Note: Descriptions are shown in the official language in which they were submitted.
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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
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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;
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`~ 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
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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
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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
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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.
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~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
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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-
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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
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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
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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
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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.
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