CA1059871A - Stressed membrane space enclosure - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A stressed membrane space enclosure having a supporting frame com-prising a plurality of spaced individually separable arch-like members with a strip of fabric stretched between each adjacent pair of arches and by means of which separable arches the fabric is tensioned. The feet of the arches rest on load-bearing pads that are individually shiftable as during the frame spreading for the purpose of tensioning the fabric and that each finds its own proper resting place when all the stresses on the structure have been nor-malized and is then secured against unauthorized movement by ground anchors, thereby achieving the greatest possible strength and stability of the support-ing frame. The fabric is applied in reinforced elongated strips one such strip between each adjacent pair of spreadable frame members and stretched to a predetermined tension to bear maximum loads of wind and snow. Reinforc-ing the strips of fabric in the direction of the tension stress and ensuring a high uniform tension on each strip aids in the discharge or dispersal of heavy environmental loads and the overall strength of the structure. A load regulated power jack may be used to spread the adjacent pairs of frame members to achieve the desired fabric tension and allow the fixing of extendable spacing bars therebetween.

Description

~S~ 7~
This invention relates to improvements in a stressed membrane space enclosure and more especially to a structure-supported fabrlc-cover~d building and method of erecting the same, being an improvement on my Paten~
No. 937,~i79, November 27, 1973.
To meet the demand for an easily erected, low cost, space enclosure various types of tent-like structures both air pressure and frame supported have been devised that satisfy different desires in some degreet From an extensive experience in providing space enclosures in many parts of the world ~ from crowded urban to relatively inaccessible hinterland areas and from equa-torial to arctic climes~ I have found the most satisfactory low cost, easily transportable, erectable and salvageable, clear span shelter able to withstand the vagaries of savage environment to be a structure-supported stressed mem-brane enclosure.
Accordingly it is an object of this invention to provide such a shelter in a readily available range of widths and of desired lengths by in-i crements of sub-module or bay lengths in sma:Ll, lightweight, easily transported - components.
A further object is to provide a space enclosing shelter that can be erected and salvaged quickly by inexperienced workmen, using nut and bolt con-' 20 nections.
A further object is to provide such a space enclosure having a sup-porting structure of spaced arch-like frame members with a membrane cover com-posed of strips of fabric stretched to a uniform tension by the controlled I spreading of the arch-like frame members whereby the magnitude of bearable -;,l environmental loads such as wind and snow and the overall strength and stabil-ity of the erection are increased.
A further object of the invention is to provide a shelter having a ~; membrane cover of horizontally reinforced fabric strips all under uniform tension exerted in the direction of the fabric reinforcement.
A further object of the invention is the provision of a structure supported stressed membrane space enclosure wherein the fabric cover is ;
stretched to a uniform predetermined tension by the controlled spreading of ~, ..
" . ' :

~ ~i9~3P7~

the spaced arch-like frame members of the supporting structure whose feet are free to shift or float during such ~abric-tensioning spreading and each to find its own compensating and stabilizing position.
A still further object is the provision of a stressed membrane space enclosure of the nature and for the purposes described having a support-ing structure that includes a plurality of spaced frame members mounted on individually shiftable load-bearing foot pads that, after the spreading of the frame members to tension the membrane and when they have each ound their own ` respective resting places, may then be secured against any unauthorized move-ment.
To the accomplishment of these and related objects as shall become apparent as the description proceeds, the invention resides in the construc-tion, combination and arrangement of parts and method of erection as shall be hereinafter more fully described, illustrated in the accompanying drawings and ,5 pointed out in the claims hereunto appended.
In the drawings: ;
Figure 1 is a plan view of one for~ of the invention with its fabric membrane shown applied only to the mid-section;
Tigure 2 is a side elevation, and - `
Figure 3 is an end elevation thereof;
., :-~ .
`~ Figure 4 is an enlarged isometric view of an assembled pair of arch frame members constituting a sub-module or bay;
Figure 5 is a further enlarged section through an arch-like frame ~:' member;
Figure 6 is an elevation of a part of a reinforced fabric strip;
Figure 7 is an enlarged section as taken on line 7-7 of Figure 6, and ~ -Figure 8 is an isometric view of an arch foot mounted on its shift-able ground pad.
Referring now to Figures 1 to 4 inclusive, it will be seen that this ` 30 embodiment of the invention is in the form of an elongate open span structure with parallel sides 4 and fan-like semi-circular ends 5. Basically the frame consists of a plurality of arch frame members 6 disposed in upstanding spaced , ~ ~ .;''~"'.!1,/ , , ' ~s~
apart relation along the length of the building each such arch frame member being disposed transversely with respect to the longitudinal axis vf the build-ing. The arch frame members 6 are available in standard widths of 30, 40, 50 , and 60 feet, with spans of 120 feet manufacturecl in the same basic geometry for custom orders. Arch members in the standa~d span width have a height of approximately one~half the width and are normally assembled in modular 10 foot sections while 15 foot modular sections are recommended for the extra wide spans. At each semi-circular end of the structure a fan of circumferentially spaced half arches 6a is arranged in radial Eorm to converge at the peak of , lO the respective end regular arch member 6.
Extendable spreader bars 7 are installed horizontally between each pair of adjacent arch frame members 6,,and/~r 6a at selected spaced apart levels.
Each arch frame member foot is mounted on a horizontal, load-bearing pad 8 that at the time of the erection of the supporting frame is free to shift in any , direction on the ground.
The membrane cover for this,f~ame s,~tructure comprises, a plurality of :, elongate fabric strips 9, each stXip extending between a single pair of adja-cent arch frame members- 6 andlor 6a. The construction of these fabric strips 9 and the method of securing their longitudinal edges, to the arch frame membersis shown in Figures 5, 6 and 7.
, Because of the demands- on these la~ge $tressed membrane space en-`, closures particular attention has been pa,i,d to the fabric coyer. Preferably the scri~ or base fabric strip 9 is a spec,ia,l ,imperyious-m,a,texial such as PVC
coated nylon, polyester, fibre glass, "Teflon", "Keylar", pQlypropQline or ~he like resistant to moisture, mildew, m sects and such factors, translucent yet treated to withstand extreme temperature changes and to inhibit deteriora-tion from sunlight, and fire retard,a,nt being self-extinguish,ing. To maxi-mize the strength of the total structure that will withstand snow and wind ~ ~, loadings up to 60 lbs./ft. (292 kg/m ) and 104 mph. (,225 km/hr.), each Eabric strip extended between an adjacent pair of arch frame members may be required eo bear the full tensioning load of a lO ton pneumatic jack as the adjacent pair of arch members is being spread. The breaking load of the fa-bric runs in excess of 600 pounds per square inch of the warp and we~t and , . .

its tear strength r~lns to upwards of 185 pounds on the warp and weft. To meet these exacting requirements the strip 9 is composed of a number of rela tively short pieces of fabric 9a, 9 , gc, etc., connected by overlapped trans-versely extending joints 10 , 10 , etc., the o~erlap being approximately one and one-half inches. These reinforcing overlaps being thermal Eusion or welded joints thereby provide transverse reinforcements at intervals spaced longitudinally of the strip that greatly exceed the strength of a single thick-ness of the fabric. Along each opposite longitudinal edge 11 the fabric is folded over a length of rope 12 running the full length of the strip and the folded over edge with substantial overlap is welded in the manner above men-tioned to from a bead 14. It is to be understood that the elongate fabric strips 9 applied between adjacent pairs o parallel frame members 6 are rec-tangular whereas those fitted bet~7een frame members 6 and radial end frame `~
members 6a and also between adjacent end members 6a are of appropriate sector shape with their Gpposite beaded sides converging at the peak.
A preferred manner of securing the beaded edge 11 of the reinforced : fabric strip 9 to a frame arch member 6 is seen in Figure 5. Here the frame member 6 is an I-shaped extrusion having on the exterior face of its outer crosshead 6 a pair of parallel, spaced, arcuate grooves 15 with rounded outer edges 16 and a central rib 17 that stands higher than the rounded outer edges 16. Mounted on the exterior of this outer crosshead of the arch frame member 6 is a fabric capturing device in the foxm of an elongate plate 18 of the same width as the crosshead with a pair of spaced channels 19 facing the respective grooves 15 with rounded outer edges 20 cQnfronting and spaced from the grooves rounded edges 16 and having a median ridge 21 between the channels 19 that lies on and is releasably secured to the rib 17 of the arch member outer cross~
head by bolts 22. The tubular-like housing constituted by each pair of con-stituted by each pair of confronting grooYes 15 and channels 19 is mQrethan ample to accommodate a beaded fabric strip edge 11 and the constricted gap between their respective confronting rounded outer edges 16 and 20 is suffi-cient to loosely pass the folded oyer and ~7elded edge of the fabric strip 9 yet restricted to ensure captively of the thickened bead of such edge.

~L~5~
~len applying the membrane cover, it will be seen that the design of this fabric attaching structure allows of the easy longitudinal sliding of the beaded edges of an elonga~e strip of fabric in the tubular-like housings of an adjacent palr of arches while the frame is slack yet when these rein-forced fabric strips are transversely tensione~ on the spreading of the arch frame members 6-6a this fabric securing assembly assures a strong, positive and weather-proof joint as the double thickness overlap of fabric at the beaded edge issues from the constricted gap and the captured thickened bead seats in self-centering and effective weatherproof seal against the inside of the outer edges of the groove and channel without in~ury to the fabric.
Following the application of a abric strip 9 between a pair of h /oc~ r`~GJ Ll/~fe~e adjacent arch members 6-6 the frame members are spread apart by a po~er jack 3 such as a 10-ton pneumatic jack applied as at X to achieve the desired ten-sioning load on the fabric that nor~ally runs around 10,000 to 12,000 pounds but may lie in the overall range of from 1 to 20,000 pounds depending upon -~
the size of the structure, climatic conditions, building codes, etc. The arch frame member 6 here shown as an extrusion of I-shape in cross-section has an inner crosshead 6b with a flange 23 extending to each side. Between each cross-head flange 23 and the confronting flange on the next adjacent arch frame member6 a plurality of the adjustable length compression spreader bars 7 are installedat selected spaced apart levels. The flat base of a male part 7 in the shape of an inverted T is secured on flange 23 by bolt 25 and projects beyond the flange in the direction of the adjacent member 6 with the flat base having a ; row of spaced perforations 7 beyond th~ edge of the crosshead flange. A tubu-lar-like female part 7c affixed to the flange of the next adjacent member 6 is longitudinally slidable in telescope relation on the part 7 and carries near its end a diametrically disposed bolt 26 extendable therethrough that, when the arches are spread to produce the desired tension on the fabric, is passed through the appropriately regi~tering perforation 7b and secured by nut 26 .
The load-bearing pad 8 mounted on each arch frame foot is seen in ; Figure ~ as a flat horizontal plate of ade~uate area tQ support its share of ,::

~359~7~
the structure's load havlng regard to the nature of the underlying ground.
It contains a number of perforations 27 to accommodate ground anchors. Here the foot of an arch frame member 6 of I-shape in cross-section is secur~d to the freely shiftable plate by angle brackets 28 fastened by bol~s 29 to both the frame member 6 and the plate 8.
In this embodiment the arch members are preferably fabricated in small lightweight components that can be easily transported and assembled at the site. A flat shiftable load-bearing pad i5 secured to each arch frame foot and a pair of arches is then set up in spaced relation with a plurality of horizontal spreader bars in retracted condition installed at selected spaced apart levels. Successive arches are added for the length of the build-ing whereupon if the structure is to have a semi-circular end, one leg or half arches are arranged to extend as fan-like radials from the peak of the respec-tive end transverse arches. An elongate strip of transversely reinforced fabric is installed between each adiacent spaced pair of arches with its opposite beaded edges loosely captured in the tubular-like housings provided on the exterior of each arch. ~ith the longitudinally extendable spreader bars ~ ;
freed for expansion, the successive pai~s of arches are spread as by a power-ful pneumatlc ~ack interposed therebetween until the reinforced fabric strip reaches a predetermined tension when the underlying spreader bars are respec-tively locked in extended condition. Du~ing the arch frame spreading each load-bearing arch foot pad is free to shift in any horizontal direction on ~-the ground as the arches adjust Lo compensate for the substantial compression and tension stresses. When all these stresses have been normalized and each foot pad has acquired its own position then each foot pad is secured as by a suitable drift pin, ground anchor or the like against any further or un-.. '~ :' authorized movement. -~
Due to unique characteristics of the strong, lightweight, spreadable frame, the membrane cover of reinfQrced elongate fabric strips, the specific nature of joining the fabric to the frame and the method of spreading the frame arches and securing them in fabric uniform tension relation by tele-: scope type compression spreaders have made it possible to provide a stressed .' ~ .
, _ '.: , : ' : , membrane space enclosure of lmusual strength and durability of llghtweight easily assembled an~ dismantled components and that can be very quickly and cheaply erected by supervised unskilled labour.
The current success of this stressed m~mbrane building of different sizes and uses in wide ranging areas of the ~orld have ~rought it under ex-cessive examination in both laboratory and experimentally in situ testing for fulfillment of building code standards. Wind loading eyaluation figures in .~-building codes are based on the assumption that the loaded structural surface is static and stiff whereas the membrane surface of the present structure is dynamic and flexible. The aerodynamic-mechanical interaction of the membrane with the air poses a nonl~near, non-conservative problem of mechanics. As the membrane is dynamically loaded, it not only deflects but also vibrates significantly disturbing the boundary layer and consequently causing changes in the dynamic loading. Load tests have indicated the ~abric over a 10 foot sub-module span can ~ithstand a high p.s.f. pressure. In arch design tests, both with and without the fabric, in axial stresses and for buckling load, ~ -experiments showed an increase in load of 1.4 due to the partial restaint of the fabric. In environmental lQad simulation tests continued with suitab]e i increments until failure of the structure, it was found that rather than buckl-ing, the arches would fail by yielding at the point of maximum moment. Thus, in the bending case~ the fabric provided sufficient restraint to the compression` flange to prevent instability prior to generation of compressive yield stresses proving conclusively the fabric-frame interaction on the stability of the entire configuration and the significance of qualized fabric tension on develop-ment of optimum strength of the fral4e-membrane composite through minimization of membrane stress concentration. In large, clear span space enclosures (up ~; to 120 feet in width and of any desired length) the overall strength of the structure to withstand snow loads of 60 p.s.f. and winds of 140 m.p.h. and to exceed building code standards by a wide margin of safety emphasize the need to eliminate all potential weakness in the assembly and maximize the gain , from complete stress equalization. In these circumstances the shape of the building, the system of joining the membrane and supporting structure and the ~ ~5~

increased load bearing strength oE the frame with stressed Eabric restraint assume added importance.
At the time of erection of the structure, :it may be found desirable to assemble the supporting structure components loosely to facilitate sliding the fabric strips in place in the frame then whel the membrane cover has been applied and the frame members are spread to tension the fabric strips, each frame pad is free to shift longitudinally9 transversely or radially to its own compensating and stabilizin~ position until all the stresses on the struc-ture have been normalized and it finds its own resting place whereupon it is secured by suitable ground anchors against any unauthorized movement.
In conclusion, while it will be seen that mounting each arch-like ~ ~-frame member on a pad that i5 initially free to shift in any direction on the ground expedites the erection of the skeletal supporting structure and facili-tates the application of the fabric strips thereto, a particular advantage lies in the ease with which the structure's co~pression members can ad~ust their ground positions as the frame members are being spread and to compensate for the substantial tensions of the strong reinforced fabric strips. By thus allowing all the stresses of compression and tension to normalize before the frame supporting pads are pinned down, the overall strength of this total space enclosure is greatly enhanced because of the complete stress equalization.` Erom the foregoing description taken in conJunction with the attached drawings of a preferred form of my stressed membrane space enclo$ure, it will be ;` .
apparent to those s~illed in the art to which this invention appertains that this embodiment is susceptible to modi~ication, variation and change without departing from the proper scope or fair meaning of the appended claims.
', ~
.'' ; ~

. ~ .

: .
.
, ' ' ' , , ~ ~ . :

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of building a space enclosing membrane covered structure comprising the steps of:
(a) erecting a plurality of transversely disposed longitudinally spaced arch-like frame members with each arch foot mounted on an individual pad freely shiftable in any direction on the ground;
(b) securing by its opposite edges an elongate strip of fabric in a loose condition between each pair of adjacent transversely disposed frame members;
(c) horizontally spreading successively at spaced apart levels and in a direction longitudinally of the structure by a removable load regu-lated power jack each fabric-connected pair of arch-like frame members until the intermediate fabric strip throughout its length reaches a predetermined uniform tension with the arch foot pads each free to shift in any direction on the ground in response to such spreading action, and (d) securing each said pair of frame members in such spread, predeter-mined uniform fabric tensioning spaced condition.

2. The method of claim 1, wherein each arch-like frame member foot pad is a flat horizontal plate free to shift in any direction on the ground and the fabric-connected pairs of frame members are spread apart successively at differ-ent levels by a load regulated power jack temporarily inserted at selected levels between each successive pair of frame members and actuated to apply a uniform predetermined fabric strip tensioning load to all parts of the strip within the range of 1 to 20,000 pounds with the frame member foot pads individu-ally shifting position in any direction on the ground in response to the stresses applied and a spreader is secured in properly extended position between said pair of frame members at selected levels to maintain the uniform predetermined fabric tension load before the temporarily inserted power jack is removed.

The method of claim 2, wherein each adjacent pair of arch members is spread apart by a load regulated power jack applying a uniform predetermined fabric tensioning load in the normal range of approximately 10,000 to 12,000 pounds.

4. The method of claim 2, including the further step after the spread-ing of the successive pairs of frame members in a direction longitudinally of the structure for the tensioning of the fabric strips with the resultant cumu-lative movement of previously spread pairs of arches of finally securing each of said pads in non-shiftable position with ground anchors when it has found its own resting place.

5. A stressed membrane space enclosure comprising:
(a) a supporting structure including a plurality of transversely dis-posed longitudinally spaced arch-like frame members;
(b) a horizontal load-bearing pad underlying and connected to each foot of each such frame member freely shiftable in any direction on the ground;
(c) an elongate fabric strip between each adjacent pair of frame members being connected by its opposite edges to said respective pair of spaced frame members and stretched transversely throughout its length to a uniform predetermined tension within the range of 1 to 20,000 pounds;
(d) spreaders between each said pair of movable frame members spaced apart at different levels and secured in extended position to main-tain the intermediate fabric strip at the uniform predetermined ten-sion;
(e) and ground anchors securing each individual pad against unauthorized movement after all the frame members of the supporting structure have been spread apart in the tensioning of the fabric with resultant cumulative longitudinal extension of the structure and the pad has found its own resting place with the stresses on the structure nor-malized.

A stressed membrane space enclosure according to claim 5, wherein the elongate fabric strip comprises a plurality of pieces of fabric connected in flat overlapped transversely extending joints lying in the plane of the strip by thermal fusion welds to transversely reinforce and greatly enhance the load bear-ing strength thereof and to enable the fabric strip to withstand the application of high uniform transverse tension, the fabric overlap of the elongate fabric strip transverse welds being approximately one and one-half inches.

7. The stressed membrane space enclosure of claim 6, wherein the arch-like frame member exteriorly carries a fabric strip-capturing device that together with the frame member provides a tubular-like housing with a constricted gap and wherein each longitudinal edge of the fabric strip with its flat overlapped transversely extending reinforcing joints has an enlarged bead formed by an edge of the strip being doubled back in a substantial overlap over a length of rope and secured by a thermal fusion weld, the tubular-like housing on the frame member being more than ample to accommodate the beaded edge of the fabric strip and the constricted gap too limited to release it, whereby the doubled back welded overlap edge of the strip issues from the gap of the fabric strip-capturing device while the enlarged bead seats in self-centering and sealing engagement within the housing.

8. The stressed membrane space enclosure of claim 6, wherein said re-inforced elongate fabric strip is of impervious material chosen from the group comprising PVC coated nylon, polyester, fibre glass, "Teflon", "Kevlar" and poly-propoline resistant to moisture mildew and insects, translucent, able to with-stand extreme temperatures, to inhibit deterioration from sunlight, is fire re-tardant and self-extinguishing and with its opposite edge so captured by the adja-cent pair of frame members between which it is connected as to be able to bear the full tensioning load of a 10 ton jack applied to spread the said pair of frame members.