US2392839A - Building construction - Google Patents

Description

Jam l5, 1946. R. l.. DAvlsoNNYl-:T AL.

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Patented Jan. 15, 1946 Y .BUILDING CONSTRUCTION Robert L. Davison, New York, N. Y., and George \M. Rapp, New Haven, Conn., assignors toiJohn B. Pierce Foundation, New York, N. Y., a corporation of New York Application October 12, 1943, Serial No. 505,904 f- 8 Claims. (Cl. 108-1`) 'This invention relates to improvements in structures; and particularly to structural supports for transverse or lateral loadings in the roof structures of buildings.

I'he trend toward low-cost'structures, in which the objectives are economy of space, material, and labor, h'as been accelerated by present conditions. Wall structures of such buildings have been improved and simplified by the employment of prefabrlcated panels embodying resin-bonded'plywood or the like, but almost universally the roof construction follows the conventional forms of built-up trusses, girders, or rafters.

It is an object of this invention to provide a roof support which will combine the high loadcarrying emciency ofthe trussand arch'types with' the simplicity of girders or rafters.

It is an object of the invention to provide a roof support which, requiring few pieces, few joints, and a minimum of fabrication, will be suitable for low-cost mass production of houses.

It is an object of the invention to provide an arch roof support of simple construction, having the emciency'of higher type structures such as trusses and complex arch types.

It is an object of the invention to provide an arch embodying pre-stressedl relatively th'in structural members, either oi wood, plywood, or metal.

It is an object of the invention to utilize to the utmost the load-carrying capacities oi' the materials, while simplifying the structure to reduce the material and labor costs to a minimum.

Our invention comprises the formation of a roof-supporting structure by springing a slender member into pre-determined arch-like shape by the applicati of forces in opposing directions at the opposi e ends of the slender member and maintaining the member in suc'h form by means of a hori'aontal tie member. By tying together the ends of the arched member, it becomes a selfcontained and self-sustained structure and accordingly does not impose any thrust against the top of the supporting walls. A slender beam, if caused to assume such calculated arcuate shape or camber by the application of endwise applied pressure, will h'ave considerable load-carrying strength, as well as resiliency, its load-carrying strength being enhanced by reason of its prestressing which is opposite in sign to that of the -subsequently applied loads. f

A roof arch according to our invention, therefore, comprises a relatively light structural member, highly pre-stressed by the application of endwise oppositely directed forces, held in arch form -by a tie member in tension, and combined with resilient sheet material of the nature of plywood which is co-extensively secured to the upper, i. e., convex, lace of the bowed or arched resilient slender member, whereby such resilient sheet material is also pre-stressed and by reason o! its coextensive securement to the resilient bowedmember high' load-carrying strength and resistance against deformation incident to wind, snow and other live load conditions, are imparted to the thus formed roof-understructure. Our invention differs from a conventional tied arch in that the curved member is highly stressed in its free or unloaded condition, and by reason ci the compression forces brought about within such v.slender member by the stated pre-stressing, the curved slender member enables vthe 'assembled roof structure to withstand "dead" and llive" loads. It will be observed that the dead and "iive loads to which the resulting roof structure may be subjected are in directions counter toxthe pre-stressed forces engendered in the slender, i. e. inherently weak, arched lmember by the forces applied at the opposite ends of the slender member in opposing directions.

As appearsmore fully h'ereinafter, sheet 'material is secured co-extensively at its underface relative to the outer, i'. e. convex, ,face of the bowed slender member, thereby completing vthe roof structure and whereby the dead" and live loads to which the roof structure may be 'subjected are uniformly distributed over the concerned surfaces of the slender bowed member.

In thel accompanying drawing:

Fig. 1- is an elevation of an arch roof-support according to the present invention;

Fig. 2 is a plan view of a portion of a lroof including two arch' supports with layers of the covering or roofing material exposed;

Fig. 3 is a detailed sectional view on line 3-3 of Fig. 2 of a preferred form of maintaininga bowed member in its arched form by means of a tie member and end-thrustblocks:

Fig. 4 is a plan view taken on lines '4-4 of Fig 3;

Fig. 5 is a central sectional lvertical elevation of Fig. 1; and l Fig. 6 is a detail view, in section, of a preferred means of joining a plywood sheathing.

Our improved arch-type roof support I0 comprises essentally an'arched member Il, a bottom chord or tie member l2, end-thrust blocks Il, I4 at the respective ends of the tie member and cover plates I5, l5 at said tie member ends overlying the ends of said member il.

For a typical room span of 24 feet, an arch rise of 2 3" provides adequate drainage vand eilicient arch action; and assuming a dead load of 5 pounds per square foot, a live Aload of 20 pounds per square foot (distributed uniformly :on the horizontal projection), and `a wind load of 10 pounds per square foot of upliftr distributed uniformly over the whole span, high-stress grade lumber such as 1800i or 2000i Douglas Vilr or yellow pine, 1% inches thick and '5% inches wide (nished four sides" dimension) is fully capable of safely sustaining the stressesresulting from the pre-stressing and such loading.

For uniformity, the tie member or bottom chord I2 is made of equal section; the tie member may be vof selected "yard lumber, and not of the high-stress material employed for the arch member II.

o! the member Il. The 24 inch spacing of arches affords a safe. span for a plywood sheath- The bottom chord I2 is prepared to receive the i arch member II by securing to the ends oi said chord I2 end-thrust or buier blocks Il. Standard high-eiciency connectors such as the Teco toothed ring connector II are employed, the illustrated bolt and washer assembly passing through the block Il, fastener It and chord I2. as shown.

The arched member II is accurately pre-cut as to length, and its ends beveled as shown at I'I in Fig. 3, so that upon the assumption of the ultimate arcuate form, the end edges o! the arched member II will be vertical to the chordA I2 and parallel to the edges of the blocks Il. Such pre- `cut and beveled material, which is at that time in a normal dat condition, is placed horizontally over its companion tie member already having the blocks Il attached, and while supported a* approximately its final position at mid-span by means of a pre-cut center strut 2| standing loosely-in position, itis slowly bent downwardl ing 23, selected because oi its availability in large size sheets, which facilitates the rapid erection of the roof structure. IIv'he plywood is preferably co-extensively secured to the arches by nailing and gluing, and thus cooperates with the arches in the carrying of live loads, the applicationV of the plywood sheathing upon the upper, i. e. convex, face of the resilient bowed arch member, causes a pre-stressing of such sheathing. and due to the resiliency ofthe bowed arch member, combined with the co-extensive securement and resiliency of the bowed sheathing, the resulting roof structure embodies high loadbearing attributes. and under the conditions oi wind. snow and other live load, including travel on the roofby a roeier or repairman, deformation of the lroof structure is minimized and the imposed forces incident to such live load condition aredistributed over the surrounding por-.

bearing lightly against the rpre-inserted double wedges I820; as it is held in this position the temporary center strut is kickedfout ofk position. allowing the full thrust of the curved member to come into-bearing against these wedges. The wedges nextare driven home, or that is, closed until the desired center rise isattained. The plates II, II are then nailed into place and the arch fabrication is completed.

It is obvious that a slight change in length to the arch member II will result in a proportionately much larger change in rise, and therefore the wedges I0, 20 of oak or other hardwood permit of adjustment. As is illustrated in Fig. 4 and indicated in Fig. 3, the wedges I l. 20 are arranged in pairs' in face-to-face engagement with their respective tapered, -reduced end portions directed in opposite directions, thus facilitating adjustment between the respective ends orheach arched member and its associated block Il, and in turn with the associated chord member I2.

The cover plates Il positively coniine the bent arch member II and cover the heads of the bolts. see Fig. 3, and combine to accommodate the cof-extensively secured sheathing and subsequently applied meting material, referred to more lfully hereinafter;

At suitably spaced intervals across the span oi' the arch it is preferable, by reason of the light material employed for the chord I 2. to ini sert struts 2|, which function to stiifen the tie member against the nailing of the ceiling Amaterial to the underside thereof. These struts 2I may be 2 x 4 vertical studs which connect the top and bottom chords;

, In construction, a succession of such arches is supported on and secured to the top of the walls tions of the roof structure. In normal timesv plywood, of inch or V2 inch thickness is ready ily obtainable from stock in 12 feet long pieces: undervpresent war-time conditions 8 feet lengths can be employed, when the longitudinal joints of the plywood -are made with ship-lap connections with speed-nut" fasteners .such as are employed in aircraft plywood work. A typical Joint is shown in Fig. 6 in which the speedmut connections are designated 25. i

The weather surface 2l of the rootis advantageously standard roll sheet roofing applied according to standard practices.

In calculating the stresses `induced in the arch member Il by the application ofendwise pressure sufficient to-obtain5enough center Yrise to i assure good drainagqafanrdeilcient archaction.

certain basic allowable unit I.

stresses have been established. f

The pre-stressbending has been established'f'as 2800 pounds per square inch: although thisstressl" is approximately 50% greater than the i800 pounds basic stress of 1800i Douglas fir, it is considered safe because of the transitory char` acter oi' this loading.

' lisation oi' the plywood sheathing as part of the stress-carrying section.

For a twenty-four foot span and an arch of 2' 3" rise, and the combination of loading and materials above set out, the maximum stresses on the arch member II under full-span loading are +1640 p. s. i. (top liber) -1220 p. s. i. (bottom fiber) and -470 p. s. i. in the plywood sheathing, all of said stress therefore being less than the maximum.v

As is set forth hereinabove, a roof of a house or other building may comprise a number of roof-understructure assemblies, each compris' ing a resilient bowed arch member, a chord member provided with thrust blocks, and plates for maintaining the ends of the bowed arch member. and sheathing of plywood or` other resilient sheet material co-extensively secured in common to a plurality of bowed arch members mutually laterally spaced from one another and in a substantial lateral alignment, whereby the attributes of high load-carrying and resilient resistance against wind, snow and like pressures are increased.

Whereas we have described our invention by reference to specic forms thereof, it will be understood that many changes and modifications may be made provided they do not depart from the scope of the claims.

We claim:

1. A roof structure comprising a tie beam; thrust blocks mutually spaced from one another and secured to said tie beam upon its upper face; an initially straight slender member bowed by application of forces at its opposite ends in opposing directions, the ends of said bowed member being lodged against said thrust blocks; plates secured to the upper faces of said thrust blocks for maintaining the ends of said member in position relative to said thrust blocks; resilient sheet material pre-stressed and secured coextensively at its under face relative to the outer bowed face of said bowed member; and s'trut means supporting said bowed member.

2. A rooi' structure comprising a tie beam, thrust blocks mutually spaced from one another and secured to said tie beam upon its upper face; an initially straight slender member bowed by application of forces at its opposite ends in opposing directions, the ends of said bowed member being lodged against said thrust blocks: wedge means disposed between the inner faces of said thrust blocks and the respective ends of said bowed member; resilient sheet material prestressed and secured relatively to the convex face of said bowed member; and strut means supporting said bowed member.

3. A roof structure comprising a tie beam; thrust blocks mutually spaced from one another and secured to said tie beam upon its upper face; an initially straight slender member bowed by application of forces at its opposite ends in opposing directions, the ends ofsaid bowed member being lodged against said thrust blocks; wedge means disposed between the inner faces of said thrust blocks and the respective ends Yof f said bowed member; plates secured to the upper faces of said thrust blocks for maintaining the ends of said member in position relative to said thrust blocks; resilient sheet material prestressed and secured relatively to the convex face of said bowed member; and strut means supporting said bowed member.

4. A roof structure comprising a tie beam: thrust blocks mutually spaced from one another and secured to said tie beam upon its upper face; an initially straightslender member bowed by application oi forces at its opposite ends in opposing directions. the ends oi said bowed member being lodged against said thrust blocks: wedge means disposed between the inner faces oi said thrust blocks and the respective ends of said bowed member; plates secured to the upper faces of said thrust blc/cin:I for maintaining the ends of said member in position relative to said thrust blocks; resilient sheet material prestressed and secured relatively to the convex face of said bowed member; strut means supporting said bowed member; and sheet roofing material secured to the outer face of said sheet material.

5. A roof structure comprising a plurality of initially straight slender members, each bowed by application of forces at its opposite ends in opposing directions, said members being laterally spaced from one another and in substantial lateral alignment; tie beams individually associated with said members; thrust blocks secured to each tie beam, the ends of its associated bowed member being lodged relative to said thrust blocks; resilient sheet material prestressed and secured co-extensively in common to said plurality of bowed members; and strut means respectively supporting said bowed members.

6. A roof structure comprising a plurality of initially straight slender members, each bowed by application of forces at its opposite ends in opposing directions, said members being laterally spaced from one another and in substantial lateral alignment; tie beams individually associated with said members; thrust blocks secured to each tie beam, the ends of its associated bowed member being lodged relative to said thrust blocks; plates respectively secured to said thrust blocks for maintaining the ends of the associated bowed member in position relative to said thrust blocks; and resilient sheet material pre-stressed and secured co-extensively in common to said plurality of bowed members: and strut means respectively supporting said bowed members.

7. A roof structure comprising a plurality of initially straight slender members, each bowed by application of forces at its opposite ends in opposing direction, said members being laterally spaced from one another and in substantial lateral alignment; tie beams individually associated with said members: thrust blocks secured to each tie beam, the ends of its associated bowed member being lodged relative to said thrust blocks; wedge means associated with each bowed member and its thrust blocks for adjusting the bowed members in substantial mutual lateral alignment; resilient sheet material prestressed and secured co-extensivel'y in common to said plurality of bowed members; and strut means respectively supporting said bowed members.

8. A roof structure comprising a plurality of initially straight slender members, each bowed by application of forces at its opposite ends in opposing directions, said members being laterally spaced from one another and in substantial lateral alignment; tiel beams individually associated with said members; thrust blocks secured to each tie beam, the ends of its associated bowed member being lodged relative to said thrust blocks; wedge means associated with each bowed member and its thrust blocks for adjusting the bowed members in substantial mutual lateral alignment; platesl respectively secured to said thrust blocks for maintaining the ends of the associated bowed member in position relative to said thrust blocks; resilient sheet material prestressed and secured co-extensive in common to said plurality of bowed members; and strut means respectively supporting said bowed members.

ROBERT L. DAWSON. GEORGE M. RAPP.

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