WO2008032281A1

WO2008032281A1 - Polymeric concrete for wind generators towers or other large structural applications

Info

Publication number: WO2008032281A1
Application number: PCT/IB2007/053696
Authority: WO
Inventors: Alexandre Francisco MALHEIRO DE ARAGÃO; Ana Margarida GONÇALVES TERRA; André FERREIRA VIEIRA; Célia Maria MOREIRA PARENTE NOVO; Paulo Manuel Ferreira Sobral; Daniel Da Fonseca Farias Rodrigues; Paulo Luís CARDOSO OSSWALD
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-09-13
Filing date: 2007-09-13
Publication date: 2008-03-20
Anticipated expiration: 2009-03-13
Also published as: PT103562A; PT103562B; US20090313913A1; EP2076642A1

Abstract

The present invention relates to towers for wind generators or other large structural applications and uses a new construction concept, based on polymeric concrete. Polymeric concrete is composed of thermosetting resin and aggregates such as sand or gravel. Polymeric concrete has low maintenance costs and exceptional high resistance to corrosion, thus justifying its main usage in non-structural applications. Additionally, polymeric concrete has been used as mortar in the rehabilitation of civil structures, especially retrofitting of bridges and heritage buildings. Its advantages for these applications are the adherence to the traditional materials, higher compressive strength than traditional concrete and low specific weight. The tower (1), according to the invention, is built of two or more superimposed ring sections (2) in conical or cylindrical shape, each ring (2) being built of one or more shell segments and the said segments being fixed by means of mechanical and/or chemical couplings, and being made of prefabricated polymeric concrete.

Description

Description POLYMERIC CONCRETE FOR WINDGENERATORSTOWERS

OR OTHER LARGE STRUCTURAL APPLICATIONS

Technical Domain

[1] The present invention relates to towers for wind generators or other large structural applications and applies a new construction concept, based on polymeric concrete. State of the Art

[2] Wind generators have gained wide acceptance as an alternative source for the production of renewable and clean energy. In recent years, state of the art wind energy converters had a dramatic development in energy output/production, by using longer blades and more powerful generators. Rotor diameter of state of the art units has reached 120 m and generator power has reached 5 MW. Wind generators are supported to a convenient height by towers, in order to expose them to a convenient wind flow and prevent interaction between the rotor blades and the ground. The towers themselves are adequately attached to the foundations. The development trend described above requires increased hub height, and tower height for the same state of the art unit has reached 120 m.

[3] These towers must support the increased weight of the energy converters, withstand the wind forces on the whole unit and provide adequate mechanical resistance to the dynamic behaviour of the generator, including stiffness and fatigue wear for a minimum 20 year life time. Thus they are a demanding design project representative of engineering state of the art for supporting large and heavy structures at extreme heights.

[4] The same energy converters have also been applied off-shore, where wind flows are more convenient and where there are fewer implications with ground occupancy. The supporting towers have been attached to steel pylons or concrete foundations that reach above maximum sea water level.

[5] The towers have a significant impact in the overall cost of the wind generator unit and several solutions have been proposed both to support the development trend to higher hub heights and to reduce the costs in manufacture, transport, assembly and maintenance, which become more and more relevant with increasing height. A variety of construction methods, from guyed poles, steel wall, steel lattice, concrete wall, hybrid steel wall & lattice, hybrid concrete & steel wall to composite materials, have been proposed for wind towers. A viable solution has to provide necessary mechanical resistance both to static and dynamic loads at increasing heights and prove cost- effectiveness in manufacture, transport, assembly and maintenance. [6] The industry has used mainly steel towers, made of cylindrical or conical sections of metal wall, flanged at the extremities, the sections being bolted together on site. However, as increased tower height implies bolder dimensioning of the tower diameter, of the wall thickness, or both, in order to assure the necessary stiffness, this solution has met increasing limitations due to materials costs and also manufacture and transport limitations due to dimensions, as a diameter of 4.2 m is the maximum allowed in many roads due to over-crossings. This is the main reason why the standard steel tower height for the multi-MW generators today is still 80 m , which was the state of the art 10 years ago.

[7] Towers of steel lattice construction were used for smaller towers in the past and have also been proposed for higher towers. Lattice towers need more ground space and imply more time consumption for on site assembly. They also have increased inspection and maintenance costs. A variant hybrid construction, made of a lower section of steel lattice and an upper section of steel wall, has been proposed as in DE 103 39 438 Al, but it requires expensive joints.

[8] Proposals have been made in order to improve the steel wall tower construction presently used by the industry. The construction of the tower has been proposed in variable forms, including various numbers of ring sections and shell segments, as in WO 2004/083633 Al. Other proposals are based on a more complex wall profile, as in EP 1561883 Al, providing more stiffness but requiring additional and costly operations both for production and on site assembly. Hybrid variants with a concrete lower section, as in WO 2005/015013, improve the load-bearing capacity and easiness of attachment to the foundation, thus allowing higher towers, but they present increased costs and fail to solve the maintenance issues.

[9] Furthermore, all the steel wall and lattice solutions require maintenance of the tower during the project lifetime of the wind generator, due to corrosion. Although corrosion usually appears late in the 20 year life-cycle of the on-shore tower, control and maintenance of corrosion spots on the external wall or in lattice construction entail important costs and risks. In more aggressive environmental conditions, such as offshore towers, corrosion becomes an even more important concern and implies increased maintenance costs and risks.

[10] A different approach is that of concrete towers, made of pre-cast concrete sections reinforced with pre-tensioned cables. They have been used for towers with heights of about 95 m and higher, as in DE 100 33 845 Al and DE 101 60 306 B4 and they have the advantage of a better weathering resistance. However, this solution is considerably heavier than the one of steel wall, with corresponding higher logistic costs and longer on-site assembly time. Summary of the Invention [11] The present invention provides a solution for building large scale towers, including towers beyond 80 m height, reducing substantially the maintenance needs, avoiding the logistics restrictions of the maximum transportable diameter and reducing the production costs of the current state of the art steel tower solutions, through the application of polymeric concrete.

[12] Polymeric concrete is composed of thermosetting resin and aggregates such as sand or gravel. Polymeric concrete has low maintenance costs and exceptional high resistance to corrosion, justifying its main usage in non- structural applications and in small size parts where corrosion is the main problem. Complementary, polymeric concrete has been increasingly used in recent years in the rehabilitation of civil structures, especially retrofitting of bridges and heritage buildings using polymeric mortar. Its advantages for these applications are the adherence to the traditional materials, a compressive strength higher than traditional concrete and low specific weight.

[13] Ongoing research has shown that an adequate amount of aggregates such as dry sands with a fine grain and gravel, with proper sizes, combined with low viscosity resin, can provide very good adhesion and compression properties preserving the other advantages of polymeric concrete. The nature of polymeric concrete allows adequate reinforcement through addition of fibre reinforced plastic materials or steel, thus complementing its mechanical properties, namely flexure strength. Thus, polymeric concrete can be successfully employed as a basis material on its own for large structures. Applied to towers for wind generators and other structural applications, the casting process of polymeric concrete allows plasticity in form modelling in a very cost-effective way, thus allowing adaptation and optimization of the structural design to loads and logistic restraints, while contributing with its chemical properties to reduce maintenance costs.

[14] Towers for large structural applications typically have a base diameter of more than 4 m and reach heights above 50 m , supporting heavy loads. Examples of towers for large structural applications are towers for windmills, lighthouses or pillars supporting highways in viaducts. For all of these polymeric concrete can be used as the base material, presenting advantages in lower maintenance and in lower logistics and production costs.

[15] The polymeric concrete is prepared by thorough mixing of the binder and filler materials in adequate ratios, and adding the hardener to promote the complete polymerization. Large scale production of polymer concrete is performed in proper equipment. Binder and filler have separate hoppers and their mixture is promoted through a screw mechanism. Granulometry and viscosity are controlled to assure the adequate flow of the resulting mixture and the final mechanical characteristics of the polymeric concrete. The finished mixture is then filled into a mould and compacted through vibration. The moulds are made of steel and/or other adequate materials. After polymerization the final product is removed from the mould. Description of the Figures [16] The annexed drawings exemplify a solution according to the invention:

Figure 1 shows a tower (1) made of several superimposed horizontal sections, or rings (2), of cast polymeric concrete, with convenient wall thickness.

Figure 2 shows a cross-section of one section (2), or ring.

Figure 3 shows the cross-section of another section(2), or ring, being built of 3 shell segments (3), joined together, using appropriate chemical bonding, like structural glue (4).

Figure 4 shows how two superimposed rings (5) and (6) are joined together using appropriate chemical bonding, like structural glue (7), between conveniently fitted ends, respectively (8) and (9), of the adjoining sections or rings. The same figure shows an example of a reinforcing element (10) within the polymeric concrete wall (11), used to adequately increase stiffness of the tower and decrease risk of fatigue failure. The casting process not only allows modelling the internal wall surface, but also allows fitting into the wall any kind of fixtures needed for installation of the internal cabling system, stairs, platforms, etc.

Figure 5 shows an inserted fixture (15) to fix cables, or other means of handling the sections or rings, inserted into the polymeric concrete wall (16) of a segment or ring. Detailed Description of the Invention

[17] The tower, according to the invention, is built of two or more superimposed ring sections in conical or cylindrical form, each ring being built of one or more shell segments, these segments are joined by means of mechanical and/or chemical bonding and made of pre-cast polymeric concrete. [18] The segments are moulded after mixture of the binder and filler materials, as described above. The binder is a thermosetting resin like polyester resin, epoxy resin, phenolic resin, vinyl ester resin or others. Before filling the moulds with polymer concrete, chopped fibres mixed with the thermosetting resin can be sprayed onto the mould external wall, to enhance the tensile resistance of the segment. [19] The rings have specially designed ends in order to assemble into each other when building a tower. Between two superimposed rings, as seen in figure 4, the one in the bottom has the top end shaped like a step with, from the interior to the exterior, first a bottom horizontal surface (12), second a inclined middle surface (13), and third a top horizontal surface (14). In turn, the top ring, in each pair of superimposed rings, has a bottom end shaped as an inverted step ( 12', 13', 14') matching the corresponding top end surfaces of the bottom ring. This kind of assembly makes the structure more stable because, as the top ring assembles with a bottom ring, both inclined middle surfaces 13 and 13' of the rings are uniformly pressed against each other, this way pressing the structural glue interposed between the two surfaces. Surfaces 12 and 12', or 14 and 14', are joined by press fit due to the top ring weight or are also glued. Furthermore, this configuration provides a conveniently extended interface for application of the structural glue at assembly, which can be subjected to shear stresses, enhancing its effect in providing the necessary stiffness and mechanical resistance of the tower. To optimize the joining efficiency and to decrease the tensions applied, the surface 13 and 13' are positioned near the internal surface of the ring.

[20] To help stabilise the tower even more, a post tensioned reinforcing element (10), such as a steel or a polymeric cable, or a composite profile, can be used within the polymeric concrete wall (11) in order to increase the stiffness of the tower and decrease risk of fatigue failure. To optimize mechanical efficiency, this reinforcement is positioned near the external surface of the ring and is stressed when fixing the top ends at assembly. Furthermore, if this reinforcing element extends through two or more adjacent rings, it can be used as a mechanical joining method between these rings, complementing or substituting the structural glue.

[21] These advantages are valid both for cylindrical and conical tower segments.

[22] It should be clear that the described embodiments are simply examples of execution of the present invention. Variations and modifications, that are obvious to a person skilled in the art, can be made within the scope of the invention and are still protected by the following claims.

Claims

[1] A tower to support on-shore or off-shore wind generators or other large structures, wherein the said tower is formed by two or more superimposed ring sections, each ring comprising one or more shell segments, which are affixed by means of mechanical and/or chemical connection and made of pre-cast polymeric concrete, which is composed of a thermosetting resin with an aggregate of at least 60% weight dry sands and/or gravel.

[2] The tower, according to claim 1, comprising a conic, cylindrical or prismatic external shape.

[3] The tower, according to claim 1 and 2, characterized in that, between two superimposed rings, the bottom (6) has the top end (9) shaped like a step comprising, from inside-out, firstly a bottom surface (12), then an inclined middle surface (13), and thirdly a top surface(14), and in that the top ring (5), in its turn, comprises in each pair of superimposed rings, has a bottom end (8) shaped as an inverted step (12', 13', 14') that matches the counterpart surfaces of the bottom ring.

[4] The tower, according to claim 1 to 3, wherein further aggregates up to a maximal content of 20% weight of the polymeric concrete are used, to enhance chemical and/or physical properties.

[5] The tower, according to claims 1 to 4, wherein a reinforcement of composite materials is used within the polymeric concrete wall along one or more superimposed rings.

[6] The tower, according to claims 1 to 4, wherein a reinforcement of steel cables is used within the polymeric concrete wall along more than two superimposed rings.

[7] The tower, according to claims 1 to 4, wherein reinforcement steel walls are used in the outer and/or inner surfaces.

[8] The tower, according to any of claims 1, 2, 4, 5, 6 or 7, wherein casting takes place on-site.