Patent Publication Number: US-2022220735-A1

Title: Method of mounting a roof structure

Description:
The present invention relates to roof structures for enclosures such as stadiums, arenas and the like. 
     BACKGROUND 
     More particularly, the invention relates to roof structures which include a tension ring made of one or more cables and a plurality of radial cables connected to the tension ring and to bearing points disposed on a compression ring located on the periphery of the enclosure. 
       FIG. 1  illustrates an arrangement of such a roof structure. The enclosure  1  is shown to have a ground area  2  supporting, for example, a sports field, and a spectator area  3  where stands  4  are disposed to receive seats. In  FIG. 1 , the vertical axis A is located at the center of the ground area  2 . The enclosure  1  may be symmetrically arranged about the axis A. 
     The enclosure  1  must be open-air when it is used for certain sports, such as football, rugby, etc., which are normally not practiced indoor. Still, most stadiums of a significant size have a roof above the spectator area. While open-air enclosures will be more particularly referred to in the description which follows, it will be appreciated that the method proposed in the present document is also applicable, with similar cable arrangements, to indoor or fully roofed enclosures. 
     It is desirable that the structure supporting the roof does not include towers, masts or other elements that may block the view of parts of the ground area  2  from some of the seats. Suspended roof structures, and more generally cable-supported structures, can achieve that advantageously. 
     As illustrated in  FIG. 1 , a suspended roof structure  10  typically includes:
         a compression ring disposed in periphery of the enclosure  1 , for example on top of its outer wall, and bearing on its foundations, bearing points  12  being disposed and spaced apart along the compression ring;   radial cables  13  fixed at the bearing points  12 ;   one or more orthoradial cables forming a tension ring  14  and fixed to the radial cables  13  by connectors  15 ;   beams  16  or similar connection members attached to the radial cables  13  and/or the tension ring  14 ; and   roof panels  17  attached to the beams  16  and to the compression ring and disposed to cover part or all of the spectator area  3 . If the enclosure is open-air, the roof panels  17  typically do not cover the ground area  2 , as shown in  FIG. 1 . They may cover the ground area too in an indoor or fully roofed case.       

     As shown in  FIG. 1 , the tension ring is not necessarily at the edge/end of the roof. In case of a fully roofed enclosure, the central area of the tension ring can be spanned with a secondary structure using girders, lattice girders, etc. 
     Putting in place such a roof structure  10 , especially the radial cables  13  and the orthoradial cable(s) forming the tension ring  14 , is not an easy task. Generally, the tension ring  14  is assembled on the stands  4 . The individual cables forming the tension ring  14  are unwound from a reel held by a crane, in order to assemble the tension ring plumbing from its final position. This prevents the seats and other stands equipment to be installed, and it requires special protective measures for the stands  4 . The tension ring  14  is then lifted and the trajectory of the cables may interfere with elements such as barriers, posts or other fixed equipment provided on the stands  4 . Temporary support structures, such as scaffoldings, may be used, but they require high-capacity cranes for installing bearing or deviation elements which may be quite heavy. 
     There is thus a need for a simpler and more efficient method to mount the roof structure. 
     SUMMARY 
     There is provided a method of mounting a roof structure for an enclosure, the enclosure including a ground area, a spectator area around the ground area and a plurality of bearing points around and above the spectator area. The method comprises: 
     assembling a tension ring at the level of the ground area, the tension ring comprising at least one first cable extending along the tension ring and a plurality of connectors spaced along the tension ring; 
     attaching a plurality of second cables to the plurality of connectors, each second cable having a first end connected to a respective one of the connectors and extending radially and outwardly from the tension ring, each second cable being associated with a respective one of the bearing points; and 
     lifting the tension ring by pulling the connectors by the second cables. 
     Assembling the tension ring on the ground area is much simpler than doing it on the stands of the enclosure. The lifting sequence by which the tension ring is raised to its final position can be controlled to avoid interference with the stands and any equipment thereon. The whole procedure is much simpler than prior art procedures, in particular because temporary support structures may be unnecessary. 
     In an embodiment, a perimeter of the tension ring increases when the tension ring is lifted. 
     The method may further comprise: 
     disposing a third cable along the tension ring at the level of the ground area, such that the perimeter of the tension ring is defined by the third cable; and 
     feeding additional length of the third cable along the tension ring when the tension ring is lifted to increase the perimeter of the tension ring. 
     In this case, the at least one first cable may be disposed in a loose state when the tension ring is assembled at the level of the ground area and become tensioned by the pulling action of the second cables once the perimeter of the tension ring has increased up to a maximum value. The at least one first cable may be disposed to have a sinuous path when the tension ring is assembled at the level of the ground area. The third cable is mounted on deviators attached to a front side of the connectors, i.e. on the radially inner side of the tension ring. Feeding additional length of the third cable along the tension ring may be performed by using a strand jack mounted on the third cable when the third cable is disposed along the tension ring at the level of the ground area. 
     In another embodiment, the at least one first cable has a plurality of segments following each other along the tension ring and is equipped with couplers for assembling the segments, and at least one of the couplers comprises: a first coupling part attached to an end of a first segment of the at least one first cable and having a first abutment surface; and a second coupling part attached to an end of a second segment of the at least one first cable and having a second abutment surface facing the first abutment surface, the first and second abutment surfaces being brought closer to each other when the tension ring is lifted, for example by using a strand jack connected to the first and second coupling parts. 
     In an embodiment, lifting the tension ring includes at least one iteration of a first phase of pulling the second cables while keeping a constant perimeter of the tension ring, whereby an inclination angle of the second cables decreases and the tension ring is lifted, followed by a second phase of increasing the perimeter of the tension ring. One way of doing that is by not pulling the second cables in the second phase, whereby an inclination angle of the second cables increases and the tension ring is lowered. In each iteration, the inclination angle of the second cables decreases more in the first phase than it increases in the second phase, and the tension ring is lifted in the first phase more than it is lowered in the second phase. 
     After the at least one iteration, there may be a final phase of pulling the second cables while keeping a constant perimeter of the tension ring. 
     In an embodiment, additional cables are disposed across the ground area and connected to the tension ring. 
     After the tension ring is lifted, the second cables may be anchored, for example at the bearing points. Alternatively, they may be anchored at positions spaced apart from the bearing points and deviated at the bearing points. 
     Other features and advantages of the method and apparatus disclosed herein will become apparent from the following description of non-limiting embodiments, with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , already discussed above, is a schematic elevation view of a stadium provided with a suspended roof structure; 
         FIG. 2  is a schematic top view of the stadium in a step of assembling a tension ring; 
         FIGS. 3 and 4  are perspective views of a connector belonging to the roof structure; 
         FIG. 5  is a diagram of a temporary cable and elements used to adjust its length; 
         FIGS. 6-10  are diagrams showing cables of the roof structure at different stages of its installation; and 
         FIG. 11  is a diagram illustrating an alternative embodiment of an assembly of cable segments forming a tension ring. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The method described below is for mounting a roof structure  10  of the kind illustrated in  FIG. 1  above the spectator area  3  of an enclosure  1  such as an open-air stadium, more particularly for mounting the cable network of the roof structure. 
     An embodiment of the method is illustrated in  FIG. 2 , which is a schematic top view of the stadium  1 . At the periphery of the stadium,  FIG. 2  shows the compression ring  18  along which the bearing points  12  are spaced. Referring also to  FIG. 1 , the bearing points  12  are located around and above the spectator area  3  which is located around the ground area  2 . 
     A first step of the method consists in assembling the tension ring  14  at the level of the ground area  2 . The tension ring as assembled includes one or more cables  20  whose trajectory follows the circumference of the tension ring, the connectors  15  spaced along the circumference of the tension ring and, in the embodiment illustrated by  FIG. 2 , a temporary cable  22  mounted on the connectors  15 . In the description which follows, the cable(s)  20  forming the tension ring  14  are also referred to as “first cable(s)”, the radial cables  13  are also referred to as “second cables”, and the temporary cable  22  is also referred to as “third cable”. 
     A radial cable  13  is attached to each of the connectors  15  disposed along the circumference of the tension ring  14 . The positions of the connectors along the tension ring  14  correspond to the positions of the bearing points  12  along the compression ring  18 . 
     In the schematic illustration of  FIG. 2 , the tension ring  14  is shown to have a generally rectangular shape. In the final position of the tension ring ( FIG. 1 ), its path, seen from above, will typically be circular, elliptical or oval, with a curvature that varies along its circumference. It is also possible that the final position of the tension ring lies in an inclined (rather than a horizontal) plane. The method described herein is not limited to any specific shape of the tension ring  14  in its initial or final position. 
       FIGS. 3-4  show a possible configuration of a connector  15  comprising a body  30  having passages  31  for receiving respective first cables  20  of the tension ring. In  FIG. 3 , the connected cables  20 - 22  are shown together with the connector  15 , while they are not shown in  FIG. 4 . In this example, there are six passages  31 , but the embodiment is not limited to that. The passages  31  are parallel to each other in a same substantially horizontal plane. The body  30  may consist of a main plate  32  having grooves formed on its lower surface and of one or more clamping plates  33  that are fixed to the lower surface of the main plate  32  after insertion of the cables  20  into the grooves so as to complete the passages  31  holding the cables  20 . The clamping plates  33  are pressed on the main plate  32 , with the cables  20  housed in the passages  31 , by means of bolts and nuts  34 . The first cables  20  may be pressed tightly in the passages of the connector  15 , or they may be allowed to slide in the passages. 
     Connecting parts such as brackets or lugs  35  may be provided on the body  30  of the connector  15  for fixing beams  16  of the roof structure  10  as shown in  FIG. 1 . 
     A rear side of the connector  15  includes an extension, such as a lug  36 , having a hole along a horizontal articulation axis B for mounting a clevis  38  provided with an anchoring device for attaching one end of a radial cable  13 . In the first step of the method, each radial cable  13  attached to a connector  15  is disposed radially from the connector  15  and outwardly from the tension ring  14 . The radial cable  13  may be laid on the stands  4  so as to extend upwardly to a corresponding one of the bearing points  12  provided on the compression ring  18 . This is best shown in  FIG. 7 . 
     A deviator  40  is attached to the front side of the connector  15 . In the example shown in  FIG. 3 , the deviator  40  comprises three sheaves  41  pivotally mounted between a pair of flanges  42  that are pivotally mounted on a front extension  43  of the connector body  30 . The flanges  42  are in a plane parallel to the plane defined by the passages of the body  30 , e.g. a horizontal plane in which case the pivot axes of the sheaves  41  and the flanges  42  are vertical. The temporary cable  22  is mounted on the deviators  40  of the connectors  15  along the perimeter of the tension ring, to be guided by the sheaves  41 . 
     When it is assembled on the ground area  2 , the tension ring  14  has its perimeter defined by the temporary cable  22  ( FIG. 2 ). A tensioning system, such as one or more jacks  45 , may be provided on the temporary cable  22  so as to set the length of the perimeter. 
     The cables  20  are, however, first disposed in a loose state. In particular, the cables  20  can be disposed to have a sinuous path. In  FIG. 2 , the sinuous path is shown as undulations in a horizontal plane. It may be more convenient to have undulations in a vertical plane as shown in  FIG. 6  by disposing small removable supports  46  on the ground at discrete locations along the perimeter of the tension ring and laying the cables  20  alternately on the ground and on the removable supports  46 . 
     It has been mentioned above that the tension ring  14  is assembled at the level of the ground area  2 . It means that the cables  20 ,  22  may be laid directly on the surface of the ground area  2 , for example around a football field as shown in  FIG. 2 , or that they may be laid close to the surface of the field, for example in a shallow trench around the field or on a protective floor disposed on the ground area  2  to avoid damaging the surface of the field with the cables and associated tools. Still, it is not necessary to provide a large supporting structure for assembling the tension ring  14 . 
     The tension ring  14  may include one first cable  20  or a plurality of first cables  20 . Each first cable  20  has its two ends anchored so as to be tensioned in the final position of the tension ring  14 . The anchoring devices may be collocated with some of the connectors  15  (for example with anchoring jaws inserted in some of the passages  31 ), or they may be provided by couplers (not shown) separate from the connectors  15 . 
     If there is only one first cable  20 , it may be disposed in one or several turns along the tension ring  14 , for example six turns if it extends through the six passages  31  shown in  FIGS. 3-4 . When the full length cannot be provided with one first cable, it may be replaced by a plurality of first cables  20 . 
     When the first cables  20  are plural, they can be connected to each other via couplers in order to follow one or several turns along the tension ring  14 , thus forming different cable segments. Another option is to have a number of first cables  20  independent from each other, anchored separately and following concentric paths. Such concentric cables can themselves be made of one or more cable segments. 
     Likewise, the temporary cable  22  can be provided as one or more segments, and it may follow one or more turns along the tension ring  14 . 
       FIG. 2  shows that, optionally, additional cables  48  may be attached to the tension ring  14  when it still rests on the ground area  2 . The additional cables  48  extend across the ground area  2 . Each of them may be attached to a pair of connectors  15  located at opposite positions on both sides of the ground area  2 . The additional cables  48  may be needed to deal with particular geometries of the roof structure  10 . They contribute to stabilizing the tension ring  14  while it is lifted. They may be removed once the roof structure  10  is completed, or left in place. 
       FIG. 5  shows the temporary cable  22  and a tensioning system used to put it under tension and define the perimeter of the tension ring  14 . In this example, the temporary cable  22  is fed from a reel  50  via a strand jack  45 . One end of the cable  22  is fixed in an anchor block  51  using a conical jaw  52 . From that end, the cable  22  loops around the tension ring  14  and reaches again the anchor block  51 , where it is held by another conical jaw  53  on an opposite surface of the anchor block  51 . Beyond the anchor block  51 , the cable  22  goes through another anchor block  54  before reaching the reel  50 . The cable  22  is also held in the other anchor block  54  by means of a conical jaw  55 . One or more hydraulic jacks  56  are provided between the two anchor blocks  51 ,  54 . According to the conventional operation of a strand jack, the distance between the two blocks  51 ,  54  is adjustable by controlling the jacks  56  so as to vary the length of the cable  22  between its two connection points to the anchor block  51  as desired. 
     In the application considered herein, the strand jack  45  is first controlled to set the perimeter the tension ring  14  by providing the appropriate length of the temporary cable  22 . Afterwards, when it is needed to increase the perimeter of the tension ring  14 , some additional length of the temporary cable  22  is fed from the real  50  by controlling the strand jack  45 . 
       FIGS. 7-10  illustrate different steps of lifting the tension ring  14  from the configuration shown in  FIG. 2  or  FIG. 6  to its final position above the stands  4 . 
     The lifting operation includes:
         a first phase in which the connectors  15  are pulled by the radial cables  13  from the bearing points  12 , as indicated by the arrow F 1  in  FIG. 7 , using respective pulling/jacking devices (not shown); and   a second phase in which the strand jack  45  feeds some additional length of the temporary cable  22  increasing the perimeter of the tension ring  14 , as indicated by the arrows F 2  in  FIG. 8 .       

     In a possible lifting arrangement, each radial cable  13  is fitted in advance with its permanent anchor head (not shown) at a predefined distance from its respective connector  15 . The radial cables  13  are pulled outwardly with their anchor heads up to their final positions at the bearing points  12 . In such arrangement, each radial cable  13  may be equipped with some extra length beyond the anchor head for applying the required traction force to the radial cable from the bearing point  12 . Alternatively, each radial cable  13  may be equipped with a temporary tool cable attached to the anchor head. In both cases, a pulling/jacking device is supported by the compression ring  18  near each bearing point  12 . Each bearing point  12  may be provided with an abutment surface against which the anchor head of the respective radial cable  13  is applied at the end of the lifting sequence or alternatively a lug for anchoring a clevis provided as the cable  13  anchor head. Then, inward radial forces are applied at the abutment surfaces of the bearing points  12  by the second cables  13  which behave similarly to spokes of a bike wheel. Such inward radial forces are withstood by the annular shape of the compression ring  18 . The bearing points  12  along the compression ring  18  take vertical loads when the tension ring  14  is lifted and then remains in its final position. 
     In each first phase of the lifting operation ( FIG. 7 ), the perimeter of the tension ring  14  is kept substantially constant, i.e. the strand jack  45  is not activated. Small variations of the perimeter may, however, take place due to the elastic elongation of the cables. The traction applied by the radial cables  13  causes a reduction of their inclination angle θ while the connectors  15  are lifted vertically. The first cables  20  sag between the connectors once they leave the removable supports  46  and are lifted along with the third cable  22  and the connectors  15  forming the tension ring  14 . 
     In the second phase ( FIG. 8 ), the radial cables  13  are blocked, i.e. the pulling/jacking devices are controlled to prevent their movements at the bearing points  12 . The increasing perimeter of the tension ring  14  causes an increase of the inclination angle θ of the radial cables  13 . Thus, the connectors  15  and the tension ring  14  are lowered. 
     The inclination angle θ of the radial cables  13  decreases more in the first phase than it increases in the second phase, and the tension ring  14  is lifted in the first phase more than it is lowered in the second phase. Therefore the first and second phases together lead to lifting the tension ring  14  and increasing its perimeter. 
     A first phase followed by a second phase as described above will generally not be enough for the tension ring  14  to reach its final position. To continue the lifting operation, first and second phases are iterated.  FIG. 9  illustrates a case where a total of four iterations is used. In each iteration i (1≤i≤4), the arrow X i  denotes the lifting of the tension ring  14  with a constant perimeter (first phase), and the arrow Y i  denotes the decrease of the ring perimeter (second phase) that goes with less sagging of the first cables  20  and some lowering of the tension ring. 
     At the end of the fourth iteration (Y 4 ), the perimeter of the tension ring  14  reaches a maximum value which is the final value that it will have when the roof structure  10  is completed. There is no more sagging of the first cables  20  which have become tensioned by the pulling action of the radial cables  13 . 
     A final lifting phase X 5  is performed by pulling the radial cables as shown in  FIG. 10  to bring the tension ring  14  to its final position. 
     The radial cables  13  are then anchored, and the other elements  16 ,  17  of the roof structure  10  ( FIG. 1 ) are subsequently installed. The temporary cable  22  can be removed, as well as the deviators  40 , but alternatively they can also be left in place. 
     The locations where the radial cables  13  are anchored may be at the respective bearing points  12 , provided with abutment surfaces as mentioned above or alternatively with lugs for anchoring devises provided as anchor heads for the cables  13 . 
     In another embodiment, the bearing points  12  have saddle configurations where the radial cables  13  are deviated and the positions of the pulling/jacking devices may be separate from the bearing points  12 . The abutment surfaces receiving the anchor heads can then be beyond the bearing points  12 , for example in the periphery of the enclosure, lower than the bearing points  12  where the cables  13  are deviated. Alternatively, the radial cables  13  are not pre-equipped with anchor heads. They are pulled in the first phases of the lifting operation and eventually blocked in respective anchor heads fixed to the structure of the enclosure. 
     The number of iterations to lift the tension ring depends on the geometry and constructional constraints of each worksite. In general, the lifting operation will start with a first pulling phase to secure tension of the temporary cable  22  and to clear the stands  4  from the radial cables  13 . After that, one or more iterations are performed. 
     In each pulling phase X 1 , X 2 , . . . , the displacements of the radial cables  13  pulled from the bearing points  12  are selected based on the geometries of the tension ring  14  in its original position on the ground and its final, elevated position. 
     Another possibility is to control the pulling/jacking devices to pull the radial cables  13  continuously at the same time as the ring perimeter is progressively increased. 
     Another embodiment of the method proposed herein does not make use of a temporary cable  22 . The first cables  20  have a plurality of cable segments following each other along the tension ring  14 . Couplers are used for assembling the segments, and one or more of the couplers are arranged to allow an increase of the perimeter of the tension ring. In this case, it is not necessary to provide a sinuous path of the first cables  20  around the tension ring. The first cables  20  are tensioned as soon as the lifting operation begins and they do not sag significantly when the tension ring is lifted. 
     An example of a coupler usable in such an embodiment is shown schematically in  FIG. 11 . The coupler has a first coupling part formed by an anchor block  60   a  where an end of a first cable segment  20   a  of the tension ring  14  is attached. A second coupling part of the coupler is formed by an anchor block  60   b  where an end of a second cable segment  20   b  of the tension ring  14  is attached. Each anchor block  60   a ,  60   b  has a first channel  61   a ,  61   b  where its respective cable segment  20   a ,  20   b  is received and anchored by means of a conical jaw  62   a ,  62   b  inserted from an anchoring surface  63   a ,  63   b . Each anchor block  60   a ,  60   b  also has a second channel  64   a ,  64   b  where the other cable segment  20   b ,  20   a  is received and allowed to slide. The anchor blocks  60   a ,  60   b  have respective abutment surfaces  65   a ,  65   b  facing each other, on opposite sides of their anchoring surfaces  63   a ,  63   b . When the tension ring  14  is assembled on the ground area  2 , a distance D is maintained between the two abutment surfaces  65   a ,  65   b . When the tension ring  14  is lifted, the distance D is adjusted to be reduced so as to increase the perimeter of the tension ring. At the end, the abutment surfaces  65   a ,  65   b  can be in contact (D=0), or a spacer can be inserted between them (D&gt;0). 
     Several pairs of cable segments can be attached to the anchor blocks  60   a ,  60   b  of the coupler, though only one pair  20   a ,  20   b  is shown in  FIG. 11 . 
     For controlling the distance D and, thus, the perimeter of the tension ring  14 , a strand jack arrangement  70  may be used. One or more auxiliary cables  71  are fixed on blocks  72 ,  73  that bear on the anchor blocks  60   a ,  60   b  of the coupler. In the example shown in  FIG. 11 , the block  73  bears on the anchor block  60   b  via a compression leg  74 . The length of the auxiliary cables  71  between the two blocks  72 ,  73  is controlled by the hydraulic jacks  75  of the strand jack arrangement  70  similarly to what has been described above with reference to  FIG. 5 . 
     It will be appreciated that the embodiments described above are illustrative of the invention disclosed herein and that various modifications can be made without departing from the scope as defined in the appended claims.