[0001] The present invention relates to a roof structure constructed of tension members
and compression members and suitable for spanning delineated areas of various size
for providing a protective roof thereover for stadiums, arenas, and the like.
[0002] In recent years, dome and roof structures have been constructed of light weight membranes
in order to achieve lower cost and to improve their performance. These structures
have been constructed of either synclastic surfaces held-up and stiffened by air pressure
or anticlastic surfaces formed by ridged arches, masts, and/or cables against which
the membrane has been pre-stressed. The synclastic surface may have a low aspect ratio,
that is, the ratio of surface area to delineated plan area. The resulting low aspect
ratio has an important advantage for permanent membrane roofs, such as low profile
air structures, since the membrane cost is as much as 70% of the roof cost, the balance
being cables, clamps, and compression ring. However, the disadvantage of the air structure
has been its dependence on mechanical systems for keeping the roof up and the resulting
requirement for providing air tight buildings, snow melting systems, emergency generators,
revolving doors, and the like. On the other hand, the anticlastic surface has a very
high aspect ratio resulting in higher roof costs per unit of delineated plan area.
For example, those anticlastic surfaces employing masts and cables have high aspect
ratios in order to provide sufficiently low membrane stress, while those utilizing
arches have high aspect ratios due to design considerations such as arch buckling.
[0003] In addition to the foregoing problems encountered with regard to the use of light
weight membranes consisting of either synclastic or anticlastic surfaces, there has
been a problem with roof insulation. Previous attempts to incorporate insulation in
air supported roofs have required the installation of snow melting systems separate
and apart from the interior heating system so as to prevent condensation of moisture
on the upper covering membrane thereby impairing the insulation value of the insulation.
In addition, it has been necessary to pressurize the insulation space to pressures
higher than the interior pressure of the enclosed delineated area in order to prevent
the collapse of the insulation. Further difficulties are often encountered in erecting
structures constructed of continuous flexible elements such as cables with discontinuous
stiff elements such as compression struts as they generally do not have the required
stiffness except in their complete assembled condition.
[0004] There is therefore a need for a tension structural system, such as a cable truss
dome, which is suitable for spanning large areas where the tension elements support
a light weight membrane, which provides a low aspect ratio eliminating the need for
supporting air pressure, and which can be erected easily.
[0005] The invention provides a roof structure for spanning a delineated area, said structure
comprising support members spanning said delineated area for supporting a roof thereon,
characterised in that said support members comprise tension members and compression
members said tension members forming top chords spanning a portion of said delineated
area and diagonal chords extending therefrom, said compression members attached between
said top chords and said diagonal chords, and lower tension members connected to the
bottom of said compression members.
[0006] According to a further aspect, the invention provides a method of erecting a roof
structure comprising tension members and compression members for spanning a delineated
area, said method comprising the steps of spanning said delineated area with said
tension members, attaching one end of said compression members to said tension members
at predetermined locations, attaching the other end of said compression members to
said tension members to form diagonal chords therefrom, and tensioning said tension
members spanning said delineated area to form said roof structure.
[0007] The roof structure preferably comprises a flexible membrane as the roof, held down
on the support members by means of tensioning means such as valley cables extending
between adjacent support members. This has the advantage of resisting wind-induced
uplift forces which sometimes exceed the deadweight of the roof structure.
[0008] In order that the invention may be better understood, two preferred embodiments of
the invention will now be described, by way of example only, with reference to the
accompanying diagrammatic drawings, wherein:-
Fig. 1 is a top plan view showing a roof structure according to a first embodiment
of the invention, constructed of a cable truss dome including a plurality of radially-arranged
arched support members and a plurality of concentric tension rings, and including
valley cables radially disposed between adjacent arched support members;
Fig. 2 is a partial side elevation of one of the arched support members of Figure
1, constructed of a plurality of tension members in the form of cables to provide
upper tension chords and diagonal tension chords, and compression members in the form
of vertical struts arranged between the upper chords and diagonal chords;
Fig 3 is a partial top plan view of a tension ring at the centre of the structure
of Figure 1, having a plurality of arched support members attached thereto and extending
radially outward therefrom along with the adjacent valley cables;
Fig. 4 is a partial side elevation of the tension ring of Fig. 3;
Fig. 5 is a partial side elevation of the top of a compression member in the form
of a strut and attached to adjacent upper tension chords by means of a hanger;
Fig. 6 is a partial front elevation of the compression member and hanger used during
construction as shown in Fig. 5;
Fig. 7 is a top plan view in cross-section of the compression member as shown in Fig.
5 and further showing a platform supported by a plurality of tension rings at the
bottom of the compression member;
Fig. 8 is a partial side elevation of the bottom of the compression member and platform
as shown in Fig.
Figs 9 to 15 are illustrations showing the erection sequence for the roof structure
of Figures 1 to 8;
Fig. 16 is a partial side elevation of a cable truss in accordance with a second embodiment
of the present invention, constructed of tension members and compression members,
wherein the tension members form both upper and lower tension chords, and diagonal
chords extending therebetween; and
Fig. 17 is a partial side elevation of the compression members shown in Fig. 16 connected
between the upper and lower tension chords by a bracket.
[0009] Referring now to the drawings wherein like reference numerals represent like elements,
Fig. 1 is a plan view of a roof structure 100 in the form of a cable truss dome. The
cable truss dome 100 forms an undulating supporting surface and is constructed of
a plurality of arched support members 102 arranged radially to a delineated area thereby
to form a dome covering a space such as a stadium or arena. As shown in Fig. 2, the
support members 102 are constructed of a plurality of stranded cables 104 constituting
a single, compound tension member and a plurality of rigid struts 106 forming compression
members. The cables 104 are attached to a continuous compression ring 108 which is
arranged to circumscribe the delineated area to be covered. The compression ring 108
acts as a foundation to the roof structure, and consists of several chords joined
end-to-end. Alternatively, the cables 104 may be secured to a plurality of individual
anchorage blocks (not shown) buried in the ground at locations spaced around the perimeter
of the delineated area. As shown in Fig. 1, the compression ring 108 can be constructed
as a portion of the perimeter wall defining the stadium or arena to be covered. The
cables 104 extend radially from the compression ring 108 overlying a portion of the
delineated area. Some cables 104 have their other inner ends secured to a central
tension ring 110; others have their inner ends secured to the top or bottom of struts
106, as shown in greater detail in Figs. 3 and 4.
[0010] Cables 104 extending from the compression ring 108 to the central tension ring 110
form upper tension chords 112 or ridge cables of the support members 102. On the other
hand, a number of these cables 104 initiating from the compression ring 108 diverge
from the upper chords and constitute diagonal tension chords 114 extending downwardly
at an angle from successive predetermined locations along the support members 102.
As best shown in Fig. 2, a plurality of cables 104 are secured to the compression
ring 108 and extend radially towards the tension ring 110. At a first outermost, predetermined
location, a number (one or more) of cables 104 are peeled away from the remaining
cables and are arranged extending downwardly from those remaining cables forming the
upper tension chord 112, to provide a first diagonal tension chord 114. Similarly,
at the next successive predetermined location, a number of cables 104 are again peeled
away from the remaining cables 104 and extend at an angle downwardly from those remaining
cables forming the next upper chord 112 to provide the next diagonal chord 114. The
upper chords 112 and underlying diagonal chords 114 form two adjacent sides of a triangle.
Struts 106 are connected between the upper chords 112 and diagonal chords 114 to complete
the third side of each triangle by means of the structure shown in Figs. 5 through
8, to be described hereinafter. These triangles are arranged in a substantially vertical
orientation lying within a common plane. Each support member 102 comprises a discrete
series of such triangles each connected to one or two neighbouring triangles only
at respective vertices, so that the triangles do not share common sides. In this manner,
the strut 106 of one triangle has its upper end attached to the cables 104 at the
intersection of the upper chord 112 and diagonal chord 114 of an adjacent triangle
nearer the centre of the structure. Thus, the number of cables 104 forming successive
upper chords 112 successively decreases towards the centre of the structure, as a
corresponding number of these cables are peeled away to provide the diagonal chords
114. The number of cables 104 contained within each diagonal chord 114 is preferably
the same, although it may vary.
[0011] To complete the support members 102, and maintain the diagonal chords in tension,
a plurality of concentric tension rings 116 each constructed of stranded cables 118
are secured to the lower ends of corresponding struts 106 of adjacent support members
102 as best shown in Figs. 7 and 8.
[0012] Overlying the support members 102 is a flexible membrane 120 serving as a roof over
the delineated area. The membrane 120 may be formed of a woven synthetic fabric, although
it is contemplated that other materials such as canvas or thin metallic formed membranes
may also be utilized. The membrane 120 is constructed to be weather resistant and
preferably of a non-combustible composition. Coated fabrics may be employed for the
membrane 120 such as Teflon (Registered Trade Mark) coated glass fibre, silicon-coated
glass fibre, silicon-coated polyester, and the like. In addition, the membrane 120
can be translucent to allow light into the enclosed volume, and may be adapted to
provide good acoustic properties. A plurality of valley cables 122 are positioned
between adjacent support members 102 and extend between the compression ring 108 and
tension ring 110. The flexible membrane 120 is maintained under tension by prestressing
the valley cables 122, for example, as disclosed in U.S. Patent No. 3,807,421. That
portion of the flexible membrane 120 extending in V-shaped cross-section between adjacent
support members 102 can be in the form of rectangles, trapezoids, triangles, wedge
shapes, and the like. In this regard, the flexible membrane 120 can be constructed
of a plurality of triangular shaped panels radiating outwardly from the central tension
ring 110 such that the joints between adjacent panels can be continuously heat-sealed
or adhered in place during field installation so that there are no joints intersecting
with those of adjacent panels.
[0013] Turning now to Figs. 5 and 6, each strut 106 is attached to the cables 104 at a predetermined
location by means of a hanger 124. The upper end of the hanger 124 is provided with
a pivotable U-shaped bracket 126 through which the cables 104 extend. To secure the
bracket 126 to the cables 104, a number of cables may be terminated and secured to
the hanger by means of a fixture 128. As previously noted, a number of cables 104
extend through the U-shaped bracket 126 and are displaced at an angle downwards to
provide the diagonal chords 114. In addition, supplemental diagonal chords 114
1 may be employed by securing same between the hanger 124 and the lower end of an adjacent
strut 106 as shown. Bracing between adjacent support members 102 is not required due
to the fact that the cables 104 forming the upper chords 112 and diagonal chords 114
are under tension. However, trussing or cross-bracing between adjacent support members
I02 can be provided for the purpose of load redistribution and facilitating the erection
of the cable truss dome 100. In this regard, the trussing or bracing can be achieved
by providing cross-bracing in the form of diagonal cables 130 secured between corresponding
struts 106 of adjacent support members 102. In particular, the diagonal cables 130
are secured at one end to the hangers 124 and attached at their other ends to the
lower ends of corresponding struts 106, as shown in Figs. 7 and 8. Although the diagonal
cables 130 are shown seven in number, it is expected that only two or three such diagonal
cables would be required. To facilitate load redistribution, these diagonal cables
are clamped at their crossing point.
[0014] The cables 104 continuing through the hangers 124 within a support member 102 are
secured to the central tension ring 110 in the manner shown in Figs. 3 and 4. In addition,
the valley cables 122 are also secured to the central tension ring 110 between adjacent
cables 104. Thus, the support members 102 have one end attached to the tension ring
110 and extend radially outward therefrom, while having their other ends attached
to the compression ring 108. The lower ends of the struts 106 are provided with a
support 132 arranged generally transverse to the strut and extending outwardly along
the direction of the support members 102. The support 132 is adapted for securing
the cables 118 of the individual concentric tension rings 116 thereto. A platform
134 is disposed overlying the cables 118 to provide a catwalk for maintenance and
installation personnel. The platform 134 overlies the concentric tension rings 116
between adjacent struts 106, and a safety handrail 136 is provided on either side
of the platform.
[0015] As thus far described, the cable truss dome 100 incorporates a structural system
that uses trusses that have upper chords 112 made of tension members comprising a
plurality of prestressed cables 104. The cables 104 are anchored to the compression
ring 108 or buried anchorage blocks (not shown). The diagonal chords 114 are discontinuous
from one another, are attached to the nested, concentric tension rings 116. As the
cable truss dome 100 is a tension dome and dome buckling is not a problem, the rise
of the dome can be made as shallow as possible consistent with water drainage and
the functions required of the enclosed space. Thus the aspect ratio, i.e. the ratio
of dome surface area to delineated plan area, can be made a minimum. The anticlastic
membrane surface can be prestressed by the valley cables 122 that pull the flexible
membrane 120 down against the upper chords 112 of each of the support members 102.
With the upper chords 112, diagonal chords 114, and tension rings 116 constructed
of cables prestressed to a perimeter restraining system, i.e. the compression ring
108, these elements can be combined with rigid elements such as beams or trusses in
such a manner so as to impart additional stiffness to these elements without introducing
compression forces.
[0016] The uniqueness of the cable truss dome 100 is demonstrated by the fact that it is
not triangulated. The rigidity of a triangular structure is not required of the cables
truss dome 100 as structural roof membranes, i.e., architectural fabrics, permit the
membrane to act as both a deck and a weathering membrane. This membrane, if properly
shaped and prestressed, can accommodate the large displacements of a structural system
that is not triangulated. Thus, non-linear large displacement structural analysis
is possible using digital computers. In addition, the cable truss dome 100 can be
formed with either circular or non-circular plan configurations based on skewed symmetric
principles, for example as in U.S. Patent No. 3,841,038. As previously noted, the
prestressed flexible membrane 120 covering the cable truss dome 100 has shallow undulations
permitting the aspect ratio to be a minimum thus allowing maximum economy in the flexible
membrane.
[0017] This economy is further enhanced by the use of individual multi-stranded cables 104
which permit maximum efficiency in the use of material in the upper chords 112 and
diagonal chords 114. This efficiency is achieved in that the number of individual
cables 104 required in successive upper chords 112 decreases from the perimeter to
the centre of the structure. This amount of decrease in the numbers of individual
cables 104 between adjacent chords can be of the same order of magnitude as the number
of cables required in the individual diagonal chords 114. Consequently, the number
of end connections required of the cables 104 is minimized. Further, the use of a
plurality of cables 118 in the construction of each of the tension rings 116 allows
the resulting structure to function as the support for a catwalk as previously described.
[0018] The use of the cable truss dome 100 is a practical consideration because of the efficiency
with which the cable end forces can be resisted through the use of skewed symmetric
compression rings or anchorage blocks. Given the flexibility of the cable truss dome
100, and the fact that it is not triangulated, such facts are advantages because the
cable truss dome can be largely assembled on the ground or in a hanging position,
with or without the flexible membrane 120, and then hoisted into position using simple
cable tensioning devices that are used to put the final tension into the cables 104,
as described below.
[0019] The method for erection of the cable truss dome 100 will now be described with reference
to Figs. 9 through 15. The erection of the cable truss dome 100 uses the natural propensity
for cables to drape in a concave upward position between anchor points under gravity.
The tension ring 110 is supported on a scaffolding 138 or alternatively may be positioned
on the ground and hoisted in place by jacking of the ridge cables. A bundle of cables
104, including the upper chords 112 and diagonal chords 114 for the support members
102, are positioned radially about the delineated area to be covered. The perimeter
ends of the cables 104 are secured to the compression ring 108 while the other ends
of those cables providing the upper chords 112 are secured to the tension ring 110.
Those cables 104 providing the diagonal chords 114 are allowed to drape downwardly
from the remaining cables at successive locations corresponding to the positions for
the struts 106 along each support member 102. The lengths of some of the diagonal
chords 114 are greater than required in the erected cable truss dome 100, in order
to facilitate the erection, as described below.
[0020] The struts 106, having attached hangers 124 and supports 132, are positioned on the
ground, scaffolding and/or stadium seating as shown in Fig. 6. The struts 106 are
securely set so that their plan position relative to each other is maintained during
the attachment of the concentric tension rings 116. The cables 118 are spun overlying
the supports 132 of corresponding 106 to provide the plurality of concentric tension
rings 116. The tension rings 116 are slightly tensioned as they are attached to the
supports 132 of each of the struts 106. The struts 106 having attached hangers 124,
supports 132 and tension rings 116, are lifted vertically upward and secured to those
cables 104 forming the upper chords 112. Alternatively, the hangers 124 may be attached
to the cables 104 first and the struts 106 can be attached later to the hangers during
final erection of the cable truss dome 100. The attachment of the hangers 124, to
the cables 104 is achieved by pivotally attaching the U-shaped bracket 126 over the
cables 104 to the upper end of the hangers 124, and securing the cables thereto by
means of the fixture 128. The cables 104 providing the diagonal chords 114 are inserted
through the lower end of the struts 106. This procedure is repeated for all concentric
rings formed by corresponding struts 106 and the tension rings 116. After the struts
106 have been set securely, cables 104 may then be arranged spanning the delineated
area by successively attaching them to the top of one strut and then to the bottom
of an adjacent strut, so as to form the diagonal chords 114 therebetween. This alternative
method allows the cable truss dome 100 to be easily assembled and erected from a ground
level position.
[0021] Engaging the free ends of the diagonal chords 114 at the outermost struts 106, these
diagonal chords are then jacked by shortening their length through the struts so that
the cables 104 forming the upper chords 112 and the diagonal chords 114 are placed
under tension, which then lifts the outer portion of the support members 102 upwardly
as shown in the sequence between Figs. 10 and 12. The jacking of the diagonal chords
114 is repeated for each of the concentric rings formed by the corresponding struts
106 and tension members 116 so as to place all cables 104 within the cable truss dome
100 in tension thereby causing the cable truss dome to invert as shown between the
erection sequence of Figs. 11 through 14. The diagonal chords 114 are then secured
to the struts 106, to complete the structure of the cable truss dome 100 is covered
with the flexible membrane 120 and prestressed by tensioning the valley cables 122
or tensioning the diagonals 114.
[0022] As thus far described, the interior tension rings 116 are spun at grade level or
on a support structure such as stadium seating and lifted with the struts 106 for
attaching same to the cables 104 providing the upper chords 112. The cables 104 forming
the upper chords 112 are in an inverted position and are subsequently made to assume
a concave downward position by simultaneous shortening of the diagonal chords 114,
one concentric ring at a time, so as to cause the support members 102 to reverse their
curvature one ring at a time. Alternatively, it is contemplated that the flexible
membrane 120 may be attached to the cables 104 and valley cables 122 for inflating
the roof structure using mechanical blowers. The upward movement of the flexible membrane
120 by means of mechanical blowers causes the reversing of the curvature of the support
members 102 and brings the struts 106 approximately into their final positions, at
which the diagonal chords 114 are then attached. Using hydraulic jacks, the struts
106 are then brought into their final position in which the support members 102 assume
a concave downward position, at which time the internal pressure created by the mechanical
blowers is no longer required to hold the cable truss dome 100 up. By performing the
erection sequence at grade level, or as close to ground as possible, such a sequence
is greatly facilitated.
[0023] Turning now to Figs. 16 and 17, there is shown half of a cable truss 140 in accordance
with the second embodiment of the present invention. The cable truss 140 is constructed
of a plurality of tension members 142 arranged to span the delineated area, to be
covered with, for example, a flexible member 120 of the type illustrated in Fig. 1.
The tension members 142 are constructed of stranded cables of the type described and
illustrated with respect to the previous embodiment, and are anchored in the same
way to buried blocks or to a compression ring 108. The tension members 142 each overlie
a portion of the delineated area and have their other ends secured to a central tension
ring 144 in the manner to be described, or, in the case of a linear truss, secured
to the other side. In addition to the tension members 142, the cable truss 140 also
includes a plurality of rigid struts 146, which may be of varying length, and which
form compression members similar in function to the struts 106 as shown in Fig. 2.
[0024] The tension members 142 are arranged in the cable truss 140 to form upper chords
148, diagonal chords 150 and lower chords 152. As shown, the number of cables within
the upper chords 148 decreases from the compression ring I08 to the tension ring 144,
while the number of cables within the lower chords 152 increases from the compression
ring to the tension ring. By way of an example, a plurality of continuous tension
members 142 are secured to the top of a first strut 146, thereby forming an upper
chord 148 between the compression ring 108 and first strut 146. A tension member 142
is attached to the bottom end of an adjacent second strut 146' to form a diagonal
chord 150 therebetween. The tension member 142 forming the diagonal chord 150 is then
attached to the bottom end of the remaining strut 146" and has its free end attached
to the lower end of the tension ring 144. The remainder of the tension members 142
attached to the top end of the first strut 146, are secured to the top end of the
adjacent second strut 146' to form an upper chord 148. The number of cables in the
upper chord 148 running between the adjacent first and second struts 146, 146' is
less than the number of cables in the upper chord running between the compression
ring 108 and first strut 146. Likewise, a tension member 142 connected to the top
of the second strut 146' is attached to the lower end of the adjacent third strut
146" to form diagonal chord 150, and ultimately to the lower end of the tension ring
144 to form a lower chord 152. The remaining tension members 142 attached to the upper
end of the second strut 146' are attached to the upper end of the adjacent third strut
146" in the previous manner described.
[0025] Thus the number of cables within the upper chords 148 between successive struts 146,
146', 146" decreases in number, while the number of cables within the tension members
142 forming the lower chords 152 increases between successive struts. In other words,
the tension members 142 extend continuously from the compression ring 108 to the tension
ring 144 in the form of an upper chord 148, a diagonal chord 150 and a lower chord
152. In turn, the struts 146, 146', 146" are secured between the upper chords 148
and lower chords 152 to maintain the tension members 142 under tension upon application
of a load.
[0026] As shown in Fig. 17, the struts 146 are secured to the tension members 142 by means
of saddle-type brackets 154, 154
t. As shown, the upper and lower brackets 154, 154' are secured to the ends of the
strut 146. The upper bracket 154 is provided with a pair of spaced ears 156 between
which the tension members 142 are retained. The lower bracket 154' is in turn provided
with a U-shaped retainer plate 158 to sandwich the tension members 142 therebetween,
which tension members are also confined between spaced bushes 160. In this manner,
the struts 146 are attached between the tension members 142, so as to maintain the
tension members under tension during an applied load.
[0027] The method for erection of the cable truss 140 will now be described briefly; it
is similar to the method of erection of the cable truss dome 100 previously described
with reference to Figs. 9-15. A bundle of tension members 142 is arranged overlying
the delineated area between the compression ring 108 and tension ring 144. A plurality
of struts a46 are attached to the tension members 142 at intermediate locations between
the compression ring 108 and tension ring 144, so that the tension members are divided
into upper chords 148, diagonal chords 150 and lower chords 152, as shown in Fig.
16. The tension members 142 and struts 146 may be assembled on the ground or using
a scaffolding 138 in the manner previously described. The cable truss 100 is erected
by tensioning the tension members 142 by engaging their free ends at their location
at the compression ring 108. The tension members 142 are respectively tensioned by
shortening their length between the compression ring 108 and tension ring 144, so
that the tension members forming the upper chords 148, diagonal chords 150 and lower
chords 152 are placed under tension, which then lifts the outer portion of the cable
truss 140 upwardly. By successively tensioning those tension members 142 which form
the next adjacent inward diagonal chord 150, all tension members within the cable
truss 140 are placed under tension, thereby causing the cable truss to be raised into
its tensioned self-supporting position, as shown in Fig. 16. Additionally, cross-bracing
130 may be provided between adjacent corresponding struts 146. The cable truss 140
can then be covered with a flexible member 120 which may be pre-stressed by the tensioning
of valley cables 122 attached between the tension ring 144 and compression ring 108.
1. A roof structure (100) for spanning a delineated area, said structure comprising
support members (102;142) spanning said delineated area for supporting a roof thereon,
characterised in that said support members comprise tension members (104) and compression
members (106;146), said tension members forming upper chords (112;148) spanning a
portion of said delineated area and diagonal chords (114;150) extending therefrom,
said compression members attached between said upper chords and said diagonal chords,
and further tension members (116;152) connected to the bottom of said compression
members (106;146).
2. A roof structure (100) for spanning a delineated area, said structure comprising
support members (102;142) spanning said delineated area for supporting a roof thereon,
characterised in that said support members (102;142) comprise tension members (104)
and compression members (106;146), said tension members forming upper chords (112;148)
spanning a portion of said delineated area and diagonal chords (114;150' extending
therefrom downwardly at an acute angle thereto, said compression members attached
to and extending between vertically spaced positions on said upper chords and said
diagonal chords, and further tension members (116;152) connected to the junctions
of said compression members with said diagonal chords to balance the forces acting
at said junctions.
3. A roof structure (100) for spanning a delineated area, the structure comprising
support members (102;142) spanning the delineated area for supporting a roof thereon,
characterized in that each of the support members (102;142) comprises an upper tension
chord (112;148) for supporting the roof thereon; a plurality of compression members
(106;146) each connected at an upper end thereof to one of a number of different positions
on said upper chord and, for each compression member, a diagonal tension chord (114;150)
interconnecting the lower end of the compression member (106;146) and the upper end
of a compression member next adjacent thereto; and is also connected to further members
(116;152) each connected to the lower end of a different compression member (106;146)
of the same support member to maintain the diagonal tension chords under tension;
whereby, upon assembly in use, each compression member (106;146) forms, with its associated
upper tension chord and diagonal tension chord, a triangle, and each support member
(102;142) comprises a plurality of such triangles which are coplanar and are each
connected to an adjacent said triangle only at an adjacent vertex.
4. A roof structure according to any preceding claim, wherein said tension members
comprise a plurality of cables arranged in a bundle.
5. A roof structure according to any preceding claim, further including a tension
ring connected to said support members at a central position overlying said delineated
area.
6. A roof structure according to claim 5, wherein said support members extend radially
outward from said tension ring spanning said delineated area.
7. A roof structure according to any preceding claim, further characterised by a roof
in the form of a flexible membrane overlying said support members.
8. A roof structure according to claim 7, further characterised by tensioning means
extending between adjacent support members for tensioning said flexible membrane.
9. A roof structure according to claim 7 or claim 8 characterised in that said flexible
membrane comprises a plurality of adjacent wedge shaped panels radiating outwardly
from a center portion of said delineated area.
10. A roof structure according to any preceding claim, further characterised by a
compression member (108) forming a closed loop circumscribing said delineated area
to which said support members (102;142) are attached.
11. A roof structure according to claim 4, characterised in that the number of said
cables within said upper chords decreases from the perimeter of said delineated area
to a central portion thereof, at each position at which a diagonal chord extracts
therefrom.
12. A roof structure according to claim 11, characterised in that the number of said
cables forming said lower tension members (152) increases in a direction from the
perimeter of said delineated area to a central portion thereof at each position at
which a diagonal chord adjoins the lower tension members.
13. A roof structure according to claim 4 or any claim dependent on claim 4, characterised
in that the number of said cables within said diagonal chords remains the same from
the perimeter of said delineated area to a central portion thereof.
14. A roof structure according to any one of claims 11 to 13 characterised in that
at a plurality of the junctions of a diagonal chord with an upper chord, the number
of cables in the upper chord to one side of said junction is not less than the sum
of the number of cables in the diagonal chord and in the upper chord to the other
side of said junction.
15. A roof structure according to claim 1, claim 2 or claim o, characterised in that
said further tension members comprise concentric tension rings (116) each connected
to the lower end of a respective compression member (108) of each support member (102).
16. A roof structure according to any of claims 1 to 3 characterised in that at least
some of said upper chords, diagonal chords, and further tension members comprise a
common cable.
17. A roof structure according to claim 15 further characterised by a platform secured
to said tension rings.
18. A roof structure according to any preceding claim characterised by bracing means
(130) extending between corresponding compression members of adjacent support members.
19. A roof structure according to claim 15, characterised in that said tension members
comprise a plurality of concentric cables.
20. A method of erecting a roof structure according to claim 3, said method being
characterised by the steps of spanning said delineated area with said tension members,
attaching one end of each of said compression members to said tension members at said
different points thereonattaching the other end of each of said compression members
to said tension members at another point thereon to form said diagonal chords therefrom,
and tensioning said tension members spanning said delineated area to form said roof
structure.
21. A method according to claim 20, characterised by tensioning said tension members
by the step of shortening the length of said diagonal chords.
22. A method according to claim 20 characterised by attaching a flexible membrane
to said tension members, and inflating said flexible membrane to tension said tension
members.