DA GUIA LÚCIO, Válter José (Al. Mahatma Gandhi, Nº 16 - 2º Esq, -502 Lisbon, P-1600, PT)
DA GUIA LÚCIO, Válter José (Al. Mahatma Gandhi, Nº 16 - 2º Esq, -502 Lisbon, P-1600, PT)
| CLAIMS TRUSS TOWER 1. Tower to support wind turbines, power lines or communication lines, water tanks, bridges, oil exploration or any other application, characterized by comprising a plurality of structural levels, each one comprising at least three or more columns U) , precast in different types of concrete, with an inclination towards the vertical lower than 15 degrees and a plurality of cross beams (2), precast in different types of concrete, crossing at joints (3) • 2. Tower, according to claim 1, characterized by further comprising bracing diagonals {4) in said columns (1) planes and/or bracing diagonals (5) in said cross beams (2) planes, made of other elements precast in different types of concrete or by tendons, in order to resist the wind, earthquakes or other similar actions. 3. Tower, according to claims 1 and 2, characterized by said precast columns (1) having cross section dimensions lower than 1/3 of their length, and said cross beams (2) and said diagonals (4, 5} being precast with suitable variable dimensions . 4. Tower, according to any one of claims 1 to 3, characterized by being precast with selected types of concrete selected from concrete, reinforced concrete, reinforced presstressed concrete, fiber reinforced concrete, high or ultra high strength concrete, or its combinations with reinforced composites or polymer-based concrete. 5. Tower, according to any one of claims 1 to 4, characterized by said columns (1) and cross beams (2) or bracing diagonals (4, 5) being hollow or solid. 6. Tower, according to any one of claims 1 to 5, characterized by said coLumns (1), cross beams (2) or bracing diagonals (A, 5) being connected together by mortar, resin, tendons, rods, bolts or any other suitable type of connection. 7. Tower, according to any one of cϊaims 1 to 6, characterized by further comprising at the top of said tower, a base (7) to support equipment selected from wind turbines, power- lines or communication lines, water tanks, bridges, oil exploration or other similar application. 8. Tower, according to any one of claims 1 to 7, characterized by comprising direct foundations (11) on soil, or indirect foundations through piles with pile caps (12), or on water through piles (13), or on a floating structure (14). 9. Tower, according to any one of claims 1 to 8, characterized by further comprising a prefabricated exterior faςade. 10. Tower, according to claim 9, characterized by comprising on different tower levels, rooms for equipments or other functions . 11. Tower, according to any of the preceding claims, characterized by being partially built in situ and partially precast. 12. Method of construction of a tower according to claims 1 to 11, characterized by being partially built in situ and partially precast. 13. Method according to claims 12, characterized by erecting over foundations (6) at least three precast, columns (1) with an inclination with the vertical lower than 15 degrees, connecting them to cross beams (2), crossing at joints (3), creating levels, and optionally to bracing diagonals (4, 5), and by making the connections of said columns (1) to said cross beams (2), and optionally to said bracing diagonals (4, 5) with mortar, resin, tendons, rods, bolts or any other suitable type of connection. 14. Method according to claim 12 or 13, characterized by the fact that direct foundations (11), foundations built over piles (12, 13) or foundations on floating structure (14) are used. |
TRUSS TOWER
TECHNICAL DOMAIN
The present invention relates to precast concrete towers with a truss structure and their method of assembling. Possible uses for such towers may be the structural support of wind turbines, of overhead power lines or communication lines, water tanks, bridges, or the support for oil exploration, among others, onshore or offshore.
STATE OF THE ART
Different structural solutions and construction methods have been proposed for towers in order to provide structural support for wind turbines or electrical cables. Current solutions are guyed poles, steel shells, steel lattice, in situ or precast concrete shells, hybrid towers of concrete shells and steel lattice or even composite or polymer concrete towers.
The structural solution to be adopted for these towers should be designed to resist the static and dynamic actions imposed on the structure. Their construction process should be characterized by quick erection and the use of easily transportable elements (which should be reduced in number) , so that the costs of production, transportation, installation and maintenance can be reduced.
So far, most towers which support the wind turbines have been steel towers with cylindrical or truncated conical staves assembled on site and connected to the reinforced concrete foundation by anchors and to each other by bolts. However, the need to increase the height of the towers, with the resulting increase in their diameter and wall thickness, and hence the amount of steel, has found increasing limitations on the use of this structural solution. This is due either to the cost of steel (whose price has large fluctuations in the market), either to limitations of production and transportation related to the dimensions of the staves required for towers higher than eighty meters.
Several proposals have been made to improve the structural solutions available with steel. There have been solutions with various ring sections and shell segments, such as in WO 2004/083633 Al, solutions with a more complex wall profile, such as in EP 15611883 Al or hybrid solutions, made of a lower section of concrete and an upper section of steel, such as in WO 2005/015013. These solutions allow the construction of tallerl towers but ifl their height is increased, the problems associated with the natural frequency of the structure cannot be solved with such techniques.
In addition, onshore steel towers require constant maintenance due to the onset of corrosion during the operating life of the wind turbine, which is around twenty years. For offshore towers, the problem of corrosion is even more important, entailing additional costs of maintenance. This type of structural solution is characterized by its simplicity of construction, once the truncated conical steel tubes - with no longitudinal stiffeners and having rigid rings only at the ends - are connected together in joints about 20 meters away. These structures are also characterized by its easiness of manufacture, handling and speed of transport and assembly, as well as the possibility of being easily dismantled after the completion of its life cycle. Thousands of towers of this type have been built and so there are many companies with the experience and skills needed to produce, transport and assemble them.
More and more powerful turbines are expected in the future of wind power (above 5^3W) , with a consequent increase in the height of the towers and a decrease in their number. With this new situation, some features of the steel towers lose the advantages outlined above. One of their limitations is the maximum diameter of their base, which for transportation reasons cannot exceed 4.30 meters and thus represents an insurmountable obstacle to increase the tower height. Besides, when the height of the towers is increased, the steel towers become structurally more susceptible to fatigue, instability, flexibility and dynamic behavior to the wind and seilsmic actions bedause of the reduced ductility of their behavior. Furthermore, the increase of the towers' height requires heavier foundations (Pliego, M. G.; Sicart, T. A, Garcia-Conde, J. S., "Torres eόlicas de hormigόn prefabricado. " IV Congresso de ACHE 24- 27 November 2008, Valencia, Spain) .
Several methods of construction for the concrete wind towers are known. The cast in situ concrete with climbing formwork has great .limitations. In structures with climbing formwork, its geometry is largely determined by the technology and cost of formwork, the runtime is heavily dependent on weather conditions, the finishing quality is very diverse and there are uncertainties associated with processes that are not uniform. As such, its use has been essentially limited to experimental towers. Other solutions in structural concrete for towers higher than 95 meters, have been proposed in DE 100 33 845 Al, DE 60 306 B4 , WO 2006/111597 Al and WO 2008/031912 Al. These solutions are characterized by precast staves in reinforced concrete and post- tensioned steel strands. However, these solutions are considerably heavier than the steel towers, with associated costs of transport logistics and assembly. The solutions that make use of reinforced concrete shells - which after in situ assembly become tubular section towers - can solve some of this assembly and transport difficulties and reduce their costs (Pliego et al, 2008) . In the meantime, other proposals using polymer concrete were put forward, being WO 2008/032281 Al an example of a tower with a tubular section consisting of precast concrete shells.
In US 2006/0277843 A by Livingston et al . a structural tower is disclosed for high elevation and heavy load applications, with longitudinal, horizontal and diagonal element's, with metallic hollow cross sections, some of them including damping devices with viscoelastic material, viscous fluid or hydraulic.
All the referred solutions have disadvantages, namely the cost of production and / or assembly and / or maintenance, the technical limitations imposed by the limitations of the gauge of transportation, the complexity or low durability and / or high maintenance required.
As a consequence, there is the need for towers that can reach great heights - taller than those currently available -, and that can be simultaneously precast, not subject to transport gauges and that are structurally optimized both in terms of strength and the control of its natural frequency of vibration.
Another perceived need is to have towers that concentrate the following features: have greater heights, support more powerful and heavier equipment, and whose construction, transportation and assembly are fast and reliable. At the same time there is the need for materials that are widely available, cheap, durable, and recyclable and the need for towers with easy repair and low maintenance, namely that resist corrosion in marine environment.
Throughout the description and the claims, the word "comprising" and its variants is not intended to exclude other technical characteristics, components or steps. Other objectives, advantages and features of the invention will become apparent to those of ordinary skill in the art upon analyzing the description or when implementing the invention. The drawings and following embodiments are meant to be merely illustrative, not limiting in scope the present invention. Furthermore, the present invention covers all possible combinations of the particular and preferred embodiments described herein.
SUMMARY OF THE INVENTION
The present invention solves the problems found in the state of the art described above and provides a truss tower to support wind generators, transmission lines, power or communication lines, water tanks, and bridges, oil exploration or the like, comprising a plurality of structural levels, each comprising at least three columns in different types of precast concrete with a inclination of less than 15 degrees from the vertical and a plurality of horizontal cross beams in different types of precast concrete.
Optionally, bracing diagonals can be used in the plans of the columns and/or plans of the cross beams made of other precast elements or tendons, in order to resist the -wind actions, earthquakes or the like.
The columns have cross-sectional dimensions not exceeding 1/3 of its length, and the cross beams and precast diagonals vary in size to suit the intended purpose.
The materials which are especially suitable for the manufacture of the precast elements are selected from concrete, reinforced concrete, prestressed concrete, fiber reinforced concrete, high or ultra high strength concrete, or their combinations with reinforced composites or with polymer concrete. Such elements, columns, cross beams or bracing diagonals may be hollow or solid.
The columns, cross beams, and optionally additional bracing diagonals, are connected together by mortar, resin, wires, rods, bolts or any other suitable type of connection.
According to the present invention the tower may have at the top a base to support equipment selected from wind turbines, power lines or communication lines, water tanks, bridges, oil exploration or any other application. The tower foundations, according to the present invention, may be direct on soil, or indirect through piles with pile caps, or on water through piles or on a floating structure.
Additionally, a prefabricated exterior faςade can be provided, if desired, to provide rooms for equipment or any other functions at different levels of the tower.
The construction process of the tower of the present invention is characterized by being partially built in situ and partially precast. Thus, the present invention also relates to a process of building towers in accordance with the present invention, which comprises the erection, over the foundations, of at least three precast columns with an inclination with the vertical lower than 15 degrees, connected to cross beams in the joints, creating levels, where the connections between said columns and said cross beams, and optionally said bracing diagonals, are made with mortar, I resin, tendons, rods, bolts or any other adequate type of connection. The foundation can be direct on soil, or indirect through piles with pile caps or on water through piles or on a floating structure.
The present invention solves the problems above identified both in steel and concrete towers built in situ, providing concrete precast construction elements such as columns, cross beams and diagonals made of other precast elements or tendons. The invention now presented has the advantage of allowing the fast construction of high-rise towers using said elements, which are easily transportable and in reduced number - thus saving costs in production, transportation and assembly, as well as maintenance. Moreover, according to the characteristics of the selected concrete, to the size and to the level of prestressing of the different elements, columns, cross beams and diagonals, as well as the spacing between them, it is possible to control the natural frequency of vibration of the tower, in accordance with its intended use requirements.
The precast reinforced concrete tower made up of columns, cross beams and diagonals - precast and optionally prestressed according to the present invention - which form a spatial truss structure, has outstanding advantages when compared to steel towers or to other towers in shell precast concrete, the most important of which are:
• The adoption of a system that is not conditioned by current dimension limits in the transportation routes, therefore allowing the freedom to choose the geometry of the tower. This enables the structural optimization of the system, both in terms of its resistant capacity and the control of its natural vibration frequency;
• The ability to build very high towers capable of supporting high-power turbines onshore and offshore;
• A significant, improvement of the structural damping, and therefore an improved dynamic behavior, allowing the reduction of fatigue actions and contributing to the increase of the equipment operating life and cost savings on maintenance;
• The connections between elements are reliable, tested, maintenance free, easy and quick to implement on site, providing all the advantages of the structural monolithism; • Excellent response to sismic actions, thanks to the high ductility of all elements of the tower and its high structural damping which increases in situations of extreme loads; this allows the structure to absorb and dissipate energy in the event of an earthquake, contrasting with the behavior of steel towers;
• The significant stiffness and vibration frequency of the towers greatly reduces the requirements for the foundation stiffness; this leads to fewer uncertainties associated with the deformabiiity of the ground and allows significant cost savings of the foundation, especially in soft ground;
• The significant weight of the tower has a stabilizing effect and allows an important reduction of the required foundation weight, leading to a reduction of costs;
• High speed assembly, thanks to the use of very long elements and appropriate quick systems of implementation of structural
I i i connections;
• The space in the base of the tower allows mounting of equipment in a single level, without constraints of space;
• Simple, cheap and reliable connections of the columns to the foundation;
• Easy mounting of equipment to the elements of the tower;
• Reduced need for maintenance, in contrast to the steel towers;
• Higher durability of concrete structures compared to steel towers - especially in maritime environments - due to the protective action of an appropriate reinforcement concrete cover. This durability increases with the use of high- performance concrete in the structure of towers for wind turbines; • The durability of concrete towers is much higher than that of the turbine equipment they support, with no structural limitations to their capacity. This opens the possibility of future reinstalling and replacing of wind turbines with larger power ones, expanding the scope of amortization of the work and infrastructure for the transport of energy costs, which are especially costly in the case of offshore facilities.
• Tolerance to impact damage or accidental actions as it is easy and economical to repair in such circumstances;
• Less noise due to the damping effect of the concrete;
• Reduction of C02 emissions in the manufacture of the tower
(around 55 to 65% of the emissions involved in the manufacture of a metal tower} ;
• Aesthetic quality due to its geometry and the industrial quality of the finishes of the elements produced in a factory. It is even possible to produce concrete with different textures and colours;
• Good integration of wind turbines in the landscape as the increased capacity of the towers enables an increase of their size and a reduction in the number of towers to obtain equal power;
• The material of the towers is totally recyclable. At the end of the structure life cycle, concrete - especially high performance concrete used in wind towers - can be used as aggregates in the production of new concrete;
Other advantages and features of the invention will become apparent from the following detailed description with reference to the attached drawings and can be accomplished through the elements and combinations particularly claimed in the claims appended. BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be now described with reference to the accompanying drawings which illustrate embodiments in accordance with the invention, in which:
Figure 1 illustrates a front view of an embodiment of the tower in accordance with the present invention without diagonals at the pJanes of the columns;
E'igure 2 illustrates a front view of another embodiment of the tower in accordance with the present invention, with diagonals at the planes of the columns;
Figure 3 illustrates a front view a third embodiment of the tower in accordance with the present invention, with diagonals at the planes of the columns and columns with variable inclination in height between levels;
Figure 4 shows cross-sections along the lines A-A of Figures 1, 2 and 3 of three preferred embodiments of the present invention, with three columns in Figure 4a) , with four columns on a square without bracing diagonals in the plane of the cross beams in Figure 4b) , and with four columns on a square with bracing diagonals in Figure 4c) ;
Figure 5 illustrates a schematic cross section of several mounted alternative foundations, 5a) to 5d) , on which the tower can be settled in accordance with the present invention;
Figure 6 represents cross-sections of embodiments of the tower foundations according with the present invention: by direct foundation in Figures 6a) and 6b) and by piles in Figures 6c) and 6d);
Figure 7 represents front views of two preferred embodiments of the tower represented in Figures 1 and 3 in its applications for the support of power lines in Figure 7a) and wind turbines in Figure 7b) .
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention and with reference to the annexed drawings a precast concrete tower is provided, consisting of a plurality of levels of precast components, forming a spatial truss, optionally prestressed. In the context of the present invention, "truss tower" refers to a spatial structure that resists external actions mainly through axial forces in its elements but where the continuity of certain elements in the joints establishes a secondary system resistant to flexural forces.
The structural elements, columns 1, cross beams 2 and joints 3, may have different shapes, be hollow or solid, and can be connected together by wires, rods, bolts, mortar, resins or other types of structural connection.
I
In another aspect, the tower of the present invention comprises at each level, three or more precast columns 1, with small inclination to vertical, braced horizontally with precast cross beams 2. The expression "with little inclination to vertical" means in the context of the present invention an inclination of less than 15 degrees from the vertical. The dimensions of the cross section of the columns do not exceed 1/3 of their length, as recommended in EN 1992-1-1 - Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings, CEN, December 2004 and ACI 319-08 - Building Code Requirements for Structural Concrete (ACI 319-08) and Commentary, American Concrete Institute, January 2008. The columns 1 project from the foundation 6 and continue up to the equipment base 7 having intersections with the cross beams 2 at the joint levels 3. Optionally, as an additional bracing, to resist the wind, earthquake, or other actions, may be used diagonals (4) in the columns planes 4 and/or diagonals in the planes of the cross beams. These diagonaJs, 4 and 5, can be precasted components or tendons .
Depending on the application for which it is designed, the tower can be built offshore or onshore. The foundations of the tower can be direct or indirect.
The tower may have several applications: it can support wind turbines, overhead power lines, or communication lines, bridges, or support oil exploration or even other applications.
'The materials ! to be used iri the towers df the present invention are dependent on the state of the art and its corresponding cost. However, the present possibilities include plain concrete, reinforced or presstressed concrete, as well as mixed solutions and those with FRP (Fiber Reinforced Polymer), SIFCON (Slurry Infiltrated Fiber Concrete), SIMCON (Slurry Infiltrated Mat Concrete), polymer concrete, high or ultra-high strength concrete, among other materials which contribute for an adequate structural solution of the tower, i. e., capable of resisting the active stresses in accordance with the required safety levels. The expression "high or ultra high strength concrete" means in the context of the present invention, concrete with the characteristic value of the compressive strength in cylindrical samples, respectively, between 60 MPa and 150 MPa to 150 MPa or higher as indicated by Eleni Sofia Lappa in "High strength fiber reinforced concrete - Static and fatigue behaviour in bending", PhD Thesis, DeIf University of Technology, Netherlands, 2007.
The precasting of _ concrete elements allows the industrialization of its production, with all the associated advantages. The industry for the manufacture of precast concrete towers will require simple technologies and materials which are widely available almost anywhere.
It is possible to have a wide range of towers embodiment according to this invention for a variety of turbines with different powers. The towers can be adapted to the requirements of different turbines just by setting their global geometry, keeping the basic geometry of the main tower elements.
Referring to Figures 1 to 3 and A, the tower of the present invention comprises a plurality of levels of structural elements: columns 1, cross beams 2, joints 3, diagonals 4 in the columns planes, diagonals 5 in horizontal planes at the cross beam 2 levels, a foundation 6 and a base to support the equipment 7.
The cross-section of the tower, by lines A-A of Figures 1 to 3, can be triangular as represented in Figure Aa) , square as represented in Figures 4b) and Ac) , or have any appropriate polygonal adequate shape. The use of diagonals A represented in Figures 2, 3 and 4c) applies to cases where the columns 1 and the cross beams 2 do not provide enough strength and stiffness capacity to resist horizontal actions on their own. En a preferred embodiment of the present invention, represented in Figure 4b), the columns 1 have variable inclination between levels.
The several structural elements 1, 2, 4 and 5 in the presented embodiment, of the tower of ±he present invention may present a plurality of different shapes, be hollow or solid and may be connected by tendons, rods, bolts, mortar, resins or any other adequate structural connection (not represented) . The materials of the structural elements 1, 2, 4 and 5 of the tower of the present invention are selected from among the concrete types referred above .
Figure 5 illustrates different types of foundation 6 in which the cower of the present invention may be based. Alternative foundations 6 are suitable for installation on land or on water. The foundations 6 of the tower can be of any kind, direct or indirect. The tower can be built either upon direct foundations 6 as represented in Figure 5a), on soil or rock, or indirect, with pile caps as represented in Figure 5b) . When it is built on water, it is preferable for the tower to be founded on piles as represented in Figure 5c), or on a floating structure as represented in Figure 5d) .
Figure 6 shows alternatives for direct foundations 6 as represented in Figures 6a) and 6b) and on piles as represented in Figures 6c) and 6d) .
Referring to Figure 7, and as an example, Figure 7a) schematically illustrates the embodiment of the tower without diagonals 4 used to support overhead power lines 19 and Figure 7b) illustrates the embodiment with diagonals 5 and columns 1 of variable inclination to support wind turbines 20.
The method of assembling the tower of the present invention is characterized by the possibility of being partially built in situ and partially precast over a foundation 6, erecting at least three precast columns 1 with an inclination with the vertical lower than 15 degrees, connecting the referred columns 1 to the cross beams 2 in the joints 3, creating levels, where the connections between the referred columns 1 and the referred cross beams 2, and optionally the referred bracing diagonals 4 and/or 5 are made with mortar, resin, tendons, rods, bolts or any other adequate type of connection, that foundation 6 may be direct, built over piles or on a floating structure.
Lisbon, April 7, 2010.