Foundations system for towers and method for installing the foundations system for towers

Abstract

Foundation system for towers, especially for onshore wind turbines, comprising a central shaft buried or partially buried, preferably hollow and formed by dowels made from precast concrete, an essentially flat lower slab and completely buried, and lateral support means in the form of inclined struts that are joined at their upper end with the central shaft and at its lower end with the lower slab, and that are preferably entirely buried. The wind tower is located on the partly buried main shaft. The foundation system may comprise other lower elements connected with the lower slab, such as radial ribs or peripheral beams. The struts are preferably prefabricated elements incorporating an efficient and economical connection system by pre-stressing. The foundation system maximizes the fraction of the weight of the foundation by gravity generated by soil or ballast material, allowing an important economy in the structural materials of the foundation.

Claims

1. A foundation system for towers, comprising: a central shaft placed below a base of tower so that a central vertical axis of the central shaft is essentially coincident with a vertical axis of the tower, and the central shaft is totally or partially buried in an installed condition, a lower slab made essentially of reinforced or pre-stressed concrete, placed below the central shaft so that it is fully buried in an installed condition and whose configuration is essentially flat, so that the maximum horizontal dimension exceeds its maximum vertical dimension, and a lateral support, which is totally or partially buried in an installed condition, and comprises at least three struts connected at their upper end to the central shaft or the tower and connected at their lower end to the lower slab, said struts having a linear or inclined configuration, whose longitudinal dimension exceeds the maximum transverse dimension and both ends are at different levels, such that the upper end is closer to the vertical axis of the tower than the lower end, wherein a connection between at least one of the struts and the central shaft or the tower comprises at least one pre-stressing cable, a part of which is housed in a sheath of the strut attached by the connection, said sheath being essentially parallel to a longitudinal axis of said strut attached by the connection; wherein said pre-stressing cable penetrates inside the central shaft or the tower, thereby connecting the strut and the central shaft or the tower at a level of said shaft or the tower which, in the installed condition of the foundation, is above the ground, wherein the central shaft is hallow and comprises a substantially horizontal and flat upper closing slab, which remains connected with a wall of the central shaft and that is prefabricated or built in-situ with concrete, steel, or a combination thereof; and wherein a hollow space inside the central shaft is delimited at the top by said upper closing slab, which is in turn delimited at the bottom by the lower slab and that can be filled with ballast material, wherein the level or height of said upper closing slab is essentially coincident with the level or height of at least one protrusion connecting the upper end of one of the at least three struts and the central shaft, wherein the struts, the lower slab and any of the shaft or the tower are arranged such that they define a hollow area therebetween that can be filled, completely or partially, with ballast material to be disposed on the lower slab to provide weight to the assembly, and wherein the hollow area coincides with a plane defined by the longitudinal axis of the strut and the vertical axis of the tower, and wherein an area in which the hollow area coincides with the plane defined by the longitudinal axis of the strut and the vertical axis of the tower can be filled with the ballast material to be disposed on the lower slab.

2. The foundation system for towers according to claim 1 further comprising at least one rib having linear configuration, with two ends and whose maximum longitudinal dimension is greater than its maximum transverse dimension, which remains attached to the lower end of at least one of the struts and the lower slab and which projects laterally so that at least one end is furthest from the vertical axis of the tower than the rest of non-end points of the at least one rib.

3. The foundation system for towers according to claim 1 further comprising at least one peripheral, top or bottom beam of linear configuration and whose maximum longitudinal dimension is greater than its maximum transverse dimension, which remains attached to the lower slab and to at least one rib or one of the at least three struts; said peripheral beam being arranged essentially circumferentially such that is kept apart from the central shaft and its position in relation to the center of the lower slab is not radial.

4. The foundation system according to claim 1, wherein the lower end of at least one of the at least three struts remains connected to at least one lower element of the foundation system, which is selected from the group consisting of lower slab, at least one rib, and a peripheral beam, delimiting one essentially triangular and hollow area which is situated between the central shaft, the lower slab and each of the at least three struts.

5. The foundation system for towers according to claim 1, wherein at least one member selected from the group consisting of at least one strut of the at least three struts, at least one rib, and a peripheral beam is integrated in a single integral support piece which is connected to the central shaft or the tower by joints.

6. The foundation system for towers according to claim 5, wherein the pre-stressing cable longitudinally crosses the one of the at least three struts and is used for attaching the lower end of one of the at least three struts or the integral support piece with at least one lower element of the foundation system.

7. The foundation system for towers according to claim 1, wherein the lower end of one of the at least three struts or an integral support piece containing said one of the at least three struts is connected to at least one lower element of the foundation system, which is selected from the group consisting of the lower slab, at least one rib, and a peripheral beam, via at least one protrusion and pre-stressing system comprising the at least one pre-stressing cable, a part of which is housed in the sheath of the one of the at least three struts which is essentially parallel to the longitudinal axis of said one of the at least three struts; and wherein said pre-stressing cable penetrates into said at least one lower element across the surface of the at least one protrusion between said lower structural element and the lower end of the one of the at least three struts or between said at least one lower element and the integral support piece containing said one of the at least three struts; wherein an anchorage of the lower end of the pre-stressing cable is housed in the at least one lower element of the foundation system.

8. A wind turbine and/or wind tower employing a foundation system according to claim 1.

9. The foundation system for towers according to claim 1, wherein the struts are strap-type tensioning struts.

10. A method for installing a foundation system for towers wherein the foundation system for towers comprises: a central shaft placed below a base of tower so that a central vertical axis of the central shaft is essentially coincident with a vertical axis of the tower, and the central shaft is totally or partially buried in an installed condition, a lower slab made essentially of reinforced or pre-stressed concrete, placed below the central shaft so that it is fully buried in an installed condition and whose configuration is essentially flat, so that the maximum horizontal dimension exceeds its maximum vertical dimension, and a lateral support, which is totally or partially buried in an installed condition, and comprises at least three struts connected at their upper end to the central shaft or the tower and connected at their lower end to the lower slab, said struts having a linear or inclined configuration, whose longitudinal dimension exceeds the maximum transverse dimension and both ends are at different levels, such that the upper end is closer to the vertical axis of the tower than the lower end, wherein a connection between at least one of the struts and the central shaft or the tower comprises at least one pre-stressing cable, a part of which is housed in a sheath of the strut attached by the connection, said sheath being essentially parallel to a longitudinal axis of said strut attached by the connection; wherein said pre-stressing cable penetrates inside the central shaft or the tower, thereby connecting the strut and the central shaft or the tower at a level of said shaft or the tower which, in the installed condition of the foundation, is above the ground, wherein the central shaft is hallow and comprises a substantially horizontal and flat upper closing slab, which remains connected with a wall of the central shaft and that is prefabricated or built in-situ with concrete, steel, or a combination thereof; and wherein a hollow space inside the central shaft is delimited at the top by said upper closing slab, which is in turn delimited at the bottom by the lower slab and that can be filled with ballast material, wherein the level or height of said upper closing slab is essentially coincident with the level or height of at least one protrusion connecting the upper end of one of the at least three struts and the central shaft, wherein the struts, the lower slab and any of the shaft or the tower are arranged such that they define a hollow area therebetween that can be filled, completely or partially, with ballast material to be disposed on the lower slab to provide weight to the assembly, and wherein the hollow area coincides with a plane defined by the longitudinal axis of the strut and the vertical axis of the tower, and wherein an area in which the hollow area coincides with the plane defined by the longitudinal axis of the strut and the vertical axis of the tower can be filled with the ballast material to be disposed on the lower slab, wherein the method comprises in any technically possible order the following steps: a) Excavating and preparing the ground for supporting the foundation; b) Placement of passive or active (pre-stressed) armor containing the lower slab, either by separated elements or by modules or rebar cages (armor) previously preassembled; c) Construction or installation of at least part of the central shaft; d) Filling with soil on the lower slab until it is completely buried; and further comprising, after step c) and in any order, the steps: e) Connecting the central shaft with the lower slab; f) Connecting the tower with the central shaft; g) Connecting the at least three struts with the central shaft or with the tower; and wherein further comprises, before step g), the step of: h) Constructing or mounting the at least three struts and at least one rib or a peripheral beam; and further comprising, after step b) and before step d), the step: i) Concreting the lower slab.

11. The installation method according to claim 10 of a foundation system for towers comprising at least one prefabricated element either the at least three struts, the at least one rib, the peripheral beam, parts of the central shaft, wherein the method further comprises, before step d), the step: j) Prefabrication and transportation to the site of the at least one prefabricated element of the foundation system.

12. The installation method according to claim 10 of a foundation system for towers comprising the at least one rib or the peripheral beam located below the lower slab, wherein the method further comprises, before step i), step of: m) Digging at least one trench at the excavation bottom of the foundation system for receiving the at least one rib or the peripheral beam, said trench being susceptible of acting as formwork against the ground if said at least one rib or the peripheral beam is constructed from in-situ concrete.

13. The installation method according to claim 10, wherein the at least one rib or integral parts of the at least one rib are prefabricated, and the method further comprises, before step i), the step of: n) placing template formwork acting as lateral formwork in the central zone with increased thickness (or the central shaft constructed from in-situ concrete), wherein time acts as a template element for positioning or fastening of the prefabricated at least one rib or the prefabricated integral parts comprising said at least one rib.

14. The installation method according to claim 10 of a foundation system for towers comprising the pre-stressing system for joining the at least one strut of the at least three struts or an integral support piece which integrates said at least one strut of the at least three strut, with the central shaft and with at least one lower element of the foundation system, either the lower slab, at least one rib or a peripheral beam, said pre-stressing system comprising at least: the pre-stressing cable that in an installed condition longitudinally crosses said at least one strut of the at least three struts, so that its upper end protrudes from the at least one strut of the at least three struts and penetrates into the central shaft or inside the upper closing slab of the central shaft, and its lower end protrudes from said strut and penetrates into a lower element of the foundation system; wherein the sheath that houses part of the at least one pre-stressing cable longitudinally crosses said at least one strut of the at least three struts and in a final status houses part of said pre-stressing cable; an anchorage of the upper end of the pre-stressing cable which is placed in the central shaft upper closing slab of the central shaft; a second sheath, with one or several aligned sections, which allows the passage of the pre-stressing cable from the upper end of said strut to said anchorage through the central shaft or the upper closing slab; an anchorage of the lower end of the pre-stressing cable which is placed at a lower element of the foundation system; a third sheath, with one or several aligned sections, which allows the passage of the pre-stressing cable from the lower end of said at least one strut of the at least three struts to said anchorage through at least one lower element of the foundation system which may or may not be integrated with said strut at an integral support piece; said method being wherein it further comprises, after step h), the steps of: q) threading said pre-stressing cable, either top-down or bottom-up, through the sheath, the second sheath, and the third sheath provided in the element the cable crosses; r) fixing the pre-stressing cable to one of said anchorages, applying tension to the pre-stressing cable, and then fixing the other anchorage; s) optionally, filling at least part of the sheath, the second sheath, or the third sheath with material for protecting the pre-stressing cable or for its adherence to the elements it crosses.

15. The foundation system for towers according to claim 1, wherein the hollow area is triangular.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other advantages and features will be better below stood from the following detailed description of exemplary embodiments with reference to the accompanying drawings, that must be considered as illustrative and not limiting, in which:

(2) FIG. 1 illustrates the most basic foundation system for towers according to the invention;

(3) FIG. 2 shows a foundation system for towers according to the invention comprising several ribs;

(4) FIG. 3 shows a foundation system for towers according to the invention comprising an upper peripheral beam and wherein the central shaft is constructed with prefabricated rings;

(5) FIG. 4a) illustrates a foundation system for towers according to the invention comprising several integral support pieces (including a strut and a rib) and a lower peripheral beam;

(6) FIG. 4b) shows an enlarged sectional view of an integral support piece attached to the central shaft, to the lower slab and the lower peripheral beam of a foundation system for towers according to the invention;

(7) FIG. 4c) shows a view of the dowel shaped prefabricated pieces that form the central shaft of the foundation system shown in FIG. 4a).

(8) FIG. 5 illustrates a foundation system for towers according to the invention in which the lower slab comprises a central zone of increased thickness.

(9) FIG. 6 shows a foundation system according to the invention comprising an upper closing slab;

(10) FIG. 7 shows an embodiment in which the central shaft comprises an upper closing slab and two prefabricated rings, one of which is located above the upper closing slab.

(11) FIG. 8 shows an embodiment in which the central shaft is prefabricated and extends above the ground level as a pedestal for the tower, and in which said lateral support means are ribs.

(12) FIG. 9 shows an embodiment with integral support pieces comprising two struts and a peripheral beam.

(13) FIG. 10 shows a cross section of an embodiment in which a pre-stressing system for connecting the strut with the central shaft and with the lower elements of the foundation system is used.

(14) FIG. 11 shows an embodiment in which the central shaft comprises an upper closing slab, through which the connection with the tower is made;

(15) FIG. 12 shows an embodiment as in FIG. 11, wherein the central shaft and the struts extend above the ground level as a pedestal for the tower, with two alternatives with respect to the path of the pre-stressing cable.

(16) FIG. 13 shows several stages of an installation method of the foundation system according to the invention;

(17) FIG. 14 shows a detail of the installation method of the pre-stressing system for connecting a strut to the central shaft of the foundation system;

(18) FIG. 15 shows several stages of an installation method of foundation system according to the invention;

(19) FIG. 16 shows an embodiment with a polygonal and star geometry of the lower slab and pre-stressed strap type struts.

(20) FIG. 17 shows an embodiment with a lower slab comprising a central module and four external modules with pre-stressed strap type struts.

DETAILED DESCRIPTION OF AN EMBODIMENT

(21) FIG. 1 shows the tower foundation system according to the invention in which it can be seen that there are the following elements: a central shaft (1) mostly buried, a lower slab (4) completely buried and lateral support means comprising, in this case six struts (2) also completely buried.

(22) The central shaft (1) is located below the base of the tower (24) so that, preferably, its central vertical axis is essentially coincident with the vertical axis (22) of the tower (24), which in this case it is a tubular metal tower.

(23) The central shaft (1) is cylindrical in this embodiment, but it can be of any shape, and it can be, without being an exhaustive list, circular, polygonal, cylindrical, tapered or with variable tilting of the walls. Also, this central shaft (1) can also be hollow or solid.

(24) The lower slab (4) is located below the central shaft (1) so that, preferably, its center is essentially coincident with the vertical axis of the tower (24) and is completely buried in an installed condition. This lower slab (4) has in this case has a circular plan and is substantially flat. The lower slab (4) may be of constant thickness or may have changing thickness zones as in this case, in which the lower slab has zones of increased thickness at the junctions with the struts (2) acting as a capital.

(25) Said lateral support means are attached in this embodiment both to the central shaft (1) and the lower slab (4) and are buried in an installed condition, but it can also be only partially buried. This lateral support means comprises struts (2) are elements with a linear and inclined configuration, whose longitudinal dimension exceeds its maximum transverse dimension and whose both ends are at a different level, thus defining an upper end and a lower end. The upper end, which is closer to the vertical axis of the tower (24) than the lower end, is connected to the central shaft (1) through attachments.

(26) The struts shown in the embodiment of FIG. 1 are of constant section, but they can also be of variable section, in particular for increasing their dimensions at their ends for connection to the central shaft (1) or lower elements (39) of the foundation system.

(27) This central shaft (1) preferably also comprises at least one protrusion (34) whose position matches one of the joints connecting the strut (2) with the central shaft (1) and whose geometry is such that, in a manner essentially perpendicular to the longitudinal axis of the strut (2), generates a surface for contact or attachment between the central shaft (1) and the strut (2). This protrusion (34) can be obtained through a thickened portion in the wall of the central shaft (1).

(28) Preferably, as in the embodiment shown in FIG. 1, the elements of the foundation system are of reinforced or pre-stressed concrete, which provides high structural ability, durability and reduced susceptibility to fatigue, and can facilitate the prefabrication of such elements.

(29) FIG. 2 shows another preferred embodiment of the foundation system for towers according to the invention comprising at least one rib (3), of linear configuration, with two ends and whose longitudinal dimension exceeds its maximum transversal dimension. The rib (3) is attached to the lower end of a strut (2) and to the lower slab (4); in this case, the ribs (3) are located above the lower slab (4), but they can also be below it. This rib (3) projects laterally so that at least one end is furthest from the vertical axis of the tower than the other non-end end points of the rib (3), preferably in radial direction.

(30) FIG. 3 shows another preferred embodiment of the foundation system for towers according to the invention which is also provided with a peripheral beam (9), in this case an upper one (11), that is, above the lower slab (4); said peripheral beam (9) is of linear configuration and is joined by one side to the lower slab (4) and in this case to the ribs (3). This peripheral beam (9) is preferably placed with a circumferential shape, so that is it kept separated from the central shaft (1) and with a non-radial positioning in relation to the lower slab (4). In this embodiment, the peripheral beams (9) are rectilinear and of constant depth, but their geometry can also be curvilinear or polygonal and their edge can be variable.

(31) Although the geometry of the lower slab (4) is preferably circular, as shown in FIG. 3 among others, it may take any form, as in this case polygonal. Also in FIG. 3 it can seen that the lower slab (4) can have a central increased thickness (27) in which in this case both the central shaft (1) and the ribs (3) are joined.

(32) In this FIG. 3 it can also be seen that the central shaft (1) is constructed from prefabricated dowels (13) connected by essentially vertical joints (18) according to any of the forms used in the prior art, and/or prefabricated rings (19) joined by essentially horizontal joints (20) of any of the forms used in the prior art, thereby facilitating greatly the transportation and installation of the central shaft (1). Alternatively, the central shaft (1) may be of a single piece of metal or concrete, prefabricated or concreted in-situ.

(33) Finally, in FIG. 3 it can be seen that the central shaft (1) can include a step or door (26), thus avoiding the tower (24) to include a door, which simplifies and cheapens its construction. It is also possible that the central shaft has other steps to allow access inside it during the installation process.

(34) Meanwhile, FIG. 4a illustrates a foundation system for towers according to the invention in which the peripheral beam (9) is a lower one (10), that is, it is placed below the lower slab (4). Also in this FIG. 4a the strut (2) and the rib (3) form part of an integral support piece (15) and the lower slab (4) comprises a central zone of increased thickness (27), in which the central shaft (1) rests, with a thickness greater than the part of the lower slab (4) surrounding it, generating a peripheral side wall of said area (27) which is connected laterally at least to one rib (3), which in this case is part of an integral support piece (15).

(35) Also, in FIG. 4a it can be seen that the central shaft (1) of the foundation system is likely to be extended above the ground level (12) so as to be partially buried. Thus, the central shaft acts as a pedestal with increased capacity and robustness that can raise from the support level of the base of the tower (24), in this case metallic, which finely may permit increasing the height of the wind turbine and thereby increasing the energy production without need for taller towers.

(36) FIG. 4b shows a sectioned and enlarged view of the integral support piece (15) which integrates a strut (2) and a rib (3) and which is connected both to the central shaft (1) through the protrusion (34) and to the lower slab (4). It can be appreciated that all the lower elements (39) of the foundation system are buried. In this case the integral support piece (15) is also completely buried.

(37) In FIG. 4c is shown from two perspectives one of the dowels (13) of precast concrete forming part of the central shaft (1) and which joins to other dowels through a vertical joint (18). It can be appreciated that such dowels can include reinforced or thickened areas, and in particular the protrusions (34) for joining the central shaft (1) to the struts (2) can be seen.

(38) The lower end of the strut (2) is connected to a lower element (39) of the foundation system, either the lower slab (4), a rib (3) or a peripheral beam (9) and delimiting a hollow and essentially triangular area between the central shaft (1), the lower slab (4) and each strut (2) (and, where appropriate, each rib (3)).

(39) It should be noted that the lower slab (4) serving for supporting the central shaft (1) also aims to make integral the different struts (2) and/or ribs (3) and/or integral support pieces (15) for providing a greater stability to the system of the invention and spreading and distributing the load to the ground (12). Also, the main objective of the peripheral beam (9) is reducing the flexion of the lower slab (4) collected between the struts (2) and/or ribs (3) and/or integral support pieces (15).

(40) In FIG. 5 a foundation system for towers according to the invention is illustrated, in which the peripheral beams (9), in this case upper beams (11) are joined just to one rib (3) in addition to the lower slab (4).

(41) In the embodiment illustrated in FIG. 5, the tower (24) is a tower of precast concrete, which has one or more essentially tubular sections formed by prefabricated dowels and the central shaft (1) which is buried in a length more than 2 m, can replace or take the place of the lower section of the tower (24).

(42) In another preferred embodiment of the foundation system for towers, shown in FIG. 6, the central shaft (1) further comprises an upper closing slab (14), which in all or part of its perimeter is connected to the internal face of the wall of the central shaft (1), which in this case is hollow. The upper closing slab (14) limit sat the top a hollow space inside the central shaft (1), which is in turn limited at the bottom by the lower slab (4) and which is capable of being filled with ballast material. Preferably, this upper closing slab (14) is essentially flat and horizontal, made from in-situ or precast concrete, and it is placed at the level of the joints connecting the upper ends of the struts (2) and the central shaft (1).

(43) In the embodiment shown in FIG. 6 is shown as in previous figures that the central shaft (1) extends above the level of the ground acting as a pedestal or lower tower section (24). In these cases, as shown in the figure, preferably the central shaft (1) maintain a cylindrical shape below the attachment level with the struts (2), and may instead adopt a frustoconical geometry, allowing to be adapted to the most appropriate diameters to adequately withstand the stresses and for its connection to the base of the tower (24).

(44) Similarly, FIG. 6 shows that the section of the ribs (3) can adopt variable and irregular geometries, as in this case where the rib section (3) has inverted T shape for a better transfer of stresses with the lower slab (4).

(45) In FIG. 7 another preferred embodiment of the invention is shown, in which as in FIG. 6 the central shaft (1) is hollow, comprises an upper closing slab (14) and extends above the ground level as a pedestal of the tower (24). As in FIG. 6, the upper closing slab (14) transversely crosses inside the central shaft (1) and is at the same level than the upper ends of the struts (2) to which is joined.

(46) Similarly, FIG. 7 shows that the central shaft (1) comprises two prefabricated rings (19) lying respectively above and below the upper closing slab (14) and forming the corresponding horizontal joints (20) in the central shaft (1). These rings are preferably prefabricated pieces, but they can also be built on site.

(47) In FIG. 8 an embodiment of the invention is shown, wherein the partially buried center shaft (1) is hollow and is formed from dowels (13) made of precast concrete, and wherein said lateral support means are ribs buried with linear joints of both the central shaft (1) and the lower slab (4).

(48) In FIG. 9 another embodiment of the present invention is illustrated, in this case with integral support pieces (15) each comprising two struts (2) and a peripheral beam (9).

(49) In FIG. 10 another preferred embodiment of the foundation system for towers is shown, in which the joining of the integral support piece (15) with the central shaft (1) and with the lower elements (39) of the foundation system is made by a pre-stressing system. Said integral support piece (15) comprises in this case a strut (2) and a rib (3). Preferably, this pre-stressing system comprises at least one pre-stressing cable (5), or a pre-stressing bar, a part of which is housed in a sheath (6) of the strut (2), and enters inside the central shaft by another sheath (7) of the central shaft (1). This pre-stressing cable (5) lengthwise crosses the strut (2) and crosses the rib (3) through a sheath (8) for attaching the integral support piece (15) with the lower slab (4) and/or the peripheral beam (9).

(50) The pre-stressing cable (5) of the pre-stressing system preferably crosses the wall of the central shaft (1), so that its upper end is connected to an anchorage (23) housed in the upper closing slab (14).

(51) Similarly, the lower end of the pre-stressing cable (5) is connected to an anchorage (29) housed in a lower element (39) of the foundation system, in this case a lower peripheral beam (9,10).

(52) In this FIG. 10 it can also be seen that the hollow central shaft (1) is filled with filler or ballast material (21).

(53) FIG. 11 illustrates another preferred embodiment of the invention wherein the central shaft (1) comprises a prefabricated ring (19) and an upper closing slab (14) through which the central shaft connection is made with the tower (24) and the struts (2)

(54) In FIG. 11 is also illustrated that a rib (3) may comprise different parts in the same linear element. In this case, each rib (3) has a farthest part from the axis of the tower that is prefabricated and forms part with a strut (2) of an integral supporting piece (15). In turn, each rib has another part closest to the axis of the tower which is connected with the area of increased thickness (27) of the lower slab and being built with in-situ concrete part, preferably as part of the concreting work of the lower slab (4).

(55) In FIG. 12a is shown another preferred embodiment of the invention analogous to that described in FIG. 11, with the difference that in this case the length in which the central shaft extends above the ground level is increased, as a taller pedestal for a tower (24).

(56) Similarly, in FIG. 12b is shown in cross section the embodiment shown in FIG. 12a, showing the pre-stressing system which contributes to the connection of the strut (2) with the central shaft (1,14) and with a lower element of the foundation system (39). The pre-stressing cable (5) is essentially parallel to the longitudinal axis of the strut, in the sense that it is placed longitudinally along the strut (2), but its layout can include certain twists or bends as shown in the figure, so that it is not exactly parallel to said axis. For example, two possible paths of said pre-stressing cable (5) are illustrated.

(57) FIG. 13 shows various stages of a method for installing a foundation system of an embodiment according to the invention as shown in FIG. 10, in which, as discussed above, the order of steps is not the only one. Thus, in the numbered letters of the procedural steps set out in previous sections, FIG. 13A illustrates the step a). FIG. 13b illustrates the step b), step m) and a first stage of step h). FIG. 13c shows step i) and a second stage of step h). The following steps c) and e) are shown in FIG. 13e. Subsequently performed steps: g), k), l), q) (consisting of threading the pre-stressing cable (5), either top down or bottom up through the sheaths (6, 7, 8) provided on the elements that the pre-stressing cable (5) crosses) and r) (consisting of fixing the pre-stressing cable (5) to one of the anchorages (23,29), applying tension to the pre-stressing cable (5) and then fixing it to the other anchorage (23,29)) that are shown in FIG. 13f. Finally, FIG. 13g shows the installed condition of the foundation system after steps d) and f).

(58) Specifically, FIG. 13a shows the excavation (37) and prior preparation of the ground.

(59) FIG. 13b shows the steps of laying the rebar (38) of the lower slab and the peripheral beams (9) that in this case are made of in-situ concrete. For the execution of these peripheral beams a trench (33) can be dug, which acts as formwork against the ground during the concreting of that peripheral beam (9).

(60) FIG. 13b also shows the process of placing the ribs (3) and the integral support pieces (15) comprising one strut (2) and one rib (3). In this case, all of them are made from precast concrete. For the placement of these elements adjustable support devices for adjusting their position may be employed. Also template means connecting with different prefabricated elements for controlling or maintaining a proper positioning can be used.

(61) FIG. 13c shows the concreting step of the lower slab (4), which makes integral and fixes all the prefabricated elements previously placed. In this case, the lower slab (4) has a central zone with increased thickness (27), for which concrete template formwork elements (28) are used, acting as lateral formwork of the central increased thickness (27) and at the same time acts as a template element for positioning and/or fastening of the prefabricated pieces of the ribs (3) or the integral parts (15).

(62) It must be noted that although in the method shown in FIG. 13 the concreting of the lower slab (4) is performed prior to the placement of the central shaft (1), it is possible to place the center shaft (1) before concreting, which may allow to adjust the position and fit the various prefabricated pieces before the concreting of the lower slab (4) that fixes them.

(63) FIG. 13d shows a step of the installation method corresponding to the assembly of prefabricated pieces of the struts (2), to which positioning and clamping fastening struts (17) can be used. Furthermore, in the figure sheaths (6) and sheaths (8) are also illustrated, which are arranged on struts (2) and ribs (3) respectively, which allow the housing of the pre-stressing system for connecting said pieces with the central shaft (1) and/or the lower elements (39) of the foundation system.

(64) FIG. 13e shows the assembly step of the central shaft (1) which in this embodiment consists of prefabricated sections (13) interconnected via vertical joints (18). The assembly of the central shaft (1) can be done mounting separately each dowel (13) in its final position, or can be done mounting previously the complete center shaft (1) in a different position to its final position, for mounting then said complete central shaft (1) into its final position. Previous assemblies of only part of the dowels or piece of the central shaft (1) can also be carried out in a different position to the final one.

(65) FIG. 13f shows the embodiment after completion of the steps of positioning and tensioning of the pre-stressing cables (5), filling with ballast material (21) inside the central shaft (1) and implementation of the upper closing slab (14). The pre-stressing cable (5) has upper anchorage elements (23) at its lower part (29), which in this case are in the upper closing slab (14) and in a lower element (39), respectively.

(66) Finally, FIG. 13g shows the installed condition of the foundation system, having disposed ballast material (21) above the lower slab (4), so that the lower slab and the other lower elements (39) of the foundation system are completely buried, and the central shaft (1) is partially buried. Also, the tower (24), in this case of tubular metal, is disposed and connected to the head of the central shaft (1).

(67) FIG. 14 shows a step in the method for installing a foundation system according to the invention; specifically the threading process of a cable (5) of the pre-stressing system for connecting a strut (2) of precast concrete with a central shaft (1) also of precast concrete.

(68) In FIG. 14a it can be seen that the cable (5) is prepositioned in a sheath (6) of the strut (2) so that its upper end protrudes. In this case, it has a curved opening (30) of the sheath (6) and with provisional securing means (31) of the pre-stressing cable, so that the cable can be provisionally maintained in a more vertical orientation than the axis of the strut (2).

(69) This allows, as shown in FIG. 14b, the cable (5) to be inserted through a sheath (7) in the wall of the central shaft (1) during its mounting process. To this end, the sheath (7) comprises in turn another curved opening (30).

(70) FIGS. 14c and 14d show the threading process of the cable, which in this case is assisted by the use of a guiding device (32); said device brings together the various strands that may be on the cable, and it has a pointing geometry and flexible material, which facilitates the threading process. The descent of the central shaft (1) or its pieces can conveniently be paused when threading the cable.

(71) FIG. 15 illustrates various phases of the construction method of a preferred embodiment of the foundation system according to the invention, in which the several steps can follow any technically feasible order.

(72) Thus, following the numbered letters of the procedural steps set out in previous sections, FIG. 15a illustrates step a) and step m). FIG. 15b illustrates step b) and placing the formwork template (28). FIG. 15c shows step c) which in this case comprises a first phase of assembling or construction of the central shaft (1) consisting in placing the frame or rebar of the wall of said central shaft (1) which is hollow and is constructed in situ in this embodiment. FIG. 15d shows step h), showing the struts that in this case comprise pre-threaded pre-stressing cables (5). FIG. 15e shows steps i) and e), and a second phase of construction of the central shaft (1) consisting of the concreting of the walls. FIG. 15f illustrates step k) and a first phase in step d). In FIG. 15g takes place the last phase of construction of the central shaft to step l) and step g). Finally, FIG. 15h shows the installed condition of the foundation system after a second phase of step d) and step f).

(73) Finally, FIGS. 16 and 17 show embodiments of the invention in which the support members are in the form of struts (2) of pre-stressed strap (25) type; in both cases such prefabricated strap type struts (25) consist of cable whose upper end is connected to the central shaft (1) and whose lower end is connected to a lower element (39) of the foundation system, namely a rib (3). Alternatively the upper end can be attached to the tower (24) and the lower end can be directly connected to the ground by anchoring means known in the art. The central shaft (1) is partially buried and is constructed using precast concrete dowels.

(74) The strap type struts (25) are pre-stressed, the lower slab (4) having preferably a high weight of lands on it, in particular in the connection area with the lower ends said strap type struts (25) so that the weight of said lands compensate at least partly the upward traction forces that said pre-stressed anchorages (25) transmit to the lower slab (4).

(75) The lower slab (4) in FIG. 16 adopts a polygonal star-shaped geometry. In FIG. 17 the lower slab (4) comprises a central module (36) located below the central shaft (1) and four exempt modules (35) separated from the central module (36) which are furthest from the vertical axis of the tower (22) than the central module (36) and that are connected with the central module (36) by ribs (3).