US2738832A - Cradled spanning board construction - Google Patents

Description

2 Sheets-Sheet 2 F. C. TORKELSON CRADLED SPANNING BOARD CONSTRUCTION i N @R March 20, 1956 FiledAug. 1, 1950 Snventor FRANK C. TORKELSON attornegs United States Patent CRADLED SPANNING BOARD CONSTRUCTION 1 Frank c. Torkelson, Salt Lake City, Utah Application August 1, 1950, Serial No. 176,952

6 Claims. or. 155-130 .Among such advantages are low heat conductivity and moderate impact resistance. Wood naturally has no uniform constitution so that a desired safety factor cannot be applied to predetermine the required strength. According ato the invention, the desired safety factor is provided by the use of a cradle preferably made of steel, which serves as a safeguard against defects that often exist in wooden material.

Another feature of the invention is that the wood need not be as carefully selected as would otherwise be re quired, this reducing the initial cost of bleacher construction and at the same time lessening the liability hazard with respect to accidents. This frequently results in lowering liability insurance rates.

The unique feature of the invention is that one or more steel rods are spaced apart from the bearing surface of the seat board or footboard and that the ends of such steel rods are securely anchored in steel end-shoes so that even if rupture in the board should tend to take place at any point between the end-shoes, the board will always be sustained by the steel rod or rods before actual occurrence of such anticipated rupture. I

In the accompanying drawing, which illustrates one embodiment of the invention:

Fig. 1 represents a top plan of a board as built into a supporting steel structure;

Fig. 2, a front elevation;

Fig. 3, a bottom plan, drawn to an enlarged scale;

Fig. 4, a longitudinal section taken on the line 4-4 in Fig. 3, portions being broken away for convenience and the scale being further enlarged;

Fig. 5, a cross-section taken on the line 5-5 in Fig. 4;

Fig. 6, a top plan of a self-contained steel cradle assembly alone, the seat board being omitted;

Fig. 7, a front elevation corresponding to Fig. 6;

Fig. 8, a cross-section taken on the line 8-8 in Fig. 6;

Fig. 9, a front elevation of a spanning board of another construction as built into a supporting steel structure after the manner of Fig. 2;

Fig. 10, a fragmentary end portion, approximately as enclosed by the broken line 10 in Fig. 9, drawn to an enlarged scale;

Fig. 11, a fragmentary end portion of a seat board illustrating the manner of pre-stressing the steel cradle during the process of forming the complete assembly.

, 2,738,832 i-Patented Mar. 20, 1956 Referring to the drawing: the numeral 20 indicates an ordinary wooden plank having a suitable thickness, for example, about two inches and of any suitable length. In the construction of Figs. 1 to 5, the bottom surface 21 ofthe plank 20 is grooved or rabbeted as indicated at 22, there being in this instance, three grooves spaced apart from one another across the plank. The ends of plank 20 are snugly fitted each into a respective end-shoe 23.

Loosely disposed in the grooves 22 are cradle rods 24 assumed inthe present instance to be made of steel having the requisite strength. The rods 24 are welded or otherwise integrally connected to the respective end-shoes 23 before these are applied to a board.

The snug fit aforesaid, between the shoes 23 and the respective ends of the plank 20 is brought about by prestressing the rods 24. This pre-stressing is accomplished byfabricating the cradle assembly so the distance between the inner faces 23a of the end shoes in the finished plank assembly is a little less than the overall length of the plank. One way of creating the pre-stress is to fabricate the cradle assembly so either one or both of the end shoes have an outwardly extending, angular, initial position 23b as illustrated in Fig. 7, which maybe termed the open position. The readied plank is placed in the open cradle and the end shoes bent up'into position under hydraulic or other pressure. Afterwards screws 25 or other suit able fastening means, are applied.

It is to be noted in Figs. 4 and 5 that the depth of grooves 22 provides a space 22a between the rods 24 and the bottom of a respective groove, the purpose of which will presently appear.

The aforementioned tare-stressing of the cradle rods occurs because the lower corners 20a of plank 20, Fig. 11, act as fulcrums for the end shoes distorted as at 23b when pressure is applied to force the end shoes up into the final position. This forcing creates a tensile stress in rods 24 opposed to the reactive force that is set up in the bottom fibers of plank 20. Thus pre-stressing of the rods is brought about.

In the form shown Figs. 3 to 8 and 11, rods 24 are welded to the inside surface of the bottom flange of each end shoe as particularly shown in Fig. 8. In the form shown Fig. 10,rods 24a are welded to the outside surface of the bottom flange of each end shoe 230. In the construction of Fig. 10 it is not necessary to groove the plank since the desired spacing-apart 26 of the rods from the bearing surface of the plank is inherent in the end shoes 23c. Welds between the stressing rods and the end shoes or other items are indicated at 33.

For the purpose of fastening the seat board assemblies in place in the finished bleacher or other structures, stud bolts 27 are welded or otherwise held substantially integrally' in place in. the various end shoes. For illustration, such stud bolts extend through the flanges of steel trusses 28 in Figs. 1 and 2, or steel trusses 29 in Fig. 9, of the finished bleachers.

In'Figs. 1 and 2 the successive seat board assemblies 30, each extends across a single span, while in Fig. 9, each of such assemblies 31, extends across two spands. In the latter, a plate 32, Figs. 6, 7 and 9, is welded to the cradle rods 24b, the plate being provided with stud bolts 27a to serve a purpose similar to that of stud bolts 27.

The utility of spacing the cradle rods apart from their ultimate bearing surfaces against the spanning seat boards, is that the initial resiliency of the boards is maintained until a load imposed on the boards becomes sufficient to cause them to deflect and settle down on the cradle rods.

length of the plank, as aforesaid, the plank normally is slightly bowed or deflected upwardly or downwardly as the case may be, to compensate for the difference in length. If and when such deflection is upwardly, the axial spacing of the stressed rods is apparent.

While the foregoing description is necessarily somewhat specific, the spirit thereof is to not limit the scope of the invention excepting as is justified by the following claims.

What is claimed is:

1. A cradled spanning board assembly, comprising a plank having longitudinal grooves; end shoes having flanges in contact with the grooved surface of the plank; and cradle rods disposed in said longitudinal grooves, said cradle rods being fixed to said contacting surfaces of said flanges. v

2. A cradled spanning board assembly according to claim 1, wherein each stressed cradle rod normally, is spaced apart axially from the bottom of the respective groove.

3. A cradled spanning board assembly comprising a longitudinally grooved plank; flange elements extending across the ends of the grooved plank; and cradle rods disposed in said grooves; the cradle rods being fixed to the inside surfaces of each said flange elements, and the depth of the grooves being such as to provide a space between the rods and the bottoms of the grooves.

4. The method of stressing a cradled spanning board assembly, said assembly including a spanning plank having a lower surface lying in a plane, end shoes, and stress rods extending between said end shoes, said stress rods lying wholly in and above the said lower surface, which method comprises making the overall length of said plank somewhat greater than the neat distance between said end shoes in the final position thereof; fulcruming the end shoes on the lower portions of said plank, and subjecting -thefulcrum'ed assembly to endwise compression, thereby imposing a tensile stress on said rods.

5. A cradled spanning board assembly, which includes a plank having a grooved, lower surface and spacedapart end portions; shoes having each a flange extending crosswise of, and below, said end portions of the plank; and a plurality of stressed rods fixed by welded means to the respective shoes, the said stressed rods throughout the lengths thereof, lying wholly within the grooves of the grooved portion, in a manner such as to provide a space between the rods and the bottoms of the grooves.

6. A spanning board cradle adapted to be included in an assembly with a plank element, said spanning board cradle comprising end shoes having upstanding portions with laterally extending 'lower flanges disposed to engage the ends of said plank element; stressing rods extending longitudinally of the cradle, said stressing rods having end portions extending across the upper surface of said lower flanges and a welded joint connecting said end portions to said upper surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 81,120 Van Horn et al Aug. 18, 1868 133,306 Cutler Nov. 26, 1872 174,062 Carter Feb. 29, 1876 207,758 Maughlin Sept. 3, 1878 489,229 'McClintock Jan. 3, 1893 981,966 'A'tnbrozy Jan. 17, 1911 1,167,692 Hinton Jan. 11, 1916 1,687,706 Bauer Oct. 16, 1928 2,601,910 Nichols July 1, 1952 FOREIGN PATENTS 5,344 Great Britain 1899

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