GRAZIOLI, Fabio (Via Emilia Est, 228, Parma, I-43100, IT)
GRAZIOLI, Maurizio (Via Emilia Est, 228, Parma, I-43100, IT)
GRAZIOLI, Fabio (Via Emilia Est, 228, Parma, I-43100, IT)
| CLAIMS 1. Tubular tower comprising a plurality of superimposed taper sections (2) connected together, characterised by comprising, in combination: - joining elements (6) fixed to the taper sections; - tie-rods (7) inserted longitudinally into the joining elements (6) and secured with nuts (8), in order to connect each taper section (2) to the taper section adjacent thereto. 2. Tower according to claim 1, wherein the joining elements (6) are bolted internally and/or externally to the taper sections (2). 3. Tower according to claim 1, wherein each taper section (2) comprises a plurality of segments (3) of taper section, bolted longitudinally to each other. 4. Tower according to any of the previous claims, wherein the tower is configured to support a wind power station. 5. Tower according to claim 1, wherein at least one of the taper sections (2) is provided with at least a fist and a second joining element (6) fixed to opposite ends of the taper section (2), to connect said taper section (2) to correspondent taper sections (2) arranged at opposite sides of said at least one taper section (2), when the taper sections (2) are superimposed to form the tower. 6. Tower according to claim 1, wherein each taper section has a polygonal section. 7. Tower according to claim 3, wherein each segment (3) has lateral flaps (4) folded towards the inside of the taper section and having a plurality of holes (5) into which bolts are fitted for connecting the various segments (3) together to form a taper section (2). 8. Procedure for constructing a tubular tower, characterised in that it includes the following preliminary stages in the factory: - cutting a sheet in a trapezoidal shape; - drilling the sheet to form a plurality of holes (5, 9) for the insertion of "joining elements" and fixing; - folding the sheet to constitute a segment (3) of a taper section (2) by creating the sides of the polygon constituting the cross-section of the segment; attaching joining elements (6) to the end holes (9) in such a way as to allow a subsequent formation/assembly of taper sections; said preliminary stages are followed by the later stages carried out on site, i.e. in the place where the tower is erected: - preparing a foundation; assembling segments (3) of taper section by means of longitudinal bolting so as to form a taper section (2); - fixing a base taper section to foundation anchor bolts; superimposing, aligning and joining further taper sections at the top until the tower is completed, using the joining elements (6) and the tie-rods (7) inserted into the joining elements (6) and secured with nuts (8). 9. Procedure according to claim 8, wherein a stage is provided of hot galvanising the folded sheet and the joining elements (6). 10. Procedure according to claim 8, wherein the attachment of the joining elements (6) is carried out on the surface of the sheet destined to become the inner surface of the tower. 11. Procedure according to claim 8, wherein the attachment of the joining elements (6) is carried out on the surface of the sheet destined to become the outer surface of the tower. 12. Procedure according to claim 8, wherein the tie-rods (7) operate in a longitudinal direction. 13. Procedure according to claim 8, wherein the following stages are provided: preparing first brackets (12) and second brackets (13) in proximity to lateral flaps (4) of segments (3); - bringing two segments (3) together; - attaching first ropes (16) to first brackets (12) and to a spar (17) attached to a beam (18) suspended from first lifting means; attaching a further rope (19) to second lifting means (20) and to holes in proximity to the lateral flaps of the segments on the opposite side from the brackets (12,13); - simultaneously manoeuvring the first and second lifting means to bring the segments into the correct position for bolting; - fastening bolts through two free holes in the internal lateral flaps of the segments which have been brought together; - attaching a tie-rod (20) to the second brackets (13) to correct or maintain the distance between said brackets; - lifting the structure previously obtained and resting it in a guide cradle (21); - detaching the ropes (16,19) and removing the first brackets (12); - fastening bolts through the two holes left vacant by the rope (19) and through all the longitudinal holes; - superimposing another similar structure to form a taper section, if necessary centring the two structures by means of thrusting/centring devices (22); - fastening bolts throughout the length of the taper section; - removing tie-rods (28) and second brackets (13). 14. Procedure according to claim 13, wherein the cradle (21) is of a width adjustable by means of movable lateral stands (23). |
TECHNICAL FIELD AND BACKGROUND ART.
The present invention has as its subject a tubular tower and a relative construction procedure. In particular it refers preferably to an entirely bolted monotubular tower for use in wind power stations as a support for wind turbines with revolving blades. For this reason this type of tower is commonly known as a "wind tower".
The forces transmitted by the wind power generator located at the top of the tower, in addition to the thrust of the wind, impose very demanding weights and dimensions (heights, diameters, thicknesses etc.) on the structure, and make it necessary to prefabricate in the factory components of small dimensions and weights which will subsequently be assembled, partly in the said factory, and partly on the site where the tower is to be erected. In particular, any components of excessive dimensions make it impossible to prefabricate the structure and transport it on ordinary vehicles, or to galvanise it in tanks of currently-used dimensions or move and assemble it on site. Since we are concerned with towers of between 30 and 100 metres high, with diameters of up to 4 metres, it is obviously necessary both to construct the tower by assembling several tapering structures (taper sections) joined transversely to each other, and to construct these structures starting from two half-shells (or several tubular portions in the case of larger diameters) assembled to each other in the longitudinal direction. Blades and towers are known having fairly limited dimensions and therefore made in monolithic taper sections longitudinally welded directly in the factory and subsequently assembled on site, joined by lapped joints or flanges welded to the ends. Wind towers are known in which the various taper sections are fixed to each other by means of welded flanges or, in the case of larger sizes, by the use of drilled plates joining the taper sections by means of bolts. Moreover, in all the most current realisations, the connection to the foundations is made by wholly or partially welded elements. These however are structural solutions whose execution is both demanding to perform and imposes limitations.
Wind towers running at full speed are subject to oscillations and vibrations of very significant size and frequency and are therefore extremely sensitive to fatigue, which becomes particularly critical especially in the area of welds, where the possible presence of cracks dangerously amplifies the effects.
Fluctuating bending effects are also critical, for example in the vicinity of welded flange joints. In addition, the presence of welds gives rise to concentrated tensions caused by shrinkage and to possible alteration of the base material in the area around the welds. The nett result is further deterioration in the strength and safety of the structure in use. Methods of constructing wind towers are described in EP 1681464 Al and EP 1681461 Al. DISCLOSURE OF THE INVENTION. An object of the present invention is to eliminate the above disadvantages, and to make available a wind tower and a procedure for constructing it which provide the tower with better functionality and resistance to stresses, as well as making it easier to assemble. Said objectives are fully achieved by the tower which is the subject of the present invention and by the relative construction procedures, which are characterised by the content of the claims set forth below and which specify exclusively bolted couplings without the use of welds. BRIEF DESCRIPTION OF DRAWINGS. This and other characteristics will become clearer in the following description of a preferred embodiment illustrated, purely by way of non- limiting example in the attached drawings in which:
- figure 1 illustrates the tower in a front view, without the turbine on the top;
- figure 2 illustrates a drilled flat sheet before folding; - figures 3a, 3b and 3c illustrate the folded sheet, respectively in a front view, on plan and in a perspective view;
- figures 4a, 4b and 4c illustrate a taper section forming part of the tower, respectively in a front view, on plan and in a perspective view;
- figures 5a, 5b and 5c illustrate the "joining elements", respectively in a front view, on plan and in a side view;
- figures 6a and 6b illustrate a top "joining element", respectively in a front view and in a sectioned side view;
- figures 7a and 7b illustrate intermediate "joining elements", respectively in a front view and in a sectioned side view; - figures 8a and 8b illustrate a base "joining element", respectively in a side view and in a front view;
- figures 9 to 13 illustrate the stages of assembly on site;
- figures 14 and 15 illustrate some details making up the tower. BEST MODE FOR CARRYING OUT THE INVENTION. With reference to the drawings, no. 1 comprehensively indicates a tower, made by assembling a plurality of overlapping taper sections 2. Each taper section, which is conical with a hexadecagonal cross-section (i.e. with 16 sides) is made by assembling four segments 3 (illustrated in figures 3a, 3b and 3c) with their lateral flaps 4 folded towards the inside of the tower.
The diameter of the taper section can even be greater than 4 metres, and numerous assembly operations carried out on site can be performed by working from inside the taper section. Assembly of the four segments (illustrated in figures 4a, 4b and 4c) is performed by longitudinal bolting of the flaps 4 , folded so as to form a single body. For this bolting operation, holes 5 are used, into which appropriate bolts are fitted.
Some operations are carried out on site, i.e. in the place where the tower is being erected, other operations are carried out in the factory, i.e. in the place where the individual constituent elements are prepared before being transported to the site.
In order to allow the taper sections 2 to be joined on site at a later stage, the constituent segments 3 are equipped with joining elements 6 pre- fitted (bolted) in the factory to the ends of the segments on the inner side of the sheet, in such a way that the corresponding joining elements can be connected by means of high-strength tie-rods 7 secured by nuts 8, thus making the joint between the taper sections as illustrated in figures
7a and 7b.
Hence, the tubular tower comprises: - a plurality of superimposed taper sections 2 connected together;
-joining elements 6 fixed (e.g. bolted) to the taper sections;
- tie-rods 7 inserted longitudinally into the joining elements 6 and secured with nuts 8, in order to connect each taper section 2 to the taper section adjacent thereto. It is noteworthy to observe that said tower is preferably (but not exclusively) configured to support a wind power station.
Hence, a taper section 2 A is connected to a taper section 2B adjacent thereto (when the taper sections 2A and 2B are superimposed to form the tower) by means of couples of joining elements 6 preliminarily fixed to the taper sections and tie-rods 7 successively (when the taper sections 2A and 2B are already superimposed) inserted therein.
Preferably, at least one of the taper sections 2 is provided with at least a fist and a second joining element 6 fixed to opposite ends of the taper section 2, to connect said taper section 2 to correspondent taper sections 2 arranged at opposite sides of said t least one taper section 2, when the taper sections 2 are superimposed to form the tower.
The joining elements intended for attaching a top plate 10 are also pre- fitted to the inside.
At the base of the tower, on the other hand, the joining elements are preferably pre-fitted to the outer surface of the sheet, in order to optimise the coupling to the anchor bolts 11 emerging from the foundations, as illustrated in figures 8a and 8b.
The joining elements 6 and the relative tie-rods 7 constitute joining devices. The procedure normally provides for the following stages: a) in the factory:
- cutting the sheet, normally in a trapezoidal shape;
- drilling the sheet to create the holes 5 and the end holes 9;
- folding the sheet to constitute a segment 3 of a taper section 2 by creating the sides of the polygon constituting the cross-section of the segment (or the faces of the polyhedron); the folding stage is fairly critical because it requires the maximum care and precision, since it must ensure that after folding, the holes 5 should coincide perfectly at the stage of longitudinally bolting the segments together; - hot galvanising the folded sheets;
- hot galvanising the joining elements;
- attaching the joining elements to the inner surface or the outer surface of the sheet, as described above. b) on site: - preparing a foundation;
- assembling the segments (preferably four) of each taper section by bolting so as to form a taper section 2 with a polygonal cross-section preferably with 16 sides but possibly also with a different number;
- fixing the base taper section to the foundation anchor bolts; - superimposing, aligning and joining further taper sections to the top, until the tower is completed.
The joining elements could be internal or external, or both internal and external, according to the type of stresses which the tower is destined to bear. In the preferred embodiment illustrated, however, they are internal to the tower, except in the case of the joining elements securing the base taper section to the anchor bolts.
The adoption of the joining elements described and of the connecting tie- rod, arranged substantially in a longitudinal direction parallel to the axis of the tower (in fact, the tower is only slightly tapered) constitutes one of the principal distinctive elements of the present invention, presenting the following advantages by comparison with the known art:
- elimination of bending effects and of welds;
- reduction in assembly difficulties, given the design conformation of the joining elements, which makes considerable allowance for construction defects and for any misalignment which may arise in the course of on- site assembly, by virtue of the particular profile of the housing for inserting the tie-rod, which does not require to be exactly "made-to- measure", indeed is best made leaving a certain amount of play to facilitate inserting the tie-rod and aligning the holes;
- greater resistance of the tower to tensile stress.
Figures 9-13 illustrate schematically a possible procedure for assembling the tower on site which includes:
- preparing first brackets 12 and second brackets 13 at the ends of the lateral flaps 4 of the segments 3, as illustrated in figures 14 and 15; in particular, figure 15 shows holes 14 and 15 respectively for fixing the first brackets and the second brackets;
- bringing the two segments 3 together;
- attaching first ropes 16 to first brackets 12 and to a spar 17 attached to a beam 18 suspended from a crane;
- attaching a further rope 19 to a hoist 20 and to holes in the ends of the lateral flaps of the segments at the opposite ends from brackets 12 and 13; the crane and the hoist constitute first and second lifting means;
- simultaneously manoeuvring the crane and the hoist to bring the segments into the position indicated in dotted lines in figure 9, ready for bolting;
- fastening the bolts through the free holes in the internal lateral flaps of the segments which have been brought together;
- attaching a tie-rod 28 to the second brackets 13 (fig. 10 ) to correct or maintain the diameter of the section, i.e. the distance between said brackets;
- lifting the structure previously obtained and resting it in a guide cradle 21 which can be adjustable for width by means of movable lateral stands 23 comprising square section tubular elements 24 and round section tubular elements 25;
- detaching ropes 16 and 19 and removing first brackets 12;
- fastening bolts through the holes left vacant by rope 19 and through all the longitudinal holes;
- superimposing another similar structure to form a taper section, if necessary centring the two structures by means of thrusting/centring devices 22;
- fastening bolts throughout the length of the taper section;
- removing tie-rods 28 and second brackets 13.
As regards the stage of superimposing another similar structure to form a taper section, as illustrated in figure 13, the following stages are included:
- lifting and extracting the structure from the cradle by means of a rope 26 and rotating the structure (in dotted lines) by the use of an opposed rope 27; - lowering and resting it on the ground;
- lifting, supporting and bolting it onto another structure or lower half- shell. Removing temporary brackets 12 and tie-rods 28.
Another construction process, not illustrated, provides for setting up two cradles adjacent to each other along a common longitudinal edge of the structures contained in them, in such a way as to allow one structure to be rotated over the other around this longitudinal edge.