The invention relates to a structural member for manufacturing
a tower of a wind power system having a delimitation surface
forming a portion of the outer surface of the tower and
comprising a through opening provided for accommodating a
door.
Conventional wind power systems comprise a tower which is
firmly anchored on the ground, a machine gondola pivoted
thereon at the top of the tower about a vertical axis of
rotation, as well as a rotor rotatably mounted on the gondola
about a substantially horizontal rotor axis and including at
least one rotor blade.
In modern wind power systems with a nominal power of more than
one megawatt, tower heights of 100 m or more and rotor
diameters of at least 70 m are achieved. For maintenance of
such systems, the tower having generally a diameter of more
than three meters has to be accessible from inside so that the
parts in the region of the rotor axis which require
maintenance can be reached without danger and without any
substantial expenditure.
For this purpose, a through opening which can be locked with a
door is generally provided at the foot of the tower consisting
usually of rolled steel plates having a thickness of up to 40
mm. In order to form said through opening, a corresponding

hole is cut into the steel jacket of the tower, and a door
case provided for accommodating the door is welded into said
hole.
In this process, the tower is weakened not only by the
formation of the hole in the jacket surface, but also by the
subsequent welding process because, by the effect of heat,
structural changes in the steel plate parts are caused
thereby. With the help of computer simulations, it has been
shown that, of the entire tower construction, the region of
the through opening is the part which is stressed most in the
case of high wind loads, and, therefore, correspondingly high
material strengths or additional reinforcement members have to
be used in this region in order to guarantee sufficient
stability of the tower construction. A conventional tower
construction of the kind just described is shown by way of
example in Fig. 2. Therein, Fig. 2 A shows a view of the lower
part of said tower construction, and Fig. 28 a sectional view
taken along cutting plane A-A. In the drawing, reference
number 10 refers to the tower, reference number 20 to the
through opening and reference number 12 refers to the case
welded into the through opening. The above-mentioned computer
simulations have shown that weak points particularly occur in
the region of the welded transition section between the case
12 and the jacket surface of tower 10 adjacent thereto. To
eliminate this problem, it has been proposed to manufacture
the through opening 20 as an oval opening, avoiding sharp
corners, as indicated in Fig. 2a. However, even by means of
said construction, weak points in the region of the transition
section between the case 12 and the jacket surface of the
tower adjacent thereto cannot be eliminated completely, so
that, even with this measure, the attachment of additional
reinforcing members and/or the increasing of the material
strength of the steel plates used for forming the jacket
surface is unavoidable.

With respect to the problems of the prior art which have been
described above, the object of the invention is to provide a
structural member of the type described at the beginning,
which can be manufactured and assembled at low costs, and
wherein weak points in the tower construction which cannot be
tolerated are avoided.
According to the invention, said problem is solved by a
development of the known structural members, which is
substantially characterized in that at least a region of the
structural member comprising the through opening is at least
partially formed as a cast part consisting of a preferably
weldable casting material such as cast steel.
This invention is based on the realization that the observed
weakening of the tower construction is primarily caused by the
welding process in the region of the through opening required
for the manufacture of conventional structural members of the
type described at the beginning, and that said welding process
can be avoided if the through opening is realized by using a
cast part because, by proper selection of the casting mold,
such cast parts can be prefabricated in such a way that it is
substantially not required to attach additional members later.
It was especially realized therein that the increase in
stability achieved by avoiding additional weld seams by far
outweighs the known disadvantage related to the use of casting
materials with respect to the limited ductility, and,
therefore, despite said disadvantages of casting materials,
altogether, an increase in stability of the tower of a wind
power system can be achieved without the use of additional
reinforcement members and/or an increase in the wall strength
of the tower construction.

Thereby, a substantial reduction with respect to costs is
achieved, while the required stability is guaranteed at the
same time, because the material used, the manufacturing time,
the required personnel used and the strength design can be
optimized using few structural members in the manufacturing
process and higher manufacturing tolerances.
Within the scope of this invention, the use of structural
members entirely consisting of a casting material is
considered, which are connected to other component parts of
the tower during a pre-assembly and/or during the final
assembly. In a particularly preferred embodiment of the
invention, however, the structural member is already designed
as a pre-assembled component having at least one steel plate
adjacent to the cast part and preferably welded thereto.
In view of the commonly used tower geometries, the
delimitation surface of the structural member according to the
invention advantageously has substantially the form of a
surface area of a circular cylinder or of a section thereof.
The connection between a cast part and a steel plate of a
structural member of the invention designed as a pre-assembled
component is advantageously effected by a butt seam. In view
of the wall thickness of more than 10 mm of the steel plates
used for the manufacture of conventional towers of wind power
systems, in order to obtain a sufficiently strong weld joint,
it is usually required that the weld seam is formed in a joint
having a wedge-shaped cross-section formed between the cast
part and the steel plate. In such a joint, proceeding from the
region having the smallest width, a number of welding beads
can be laid successively, which will finally completely fill
the joint. If structural members of the invention are used,
the V-shaped chamfering required for forming such a joint
having a wedge-shaped cross-section can be integrated into the

cast part already during the manufacture of the cast part by
suitably selecting the casting mold.
As already explained at the beginning, an increase in
stability can also be achieved by avoiding sharp corners or
the like in the formation of the through opening. For this
reason, the through opening of structural members according to
the invention thus preferably shows substantially an oval
shape.
In wind power systems, in the region of the through opening,
usually further functional elements have to be provided such
as the door case for attaching a door leaf in an articulated
manner, fastening elements for fire extinguishers or the like,
antenna holders, suction pipes and/or exhaust pipes for an
emergency power generating unit provided with a diesel engine,
an accommodation for a stair railing, an orifice or an exhaust
opening for the cooling or fresh air supply and/or a safety
device for the door. In conventional towers of wind power
systems, said functional elements are welded to the tower
jacket. This causes additional weakened points in the tower
jacket. If structural members according to the invention are
used, said problem can be solved by casting at least one of
the additional functional elements together with the cast part
as an integral part thereof.
In the following, the invention is explained with reference to
the drawing; with respect to any details which are essential
for the invention and which have not further been emphasized
in the description, reference is explicitly made to said
drawing. In the accompanying drawing,
Fig. 1 shows a sectional view of a structural member
according to the invention, and

Fig. 2 shows the tower of a wind power system of the
prior art.
In Fig. 1, a structural member of the invention forming a
through opening 20 of the type shown in Fig. 2 is shown. Said
structural member is a cast part manufactured from cast steel
and comprises a fastening element 32 for attaching a door leaf
in an articulated manner, a door leaf stop 34 and altogether
three fastening elements 36, which can be used as holders for
fire extinguishers, antenna holders and/or door safety
devices. The structural member shown in Fig. 2 has an outer
delimitation surface in the form of a section of a surface
area of a truncated cone. For assembling a tower of a wind
power system, said structural member is welded together with
further structural members formed in the form of rolled steel
plates in order to manufacture a tower for the wind power
system in this manner. In the embodiment of the invention
shown in Fig. 1, the through opening is formed such that it
has the size of a conventional door (standard door).
The invention is not limited to the embodiment explained by
means of the drawing. For example, also the use of structural
members is considered where only part of the through opening
is limited by the cast part, and the rest of the through
opening is limited by a rolled steel plate. Furthermore, also
the use of structural members according to the invention
having delimitation surfaces having the shape of a surface of
a circular cylinder and/or plane delimitation surfaces is
considered. Moreover, further functional elements can be
provided at the cast part of the structural member according
to the invention.

We Claim
1. A structural member (30) for manufacturing a tower (10) of a wind power
system having a delimitation surface (40) forming a portion of the outer
surface of the tower, and comprising a through opening (20) provided for
accommodating a door, characterized in that at least a region of the
structural member (30) having the through opening (20) is at least
partially formed as a cast part consisting of a weldable casting material.
2. The structural member as claimed in claim 1, comprising at least one steel
plate adjacent to the cast part (30) and preferably welded therewith.
3. The structural member as claimed in claim ! or claim 2, wherein the
delimitation surface (40) comprises a surface area substantially in the
form of a circular cylinder, a truncated cone or a section thereof.
4. The structural member as claimed in claim 2 or claim 3, wherein the weld
seam is formed in a joint having a wedge-shaped cross-section formed
between the cast part and the steel plate.
5. The structural member as claimed in any one of the preceding claims,
wherein the through opening (20) is substantially oval shaped.
6. The structural member as claimed in one of the preceding claims, wherein
the cast part comprises at least one functional element as an integral
component part.

7. The structural member as claimed in claim 6, wherein the functional
element is one of a door case, a door journal, a fastening element for a
fire extinguisher, an antenna holder, a suction pipe and/or exhaust pipe
for an emergency power generating unit, an accommodation for a stair
railing, a vent hole and/or a door safety device.
8. A wind power system comprising a structural member as claimed in one of
the preceding claims.
DATED THIS 23RD DAY OF APRIL 2004

This invention relates to a structural member (30) for manufacturing a tower
(10) of a wind power system having a delimitation surface (40) forming a portion
of the outer surface of the tower, and comprising a through opening (20)
provided for accommodating a door. A region of the structural member (30)
having the through opening (20) is at least partially formed as a cast part
consisting of a weldable casting material.