Patent Application
20180171575
The present invention relates to tower foundations and particularly to foundations of wind turbine towers.
A known configuration of the foundation of wind turbine towers comprises a base slab, a pedestal (in which the tower is supported) and radial walls extending from the pedestal to the edge of the base slab.
Given the situation away from the urban centers of wind turbine towers and the size of the foundation its construction by in-situ concreting methods poses several problems that have led to a number of proposals of construction methods using prefabricated elements as those described in US 2007/181767 A1, WO 2008/036934 A1 and WO 2015/124815 A1.
Proposals to reduce the size of the foundation are also known such as that described in WO 2010/138978 A1 in which a three dimensional network of post-tensioning elements to achieve a desirable combination of high stiffness and greater fatigue resistance is used. The foundation design reduces the weight and volume of materials used, reduces cost, and improves heat dissipation conditions during construction by having a small ratio of concrete mass to surface area thus eliminating the risk of thermal cracking due to heat of hydration.
However, the construction of foundations of wind turbine towers (and other type of towers) by in-situ concreting methods has the great advantage that a monolithic structure is achieved so that the industry demands foundation construction methods that solve the problems of known in-situ construction methods, particularly the high cost of the curing step.
The invention provides an in-situ concreting construction method of tower foundations (particularly wind turbine tower foundations) configured by a base slab, a pedestal and a plurality of radial walls extending from the pedestal towards the outer edge of the base slab.
Relevant steps of the construction method are the placing in position of the anchor cage of the pedestal using leveling legs and the curing of the foundation supplying water in an automatically controlled mode to the foundation from a plurality of water emitters arranged in water distribution pipes placed over predetermined locations of the foundation.
A tower foundation constructed with the method of the invention can be configured with a base slab with a circular or a polygonal shape and having a uniform thickness or a decreasing thickness between the pedestal and its outer edge, with a pedestal of a cylindrical or a prismatic shape, and with radial walls of a prismatic-triangular shape having a uniform thickness or a decreasing thickness along its length or radial walls of prismatic-trapezoidal shape leaving a void space between them and both the pedestal and the base slab.
Said configurations provide suitable options for choosing the configuration of the foundation having a better ratio steel/concrete taking into account their market prices.
Other characteristics and advantages of the present invention will be clear from the following detailed description of embodiments illustrative of its object in relation to the attached drawings.
Construction Method
The construction method of the invention is applicable to a foundation 10 of a tower configured by a circular base slab 11, a cylindrical pedestal 13 and a plurality of prismatic-triangular radial walls 15 extending from the cylindrical pedestal 13 towards the outer edge of the base slab 11 (see
The construction method of the invention comprises the following main steps (see
a) Preparation of the Site
The site is cleared of trees, shrubs and all objectionable material which will interfere the construction.
The excavation of foundation is carried out by excavator machine to the exact length, thickness, depth and profile required.
The bottom of excavation is slightly watered and thoroughly rammed.
Thereafter plain cement concrete is laid to form a pavement 25 and, at least 12 hours, are needed for setting. During that period no works are performed over the pavement 25.
b) Placing the Anchor Cage and the Reinforcement
The anchor cage 21, that comprises a lower flanges 33, a plurality of bolts 35 and cooperating nuts to fasten them to flange 33 is assembled and placed in position with the aid of leveling legs 37 with base plates 39 (see
Firstly, the position of the base plates 39 is marked on the pavement 25.
Secondly, the leveling legs 37 with the base plates 39 are fixed to the pavement 25.
Thirdly, the lower flange 33 is introduced on the leveling legs 37, a first set of guide bolts 35 are positioned and tightened to the lower flange 33. Then the remaining bolts 35 are placed in the lower flange 33. A torque minimum preload is applied to the nuts positioned under the lower flange 33 using a wrench.
The reinforcement 41 of the base slab 11, the reinforcement 43 of the pedestal 13 and the reinforcement 45 of the radial walls 15 are positioned in place firmly wired (see
Reinforcements 41, 43, 45 shall have the required cover and where not specified the thickness of cover shall be a minimum of 50 mm.
c) Formwork
The formwork panels shall be adequately strutted, braced and propped to prevent deflection under deadweight concrete and superimposed live load of work men, materials and to withstand vibration and wind.
d) Concreting
A pump shall be preferably used to deliver concrete of the required consistency and plasticity without segregation or loss of slump.
Pouring of concrete will start in a circular way from the edges of the foundation and in layers with a thickness of 30 cm approximately.
The concrete will be compacted to achieve maximum density using mechanical vibrators. The minimum diameter of the vibrator needle for raft concrete is 60 mm. However smaller diameter vibrator needle also can be used for the congested reinforcement areas around embedment.
e) Formwork Stripping
The formwork panels shall be removed after a predetermined period from the finishing time of concrete pouring.
f) Curing
After the formwork stripping, the exposed concrete surfaces shall be properly cured keeping them constantly wet for at least 10 days, a period that can be extended by maintaining the concrete in a damp condition for an additional period depending on 7th day cube test results. The vertical side of the concrete surfaces shall be covered by wet gunny bags tied with ropes all around.
Unlike known curing methods, the invention contemplates the use of an automatic curing system by means of a water supply system that is installed on the foundation immediately after the formwork stripping.
In an embodiment the water supply system comprises (see
In an embodiment, the distribution pipes 55, 57 are PVC pipes of 1.5 inches with water emitters 59 (having typically a diameter of 2 mm) placed 1 m apart from each other.
One advantage of this curing method is that allows reducing manpower costs and ensures that curing is perfectly done and hence a quality foundation can be achieved because it can be assured that all locations of the foundation are effectively cured. On the other hand water losses are avoided.
These advantages are particularly relevant for curing the vertical faces of the foundation 10.
g) Backfilling and Grouting
Once the curing is completed, backfilling can be proceeded layer wise with each layer of backfilling not exceeding 300 mm thickness after each layer of backfilling. Necessary tests are conducted to ensure that backfilling has achieved the required density. The grouting can be done only once the concreting is completed.
Foundation Configurations
The construction method of the invention is also applicable to tower foundations having different configurations to that shown in
Foundations where the pedestal 13 is configured with a prismatic shape instead of a cylindrical shape and/or where the base slab 11 is configured with a polygonal shape (see
Foundations with a different ratio steel/concrete than that of the embodiment shown in
In the first case, the reduction of the ratio steel/concrete of the foundation 10 is achieved with radial walls 15 having a variable thickness from the pedestal 13 to the outer edge of the base slab 11.
In the second case, the reduction of the ratio steel/concrete of the foundation 10 is achieved with a base slab 11 having a variable thickness from the pedestal 13 to its outer edge.
A combination of the configurations shown in
An increase of the ratio steel/concrete can be achieved with the configuration shown in
Although the present invention has been described in connection with various embodiments, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, are within the scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201600833 | Dec 2016 | ES | national |
