Abstract:
The invention relates to a floating body, especially a floating body used as a support for an underwater tunnel ( 11 ). In order to obtain a high degree of freedom and a large amount of stability while at the same time guaranteeing easy assembly, a frame structure ( 49 ) is provided in the form of a horizontal grating, wherein floats, ballast bodies, dam chambers or similar useful hollow bodies ( 50 ) are fixed in the rectangular, especially quadratic free areas of said grating as tanks.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a floating body, in particular as a carrier of an underwater tunnel. 
     Floating bodies which have a cabin, underwater tunnel, etc. which lies below the water line and is made from transparent material, are known in the leisure sector. By way of example, the aqueous fauna can preferably be observed from there. In terms of their structure, floating bodies of this type are configured in the shape of a boat, and the corresponding floating body can be moved by means of muscle power or by being driven by engines. 
     SUMMARY OF THE INVENTION 
     The subject matter of the invention is based on the object of configuring a floating body of the type in question in such a manner that it is stable in use, so that it is able to accommodate a greater number of people yet nevertheless allows optimum observation of, for example, the aqueous fauna. 
     This object is achieved first of all and substantially in a floating body having the introductory-mentioned features, in which it is provided for there to be flexurally rigid supporting framework in the form of a horizontal grid, in the rectangular, in particular square grid open spaces or which hollow bodies, which can be used as tanks, buoyancy bodies, ballast bodies, storage chambers or the like, are secured. 
     On account of configuration of this nature, a floating body of the generic type, as well as having a particularly good load-bearing structure, provides a high quality of leisure and is able to accommodate a greater number of people. A significant component of the floating body is the flexurally rigid supporting framework. It is configured in the form of a horizontal grid. The grid openings or open grid spaces are used to accommodate the corresponding hollow bodies. Various possible ways of using the hollow bodies are available in this case. For example, they can be used as tanks, buoyancy bodies, ballast bodies, storage chambers or the like. The floating body itself is distinguished by two companionways, which lead below the water line, are spaced apart from one another and are connected to one another by a tunnel which lies below the water line and has an at least partially transparent wall. This makes the floating body suitable, for example, for a prescribed traffic passing through it. It is preferable for the tunnel lying below the water line to be reached through one companionway. After a certain residence time within the tunnel, it can be left via the other companionway, so that to a certain extent a circuit is walked through. The tunnel, which is equipped with an at least partially transparent wall, allows favorable observation of the underwater world which lies below the water line. In this case, the floating body is additionally stabilized by the tunnel connecting the two companionways, so that this also leads to an increased level of safety. Furthermore, the use of the two companionways which are spaced apart from one another by the tunnel brings benefits in terms of ventilation technology, which makes the time inside the tunnel very pleasant. Specifically, to a certain degree forced ventilation is produced. In particular, the inventive concept makes it possible to configure the floating body in frame form, specifically so that it surrounds an area of open water. In this case, the companionways are associated with two frame sections which lie opposite one another. The companionways, together with the tunnel connecting them, which crosses below the area of open water, stabilize this frame shape. The surface of the frame sections can be used as an accommodation area as a result of it accommodating, for example, lounger chairs, tables, etc. Moreover, it is possible to pass from one companionway to the other without using the tunnel. The frame shape then leads to a stabilization of the floating behavior of the floating body, so that the latter remains relatively stationary even in the event of high seas. The visitor who is inside the tunnel is provided with an optimum observation quality by the tunnel having a transparent floor. The observation quality is optimized through the fact that the tunnel wall as a whole is see-through. This creates a view on all sides, which is not to be found in, for example, submarines in use in the leisure sector. Construction advantages result from the fact that the tunnel comprises an arched piece and a straight floor piece, each made from see-through plastics. This material allows a tunnel length of approx. 10 m. The tunnel wall thickness, on the other hand, can be approx. 10 cm. Despite this relatively great length, the result is a high-strength structure which is able to withstand high forces. To ensure a high-strength connection between the tunnel and the companionways, the tunnel is bolted to the companionways by means of flanges, which flanges absorb the buoyancy forces. This is very important, since the relatively large-volume tunnel acts as a buoyancy body. In detail, what this means is that the flanges form steel-securing elements which have been cast into the plastics. As a result, bolted connection makes it possible to produce a highly stable connection between the companionways and the tunnel. To obtain an observation effect not only in the area of the tunnel but also in the area of the companionways, at least the area of the companionway which lies below the water line consists of see-through plastics. Therefore, there is uniformity of materials between tunnel and companionway, which leads to structural benefits. Furthermore, advantages in terms of the stability are achieved by the fact that the end side of the tunnel rests in a recess of matching shape in the companionway wall. To ensure that the platform of the floating body takes up little space compared to the tunnel, the companionways are equipped with spiral staircases, in particular made from see-through plastics. This once again has the effect that the spiral staircases, which consist in particular of see-through plastics, represent only an insignificant viewing obstacle. Furthermore, emphasis should be given to the fact that a space of increased cross section is provided disposed approximately in the center of the tunnel. Accordingly, more people can spend time there. This space of larger cross section also makes it possible, for example, to accommodate tables as well as chairs. To counteract the buoyancy forces acting on the tunnel, a ballast body is provided disposed in the center of the tunnel. This may, for example, be an island disposed on the tunnel. By way of example, the island may accommodate plants, so that the floating body acquires a favorable appearance. To ensure that, for example, no rain enters the companionways and therefore the tunnel, the companionways have cabins built above them. Furthermore, the cabins can be used to hold sanitary fittings. The floating body is then made virtually unsinkable by buoyancy bodies which extend virtually along the entire frame periphery. The fact that the ballast tanks are hollow bodies on the inner side of the frame contributes to the stable floating and load-bearing properties. The ballast tanks can be filled, for example, by means of sea water and/or drinking water. Furthermore, it is provided that the ballast tanks are individual hollow plastics bodies. Furthermore, the floating body may include buoyancy chambers which are flap-closed at the top side. They can be used, for example, as spaces for holding utensils belonging to the floating body, specifically when the latter is not in use. Structural and transportational benefits result from the floating body having a dismantleable framework comprising carriers. The horizontally running carriers carry the ballast tanks. To stabilize the dismantleable framework, the horizontal carriers are supported by vertical carriers, which are formed as gusset plates and which are secured to the companionways. The gusset plates are preferably of perforated configuration, so that reflections are minimized. However, the gusset plates may also be produced in frame form, for the abovementioned reason. Float engineering benefits for the floating body result from the fact that the ballast tanks are disposed parallel to the direction in which the tunnel extends, adjacent to the companionways. Furthermore, it should be noted that the vertical carriers consist of see-through plastics. To increase the surface area of the floating body, there is provision for there to be platforms fitted to the outer sides of the frame sections. The abovementioned buoyancy bodies which lie on the outer side of the frame may preferably consist of foamed plastics. In terms of weight, they can be kept very light yet can nevertheless have a high ability to float. With regard to transportation of the frame-like floating body, it has proven advantageous if the entire floating body, in the dismantled state, finds space to be accommodated in a plurality of 40-foot containers. In order then, when constructing the floating body, to be able to stably connect the cabin to the companionway, the upper edge of the companionway is adhesively bonded in a positively locking manner into a groove in the cabin wall. A floating body which comprises a multiplicity of individual elements which are connected to one another at vertical faces and are in the form of hollow cuboidal bodies is used to form the floating body. These hollow bodies are stabilized by tubes which are disposed therein, run in a straight line and open out in different vertical faces as spacer-stabilization elements to which pressure can be applied, a clamping element being guided through at least two mutually aligned tubes of two individual elements. Therefore, the entire floating body can be assembled in modular form from the hollow bodies, which for their part are stabilized by the tubes. For inexpensive production, it is recommended for the individual elements to be made from plastics and for them to be made using the rotational process. In this process, both the outer walls and the tubes are produced. It is even possible for the tubes to run on an incline, i.e. diagonally with respect to the longitudinal direction of the individual elements. In this way, it is possible to create a grid-like composite system in combination with a particularly high stability on the part of the floating body. It is even possible to provide a plurality of tubes which cross one another, specifically taking account of different planes. In this case, it is possible for individual elements which are of the same shape to acquire different functions. For example, if they are foamed they serve as hollow floating bodies. Furthermore, the individual elements may be fillable ballast tanks or storage spaces provided with a flap. The range of possible uses of the floating body can be widened by a net which is laid around the floating body, extends as far as the seabed or is closed at the bottom side. On this basis, it is possible to use the floating body as a dolphinarium. The visitors can take up position above or below the water line in the corresponding rooms. It is also advantageous for the edge-side individual elements to form a breakwater bead and, below it, a wave-rolling niche. This prevents the people on the platform of the floating body from being at risk of being sprayed in the event of normal wave motion. The fact that the grid webs, which border the open grid spaces, have upper and lower struts which are spaced apart from and parallel to one another, the spacing position of which is defined by vertical struts associated with the grid crossing points and which are reinforced by means of diagonal struts, leads to a highly loaded configuration. The supporting framework produced in this way has proven particularly stable under load, and in particular the forces which are active from different directions can be absorbed without damage. The measure whereby the grid webs which adjoin the companionways and the grid webs which delimit the area of open water consist of steel, in particular stainless steel, and the peripheral grid webs consist of fiberglass, has proven to be both stabilizing and weight-saving. The square open grid spacers can be dimensioned in such a way that they are each able to accommodate two hollow bodies. Production engineering and also stabilizing benefits result from the fact that the tunnel and the companionways are each see-through planked steel frame structures. Since considerable buoyancy forces emanate from the tunnel and the companionways and these forces have to be absorbed, the measure is taken whereby the companionways each use two laterally protruding bearing journals to divert the buoyancy forces into yokes of the supporting framework which are associated with the bearing journals. To increase the useable surface area of the supporting framework, the area of open water can be covered by boards. This additional area which is covered with boards can then be used, for example, as a dancefloor, etc. The boards are held in their position covering the area of open water by means of carriers which are stored below the edges of the frame and can be displaced over the area of open water. These carriers can roll over edge-side rails by means of rolls disposed at their ends, in order to move out of their concealed position into their supporting functional position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Three exemplary embodiments of the invention are explained below with reference to the drawings, in which: 
     FIG. 1 shows a view of the floating body in accordance with the first embodiment, 
     FIG. 2 shows a side view, rotated through 90°, of FIG. 1, 
     FIG. 3 shows a plan view of the floating body, 
     FIG. 4 shows the section on line IV—IV in FIG. 3, on a larger scale, 
     FIG. 5 shows the detail indicated by line V—V in FIG. 4, 
     FIG. 6 shows the section on line VI—VI in FIG. 4, 
     FIG. 7 shows the section on line VII—VII in FIG. 1, 
     FIG. 8 shows a similar view to FIG. 4 but of a modification of the floating body, 
     FIG. 9 shows the section on line IX—IX in FIG. 8, 
     FIG. 10 shows a plan view of the floating body in accordance with the second embodiment, 
     FIG. 11 shows a view of a plurality of the cuboidal hollow bodies which are used in the embodiment shown in FIG.  10  and are connected to one another by means of clamping elements, 
     FIG. 12 shows a view on a larger scale in the connecting region of two clamping elements, 
     FIG. 13 shows a perspective illustration of a hollow body which represents an individual element, 
     FIG. 14 shows a cross section through a buoyancy body which is located on the outer side of the frame and forms a breakwater bead and a wave-rolling niche below it, 
     FIG. 15 shows a view of the floating body according to the third embodiment, 
     FIG. 16 shows a side view, rotated through 90°, of FIG. 15, 
     FIG. 17 shows a plan view of the flexurally rigid supporting framework with associated tunnel, 
     FIG. 18 shows a perspective view of part of the supporting framework, 
     FIG. 19 shows a partial plan view of the supporting framework with associated hollow bodies, 
     FIG. 20 shows a longitudinal section through half a tunnel, 
     FIG. 21 shows the section on line XXI—XXI in FIG. 20, 
     FIG. 22 shows the section on line XXII—XXII in FIG. 20, 
     FIG. 23 shows a plan view of the boards which cover the area of open water and are supported by carriers which can be displaced over the area of open water, 
     FIG. 24 shows the section on line XXIV—XXIV in FIG. 23, 
     FIG. 25 shows a detail indicated by XXV—XXV in FIG. 24, on an enlarged scale, 
     FIG. 26 shows a side view of a hollow body, and 
     FIG. 27 shows a plan view of the hollow body. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The floating body which is illustrated in accordance with the first embodiment in FIGS. 1 to  7  and is denoted overall by the numeral  1  is produced in frame form and has the mutually opposite frame sections  2 ,  3  and  4 ,  5 . In the exemplary embodiment, it is provided that the frame sections  4 ,  5  are longer than the frame sections  2 ,  3 . 
     In the center, in each case one companionway  6 ,  7 , which leads below the water line W and is approximately square in contour, originates from the shorter frame sections  2 ,  3 . This companionway  6 ,  7  is closed off by a floor  8 , so that it is impossible for any water to penetrate into the companionway  6 ,  7 . 
     The mutually facing side walls  9 ,  10  of the companionways  6 ,  7  are connected to one another by a tunnel  11  which lies below the water line W, leaving clear a passage opening D. The tunnel floor  12  is flush with the floors  8  of the companionways  6 ,  7 . The tunnel  11  is formed from an arched piece  13  and the straight floor piece which forms the tunnel floor  12 . See-through plastics, for example acrylic sheet with a wall thickness of approx. 10 cm, is used as material for the arched piece  13  and the floor piece  12 . The arched piece  13  can be produced, for example, by shaping in a heated mold, two halves which form the arched piece then being joined to one another. The two free ends  13 ′ of the arched piece  13  penetrate in a positively fitting manner into longitudinal cutouts  14  in the tunnel floor  12 , where they are welded or adhesively bonded in a suitable way, cf. FIG.  6 . This figure also shows that the arched piece  13  is configured to be virtually in the shape of a circular ring. 
     According to the first embodiment, the tunnel  11  is approximately 10 m long. The tunnel  11  is connected to the companionways  6 ,  7  by means of flanges  15  which are incorporated at the tunnel ends. Each flange  15  represents a steel securing element which has been cast into the plastics. Each end side of the tunnel  11  rests in a recess  16  of matching shape in the corresponding companionway wall  9 ,  10 . The buoyancy forces acting on the tunnel  11  are reliably absorbed by this positive lock, cf. in particular FIGS. 4 and 5. A seal  17  which lies within the recess  16  is associated with each end side of the arched piece  13 . Securing bolts  18  which penetrate through the side walls  9 ,  10 , engage in aligned threaded bores  19  in the flange  15  and thereby connect the tunnel  11  to the companionways  6 ,  7  to form a rigid, highly stable assembly, are used to connect the side wall  9 ,  10  to the arched piece  13 . 
     At least the area of the companionway  6 ,  7  which lies below the water line W consists of see-through plastics. Once again, acrylic sheet can be used for this purpose. 
     Each companionway  6 ,  7  is equipped with a spiral staircase  21  which leads from the platform  20  of the floating body. See-through plastics are likewise suitable as material for the spiral staircase. 
     In the exemplary embodiment, it is illustrated that the tunnel  11  has the same cross section over its entire length. By way of example, however, it is also possible to create a space of larger cross section in the center of the tunnel, in order to create options for chairs, small tables, etc. to be accommodated there. To counteract the buoyancy forces which are acting on the tunnel  11 , a ballast body  22  is provided in the center of the tunnel. In the exemplary embodiment, this ballast body forms an island disposed on the tunnel  11 . It is possible for the island to be planted up and/or for it to have a mast  23  associated with it, the mast tip of which may, for example, bear a warning light. It is preferable for it to be possible to vary the mass of the ballast body  22 . 
     Each companionway  6 ,  7  has in each case one cabin  24 ,  25 , which projects above the platform  20 , built above it. The contour of this cabin corresponds to that of the companionway  6 ,  7 . In the exemplary embodiment, the cabins  24 ,  25  include sanitary fittings  26 , in such a manner that, for example, the sanitary fittings  26  of the cabin  24  are intended for men and the sanitary fittings of the cabin  25  are intended for women. The cabins  24 ,  25  themselves are entered through entry openings  27 . The cabins  24 ,  25  themselves may in turn also have viewing platforms  28 ,  29  built above them. Stairs  30  leading from the platform  20  of the floating body  1  lead to these viewing platforms. 
     Along its entire frame periphery, the frame includes buoyancy bodies  31 , which for their part may be foamed hollow bodies. In this case, the frame-shaped floating body includes ballast tanks  32  on the inner side of the frame, in the form of hollow plastics bodies which lie parallel next to one another. They are disposed parallel to the direction in which the tunnel extends, in each case adjacent to the companionways  6 ,  7 . Some of these ballast tanks  32  may be filled with drinking water, others with sea water, while the remaining ballast tanks can be used to hold waste water. In the exemplary embodiment, there are four ballast tanks  32  on both sides of each companionway  6 ,  7 . Furthermore, the floating body  1  includes flap-closed buoyancy chambers  33  on the inner side of the frame. These can be used, for example, to hold lounger chairs, tables, parasols, etc. Electrical power supply components can also be accommodated therein. 
     The floating body  1  has a dismantleable framework  34 , the horizontally running carriers  35  of which carry the ballast tanks  32 . The horizontal carriers  35  which lie at the bottom are in this case supported by vertical carriers  36  which are formed as gusset plates and for their part are secured to the companionways  6 ,  7 . In each case two horizontal carriers  36 ′ which are triangular in contour are associated with each side of the companionway  6 ,  7 . The gusset plates or vertical carriers  36  are provided with apertures  36 ′ in order to keep reflections at a low level. However, as an alternative to triangular gusset plates, it would also be possible to use corresponding supporting struts. See-through plastics are used for the gusset plates or vertical carriers  36 . To increase the size of the area of the floating body  1  which can be walked upon, platforms which are fitted to the outer sides of the frame sections  2  to  5  may be provided. 
     The dismantleable framework  34  and the carriers  35 ,  36  and buoyancy bodies are created in such a way that, in the dismantled state, they can be fitted in a plurality of 40-foot containers. 
     The floating body is assembled at the site of use. In this context, it is advantageous in terms of assembly technology for the upper edge of the companionway  6 ,  7  to be adhesively bonded into a groove  37  on the lower edge of the cabin, cf. FIG.  4 . 
     To take account of the required safety regulations, a railing  38  is associated with the platform  20  on both the outer side of the frame and the inner side of the frame. 
     It can be seen in particular from the plan view in FIG. 3 that the area of water which lies inside the frame can be used, for example, as a swimming pool. It is also possible to use the floating body in a dolphinarium. This purpose is served by a net  39  which is laid around the floating body  1  and extends as far as the seabed or is closed at the bottom side. If it extends as far as the seabed, by way of example the lower edge of the net can be made heavier by suitable weights in order to stabilize the position of the net  39 . 
     The modification to the first embodiment shown in FIGS. 8 and 9 shows that there is a differently configured basic contour of the companionway  6 ,  7 . The side wall  40  which lies opposite the tunnel  11  now runs in the form of a semicircular curve, which brings advantages when observing the underwater world. To be able to ensure sealed connection of the lower edge of the cabin  24 ,  25  to the companionway  6 ,  7 , the lower edge of the cabin is equipped with adapter fittings  41  which enable the lower edge of the cabin to be matched to the upper edge of the companionway  6 ,  7 . 
     The second embodiment of the floating body  1 ′ shown in FIGS. 10 to  14  largely corresponds to the first embodiment. Identical components are provided with identical reference symbols. The floating body  1  includes a multiplicity of individual elements which are connected to one another and for their part are configured in the form of cuboidal hollow bodies. The individual elements which lie on the outer side of the frame are foamed buoyancy bodies  42 . Storage spaces  43  which are closed off by a flap extend toward the inner side of the frame. Then, the fillable ballast tanks  44  are provided on both sides of each companionway  6 ,  7 . 
     The individual elements, which have largely an identical structure, namely the buoyancy bodies  42 , the storage spaces  43  and ballast tanks  44 , consist of plastics and are made using the rotational process. In this process, tubes  45 , which are disposed in the corresponding hollow bodies  42 ,  43 ,  44 , run in a straight line and open out into different vertical surfaces, are formed integrally as distance-stabilizing elements to which pressure can be applied. These elements are used to accommodate clamping elements  46 , a clamping element  46  being guided through at least two tubes  45 , which are flush with one another, of two individual elements. As illustrated in FIGS. 11 and 12, the clamping can be effected by means of bolted connection. 
     It can be seen in particular from FIG. 13 that the tubes  45  which cross one another are disposed in such a way that the crossing points lie in different planes. FIG. 11 uses dot-dashed lines to illustrate that it is also possible for the tubes  45 ′ to be allowed to run obliquely. As a result, it is possible overall to produce a highly stable clamping structure in grid form, associated with the advantage of a stable floating body. 
     FIG. 14 illustrates that the edge-side individual elements, i.e. the buoyancy bodies  42 , include an integrally formed breakwater bead  47 . Below this there is additionally a wave-rolling niche  48 . The result of this is that a wave is diverted downward and the formation of spray is greatly reduced as a result. A further function is fulfilled by the breakwater bead  47  through the fact that it serves as an encircling washboard, providing advantages during the mooring of vessels which are used to bring aboard and take away people visiting the floating body, for example. The size of the floating body described above is dimensioned in such a way that there is space for at most 250 people thereon. 
     The floating body  1 ″ in accordance with the third embodiment, illustrated in FIGS. 15 to  27 , is likewise a carrier for an underwater tunnel  11 , and specifically a flexurally rigid supporting framework  49  in the form of a horizontal grid is used for this purpose. Hollow bodies  50  which can be used as tanks, buoyancy bodies, ballast bodies, storage chambers or the like are secured in the rectangular open grid spaces  51 ,  52 ,  53  of this grid. 
     The grid webs which border the open grid spaces  51 ,  52 ,  53  have upper and lower struts  54 ,  55  which are spaced apart from and parallel to one another, the spacing position of which is defined by vertical struts  57  associated with the grid crossing points  56 . In addition, diagonal struts  58  are used to reinforce the spacing position of the upper and lower struts  54 ,  55  with respect to one another. 
     Centrally, the grid framework  49  includes an area of open water F which is of substantially rectangular configuration. Adjacent to the two mutually opposite longitudinal edges of the area of open water F are open grid spaces  59 ,  60 , from which the companionways  6 ,  7 , which for their part are connected to one another in a watertight manner by the tunnel  11 , originate. The grid webs which adjoin the companionways  6 ,  7  and the grid webs which delimit the area of open water F consist of steel, in particular stainless steel, and are indicated by hatching in FIG.  17 . The adjacent peripheral grid webs, by contrast, consist of fiberglass and are not indicated by hatching in FIG.  17 . 
     The open grid spaces  51 , which are of square configuration, are dimensioned in such a way that they are each able to accommodate two hollow bodies  50 . The open grid spaces  52  are of rectangular contour and are each only able to accommodate one hollow body  50 . By contrast, three hollow bodies  50  lying next to one another may be provided in the open grid spaces  53 , which are larger than the open grid spaces  51 . 
     The open grid spaces  61 ,  62  which are adjacent to the narrow sides of the area of open water F do not hold any hollow bodies. There, as can be seen from the dot-dashed illustration in FIG. 16, it is possible for there to be additional tanks  64 ,  65 , which project below the water line W, as rooms. These can be used, for example, to take a snack, etc. These tanks  64 ,  65  too may be made transparent. 
     The tunnel  11  and the companionways  6 ,  7  are see-through planked steel frame structures. Steel frame profiled sections  66  of different cross-sectional shape, which are planked with the tunnel walls and the tunnel floor  12  and with the walls of the companionways  6 ,  7 , are used for this purpose. With regard to the either planar or curved walls, they are plates consisting of transparent plastics with a thickness of approx. 100 mm. 
     Since considerable buoyancy forces act on the tunnel  11  and the companionways  6 ,  7  and these forces have to be absorbed, two laterally protruding bearing journals  67 , which for their part divert the buoyancy forces into yokes  68 , which are associated with the bearing journals  67 , of the supporting framework  49 , originate from each companionway  6 ,  7 . These yokes  68  are for their part adjacently associated with the open grid spaces  59 ,  60 . 
     The hollow bodies  50  are substantially cuboidal tanks. They are produced from suitable plastics using the rotational process. Each hollow body  50  is rectangular in form and is equipped with means (not shown in more detail) for fixedly connecting the hollow bodies to the supporting framework. This connection option is also available among the hollow bodies  50  themselves. Each hollow body can be closed off by means of a cover  69 . In this way, it is possible to use the hollow bodies as tanks or buoyancy bodies. They may also form ballast bodies, storage chambers, etc. 
     As is also the case in the first embodiment, a ballast body  22 , which is configured as an island and for its part is supported by means of its lower end on the tunnel ceiling, is associated with tunnel  11 . The ballast body  22  or the island which it forms may, for example, be continuously connected to the walking area of the supporting framework  49  via a bridge web, which is not illustrated. 
     By way of example for a special event, such as a dance, the area of open water F can be covered by boards  70 . Carriers  71 ,  72 , which are preferably stored beneath the edges of the supporting framework and can be displaced over the area of open water F, are used as carriers for the boards  70 . These carriers are equipped at their ends with rollers  73 , which for their part roll over edge-side rails  74 . In the storage position, the boards  70  are situated next to one another, in a fan-like disposition, connected by means of hinges, bellow the control area of the supporting framework  49 . In combination with a displacement of the carriers  71 ,  72  into the supporting position, the boards  70  are moved into a flat plane with respect to one another, so that the total walkable area of the supporting framework is additionally enlarged by the size of the area of open water F. FIG. 24, left-hand side and FIG. 25 show the stored position of the carriers  71 , while the right-hand side in FIG. 24 illustrates the supporting position of the carriers  71 . 
     All the features disclosed are (inherently) pertinent to the invention. The content of disclosure of the associated/appended priority documents (copy of the prior application) is hereby incorporated in its entirety in the disclosure of the present application, partly with a view to including features of these documents in claims of the present application.