 and it will be observed that when such wedge is manually lifted to the uppermost position of which it is capable of assuming as shown in dotted lines, the lower or bottom edge thereof lies slightly above the level of the bolt-receiving slot 102 in the outer side rail portion 30 so that the associated T-bolt may be projected through the slot and the shank of the T-bolt caused to underlie the wedge member 92. With the T-bolt fully projected through the slot 102, as well as through a corresponding slot 102 in the outer side rail portion of the adjacent vertical frame member 24 of the adjacent panel 12, the lower foot portion 114 of the wedge member 92 will be in vertical register with the elongated slot 108 in the shank 106 of the T-bolt 90. Thereafter, the wedge member 92 may be forced downwardly so that the bight portion passes through said slot 108. Thereafter a blow imparted to the upper foot portion 112 of the wedge member by an impact tool will tighten the wedge as heretofore described. It should be observed at this point that captured wedges 92 are not necessarily employed in connection with each of the various crossbars 28 since two or three fastening devices are considered adequate to secure two panels 12 together in their edge-to-edge relationship. The number of wedges that are associated with any given concrete wall form panel will be a function of the length of such panel. Thus in FIG. 1 no wedge is shown as being associated with the upper-most crossbars 28 of the panels 12. Ordinarily, the crossbars are disposed on one foot centers so that the use of Wedge members 92 with alternately disposed crossbars will suffice for a firm connection between adjacent panels. It will be understood that wherever a wedge member 92 is employed, such wedge will serve not only as a clamping means between adjacent panels but also as an anchor device for the adjacent end portion of an associated tie rod 96. The various tie rods are slotted as shown at 120 for reception of the shanks of the associated T-bolts 90 with the tie rod end portion projecting through the voids which are established by the pairs of dados 94 as is customary in connection with the fastening together of certain forms or types of steel-studded concrete wall form panels.

From the above description it will be apparent that concrete wall for-m panels embodying the present invention are capable of being readily assembled at the factory or dismantled and reassembled in the field for replacement of parts if necessary. The nuts 88 which are associated with and normally mounted on the pretensioning rods 82 and the nuts 60 which are associated with the fastening bolts 52 of the corner clamping assemblies are the only devices which hold the panel in its assembled relationship. With these nuts removed, the vertical frame members 24 are readily removable from the horizontal frame members 26, as well as from the ends of the crossbars 28. With the vertical frame members 24 removed, the horizontal frame members 26 are freed for removal. So also are the pretensioning rods 82 which may be slid endwise from the crossbars 28 which normally enclose them. Furthermore, as soon as the vertical frame members 24 of the rectangular reinforcing studding are removed from the panel 12, the

foot portions

112 and 114 of the various Wedge members 92 are no longer obstructed and at least one foot portion of each wedge is so dimensioned that it will slip through the two aligned slots 110 in the sides 70 of the crossbar with which it is associated.

It should be observed that in assembling a given concrete wall form panel 12, as soon as the nuts 88 on the ends of the pretensioning rods 80 are tightened, not only are the two vertical frame members 24 drawn inwardly against the adjacent side edges of the plywood facing 20, but the tension in the angular pretensioning rods is such that the reaction rivets 80 (see FIGS. 4 and 5) are urged in an inward or forward direction, thus tending to flex the crossbars inwardly against the direction of outward thrust of the wet concrete when the latter is poured against the plywood facing 20 of the panel. This pretensioning of the crossbars 28 is instrumental in resisting such outward thrust of the concrete and preserving a truly straight linear configuration across the form panel at each crossbar level.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construction may be resorted to without departing from the spirit or scope of the invention. For example, whereas the various pretensioning rods 82 are shown as being provided with threaded portions 84 at the opposite ends thereof, it is contemplated that these rods may be in the form of elongated bolts which are bent to their proper wide angle V-shape configuration and have enlarged heads so that the use of two nuts in connection with the tensioning thereof is eliminated, at single nut for each rod being adequate for tensioning purposes. The use of the wood screws 76 for securing the plywood facings 20 to the outturned flanges 74 of the crossbars 28 is purely optional and in instances where the plywood facing 20 is so dimensioned that it fits snugly between the two vertical frame members 24 and between the two horizontal frame members 26 before the nuts 60 and 88 are fully tightened, such wood screws may be omitted since the subsequent pressure incident to further tightening of the aforesaid nuts will compress the plywood facing to such a degree that it will be captured between the four frame members of the steel reinforcing studding. In any event, the number of wood screws that need be employed will be few since no appreciable degree of pressure on the panel facing tending to dislodge it is ordinarily encountered. It is further contemplated that, if desired, rivets may be substituted for the wood screws but in such an instance that stated advantage of preserving a smooth unbroken panel facing contour throughout the entire life of the panel is dispensed with. Other minor changes in the details of construction of the concrete wall form panel 12 are contemplated.

Having thus described the invention what I claim as new and desire to secure by Letters Patent is:

1. A concrete wall form panel comprising a rectangular facing surrounded by studding in the form of a rectangular metal frame including a pair of oppositely disposed longitudinal frame members and a pair of oppositely disposed transverse frame members, the front wall-forming side of said facing and the front rim of the frame lying in a common plane, and a series of spaced parallel metal crossabrs which are of channel shape in transverse cross section extending between the longitudinal frame members at a right angle thereto and arranged so that their channel edges bear against the rear side of the facing in reinforcing relation with respect thereto, thus dividing the rectangular frame opening into a series of included rectangular frame openings, a reaction pin projecting across the channel sides of each crossbar at a region outwardly displaced fro-m the plane of the rectangular facing, and an elongated tensioning rod projecting through each crossbar and having its ends attached to the longitudinal frame members at regions which are in close proximity to the plane of the facing and its medial region passing across and bearing against said reaction pin on the side thereof remote from the facing, said tensioning rod serving to bias the crossbar in flexion so as to urge said medial region toward the facing.

2. A concrete wall form panel as set forth in claim 1 and wherein the opposite ends of the tensioning rods are threaded, the longitudinal frame members are provided with holes through which said opposite ends of the tensioning rods project, and nuts are threadedly received on said threaded ends and, when tightened, serve to place the rods under tension.

3. A concrete wall form panel as set forth in claim 2 and wherein the longitudinal frame members are formed with inwardly offset wall portions establishing trough-like recesses which are coextensive with said frame members, the holes are formed in such inwardly offset wall portions, and'the nuts and threaded ends of the tensioning rods lie wholly within the confines .of said recesses.

4. A concrete wall form panel as set forth in claim 2 and including, additionally, releasable means at each corner of the rectangular metal frame for securing the adjacent ends of the longitudinal and transverse frame members together, said releasable means, in combination with said tensioning rods and their associated nuts constituting means for maintaining the various components of the panel in its assembled relationship.

5. A concrete wall form panel as set forth in claim 3 and wherein said inwardly offset wall portions have bottoms which are inclined at a small angle to a plane at right angles to the facing, and said threaded ends of the tensioning rods extend at right angles to said inclined bottoms of the offset wall portions and project therethrough.

6. A concrete wall form panel as set forth in claim 4 and wherein each releasable means comprises a bolt having a head portion seated within the trough-like recess of the associated transverse frame member and secured to the inwardly offset Wall portion of said associated transverse frame member, a shank projecting through an opening in the inwardly offset wall portion of the associated longitudinal frame member, and a nut threadedly received on said shank and adapted to be tightened against the last mentioned inwardly offset wall portion.

References Cited UNITED STATES PATENTS 2,258,694 10/1941 Wedberg 249-28 X 2,818,629 1/1958 Wedberg 249-489 X I. SPENCER OVERHOLSER, Primary Examiner R. D. BALDWIN, Assistant Examiner US. 01. X.R. 249- 45