SECTION OF CONCRETE
The present invention relates to the technical field of superstructures.
More particularly, the subject of the present invention is a section of concrete
intended to form a mast, notably for a windmill, a mast of concrete comprising a set of
sections comprising one or more of this section and a method to construct such a mast.
As the technology for producing electricity from wind energy has developed, it has
been noted that there is a link between the power which can be delivered by the windmill
and the dimensions of the windmill.
It is thus accepted that, in order to construct windmills capable of delivering high
production powers, it is necessary to increase the length of the blades and therefore the
height of the mast.
However, when increasing the height of a mast it is necessary to take into account a
set of criteria which are connected on one hand to the desired technical performance of
the mast, and on the other hand to the logistics of constructing the mast.
The technical performance criteria can comprise the load that has to be supported
by the mast, and hence the compression resistance of the used materials, but also the
tensile resistance of these materials.
Indeed, the tensile resistance is important as the loadings on the mast can cause
significant tensile stresses.
The criteria linked to the logistics to be applied during the construction of the mast
can, for their part, comprise the transportation of the various elements forming the mast
from the production site where these elements are produced to the installation site, but
also the conditions of assembling these elements on the installation site.
Together, these criteria have led to the production of masts made of concrete, to the
detriment of steel, notably in order to facilitate transportation to the installation site and to
reach higher heights.
This is because a concrete mast generally comprises a plurality of first elements
named sections divided into a plurality of second elements named segments distributed
on their periphery.
The use of segments greatly facilitates the transportation to the site. The segments
can be stacked horizontally one on top of the other on a truck then assembled in sections
on the installation site.
Furthermore, the use of segments also makes it possible to significantly increase
the diameter of the sections and therefore the height of the mast.
However, the use of segments requires an additional step for assembling on the
installation site all the segments forming the sections and this additional step can do
waste a lot of time.
The use of concrete to form the segments allows, for its part, to increase the
thickness of the sections and therefore also the height of the mast.
Moreover, unlike steel welds, concrete joints present a good resistance to fatigue
loading, which increases the durability of the mast and makes it a material of choice for
the construction of masts of great height.
It is known practice to use prestressing device to increase the tensile resistance of
the concrete elements forming the mast.
This improvement of tensile resistance improves the transportability when it is
applied in a production site.
It therefore appears necessary to increase the tensile resistance of the concrete
elements from its release from the production site.
Furthermore, the stress exerted on the concrete can vary over time because of the
phenomena of creep of the concrete and of relaxation of the prestressing device, in some
cases, it is no longer possible, once the mast is erected, to control the prestressing device
which could inform about the effect of the phenomena of creep of the concrete and of
relaxation of the prestressing device.
That can considerably increase the industrial risk and can even make the installation
of such masts made of concrete prohibitive.
It therefore appears necessary to retain the possibility of controlling, and even more
the possibility of readjusting if needed, the stress exerted on the concrete during the
service life of the mast.
Finally, the construction of the mast, which includes the application of the stress by
the prestressing device on the installation site, can be lengthy and tedious and can be
slowed down or stopped because of the weather.
The present invention aims to resolve all or some of these drawbacks mentioned
above.
To this end, the present invention relates to a section of concrete intended to form a
mast for a windmill, said section comprising:
- a first portion, intended to exert a bearing force on a lower adjacent part of the
windmill, said first portion comprising a first flange extending substantially transversely
from an internal face of the section opposite the internal volume of the section,
- a second portion, intended to form a bearing support for an upper adjacent part of
the windmill, said second portion comprising a second flange extending substantially
transversely from the internal face of the section opposite the internal volume of the
section,
- a prestressing device arranged to apply a stress between the first portion and the
second portion, said prestressing device comprising at least one visible part extending
outside the section of concrete and located between the first flange and the second
flange.
- a first attaching device arranged to be connected to the first flange and intended to
be used to attach the section on the lower adjacent part of the windmill, and/or
- a second attaching device arranged to be connected to the second flange and
intended to be used to attach the section to the upper adjacent part of the windmill.
This arrangement makes it possible to apply a stress to the concrete elements on
the production site in such a way that the concrete elements better withstand the loadings
from the transportation and construction, notably the tensile stresses.
This arrangement makes it possible to easily check the effects of the phenomena of
creep of the concrete and of relaxation of the prestressing device during the service life of
the mast, notably by checking the strain of the visible part of the prestressing device
extending out of the section of concrete between the first flange and the second flange,
while making it possible to easily control and eventually readjust the value of the stress on
the concrete as a function of the result of this check.
Finally, this arrangement allows a simple and rapid construction of the mast on the
installation site without any needs to use the prestressing device.
At last, it must be understood that a prestressing device may comprise a
prestressing device by pre-tension wherein the stress is applied to the prestressing device
before the setting of the concrete, and/or a prestressing device by post-tension wherein
the stress is applied to the prestressing device after the setting of the concrete.
Furthermore, it must be understood that a production site is a place where the
concrete elements are produced, and it may be or not in close proximity of the installation
site, the installation site being the place where the windmill is intended to be erected.
According to one aspect of the invention, the concrete is an ultra-high performance
concrete or an ultra-high performance concrete reinforced with fibres and/or with ordinary
reinforcement.
Ultra-high performance concrete (UHPC) and ultra-high performance concrete
reinforced with fibres (UHPFRC) should be understood to mean a concrete that has a
characteristic compression strength value at 28 days greater than or equal to 120 MPa.
This arrangement makes it possible to increase the resistance of the concrete
element and therefore reduces the thickness of a section compared to the thickness of a
section made of traditional concrete.
The reduction of the thickness allows to increase the height of the section for a
similar weight.
The increase of the height of the sections reduces the amount of horizontal joints
and therefore the amount of weak zones.
Thus, the reduction of the thickness of the section can make it possible to transport
a section presenting a length up to 20 m, preferencialy up to 40 m length, and more
preferentialy up to 100 m lenght as one entire section without exceeding a transportation
weight.
According to one aspect of the invention, the prestressing device comprises a
plurality of holes formed on the first flange and on the second flange and cables and/or
bars.
Cables can be of monostrand type or of multistrand type.
According to one aspect of the invention, each hole comprises a recess formed on
the surface of the first flange on the opposite side of the second flange and/or a recess
formed on the surface of the second flange on the opposite side of the first flange.
This arrangement makes it possible to limit the interaction that there could be
between the ends of the cables and/or the ends of the bars and a portion of an adjacent
part of the windmill forming a bearing support or exerting a bearing force on said adjacent
part of the windmill.
According to one aspect of the invention, the first portion and/or the second portion
comprise a reinforcing element.
This arrangement makes it possible to reinforce the first portion and/or the second
portion, notably to reduce the risk of the formation of cracks upon the application of a
stress by the prestressing device.
According to one aspect of the invention, the section is a modular section
comprising a plurality of segments.
This arrangement makes it possible to facilitate the transportation of the sections of
the mast and makes it possible to increase the diameter of the sections.
According to one aspect of the invention, the section is a one-piece section.
This arrangement makes it possible to facilitate the assembly of the mast on site.
According to one aspect of the invention, the section has a hollow cylindrical form,
polygonal form or frustoconical form.
According to one aspect of the invention, the first attaching device comprises a
plurality of holes formed on the first flange, and bolts and/or threaded bars intended to
traverse said holes, and/or the second attaching device comprises a plurality of holes
formed on the second flange, and bolts and/or threaded bars intended to traverse said
holes.
This arrangement makes it possible to attach together a section and an adjacent
part of the windmill using simply threaded bars and/or bolts.
According to one aspect of the invention, the plurality of holes for the prestressing
device on a determined flange form a first set of holes and the plurality of holes for a
determined attaching device on the determined flange form a second set of holes, the
holes of each set being located at different distances from the free end of the determined
flange.
According to one aspect of the invention, the holes of the first set of holes are farther
from the free end of the determined flange than the holes of the second set of holes.
This arrangement makes it possible to limit the stress applied on the flanges by the
prestressing device and thus reduces the risk of cracks, and at the same time provides a
better partitioning of this stress on the other parts of the section.
According to one aspect of the invention, the first attaching device comprises
portions connected to the prestressing device, said portions protruding beyond the first
flange and being intended to traverse a lower adjacent part of the windmill, and/or the
second attaching device comprises portions connected to the prestressing device, said
portions protruding beyond the second flange and being intended to traverse an upper
adjacent part of the windmill.
This arrangement makes it possible to use a same element as a bar and/or cables
to apply a stress to the concrete element and to fasten this element to an adjacent part of
the windmill.
Moreover, this arrangement allows adjusting stress by using the attaching devices.
Thus, the prestressing device can be used for the application of a first stress on the
production site for example to increase the tensile resistance of the concrete element with
a view to its transportation and construction.
Subsequently the first and/or the second attaching device can be used for the
application of a second stress on the installation site during the construction of the mast.
This arrangement also makes it possible to apply a stress to the concrete element
during the service life of the concrete mast.
Also the subject of the present invention is a mast of concrete intended for a
windmill comprising a set of sections comprising one or more sections as described
previously.
Also the subject of the present invention is a method to construct a mast of concrete
intended for a windmill comprising the following steps:
- having a set of sections available, said set of sections comprising at least one
section as described previously,
- constructing the mast on an installation site by stacking all the sections of the set
of sections one on top of the other.
According to one implementation of the method, the method comprises a step
wherein all the sections of the set of sections are transported to the installation site as an
entire section.
According to one implementation of the method, during the constructing step of the
mast, an upper adjacent part of the windmill is attached to at least one section using the
second attaching device and/or at least one section is attached to an adjacent lower part
of the windmill using the first attaching device.
According to one implementation of the method, the method comprises a step of
applying, on the production site, to at least one section, a first value of stress between the
first portion and the second portion using all or part of the prestressing device.
This arrangement makes it possible to increase the tensile resistance of the
concrete element forming the section with a view to its transportation and construction.
All parts of the prestressing device are not necessarily stressed on the production
site but just those necessary to secure the transportation and the assembly on the
installation site.
According to one implementation of the method, the method comprises a step of
applying, on the installation site, to at least one section, a second value of stress between
the first portion and the second portion using the first attaching device and/or the second
attaching device.
This step makes it possible to apply a second value of stress that enables the mast
to withstand the various stresses that can be encountered during its service life.
According to one implementation of the method, the second value of stress is the
same or greater than the first value of stress.
According to one implementation of the method, the second value of stress is
applied after an upper adjacent part of the windmill is put in place.
This step makes it possible to facilitate the application of the second value of stress
and allows applying stresses that would not be possible to apply on an isolated section.
According to one implementation of the method, the method comprises a step of
adjusting a value of stress applied between the first portion and the second portion of a
section of the mast during the service life of the mast.
This step makes it possible to limit and check the effect of phenomena of creep of
the concrete and of relaxation of the prestressing device.
In any case, the invention will be well understood from the following description, with
reference to the attached schematic drawings representing, by way of nonlimiting
example, an exemplary section and mast according to the invention as well as a step of
construction of the mast according to the invention.
Figure 1 shows an overview of a mast according to the invention in situ for a
windmill, and an exploded projection of the same mast.
Figure 2 shows an overview of a section according to the invention of the mast
illustrated in Figure 1.
Figure 3 shows an overview of a variant of the section illustrated in Figure 2.
Figure 4 shows a detail view over a part of a horizontal joint between two adjacent
sections of the mast illustrated in Figure 1 according to a first embodiment.
Figure 5 shows a cross-sectional view of the part of the horizontal joint illustrated in
Figure 4.
Figure 6 shows a detail view over a part of a horizontal joint between two adjacent
sections of the mast illustrated in Figure 1 according to a second embodiment.
Figure 7 shows a cross-sectional view of the part of the horizontal joint illustrated in
Figure 6.
Figure 8 shows a variant of the first embodiment illustrated in Figures 4 and 5.
Figure 9 shows a variant of the second embodiment illustrated in Figures 6 and 7.
Figure 10 illustrates a step of the method for constructing a mast made of concrete
according to the invention.
As illustrated in Figure 1, a mast 1, notably for a windmill 2, comprises a plurality of
sections 10 of concrete stacked one on top of the other.
As illustrated in Figure 2, a section 10 can be of a single piece or else, as illustrated
in Figure 3, a section 10 can comprise a plurality of segments 3. Then, such a section 10
is a modular section 10.
In the example shown in Figure 3, the modular section 10 comprises four segments
3a, 3b, 3c, 3d.
Obviously, the present invention is in no way limited by the number of segments 3
nor by the size of the section 10 which results therefrom.
These segments 3 can be assembled together by using means known to those
skilled in the art, for example with vertical joints like those described in the document
WO 2013/029743 A 1.
The section 10 can be also of a single piece without segments 3.
In the example presented, the section 10 is in the form of a hollow cylinder defining
an internal volume V of the section 10 and an outer face E and an inner face I opposite
the outer face E and arranged facing the internal volume V of the section 10.
Advantageously, the section 10 is made of ultra-high performance concrete or of
ultra-high performance concrete reinforced by fibres.
Of course some ordinary reinforcement devices, as steel grids, could have been
used.
This concrete can, for example, be of the type of that marketed by the company
Lafarge under the trademark Ductal®.
The use of this type of concrete makes it possible to produce a lighter mast 1 than
with a traditional concrete while retaining a reduced section diameter that notably allows
for the transportation of sections 10 presenting a length from 15, 20 or 25 m up to 40 m as
one entire section from the production site to the installation site.
In particular, a section made of one entire concrete section, which can also be made
of one-piece concrete section if it is not formed from a plurality of segments, can have an
outer diameter that can range up to for example 4.40 m.
As illustrated in the various Figures 4 to 9, a section 10 according to the invention
comprises a first portion 11 intended to exert a bearing force on a lower adjacent part of
the windmill 2, and a second portion 12 intended to form a bearing support for an upper
adjacent part of the windmill 2.
The considered parts of the windmill 2 can be a lower adjacent section 10a of the
mast 1, an upper adjacent section 10b of the mast 1, but also a nacelle, a transition piece
of the windmill 2 or the foundation structure of the mast 1.
Figures 4 to 9 show a part of horizontal joints between two adjacent sections 10a,
10b according to the invention.
Thus, these different figures show only one of the two portions 11, 12 for a
determined section 10.
However, in the different embodiments presented, the non-illustrated first portion 11
of a lower adjacent section 10a of the mast 1 is similar to the illustrated first portion 11 of
the upper adjacent section 10b of the mast 1.
Similarly, the non-illustrated second portion 12 of an upper adjacent section 10b of
the mast 1 is similar to the illustrated second portion 12 of a lower adjacent section 10a of
the mast 1.
Obviously, the present invention is in no way limited to these particular
embodiments which are given here by way of examples, and could, for example, comprise
a combination of these embodiments or of other embodiments covered by the present
invention.
The first portion 11 comprises a first flange 11' extending substantially transversely
from the internal face I of the section 10 opposite an internal volume V of the section 10.
Similarly, the second portion 12 comprises a second flange 12' extending
substantially transversely from the internal face I of the section 10 opposite an internal
volume V of the section 10.
Obviously, the present invention is in no way limited to the form and the size of
these flanges 11' , 12'.
In the example presented, the thickness of the first flange 11' and of the second
flange 12' is, for example, 300 mm.
Furthermore, a section 10 comprises a first attaching device 13a arranged to be
connected to the first flange 11' and intended to be used to attach said section 10 on the
lower adjacent part of the windmill 2, for example the lower adjacent section 10a of the
mast 1 or else a foundation structure of the mast 1.
Similarly, a section 10 comprises a second attaching device 13b arranged to be
connected to the second flange 12' and intended to be used to attach said section 10 to
the upper adjacent part of the windmill 2, for example the upper adjacent section 10b of
the mast 1 or else a nacelle or a transition piece of the windmill 2.
At last, a section 10 according to the invention comprises a prestressing device 20
arranged to apply a stress between the first portion 11 and the second portion 12 of the
section 10.
In the presented examples, this prestressing device 20 comprises a plurality of steel
bars 2 1 of determined length and having threaded ends 23 as well as a plurality of holes
26 formed on the flanges 11' , 12' and intended to accommodate said bars 2 1.
These holes 26 are uniformly distributed over the circumference of the flanges 11',
12'.
Moreover, a hole 26 formed on the first flange 11' is arranged coaxially with a hole
26 formed on the second flange 12'.
The coaxial alignment between a hole 26 formed on the first flange 11' and a hole
26 formed on the second flange 12' of a same section enables a bar 2 1 to have a
substantially vertical orientation in the section 10 after the construction of the mast 1.
The distance separating two consecutive holes 26 of a same flange 11', 12' is for
example 600 mm.
Furthermore, each hole 26 can have a recess 27 formed on the surface of the first
flange 11' on the opposite side of the second flange 12' of a same section 10 and a
recess 27 formed on the surface of the second flange 12' on the opposite side of the first
flange 11' of a same section 10.
In the example presented, this recess 27 has a square profile to ensure that a
square washer 25 positioned at the bottom of the recess 27 is rotationally immobilized.
This recess 27 also has a depth enabling the threaded end 23 of a bar 2 1 protruding
inside the recess 27 and with a nut 24 screwed on top not to protrude outside the recess
27.
Thus, the bar 2 1 and the nut 24 do not disturb the support of a portion 11, 12 of an
adjacent section 10a, 10b on a portion 11, 12 of a determined section 10.
Furthermore, the prestressing device 20 comprises a visible part 2 1 extending
outside the section 10 of concrete and located between the first flange 11' and the second
flange 12' in the internal volume V of the section 10.
This visible part 2 1 makes it possible to easily check the stress applied by the
prestressing device 20 and the trend of this stress over the service life of the mast 1.
Thus, this arrangement makes it possible to apply a stress to a section 10 of
concrete from its production on the production site, notably to resist to the transportation,
and then control this stress on installation site.
Obviously, the present invention is in no way limited to a particular type of
prestressing device 20 and can comprise any equivalent technical means arranged to
apply, from production on the production site, a stress between the first portion 11 and the
second portion 12.
In particular, this prestressing device 20 can be of pre-tension type or of posttension
type.
For example, such a prestressing device 20 could comprise a part formed from
cables gripped in the concrete during the casting of the section 10 or cables blocked by an
insert or even a combination of bars and cables.
Cables can be of monostrand type or of multistrand type.
According to a variant presented in Figures 8 and 9, the first portion 11 and the
second portion 12 of the section 10 comprise a reinforcing element 40.
This reinforcing element 40 can be made of steel and increases the resistance of
the first portion 11 and of the second portion 12 of a section 10.
This is because these portions 11, 12 arranged overhanging are subject to
significant stresses, notably to the stresses exerted by the prestressing device 20.
This reinforcing element 40 closely follows the form of the portion 11, 12 considered
and comprises a plurality of steel rods crossing the outer face E and the inner face I of the
section 10 and linking two opposite portions of the reinforcing element 40.
This reinforcing element 40 can be for example a lost formwork used for the casting
of the portions 11, 12 during the casting of the concrete on the production site to form a
section 10.
In a first embodiment and its variant illustrated in Figures 4, 5 and 8, each attaching
device 13a, 13b comprises a plurality of holes 14 formed on the considered flange 11',
12'.
Each of these holes 14 is arranged between two holes 26 of the prestressing device
20.
In this first embodiment, each attaching device 13a, 13b comprises also threaded
bars 15 intended to traverse the holes 14 and nuts 17 intended to be screwed on said
threaded bars 15.
In the presented example, the holes 14 are uniformly distributed over the
circumference of the flanges 11' , 12'.
The threaded bars 15 are made from steel and present a determined length.
According to a variant that is not illustrated, the threaded bars 15 could, for example,
be replaced totally or partially by a plurality of tightening bolts.
In the example presented, a square washer 18 is positioned between a nut 17 and a
surface of the first flange 11' opposite the second flange 12' and a surface of the second
flange 12' opposite the first flange 11' .
Obviously, the present invention is in no way limited to a particular type of attaching
device and can comprise any equivalent technical means arranged to produce a link
between two adjacent sections 10 or even a combination of these means.
In a second embodiment, and its variant illustrated in Figures 6, 7 and 9, the second
attaching device 13b comprises portions 3 1 connected to the prestressing device 20.
These portions 3 1 are protruding beyond the second flange 12' and being intended
to traverse an upper adjacent part of the windmill 2, here the first flange 11' of an upper
adjacent section 10b.
In the presented example, the first attaching device 13a does not comprise portions
3 1 connected to the prestressing device 20 of the determined section 10.
However, the first attaching device 13a could have some portions from the same
manner than the second attaching device 13b.
In the presented example, the first attaching device 13a of the determined section
10 comprises portions 3 1 connected to the prestressing device 20 of the lower adjacent
section 10a.
These portions 3 1 are connected to the threaded end 23 of the bars 2 1 of the
prestressing device 20 from manufacturing to form one unit and are arranged to receive a
second washer 33 and a second nut 32.
In the presented example, a given bar 2 1 of a prestressing device 20 of a
determined section 10 is arranged between two bars 2 1 of a prestressing device of an
adjacent section 10a, 10b.
Therefore, the second embodiment allows to implement a method comprising a first
step consisting to apply on the production site, to the section 10, a first value of stress
between the first portion 11 and the second portion 12 using all or part of the prestressing
device 20, which enables the section 10 to withstand transportation, and a second step
consisting to subsequently apply, on installation site, to the section 10, a second value of
stress between the first portion 11 and the second portion 12 using the second attaching
device 13b, particularly the portions 3 1, which enables the section 10 and therefore the
mast 1 to withstand the different stresses that can be encountered during the service life
of the mast 1.
Thus, many options are conceivable.
Each cable or bars can be used fully or partially accordingly to their designed value
of stress.
The first option consists to fully or partially use some or all bars 2 1 or cables of the
prestressing device 20 to apply the first value of stress to the section 10 on the production
site, and then to use the portions 3 1 of any attaching devices 13a, 13b connected to all
the bars 2 1 or cables to apply the second value of stress to the section 10 on the
installation site.
The second option consists to fully use a set of bars 2 1 or cables of the prestressing
device 20, which are not connected to any attaching devices 13a 13b, to apply the first
value of stress on the production site, and then to use the portions 3 1 of any attaching
devices 13a, 13b connected to the bars 2 1 or cables, to apply the second value of stress
to the section on the installation site.
In the second option, each bar 2 1 or cable of the prestressing device 20, which are
connected to the portions 3 1 of the attaching devices 13a and/or 13b can be fully, or
partially, or not used for the application of the first value of stress on the production site.
The value of stress applied between the first portion 11 and the second portion 12 of
a section 10 of the mast 1 can be adjusted during the service life of the mast 1, which
makes it possible to compensate the phenomenon of creep of the concrete and of
relaxation of the prestressing device 20 and/or attaching devices 13a, 13b.
In the presented example, the application of this second value of stress is applied by
screwing the second nut 32 on a portion 3 1 of the second attaching device 13b.
The screwing of the second nut 32 may reduce or annihilate the action of the first
nut 24 of the prestressing device 20 used previously to apply the first value of stress on
the production site.
Indeed, the screwing of the second nut 32 on a portion 3 1 connected to a bar 2 1
exerts a force on the first flange 11' of an upper adjacent section 10b but also on the
second flange 12' of the considered section 10.
Therefore, this force leads to oppose the force exerted by the first nut 24 on this
second flange 12' of the considered section 10.
In order to prevent the first nut 24 from coming into contact with the first flange 11' of
the upper adjacent section 10b, the depth of the recess 2 1 must be sufficient.
The second value of stress is applied after an upper adjacent part of the windmill as
an upper adjacent section 10b is put in place.
The second value of stress may be the same or greater than the first value of stress,
this value of stress corresponding to the absolute value of stress undergone by the
section 10 of concrete.
In a third embodiment not illustrated, the plurality of holes 26 for the prestressing
device 20 on a determined flange 11' , 12' form a first set of holes and the plurality of holes
14 for a determined attaching device 13a, 13b on the determined flange 11', 12' form a
second set of holes, the holes of each set being located at different distance from a free
end of the determined flange 11', 12'.
In particular, the holes 26 of the first set of holes are farther from the free end of the
determined flange 11', 12' than the holes 14 of the second set of holes.
This arrangement makes it possible to limit the stress applied on the flanges 11' , 12'
by the prestressing device 20 and thus reduces the risk of cracks, and at the same time
provides a better partitioning of this stress on the other parts of the section 10.
Thus, the holes 26 of the first set of both flanges 11' , 12' can be used in production
site for allowing all or part of cables and/or bars 2 1 of the prestressing device 20 to apply
a first value of stress on the section 10 for example to increase the tensile resistance of
the concrete element with a view to its transportation and construction.
All or part of the holes 14 of the second set of both flanges 11' , 12' can be used on
installation site for allowing cables and/or bars 2 1 to attach the section 10 to an adjacent
part of the windmill 2 accordingly to the second embodiment and/or all or part of the holes
14 of the second set of both flanges 11', 12' can be used on installation site to attach
together a section 10 and an adjacent part of the windmill 2 using simply threaded bars 15
and/or bolt accordingly to the first embodiment.
All of these three embodiments are mutually compatible.
In particular, the first embodiment can be compatible with the second embodiment
since the prestressing device 20 and/or the attaching devices 13a, 13b may comprise
different types of elements for a determined section 10, for example bars 15 according to
the first embodiment and portions 3 1 connected to bars 2 1 according to the second
embodiment.
The third embodiment only specifies the localisation of the elements of the attaching
devices 13a, 13b and of the elements of the prestressing device 20 on the flanges 11',
12'.
Also the subject of the present invention is a method for constructing a mast 1 made
of concrete for a windmill 2 by stacking in an installation site all the sections of a set of
sections one on top of the other, at least one section of this set of sections being as
described previously.
Such a method can comprise individually or in combination the methods previously
described in relation to the second embodiment and to the third embodiment.
Advantageously, the method can comprise a step illustrated in Figure 10 consisting
in transporting, as one entire section from the production site to the installation site all the
sections 10 of the set of sections.
This section 10 can be modular or not.
Although the invention has been described in conjunction with particular exemplary
embodiments, it is obvious that it is in no way limited thereto and that it comprises all the
technical equivalents of the means described and their combinations.

CLAIMS
1. A section (10) of concrete intended to form a mast ( 1 ) for a windmill (2), said
section (10) comprising:
- a first portion ( 1 1) , intended to exert a bearing force on a lower adjacent part of the
windmill (2), said first portion ( 1 1) comprising a first flange ( 1 1') extending substantially
transversely from an internal face (I) of the section (10) opposite the internal volume (V) of
the section ( 1 ) ,
- a second portion (12) intended to form a bearing support for another upper
adjacent part of the windmill (2), said second portion (12) comprising a second flange (12')
extending substantially transversely from the internal face (I) of the section (10) opposite
the internal volume (V) of the section (10),
- a prestressing device (20) arranged to apply a stress between the first portion ( 1 1)
and the second portion (12), said prestressing device (20) comprising at least one visible
part (22) extending outside the section (10) of concrete and located between the first
flange ( 1 1') and the second flange (12'),
- a first attaching device (13a) arranged to be connected to the first flange ( 1 1') and
intended to be used to attach the section (10) on the lower adjacent part of the
windmill (2), and/or
- a second attaching device (13b) arranged to be connected to the second
flange (12') and intended to be used to attach the section (10) to the upper adjacent part
of the windmill (2).
2. The section (10) according to claim 1, wherein the concrete is an ultra-high
performance concrete or an ultra-high performance concrete reinforced with fibres and/or
with ordinary reinforcement.
3. The section (10) according to claim 1 or claim 2, wherein the prestressing
device (20) comprises a plurality of holes (26) formed on the first flange ( 1 1') and on the
second flange (12'), and cables and/or bars (21 ) .
4. The section (10) according to claim 3, wherein each hole (26) comprises a
recess (27) formed on the surface of the first flange ( 1 1') on the opposite side of the
second flange (12') and/or a recess (27) formed on the surface of the second flange (12')
on the opposite side of the first flange ( 1 1').
5. The section (10) according to any one of claims 1 to 4, wherein the first
portion ( 1 1) and/or the second portion (12) comprise a reinforcing element (40).
6. The section (10) according to any one of claims 1 to 5, wherein the section (10) is
a modular section (10) comprising a plurality of segments (3).
7. The section (10) according to any one claims 1 to 5, wherein the section (10) is a
one-piece section.
8. The section (10) according to any one claims 1 to 7, wherein the first attaching
device (13a) comprises a plurality of holes (14) formed on the first flange ( 1 1'), and bolts
and/or threaded bars (15) intended to traverse said holes (14), and/or the second
attaching device (13b) comprises a plurality of holes (14) formed on the second
flange (12'), and bolts and/or threaded bars (15) intended to traverse said holes (14).
9. The section according to claim 8 and claim 3, wherein the plurality of holes (26)
for the prestressing device on a determined flange ( 1 1', 12') form a first set of holes and
the plurality of holes (14) for a determined attaching device (13a, 13b) on the determined
flange ( 1 1', 12') form a second set of holes, the holes of each set being located at different
distances from the free end of the determined flange ( 1 1', 12').
10. The section according to claim 9, wherein the holes (26) of the first set of holes
are farther from the free end of the determined flange ( 1 1', 12') than the holes (14) of the
second set of holes.
11. The section (10) according to any one claims 1 to 10, wherein the first attaching
device (13a) comprises portions (31 ) connected to the prestressing device (20), said
portions (31 ) protruding beyond the first flange ( 1 1') and being intended to traverse a
lower adjacent part of the windmill (2), and/or the second attaching device (13b)
comprises portions (31 ) connected to the prestressing device (20), said portions (31 )
protruding beyond the second flange (12') and being intended to traverse an upper
adjacent part of the windmill (2).
12. A mast ( 1 ) of concrete intended for a windmill (2) comprising a set of sections
comprising one or more sections (10) according to any one of claims 1 to 11.
13. A method to construct a mast ( 1 ) of concrete intended for a windmill (2)
comprising the following steps:
- having a set of sections available, said set of sections comprising at least one
section (10) according to any one of claims 1 to 11,
- constructing the mast ( 1 ) on an installation site by stacking all the sections of the
set of sections one on top of the other.
14. The method according to claim 13, comprising a step wherein all the sections of
the set of sections are transported to the installation site as one entire section.
15. The method according to claim 13 or claim 14, wherein during the constructing
step of the mast (1), an upper adjacent part of the windmill (2) is attached to at least one
section (10) using the second attaching device (13b) and/or at least one section (10) is
attached to an adjacent lower part of the windmill (2) using the first attaching device ( 13a).
16. The method according to any one of claims 13 to 15, wherein the method
comprises a step of applying, on the production site, to at least one section (10), a first
value of stress between the first portion ( 1 1) and the second portion (12) using all or part
of the prestressing device (20).
17. The method according to claim 16, wherein the method comprises a step of
applying, on the installation site, to at least one section (10) according to claim 11, a
second value of stress between the first portion ( 1 1) and the second portion ( 12) using the
first attaching device ( 13a) and/or the second attaching device ( 13b).
18. The method according to claim 17, wherein the second value of stress is the
same or greater than the first value of stress.
19. The method according to claim 17 or claim 18, wherein the second value of
stress is applied after an upper adjacent part of the windmill (2) is put in place.
20. The method according to any one of claims 13 to 19, wherein the method
comprises a step of adjusting a value of stress applied between the first portion ( 1 1) and
the second portion (12) of a section (10) of the mast ( 1 ) during the service life of the
mast ( 1 ) .