US2239399A - Construction of roofs of buildings and the like - Google Patents

Description

April 22, 19411. A. H, PANDYA 2,239,399

CONSTRUCTION OF ROOFS 0F BUILDINGS AND THE LIKE Filed March 17, 195.9 5 Sheets-Sheet l April 22, 1941. A. H. PANDYA 2,239,399

7 CONSTRUCTION OF RQOFS 0F BUILDINGS AND THE LIKE FiledMarch 17, 1939 JSheets-Shet s Patented Apr. 22, 1941 CONSTRUCTION OF ROOFS OF BUILDINGS- AND THE LIKE Anant I-Iiralal Pandya, Westminster, London;

England Application March 17, 1939, Serial No. 262,346 In-Great-Britain March 23, 1938 5. Claims.

This invention relates to" roofs or other parts of structures or of subdivisions of structures required to carry loads distributed over a large area without the aidof supporting members disposed within the boundaryof theroof or other part.

An object of this'ijnvention is to provide a ridged roof or other ridged construction (-e. g. a hopper floor) adapted to cover extensive substantially rectangular spaces without any trusses or otherstructural members projecting below the planes of the ridged structure. A further object is to reduce-materially the maximum positive bending momentsin the structural members and to provide a structure having a high strength factor per unit of weight. Another object is to provide simplified roof construction which enables satisfactory lighting and ventilation to be easily attained and the cost of maintenance to be kept-low.

In accordance with this invention, a ridged roof or other ridged part comprises a plurality of continuous beams which are disposed perpendicularly or substantially so to the ridge line and which are supported by means of columns or equivalent supports at their ends only, said continuous beams being'cranked at the ridge line so as to lie in the planes of the roof or other ridged part and receiving the roof or equivalent loading/and three boom members disposed respectively along said ridge line and along eave or valley or other fold lines of the roof or other ridged part, said boom membersco-operating with said continuous cranked beams to form two inclined or vertical girders which provide virtual support for said beams at cranking points therein.

By the term continuous cranked beam is therefore meant. a beam in the form of a series ofstraightlengths lying in a common plane and meeting one another at a sharp elbow at the cranked portion orportions, each cranked" portion beingrigid enough to transmit substantial bending moment from one to the other of the adjoining straightportions of the cranked beam; The several straight portions, of each continuous cranked beam thus. form vertical" members of the said girders.

Thisinvention is especially applicable to,mu1 tiple-pitch structures, and according-to the invention in another aspect a roof or other part of the multiple-pitch type comprises a plurality of continuous beams which are disposed perpendicularly, or substantially so to the ridge lines, said continuous beams being cranked atthree or more points so as to lie in the planes of the roof crating with the portions of said continuous cranked beams between said two ridge lines to form a plurality of inclined or vertical girders which are supported at their ends only andwhich provide virtual support for said beams at cranking points therein. The continuous cranked beams in this case are conveniently providedwith supporting columns at their ends, or in placerof some or all of the columns there may be employed equivalent relatively rigid supports such as walls or stiii girders.

The invention will be further described with reference to various examples of roof construction shown in the accompanying drawings, in which: i i

Fig. I is a diagram of a single-pitch roof with a central ridge,

Fig, 2 shows a multiple-pitch roof with a middle valley and two ridges,

Fig. 3 shows a multiple-pitch roof with tw valleys and'three ridges, I V

Fig. 4 shows a north-light or saw-tooth type of roof with multiple gables,

Fig. 5 shows a single-pitch roof with the middle portion raised to accommodate sky or lantern lights, or ventilators,

Fig. 6 shows a double-pitch roof with the middle portion of each gable raised, and

Figs. 7 and 8 are sections of constructional de- In the construction shown'in Fig. 1 there are shown by way of example five continuous cranked beams each consisting of two straightportions 2a and 2b united by an elbow portion 4 or 4". These cranked beams are supported only at their ends on columns I uniformly distributed along the longitudinal sides of the structures. A ridge member 3 crosses the cranked beams at right angles, the points of intersection being coinci- '-dent with the cranking points 4 and 4 of the cranked beams. The cranked beams are further tom booms of a second girder, which lies in the other roof plane and of which the straight portions 2b of the cranked beams form verticals. The two end cranked beams are each provided with a gable tie 6 which takes up the horizontal components of the girder reactions.

The roof loads due to any causes and applied in any direction are transferred to the straight portions of the cranked beams by any suitable secondary system (not shown) such as purlins or roof slabs, which rest directly on the cranked beams. These roof loads thus cause the cranked beams to bend. However, since at the cranking points 4 the cranked beams receive virtual support from the relatively stiff girders of which they form the verticals, and furthermore since the cranked beams are continuous over the cranking points 4 which receive this virtual support (that is, since negative bending moments can be transmitted from one straight portion 2a through the cranking portion 4 or 4 to the adjoining straight portion 2b), the maximum positive bending moments in the cranked beams are substantially lower than they would be in corresponding discontinuous beams of the same span as the straight portions of the cranked beams.

It will be evident that the cranked beams are subjected both to bending in directions transversely to the planes of the roof under the influence of the roof loads incident on them, and also to axial strain or bending in the planes of the roof due to their acting as elements of the longitudinally disposed roof girders.

These girders areshown as trus es without diagonal bracing in their own planes, such bracing may be introduced if desired, or the girders may be of the Vierendeel type, which is especially advantageous in reinforced-concrete construc tion. (In the Vierendeel truss the verticals are rigidly fixed to the booms and are designed to take up the bending moments imposed on them by the shear load in the truss, so that diagonal bracing is dispensed with.)

As a further alternative, which is particularly suitable for reinforced-concrete construction, the girders, instead of being trusses, may have continuous webs of slab form.

It is not essential for the end cranked beams to be continuous. For example these beams may be discontinuous at the ridge points 4', these points in this case each being supported by an additional column I. The construction shown in Fig. 1, when so modified, would have only three continuous cranked beams arranged in accordance with this invention.

The girders lie wholly in the planes of the roof and are supported without the agency of tie rods, bracings or columns extending below the roof planes within the area covered by the roof.

Figs. 2 and 3 show how the construction described with reference to Fig. 1 may be developed for roofs of wider span, without introducing any internal-columns or equivalent supporting members. In Fig. 2 each of the cranked beams is continuous from the eave member 5a to the eave member 5b and consists of four straight portions 2a, 2b, 2c and 2d united by rigid cranking portions 611, 8 and 4b. The cranking portions 4a and 4b coincide with the ridge members 3a and 31) respectively, and the cranking portion 8 coincides with a valley member 1 which forms the common bottom boom of two longitudinal girders having respectively top booms 3a and 3b and verticals 2b and 2c. The only additional columns required, as compared with Fig. 1, are the two columns H placed one at each end of the valley member 7.

Provided the span of the roof girders is kept constant, the continuous cranked beams can be lengthened indefinitely by the introduction of additional cranking points along their total length and additional ridge and valley boom members, with the additional columns for the last. Fig. 3 shows by way of example a roof having three ridges.

In Fig. 4 a similar arrangement of continuous cranked beams is used for a north-light or sawtoothed type of construction in which the northerly and southerly facing roof planes lie at different angles to the horizontal and consequently the depth of the corresponding girders are different. The action of the continuous cranked beams is, however, similar to that described with reference to Figs. 1 to 3, it being immaterial that successive straight portions of the cranked beams are alternately long and short.

Fig. 5 is an example of the application of the continuous cranked beam construction to a roof in which the points of cranking and the deviations of the beams at these points are arranged to suit particular practical requirements such as lighting, ventilation, head room and so forth. Each continuous beam is cranked at five points, coinciding with the intersection points with the beams of five longitudinal boom members l2a, 13a, 3, 13b, and'l2b. The end reactions of the girders incorporating these boom members are taken by ties 6a, 6b and 6c and the end columns I. Fig. 6 shows a development of the design of Fig. 5 to a double-pitch roof. In both these designs internal columns and internal ties or bracings projecting below the roof planes are unnecessary.

The improved structure may be carried out in any desired structural material such as structural steel or reinforced concrete.

Fig. 7 shows by way of example one form of ridge cranking point, such as 4 in Fig. 1, in welded structural steel construction. The continuous cranked beam comprises two straight portions 2a and 2b having their ridge ends cut off obliquely. The oblique ends are fillet welded to opposite sides of a fiat junction plate 20. The ridge boom member is composed of the uppermost two purlins Zia and 2| b welded to the top flange of the cranked beam and an angle bar 22 welded to the bottom flange of the cranked beam and to the plate 20.

Fig. 8 shows an alternative example of cranking point, such as a valley point 8 in Fig. 2. The lower ends of the two straight portions 2b and 2c of the cranked beam are cut off square, and their webs are butt welded to a filling plate 24. The ends of the upper flanges of the portions 2b and 2c, which are suitably bevelled, are butt welded together, and the lower flanges are butt welded to a bent filling strap 25 which is fillet welded to the plate 24. The valley boom member comprises the two channels 26 fillet welded to the continuous web of the cranked beam at the cranking point.

Although the invention has been described by way of example as applied to roofs, it is to be understood that it is applicable to other structural elements required to carry loads distributed over a large area without intermediate supporting members, such for example as floors of hoppers and bins.

I claim:

1. A ridged structure comprising a plurality of parallel, continuous cranked beams located substantially in vertical planes and being rigid across their cranking points, booms disposed at right angles to said vertical planes along and rigidly secured to the aligned ends and cranking points, respectively, of said beams, a tie for each of the two outermost cranked beams, each tie connecting the two ends of one of said outermost beams, and supports at the ends of all said cranked beams.

2. A ridged structure covering a substantially rectangular area and comprising a plurality of girders occupying the respective roof planes, said girders including booms disposed along the folds and side edges of the structure and beams disposed transversely of and rigidly secured to said booms and extending from side edge to side edge of said area, said beams being cranked so as to lie in the several roof planes and rigid across their cranking points, means disposed at the ends of said beams along the edge of said area for supporting said structure and horizontal ties connecting the corresponding lower edges of pairs of girders at the ends of the latter, said beams being capable of developing substantial negative bending moments across said cranking points under the influence of the virtual support afforded at such points by said girders, so that said beams serve as continuous rafters, while their several straight portions act as stressed web bracing elements of said girders.

3. A ridged structure for carrying loads distributed over a large plane area, said structure being of the multiple-pitch type and comprising a plurality of girders which occupy respectively the several roof planes, supports for said girders disposed on the boundary of said plane area, and horizontal ties between the ends of each two of said girders adjoining each ridge line for taking up the horizontal components of the girder end I reactions, said girders comprising boom members disposed respectively along the ridge lines and the other fold and side boundary lines of the ridged part, and beam elements which serve both as web members of said girders and as means for receiving the working loads, said beam elements' said girders to said continuous cranked beams at said points.

4. A multiple-pitch ridged structure for carrying loads distributed over a large area and comprising a plurality of beams disposed transversely of the ridge lines and spanning in a continuous length from edge to edge of said area, said beams being cranked in vertical planes respectively at a plurality of points so as to lie in the several planes of said structure, said cranked beams being rigid across their cranking points, booms disposed respectively along said ridge lines, other fold lines and side boundary lines of said structure at right angles to the vertical planes of the cranked beams, said booms being rigidly secured to the aligned ends and cranking points respectively of said cranked beams and cooperating with said beams to form girders lying parallel to said ridge line and in each of said several planes, respectively, means disposed on the boundary of said structure for supporting the same, and means for resisting the horizontal components of the end reactions of said girders, said beams having continuity of effective section modulus over said cranking points so that they are able to develop at said points, under the influence of superficial loading and the virtual support afforded to them at said points by said girders, negative bending moments of the same order of magnitude as the maximum positive bending moments developed in them intermediate said cranking points by such loading.

5. A ridged structure of the multiple-pitch type which is required to carry loads distributed over a large area, said structure comprising a plurality of girders disposed parallel to the ridge lines and each occupying a plane of the roof, so that said girders lie longitudinally side by side, each being inclined to the adjacent girders and each pair of adjacent girders having one common boom, means disposed along the boundary of said area for supporting said structure, and means for taking up the horizontal components of the end reactions of said girders, said girders comprising beams to receive said loads, said beams being continuous over and cranked at said common booms and being rigidly secured to said booms to serve both as web bracing elements of said girders and as continuous rafters which, under the influence of the roof loads and the virtual support afforded to them by said girders, develop maximum positive and negative bending moments of similar orders of magnitude, the former between and the latter at said cranking points.

ANANT HIRALAL PANDYA.

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