Patent Application
20200208612
The presented invention relates to a tree-root-like foundation for onshore wind turbine generators. The present invention is applicable to onshore wind energy industry to support wind turbine generators and tubular towers, as well as applicable to civil engineering and other large facility, if supported superstructure has a base flange.
Foundations, defined as the engineering structures embedded fully or partially in ground to support superstructure, have been used since the civilization of human beings, for different disciplines, including wind energy engineering, civil engineering, and other large facility. The foundation typically subject to compression loadings, pull-out loadings, overturning moments and fatigue loadings. The magnitude of the loadings is dependent on superstructure. Loadings from wind turbine generators (WTGs) not only are significant in magnitude, but also have cyclic characteristics since wind directions change periodically, and therefore it is important for WTG foundations to meet specific requirements to ensure the facility safe. Typical requirements for all foundations including bearing capacity, settlement, horizontal displacement etc. For WTG foundation, horizontal and rotational stiffness is particularly important to prevent excessive gapping existing between foundation and surrounding soils as well as the resonance between wind turbine generator and the foundation supporting it.
Existing foundation types that are widely used in wind industry include inverted T-type spread footings, cap with drilled piers and cap with rock anchors, etc. A connection part has to be used to connect the superstructure to foundation. For wind turbine generator foundation, anchor bolt system is widely used to connect the base flange of wind turbine tubular tower to foundation, whereas the ground at foundation bottom or piles provide resistance to the loadings or ground anchors are used to mount the foundation to the deeper ground. Particularly, the size of foundation supporting the wind turbine generators is considerably large, and the construction cost is approximately $200,000 per foundation. It is not unusual that subsurface conditions impose limitations on construction. For example, high groundwater level may bring troubles to excavating a pit for invert T-type foundation, and requires extra measures such as shoring, bracing and dewatering. In addition, excavation will remove the earth surface vegetation, and thus excavation with relatively large footprint will negatively impact on the environment.
The present tree-root-like foundation is invented to address the above challenges. The present foundation comprises one short hollow pier positioning in center of the system, one continued grade beam arranged circumferentially in outer periphery of the system, several solid piles built below the continued grade beam, and several arm grade beams which are utilized to connect the short hollow pier to the continued grade beam as well as the solid piles. The presented foundation is constructed of cast-in-place concrete reinforced with rebars. All connections for these structural members are fixed and rigid. In addition, all these structural members are embedded in ground with a stickup in the short hollow pier which elevates the foundation and matches the configuration of the base flange of the superstructure supported by the present foundation.
Various forms of foundations utilizing general structural and function features heretofore have been known. Those included disclosed U.S. Pat. Nos. 1,048,993, 2,347,624, 2,706,498, 2,724,261, 3,186,181, 3,382,680, 3,600,085, 3,842,608, 3,963,056, 4,228,627, 4,618,287, 4,842,447, 5,228,806, 5,379,563, 5,586,417, 5,826,387, 7,533,505, 7,987,640, 8,161,698, 9,670,909, etc. However, these previously invented foundations do not include the forms and features of the instant invention, and the combined forms and features of the instant invention enable the presented invention heavy duty as well as adaptive, constructible and cost-efficient. The invented foundation comprising features disclosed results in fully utilizing the further and deeper ground to resist tremendous overturning moment loadings. The present foundation results in very low vertical and horizontal deflections with surprisingly high translational and rotational stiffness under loadings transferred from wind turbine generators. In the meanwhile, relatively lengthy arm grade beams enable the capability to lower the requirements for the bearing capacity of the solid piles, and thus the length of the solid piles is reduced.
U.S. Pat. No. 1,048,993 to C. Meriwether discloses a simple and inexpensive construction method of reinforced concrete caisson sunk by a usual way. The caisson may be filled with concrete and then works as a pier. The caisson is pre-casted into tubular sections of concrete; heavy reinforcements and metal rings which are in a bell and spigot joint are used in section ends. The rod is tensioned and extended through the connecting rings embedded partially inside of the reinforced concrete. The rod works as a tie to connect the embedded rings which are spaced inward of the inner peripheries of the concrete tube and do not embed fully in the concrete wall. The Meriwether's caisson is a concrete pier with relatively large diameter, no continued grade beam, solid piles and arm grade beams are included which transfer and distribute the loadings to further and deeper ground as the present foundation.
U.S. Pat. No. 2,374,624 to P. J. Schewendt discloses a precast foundation with concrete bolted together intended for supporting transportation signal masts. The foundation embedded in the ground, but the precast sections impose size limitations and thus the foundation can only support light superstructures which subject to relatively small overturning moment. The present foundation has forms and features which are constructed of cast-in-place concrete reinforced with rebars, to resist tremendous overturning moment loadings from tall superstructures with surprisingly high translational and rotational stiffness.
U.S. Pat. No. 2,706,498 to M. M. Upson discloses a pre-stressed tubular concrete structure for use as pipe conduits, piles and caissons. The structural tubular structure is pre-casted and can be assembled one by one with joint means at the end. Tension is applied to the longitudinal reinforcing steel placed in the preserved holes and grout then is poured to the holes to make the steel and concrete bond tightly. The Upson's structure is pre-stressed and not suitable for use as foundations for wind turbine generators or other tall structures which subject to tremendous overturning moment. The joint means the connections for the pipes are not rigid, which may cause problems in stiffness of the foundation. And, the structure would be difficult to transport to wind farm site. Enabled by the comprised forms and features which are constructed of cast-in-place reinforced concrete, the present foundation in contrast results in very high translational and rotational stiffness, and construction materials are convenient to transport to the construction site.
U.S. Pat. No. 2,724,261 to E. M. Rensaa discloses a method attaching precast concrete column to a supporting base, the diameter of the column is relatively small, and the base typically embeds in shallow subsurface. Obviously, the Rensaa's method is rather for construction, and the Rensaa's entire structure is not suitable for use as a large foundation for tall superstructure like wind turbine generators. In contrast, the present foundation is suitable to support tall superstructure enabled by comprised forms and features which transfer and distribute loadings to further and deeper ground, and the comprised structural members are constructed of cast-in-place reinforced concrete, not pre-casted.
U.S. Pat. No. 3,186,181 to R. K. Show et al. discloses a method and apparatus of filling the pile shells with concrete to address the problems caused by turbulent air that segregates the rocks from cement in long pile shells. The apparatus is a pre-compression chamber, which holds the concrete from segregating and discharges the concrete to the bottom of the pile shells. The Show's invention is rather a construction method, not as the present foundation improves structure's engineering behavior by comprised forms and features which are constructed of cast-in-place reinforced concrete to transfer and distribute loadings to further and deeper ground.
U.S. Pat. No. 3,382,680 to T. Takano discloses a pre-stressed concrete pile section comprising a tubular body of concrete with a pair of annular mental discs at opposite ends. The invention provides a pre-stressed concrete pile or pile section which results in an improved structure particularly designed to enable effective pre-tensioning of the axial reinforcement, which takes the form of reinforcing steel wires, and is high in structural strength. The pre-stressed axial reinforcing steel wires are bonded with concrete, and the steel wires have enlarged head to anchor to the steel ring embedded in concrete. Assembly the reinforcing system and applying pre-stress is cumbersome, and, the principles of the Takano's pre-stressed concrete pile is different from the present foundation, which comprises forms and features to improve the engineering behavior by transferring and distributing the loadings to further and deeper ground. The comprised forms and features are constructed of cast-in-place reinforced concrete, not using pre-stressed reinforcements.
U.S. Pat. No. 3,600,865 to F. Vanich discloses a single-column borne house erected and supported on a cast in place foundation pillar. The column is bolted to the pillar while beams are bolted to the column as cantilever beams. The foundation pillar is supported on a large diameter pile or insert into ground with a small pit which will be used to place concrete. In contrast, the present foundation comprises features and forms to transfer and distribute the tremendous loadings to further and deeper ground, that is obviously different from the Vanich's invention.
U.S. Pat. No. 3,842,608 to L. A. Turzillo discloses a method of installing a pile using screw-like means to drill the hole for the pile. Then cementitious material is then poured into the hole, and a pile is formed. The Turzillo's invention is rather a construction method than improving the engineering behavior as the present foundation by utilizing the comprised features and forms to transfer and distribute loadings to further and deeper ground.
U.S. Pat. No. 3,963,056 to A. Shibuyya et al. discloses pre-stressed concrete piles, poles or the like. Pillar covered with an outer shell of steel pipe on a circumferential surface of a cylindrical pre-stressed concrete tube or a pillar shaped pre-stressed concrete pole at least one end being in an independent state to the concrete article. The invention provides the joint effects of the good compressive strength of the said pre-stressed concrete tube or pole and the good bending strength by adding the outer shell. However, the outer steel shell filled with concrete can be regarded as increasing the pile diameter. The Shibuyya's structure is not as the present foundation improves structure's engineering behavior by comprised forms and features which transfer and distribute loadings to further and deeper ground, and the forms and features are constructed of cast-in-place reinforced concrete, not using pre-stressed reinforcements.
U.S. Pat. No. 4,228,627 to J. O'Neill discloses a reinforced foundation structure for supporting high light pole by using a plurality of vertically extending reinforcing rod assemblies with the top bolted to a base plate on the bottom of the pole. The structure extends downwardly into a vertical earth bore of relatively small diameter. Accordingly, the O'Neil Structure is not capable of being used to support superstructure subject to high overturning moment or being placed under high unit compressive loading. In contrast, the present foundation improves structure's engineering behavior by comprised forms and features which transfer and distribute loadings to further and deeper ground, and the forms and features are constructed of cast-in-place reinforced concrete.
U.S. Pat. No. 4,618,287 to F. Kinnan discloses a method for establishing in ground footings to support poles by using a threaded steel casing. The casing is threaded into ground, and grout is penetrated into the ground via the holes through the steel casing. The diameter of casing and the depth threaded into ground are relatively small. Accordingly, the Kinnan's structure is not capable of being used to support superstructure subject to high overturning moment or being placed under high unit compressive loading. The Kinnan's invention is rather a construction method than improving structure's engineering behavior as the present foundation by comprised forms and features, which transfer and distribute loadings to further and deeper ground. The forms and features of the present foundation are constructed of cast-in-place reinforced concrete, no grout is used to improve the existing ground.
U.S. Pat. No. 4,842,447 to J. J. Lin discloses a fabrication method and device of hollow reverse circulation piles. Firstly, a central hollow portion is installed with a movable sand barrel between which and the surrounding reinforcing cage, positioning device for movable sand barrel is installed. Upon start of work, grouting is poured to a scheduled height from the bottom of the pile bore first. Grouting is then poured between pile bore wall and outer wall of movable sand barrel. The Lin's invented construction method and device is expensive, and the construction process is impractical. In contrast, the present foundation improves structure's engineering behavior by comprised forms and features which transfer and distribute loadings to further and deeper ground, and the forms and features are constructed of cast-in-place reinforced concrete, and no need for extra device for construction.
U.S. Pat. No. 5,228,806 to C. J. De Medieros et al. discloses a gravity pile for subsea platform foundations. The gravity pile comprises a series of pile sections made from two concentric tubes, the annular space between which is filled with an elevated specific weight composition. Individual pile sections can be joined together by means of tubular connecting rings welded to the ends of the sections. The Medieros' foundation is complicated in construction, and thus not cost-efficient. Moreover, the welding connecting the gravity piles is vulnerable to high fatigue, cyclic loadings provided by wind turbine generators. In contrast, the present foundation improves structure's engineering behavior by comprised forms and features which transfer and distribute loadings to further and deeper ground, and the forms and features are constructed of cast-in-place reinforced concrete. The present foundation utilizes the resistance from further and deeper ground, not the weight of the foundation, to resist the tremendous overturning moment loading.
U.S. Pat. No. 5,379,563 to C. R. Tinsley discloses an anchoring assembly by which heavy machinery may be anchored to a foundation. Anchoring plates used to fasten the anchors in lower and upper part are separate. Such separated plates and anchors may be pulled out when the overturning moment is large. Thus, the Tinsley's foundation is not capable of supporting superstructures such as wind turbine generators which subject to high overturning moment. In contrast, the present foundation is suitable to support tall superstructures by bolting the base flange of the superstructure to foundation. The present foundation improves structure's engineering behavior with comprised forms and features which transfer and distribute loadings to further and deeper ground, and the forms and features are constructed of cast-in-place reinforced concrete, the embedment ring used in present foundation is intact, not separated, to ensure the pullout safety.
U.S. Pat. No. 5,586,417 to A. P. Henderson et al. discloses a hollow, cylindrical pier foundation which is constructed of cementitious material poured in situ between inner and outer cylindrical corrugated metal pipe (CMP) shells. The foundation is formed by CMPs within a ground pit. External and internal spaces beyond the CMPs need to be backfilled. The lengthy anchors are adopted to bolt the base flange of superstructures to the foundation bottom intended to make the foundation tensionless. In contrast, the present foundation does not use CMPs to form the foundation, it utilizes ground to form the foundation and no need to excavate a pit to place the foundation, and no backfill and no compaction is needed. Moreover, the present foundation comprises forms and features to transfer and distribute the tremendous overturning moment loadings from tall superstructure to further and deeper ground that the Henderson's invention does not have. The length of the bolts used in present foundation are much shorter, and the reinforcements and concrete of the present foundation take the tensions, compressions and the moments, and these loadings are transferred and distributed to further and deeper ground by the comprised forms and features. Compared with Henderson's invention, more reinforcements are used in central hollow pier to keep it as a rigid body and the usage of reinforcements decreases in other structural members with distance increasing from the foundation center. The principle and the comprised forms and features of the present foundation are obviously different from Henderson's invention.
U.S. Pat. No. 5,826,387 to A. P. Henderson et al. discloses an upright cylindrical pier foundation which is constructed of cementitious material. Compared with U.S. Pat. No. 5,586,417, the pier is formed similarly by using the corrugated metal pipe (CMP) shells, while more rods are added and arranged radically to the upper part of the system to ensure higher bearing capacity for high compression. Refer to comparisons between the present foundation with U.S. Pat. No. 5,586,417, the present foundation does not use CMPs to form the structural members, it utilizes ground to shape and form the foundation and no need to excavate a pit to place the CMPs, and no backfill and no compaction is needed. Moreover, the present foundation comprises forms and features to transfer and distribute the tremendous overturning moment loadings from tall superstructure to further and deeper ground that the Henderson's invention does not have.
U.S. Pat. No. 7,533,505 to A. P. Henderson discloses a circular concrete cap foundation poured in-situ within a perimeter forming using corrugated metal pipes (CMPs). The CMPs are set at top or within an excavated pit and enclosing a series of circumferentially spaced pile anchors. The pile anchors are also formed with corrugated metal pipes (CMPs) which are set deep in subsurface soils and poured with cementitious material. Refer to the comparisons with U.S. Pat. No. 5,586,417, the present foundation does not use CMPs to form, manufacture the comprised forms and features. The present foundation utilizes ground to shape and form the foundation and no need to excavate a pit to place CMPs, no backfill and no compaction is needed. Moreover, the present foundation comprises forms and features to transfer and distribute the tremendous overturning moment loadings from tall superstructure to further and deeper ground that the Henderson's invention does not have.
U.S. Pat. No. 7,987,640 to B. Oiigaard et al. discloses a technique preventing water intrusion into foundation by adding sealing compound and cover into foundation concrete. The technique is helpful to increase the lifetime of the foundation but not improving the mechanical behavior of the foundation by inventing forms and features.
U.S. Pat. No. 8,161,698 to P. G. Migliore discloses a circular foundation using fiber reinforced concrete with circular reinforcement rods. The foundation includes a vertical stanchion that rests on the bottom of an excavated hole with relatively large diameter, vertical anchor bolts and radical reinforcements are placed in the hole, and then concrete is poured into the hole. The invention essentially follows the principle of single pier foundation, a stanchion and radial reinforcement around the stanchion are placed within the concrete of the pier to increase the internal strength of the structure. Thus, the Migliore's invention only improves the material properties within the pier, not related to the foundation shape and interactions with surrounding soils. In contrast, the present foundation comprises forms and features to transfer and distribute the tremendous overturning moment loadings from tall superstructure to further and deeper ground, these comprised forms and features improve engineering behaviors of the present foundation greatly.
U.S. Pat. No. 9,670,909 to N. Holscher discloses a foundation constructed with a plurality of concrete segments. The segments are pre-casted with curved surfaces, and two sheaths are preserved to install tensioned wires to tie up the segments. In contrast, the present foundation comprises forms and features to transfer and distribute the tremendous overturning moment loadings from tall superstructure to further and deeper ground. The present foundation is constructed of cast-in-place concrete reinforced with rebars, not using pre-casted segments which are tied up with tensioned wires.
Based on above comparisons with state-of-the-art technique in relation to the present foundation, it is finally concluded that the present foundation comprises different forms and features from above listed inventions, and the comprised forms and features greatly improve the engineering behavior of the present foundation.
The foundation of the instant invention is unique because the new foundation type is invented by imitating the tree root system, which is selected by nature and the roots ensure the trunk erect in wind. In summary, the short central hollow pier and solid piles circumferentially arranged in outer periphery imitate vertical tree roots, whereas the continued grade beam and the arm grade beams mimic laterally-support roots. All these members are embedded in ground and all connections for the structural members are fixed and rigid.
For a conventional concrete pier foundation, all loadings from superstructure are transferred and taken by the single pier and then the ground around the pier provides resistance to balance the loadings. This is similar for a conventional pile foundation.
For the present foundation, the short central hollow pier elevates the foundation with a stickup and its plan configuration matches the base flange of superstructures. The short central hollow pier functions as a hub to take the loadings transferred from the superstructures, and continuously to transfer and distribute the loadings further to the continued grade beam and deeper to solid piles, through the arm grade beams. The bearing capacity required for the solid piles to resist the tremendous moment loadings from superstructures is also lowered by the relatively lengthy arm grade beams, thus the length of the solid piles can be reduced. The continued grade beam functions to link all structural members, and make them work together, certainly itself also provides resistances to the loadings.
The anchor bolt system, which is widely used in industry for wind turbine generator foundation, bolts the superstructure and foundation together, and transfer loadings from superstructure to the present foundation. Thus, the foundation is loaded by the structure supported therefrom, the unit is subjected to varying tensile and compressive loads, and the tensile and compressive loads form a coupled moment to resist the overturning moment transferred from tall superstructures. In the present foundation, the anchor bolts are approximately 6 feet long which enables the embedment ring being placed at a lower position below the bottom of the arm grade beams. This length is much shorter than those typically used in other type foundations. However, resistance to pull-out loadings is ensured as the embedment ring is placed below the bottom of the arm grade beams. The more details related to mechanical analysis are described in the following paragraphs.
The tensile and compressive loads form a coupled moment that resists the overturning moment transferred from tall superstructures. More specifically, overturning moment loadings and dead weight of superstructures generate compressions on foundation top, where high-strength grouting material is used to prevent breaking of the foundation top concrete. In the meanwhile, overturning moment loadings also cause tensions in anchor bolts. The compression reaction from the high-strength grouting and the tension reaction from the anchor bolts form a coupled moment to resist the overturning moment loadings that the foundation subject. The coupled moment formed in short central hollow pier will also be transferred to continued grade beam as well as solid piles through arm grade beams which are connected to the short central hollow pier, the continued grade beam as well as solid piles. Horizontal shear that superstructure subjects to is also transferred and distributed to the foundation. The short central hollow pier takes the transferred shear and continuously transfers and distributes it to continued grade beam as well as solid piles through arm grade beams. Finally, all these loadings are transferred and distributed to further and deeper ground through the comprised forms and features of the present foundation.
The present foundation is initially intended to mimic the tree root system as well as it is working mechanism. However, the above description for mechanical analysis of the present foundation follows the principles of soil mechanics as well as the loading distribution among rigid, fix-connected structural members. Earth pressure acts on the structural members of the present foundation as they are embedded in ground. The magnitude and directions of earth pressure depend on displacement of the structural members and the embedment depth. Moreover, earth pressure interacts with the structural members and offsets the loadings transferred and distributed.
Design engineers are familiar with the comprised forms and features of the present foundation. In addition, a bunch of standards/codes that the design shall comply with are available. The design is thus conventional and not challenging. Following the principles of loading distribution among structural members and soil mechanics for embedded engineering structures, the usage of reinforcements should follow a trend decreasing from the short central hollow pier with the distance increasing from the central hollow pier. Hand calculations can provide close-form solutions for design use, while 3-D geotechnical and structural design and analysis software is better as they can provide more accurate solutions.
No special construction equipment is needed. Typical and widely-used construction equipment and construction procedure can be used to construct the present foundation. Moreover, the present foundation utilizes ground to shape and form structural members, no formworks as well as no backfill and no compaction is needed. Thus, the construction procedure is simplified, and the construction time is saved. Since the footprint of the structural members is relatively small, the removal of the earth surface vegetation is minimal, and thus, the present foundation is environment-friendly.
Finally, the invented foundation fully utilizes the further and deeper ground to resist the loadings, and ensures the present foundation meets the requirements for horizontal deflection, vertical displacement as well as translational and rotational stiffness. The present invention to be specifically enumerated herein is to provide a bionic root foundation in accordance with the proceeding forms and features of manufacture, be of simple construction, cost-efficient, environment-friendly, constructible and suitable to most subsurface conditions of the sites. All technical requirements from superstructures are more easily to be satisfied, the forms and features of the foundation comprises of are economically feasible, durable, reliable and cost-efficient.
Compared with industry-widely used invert T-type spread foundation under the same loadings with the same site conditions, approximately 30% construction cost can be saved if the present foundation is constructed accordingly. These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to the like parts throughout.
Designations for numerals in
1—Short Central Hollow Pier; 2—Continued Grade Beam; 3—Arm Grade Beams; 4—Solid Piles in Outer Periphery of the System; 5—Tower Flange; 6—Grouting Trough; 7—Anchor Bolts; 8—PVC Wrap; 9—Embedment Ring; 10—Washers; 11—Nuts; 12—Concrete; 13—Longitudinal reinforcements of Central Hollow Pier; 14—Hooping of Central Hollow Pier; 15—Longitudinal Reinforcements of Arm Grade Beams; 16—Hooping of Arm Grade Beams; 17—Longitudinal Reinforcements of Solid Piles; 18—Hooping of Continued Grade Beam; 19—Longitudinal Reinforcements of Continued Grade Beam; 20—Preserved Holes in Flange; 21—Predrilled Holes in Embedment Rings; 22—Hooping of Solid Piles
Referring specifically to the drawings,
As shown in
The following construction steps are for illustrative purpose only, and may be adjusted in accordance with project conditions:
The above description uses examples to disclose the invention, and to enable any person skilled in the art to practice the invention, including making and using any forms and features and performing any incorporated methods. All the dimensions for the four major structural members and the reinforcement shape, size and grade shall be detailed in design phase. The construction steps described above are duly for further clarification for construction of the invented foundation, the construction steps may be adjusted and optimized per project conditions. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201811630498.4 | Dec 2018 | CN | national |
