US2545556A - Roof of large span - Google Patents

Description

March 2o, 1951 H M, PONT 2,545,556

' ROOF` OF LARGE SPAN Filed July 8, 1947 2 Sheets-Sheet l hml @w March 20, 1951 H. M. PONT RooF oF LARGE SPAN 2 Sheets-Sheet 2 Filed July 8, 1947 I 1V WFM-fak s Patented Mar. 20, r1951 ROOF OF LARGE SPAN l Henri Maclaine Pont, The Hague, Netherlands Application .luly 8, 1947, Serial No. 759,584 In the Netherlands March 5, 1941 section 1, Public Law 69o, August s, 1946' Patent expires March 5, 1961 3 Claims.

The invention relates to a roof of large span and has for its object to provide a roof, which in comparison with known roofs is extraordlnarily simple and cheap, has a light construction, can be heavily loaded and requires very few abutments.

According to the invention this object is attained by this, that the roof has an elastic structure balanced by tensioned connections and consisting merely of resiliently flexible curved rafters or rafter principals, which rest on corner abutments only meet in the top of the roof and are turned with their hollow sides to the inside, and of roong networks interconnecting under tension said principals and a taut eaves-cable provided round about the roof on the level of the feet of the principals, said networks being situated in the roong planes and composedof wires, tapes, cables or like completely flexible tightening means. Such a taut elastic roof, which, when dome-shaped, may be compared with an umbrella standing on the tips of`its ribs only, has, as will be explained hereinafter, many advantages over rigid roofs, to which the known domestructures also belong.

In a simple beam having a span l and supporting a specific load q .the greatest bending moment is 1/8 Q12. This moment must be taken up by the cross-section of the beam. Consequently, the beam must have a neutral zone, above which compressive stresses and below which tensile stresses are produced in said beam Although in the neutral zone the stresses are reduced to nothing, the material in that Zone cannot be spared, since it is required for the interconnection of the upper and the lower iibers of the beam. In framed beams certain members are provided for this connection. The result ci these facts is, that the specific weight of a rigid beam increases with about the square of the span l. In a completely exible wire, cable or the like suspending from two points there is, when loaded, no moment, but tensile stresses are produced only. There is no neutral zone. The cross-section of the wire is loaded uniformly, that means as eilicient as possible. If the load is equally divided over the length of the wire, the latter will hang in the curve of a catenary and in the connecting points of the wire a maximum tensile force R will be produced, which is given by weight and material is made with said construction.

The `disadvantage of a structure suspended under tension from columns, that in the connecting points horizontal forces equal to are produced, which forces would increase the danger of buckling of the columns, does not exist in the construction according to the invention, since it has rafter principals which are bent towards the top. These horizontal'forces set up in the curved principals only resultants, which lie in the meridian planes of those principals, are directed inwards and thus prevent the principals from bending further to the outside. Owing to their curved shape the rafter principals cannot buckle inwards. If sufliciently close networks are used, so that the principals are tied between the roofing planes along their entire length, the principals cannot buckle to the left or to the right either.

The construction must be protected from torsion. This can be obtained by a suitable manner of weaving the network of the roofing planes between the rafter principals. or by providing bracings in said roong planes. Said braoings can best be placed under the network of the roofing planes. In that case they can also take up part of the weight of the roof covering.

Another advantage of the construction according to the invention is, that the network of the roofing planes, which obviously in the first place serves for the tightening of the structure, can be used directly for the support of the roof covering. In the known rigid roof-constructions the purlins and the roof-joint-grids actually form a dead Weight, since they are not an essential part of the supporting structure. They only serve for carrying the weight of the roof covering to the roof principals.

If the eaves-cable and the rafter principals are interconnected by rafter-wires and anti-torsionbracings walls or doors can be suspended from the eaves-cable for closing the roofed space, without reinforcement of the construction being necessary.

The roof, which is iiexible and taut in all its parts, has the further important advantage, that, when loaded on one side, it regains its internal equilibrium automatically by deformation. If, for instance, one of the roofing planes is heavier loaded by strong wind pressure or dust snow than the other roofing planes, the network or" the heavier loaded side deiiects a bit more, whereas the other rooiing planes are tightened somewhat more. The rafter principals extending along the extra loaded roofing plane are pulled to one another a bit, so that the purlin-wires of the network in that plane are eased oli, whereas these wires in the other roorlng planes are more tightened. The same applies to the rafter-wires of the network. The result thereoi is, that the whole top of the roof is moved in the direction of the most loadedzside, consequently, in the case of heavy wind pressure, rnoves against the wind. A small shortening of the span between two rafter principals causes a considerable increase of the sag of the roof network. On the contrary a slight increase of the span causes a considerable de crease of the sag. From the formula 2 sin ag it appears, that in the extra loaded roofing plane the stresses increase by the increase of q, but decrease by the increase of the sag-angle a, whereas in the remaining roofing planes, in which planes q does not vary, the stresses increase by the decrease of the sag-angle a. It appears that, depending on the shape of the roof, the stresses in the various planes (which stresse., will, of course, balance each other) will not increase more than 2530% when the load on one of the planes is doubled. All stresses in the liexible roof are controllable. Therefore the factor of safety be chosenlow.

Onk the contrary in a rigid construction the stresses in the parts of the roof, the load on which` is doubled, are twice as heavy in those parts, whereas in the parts not being er' a loaded uncontrollable stresses are produced. Ir iis case a` high factor of safety, which means a heavy construction, is necessary.

Ina roof according to the inve sive stresses are found only in the r pals and tensile stresses occur only works. The rafter principals must be resilient and massive as much as possible. Hollow oonstructions and frame work are less suitable these members. Abutments are only required at the corners of the polygon roof. According to the invention the abutments may be construct in such a manner, that they have e. tightening action on the roof. This is obtained, when the feet of the rafter principals rest on abutments, each of which consists of posts sloping inwards from the bearing surface of the involved principal and of a Vertical tie between the joint of said posts and a ground anchorage.

` For the elucidation of the invention reference is had to the drawing which illustrates in diagrama square roof according to the invention; in the drawing:

Fig. 1 is a plan view of the roof,

fter princiin the net- Fig. 2 is a sectional view on the line II-II in Fig. 1,

Fig. 3 is a plan view of the roof under wind load,

Fig. 4 is a sectional view on the line IV-IV in Fig. 3, andk Fig. 5 is a perspective View of aroof seen in a slanting direction from above.

In the drawing l designates a number of resiliently liexi'ole curved rafters or rafter principals meeting in a top 2. In the roofing planes networks of, for instance, steel wire or cable are connected under tension between said principals. These networks consist of purlin-wires 3, rafterwires and anti-torsion bracings 5. The nearly horizontal lower wire El is the eaves-cable. It appears from Fig. 2 that due to the sag of the network the middlemost rafter-wires have a at S-shape. The anti-torsion bracings 5 extend from the rafter principals to the eaves-cable 6. Although in the drawing a network having relatively coarse meshes is shown, actually it can be easily made so, that it is adapted to support the roof covering, for instance tiles, directly.

The rafter principals l rest on abutments, each of which consists of two posts l, which slope inwards from the joint S and enclose an angle. These posts are' pressed outwards by the weight of the roof, so that a tightening action is exerted on the roof on the base thereof. In order to pre,-V

vent the whole from tilting the joints 8 are connected to an earth-anchorage lll by a tie S.

It appears from Figs. 3 and 4, that the sag ef the extra loaded roofing plane increases andthat of the othery roofing planes decreases, when the roof is extra loaded on one side, for instance byy the wind (see arrow Il). In that case the top 2 is displaced against the wind till the equilibrium between the forces acting on the principals is restored. In Figs. 3 and 4 the full lines show the construction, when an extra load is exerted on one side, whereas the situation is shown in dotted lines when the load is uniformly divided. Thereby it can be clearly seen, how the rafter` principals, the purlin-wires andthe rater-wires are deformed during an ori-sided load.

If it is required to close the roof on the sides,V the necessary walls, doors or flaps can be suspended from the eaves-cable 6.

Roofs of the described kind are suitable for very large spans, varying for instance from several tens to several hundreds of meters.

What I claim is;

l. A roof oflarge span comprising, in combination, abutment structures at the corners of the, roofed space only, resiliently i'lexible curved rafters, which rest on said abutment structures, meet in the top ofthe roof and are turned with their concave sides toward the inside, eaves,- cables provided round about the roof on the level; of the lower ends of said rafters, networks composed of completely flexible stretchable wire-like means provided in the roofing planes between said rafters said eaves-cables and keeping tl latter bent upwards, and a roof covering sup# i directly by sais roong networks, said rait-. s, said eaves-cables and said roofing networks constituting a balanced elastic umbrella- 'ke structure standing on the tips of its ribs only.

2. A roof according to claim 1, in which the abutment structures are adapted to move in the meridian planes of the rafters and to force the lower ends of said rafters to the Outside by the weight of the roof.

3. A roof according to claim 1, in Which the abutment structures each consists of pivotally supported posts jointed at their upper ends and sloping inwards from said upper ends, a resilient tie and an earth-anchorage, said tie interconnecting the jointed upper ends of said posts and said earth-anchorage, and the rafters resting on and being hinged to the jointed upper ends of the posts of the abutment structures.

HENRI MACLAINE PONT.

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

UNITED STATES PATENTS Number Name Date 2,103,859 MacFauen Dec. 29, 1937 FOREIGN PATENTS l0 Number Country Date France 1937

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