US2577581A - Roof construction - Google Patents

Description

ROOF CONSTRUCTION Filed Nov. 13, 1946 INVENTOR.

7.. m MW 4 Hw N 5 m L WT W ER E A DB R AM Y B E l- F Patented Dec. 4, 1951 UNITED STATES PATENT OFFICE 2,577,581 Root CONSTRUCTION Andrew B. Hammitt and Herbert L. Birum, J r., Trenton, N. J.

Application November 13, 1946, Serial No. 709,556

1 Claim.

a Our invention relates to roof constructions and particularly to structures wherein corrugated cement-asbestos sheet material is applied to purlins or other structural members of the framework of a roof.

The roofs of many buildings, such as industrial and agricultural buildings, frequently embody corrugated cement-asbestos sheet material laid in successive courses with their ends overlapping and supported by purlins or other structural members forming a framework for the roof. It is conventional practice in the erection of the framework for such roofs to space the roof trusses from 16 to feet or more apart forming bays and to provide purlins spanning the distance between the roof trusses for supporting the sheet material which constitutes the actual covering for the roof. The manufacturers of corrugated cement-asbestos sheets generally recommend that the purlins supporting the sheets should be spaced apart only about four and a half feet in order to prevent breaking, sagging or vibration of the sheet material under a load of snow or under other conditions. With roof trusses spaced apart sixteen feet or more the span of the purlins for correct structural design to take care of various kinds of stresses calls for a purlin considerably greater in strength than is necessary merely for support of the roofing material and therefore the inforced in such a way that sagging and danger of breaking is substantially eliminated and the sheets are capable of sustaining a relatively great load even when supported at widely spaced points. The space between the purlins of a roof framework therefore may be increased considerably and the cost of the extra and unnecessary purlins may be eliminated, whereas breaking, sagging or vibration of the sheet'material is-Jreduced or eliminated altogether. Moreover, by means of the present invention corrugated cement-asbestos sheet material may be used in replacing other types ofroof material in constructions where the purlins are" already in place and spaced relatively far apart.

These advantages are attained by employing strengthening means in the form of a truss which cooperates with the sheet material to establish a stress couple in which the sheet material acts as a compression member. Elements of the strengthening means act as tension: members and.

vent or reduce sagging of that portion of the sheet between the purlins.

One of the objects of our invention is to reduce the cost of roofs embodying sheet material.

Another object of our invention is to reduce the breakage or sagging of sheet material applied to a roof.

A further object of our invention is to provide roof constructions wherein sheet material is sup ported by purlins which are spaced relatively far apart. a

A particular object of our invention is to provide a truss construction adapted to be'applied to sheet material to form therewith a stress couple in which the sheet material is a compression mem her and the truss construction includes tension members; 7

These and other objects and features of our invention will appear from the following de-- scription thereof in which reference is made to the figures of the accompanying drawing.-

In the drawings: a

Fig. 1 is a perspective of a portion of a roof embodying one form of our invention as seen from below; I I

Fig. 2 is a longitudinal sectional view struction illustrated in Fig. 1;=

Fig. 3 is a transverse sectional view taken on the line 3-3 of Fig. 2; and

Figs. 4, 5 and 6 are diagrammatic illustrations of typical alternative constructions embodying my invention.

In that form of our invention illustrated in Figs. 1, 2 and 3 the roof embodies a sheet 2, such as a conventional corrugated cement asbestos sheet, supported adjacent its upper end 4 by a purlin 6 and supported adjacent its lower end 8 by a'purlin I0."The upper end 4 of the sheet '2 of the con is overlapped by the lower end of a sheet l2 of an adjacent upper course. of sheet material, whereas the lower end 8 of the. sheet-2 overlaps the upper end of a sheet l4 ofv an adjacent lower 5 course of sheet material. The sheets 2.312 and M are secured in place'on'the purlins by means of fastening means 16 which may betof any suitable type, although we prefer to employ fastening means capable of application from the exterior of the roof, such as those shownand described in our'copending: application Serial -No. 642,636 and in our copending applications Serial Nos. 667,682, 676,563 and 693,410, the latter three now abandoned. However, other types of fastening means may be employed and the sheets-ai material may be assembled in various waysupon the structural framework of the roof and other types of sheet material may be used in the practice of our invention.

In the construction shown in Figs. 1, 2 and 3, the purlins 6 and ID are spaced apart a considerable distance, say 9 feet, from each other, and the sheet material is of greater length than the distance between the purlins, say 10 /2 feet. In order to prevent breaking or sagging of the sheet material between the purlins we provide the sheet 2 with a truss construction indicated generally at l8 which cooperates with the sheet material to strengthen the assembly and establish a stress couple wherein the sheet 2 constitutes a compression member and members 20 constitute tension members.

The tension members 20 are provided at their opposite ends with hearing portions or feet 22 which conform to the corrugations of the sheet and are fixedly secured to the sheet 2 by bolts 24 or other attaching means at points adjacent the opposite ends of the sheet and preferably at pointsbetween the purlins 6 and ID. The tension members 20 are spaced from the sheet 2 near the center of the sheet by a web member 26 which serves as the king post of the resulting truss assembly and establishes the necessary triangular relation of elements characteristic of all truss constructions.

The web member 26 is in the form of a transverse truss embodying a saddle 28 which extends across two or more corrugations of the sheet material adjacent the center thereof to distribute the forces applied to the web member 26 through out a substantial width of the sheet. Arms 29 of the web member 26 are secured to the saddle 28 and as shown project from the saddle so as to be inclined toward each other and provide a bearing portion 3|] engaged by the central portions of the tension members 20. The tension members are preferably welded or otherwise secured to the bearing portion 30 of the web member and the saddle 28 is preferably secured to the sheet material by means of bolts or other. attaching means 32.

- The truss constructions described may be applied to the sheets before they are assembled in place and the sheets thereafter may be arranged in place on the framework of the roof and secured to the purlins in any desired manner or arrangement as in conventional roofing operations. If preferred the truss construction may be applied to the sheets after the sheets have been secured in place on the purlins or roof framework or truss means may be applied to the sheets of an existing roof to strengthen the roof and overcome sagging of the sheet material.

The purlins of roof framework may be spaced apart 9 feet or other'relatively great distances apart in accordance with my invention without danger of breakage, sagging or undesired vibration of the sheets under a load or a high wind. Furthermore, when the purlins are irregularly spaced or the roof is subjected to different loads in different areas thereof, the truss construction may be applied to certain sheets of the assembly and omitted from other sheets, as desired, or necessary to provide a strong, rigid and durable constructure. Our invention also may be employed on roofs which have the purlins spaced the conventional four and a half feet apart, or other relatively short distances apart, when the roof is liable to be subjected to unusually heavy loads or when-relatively light or weak sheet material is employed.

With the construction described a weight or load applied to the sheet material is supported by the combined strength and resistance of the stress couple wherein the compression strength of the sheet material 2 is utilized in combination with the tensile strength of the tension members in supporting the load. Thus in contrast with prior roof constructions the load supported by the sheet material is determined to a great extent by the compression strength of the sheet 2 rather than by its resistance to flexing or bending under a load. Therefore, the rigidity or flexibility of the sheet material is of secondary importance and the span between the points of support of the sheet can be increased or the strength and rigidity of the sheet can be reduced with perfect safety in supporting a given load.

The tension members 20 may be secured to the sheet material in such positions as to produce a slight normal upward bowing of the sheet ma terial prior to its application to a roof so that when subjected to a load the full compressive strength of the sheet material is utilized. However, the truss effect of the assembly serves to increase the strength of the sheet so that such bowing of the sheet 2 is not ordinarily necessary for overcoming undesired sagging of the sheet due to its own weight or under a snow load or the weight of a person walking upon the roof.

While the assembly illustrated in Figs. 1, 2 and 3 illustrates one typical form and application of a. truss construction embodying my invention many alternative forms and arrangements of the truss members may be employed. Thus, as illustrated in Fig. 4 the sheet material 40 may be provided with a truss embodying two or more web members 42 and M spaced apart suitable distances and spanned by the tension member 46. The ends of the tension member are inclined from the web members 42 and 44 as shown at 48 and are attached to the sheet material adjacent opposite ends thereof as indicated at 50. Constructions of this type are particularly adapted for use when the sheet material is relatively long and is supported by purlins which are spaced relatively far apart.

As illustrated in Fig. 5 a plurality of truss constructions may be applied to a single sheet of material 52 and arranged in parallel relation as indicated at 54 and 56. In this way relatively wide sheets of material may be provided with the necessary strength to resist sagging under load or the materials used in forming the truss means may be relatively light in weight and economical to produce and assemble.

In the construction illustrated in Fig. 6 a single tension member 58 is provided at its opposite ends with spaced feet 60 for distributing the forces applied to the sheet throughout substantially the entire width of the sheet.

In each of the constructions shown, the sheet is materially strengthened and breaking or sagging of the sheet is reduced or substantially eliminated. This is clearly indicated by tests which have been conducted to compare and determine the amount of deflection and the breaking point of sheets of corrugated cement asbestos material when used with and without our invention. These tests indicate very clearly that the strength of the sheets, even with purlin spacing up to 10 feet and more is substantially equal to that of a conventional sheet when supported by purlins only four and one-half feet apart. Moreover, sagging of the sheet material over a long span and while under load is substantially no greater and in some instances even less than sagging of conventional sheets supported by purlins which are relatively close together. It is therefore apparent that the strength of the sheet material may be materially increased in accordance with our invention and the cost of the whole roof may be substantially reduced without weakening the structure.

While we have illustrated and described typical constructions embodying our invention it will be apparent that numerous other forms and arrangements of elements may be employed and conventional forms and arrangements of sheet material may be used in the practice of my invention. In view thereof it should be understood that the particular embodiments thereof shown in the drawing are intended to be illustrative only and are not intended to limit the scope of our invention.

We claim:

A roof construction comprising a substantially rigid framework embodying spaced purlins held in fixed relative positions, corrugated sheet material which is substantially rigid and formed of cement-asbestos composition supported adjacent opposite ends thereof by said purlins, means for securing said sheet material to said purlins and means cooperating with the sheet material to form a stress couple in which the sheet material acts as a compression member, said means including a transverse truss having a saddle extending transversely of the sheet substantially midway between said purlins and formed to engage a plurality of said corrugations and having a support projecting from the saddle substantially at right angles to the sheet material, and tension members connected to said sheet material adjacent the ends thereof and between said purlins and having the central portion thereof spaced from the sheet material by said support to provide the triangular relation of elements characteristic of a truss.

ANDREW B. HAMMITT.

HERBERT L. BIRUM, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,145,608 Morton July 6, 1915 2,183,015 Foulds Dec. 12,1939 2,183,451 Forster Dec. 12, 1939 2,319,303 Crawford May 18, 1943 2,417,899 Ashman Mar. 25, 1947 2,427,021 Rapp Sept. 9, 1947 I OTHER REFERENCES Page 108-109, Practical Job Pointers, by

Burbank, pub. by Simmons-Boardman Publ. 00.,

New York city, copyright 1940.

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