Patent Publication Number: US-6698141-B2

Title: Convertible stadium and method of operating

Description:
This application claims priority under 35 USC §119(e) based on U.S. Provisional Application Ser. No. 60/263,645, filed Jan. 23, 2001, the entire disclosure of which is hereby incorporated by reference as if set forth fully herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of large stadiums, such as athletic stadiums, and in particular to stadiums in which is desired to have a natural grass activity area, such as athletic playing field. 
     2. Description of the Related Technology 
     Historically, when most professional sports stadiums were of the fully outdoor, open bowl design, growing and maintaining a natural grass playing field was not considered difficult, and was in fact the norm. This changed, however, with the advent of the large, indoor domed professional sports stadiums in the 1970s. It being impractical to grow natural grass in a domed stadium because of the lack of sunlight and natural precipitation, all of the large, domed athletic stadiums utilize artificial turf when hosting athletic events, such as baseball or football, that require a grass-like playing surface. 
     In recent years, however, professional athletes, their unions, and the teams and leagues themselves have begun to express a clear preference for natural grass playing fields. This is particularly true for baseball and football players in the United States. Natural grass is felt by many players to be safer, more pleasant, and less physically taxing to play on than artificial turf. 
     In the last few years, retractable roof stadiums have come into play with the intention of providing sufficient sunlight to the field to grow natural turf. While this has worked reasonably well in most cases, it has been difficult to aggressively grow grass. Even though the stadium roof will open, it generally does not adequately provide the two most important elements to grow grass, which are direct sunlight for a maximum period of time each day and a warm, moist environment at field level to promote growth. It is problematic that most stadiums only allow a shaft of light onto the field because the stadium support walls and other devices block the sun early in the morning and late in the afternoon. Secondly, most stadiums are air-conditioned, and since most stadiums are built in a depressed cavity below ground level, the cold air-conditioned air, even when the roof is opened, tends to linger at field level. This cool, dry air tends to inhibit the growth of grass and has caused problems in the industry. 
     Another factor that has been an impediment to be widespread deployment of natural grass to playing surfaces in retractable roof type stadiums is the relative difficulty in reconfiguring the exhibition area in a stadium that utilizes natural grass to an alternative purpose, such as for basketball, rodeo exhibitions, circuses and the like. Unlike artificial turf, natural grass cannot be covered for an indefinite period of time, it is difficult to temporarily move and further can cause problems of condensation in the event that a temporary surface is erected above it. 
     Attempts have been made to design a movable game field that can be moved from one location to another. U.S. Pat. No. 5,746,028 to DiBenedetto discloses a movable grass field that is mounted on a superstructure base that is secured to and spans a system of wheels for movement in and out of a sports stadium. To the best of the knowledge of the present inventors, such a system has never been successfully deployed in a large sports stadium. As the inventors are aware based on their widespread experience in the design and construction of very large structures, a number of practical problems are presented that have deterred the practical implementation of large mobile platforms bearing natural turf. One practical problem is that existing stadiums are designed so as to have exhibition levels that are at a predetermined elevation with respect to the surrounding seating area. It has long been felt that a movable turf platform would necessarily because of the tremendous weight of the turf and underlying soil itself need to be made so as to be prohibitively thick and bulky. In addition, vibrational characteristics are a major concern. In sports such as professional American football, for example, twenty-two large men will periodically be simultaneously exerting themselves on the field. In order for game play to be acceptable to the athletes, the field must have a solid feel to it, as if no independent platform existed. This is problematic and is also antagonistic to the requirement that the platform be as compact and unobtrusive as possible. 
     A need exists in the industry for an improved stadium design and method that will permit more effective growth of natural grass for a stadium, provide an acceptable surface for athletic play and that will further permit efficient reconfiguration of the stadium in the event that an alternative event not requiring natural grass is to be hosted. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide an improved stadium design and method that will permit more effective growth of natural grass for a stadium, provide an acceptable surface for athletic play and that will further permit efficient reconfiguration of the stadium in the event that an alternative event not requiring natural grass is to be hosted. 
     In order to achieve the above and other objects of the invention, a method of operating a stadium according to a first aspect of the invention includes steps of positioning a natural grass activity platform in a first location that is outside of the stadium, the natural grass activity platform having a surface area of natural grass that is at least 10,000 square feet and being constructed and arranged to have a characteristic frequency that is at least 6 Hz; and moving the natural grass activity platform as a complete unit to a second location that is within the stadium, the step of moving the natural grass activity platform being performed without disassembly and reassembly of the natural grass activity platform. 
     According to a second aspect of the invention, the convertible public exhibition facility may include a stadium having an exhibition area and a seating area that is situated about the exhibition area for permitting spectators to view activities taking place in the exhibition area; a movable natural grass activity platform that has a surface area of natural grass that is at least 10,000 square feet and is constructed and arranged to have a characteristic frequency of at least about 6 Hz; and a transport mechanism that is constructed and arranged so as to be able to move the natural grass activity platform as a complete unit from a first location outside of the stadium to a second location that is within the exhibition area. 
     These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a convertible public exhibition facility that is constructed according to a preferred embodiment of the invention; 
     FIG. 2 is a fragmentary partially exploded isometric view depicting a portion of the facility that is shown in FIG. 1; 
     FIG. 3 is a diagrammatical depiction of a portion of the facility; 
     FIG. 4 is a second diagrammatical depiction showing another portion of the facility; 
     FIG. 5 is a schematic diagram depicting a control system that is preferably employed in the facility that is shown in FIGS. 1-4; 
     FIG. 6 is a diagrammatical view depicting another aspect of the invention; and 
     FIG. 7 is a schematic diagram of a motor control enclosure according to the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIG. 1, a convertible public exhibition facility  10  that is constructed according to a preferred embodiment of the invention includes a stadium  12  having an exhibition area  14  and a seating area  16  that is situated about the exhibition area  14  for permitting spectators to view activities taking place in the exhibition area  14 . Public exhibition facility  10  further includes a movable natural grass activity platform  18  that has a surface area of natural grass that is at least 10,000 square feet in area. More preferably, the surface area of natural grass is at least 40,000 square feet in area and even more preferably at least 80,000 square feet. It is anticipated that the surface area of natural grass will be large enough to fit an entire playing field that is desired for a particular stadium  12 , so that there will be no need to piece together the playing field or other exhibition area using more than one activity platform  18 , although this could be done within the scope of the invention if so desired. For example, in a stadium design that has been completed to be used by a professional American football team, the dimensions of the surface area of natural grass are about 400 feet in length and about 240 feet in width, making a surface area of about 96,000 square feet. It is anticipated that this will be typical of the dimensional requirements of professional and major collegiate sports stadiums constructed according to the invention in the future. 
     As may be seen in FIG. 1, the movable natural grass activity platform  18  is constructed and arranged so as to be movable by a transport mechanism  26 , visible in FIG. 2, as a complete unit from a first location  20  that is located outside of the stadium  12  to a second location that is within the exhibition area  14  of the stadium  12 . Preferably, the first location  20  is located in an area that will enjoy growing conditions that are superior to growing conditions within the stadium  12 . When the activity platform  18  is positioned in the first location, the exhibition area  14  may be configured as an alternative activity area for a public event that does not require the natural grass activity platform  18 . For example, exhibition area  14  may be fitted with a hardwood floor for a basketball, or for other convention activities such as auto shows, boat shows, tractor pulls, etc. To achieve the ability to move the natural grass activity platform  18  between the first and second positions  20 ,  22 , on one edge of the stadium  12  a structural spanning truss system must be developed so there is a raceway, or channel for the platform  18  to exit the stadium  12 . Secondly, as will be discussed in greater detail below, a plurality of rails or guides must be embedded in the base concrete slab for the stadium  12  to give adequate structural support for the immense weight of the platform  18  as it travels between the two positions. The activity platform  18  is then constructed to ride upon the embedded rails. Additionally, a door  24  is preferably provided at the location where the raceway or channel exits the stadium  12 , as is shown in FIGS. 1 and 4. Door  24  must be constructed to be wide enough to allow the retractable activity platform  18  to exit the stadium  12  and then be closed up so that air-conditioning can continue without the exchange of air. The door  24  must have the ability to open completely out of the way to clear the field and then close up tight and encompass a locking system, which will resist wind loads and suction loads from internal and external forces. Thus, a system of wind locks must be incorporated into the retractable field door  24 . The retractable field door  24  is preferably interlocked with the retractable field to prevent accidents. 
     According to one important aspect of the invention, the platform  18  is constructed so as to have a characteristic frequency that is at least about 6 Hz and more preferably about 7 Hz or greater. The specific techniques that are used to ensure the platform  18  enjoys a characteristic frequency within the preferred range are discussed in greater detail below. 
     According to another important aspect of the invention, the platform  18  is constructed so as to have a height H P , calculated as being the vertical distance from the plane of the playing field to the portion of the wheel that context the underlying rail, as shown in FIG. 4, that is no more than about 60 inches, and is more preferably no more than about 45 inches. Most preferably, the vertical distance H P  is no greater than about 36 inches. The goals of minimizing the vertical distance H p  and maximizing the characteristic frequency of the platform  18  tend to be mutually antagonistic, so it should be understood that the ability of the platform  18  to achieve both of these goals is quite advantageous. 
     Looking now to FIG. 2, it will be seen that the movable natural grass activity platform  18  includes a containment pan  28  having a peripheral lip portion  30  upon which cushioning material  32  such as a foam rubber material is provided for protecting athletes and other bystanders against injury that might otherwise occur as a result of contact with the containment lip  30 . Containment pan  28  is secured to and supported by a structural framework  34  that in the preferred embodiment includes a plurality of I-beams  36  that are interconnected as shown in FIG. 2 to form a grid. As shown in FIG. 3, the facility  10  preferably includes a concrete floor  38  having an upper surface  40  that is generally flat, although it should be understood that is typical for a slight grade to be incorporated for purposes of drainage. According to another important aspect of the invention, a plurality of substantially parallel rails are secured to the floor  38  and extend substantially between the first and second locations  20 ,  22 . The substantially parallel rails, which are shown in cross-section in FIG. 3, preferably include at least one lateral stability control rail  42  that is embedded within the concrete floor  38  so that its upper surface  58  is substantially flush with the upper surface  40  of the floor  38 . Recesses  44 ,  46  are defined in the concrete floor  38  on each side of the top surface  58  of the lateral stability control rail  42 . As is further shown in FIG. 3, the transport mechanism  26  includes a plurality of lateral stability control wheels  50 , each of which has a first flange  52 , a second flange  54  and a surface  56  that is sized and shaped to be supported by the upper surface  58  of the lateral stability control rail  42 . In operation, the first flange  52  of the wheels  50  is received within the first recess  44  on one side of the rail  42 , while the second flange  54  is received in the second recess  46 . The presence of the first flange  52  prevents lateral displacement of the wheels  50  and thus the platform  18  in a direction that would be to the right as shown in FIG.  3 . Similarly, the presence of the second flange  54  prevents lateral displacement of the wheel  50  and thus the platform  18  in a leftward direction as it would be viewed in FIG.  3 . As may further be seen in FIG. 3, elastomeric material  48  is provided within each of the recesses  44 ,  46 . The purpose of the elastomeric material  48  is to maintain a flat surface throughout the facility that is flush with the upper surface  40  of the fourth  38 , so as to minimize inconvenience or potential safety risks to machines and pedestrians within the facility. 
     As may be seen in FIGS. 2 and 3, electric motor M 1  is provided to drive the lateral stability control wheel  50 , as will be discussed in greater detail below. Also embedded in the concrete floor  38  are a plurality of additional rails  60  that are spaced so as to be substantially parallel to the lateral stability control rail  42 . Each of the rails  60  has an upper surface  62  that is preferably positioned so as to be flush with the upper surface  40  of the concrete floor  38 . The transport mechanism  26  further includes a plurality of wheels  64  each having a peripheral engagement surface  66  that is shaped to traverse the upper surface  62  of the respective guide rail  60 , as may be seen in FIG.  3 . In addition, as may also be seen in FIG. 3, the peripheral engagement surface  66  is preferably constructed so as to be substantially wider than the upper surface  62  of the respective guide rail  60 , so as to ensure that the respective surfaces remain in contact even in the event of significant thermal expansion or contraction. The wheels  50 ,  64  are preferably laterally spaced with respect to reach other so as to ensure the best possible alignment with the corresponding rails  42 ,  60 . In practice, however, dimensional variations resulting from thermal expansion and contraction as well as other factors including the tendency of all large structures to experience some settling over time will tend to change the lateral distance between the rails  42 ,  60 . One significant advantage of this aspect of the invention is that because the lateral stability is governed exclusively at one rail  42  and with one corresponding wheel  50 , dimensional variations that change the distance between the lateral stability control rail  42  and the other rails  60  or dimensional variations that occur between the wheel  50  and the other wheels  64  will be tolerated to some extent and simply resulting in minor shifting of the position of one or more of the wheels  64  upon the respective rail bearing surface  62 . 
     Referring now to FIG. 2, it will be seen that the transport mechanism  26  includes a plurality of electric motors M 1 , M 2 , . . . M n , each of which is coupled to the corresponding lateral control stability wheel  50  by an appropriate transmission assembly including a reduction gear  68 . Each of the wheels  50  are supported for rotation with respect to one of the longitudinally extending I-beams  36  by means of a first bearing  70  and with respect to a similar longitudinally extending sister I-beam  72  by a second bearing  74 . The longitudinally extending sister I-beam  72  is mounted so as to be parallel to and spaced from the first longitudinally extending I-beam  36  by a distance that is just sufficient to permit placement of the wheel  50 . As may further be seen in FIG. 2, cellular decking  80  is applied to the top of the framework  34 . The cellular decking  80  is constructed as a number of steel channel elements that have concrete hardened within the recesses and channels thereof so as to create a composite concrete/steel construction, the benefits of which are described below. 
     Several aspects of the invention are together responsible for maximizing the characteristic frequency of the platform  18  while minimizing its bulk. First, the structural steel system is composite to the concrete deck above, better described as a monolithic assemblage of structural steel elements, anchor collars and poured reinforced concrete, all acting together and referred to as composite concrete deck. This feature tends to achieve a more rigid structural assembly producing a higher frequency. 
     Secondly, the structural steel beams are designed and implemented as multi-span structural members rather than simple span. Embodying this feature produces a more desirable structural system with less steel and more rigidity, producing a higher frequency when it is excited by players on the top of the field. 
     Third, the span between rails is minimized, which reduces the amount of steel required and increases the rigidity of the field in general, producing a higher frequency of resonation. In situating the rails closer together, on the surface we have cluttered up the secondary playing field beneath the main playing field. However, by implementing an embedded track flush with the concrete surface above we have saved the floor and made it even more serviceable for various events than any other patent holder, thereby achieving the best of both worlds. 
     A thin layer  78  of waterproof concrete is provided on top of the cellular decking  80 , and a stratified biolayer  81  is positioned on top of the layer  78  of waterproof concrete. In the preferred embodiment, the stratified biolayer  81  includes a first layer of coarse sand or crushed rock that is approximately two inches in depth, and then a layer of permeable Geo fabric for entering purposes. Approximately eight inches of grated soil is positioned on top of the Geo fabric, with a layer of sod that is about two inches in thickness being applied to the top of the grated soil. It should be understood that the biolayer could alternatively be constructed in an almost infinite number of different methods of placement and construction, which would all be within the scope of the invention. 
     Referring now to FIG. 4, it will be seen that another advantageous feature of the invention is the provisions of a pit  82  that is defined as a recess within the concrete floor  38  of the facility  10 . Pit  82  is preferably large enough for maintenance personnel and their equipment, and is preferably provided with a supply  84  of electricity and a supply  86  of hydraulic or pneumatic pressure. In addition, pit  82  is provided with a drain  88  for draining any water or other fluids that may end up in the pit  82 . A grate  90  is preferably positioned over the pit  82  so as to have a top surface that is flush with the surface  40  of the floor  38 . 
     As is further shown in FIG. 4, platform  18  is further preferably provided with an internal irrigation system that is connected to a source of water via a plurality of pipes and valves V 1 , V 2 , . . . Vn that are interposed within the pipes. In addition, a drainage system is provided in the platform  18  that is also controlled at least one valve V 3 . The valves are preferably solenoid operated and are controlled automatically by a controller  92  that is schematically depicted in FIG.  5 . As FIG. 5 shows, a plurality of position sensors PS 1 , PS 2 , . . . PS n  are provided to sense the longitudinal position of one specific portion of the platform  18  with respect to the it underlying facility. Controller  92 , based upon input received from the different position sensors will control of the plurality of different motors M 1 , M 2 , M 3 , . . . M n  so as to ensure that the platform  18  and its different sides remain in alignment as it may travel between the first and second locations  20 ,  22 . For example, if the position sensors indicate that one side of the platform  18  is longitudinally trailing the other side by even a small amount during movement, power may be reduced to motors that are located near the leading side for power may be increased to motors that are located near the trailing side in order to correct alignment. A plurality of moisture sensors MS 1 , . . . MS n , may further be provided within the biolayer  81  of the platform  18 , and the sensors will provide input to the controller  92 . In response to this input, controller  92  may selectively actuate one or more valves V 1 , V 2  in order to raise the moisture level in a particular zone or location of the biolayer  81 . Similarly, controller  92  may actuate one or more of the drainage valves in order to cause excess moisture to drain from the platform  18  in an area that has received excess precipitation. 
     The acceleration and deceleration of the electric motors is an important aspect of the invention. The conventional method of operating equipment is referred to as “across the line starting”, whereby a magnetic contactor energizes the electric motors and the motors begin outputting fall torque within 1 or 2 seconds. Traditionally, when the mechanism begins to move a conventional 3-phase motor will output 3 times its nameplate horsepower and torque. On startup, when natural initial forces resist the acceleration of the mechanism, the traction wheel assembly will frequently slip slightly on the track as it tries to accelerate the mechanism. This slipping action will cause excessive wear, significant building vibration and general abuse of the collateral machinery. The same is true on a conventional mechanism when stopping. When the power is removed a fail-safe spring set brake is normally energized, which brings the mechanism to a rapid stop causing the traction wheel to slip and significant vibrations, wear &amp; tear, and other objectionable phenomena to occur. 
     As shown in FIG. 7, the preferred embodiment of the invention utilizes a Variable Frequency Drive (VFD), which captures conventional AC current and converts it to DC current, then reconstructs the sine wave of the current back to a regulated AC sign form. This feature is very useful in the acceleration/deceleration phase. For example, on start-up the VFD will output current at approximately 5 to 10 Hertz rather than the conventional line current of 60 Hertz. Most all 3-phase AC motors are 4-pole motors. Preferably, conventional 3-phase 4-poles motors are used because they are extremely economical to purchase. A conventional 4-pole motor when powered with 60 Hertz current always turns at exactly 1750 RPM. The relationship of the 4-poles and the alternating current at 60 Hertz is fundamental, and the machine will always seek to run at 1750 RPM. With the application of the VFD the frequency can be reduced to as low as 5 Hertz, causing the motor to start at “creep” speed outputting a constant torque. At these low speeds it is required to inject a higher voltage to prevent rapid heat build-up, which is also a function of the micro-processor within the VFD. This micro-processor can be adjusted to output frequency on a sliding scale. Example: Over a period of 20 seconds the frequency will increase by 10 Hertz every 2 seconds. Thus, if the frequency begins at 10 Hertz, at the end of 10 seconds it will be at 100 Hertz causing the motor to run slightly faster than its normal RPM of 1750. This gives a gradual start, a gradual application of torque protecting the machinery, the building and all other mechanical equipment. The micro-processor is programmed based on a predetermined calculation regarding the maximum torque and inertia that collateral equipment can withstand. It is a function of the stiffness of the building structure, the weight of the retractable roof, and the stiffness of the collateral machinery. One important point is that the VFD is adjustable, and that by calculation is possible to arrive at the most favorable acceleration and/or deceleration curve. 
     The application of VFD&#39;s allows the equipment to be started at a very slow speed, and, in addition, to accelerate the equipment up to twice the normal speed of a standard 3-phase motor, thereby completing the cycle time at a much faster speed than a conventional arrangement. The VFD with the application of the Programmable Logic Controller (PLC) can also monitor the wind in and around the stadium. If it is found that the wind is of an excessive speed we can prevent the VFD from accelerating past a slower speed, thus protecting all of the machinery. This application of both the VFD and the PLC allows our mechanism to complete the opening cycle most of the time in half the speed of a conventional machine, while still maintaining the capability to slow down to ¼ the speed during high wind conditions to maintain safety. This arrangement is a significant improvement over conventional drives. 
     Another feature provided by the PLC, coupled to the VFD, is the ability for the operator to continuously monitor the motor voltage, the motor frequency, and the motor output torque. These figures are displayed on the operator&#39;s information screen and recorded continuously for historic reference and troubleshooting. These diagnostic features allow the operator confidence that the mechanism is functioning as intended and offer an early warning as soon as an inconsistency develops in the mechanism long before a serious failure would occur. The historical data logging is programmed to download through the internet on a high-speed communications link to a remote facility, thus enabling engineers to monitor all systems in the field to be sure they are working properly. This offers a much higher level of safety than was achievable in the past. The combination of these devices allows an unsophisticated owner with no engineering staff to operate highly technical equipment that heretofore could not be operated without a staff of engineers on-site, thereby significantly reducing the cost of ownership. 
     Referring now to FIG. 6, an alternative method of constructing a biolayer  100  and support therefore would be to embody the same concrete deck with a layer  102  of course gravel, after which the application of a geo-technic technical membrane would be applied. Then, a system of course sand  104  would be installed above the membrane. The course sand would be installed in a wave pattern perpendicular to the long dimension of the field. The wave pattern more aptly described would be a series of peaks and valleys raked into the course sand whereby at its highest point the sand would be just 2″ below the turf  106 , and at its lowest point the course sand would be 8″ below the turf field. The frequency or distance between the peaks would be approximately 3′-6′ depending on the climatic conditions. The valleys between the peaks would then be filled with soil rich in nutrients and suitable to grow turf. 
     The advantage of this scheme would be evident in climates where torrential rains may occur from time to time. A torrential rain on the field may cause flooding sufficient to damage the turf  106  because the water could not drain through the subsoil fast enough. Thus, by having course sand very close to the surface we can prevent the accumulation of water puddles and degradation of the sod that would result. A field construction as described above would be useable, or playable, in a very short time after a torrential rainfall because it would improve its ability to quickly drain. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.