Abstract:
A concrete tower manufactured by an apparatus comprising a slipform, which is circumferentially guided in such a way that the slipform slides helically on top of the end face of the tower is provided. During the sliding, concrete is disposed by the slipform to the end face of the tower. After numerous revolutions, a low-cost tower is erected.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/EP2013/052858, having a filing date of Feb. 13, 2013, based off of U.S. Application No. 61/601,270 having a filing date of Feb. 21, 2012 and U.S. Application No. 61/600,165 having a filing date of Feb. 17, 2012, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to a tower. 
     BACKGROUND 
     Wind turbine towers, especially tubular steel or concrete towers for large wind turbines, are large in diameter and weight. This may cause difficulties concerning the transportation of a tower to the wind farm and the used infrastructure. Usually, the steel or concrete towers for wind turbines are produced as sections in shops and the sections are then transported to the place of installation. The towers are typically constructed of a number of sections which have a cylindrical or conical shape. In the wind industry, the requirements for larger turbines have resulted in corresponding requirements for larger wind turbine towers. Larger wind turbine towers have typically lead to larger tower section diameters and longer and heavier tower sections. The dimensions of tall towers for large wind turbine have reached limits defined by the infrastructure of various countries. The limiting aspects are typically physical limits such as free height under bridges and tunnels, allowable weights or the turning radii of roundabouts. 
     The increasing number of turbines in large wind projects has also caused difficulties since the equipment which is needed to transport the largest tower sections by road or by rail is highly specialised and is not found in the quantities necessary for the present number of transportations. Consequently, when a large number of projects require a substantial amount of transportation time by road, the availability of special equipment may become difficult in the project phase. 
     The problem has been addressed by dimensioning, by the use of hybrid towers or by the use of modular towers. Dimensioning accepts the height and width restrictions of transportation routes and uses the restrictions as a design basis. This means in practice that the external tower diameter is fixed at a certain maximum value, typically 4.2 meters. When the diameter is fixed, then the wall thickness is dimensioned to provide the necessary stiffness and strength. For large turbines and tall towers this will typically lead to significantly higher weight. This causes higher costs compared with when no diameter restrictions are applied. 
     In a hybrid solution, the problem is circumvented by extending the concrete foundations significantly above ground level, for example, as a cylindrical structure of, for instance, 10 meters height. This increases the effective hub height of a wind turbine where the tower design is not significantly influenced by a diameter restriction. However, above a certain practical height an extended foundation is expensive. Compared with a diameter restricted tower, a hybrid solution tower reaches an additional height of perhaps 15 meters. 
     A wide range of modular precasted concrete towers are well known in literature and in practice. Using a longitudinal split, such solutions overcome the dimensional restrictions on transportation. However, difficulties occur in the assembly and the complexity of the modular elements. 
     WO 03/069099 A1 discloses a wind turbine comprising a stationary vertical tower on which the moving part of the wind turbine is arranged, which mast is at least partly composed from prefabricated wall parts with several adjacent wall parts forming a substantially annular mast part. WO 01/07731 discloses a tower manufactured by a slip form technique. This slip form technique uses vertical moving slip forms which are casting the whole circumference of tower in one process. However, it is difficult to vary the diameter of the tower. 
     SUMMARY 
     An aspect relates to a low-cost wind turbine tower with a variable dimensions. 
     Embodiments of the technique is a spiral moving continuous pouring process, where a slip form is moved substantially horizontally along the circumference of the structure to be built, while constantly building new concrete on top of already casted and hardened concrete. Embodiments of the invention can be advantageous in that the assembly is relatively simple with low moulding-tool and production costs. Embodiments of the invention can be further advantageous in that the circular reinforcement can be applied as the spiral is made. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
         FIG. 1  shows a first embodiment of a section of a tower and a device to manufacture the tower in a three-dimensional view; 
         FIG. 2  shows an embodiment of the tower and the device of  FIG. 1  in cross section; 
         FIG. 3  shows an embodiment of a precasted tower segment on which the tower will be erected in three-dimensional view; 
         FIG. 4  shows a second embodiment of a section of a tower and a device to manufacture the tower in a three-dimensional view; and 
         FIG. 5  shows a third embodiment of a section of a tower and a device to manufacture the tower in a three-dimensional view. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show a first embodiment of a section of a tower  1  and a device  2 ,  5 ,  7  to manufacture the tower  1  in a three-dimensional view and a cross-sectional view. The casted walls of the tower  1  comprise ducts  26  prepared for receiving wires to prestress the concrete tower axially or circumferentially once casted. These ducts  26  are constructed while slipforming, and may be lined or may not be lined. 
     The ducts  26  are vertical holes  26  which are introduced circumferentially into the tower  1  and can be used for pre-tensioning wires. The holes  26  can be produced by fixing cylindrical, preferably slightly rejuvenating pins  27  vertically into the holes  26  of hardened concrete  10 , by disposing the fluid concrete  10  on the top of the end face  11  of the tower  1  and by removing the pin  27  after hardening of the disposed concrete  10 . 
     The device to manufacture the tower  1  comprises some carrying structure  5  which supports the slip form  2  itself. The carrying structure  5  is at least partly able to perform a spiral formed guidance of the slip form  2  as indicated by arrows in  FIG. 1 . The slip form  2  has an inner design which is complementary to the desired outer design of the tower  1 . 
     Wet, i.e. liquid and non-hardened concrete  10  is pumped by a concrete pump  20  through a concrete guide  9  and poured into the slip form  2  which distributes the concrete  10  to the top of the tower. The slip forming is a spiral/helical moving continuous pouring process, where the slip form  2  is moved substantially horizontally along the circumference of the structure, e.g the tower  1  to be built, while constantly building new concrete  10  on top of already casted and hardened concrete of the tower  1 . 
     The concrete tower  1  is made by an apparatus comprising a slipform  2 , which is circumferentially guided in such a way that the slipform slides helically on top of the end face  11  of the tower  1 . Concrete is disposed through the concrete guide  9  and by the slipform  2  to the end face  11  of the tower  1 . The slipform  2  is carried by the support device  5 ,  7 , which is circumferentially guided by a geometric shape  11 ,  21 ,  22  of the tower  1  in such a way that the slipform  2  slides helically on top of the end face  11  of the tower  1 . The support device  5 ,  7  is guided on wheels  8  on the end face  11  of the tower  1  in vertical direction. The inner vertical walls of the slipform  2  are guided by the inner surface  21  and outer surface  22  of the tower  1  in radial direction. The diameter of the support device  5 ,  7  can be varied to create a tower  1  with varying diameters. The geometric shape  11 ,  21 ,  22  of hardened concrete  10  provided in one of the previous circumferential rotations of the slipform  2  on top of the tower  1 . 
     Optionally, the thickness, i.e. the inner width W, the angle α in relation to the axis A of the tower  1  and/or the height h of the slip-form  2  can be varied, so that the tower  1  can be designed free, e.g. to create a different width or diameter DT of the tower  1  or a tapered tower  1  with a diameter decreasing with increasing height of the tower  1 . 
     In  FIG. 1 , the support device  5 ,  7  is connected to a protection element  25  which protects at least the non-hardened concrete  10  disposed on the end face  11  of the tower  1  against environmental impacts. 
     As can be seen in  FIGS. 1, 2, 4 and 5 , the function of the different carrying structures (support devices)  5 ,  7 ,  8  of  FIGS. 1 and 2 ; support means  18 ,  30  of  FIG. 4 ; or support device  50  of  FIG. 5 , is to hold and support the slip form  2  and also some supporting means  8 ,  18  which holds the respective carrying structure in the correct vertical position for the slip form assembly  2  in relation to the already casted concrete of the tower  1 . Alternatively, the carrying structure  5  and the support means  8  are not necessary if it is just a wagon in front of the slip-form  2 . 
     The slip form  2  has a degree of freedom so that the assembly is possible to move in the horizontal direction in order to vary the diameter of the casted tower  1 —as indicated by arrows  7  in  FIG. 2 . Wet concrete  3  is poured into the slip form  2  by the concrete guide  9  and is processed to take a solid form  4  and to fill the entire height h and width w of the slipform  2  so as to cast a defined concrete piece on top  11  of the already casted concrete  1 . For this embodiment of the invention, the supporting means (wheels or sliding elements)  8  running on top  11  of the tower  1  and supporting the carrying structure  5  is constructed so as to carry while supported on top  11  of the already casted and hardened concrete tower  1 . 
     For one embodiment of the invention shown in  FIG. 3 , the slip casting process is only applied for building a part of the tower  1 . For such situation, it might be necessary to build or cast a lower distal part  40  of the tower  1  separately as schematically indicated on the  FIG. 3 . 
     This distal part  40  may comprise a linear (spiral) increase in height along its top-circumference with an abrupt discontinuity  44  at some “full circle” point. This abrupt discontinuity  44  may be the starting location for the invented moulding assembly to be applied. From this point, the moulding assembly/slipform  2  will take over and mould the rest of the tower  1  in a spiral slip form moulding manner. 
     The sliding of the slipform  2  starts on top  11  of a precasted tower element  40  at the step, i.e. the discontinuity  44  of the precasted tower element  40  in circumferential direction. This distal part  40  may be casted in one piece on site, multiple pieces on site or may be precasted elements casted from an external element production site. 
     In the  FIG. 4 , another embodiment of the device to slipform a tower  1  with alternative support means  18 ,  30  is shown. The supporting means (wheel or sliding construction)  18  carries a platform  31  which carries the concrete guide  9  and the slipform  2 . The supporting means  18  are horizontally movable in relation to the platform  31  thus enabling changing the radial position of the slipform  2  and to vary the diameter DT of the tower  1 . The inner surface of the tower  1  comprises casted spiral nosing  19  and a spiral groove  49  produced by the casting form of the slipform  2 . This is schematically illustrated in  FIG. 4 . The slipform  2  comprises a container  3  with a negative shape of a geometric form (defined by spiral nosing  19  and spiral groove  49 ) to produce the tower  1  with said geometric form with a spiral groove  49  and a spiral nose  19  during the circumferential sliding of the slipform  2 . 
     In another embodiment, the mould assembly with a slipform  2 , a concrete guide  9  and a carrying structure/support device  50 ,  46 ,  47 ,  48  is schematically illustrated in  FIG. 5 . Two parallel balks  47  run diametrical on top  11  of the tower  1  and carry the slipform  2  and a part of the concrete guide  9 . Each two vertical rollers  46  are connected to the bottom of the slipform  2  contacting the inside and the outside surfaces of the tower  1 . While slipforming, circular  41  and/or vertical concrete reinforcements  42  are being applied to the tower  1 . While slipforming, the dimensions of the tower  1  are measured and controlled.