HYBRID TOWER SYSTEM

FIELD OF THE INVENTION

The present invention relates to systems and methods for fabricating towers and other structures from hybrid materials. More particularly, the present invention relates to systems and methods for constructing jacketed steel-concrete hybrid structures, such as may be useful for towers, including those commonly used for wind turbine systems.

BACKGROUND OF THE INVENTION

The choice of materials for fabrication of structures represents a tradeoff between the good and bad properties of different materials. The type of structure to be fabricated may, at times, result in the absence of any one ideal material from which to fabricate the structure. For example, steel can be very efficient in tensile applications, but can be subject to buckling under compression forces, particularly when steel is relatively thin. Buckling is a huge concern for steel towers in seismic zones. Such buckling can prevent the full utilization of the material yield strength of the steel. As a result, there may be no advantage in using higher strength steel for many applications. The design steps associated with reducing buckling in steel are time consuming and, in many cases, requires the use of advanced methods of analysis, such as three dimensional non-linear finite element analysis. Steel is also prone to fatigue, which can be a major concern in its use for structures. Concerns with buckling and fatigue can be particularly disadvantageous for use in steel tower systems. However, steel's desirable attributes under tensile forces can be useful in a tower application.

Concrete, unlike steel, possesses very good characteristics under compression and, additionally, can be cheap in comparison to steel. Unfortunately, concrete possesses an extremely low tensile capacity, so low, in fact, that design calculations often assume a zero tensile capacity for concrete. The concrete compressive strength can be increased if confined, thereby enabling it to perform even better. Confinement of concrete also increases the concrete's inelastic deformation capabilities, such as displacement or curvature ductility.

Thus, any individual material, such as steel or concrete, may possess some but not all of the characteristics desired for a given structure fabrication. For example, in the fabrication of a tower, such as may be used to support a wind turbine for generating electricity, steel can provide desirable properties under tensile forces, but can be subject to failure by buckling before reaching its yield strength under compression, while further being prone to fatigue and cracking. In order to account for buckling type failure of steel, difficult and expensive analysis is required. On the other hand, concrete possesses desirable qualities under compression, while also being comparatively cheap to employ. Concrete's desirable compressive strength can be further increased by confining the concrete, and such confinement can further significantly increase the inelastic deformation capacity of the concrete. However, the tensile capacity of concrete is nearly zero.

SUMMARY OF THE INVENTION

The present invention utilizes a jacketed hybrid system of steel and concrete to take advantage of the desirable properties of both steel and concrete while alleviating the less desirable properties of the two materials. Systems and methods in accordance with the present invention may be particularly useful for the fabrication of towers, such as may be used to support wind turbine systems for electricity generation. In structures built in accordance with the present invention, the whole of the structure may be viewed as greater than the sum of its parts, as the resulting structure possesses the tensile strength of steel, while also possessing the compressive strength of concrete. A structure in accordance with the present invention may further take advantage of the relative low cost of concrete, while further avoiding the difficult and expensive analysis required to account for buckling failure in steel. Structures in accordance with the present invention may use a structural steel

"jacket" into which concrete is poured. The concrete is thus confined, thereby further increasing the compressive strength and inelastic deformation capacity of the concrete. The steel jacket utilized in accordance with the present invention may optionally be substantially circular, which has been found to further improve the compressive and inelastic deformation capacity of the concrete.

BRffiF DESCRIPTION OF THE DRAWING

Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein: FIG. 1 depicts an example of a tower in accordance with the present invention;

FIG. 2 represents a tower base in accordance with the present invention;

FIGS. 3-5 illustrate possible tower base details in connection with the present invention;

FIGS. 6-8 illustrate splice details in accordance with the present invention; FIGS. 9-15 further illustrate foundation connection details in accordance with the present invention; and

FIG. 16 illustrates a method of erecting a hybrid structure in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides systems and methods for constructing hybrid structures. Structures in accordance with the present invention may utilize a hybrid jacketed construction system. The jacket may be a thin steel that is subsequently filled with concrete. In this manner, the high tensile capacity of steel may be combined with the compressive strength of concrete to form an easily erected, relatively inexpensive structure. Structures in accordance with the present invention may be particularly useful in wind tower systems, where the structure is used to support a nacelle (the gear box and generator) and the rotor (blades) of an electricity generating winded turbine. However, one skilled in the art will realize that the present invention may be used beyond wind turbine tower systems, such as bridge gurters, building components, railing systems for bridges, power line towers and other structures.

A structure, such as a tower, may be formed in accordance with the present invention by stacking jacket sections and connecting them together. Concrete placed within the jacket sections provide compressive strength and other desirable structural properties for the tower. Each jacket section may comprise double walls of a thin steel plate, which may, for example, be constructed using high performance steel (HPS). The functionality of steel is measured using several different properties such as strength, weldability, toughness, ductility,

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corrosion resistance, and formability. HPS can be defined as having an optimized balance of all of these properties to give maximum performance while remaining cost-effective. The main two differences compared to conventional 485-megapascal (MPa) steels are improved weldability and toughness. The thickness of the steel plate used in forming a double wall could vary, but can be very small, even to the order of ¹ A of an inch. Someone possessing skill in the art would appreciate that the present invention is not limited to steel that is exactly ¹ A of an inch and should also be mindful of normal manufacturing tolerances. Also, a particular application may dictate thinner or thicker dimensions which is fully within the scope of the present invention. Referring now to FIG. 1, a tower 100 in accordance with the present invention is illustrated. Tower 100 is supported by a foundation 110. A first jacket section 120, which may also be thought of as a base jacket section, is affixed to foundation 110 by a base detail 115. A few of the various options for base detail 115 to connect tower 100 with foundation 110 are described subsequently. First jacket section 120 may connect to second jacket section 130 via splice detail 125. Various examples that may be used for splice detail 125 are described subsequently. Tower 100 may comprise any number of sections. As illustrated in FIG. 1, tower 100 further comprises a third jacketed section 140 connected to second jacketed section 130 by splice detail 135, and a fourth jacketed section 150 connected to third jacketed section 140 by splice detail 145. One skilled in the art will appreciate that the present invention is not limited to any particular number of jacketed sections.

The tower anchorage detail secures the tower 100 to the ground. Several options are available including but not limited to a bolted system and an embedded system. These systems are illustrated in FIGS. 4-5 and described in more detail below.

Referring now to FIG. 2, a portion of a base detail is illustrated. Foundation 110 and base section 120 may be joined using base detail 115. Further descriptions of possible configurations of a base detail 115 are described below. FIG. 2 further illustrates a cut away view of base jacketed section 120. As shown in FIG. 2, jacketed section 120 includes an outer wall 210 and an inner wall 220. Between inner wall 210 and outer wall 220 is compressed concrete 230. Outer wall 210 and inner wall 220 may be constructed, for example, using high performance steel and may be approximately ¹ A inch thick, although other materials and other dimensions may be utilized without departing from the scope of the present invention. Concrete 230 may occupy a cavity between outer wall 210 and inner wall

220 of approximately six inches, although this dimension may vary without departing from the scope of the present invention.

FIG. 3 further illustrates a base detail in accordance with the present invention. Foundation 110 supports tower 100. One skilled in the art will appreciate that only a portion of tower 100 is illustrated in FIG. 3. Foundation 110 may be further supported by a substructure such as compiles 310. Tower 100 may comprise an outer wall 210 and an inner wall 220 with concrete fill 230 between them. Concrete inlet 340 may be provided to permit concrete to flow between outer wall 210 and inner wall 220. Concrete inlet 340 may be any type of coupling compatible with concrete equipment permitting concrete to be transported into the cavity between outer wall 210 and inner wall 220. One skilled in the art will appreciate that concrete inlet 340 may be positioned at varying locations in any given jacket section, and will further appreciate that more than one concrete inlet 340 may be provided within any given jacket section. Base jacket section 120 may be affixed to foundation 110 via base connection detail 330. Options for use as base connection detail 330 are further illustrated in FIG. 4 and FIG. 5. One skilled in the art will appreciate that either of the options for base connection detail 330 illustrated in FIG. 4 and FIG. 5 may be used in accordance with the present invention, and will further realize that various combinations of these options and other options may be utilized without departing from the scope of the present invention. Referring now to FIG. 4, a bolted base connection detail 330 is illustrated. A first bolt 430 and a second bolt 440 may be cast into foundation for subsequent use in attaching an outer base plate 410 and an inner base plate 420 to foundation 110. One skilled in the art will appreciate that more than a first bolt 430 and a second bolt 440 may be used in accordance with the present invention, and that two bolts are illustrated for the sake of simplicity. Similarly, a first attachment bolt 450 and second attachment bolt 460 may be utilized to attach a base jacketed section 120 to plate 410 and plate 420. Bolt 450 and bolt 460 may extend through plate 410, plate 420, outer wall 210, inner wall 220 and concrete fill 230 (which may be cast around bolts 450, 460) in order to ultimately secure base plate 120 to foundation 110. One skilled in the art will appreciate that bolts beyond first bolt 450 and second bolt 460 illustrated in FIG. 4 may be utilized in accordance with the present invention.

Referring now to FIG. 5, a further option for foundation base detail 330 is illustrated. As illustrated in FIG. 5, a portion of jacketed base section 120 may extend into foundation 110. The connection between base jacketed section 120 and foundation 110 may

be enhanced by extending metal rebar 530 through base section 120 prior to casting the concrete used for foundation 110. Concrete fill 130 may subsequently or contemporaneously be placed between outer wall 210 and inner wall 220.

The jacket sections used to construct a tower 100 in accordance with the present invention may be connected using a variety of splice details. Three examples of splice details are illustrated in FIGS. 6-8. One skilled in the art will appreciate that the splice details illustrated in FIGS. 6-8 are exemplary only, and that they may be combined in varying ways beyond those depicted herein, and will further appreciate that any other form of splice may be utilized in accordance with the present invention. Referring now to FIG. 6, a slip connection splice 600 is illustrated. Slip connection splice 600 utilizes a lower jacket portion 610 that has a wider gap between outer wall 611 and inner wall 612 bend upper jacket section 620 has between outer wall 621 and inner wall 622. This enables upper jacket section 620 to slide within the cavity between outer wall 611 and inner wall 612 of lower jacket section 610. Upper jacket section 620 may then be affixed to lower jacket section 610 using one or more bolts 630. Lower concrete fill 613 may be placed between outer wall 611 and inner wall 612 of lower jacket section 610, and upper concrete fill 623 may be placed between outer wall 621 and inner wall 622 of upper jacket section 620. One skilled in the art will further appreciate that lower concrete fill 613 and upper concrete fill 623 may be placed within the cavity of the combined lower jacketed section 610 and upper jacketed section 620 as part of a single concrete pouring process.

Referring now to FIG. 7, a further splice detail option is illustrated. Plate splice 700 utilizes a outer plate 730 and an inner plate 740. As illustrated in FIG. 7, lower jacketed section 710 and upper jacketed section 720 possess similar dimensions between their outer walls and inner walls. For example, lower jacketed section 710 inner wall 711 and outer wall 712 are separated by approximately the same distance as upper jacketed section outer wall 721 and inner wall 722. Thus outer plate 730 may extend over both upper jacketed section outer wall 721 and lower jacketed section 710 outer wall 711, and inner plate 740 may extend over both upper jacketed section 720 inner wall 722 and lower jacketed section 710 inner wall 712. A plurality of bolts 750 may be utilized to extend through outer plate 730 outer jacketed section walls 711 or 721, inner jacketed section walls 712 or 722, and inside plate 740. Lower concrete fill 713 may be used to fill between outer wall 711 and inner wall 712 of lower jacketed section 710, and upper concrete fill 723 may be used to fill between outer wall 721 and inner wall 722 of upper jacketed section 720. Alternatively,

lower concrete fill 713 and upper concrete fill 723 may be formed from a single concrete pouring process.

Referring now to FIG. 8, a base plate splice 800 is illustrated. As illustrated in FIG. 8, a lower jacket section 810 may be affixed to an upper jacketed section 820 using base plates. Lower jacketed section 810 includes a base plate formed from an inner plate 842 that extends from inner wall 812 and an outer plate 841 that extends from outer wall 811. Similarly, upper jacketed section 820 possesses a base plate that includes inner base plate section 832 extending from inner wall 822 and an outer base plate section 831 extending from outer wall 821. Bolts 850 may be used to join base plates in a base plate splice. Further illustrated in FIG. 8 are optional studs 860 that may extend through a base plate splice 800 into lower concrete fill 813 within lower jacket section 810 and upper concrete fill 823 within upper jacketed section 820. Studs 860 may, for example, comprise steel rebar. Welds 870 may further strengthen the connection between a base plate section and a jacketed section wall. Optionally, air hole 880 may permit air to escape from between an inner wall such as inner wall 812 and outer wall such as outer wall 811, when concrete is placed within a jacketed section, such as jacketed section 810. One skilled in the art will further appreciate that air holes such as air hole 880 may be utilized in conjunction with other splices in accordance with the present invention.

Regardless as to the type of foundation base detail and/or splice detail used in the construction of a tower in accordance with the present invention, the present invention provides several advantages in the fabrication of towers or similar structures. For example, structures in accordance with the present invention benefit from the positive properties of both steel and concrete, while not suffering from the negative properties of either. Jacket sections in accordance with the present invention may be shipped to a construction site empty, thereby enabling them to be light, easily transported, and easily erected. After erection, or during erection, concrete may be placed within the cavity of a jacketed section, allowing it to be obtained locally, and only when needed. The confinement of concrete, as between an inner wall and an outer wall of a jacketed section in accordance with the present invention, enhances the structural performance of the concrete. The concrete placed within the cavity prevents the buckling of the double wall steel plates of the jacketed sections, which allows for the optional use of much thinner steel plates for the double wall portion than would be otherwise possible. In order to permit the jacketed sections and encased concrete to work compositely, there is no need to attach mechanical devices such as shear studs to the steel

plates, although such devices may optionally be utilized. Because of the relatively thin steel walls that may be utilized in accordance with the present invention, and because shear studs or similar devices are not necessary, the amount of steel used in structures in accordance with the present invention is very small. FIGS. 9-15 illustrate further options for attaching a base jacketed section to a foundation. FIG. 9 illustrates embedding the base jacketed section into the foundation and then filling the foundation with concrete. FIG. 10 illustrates securing the base jacketed section to the foundation using extended fasteners such as bolts. FIG. 11 illustrates barely embedding the base jacketed section into the foundation and filling only the portion that is embedded. FIG. 12 illustrates embedding the base jacketed section into the foundation without pouring any concrete. Then placing strengthening tools such as rebar and filling the entire cavity with concrete. FIG. 13 illustrates a similar system as FIG. 10 but with different fasteners. FIG. 14 illustrates a combination of several of the embodiments described herein.

Referring now to FIG. 16, a method 1600 of constructing a structure in accordance with the present invention is illustrated. In step 1610, a foundation is prepared. A foundation prepared in step 1610 may comprise a concrete foundation with, optionally, a sub-structure such as pilings to provide further support. However, one skilled in the art will appreciate that step 1610 does not require a concrete foundation, but that any other type of foundation, with or without a sub-structure, may be utilized. In step 1620 a base jacket section is secured to the foundation. Base jacket section may be secured to the foundation in step 1620 after the foundation has been prepared in step 1610 or as part of the performance of step 1610, for example, by casting a foundation around an embedded jacket section.

In step 1630, the base jacket section is filled with concrete. Step 1630 may utilize an inlet, but may also utilize an open portion at the top of the jacket section for the insertion of concrete. In step 1640 the next jacket section is secured to the underlying jacket section, which may be the base jacket section. Jacket sections may be secured to lower jacket sections through any means, including the use of splices as described previously. hi step 1650 the secured jacket section may be filled with concrete. Step 1650 may be performed using a concrete inlet or by inserting concrete through an open top portion of the jacket section. One skilled in the art will further realize that step 1630 of filling the base jacket with concrete and step 1650 may be performed as a single step, and further may be performed as part of the step of preparing the foundation 1610.

In step 1660 it is determined whether an additional jacket section remains to be erected. If the result of step 1660 is the conclusion that there is another jacket section to be erected, method 1600 returns to step 1640 and the next jacket section is secured. If there is no further jacket section to erect as a result of step 1660, construction may be completed in step 1670. Step 1670 may comprise, for example, of permitting the cast concrete to cure, the erection of other structural components, such as bracing or other members, or the attachment of equipment such as blades or sails to the structure.

One skilled in the art will appreciate that the hybrid structure described herein may take a variety of forms within the scope of the present invention. The shape of jacketed sections may take any form, not merely the substantially circular forms largely depicted herein. The thickness of wall sections may vary in accordance with the present invention, and may vary for different portions of a jacketed section or for different jacketed sections assembled as part of a structure in accordance with the present invention. The types of metal used for a jacket section may vary in accordance with the present invention, and may optionally comprise any type of structural steel. The type of concrete used to fill the jacketed sections erected in accordance with the present invention may vary depending upon the precise structural properties desired, as well as what may be available at a given construction location. The types of foundation, how a base jacket section is attached to a foundation, and how different jacket sections are joined to one another may vary from that described herein without departing from the scope of the present invention.