Flangeless support structures
A flangeless assembly for connecting tubular sections of a tubular support structure. A flangeless finger plate assembly connects adjacent tubular sections of a tubular support strucure. The finger plate assembly includes an outer finger plate, an inner finger plate, and corresponding ends of the adjacent tubular section butted at a point. Throughhole arrays are provided on each finger plate such that one throughhole array connects to a matching throughhole array on the corresponding end of the adjacent tubular section. Fastening means are provided to connect the inner and outer finger plates to the adjacent tubular sections according to the throughhole array.
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The invention relates generally to tubular structures and more specifically to flangeless connections between sections of tubular support structures.
Tubular support structures have many and varied types of application. Some types of support structures exist where equipment is supported at elevated heights from the ground. These support structures may be tall and carry operating equipment of various weights at the top, thereby subjecting joints in these structures to high stress. The support structures may be used in many applications, including cellular phone towers, radar towers, and wind towers.
Wind turbine support towers are large structures, sometimes extending to significant heights to accommodate large wind turbine rotor blades and to strategically place the rotor blades within a wind path. For example, a typical tower may have a height of about 80 m.
The tubular structure 10 of
For example, a tower height of 50 meters may be employed for high wind conditions and 110 meters for low wind conditions. The horizontal cross section of the exemplary tower is generally circular and may be tapered at upper levels. Tapering may be achieved by use of individual tubular segments, the tubular segments tapered as right conical sections along an axial direction. However, the horizontal cross section for the tubular segments of other representative structures may be of different geometries.
On-going problems with the exemplary wind turbine support tower include weld cracking, flange distortion and bolt failure during tower flexure, each contributing to the life cycle cost of the tower. Moreover, the heat generated during the flange welding process distorts the flanges.
Welds, by nature, have inherent stress concentration features. When tubular structures, such as towers are subjected to high wind loads, the tower experiences flexural stresses. Superimposed on theses are high cycle vibration flexural stresses driven by the mass at the top of the tower. This combination of factors, in addition to the pre-stressing of assembly, places high tensile stresses on the welds and bolts leading to a high probability of weld cracking or bolt failure with the associated high maintenance costs. Bolt failure has become such a significant issue that suppliers have to machine the flange after welding to meet the flatness requirement Some tower requesters, for example, may require the supplier to measure flange flatness using a laser measurement, with anything in excess of 1.5 mm deviation from planar requiring further machining. A supplier may have to cut and re-weld flanges to meet this requirement. This may have a major impact on cost and schedule, as well as tower strength.
An additional area of concern is the flange weld inspection. It is difficult to get an accurate assessment of weld integrity since prevailing inspection techniques rely on a calibrated, non-direct, detection procedure.
Accordingly, there is a need to provide an assembly for wind turbine support tower modular sections that do not result in high stress in the connecting joints and which allow the stresses to be checked.
BRIEF DESCRIPTION OF THE INVENTIONThe present invention relates to in general to a joint for joining sections of a tubular structure together, and in particular to a flangeless joint for joining sections of a wind turbine support tower.
Briefly, one aspect of the invention provides a finger plate assembly for connecting two adjacent tubular sections of a tubular support structure. The finger plate assembly includes an outer finger plate; an inner finger and corresponding ends of the adjacent tubular sections butted at a point. Throughhole arrays are provided on each finger plate, where each throughhole array provides connection to one of the two adjacent tubular sections. A matching throughhole array is located on the corresponding ends of the adjacent tubular sections. Means for fastening the inner and outer finger plate to the tubular sections is provided.
Briefly, in accordance with another aspect of the present invention, a flangeless joint is provided for connecting two sections of a tubular support structure. The flangeless joint includes two adjacent sections of the tubular support structure and a plurality of finger plate assemblies uniformly distributed around the periphery of the two adjacent sections of the tubular support structure.
Briefly, in accordance with a third aspect of the present invention, a tubular support structure is provided. The tubular support structure includes a plurality of tubular sections and a plurality of flangeless joints employing finger plate assemblies for connecting adjacent tubular sections, the finger plate assemblies being uniformly distributed around the periphery of the adjacent tubular sections.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The following embodiments of the present invention have many advantages, including avoidance of high tensile stresses on welds and bolts leading to a probability of weld cracking or bolt failure and the associated high maintenance costs.
One aspect of the present invention provides finger plate assemblies to join adjacent sections of a tubular assembly.
For the exemplary 80 m tower, the finger plate may have an arc dimension of about 2 m, a height of about 1 m, and a thickness of about 30-40 mm. The material for finger plates may preferably include ASTM A 572 Gr 50 steel plate. Bolt throughhole arrays 76 and 78 on the finger plates may be preferably configured in double rows applied to each adjacent section of tower for a total of about 48 bolt holes per finger plate. Diameter for the bolt throughholes may preferably be sized about 1.25 inch. Minimum spacing between the bolt throughholes may be about 5 inches. Typical bolts for the finger plates in the 80 m tower may preferably be M36 10.9 grade bolts that are torqued to a bolt prestress of about 510 Mpa (74 ksi).
In addition to eliminating the end flanges, the discrete nature accommodates slight aberrations in tower section geometry to speed up assembly and minimize expensive re-work. The finger plate assemblies are designed with sufficient thickness, length and width to provide acceptable local and overall stiffness to address tower side-sway and stability requirements. Standard bolt design practice will determine finger plate dimensions.
A typical flangeless joint with finger plate assemblies according to one aspect of the present invention uniformly distributes a plurality of finger plates around the periphery of adjacent sections of the tubular support structure.
The curved nature of the finger plates contributes to joint stiffness. Appropriate design of the finger plate length, thickness, and width will stiffen the joint locally and provide prescribed over-all tower stiffness for side sway, stability, and tower-head eccentric loading in a much more structurally efficient manner compared to flanged joints of prior art. The thickness and spacing of the finger plates will also be a function of the prevailing standard practice for bolted joint design. The bolt hole diameter and spacing will be a function of service conditions.
The use of finger plate assemblies replaces welding flanges to the can assemblies as the means of joining modular sections of the tower. Consequently, the distortion and prestressing problems associated with these welds and the bolts is eliminated. Further, it is difficult to get an accurate assessment of weld integrity since prevailing inspection techniques rely on a calibrated, non-direct, detection procedure. Replacing the welds with bolts allows an inspector to check each bolt for allowable pre-load using a torque wrench.
According to yet another aspect of the present invention, a tubular structure is provided that includes a plurality of tubular sections and a plurality of flangeless joints employing finger plate assemblies for connecting the adjacent tubular sections. The finger plate assemblies are uniformly distributed around the periphery of the adjacent tubular sections. The tubular structure may define a support tower and more specifically a wind turbine support tower that utilizes the finger plate assemblies for joining modular sections of the tower. The modular sections of the tower are assembled by welding tubular segments to form tower sections.
In this exemplary wind turbine support tower, five finger plate assemblies may be uniformly distributed around the periphery of the flangeless joint. The tower sections may be cylindrical shaped or have a generally truncated right conical section to provide for overall reduction in cross section of tower sections at higher elevations. Further individual tubular segments may be individually tapered along the axial length to provide for the progressive reduction in cross section for each individual tower section along the axial length of the tower section.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
1. A finger plate assembly for connecting two adjacent tubular sections of a tubular support structure, the finger plate assembly comprising:
- an outer finger plate;
- an inner finger plate;
- corresponding ends of the adjacent tubular sections butted at a point;
- throughhole arrays on each finger plate, wherein each throughhole array provides connection to one of the two adjacent tubular sections;
- a matching throughhole array located on the corresponding ends of the adjacent tubular sections; and
- means to fasten the inner and outer finger plates to the adjacent tubular sections.
2. The finger plate assembly as claimed in claim 1, wherein horizontal cross-section of tubular sections are circular-shaped.
3. The finger plate assembly as claimed in claim 2, wherein:
- the outer finger plate comprises a plate curved inner diameter matched to a curvature of an outer surface of the tubular sections; and
- the inner finger plate comprises a plate with a curved outer diameter matched to a curvature of an inner surface of the tubular sections.
4. The finger plate assembly as claimed in claim 3, wherein the tubular sections comprise sections of a support tower.
5. The finger plate assembly as claimed in claim 3, wherein the tubular sections comprise sections of a wind turbine support tower.
6. The finger plate assembly as claimed in claim 1, wherein bolts and nuts comprise the means for fastening according to the throughhole array.
7. The finger plate assembly as claimed in claim 1, wherein the throughhole array is symmetric with respect to the adjacent tubular sections of the tubular support structure.
8. The finger plate assembly as claimed in claim 1, wherein the throughhole arrays on the inner finger plate, the outer finger plate, and the adjacent ends of the tubular sections are machined prior to assembly of finger plate assembly.
9. A flangeless joint for connecting two sections of a tubular support structure, the flangeless joint comprising:
- two adjacent sections of the tubular support structure;
- a plurality of finger plate assemblies uniformly distributed around the periphery of the two adjacent sections of the tubular support structure.
10. The flangeless joint for connecting two sections of a tubular support structure as claimed in claim 9, wherein the two adjacent sections of the tubular support structure comprise sections of a support tower.
11. The flangeless joint for connecting two sections of a tubular support structure as claimed in claim 10, wherein cross-sections of the adjacent sections of the tubular support structure are circular-shaped.
12. The flangeless joint for connecting two sections of a tubular support structure as claimed in claim 11, wherein the two adjacent sections of the tubular support structure comprise sections of a wind turbine support tower.
13. The flangeless joint for connecting two sections of a tubular support structure as claimed in claim 12 wherein five finger plate assemblies are uniformly distributed around the periphery of the adjacent sections of the wind turbine support tower.
14. The flangeless joint for connecting two sections of a tubular support structure as claimed in claim 13, wherein the uniformly distributed finger plate assemblies employ bolting as a fastening means.
15. A tubular support structure comprising:
- a plurality of tubular sections; and
- a plurality of flangeless joints employing finger plates assemblies for connecting adjacent tubular sections, the finger plate assemblies being uniformly distributed around the periphery of the adjacent tubular sections.
16. The tubular support structure as claimed in claim 15, wherein the tubular support structure comprises a support tower.
17. The tubular support structure as claimed in claim 16, wherein the support tower comprises a wind turbine support tower.
18. The tubular support structure as claimed in claim 17, wherein the flangeless joints further comprise five finger plate assemblies uniformly distributed around the periphery of adjacent tubular sections.
19. The tubular support structure as claimed in claim 18, wherein the wind turbine support tower further comprises:
- a base supporting the tower;
- tower sections joined by the flangeless joints;
- a platform connected to the top of the modular sections; and
- a wind turbine and wind turbine rotor supported on the platform section.
20. The tubular support structure as claimed in claim 18, wherein the tower sections further comprise modular sections of welded tubular segments.
Type: Application
Filed: Aug 18, 2006
Publication Date: Feb 21, 2008
Applicant:
Inventors: Ronald R. Cairo (Greer, SC), Sujith Sathian (Simpsonville, SC)
Application Number: 11/506,421
International Classification: E04H 12/00 (20060101);