Screw prestressed prefabricated radial beam slab type fan foundation and construction method thereof

Abstract

The application discloses a screw prestressed prefabricated radial beam slab type fan foundation and a construction method thereof, and relates to the technical field of fan foundations. The fan foundation is formed by splicing a plurality of beam pier combined prefabricated parts in a ring shape, a plurality of rows of horizontal reserved holes are arranged on the variable-step beam slabs, horizontal anchor rods are anchored on the connecting anchor plates at the center position of the foundation and outside the foundation to lock the foundation. Connecting plates are arranged between the variable-step beam slabs to improve the consistency of the overall structure. The middle pier on the inner side of the variable-step beam slab is provided with vertical reserved holes, and anchor plate grooves for fan tower anchorage plates are reserved on the upper and lower surfaces of the middle pier, so that the vertical anchor rods are convenient to install. The foundation form is reasonable in stress, the connection anchor plate pulling connection mode is adopted to avoid the collision problem between the horizontal anchor rods, the dry construction without grouting can be realized on the construction site, the installation is convenient, efficient and environment-friendly, and the problem of excessively high temperature in the core area in the construction process of the traditional fan foundation is solved.

Description

Technical Field

[0001] This invention belongs to the field of wind power generation technology and relates to a screw-prestressed precast radial beam-slab wind turbine foundation and its construction method. Background Technology

[0002] The wind turbine foundation, as the structural basis of the wind turbine system, bears the weight of the wind turbine itself and the wind load, playing a crucial role in load-bearing support. Because wind turbines are tall structures, they experience significant horizontal forces and bending moments at the base under horizontal wind loads. Furthermore, wind turbines are highly sensitive to tower tilt and require strict control over uneven foundation settlement. The wind turbine foundation must withstand vertical loads, horizontal loads, uplift forces, and vibrations or dynamic forces generated by the wind turbine. Wind turbine foundations generally come in various types, including spread foundations, pile foundations, and anchor foundations. They are typically cast-in-place concrete structures, requiring on-site reinforcement binding, concrete pouring, and curing, which takes approximately one month. The pouring process for wind turbine foundations is highly sensitive to environmental conditions; excessively high or low temperatures can affect foundation quality, and construction sites with variable climates may experience prolonged construction interruptions. Moreover, on-site pouring and curing by the construction unit exposes the wind turbine foundation construction quality to numerous uncertainties, including the experience of the construction team. In general, the mainstream form of wind turbine foundations on the market is on-site casting. However, the construction quality of on-site casting foundations is difficult to control, the construction period is long, and the environmental impact is significant. In special areas, ready-mixed concrete cannot be effectively transported, and the quality of concrete from self-built mixing plants is uncontrollable, which can have a great impact on the project construction. Summary of the Invention

[0003] The purpose of this invention is to design a screw-prestressed precast radial beam-slab wind turbine foundation to solve the problems mentioned in the background art, such as the long on-site construction cycle and difficulty in controlling the construction quality of current wind power foundations. At the same time, it ensures that the wind turbine foundation is easy to install and safe and reliable.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A screw-type prestressed radial beam-slab wind turbine foundation is characterized by comprising precast beam-pier composite components, anchor plates, horizontal anchor rods, connecting plates, vertical anchor bolts, and anchor plates. The precast beam-pier composite components are composed of a central pier, a main beam, and a base plate. These components have a fan-shaped feature and can be assembled in a ring to form a hollow ring-shaped foundation structure. Connecting plates are provided between adjacent precast beam-pier composite components, connected by horizontal groove socket joints. Each precast beam-pier composite component has multiple horizontal and vertical anchor bolt pre-drilled holes for arranging horizontal anchor rods and vertical anchor bolts. The end of the horizontal anchor rod near the central pier is fixed to the anchor plate, and prestress is applied from the other end before fixing it to the precast beam-pier composite component.

[0006] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions:

[0007] The main beam of the beam-pier precast assembly is connected to the middle of the circumferential center of the pier as a whole; radially, the middle of the main beam is provided with a step, and the surface of the step is provided with horizontal anchor bolt reserved holes, which are arranged radially, pass through the main beam and the middle pier and are aligned with the center of the foundation.

[0008] The precast beam-pier assembly has vertical anchor bolt pre-drilled holes on the middle pier. These holes are arranged in a ring around the foundation center, penetrating the middle pier. Grooves are provided at the top and bottom of the middle pier at corresponding positions for the installation and positioning of the top and bottom anchor plates.

[0009] In the radial direction, the base plate is located on both sides of the bottom of the main beam. The base plate starts from the side of the middle pier and extends to the outer edge of the main beam. The side of the base plate has a fan-shaped side that forms a beam-pier prefabricated component. Furthermore, a cut parallel to the main beam is formed at the outer edge of the middle of the main beam. A horizontal groove is provided at the cut for connecting plate socket connection.

[0010] The connecting plate has a protrusion on its side that matches the groove of the bottom plate cut. The connecting plate is connected to the beam-pier precast component through the protrusion. The connecting plate is flush with the bottom plate of the beam-pier precast component.

[0011] The anchor plate is disc-shaped with threaded holes on its side, and the end of the horizontal anchor rod is also provided with threads of matching size. The two are connected by threads.

[0012] The connection between the precast beam-pier composite component and the upper wind turbine tower flange is achieved by vertical anchor bolts passing through the vertical reserved holes in the middle pier, anchoring to the top and bottom anchor plates, and applying prestressing tension for fixation.

[0013] According to a second aspect of the present invention, the present invention also provides a construction method for constructing a screw-prestressed precast radial beam-slab wind turbine foundation as described in any of the preceding claims, the technical solution of which is as follows:

[0014] A construction method for a screw-type prestressed precast radial beam-slab wind turbine foundation, the steps of which are as follows:

[0015] Step 1: Excavate the installation pit for the wind turbine foundation according to the design drawings, and complete the cable duct laying path at the same time. Continue to excavate to a certain depth within a circular area with the outer diameter of the middle pier of the beam-pier composite precast component as the diameter, and reserve the construction space for the anchor plate and vertical anchor bolts at the bottom. For areas with poor geological conditions, a cushion layer needs to be poured. When pouring the cushion layer, first pour the area outside the middle pier. After the anchor plate and vertical anchor bolts are installed, pour the middle low-lying area to the same elevation as the top of the bottom slab.

[0016] Step 2: Assemble the precast beam-pier composite components. First, position each precast beam-pier composite component. Before assembling the precast beam-pier composite component 1, clean the surface of the pad layer and the foundation interface, and apply a certain thickness of structural adhesive material. Then, assemble each precast beam-pier composite component in the design position.

[0017] Step 3: After the precast beam-pier composite components are assembled, begin installing the horizontal anchor bolts. Place the anchor plate at the designated height within the hollow area enclosed by the central pier. Connect the horizontal anchor bolts to the anchor plate through the pre-drilled horizontal holes in the precast beam-pier composite components and fix them in place. Install the anchor bolts layer by layer from low to high. After all horizontal anchor bolts are installed, tension them at the anchoring end on the other side of the precast beam-pier composite components. During tensioning, ensure that tensioning is performed simultaneously on both sides to ensure overall stress balance of the wind turbine foundation.

[0018] Step 4: Clean the foundation interface, insert the concrete connecting plate into the horizontal groove of the bottom plate of the beam-pier composite precast component, and apply structural adhesive.

[0019] Step 5: After the horizontal anchor bolts and concrete connecting plates are installed, the vertical anchor bolts are installed. After the vertical anchor bolt 5 is fixed and locked to the bottom anchor plate, the top anchor plate and wind turbine tower flange are installed, and the upper end of the vertical anchor bolt is tensioned to achieve the prestress value required by the design.

[0020] Step 6: After the prestress values ​​of each part reach the design requirements, backfill the foundation.

[0021] In summary, the novel screw-prestressed precast radial beam-slab wind turbine foundation proposed in this invention greatly reduces on-site operation time, shortens the construction period, and is highly efficient and environmentally friendly while possessing good applicability and economy. It can be widely applied to the construction of wind farms on natural foundations under various terrain conditions.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The precast modules are mainly connected together by prestressed tie bolts. The prestressed tie bolts can enhance the shear bearing capacity of the inclined section of the main beam of the precast module, thereby reducing the required height and thickness of the main beam, further reducing the volume of concrete in the precast modules, and improving economy. Compared with the traditional disc-type spread foundation, the screw prestressed precast radial beam-slab wind turbine foundation under the same load conditions requires less steel and concrete while having the same bearing capacity, thus having good economy.

[0024] (2) The present invention produces prefabricated components in the factory, which is less affected by interference factors compared to on-site construction. It can avoid long-term work stoppages caused by prolonged rain, snow or extremely low temperatures, and is more flexible and reliable in terms of schedule. Since the prefabricated concrete structure is used, the prefabricated blocks and wedge-type concrete base plates can be made in the early stages of site leveling and foundation pit excavation. The reinforcement binding and concrete pouring and curing can be completed in advance. After the foundation pit is excavated, the prefabricated blocks can be hoisted and spliced. Compared with the traditional cast-in-place foundation, it can save one month of time required for reinforcement binding and concrete pouring and curing, which greatly saves the construction period.

[0025] (3) The wind turbine foundation of the present invention is reasonably stressed, and the method of connecting anchor plates avoids the collision problem between horizontal anchors; and it can realize dry operation without grouting on the construction site, which is convenient, efficient and environmentally friendly, and effectively solves the problem of excessive temperature in the core area during the construction of traditional wind turbine foundations.

[0026] (4) The wind turbine foundation is divided into prefabricated blocks of uniform size and produced in the factory. This enables mass production on an assembly line, thereby unifying the manufacturing standards for concrete blocks and ensuring the production quality of the concrete blocks. Attached Figure Description

[0027] Figure 1 This is a three-dimensional schematic diagram of the wind turbine foundation according to an embodiment of the present invention;

[0028] Figure 2 This is a top view of the wind turbine foundation according to an embodiment of the present invention;

[0029] Figure 3 This is a three-dimensional schematic diagram of the beam-pier composite prefabricated component according to an embodiment of the present invention;

[0030] Figure 4 This is a front view of the precast beam-pier composite component according to an embodiment of the present invention;

[0031] Figure 5 This is a side view of the beam-pier composite prefabricated component according to an embodiment of the present invention;

[0032] Figure 6 This is a three-dimensional schematic diagram of the connecting plate according to an embodiment of the present invention;

[0033] Figure 7 This is a top view of the connecting plate according to an embodiment of the present invention;

[0034] Figure 8 This is a schematic diagram of the anchor plate according to an embodiment of the present invention;

[0035] Figure 9 This is a schematic diagram of the anchor bolt connection according to an embodiment of the present invention;

[0036] Figure 10 This is a basic cross-sectional view of an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0038] In the screw-driven prestressed radial beam-slab wind turbine foundation of this invention, the main structure consists of multiple precast beam-pier components arranged radially, which are connected to a central anchor plate by multiple horizontal anchor rods arranged radially to form an effective whole. The precast beam-pier components have a fan-shaped feature, allowing multiple precast beam-pier components to be assembled into a ring-shaped foundation structure. The inner central pier is also assembled into a ring shape. Several rows of horizontal reserved channels are set on the stepped beam slab. The horizontal anchor rods are anchored to the connecting anchor plate at the center of the foundation and the outer side of the foundation through the reserved channels. The foundation is tensioned and locked by applying prestress through the horizontal anchor rods. Connecting plates are arranged between the stepped beam slabs, and the bottom plates are connected by socket-type connecting plates, thereby making the foundation more coordinated and stable as a whole and improving the overall structural consistency. The inner side of the stepped beam slab has vertical pre-drilled holes in the middle pier, and the upper and lower surfaces of the middle pier have pre-drilled grooves for the wind turbine tower anchor plates, facilitating the installation of vertical anchor bolts. The wind turbine foundation of this invention is suitable for connection with the upper wind turbine tower using the mainstream anchor cage connection method on the market, and the anchor cage is installed and fixed by pre-drilling vertical anchor bolt holes in the middle pier. The following is a more detailed description in conjunction with the accompanying drawings.

[0039] Please see Figure 1-10 This embodiment provides a screw-prestressed precast radial beam-slab wind turbine foundation, including a beam-pier precast component 1, an anchor plate 2, a horizontal anchor rod 3, a connecting plate 4, a vertical anchor bolt 5, and an anchor plate 6. The inner end of the beam-pier precast component 1 is the middle pier 101. The beam-pier precast component 1 and the connecting plate 4 are reinforced concrete structural components, while the anchor plate 2, the horizontal anchor rod 3, the vertical anchor bolt 5, and the anchor plate 6 are steel structural components.

[0040] like Figure 3 , 4 As shown in Figure 5, the precast beam-pier assembly 1 is a combination structure of a variable-step beam, a middle pier 101, and a bottom plate 105. The variable-step beam is arranged radially, and the bottom plate 105 is located on both sides of the bottom of the variable-step beam to form two fan-shaped sides. The middle pier 101 is located on the inner end of the variable-step beam, and its cross-section is fan-shaped.

[0041] The main beam of the beam-pier composite precast component, i.e., the stepped beam, is integrated with the circumferential center of the middle pier. Radially, the main beam has a step at its center, with horizontal anchor bolt pre-drilled holes 102 on the step surface. These holes 102 are arranged radially, passing through the main beam and the middle pier and aligning with the foundation center. Multiple rows of horizontal anchor bolt pre-drilled holes 102 are provided at different heights. In this embodiment, four rows of holes 102 are provided, with four holes in each row. The anchoring ends of the two middle holes 102 are on the step surface, while the anchoring ends of the two outer holes 102 are located on the middle pier 101 outside the step surface. The horizontal anchor bolt 3 passes through these pre-drilled holes 102, with one end threadedly connected to the anchor plate 2 in the middle of the wind turbine foundation, and the other end bolted to the anchoring end of the beam-pier composite precast component 1 and tensioned and locked. The middle pier 101 has grooves 104 at its top and bottom for installing anchor plates 6. Vertical pre-drilled holes 103, matching those provided by the wind turbine manufacturer, are located at the bottom of the grooves 104. The vertical pre-drilled holes 103 on the anchor plates 6 of each middle pier 101 are arranged in a circle with the center line of the wind turbine foundation as the center. The lower end of the vertical anchor bolt 5 is anchored to the bottom anchor plate 6, and the upper end passes through the top anchor plate 6 to connect with the flange of the wind turbine tower and is tensioned and locked. All pre-drilled holes are hollow steel pipes of a certain thickness. The bottom plate 105 of the beam-pier composite precast component 1 has a cut surface, and a horizontal groove 106 is provided at the cut surface for socket connection with the connecting plate 4.

[0042] like Figure 6 and Figure 7 As shown, the connecting plate 4 is a fan-shaped concrete slab. The three sides of the connecting plate 4 are provided with protrusions 401 that match the horizontal grooves 106 on the side of the bottom plate 105 of the beam-pier precast component 1. After the beam-pier precast component 1 is installed and fixed, the two sides of the connecting plate 4 are horizontally inserted into the horizontal grooves 106 of the bottom plate 105 of the beam-pier precast component 1 by means of socketing, and structural adhesive material is applied for reinforcement.

[0043] like Figure 8 , 9 As shown in Figure 10, the anchor plate 2 is a steel disc structure with a certain thickness, which meets the requirements for connection with the horizontal anchor rod 3 and prestressing tension. The anchor plate 2 is provided with multiple threaded pre-reserved holes 201 radially at a certain angle. After the horizontal anchor rod 3 passes through the pre-reserved hole of the beam-pier precast component 1, one end is connected to the anchor plate 2, and the other end is anchored on the beam-pier precast component 1 and tensioned and locked. The diameter of the anchor plate 2 is smaller than the central hole of the wind turbine foundation formed by the central pier 101, and it is located at the center of the central hole. After the anchor plate is tightened by the horizontal anchor rods 3 in all directions, it is in a suspended stress state. The gap between the horizontal anchor rods 3 can be used for maintenance and installation personnel to go up and down.

[0044] The construction steps for the screw-type prestressed precast radial beam-slab wind turbine foundation are as follows:

[0045] Step 1: Excavate the installation pit for the wind turbine foundation according to the design drawings, and complete the cable duct laying path at the same time. Continue to excavate to a certain depth within a circular area with the outer diameter of the middle pier 101 of the beam-pier composite precast component 1 as the diameter, reserving construction space for the anchor plate 6 and vertical anchor bolts 5 at the bottom. For areas with poor geological conditions, a foundation layer needs to be poured. When pouring the foundation layer, first pour the area outside the middle pier. After the anchor plate 6 and vertical anchor bolts 5 are installed, pour the middle low-lying area (i.e., the construction space) to the same elevation as the top of the base slab.

[0046] Step 2: Assemble the precast beam-pier composite component 1. First, position each precast beam-pier composite component 1. Before assembling the precast beam-pier composite component 1, clean the surface of the pad layer and the foundation interface, and apply a certain thickness of structural adhesive material. Then, assemble each precast beam-pier composite component 1 in the design position.

[0047] Step 3: After the precast beam-pier assembly is completed, begin installing the horizontal anchor rods 3. Place the anchor plate 2 at the designated height within the hollow area enclosed by the central pier 101. Connect the horizontal anchor rod 3 to the anchor plate 2 through the horizontal pre-drilled holes 102 in the precast beam-pier assembly 1 and fix it in place. Install the anchor rods layer by layer from low to high. After all the horizontal anchor rods 3 are installed, tension them at the anchoring end on the other side of the precast beam-pier assembly 1. During tensioning, ensure that tensioning is performed simultaneously on both sides to ensure overall stress balance of the wind turbine foundation.

[0048] Step 4: Clean the foundation interface, insert the concrete connecting plate 4 into the horizontal groove 106 of the bottom plate of the beam-pier composite precast component, and apply structural adhesive material.

[0049] Step 5: After the horizontal anchor bolts 3 and concrete connecting plates 4 are installed, the vertical anchor bolts 5 are installed. The bottom anchor plate 6 can be supported by a bracket. After the vertical anchor bolts 5 and the bottom anchor plate 6 are fixed and locked, the bracket can be removed. The top anchor plate 6 and the wind turbine tower flange are installed. The upper end of the vertical anchor bolts is tensioned to achieve the prestress value required by the design.

[0050] Step 6: After the prestress values ​​of each part reach the design requirements, backfill the foundation. When backfilling, only backfill the area of ​​the beam and slab of the beam-pier composite precast component 1. The inner side of the middle pier can remain hollow. A steel structure operating platform can be set up inside the tower at the top of the wind turbine foundation. If necessary, maintenance, inspection and monitoring work can be carried out by entering the middle pier at the bottom of the foundation through the inside of the tower.

[0051] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A screw-type prestressed precast radial beam-slab wind turbine foundation, characterized in that, The precast beam-pier assembly includes a beam-pier precast component (1), an anchor plate (2), a horizontal anchor rod (3), a connecting plate (4), a vertical anchor bolt (5), and an anchor plate (6). The beam-pier precast component is a component composed of a middle pier (101), a main beam, and a bottom plate (105). The beam-pier precast component has a fan-shaped feature and can form a hollow ring foundation structure by arranging and splicing multiple beam-pier precast components in a ring. The connecting plate (4) is set between two adjacent beam-pier precast components (1) and connected by a horizontal groove socket. The beam-pier precast component is provided with multiple horizontal and vertical anchor bolt reserved holes for arranging horizontal anchor rods and vertical anchor bolts. The end of the horizontal anchor rod near the middle pier is fixed to the anchor plate and is fixed to the beam-pier precast component after applying prestress from the other end. The anchor plate (2) is disc-shaped and has a threaded hole (201) on the side. The end of the horizontal anchor rod (3) is also provided with a thread of matching size. The anchor plate is placed at a specified height in the inner hollow area enclosed by the middle pier. The horizontal anchor rod is connected to the anchor plate and fixed through the horizontal reserved hole of the beam-pier prefabricated component. The two are connected by threads.

2. The screw-type prestressed radial beam-slab wind turbine foundation according to claim 1, characterized in that: The main beam of the beam-pier precast component is connected to the middle part of the circumference of the middle pier as a whole; in the radial direction, the middle part of the main beam is provided with a step, and the surface of the step is provided with horizontal anchor bolt reserved holes (102). The horizontal anchor bolt reserved holes (102) are arranged radially, passing through the main beam and the middle pier and aligning with the center of the foundation.

3. The screw-type prestressed radial beam-slab wind turbine foundation according to claim 1, characterized in that: The middle pier (101) of the beam-pier prefabricated component (1) is provided with a vertical anchor bolt reserved hole (103). The vertical anchor bolt reserved hole (103) is arranged in a ring around the center of the foundation, passes through the middle pier, and grooves (104) are provided at the top and bottom of the middle pier at the corresponding positions for the installation and positioning of the top anchor plate (6) and the bottom anchor plate (6).

4. The screw-type prestressed radial beam-slab wind turbine foundation according to claim 1, characterized in that: In the radial direction, the base plate (105) is located on both sides of the bottom of the main beam. The base plate (105) starts from the side of the middle pier and extends to the outer edge of the main beam. The side of the base plate has a fan-shaped side forming a beam-pier composite prefabricated component. Furthermore, a cut parallel to the main beam is formed at the outer edge of the middle of the main beam. A horizontal groove (106) is provided at the cut for the connection plate (4) to be socketed.

5. A screw-type prestressed radial beam-slab wind turbine foundation according to claim 4, characterized in that: The side of the connecting plate (4) is provided with a protrusion (401) that matches the groove (106) of the bottom plate cut. The connecting plate (4) is connected to the beam-pier precast component (1) through the protrusion. The connecting plate (4) is flush with the bottom plate (105) of the beam-pier precast component (1).

6. The screw-type prestressed radial beam-slab wind turbine foundation according to claim 3, characterized in that: The connection between the precast beam-pier assembly (1) and the upper wind turbine tower flange is achieved by vertical anchor bolts (5) passing through the vertical reserved hole (103) of the middle pier, anchoring to the top anchor plate (6) and the bottom anchor plate (6), and applying prestress tensioning for fixation.

7. A construction method for a prestressed radial beam-slab foundation for a screw-driven wind turbine, characterized in that: The steps for constructing a screw-prestressed precast radial beam-slab wind turbine foundation as described in any one of claims 1-6 are as follows: Step 1: Excavate the installation pit for the wind turbine foundation according to the design drawings, and complete the cable duct laying path at the same time. Continue to excavate to a certain depth within a circular area with the outer diameter of the middle pier of the beam-pier composite precast component as the diameter, and reserve the construction space for the anchor plate and vertical anchor bolts at the bottom. For areas with poor geological conditions, a cushion layer needs to be poured. When pouring the cushion layer, first pour the area outside the middle pier. After the anchor plate and vertical anchor bolts are installed, pour the middle low-lying area to the same elevation as the top of the bottom slab. Step 2: Assemble the precast beam-pier composite components. First, position each precast beam-pier composite component. Before assembling the precast beam-pier composite component 1, clean the surface of the pad layer and the foundation interface, and apply a certain thickness of structural adhesive material. Then, assemble each precast beam-pier composite component in the design position. Step 3: After the beam-pier prefabricated components are assembled, begin installing the horizontal anchor bolts. Place the anchor plate at the designated height in the hollow area enclosed by the middle pier. Connect the horizontal anchor bolts to the anchor plate through the horizontal pre-drilled holes in the beam-pier prefabricated components and fix them in place. Complete the installation layer by layer from low to high. After all the horizontal anchor bolts are installed, tension and fix them at the anchoring end on the other side of the beam-pier prefabricated components. When tensioning, the opposite side must be tensioned simultaneously to ensure the overall force balance of the wind turbine foundation. Step 4: Clean the foundation interface, insert the concrete connecting plate into the horizontal groove of the bottom plate of the beam-pier composite precast component, and apply structural adhesive. Step 5: After the horizontal anchor bolts and concrete connecting plates are installed, the vertical anchor bolts are installed. After the vertical anchor bolts (5) are fixed and locked to the bottom anchor plate, the top anchor plate and wind turbine tower flange are installed, and the upper end of the vertical anchor bolts is tensioned to achieve the prestress value required by the design. Step 6: After the prestress values ​​of each part reach the design requirements, backfill the foundation.

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