INFLATABLE ROOF SUPPORT SYSTEMS

Abstract: A sports stadium or building complex is covered by a huge fiberglass fabric dome that is supported by an inflatable dual-membrane bladder means on a hollow concrete compression ring with a diameter of 800 to 1200 feet. A central vertical spreader means having upper and lower tension rings connected to the membranes of said bladder is supported from above or below by separate suspension cables in a position above the compression ring. Containment cable means limit the expansion of and shape said bladder means to provide a closed pressurized air space of narrow crescent-like cross section and include 70 to 90 or more radial ceiling cables and the same number of radial hold-down cables of the same length.

Description: INFLATABLE ROOF SUPPORT SYSTEMS This application is a continuation-in-part of my copending application No. 08/489,549, filed June 12, 1995, which is a continuation-in-part of my copending application Serial No. 08/384,664, filed February 6, 1995. The present invention relates to inflatable roof structures and more particularly to a method and apparatus for supporting a roof or dome of a convention center, sports arena, stadium or other large building complex in which inflatable bladder means form a closed pressurized air space and are supported by cables or other suspension means below the roof. One embodiment of the invention relates to a unique convention center, trade center or building complex that includes a sports arena and utilizes the novel roof support system. BACKGROUND OF THE INVENTION The use of air pressure to support the roofs of building structures has been well known for several decades as described, for example, in U. S. Patent Nos. 2,837,101 and 2,850,026. The so-called "air domes" and various air-supported roofs are known or have been used including roof systems that employ inflatable air bags or bladder means. Such roof systems have been used in inflatable buildings as in U. S. Patent No. 2,837,101 and in green¬ houses and mobile or portable buildings as disclosed in U. S. Patents Nos. 3,338,000; 4,805,355; 4,924,651 and 4,976,074. Inflatable roofs have been proposed for covering airplane hangers using many tubular air bags mounted side by side as in U. S. Patents Nos. 4,257,199 and 4,976,074, sometimes using helium in the bags to pro¬ vide buoyancy as in U. S. Patent No. 2,850,026. Also shown in the prior art patents are building structures having inflatable bladder means supported on a fixed ceiling between the ceiling and the roof to support the roof by air pressure as disclosed in U. S. Patents Nos. 2,837,101; 3,057,368; 4,452,017 and 4,805,355. As pointed out in Patent No. 3,057,368 (1962) the air-supported dome can be subject to severe wind and snow loads. For that reason the use of air domes has been limited. U. S. Patent Nos ' . 4,805,355 and 4,924,651 dis¬ close portable inflatable building structures for use as greenhouses wherein relatively large bladder means of lenticular cross sections are mounted on generally hori¬ zontal suspension cables to provide an inflatable bubble roof. Neither patent discloses an inflatable roof suit¬ able for covering a sports arena or other large building. U. S. Patent No. 4,976,074 discloses an inflat¬ able roof designed for use as an airplane hanger and described as possibly suitable for covering a sports stadium. However, it appears to be unsafe and impractical for a sports arena. Sports stadiums have been covered by the so- called "air domes" as disclosed in U. S. Patent No. 3,744,191, for example, wherein a network of crossing cables is employed to provide the needed strength. Large stadiums have also been covered by "cable domes" having a network of crossing cables in the roof and a similar net¬ work of suspension cables with rigid upright struts or spreaders to maintain tension in the cables as disclosed 30 years ago in U. S. Patent No. 3,410,039. Spaced radial cables have been proposed for reinforcing the roof as in U. S. Patent No. 3,740,902 but cable networks have been favored by the experts in stadium technology because of added strength, resistance to vibra¬ tion and other advantages. The roof systems of U. S. Patents Nos. 3,410,039; 3,772,836; 3,835,599; 3,841,038; 4,452,017 and 4,581,860 employ such cable networks. While air domes and cable domes, such as those previously mentioned, have been known or proposed for use on sports arenas for decades, the number actually used for that purpose has been limited. Ten years ago only seven cities in this country had enclosed domed stadiums for professional sports. However, interest in such stadiums has grown rapidly since the mid-1980s. The first enclosed stadiums used steel or rein¬ forced concrete domes but such roofs were expensive, heavy and difficult to waterproof. The glazing and trusswork of stadiums, such as the Astrodome, also created problems. Such problems led to a second generation of air- supported fabric-covered stadium roofs, lightweight and inexpensive structures, capable of covering large spans. Such air domes presented a number of serious problems including high annual costs for heat, electricity and maintenance and excessive crowd noise. The continual positive air pressure necessary to support the roof required that the stadiums have revolving doors, air locks for trucks, reinforced elevator shafts, additional fan rooms, and other expensive and inconvenient items. Other serious problems stemmed from damage to the roof fabric during construction and deflations of the domed roofs after completion caused by malfunctioning or poorly operated mechanical or snow removal systems. The above-mentioned drawbacks and problems and extensive litigation associated with the air-supported domes discouraged further use of such roof systems for profes¬ sional sports stadiums so that they are rarely used on new stadiums and are perhaps obsolete. The demise of air domes led to the third genera¬ tion of enclosed stadiums that have fabric roofs supported, not by air pressure, but by tension cables held taut either by large masts or arches, or by smaller compression struts and a compression ring. The leading experts in the engineering of these cable domes are David Geiger and Horst Berger (See U. S. Patents Nos. 3,772,836; 3,807,421; 3,841,038; 4,452,848; 4,581,860 and 4,757,650) . They designed the cable-supported roof system for one of the largest enclosed stadiums in this country, the Georgia dome. The advantages of the new cable domes over the lOprevious air-supported domes were many. The cable domes are more easily insulated. They also can take greater snow loads and demand less exacting maintenance. Their higher cost remain a major drawback, but the elimination of the equipment and details required for pressurization make them superior to the previous air-supported domes. The annual costs associated with operation and maintenance of a conventional air dome, such as Pontiac's Silverdome, are enormous and usually substantially greater than one million dollars because of the large volumes of 20air involved, the difficulty in heating and cooling the structure, and the general inefficiency of the system. These problems are magnified when attempting to design large structures with a clear span of 700 feet or more. In recent years there has been no serious interest in using air-supported roof systems for sports stadiums or large building complexes. It can be difficult and expensive to provide a durable roof structure with a clear span of 800 feet or more because of the great weight to be supported. The 30weight of the roof limits the practical maximum size for a dome even when the dome is covered with the conventional Teflon-coated fiberglass fabric, as used on the Georgia dome. Prior to the present invention cable-supported stadium domes with a clear span in excess of 900 feet have not been built because of the enormous expense involved. The experts on stadium technology heretofore have failed to provide a satisfactory solution to the problem or to provide a versatile, safe, reliable roof system that is commercially practical for huge building complexes. SUMMARY OF THE INVENTION The present invention provides a simple, econom¬ ical, safe and reliable roof support system for a multi¬ purpose business or convention center, sports complex, lOtrade center, shopping center or other large building complex. Huge domes with a clear span of 800 to 1000 feet or more can be provided having remarkable ability to with¬ stand high wind and snow loads. Basic features of the invention, as disclosed in parent application Serial No. 08/384,664, include a huge compression ring supported on spaced columns or perimeter wall means, suspension cable means connected to said ring to form a suspended ceiling covering several acres of land, and a series of regularly-spaced radial hold-down cables 20arranged somewhat like the spokes of a bicycle wheel. The hold-down cables are closely spaced and are connected between the outer compression ring and a central connecting means or hub means located at the top of the dome. Inflatable bladder means coextensive with said dome and said ceiling have upper and lower fabric walls or membranes providing a closed pressurized air space between the hold-down cables of the dome and the suspension cables of said ceiling. When the bladder means is normally inflated to maintain tension in the hold-down cables and 0 ceiling cables, the upper and lower fabric membranes are under tension and held taut with their outer marginal portions connected to the compression ring. The radial hold-down cables limit the expansion of the upper fabric membrane, but the air pressure causes it to expand and bulge in the spaces between the adjacent cables as described in U. S. Patent No. 3,744,191. The hold-down cables are closely spaced to prevent excessive bulging of the fabric. As indicated in said parent application Serial No. 384,644, the cable-supported air domes of the present invention can be used to cover large sports stadiums, such as the Georgia Dome, that seat more than 65,000 people while providing clear spans of at least 860 feet. When employing large domes with diameters of 800 o 1200 feet covering 5 to 10 acres, it is preferable to provide radial suspension cables in the ceiling and to elevate those cables so as to reduce and limit the volume of air in the inflatable bladder means. In the preferred embodiments of the invention, a radial ceiling cable can be aligned with and located directly below each of the radial hold-down cables and rigid strut means or spreader means can be employed to limit the separation of the cables and thereby provide the bladder means with a narrow cres¬ cent or crescent-like cross section (e.g., as shown in Figures 4 and 5) . For example, a central rigid spreader means may be supported from above or below the dome as by overhead suspension cables or by suspension cables carried by the outer compression ring below the ceiling cables. The hold-down cables and ceiling cables would be connected to the spreader means to provide the inflated bladder means with a narrow cross section and a limited air volume. The cross-sectional length is preferably 10 to 20 times the average cross sectional width of the inflated bladder means in preferred embodiments of the invention, such as those illustrated in Figures 4, 4AA and 4C. The present invention makes it feasible to build extremely large domed-roof structures even in locations where wind or snow pose serious problems. This is very important and can be a great advantage in the construction, improvement or renovation of a large sports stadium, for example, because it permits an addition to or an enlarge¬ ment of the stadium so that it can be used as a convention center, an exhibition center, and an impressive year-round facility which may generate enough revenue to pay for itself independently of the baseball or football team. In one preferred embodiment of my invention a primeter wall is constructed that extends around a new or existing sports stadium and a dome is erected and supported by that wall. If the perimeter wall is constructed around an existing sports facility (See Figures 10 to 12) and is outwardly spaced 60 to 90 feet or so from the periphery of that facility, then from one to two million square feet of additional floor space can be created and become available under the dome, assuming that the added space between the existing facility and the new perimeter wall is developed to provide a structure with 10 to 15 or more floors. The domed roof structure can be huge and capable of covering an area of 5 to 8 acres or more. The unique combination described briefly above with an existing stadium surrounded by a perimeter wall of much larger diameter is cost-effective and enables a large city to provide an impressive convention center and/or trade center combined with a multipurpose entertainment, recrea¬ tion and sports center. That all-purpose facility, more fully described hereinafter, can be used more than 300 days per year to provide revenue for the city and is likely to pay for itself in a relatively short period of time while upgrading the city's image. The invention makes it feasible to provide a huge multifaceted center and recreation area that includes restaurants, retail stores, hotels, movie theaters and other entertainment facilities, an aquarium, museums, trade centers, exhibition centers or the like and that can be used for political and business conventions, national sports playoffs, basketball, baseball, football, soccer, tennis, Olympic games, junior Olympics, dog racing, vehicle competitions, track and field events, or the like. The huge all-purpose facility is also extremely energy efficient and economical to maintain. The new domed stadium technology provides unparalleled economies. Air is encapsulated in a separate inflated roof structure that can be maintained at lower temperatures. New roof designs contemplated by this invention make it possible to provide large domed stadiums with a seating capacity in excess of 60,000 which can withstand wind and snow loads at least 50 per cent more than existing domed stadiums. If the dome of this invention employs a special reinforced fabric or an extremely strong fabric, such as a tight- woven fiberglass fabric, it is possible to withstand extremely strong winds or wind gusts of hurricane strength and also high snow loads. An important feature of the present invention is the unique combination of a huge reinforced concrete hollow compression ring and a huge inflatable multi-acre bladder means of narrow cross section that is in communication with the interior of said ring around its outer margin. A typical compression ring is made up of 50 or more box-beam sections that fit together end-to-end to provide an annular air conduit surrounding the dome. Each hollow beam section preferably has a length of 40 to 50 feet and can weigh 200 to 300 tons or more with concrete walls 1 to 3 feet thick and can provide a large room 20 to 30 feet wide, 8 to 10 feet high, and 40 to 50 feet long suitable for a variety of activities. The individual concrete box-beam sections (See Figure 9) are preferably prefabricated at the site, lifted by a huge crane, and placed on two vertical columns located at its opposite ends. This method is unusual but is cost- effective and reduces the construction time. The huge hollow compression ring has a number of important advantages and permits unique methods of opera¬ tion. It facilitates rapid heating and cooling of the air in the bladder means and rapid increases in air pressure in emergency situations. It is preferable to provide an air heater and/or a motor-driven fan means in each section of the hollow compression ring (See Figure 9) or to provide at least 30 air heaters and at least 30 fans spaced around the ring to permit rapid heating or rapid pressure increases. A preferred way to maintain the desired air pressure and to facilitate air circulation is to direct the air from such fans radially inwardly at regularly spaced locations and to provide controlled vent means at the top of the dome to permit rapid air flow out of the bladder means when desired. If, for example, fans delivering air to the interior of the stadium provide 2 to 4 or more air changes per hour, as may sometimes be required in a crowded stadium, the present invention facilitates rapid air changes in the bladder means supporting the dome to effect adequate heating or cooling of the air during cold or hot weather. The large number of fans provides rapid air movement and rapid increases in air pressure when needed. The equipment can be designed to provide a rapid increase is air pressure, such as a 50 percent increase in 20 minutes, or a rapid replacement of the air in the bladder means, such as 2 to 5 air changes per hour. The dome of this invention can be specially constructed to minimize water pooling problems, which were nearly disastrous in the Georgia Dome. The risks posed by possible deflation of the dome can be minimized or reduced by mounting one or both of the two central tension rings for vertical movement as illustrated hereinafter (Figure 4D) . BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a schematic side elevational view on a reduced scale showing the inflated air supporting system of this invention and portions of the stadium on which it is mounted; Figure 1A is a fragmentary sectional view; Figure 2 is a schematic fragmentary top plan view of the equipment shown in Fig. 1 including the oblate inflated bag or envelope, the containment cables and the compression ring; Figure 2A is a schematic fragmentary top view showing a portion of the dome fabric with a series of square reinforcing patches associated with a removable drain plug; Figures 3 and 3A are fragmentary schematic ver¬ tical sectional views of a domed stadium on a reduced scale with the radial cables omitted showing the inflated air-supporting means of the fabric dome; Figure 4 is a schematic elevational view on a reduced scale showing a modified form with a ceiling supported in an elevated position above the radial suspen¬ sion cables (6) ; Figures 4A and 4B are schematic views similar to Figure 4 showing modified forms of the invention; Figures 4AA and 4BB are schematic elevational views showing modifications of the embodiments shown in Figures 4A and 4B; Figure 4C is a schematic elevational view showing another modification of the invention; Figure 4D is a schematic elevational view of the spreader; Figure 4E is a top view showing one of the tension rings of the spreader; Figure 5 is a schematic view similar to Figure 4 showing another modified form; Figures 5A and 5B are schematic top and sectional views showing a modified form wherein the hold-down cables are covered by fabric strips; Figures 6, 7 and 8 are schematic top views on a reduced scale showing various arrangements of compartmented bladder means or air bag means; Figure 9 is a schematic top view showing one section of the huge hollow compression ring containing associated fan and heater means for pressurizing and heating the air; Figure 9A is a schematic fragmentary sectional view showing that ring section on a larger scale; Figure 9B is a schematic fragmentary elevational view; Figure 10 is a top plan view on a reduced scale showing a combination sports complex and convention center that can be covered by the dome of Figures 1 and 2; Figure 11 is a perspective view on a reduced scale showing a scale model of the combination illustrated in Figure 10; and Figure 12 is a photocopy showing the exterior of a proposed sports and convention center having an inflat¬ able dome with a diameter of at least 900 feet suitable for covering a new or renovated football or soccer stadium. The roof structures shown schematically in Figures 1 to 9C are merely examples to illustrate basic principles of the invention and are not intended to show a domed structure that includes the refinements and improve¬ ments. Likely to be present in a completed facility while these figures do not attempt to show relative thicknesses of parts or other structural details, they do show the shape, position and relative proportions of basic elements as could be employed in the practice of this invention including a suitable cross section of pressurized air space provided by the inflatable bladder means. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method and apparatus for supporting a conventional fabric dome or other roof above a football stadium, convention center, shopping center or other large building complex and is characterized in that inflatable bladder means or the like are provided above the playing field to form a closed air space below the roof and in that air is supplied to the bladder means to maintain an air pressure adequate to support the weight of the roof or to maintain its shape. The roof support system can be employed to cover a huge building complex and permits economical construc¬ tion of unique municipal centers and combined sports centers and convention centers as shown, for example in Figures 10 and 12 and described hereinafter. The inflated support system of my invention is suitable for domed sports stadiums and the like which can be employed on new or existing stadiums or used to replace the air-supported or cable-supported domes of existing stadiums. The basic principles of my invention are illus¬ trated, for example, in the embodiment shown schematically in Figures 1 and 2 of the drawings. As shown a domed air-bag assembly A is provided that includes an inflatable bladder means 2 comprising a two-layer envelope, a hollow compression ring 3, and containment cable means comprising a series of evenly spaced radial hold-down cables 5 and a series of evenly spaced radial suspension cables 6 connected to central hubs or tension rings 7. The bladder means or envelope 2 comprises imperforate lower and upper wovenfabric sheets 8 and 9 which may be formed of fiberglass or a suitable synthetic plastic. As shown in Figure 3 a dome or roof 10 is sup¬ ported by the air pressure in the bladder means 2. The dome 10 is preferably formed of woven fiberglass or a conventional translucent architectural fabric or composite. The fabric sheets 8 and 9 of the dome may, for example, be a conventional architectural fabric made of the same material used in the dome of Atlanta's Georgia Dome — a fiberglass-reinforced, Teflon-coated material approxi¬ mately one-sixteenth inch thick. Commercial dome fabric of this type is used extensively and sold under the trademark SHEERFILL. The radial suspension cables 6 provide a ceiling 11 suspended in a fixed position above the playing field. The inflatable bladder means 2 provides a closed pressur¬ ized air space 12 between the fabric dome 10 and the suspended cable ceiling 11. This air space is supplied with compressed air and maintained under a regulated pressure by conventional blower means, shown schematically at 130, and/or a series of separate fan means f located in the compression ring as indicated in Figures 2, 9 and 10. An air pressure is maintained which is adequate to support the full weight of the dome and to maintain tension in all of the hold-down cables so that the shape of the assembly A and the dome 10 is fixed. The assembly A and the dome 10 could be used to replace a cable dome, such as is employed on the stadium of the Georgia Dome in Atlanta. This is illustrated schemat¬ ically in Figure 3 where the building structure B of that stadium is covered by the assembly A of my invention. That stadium has more than 65,000 seats divided among lower, middle and upper tiers 16, 17 and 18, each with twenty to thirty rows of seats. An executive concourse 19 is provided between the middle and upper tiers. In the modification of the stadium shown in Fig¬ ure 3, a peripheral wall or supporting means 14 extends vertically above building B in alignment with the horizon¬ tal compression ring 3 to support the ring around its circumference. The ring is attached throughout its circumference to the marginal portions of the inflated bladder means 2 and to the marginal portions of the fabric sheets 8 and 9 so that they are held taut or under tension when the bladder means is in its normal expanded position as shown in Figure 1. The compression ring 3 is also attached to the outer ends of a series of regularly spaced hold-down cables 5. These cables can, for example, be arranged radially and spaced apart 5 degrees or less throughout the circumference of the compression ring. Similarly spaced suspension cables 6 are provided to form a ceiling 11 below the dome to support the inflatable bladder means 2 which is shown as a two-layer composite envelope which provides a closed or sealed air space 12 between the dome and the cable ceiling. In a large dome, the radial cables 5 and 6 could have a length of from 400 to 500 feet. When the two-layer airtight bladder is inflated as shown in the drawing, the upper hold-down cables 5 fit against the outside of the dome fabric to support and protect it (See Figure 1A) . The cables 5 and 6 are not shown in Figures 3 and 3A. The cables 5 are preferably interconnected to a central hub member, such as a tension ring 7, located near or below the central portion of the dome. The central tension ring can be of relatively small diameter or, if desired, can have a substantial diameter of 30 feet or more (See Figures 4D and 4E) . A similar central tension ring of small or large diameter can also be used to interconnect the suspension cables 6 forming the ceiling 11 at the bottom surface of the two-layer bladder means 2. The upper and lower tension rings 7 shown schem¬ atically in Figures 1 and 2 could have a substantial diameter and would preferably be connected together to limit expansion of the bladder means 2. These rings can be connected by vertical struts or cables or by spreader means comparable to the spreaders 20 of Figures 4 and 5, for example. It will be understood that the inflatable bladder means can be designed in different ways and that the closed air space between the dome 10 and the supporting ceiling 11 can be divided into separate compartments, or substan¬ tially filled with a number of separate air bags as in the optional structures of Figures 6 to 8. As shown the compression ring connected to the radially outer ends of the upper hold-down cables and the lower suspension cables is in the form of a huge hollow reinforced concrete air conduit 3 and is designed to carry compressed air from the fan means f to the closed air space 12 between the upper and lower membranes of the inflatable bladder means 2. The fans f maintain a controlled or regulated positive air pressure, preferably from 10 to 20 (psf) pounds per square foot, sufficient to expand the bag fully and to support the weight of the dome or roof 10. Sometimes a higher pressure may be employed, such as 30 to 40 psf. The perimeter of the compression ring 3 can be round or oval shaped and can have a diameter or width of 500 to 1000 feet or more. The ring can have a uniform cross section throughout its circumference so as to provide an air conduit means extending around the dome providing for rapid or ample air flow into an out of the closed air space 12. As herein shown, a tensioned fabric dome 10 is provided having an air bag assembly A with hold-down cables 5 that fit against the upper sheet 9 of the bladder means 2. The fabric of the dome can be connected to the ring 3 throughout the periphery of the dome and held taut or under tension in a predetermined position as permitted by the hold-down cables 5. The pressure maintained in the air space 12 is sufficient to maintain tension in each of the cables 5 so that the cables and the dome or shell 10 are maintained in fixed positions. It will be understood that the ceiling 11 can have various shapes. It can be rigid and generally flat or curved as in Figures 4 to 4BB. When using suspension cables 6 as shown, some sagging of the cables is necessary, but the amount of sag can be limited as when using a lightweight dome 10. The degree of sag depends somewhat on the weight of the dome and is exaggerated in Figure 1 for convenience of illustration. Actually the cables 5 and 6 have a gentle slope and converge gradually near the compression ring. It is preferable to elevate the ceiling 11 above the suspension cables 6 as by the use of struts, spreaders or vertical supports. Modified forms of the invention with elevated ceilings 11a and lib are illustrated in Figures 4 and 5 in which the parts corresponding in form or function to similar parts described in said patent application are identified by same numbers, sometimes with suffix letters added. Other modified forms shown in Fig¬ ures 4A, 4AA, 4B, 4BB and 4C can be important and are described hereinafter. In the embodiment of the invention shown in Fig¬ ure 4, the dome 10 a is supported by 50 to 70 or more radial suspension cables 6 connected between the hollow compres¬ sion ring 3 and the lower tension ring 7 b . A series of circumferentially spaced parallel vertical spreaders or supports 20 are provided to support similar tension rings 7 a and 7 C associated with the upper set of radial contain- ment cables 5 and the intermediate set of radial support cables 6a, each of which may be in vertical alignment with an upper cable 5 and a lower cable 6 as in Figure 4. The cables are evenly spaced as shown in Figure 2 with each cable spaced 4 to 5 degrees from the next adjacent cable. From 50 to 70 or more support cables 6 a may be provided to form an elevated ceiling ll a covered by the fabric 8 a of the air bag or bladder means 2 a . The pres¬ surized air in the closed air space 12 a of the air bag supports the fabric dome 10 a and maintains the cables 5 under tension. In the embodiment of the invention shown in Fig¬ ure 5, a similar arrangement is provided to support the tension rings 7 a and 7 C above the lower hoop or ring 7 b and to provide the desired elevated ceiling, but the fabric-covered ceiling 11° in Figure 5 can be generally flat or slightly convex, if desired, because of the support provided by a multitude of vertical spreaders 01 to 05. The air bag or bladder means 2 b of Figure 5 is inflated to apply pressure to the upper radial cables 5 of the dome 10^ and the multitude of intermediate radial support cables 6b resting on the vertical spreaders 01 to 05. A controlled positive air pressure is maintained in the air space 12". The number of intermediate support cables 6^ can be from 60 to 90 or more and can be the same as the number of upper and lower cables 5 and 6 with each intermediate cable in the same vertical plane as the corresponding cables 5 and 6. In each such vertical plane the cables 5, 6 and 6b and the spreaders 01 to 05 could be arranged in the same way as shown in Figure 5. While the roof support system of the present invention is particularly well suited for spanning large playing fields in sports stadiums and can be cost-effective with clear spans of 1000 feet or more, it will be under- stood that the cost of construction can be reduced when vertical supporting posts are tolerable or appropriate for the intended usage. Various types of masts, posts or stanchions can sometimes be used to advantage as shown, for example, in Figure 3 (inclined posts or masts 22a) , Figure 3A (posts 23), Figure 4A (mast 21) and Figure 4B (masts 22) . Vertical posts could, for example, be employed directly below some of the struts or spreaders 01 to 05 of Figure 5 to help support the cables 6b. A tall central tower or lengthy vertical central mast comparable to the post 21 of Figure 4A is appropriate in some building complexes as primary support for the central portion of the dome. It will be understood that the inflatable air bags or bladder means employed in the practice of my invention may be modified in various ways and may contain auxiliary supporting means. The air space 12b of the bladder means 2b of Figure 5 may, for example, contain a number of gas balloons, air bags or air pillows and/or vertical supports or vertical air columns. The bladder means may be divided or separated to provide individual compartments and the walls of the bags or the compartments may incorporate reinforcing cords or the like to limit expansion or to maintain the desired shape. Figures 6, 7 and 8 illustrate modified forms wherein the fabric dome is supported from the suspension cables 6 (or the intermediate support cables 6a or 6b) by eight separate triangular or pie-shaped air bags of the same size. Figure 6 shows the eight individual triangular bags 30 fitting together and extending from the hoop or tension ring (7) to the main outer compression ring 3 with the flat vertical walls in engagement at 31. Figure 7 shows a similar arrangement wherein the flat vertical walls of the air bags 30a are spaced apart, perhaps five degrees or more, to provide a narrow space at 31a that facilitates transmission of light to the playing field or the interior of the building. Figure 8 shows a somewhat similar arrangement of eight triangular air bags 30b which are spaced from the main compression ring 3 to provide a peripheral space 32 in addition to the radial spaces 31b to facilitate trans¬ mission of light. These spaces provide windows to admit light and may be covered at the top of the dome (10) with clear plastic or glass sheets. In the embodiments of the invention shown in Figures 6 to 8, six to twelve individual wedge-shaped, deltoid or generally triangular air bags of the same or similar size and shape can provide adequate support for the dome (10) . Such air bags are advantageous because they can be handled conveniently during construction of the domed roof and can be repaired or replaced easily. The use of a substantial number of individual air bags can be advantageous in the construction of huge air domes having a clear span of 800 to 1000 feet or more as may be employed to enclose and cover an existing sports stadium or arena. The hollow compression ring 3 is preferably a massive reinforced concrete structure. The wall or supporting means 14 required to carry the weight of a very large dome would necessarily be quite substantial. A high peripheral wall could involve major expense. That is obviously different from what was illustrated for conven¬ ience in Figure 3. The concrete compression ring can be supported by regularly spaced columns as in Figure 11. It will be understood that modifications and improvements in the basic combination illustrated for convenience in Figures 1 and 2 can be very important and that changes may be appropriate, desirable or necessary depending on the particular application and the size or shape of the domed roof. Figure 3A shows a modification of the structure shown in Figure 3 wherein a series of vertical posts 23 are located at the upper tier 18 of the stadium B parallel to the supporting means 14 to support the ceiling 11 and its 70 or more radial cables 6 carried by the main compression ring 3. The dome 10 and its radial cables 5 can be the same as in the structure of Figure 3. Figures 4A and 4B show modifications of the structure shown in Figure 4 which include features that can be important or desirable. Figure 4 is a schematic view showing the lenticular cross section of the dome 10 a at each of the 50 to 70 or more vertical planes that contain the vertically aligned radial cables 5 and 6. Figure 4A shows a similar dome 10a of the same diameter which has been modified to raise the ceiling (11) formed by the suspension cables while eliminating the cables 6. The latter cables are replaced by a multitude of short radial suspension cables 26 connected to the main ring 3 and a large circular tension ring or cable 25. Fifty to seventy or more radial cables 26 could be evenly spaced and located in vertical alignment with an equal number of similarly spaced cables 6a forming the ceiling and cables 5a forming the dome 10a. Figure 4A, like Figures 4, 4AA, 4B, 4BB and 4C is a schematic representation of the cross section at all of the 50 to 70 or more vertical planes containing the vertical axis of the circular dome. As shown, the ceiling (corresponding to ceiling 11) is formed by radial suspension cables 6a which are connected to a rigid central vertical spreader means 7a similar to that of Figure 4 and which extend outwardly to the main ring 3. The ceiling is elevated by rigid vertical struts or poles 24 connected between tension ring 25 and an upper circular ring 27. The inflatable bladder means 2a surrounds the spreader 7a with its lower wall or mem¬ brane 8a engaging the cables 6a and its upper wall 9a engaging the cables 5a, thus providing a huge pressurized air space 12 * around the tube. Optionally redundant support may be provided to help support the cables 6 or 6a and the dome, such as a removable or retractable vertical mast or post 21 at the center or a series of circumferentially spaced masts or posts 22 or 22a of the type shown in Figure 3 or Figure 4B. The mast 21 could be stored underground during a football game and thereafter raised to an operative supporting position in engagement with the rigid tube 7a. When the mast or support 21 is a fixed permanent element of the roof system, then the suspension cables, such as cables 6 or 6a, could be omitted. Figure 4B shows another modified form with the ceiling raised by the struts 24 as in Figure 4A. For convenience of illustration, inclined posts or masts are shown to help support the tension ring 25 and the ceiling cables 6b. Such redundant support may sometimes be desirable, but it may be better to have direct support of the ceiling cables as by providing posts or masts (22) extending from the ground to the ring 27, thereby elimi¬ nating some or all of the struts 24 and/or the elements 25 and 26. For example, the optional posts or masts 22a would engage the suspension cables 6 of the ceiling 11 in the structure of Figure 3 to elevate the ceiling as in Figure 4A (See also Figure 3A, post 23) . The convertible dome 10b of Figure 4B is quite different from the dome lOaa in that it has a circular (or elongated) central opening to admit light to the playing field and a removable cover or lid C to close the opening. As shown the radial ceiling cables or suspension cables 6b, preferably spaced about 5 degrees apart throughout the circumference of the dome, are connected between a central tension ring or cable 28 and the main ring 3 and support an annular inflatable bladder means 2b below the radial containment cables 5b. A large number of circumferen¬ tially spaced upright struts or spreaders 7b extend between the lower tension ring 28 and a similar upper tension ring 29 that is connected to the 50 or more hold- down cables 5b. The upright struts 7b and optional adja¬ cent cables (not shown) limit inward expansion of the annular inner wall 2 W of the bladder means 2b and allow II the annular air space 12 between membranes 8b and 9b to be pressurized so that the cables 5b and 6b are maintained under the desired tension. The removable cover or lid C may be of rigid or semi-rigid lightweight construction with clear or translu¬ cent panes or panels formed of glass or synthetic plastic or may be an inflatable air bag or bladder means of lenticular cross section similar to those previously described and having upper and lower ropes or cables 31 and 32 to limit the expansion. An airtight loose-woven or open-net fabric may be employed to form the membranes of the envelope and to improve light transmission through the cover. Figure 4BB is a schematic elevational view showing an improvement in the embodiment of Figure 4B wherein fifty to seventy or more radial cables 60 are connected between the tension rings 27 and 29 to form an inclined bladder means 2bb that fits between and fills the space between the fabric 8bb of ceiling 111 and the dome fabric 9bb to maintain tension in the cables 5b, 6b and 60. The lid or cover C and the other elements of the structure shown in Figure 4BB can be the same as shown in Figure 4B. Optionally an annular flexible tube 100 can be employed with an average diameter about the same as the tension ring 27. That tube when expanded under pressure 0would maintain the cables 5b under tension and help to rigidify the dome during wind storms. That tube could be designed to receive air under a pressure of from 1 to 5 pounds per square inch or greater. The optional tube 100 is located between the walls or membranes 8bb and 9b of the inflatable bladder means and can be integrally attached to them to form separate sealed annular air compartments 101 and 102. Optionally, during windstorms, the pressure in the radially outer compartment 101 could, for example, be increased to 30 psf or more. The air pressure in the cover C could also be increased. Figure 4C is a crude schematic elevational view showing another modified form of my invention wherein a multitude of upright rigid struts or posts 101 to 104 are employed to provide an elevated convex domed ceiling lie. This embodiment of the invention is similar to that of Figure 4AA or 4BB in that the radial tension cables 5c and 6c are evenly spaced as in Figure 2 and the ceiling (lie) is raised by successive circular rows of upright rigid posts or struts that are suspended by steel cables. In the preferred embodiment of Figure 4AA, each row of struts is carried by a large circular tension ring. A separate tension ring (4) may in like manner be employed in Figure 4C to support each of the four rows of struts 101 to 104, but four concentric rings are not essential. Other means may be employed to hold the struts in the desired position as disclosed, for example, in Berger Patent No. 4,757,650 where bracing cables provide a system of triangles to hold the struts in fixed positions. Optionally similar bracing cables can be employed in the embodiment of Figure 4C, some of which are indicated at 200. Figure 4C is a schematic view representing the structure at each of the 70 or more radial vertical planes containing the cables 5c and 6c and the associated rigid struts 101 to 104. The roof structure in this embodiment is similar to or comparable to that of previously des¬ cribed embodiments and includes an outer compression ring 3, lower and upper connecting rings 107 and 108 separated by a cylindrical row of twenty to forty or more rigid struts 70, and evenly spaced upper and lower radial cables 5c and 6c extending between the outer ring 3 and the inner rings. The ceiling cables 6c are supported by the rigid struts 101 to 104 to provide a dome-shaped ceiling lie that supports the lower fabric membrane 8c of an inflatable bladder means 2c that covers the entire ceiling. The upper membrane 9c engages the upper cables 5c (as in Figure 1A) and covers the closed air space 120 defined by the bladder means 2c. The lower ends of the rigid struts 101 to 104 at 4a, 4b, 4c and 4d are supported from ring 3 or cable 6c by short cables 201 to 204, respectively, and the upper ends engage or support the cable 6c to provide a raised ceiling with the desired dome shape. The inner portion 106 of each ceiling cable 6c sags between the upper end 105 of each strut 104 and the tension ring 107 while supporting the struts 70 and the upper ends of the hold-down cables 5c. As shown one of the bracing cables 200 extends between upper end 105 of strut 104 and the lower end of strut 103. Such bracing cables are not needed when the struts are supported on four large concentric tension rings 4a to 4d. Each of these tension rings can have a catwalk as shown for access to lights, for example. One of the preferred embodiments of the inven¬ tion is illustrated schematically in Figure 4AA and is almost the same as the embodiment of Figure 4A except for the raised radial ceiling cables 60, the inflatable bladder means 3aa and its lower fabric membrane 8aa. The dome lOaa of Figure 4A can be basically the same as the dome 10a and preferably has from 70 to 90 evenly spaced radial hold-down cables 5a engaging the upper fabric membrane 9aa of the bladder means 2aa substantially in the manner shown in Figure 1A. The cables 5a extend from the outer compression ring 3 to the upper tension ring 7 a of a vertical spreader means 70 comparable to or essentially the same as the spreader means of Figure 4. The raised ceiling llaa is formed by 70 to 90 evenly spaced radial suspension cables 60 connected between the outer ring 3 and the intermediate tension ring 7 C of the spreader means 70 and engaging the lower surface of the fabric membrane 8aa of the bladder means which can also be connected to the ring 3 (as in Figure 9A) . The bladder means provides a closed air space 120 a with a diameter almost the same as that of the air chamber 12 but of much less volume. The ceiling llaa is supported by 70 or more short evenly spaced radial suspension cables 26 and an equal number of rigid upright posts or struts 24 that extend between the tension rings 25 and 27 as in Figure 4A. An equal number of evenly spaced radial suspension cables 6aa are connected between the upper tension ring 27 and the lower tension ring 7 D of the spreader 70 to support the spreader and the cables 5a and 60 connected thereto, whereby the central portion of the ceiling llaa is supported in an elevated position. Optionally an annular tube 100 can be provided in the bladder means 2aa as in the embodiment shown in Figure 4BB to maintain tension in the cables 5a and/or to provide a separate annular air chamber 101 comparable to air compartment 101. The optional tube 100 could be used in the manner more fully described in connection with the embodiment of Figure 4BB. The embodiment of schematic Figure 4AA and the mode of operation are described herein in more detail as an example to facilitate an understanding of my invention including other embodiment of Figure 4. Cable connections and other structures commonly used in stadium roof systems are not described. There are well known and described in various patents including U. S. Patents Nos. 3,744,191 and 4,345,410. Likewise, the architectural fabric employed in the upper and lower membranes of the inflatable bladder means can be a conventional material including the fabrics disclosed in U. S. Patent No. 4,452,848 (e.g., coated woven fiberglass fabric) . For example, in carrying out my invention the hollow compression ring 3 may be round or elongated with a diameter or width of 800 or 900 feet and may be a massive sectional reinforced concrete structure with a cross sec- tion throughout its perimeter which is generally uniform or comparable to that shown in Figure 9A with top, bottom and side walls with a thickness of 18 to 24 inches or more. Each curved section 3 a of the concrete ring can have a width of from 20 to 30 feet, a height of from 7 to 10 feet or more, and a length of from 90 to 120 feet or more. Each section 3 a or every other section would preferably contain a fuel-fired air heater H with suitable air ducts or conduits 51 and 52 to conduct the air from the bladder means into the heater and direct the heated air into the bladder. When desired, a vent conduit 53 could be provided to exhaust the combustion gases to the outside. The 70 or more hold-down cables (5) and the upper fabric wall (9) of the dome are preferably supported at the top of the ring 3 and sloped to facilitate removal of rain water, and the upper surface 55 of each section 3 a is also sloped to allow rain flow to a peripheral water trough or gutter means 56. A door 57 is provided in the top wall to provide maintenance personnel with ready access to the top of the dome. Six to thirty or more fans or blowers f are regularly spaced around the periphery of the compression ring to maintain the desired air pressure in the inflatable bladder means. Such fan means can be provided in the ring section 3 a as indicated schematically in Figure 9 to direct air under pressure to the interior of the ring 3 and the bladder means (2 or 2aa) . A suitable vent means 58 may also be provided to facilitate controlled or rapid reduction in the air pressure when desired. The normal air pressure in the inflatable bladder means of the dome could be from 10 to 15 pounds per square foot (psf) and could be increased to 20 psf or higher when desired. The air inside the stadium below the dome can be caused to circulate by use of fan means 50 at opposite sides or opposite ends of the stadium as indicated schem¬ atically in Figure 4AA, for example. Such fan means could, for example, provide from 2 to 5 air changes per hour in a stadium with a capacity of 50,000 or more spectators. Likewise the fan means f could provide rapid air changes in the closed air space (12) of the bladder means, when suitable vent means are provided to promote air circulation. Vents or louvers v can be provided for that purpose that open inwardly and are held closed by the internal air pressure. Such vents can be provided at both rings 7 a and 1° of the spreader means 70 in the embodiments of Figures 4 and 4AA. Such vents can similarly be provided in the embodiments of Figures 4A, 4C and 5 as shown. Venting of the air in this manner facilitates efficient cooling of the air in the bladder means in hot summer weather and rapid heating of the air to heat the stadium or to melt snow in the winter. The vent means v at or near the top center or the bottom center of the inflatable bladder means can be opened or closed or regulated using a suitable electrical system with control panels inside the huge compression ring 3. The preferred embodiments of my invention shown in Figures 4 and 4AA are advantageous and commercially attractive for large stadium domes. The inflatable bladder means 2 a of Figure 4 and 2aa of Figure 4AA have a narrow lenticular cross section which has superior utility and limits the required volume of pressurized air. In carrying out my invention, it is usually preferable to provide bladder means or similar inflatable means of lenticular cross section where the cross-sectional length is at least 15 to 20 times the average cross-sectional width or height (as in Figures 4, 4AA, 4BB and 4C) . The roof structures exemplified by schematic Figures 4 and 4AA are particularly well suited for covering wide spans of 850 to 950 feet. For example, when the radial cables are uniformly spaced five degrees apart, the dome can be supported by seventy-two steel cables 6 (Figure 4) or seventy-two steel cables 26 (Figure 4AA) with a diameter of 3-1/2 to 4 inches. The same number of ceiling cables 6 a or 60 of that same diameter could be used. The length of each cable 6, 6 a , and 60 could, for example, be 420 to 460 feet. The steel hold-down cables 5 (Figure 4) and 5a (Figures 4A and 4AA) would be at least as long and could be of comparable size and strength, but the diameter could be substantially less (e.g., 2 to 3 inches) depending on the internal air pressure believed necessary for a particular application. An air pressure of 5 to 10 psf may be adequate in localities where wind¬ storms do not pose a problem. In the embodiments of Figures 4 and 4AA the rigid vertically elongated spreader means 70 at the center of the dome has three annular rings 7 a , 7 b , and 7 C connected to a large number of evenly spaced parallel posts or struts 20 arranged in a circle to provide an open-type cylinder. In a typical large stadium dome, said rings could have a diameter of 20 to 40 feet, for example, and the struts 20a and 20b of the spreader means 70 could be vertical steel tubes with a diameter of about 4 inches. When using radial cables spaced five degrees apart, thirty-six tubes 20a could be connected between the rings 7 a and 7 C and seventy- two tubes 20b could be connected between the rings 7" and 7 C . Each of the fabric membranes 8 a and 9 a (Figure 4) or 8aa and 9aa (Figure 4AA) would have a central circular opening to receive the spreader means 70 and reinforced by a rigid metal ring (7 a or 7 C ) that fits the struts 20a. Such a reinforcing ring would maintain the desired tension in the fabric membrane and could be mounted to slide ver¬ tically on the struts 20a as described hereinafter. The upper and lower ends of the spreader means 70 would be closed and sealed to prevent escape of air from the closed chamber i2 a or 120 a of the inflatable bladder means. Glass or clear plastic panels or framed windows could be employed for this purpose, to enhance light transmission, and to improve the appearance of the dome (See the covers 170 of Figure 4D) . In the examples described above, the dome 10 a or 10 aa could employ a conventional coated woven glass-fiber fabric, such as Birdair's 30-year SHEERFILL fabric, with a thickness of at least one-sixteenth inch or other fabric similar to that used on Atlanta's Georgia Dome. Both the lower and upper membranes 8 a and 9 a or 8aa and 9aa of the bladder means can be made of the same high-strength fabric. The domes of Figures 4 and 4AA are designed to provide remarkable resistance to storm damage even in hurricane-like conditions. In the unlikely event of a large tear in the dome fabric, means are preferably provided to prevent dangerous accumulations of water and to facilitate rapid water removal. As shown schematically in Figures 1, 2, and 4, a large number of evenly spaced drain plugs d or d are provided in the top and bottom fabric walls or membranes of the inflatable bladder means. Drain plugs of this type can be employed in all of the disclosed embodiments of my invention to minimize the risk of excessive pooling of water if the bladder means is deflated. As shown in Figure 2A the fabric wall or membrane 9 of the bladder means 2 can be reinforced around each drain plug d (or d ) by several layers of fiberglass fabric in the form of different size square patches 61, 62 and 63. The plug would close and seal the associated drain opening and be held closed by the internal air pres¬ sure. In emergencies each plug could be opened rapidly by moving it inwardly, for example, by pulling a wire cable controlled manually or automatically from inside the ring 3. The optimum or preferred locations for the drain plugs depends on the type of roof and the shape of the inflatable bladder means. In the embodiments of Figures 2 and 4A, the drain plugs d are preferably located near the center portion of the dome. In the embodiments of Figures 4, 4AA, 4BB and 4C, the drain plugs d could be located closer to the outer ring 3. If the domed roof structures of the present invention are to be used in locations where hurricanes or wind storms pose a serious problem, it may be desirable to increase the size and strength and/or the number of radial hold-down cables in the dome so that a greater air pressure can be provided in the bladder means during periods of emergency. For example, the spacing between said radial cables can be reduced from 5 to 4 degrees or the diameter of the cables can be increased to 3 or 4 inches. Optionally, vertical tension cables could be connected between the upper hold-down cables and the ceiling cables supporting the bladder means to limit upward expansion and thereby reduce the tension in the hold-down cables. This option is indicated schematically in Figure 4B wherein seventy to ninety or more vertical cables 60 extend between the ceiling cables and the hold- down cables of the dome. Similar means may, of course, be employed as a viable option in other embodiments of my invention, such as those illustrated in Figures 4, 4AA and 4C. It thus becomes possible to increase the air pressure in the bladder means 50 percent when the dome is subjected to dangerous winds or wind gusts of hurricane strength. One of the preferred embodiments of the present invention is illustrated in Figures 10,. 11 and 12 and relates to a proposed renovation of Cleveland Municipal Stadium, one of the larger baseball stadiums. That stadium (S) is drawn to scale in the top view of Figure 10 and includes U-shaped grandstands G which extend around the natural grass playing field and terminate at the center field bleacher section 33. The grandstands include a rounded portion 34 near home plate and the baseball infield, squared corner portions or buildings 35 at opposite sides of portion 34, and similar corner portions 36 at opposite sides of the bleacher grandstand 33. The building structures 35 and 36 project outwardly from the outer periphery of the stadium S as defined by the outer walls 37 and 38 of the grandstand G and the bleacher section 33, respectively. The proposed renovation involves removal of the old roof above the upper deck of the stadium S and the associated supporting structure and construction of a huge circular perimeter wall W with a diameter of at least 900 feet that is spaced radially from the outer walls 37 and 38 of the stadium a distance of from 30 to 80 feet and that encloses an area of 6 acres or more. Figure 11 shows a scale model of the proposed structure with the compression ring 3 and associated cables, such as cables 5 and 6, and other parts of the dome omitted. The stadium S of the model was carefully prepared and is substantially to scale, the old stadium roof being removed. The wall W of the model has a vertical height greater than that of the stadium S and comprises evenly spaced columns 43. In the model these columns extend between flat annular top and bottom rings 41 and 42. When the proposed structure is constructed the perimeter wall W may have a vertical height from 40 to 80 feet greater than the height of the renovated stadium S. The wall may, for example, be 12 to 18 stories high so that it is eventually possible to provide 1 to 2 million square feet of future usable floor space around the existing stadium even when the average radial width of the space between the peripheral stadium walls 37-38 and the perimeter wall W is only 60 to 70 feet or so. The model illustrated in Figure 11 does not show details of the massive compression ring 3 (which would replace the upper ring 4) and does not show the box-beam ring sections 3 a or the end-to-end arrangement of Figure 9. A structure of the type indicated in Figure 11 would probably employ massive hollow reinforced concrete columns 43 with a height of 90 feet or more capable of supporting hundreds of tons. These could be spaced 40 to 50 feet apart to support hollow concrete box beams 3 a weighing 200 to 300 tons or more and having a length corresponding to the center-to-center distance between the columns 43 so that the ends of the box beams are directly above and supported by the columns 43. The box beam 3 a could be prefabricated at the site and formed of prestressed steel-reinforced concrete. It could have a cross section generally as indicated in Figure 9A with side walls 301 and 302 having a thickness of 20 to 30 inches and top and bottom walls 303 and 304 having less thickness, such as 10 to 18 inches. The opposite ends of the beam 3 a can be notched at 305 to fit the adjacent beams. Each section 3 a could have a length of from 40 to 50 feet and would provide a large room for a variety of activities having a width of 20 to 30 feet and a substantial height (e.g., an average height of at least 8 feet) . The ring 3 and its sections 3 a are preferably located substantially in a plane that is almost horizontal and usually slanted or sloped a few degrees. The resist¬ ance to wind loads can sometimes be improved by providing a slope of 3 to 6 degrees, depending on the location of the domed facility and the likely direction of the wind. The wind resistance can also be improved by temporarily increasing the air pressure in the bladder means 50 to 100 percent from the pressure normally used. If, for example, the bladder means has separate compart- ments, (e.g., See tube 100 of Figure 4AA or Figure 4BB) , a portion of the bladder means could be provided with air at a pressure of 30 to 50 pounds per square feet. The air pressure appropriate for or recommended for an inflatable domed roof made in accordance with my invention depends on the diameter or strength of the radial cables employed, the number of cables used, and the diameter or span of the dome. A relatively large dome could, for example, be constructed so as to withstand a pressure of 40 psf or more. Smaller domes probably could be constructed to withstand much higher pressures, such as 60 psf or more. The normal air pressure maintained in the inflat¬ able bladder means would be less. For example, a very large dome made in accordance with the invention and designed to tolerate and withstand a maximum pressure of 40 psf or more may normally employ an inflation pressure of from 10 to 20 psf, and the fan means f of Figures 2 and 9 may be designed for and used to increase that pressure at least 50 percent in a short period of 20 to 30 minutes during a dangerous windstorm. If greater resistance to wind loads is necessary because of high risks associated with the particular location of the domed stadium, other means may be added to or incorporated in the roof structure. For example, special improved reinforced fabrics and special hold-down means can be used for this purpose. A removable vertical mast 21 of the type shown in Figure 4A can be used to provide a greater factor of safety. Figures 5A and 5B show a modified form wherein each cable 5 is positioned on the fiberglass fabric membrane 9 midway between the straight parallel edges 81 of a fabric strip 80. The strip 80 is preferably formed of the same fiberglass fabric as membrane 9 and is securely adhered and attached to said membrane. A strong connection between the membrane 9 and the strip is provided along the full length of the strip, which can extend 400 feet or more and usually extends almost the full length of the associated hold-down cable 5. This arrangement holds each cable 5 in place relative to the membrane 9, prevents separation in the event the bladder means is deflated, and is particularly useful when the roof structure employs the special spreader means 70 of Figure 4D. The strip 80 assumes a normal curved cross section throughout its length generally as indicated in Figure 5B and forms a groove or trough over the cable 5 to direct water off the dome. Figures 4D and 4E are schematic views showing a unique central spreader means 70 which can be used in the practice of the invention in the embodiments of Figures 4 and 5 and in other embodiments as an important safety feature in the event the dome is deflated as the result of storm damage. Such spreader means is shown in schematic Figure 4, for example, as having parallel upper, interme¬ diate and lower tension rings 7 a , 7 D and 7 C in vertical alignment, the intermediate ring being connected to the fabric membrane 8 a and the ceiling cables 6 a to hold the central part of the ceiling ll a in an elevated position so that the closed annular air space 12 a has a narrow lentic¬ ular cross section. If desired, these tension rings can have a diam¬ eter of 30 to 40 feet and provide a central opening to admit air or sunlight. If the central opening is left open, the space between the membrane 8 a and 9 a would, of course, be closed or sealed, as by a cylindrical wall or sheath extending between the rings 7 a and 7 C . In the embodiment of Figure 4D, such central opening is closed by dome-shaped covers 170. In that embodiment each of the tension rings, 7 a , 7 D and 7 C could be a heavy steel annulus with a series of regularly spaced cylindrical holes 20 a as shown in Figure 104E, preferably 20 to 50 or more holes of a size to fit the tubular vertical struts 20 carried by ring 7 D . The normal fixed positions of the tension rings 7 a and 7 C when the bladder means 2 a is fully inflated are shown in solid lines in schematic Figure 4D, and a raised position of ring 7 C is shown in broken lines in that figure. The circular covers 170 mounted on the rings can be dome- shaped and can, for example, employ a rigid network for framing a large number of window panes or panels. As will be apparent from Figure 4, all of the 70 20 or more hold-down cables 5 and the radially inner portions of the upper fabric membrane 9 a are connected to the upper tension ring 7 a . Likewise, all of the ceiling cables 6 a and the radially inner portions of the lower fabric membrane 8 a are connected to ring 7 C . These glass-fiber membranes are attached to the compression ring 3 and the tension rings 7 a and 7 C (and optionally to the end portions of cable 5 and 6 a ) so that the membranes are held taut when the bladder means is in its normal inflated position. The attaching means used for this purpose can be of 30 various types including the clamping means disclosed in U. S. Patents Nos. 4,345,410 and 4,559,746. The cables 5 and 6 a can have a length of 400 feet or more and preferably have substantially the same length. The length of each ceiling cable 6 a can be such as to permit raising of the tension ring 7 C to a position near or almost in engagement with the ring 7 a or such as to cause a desirable increase in tension when that ring is raised to the uppermost position. In accordance with the invention, at least one of the tension rings 7 a and 1° of the spreader means 70 is mounted for vertical sliding movement on the tubular vertical struts 20 so that the two rings can be allowed or caused to move together when the inflatable bladder means 2 a is deflated. As shown in Figure 4D, the upper tension ring 7 a is fixed at the top of the spreader means 70 and the lower ring 7 C is mounted on the tubes 20 for vertical sliding movement. Suitable motor-operated screw means or hydraulic lifting means may be employed to raise the ring to and above the position shown in broken lines in Figure 4D. The method of the present invention, carried out when the bladder means is deflated or unable to hold air under pressure, is to cause relative vertical movement between the rings 7 a and 7 C so that they come together and to cause the sagging cables 5 and 6 a and the membranes 8 a and 9 a to have the same or generally the same shape, curvature and configuration and to remain taut or assume desirable positions in which the cables 5 and 6 a reinforce each other or serve as suspension cables and in which both membranes are sloped to facilitate rapid removal of water through suitable drain openings, such as those indicated at d' in Figures 1 and 2. This method can prevent danger¬ ous pooling of rain water resulting from stormy weather in the event that the dome fabric is torn or seriously damaged. Recent experience in Atlanta's Georgia Dome indicated that such pooling of water can be catastrophic. The special spreader means 70 of Figure 4D as described above (with movable lower tension ring 1° that can be raised at any time by hydraulic means) makes it possible to carry out the above-described method in a simple manner. This safety feature can be very important especially for domed stadiums in localities where snow and wind storms pose serious problems. It will be understood that the unique combination of the present invention with an inflatable bladder means for supporting the dome includes means for supporting central portions of the bladder so that it has a narrow crescent-like cross section and provides an annular pressurized air space of narrow lenticular cross section between the upper hold-down cables and the ceiling cables. In this combination the means for supporting the bladder and the ceiling cables or associated central spreader means (70) can be overhead suspension cables, such as those employed in the Alamodome (San Antonio) , or a huge structural steel arch above the dome, or suspension cables carried by the outer compression ring 3 below the ceiling as in Figure 4, for example. If the spreader means (e.g., means 70) at the center of the dome is not located above or near an athletic playing field or a sports stadium, it can be supported by a permanent vertical post comparable to the temporary mast 21 of Figure 4A. Likewise, the present invention contemplates building complexes with multiacre domes supported at the center by a tower or tall building and having 90 or more radial tension cables with a length of 400 to 600 feet or more. In domed baseball or football stadiums constructed in accordance with the invention, the playing fields would normally be covered with artificial turf that could be covered temporarily with six-inches of natural grass before a football or soccer game as will be done this year in the Alamodome and was done in the Pontiac Silverdome for World Cup soccer games using more than 1000 interfit¬ ting hexagonal metal pallets to carry the sod. This patented pallet system is being used commercially (Three Dimensional Services) and provides a superior natural grass playing field. It is obviously less costly than growing and maintaining grass in an open-top football-only stadium used for only 10 to 12 football games per year. A natural grass playing field is not needed for baseball and is not necessarily important for football. Improved types of artificial turf, such as PAT, are often preferred for both football and baseball, even in open-air stadiums, such as Joe Robbie Stadium in Miami and Three Rivers Stadium in Pittsburgh. In Los Angeles, the natural grass playing field of Dodger Stadium was recently ripped out and replaced by PAT artificial turf. At present most football players prefer to play on natural grass, but that may not be true in the near future due to improvements in artificial turf technology and improvements in cleated athletic shoes. In any event, a multipurpose domed sports stadium is desirable and appropriate in any part of the country whether or not there is a preference for natural grass turf. Roof structures of the type shown in Figures 1, 2, 4, 4A, 4AA, 4C and 5 usually employ inflatable bladder means formed of high-strength woven-fabric architectural membranes, such as SHEERFILL, made by Chemfab Corp. of New Hampshire, or other coated glass fiber fabric. Teflon- coated fiberglass offers the advantage of translucency and the concurrent advantage of high reflectance. Also inter¬ nal lighting is efficient due to the high reflectivity of the fabric. It will be understood that the specific embodi- ment of the invention shown in the drawings and described herein is presented to illustrate basic principles of the invention and is not intended to limit the scope of the invention. Modifications and various improvements of the specific methods, uses and devices disclosed herein will be apparent and are within the spirit of the invention.

Claims: I CLAIM : 1. A building structure for covering a sports arena, stadium or building complex having a central fabric dome with a clear span of at least 500 feet supported above a circumferential wall means having vertical supports around the perimeter, an outer compression ring carried by said supports, suspension cable means connected to said compression ring to form a suspended ceiling within said ring and below the dome, central connecting means at the top of the dome, a series of closely and evenly spaced radial hold-down cables connected to and extending between said central connecting means and said compression ring, inflatable bladder means coextensive with said dome and said ceiling and providing a closed pressurized air space between said hold-down cables and said ceiling, blower means supplying air to said air space to maintain tension in said hold-down cables, said bladder means having an upper fabric membrane defining the outer surface of the dome, said membrane having outer marginal portions connected to said compression ring to hold the membrane taut, and means for limiting the vertical separation of said ceiling and said central connecting means to limit the volume of air in said air space. 2. A building structure according to claim 1 wherein said means for limiting the vertical separation comprises a rigid upright spreader means connected between said ceiling and said central connecting means. 3. A building structure according to claim 2 wherein suspension cable means are provided to support said spreader means and elevate the central portion of said ceiling. 4. A building structure according to claim 2 wherein suspension cables are connected between said spreader means and said compression ring, and said spreader means supports the central portion of said bladder mean so that it has a narrow crescent-like cross section. 5. A building structure according to claim 1 wherein said radial hold-down cables engage the upper fabric membrane of the dome at regularly-spaced locations while allowing the tensioned membrane to expand and bulge outwardly between adjacent cables. 6. A building structure according to claim 1 wherein said dome has a span of at least 800 feet and covers a sports stadium with a seating capacity of at least 65,000. 7. A building structure according to claim 6 wherein the perimeter wall means supporting said compression ring is spaced radially from said stadium to increase the acreage covered by the dome and to enclose a multipurpose municipal center. 8. A roof structure for covering sports stad¬ iums, building complexes and the like comprising an outer compression ring, a fabric dome with a clear span of at least 800 feet, central connecting means located near the top of the dome, suspension cable means connected to and supported by said compression ring to form a suspended ceiling under the dome, a multiplicity of regularly spaced radial hold-down cables connected between said central connecting means and said compression ring, and inflatable bladder means coextensive with said ceiling and having upper and lower fabric membranes providing a closed pressurized air space between said hold-down cables and the suspension cables of said ceiling, said upper fabric membrane being expanded against the hold-down cables to maintain tension in the cables. 9. A roof structure according to claim 8 wherein said ceiling includes a central connecting ring and said suspension cable means comprises a multiplicity of radial tension cables connected to and extending between said central ring and said outer compression ring. 10. A roof structure according to claim 8 where¬ in said compression ring comprises air conduit means extending around the dome to facilitate air flow into said closed air space, said ring having blower means to maintain pressure in said air space. 11. A roof structure according to claim 8 wherein said upper fabric membrane engages at least 70 of said hold-down cables, each of which has a length of at least 10 400 feet and is spaced no more than about 5 degrees from the next adjacent cable to limit the radial expansion of said membrane between cables. 12. A roof structure for covering large sports arenas, stadiums or building complexes comprising a compression ring, a central tension ring, a shaped dome with a span of at least 500 feet formed of architectural fabric which is connected to said compression ring around the periphery of the dome and held taut in a predetermined position, inflatable bladder means substantially 20 coextensive with said dome and having marginal portions connected to said ring, ceiling cable means supporting said bladder means and containment cable means limiting the expansion of said bladder means and causing it to conform to the shape of said dome, said containment means including a series of closely spaced radial cables connected to said compression ring and said tension ring and located at the convex outer surface of said bladder means, said bladder means providing closed pressurized air space for maintaining tension in said cables. 30 13. A roof structure according to claim 12 wherein said hollow compression ring provides air conduit means extending around the dome providing for rapid air flow into said closed air space, and blower means are provided for maintaining and regulating the air pressure in said space. 14. A roof structure according to claim 12 wherein said compression ring has a diameter or width of at least 800 feet and a central vertical mast provides a fixed rigid support for said tension ring and the central portion of said dome. 15. A roof structure according to claim 12 wherein said inflatable bladder means comprises a series of air bags providing said closed air space with circum- ferentially spaced pressurized air compartments. 16. A roof structure according to claim 15 wherein said air bags are generally triangular and are supported on regularly spaced radial cables that extend inwardly from the compression ring to a central connecting ring. 17. A roof structure according to claim 16 wherein said air bags are spaced apart at least a few degrees circumferentially to provide a series of narrow radially elongated gaps or window openings to facilitate admission of direct sunlight to the central playing field below the dome. 18. A building structure of the character des¬ cribed having a central dome with a span of at least 800 feet and outer peripheral walls with a series of vertical supports, a hollow compression ring carried by said sup¬ ports providing an air conduit extending around the periphery, a series of closely spaced radial hold-down cables extending radially inwardly from said ring to the central portion of said dome to limit the upward expansion, cable means supporting the dome and forming a ceiling below the dome, inflatable bladder means coextensive with said dome and said ceiling and providing closed pressurized air space between the dome and the ceiling that supports the dome with air pressure, and blower means supplying air to said space to maintain an air pressure sufficient to support the dome. 19. A domed building building structure accord¬ ing to claim 18 wherein said ceiling includes a central tension ring and a series of closely spaced supporting cables extending radially inwardly from said compression ring to said central ring. 20. A building structure according to claim 18 wherein said ceiling is supported from below in an elevated position by a series of closely spaced lower suspension cables and spreader means or supports extending upwardly from the suspension cables to the supporting cables of said ceiling. 21. A building structure according to claim 21 wherein the supporting cables of said ceiling are covered by an architectural fabric and are supported by a series of vertical spreaders spaced along the length of each of the suspension cables. 22. A building structure according to claim 1 wherein said dome is located above a sports stadium having an outer wall extending around the periphery, a perimeter wall means is radially spaced from and surrounds said stadium and has a vertical height greater than that of the stadium, a compression ring is provided at the periphery of said bladder means, and a multitude of spaced hold-down cables are connected to said ring. 23. A building structure according to claim 19 wherein said ceiling is supported from below in an elevated position by a series of spaced short lower suspension cables connected to said compression ring and to a large tension ring and by a series of upright struts connected between said tension ring and the cables of said ceiling. 24. A building structure according to claim 19 wherein the cables of said ceiling are supported in an elevated position by a series of upright supporting posts. 25. A building structure according to claim 18 wherein said bladder means has a flexible inner wall defining a central opening encircled by lower and upper tension rings which are located at the bottom and top of said inner wall and are connected to the upper and lower cables, and a removable cover is mounted on the upper tension ring to close said opening. 26. A multipurpose municipal center for entertainment, recreational, educational, political and business activities comprising a sports arena or stadium having an outer peripheral wall, a perimeter wall means surrounding said arena and enclosing an area of more than 6 acres, said wall means having a diameter or width of at least 800 feet and being spaced radially from said peripheral wall a distance of from 50 to 100 feet to provide room for such activities, a compression ring supported by said perimeter wall means, a shaped dome, and inflatable bladder means for supporting said dome having lower suspension cables and upper hold-down cables connected to said ring. 27. A building structure according to claim 26 wherein said dome has a span of from 800 to 1200 feet and said compression ring comprises a large number of hollow reinforced concrete sections arranged end-to-end around the perimeter wall means to define an annular air conduit, each section comprising a prefabricated steel-reinforced concrete box beam with a weight of at least 200 tons and a length of from about 40 to about 50 feet having vertical side walls with a thickness of at least 20 inches and top and bottom walls providing that section with a room with a width of at least 20 feet and an average height of at least about 8 feet. 28. A roof structure for covering sports stad¬ iums or building complexes comprising a dome, an outer compression ring surrounding said dome, central spreader means having an upper connecting ring and a lower connect¬ ing ring, a series of evenly spaced radial suspension cables extending between said compression ring and said lower connecting ring to form a ceiling, a series of evenly spaced hold-down cables extending between said connecting ring and said upper connecting ring, inflatable bladder means between said ceiling and said hold-down cables to shape the dome while maintaining tension in said cables, and means for supporting said spreader means. 29. A roof structure according to claim 28 wherein said last-named means includes suspension cables carried by said compression ring below said spreader means, and said spreader means includes rigid upright strut means extending between the ceiling cables and the hold-down cables. 30. A roof structure according to claim 28 wherein said last-named means holds the ceiling in an elevated position in which the inflated bladder means has a narrow crescent-like cross section. 31. A roof structure according to claim 28 wherein said dome has a span of at least 800 feet, the ceiling cables and hold-down cables provide means for limiting the expansion of the inflated bladder means to provide it with a narrow cross section, and cable means extend downwardly from each radial hold-down cable to the underlying radial ceiling cable to provide means for resisting expansion of said bladder means. 32. A roof structure according to claim 8 wherein said upper fabric membrane is attached to a multiplicity of fabric strips arranged in radial positions to cover said radial hold-down cables, each cable being held between and engaging its associated fabric strip and the fabric membrane. 33. A roof structure of the character described comprising an outer compression ring, a central connecting means providing a hub above said ring, a multiplicity of evenly spaced radial hold-down cables connected between -46- said compression ring and said connecting means, a multiplicity of radial suspension cables connected between said compression ring and said connecting means below said hold-down cables, inflatable bladder means providing a closed pressurized annular air space between said hold-down cables and said suspension cables to maintain tension in said cables and to form a dome, and means for supporting said central connecting means and the radially inner end portions or said suspension cables above the plane of said compression ring so that said annular air space has a narrow lenticular cross section. 34. A roof structure comprising a compression ring for supporting a dome, a central spreader having upper and lower tension rings, a series of regularly spaced radial suspension cables of substantial length connected between said compression ring and the lower tension ring to form a suspended ceiling under the dome, a series of radial hold-down cables of the same length connected between said compression ring and the upper tension ring, and inflatable bladder means coextensive with said ceiling and having upper and lower membranes providing a closed pressurized air space between said hold-down cables and said suspension cables, said membranes being connected to and extending between said compression ring and the tension rings of said central spreader and being held taut when the bladder means is inflated, one of said tension rings being mounted on said spreader to move vertically from its normal position to a position adjacent the other tension ring whereby the normally convex upper membrane can assume the same shape and generally fit the lower membrane when the bladder means is deflated. 35. A roof structure comprising a dome, an inflatable bladder means supporting said dome, and forming a closed pressurized air space, a compression ring with a diameter or width of at least 500 feet surrounding said dome, connecting means below the central portion of said dome having upper and lower tension rings, suspension means for supporting said bladder means and said connecting means below said dome, containment cable means shaping and limiting the expansion of said bladder means to provide the pressurized air space with a narrow crescent-shaped cross section, said cable means including a series of spaced ceiling cables supporting said bladder means above said compression ring and a series of spaced radial hold-down cables engaging the outer portions of the dome, said radial cables being connected to said compres¬ sion ring and said tension rings. 36. A roof structure according to claim 35 wherein said suspension means comprises a multiplicity of radial suspension cables connected between said compres¬ sion ring and said central connecting means.

Inventors: SIMENS ROBERT R, SIMENS, ROBERT, R.
Applicants: SIMENS ROBERT R, SIMENS, ROBERT, R.
Application year: 1996
Main classification: E04H
IPC codes: E04H15