Abstract:
The invention relates to a connector assembly ( 20 ) for joining a main tower ( 102 ) to a base structure ( 104 ) where the axial alignment of the tower to the base structure needs to be adjustable, and to a method of using such a connector assembly to assemble a tower structure.

Description:
RELATED APPLICATIONS 
       [0001]    The application claims priority to U.K. Patent Application No. 1017555.2, filed Oct. 18, 2010, the contents of which are hereby incorporated by reference in their entirety. 
       BACKGROUND 
       [0002]    a. Field 
         [0003]    The disclosure relates to a connector assembly for joining a tower to a base structure where the axial alignment of the tower to the base structure needs to be adjustable, and to a method of using such a connector to assemble a tower structure. 
         [0004]    b. Related Art 
         [0005]    Currently offshore wind turbine towers have a main tower with a tubular body, the lower end of which has a flange to which is welded a tubular transition piece that extends downwards from the tubular body for connection to a tubular base of a lower supporting structure. The lower supporting structure may be a single tubular pile driven into relatively shallow water and a transition piece is then attached. The upper end of the pile then provides the tubular base. Alternatively, when the water is deeper, the lower supporting structure may include a framework structure formed from a lattice of structural members supported by a number of seabed piles and terminated at an upper end by a tubular member that forms the tubular base for the turbine tower. 
         [0006]    When the main tower is to be connected to the tubular base of the lower supporting structure, the tubular transition piece, which has an inner diameter greater than the outer diameter of the tubular base, is inserted over the tubular base. Typically, the drilled or driven pile is installed with its axis aligned to within 0.5° of vertical. 
         [0007]    Wind velocities increase at higher altitudes due to decreased surface aerodynamic drag by land or water surfaces, and so there is the need to maximize the height of the turbine blades. The tallest wind turbines have a main tower more than 100 m in height. At a height of 100 m, a misalignment of 0.5° of the main tower with respect to vertical will result in a tilt of about 90 cm from vertical at the top of the main tower. Such a lean will add to the moment loads to be applied to the foundations of the wind turbine. To compensate for this amount of misalignment, it then becomes necessary to increase the strength of the main tower and lower supporting structure and foundations. Ideally the tower needs to be as close to vertical a possible to ensure even loading on the tower and turbine. 
         [0008]    Therefore, in order to permit the axial alignment between the tubular body of the main tower and the tubular base to be adjusted, it is known to provide a clearance gap between the outer tubular transition piece and the inner tubular base. The gap allows a certain degree of movement between the tubular body of the main tower and the tubular base prior to these being fixed in place with respect to each other, and also accommodates the fact such tubular members, which may be around 6 m in diameter, may be slightly oval with a deviation from circularity of up to about ±1.5% and with a tolerance on nominal diameter of about ±1.0%. 
         [0009]    The transition piece, which may weigh 200 tonnes, is suspended by a crane, and then the orientation of the transition piece is adjusted until this is sufficiently close to vertical. The orientation and spacing transition from the tubular base is then set by internal pads inside the gap at the top of the pile and then fixed in place with a high quality epoxy grout inserted between the outer wall of the pile and the inner wall of the tubular transition piece. The grout may take about one week to cure. 
         [0010]    A number of problems have been noted with this alignment and setting procedure. 
         [0011]    It takes time for the grout to set, during which the main transition piece has to be kept carefully in place by the crane, all of which is very expensive. Furthermore the grout interface has in some cases shown a tendency over time to break, up resulting in an insecure foundation and expensive remedial work. 
         [0012]    It is therefore an object of the present disclosure to provide a connector assembly for joining a pair of tubular members where the axial alignment of the tubular members needs to be adjustable, and to a method of using such a connector assembly. 
       SUMMARY 
       [0013]    According to a first aspect of the disclosure, there is provided a connector assembly for affixing a main tower to a lower base structure, the connector assembly comprising two connector portions, a first one of said connector portions being for affixing at an upper end of said lower base structure and a second one of said connector portions being for affixing at a lower end of said tower, one of said connector portions having a ring and the other of said connector portions having a collar, the ring defining a ring axis and the collar defining a collar axis and having an opening for receiving the ring, and said connector portions including clamping means for clamping engagement of the ring within the collar, wherein:
       the ring includes a seat and the collar includes an abutment, the abutment being in contact with the seat for transferring the weight of said tower to said base structure when the ring is clamped within the collar by the clamping means;   the ring has a main body and a flange, the flange extending radially outwards from the main body of the ring and said flange providing said seat; and   the contact between the seat and the abutment is along an interface that permits tilt adjustment of the ring axis and collar axis prior to said clamping engagement of the ring within the collar.       
 
         [0017]    In use, the seat bears the weight of the tower and the abutment transfers the weight of the tower to the base structure when the tower is affixed to the base structure. 
         [0018]    In an embodiment of the disclosure, the curved surface is curved in a plane that includes either the collar axis or the ring axis, and the interface also permits the tilt adjustment of the ring axis and collar axis in two orthogonal directions so that any tilt misalignment between the main tower and lower base structure can be accommodated by the connector assembly. 
         [0019]    The interface preferably includes at least one surface that is curved to permit ball and socket type movement between the first and second connector portions. In this case, it is not necessary that surfaces of the interface form a complete ball surface or a complete socket, but only that the curved surface is sufficiently extensive that the movement provided by a ball and socket joint is provided. In an embodiment of the disclosure, the curved surfaces are annular and each is centered on an axis defined by the annular surface. 
         [0020]    The interface that permits tilt adjustment of the ring axis and collar axis may include surfaces on both the seat and abutment that are curved to permit ball and socket type movement of the first and second connector portions. Alternatively, just one of these surfaces may be curved, for example being convex in cross-section through its axis, and the other of the surfaces may be flat in cross-section through its axis. 
         [0021]    The clamping means may include a plurality of movable members mounted in the collar and actuation means for driving the movement of the moveable members to engage with the ring. Each movable member may comprise a dog movable in a radial direction, the movement of each dog being driven by a corresponding drive dog movable in an axial direction, with each dog and drive dog having oppositely inclined surfaces in contact with each other such that the axial movement of a drive dog causes a radial movement in the corresponding dog. 
         [0022]    In an embodiment of the disclosure, collar has an inner wall and an outer wall, the inner wall being adapted to surround the ring with a gap between collar and the ring. The inner wall may have a plurality of apertures, each aperture leading to a passage through the inner wall. Then, each of the dogs may be slidably seated in one of the passages for movement in a radial direction with respect to the ring axis. 
         [0023]    The contacting sliding surfaces of each drive dog and dog are oppositely inclined, such that when the drive dog is moved in one axial direction relative to the dog, the dog is driven in a radially inwardly direction across the gap to grip the ring. 
         [0024]    In use, the contact between the drive dog and the outer wall of the collar provides a restoring force to a gripping force transmitted radially outwards from the dog when this contacts the ring. The gripping force exerted by the dogs, which are preferably evenly spaced circumferentially around the collar, then clamps the collar to the ring. 
         [0025]    It is advantageous if the movement means for each drive dog is independent of the movement means for other drive dogs so that a plurality of drive dogs may be independently moved. Each corresponding dog is then independently driven in a radially inwardly direction across the gap. 
         [0026]    The actuation means may be any convenient means for moving the drive dog. In an embodiment of the disclosure, the actuation means includes a threaded member, for example a bolt, which when turned, engages with an internal threaded bore in the drive dog to move the drive dog in an axial direction. Other actuation means may, however be used, for example hydraulic actuation. 
         [0027]    The collar may include a radially extending flange that extends outwards from a main body of the collar. In an embodiment of the disclosure, the bolt extends through this flange. 
         [0028]    The ring may have a recess in which the movable members, or dogs, are located to clamp the ring within the collar. 
         [0029]    The ring may have a main body and a flange, the flange extending radially outwards from the main body of the ring and the flange providing the seat. 
         [0030]    The flange of the ring may have a pair of opposite side surfaces, one of these side surfaces providing the seat and the other of the side surfaces providing a clamping surface for the clamping engagement of the ring within the connector. 
         [0031]    The side surfaces may extend away from the main body of the ring such that the side surfaces are inwardly inclined with respect to each other and to a radially extending plane. Preferably, the inclined surfaces are inclined at the same but opposite angle with respect to a radially extending plane so that clamping forces and the forces stemming from the weight of the tower can be balanced. 
         [0032]    The flange is also preferably in the form of a lip that extends around the circumference of the ring. 
         [0033]    The flange may be bounded by an adjacent channel in the main body of the ring, this channel providing the recess so that the flange is held between the abutment and the movable members, or dogs, when the ring is clamped within the collar. 
         [0034]    According to a second aspect of the disclosure, there is provided a turbine tower, comprising a main tower for supporting a turbine generator, a lower base structure for supporting said main tower, and a connector assembly for affixing the main tower to the lower base structure, the connector assembly comprising two connector portions, a first one of said connector portions being for affixing at an upper end of said lower base structure and a second one of said connector portions being for affixing at a lower end of said tower, one of said connector portions having a ring and the other of said connector portions having a collar, the ring defining a ring axis and the collar defining a collar axis and having an opening for receiving the ring, and said connector portions including clamping means for clamping engagement of the ring within the collar, wherein:
       the ring includes a seat and the collar includes an abutment, the abutment being in contact with the seat for transferring the weight of said tower to said base structure when the ring is clamped within the collar by the clamping means;   the ring has a main body and a flange, the flange extending radially outwards from the main body of the ring and said flange providing said seat;   the contact between the seat and the abutment is along an interface that permits tilt adjustment of the ring axis and collar axis prior to said clamping engagement of the ring within the collar; and   one of the connector portions is affixed to a lower end of the main tower and the other of the connector portions is affixed to an upper end of the lower base structure.       
 
         [0039]    In an embodiment of the disclosure, the first one of the connector portions has the seat and the second one of the connector portions has the abutment. 
         [0040]    The upper end of the lower base structure may be substantially tubular, for example having a substantially circular cross-section, in which case the first connector portion where this is affixed to the upper end of the base structure may be substantially cylindrical. 
         [0041]    The lower end of the main tower may also be substantially tubular, for example having a substantially circular cross-section, in which case the second connector portion where this is affixed to the lower end of the main tower may be substantially cylindrical. 
         [0042]    The disclosure further provides a method of assembling a turbine tower, the turbine tower comprising a main tower for supporting a turbine generator, a lower base structure for supporting said main tower, and a connector assembly for affixing the main tower to the lower base structure, the connector assembly comprising two connector portions, one of said connector portions having a ring and the other of said connector portions having a collar, the ring defining a ring axis and the collar defining a collar axis, the ring having a main body and a flange, the flange extending radially outwards from the main body of the ring and the collar and ring having mating surfaces shaped so as to allow tilt adjustment of said axes, and said connector portions including clamping means, wherein the method comprises the steps of:
       affixing a first one of said connector portions to a supporting surface of the earth;   joining a first one of said connector portions at an upper end of said lower base structure;   joining a second one of said connector portions at a lower end of said main tower;   bringing the free ends of the of the ring and the collar together until said mating surfaces come into contact;   adjusting the tilt of said axes to achieve a desired orientation of the main tower with respect to vertical;   using the clamping means to clamp the ring within the collar in order to fix the orientation of the main tower with respect to vertical.       
 
         [0049]    The method may also comprise the steps of:
       forming the connector portion for connection to the lower base structure with a rim that is relatively stronger than the upper end of the base structure;   joining said first one of said connector portions to the upper end of the base structure prior to said affixing of said connector portions to a supporting surface of the earth, such that the rim is at an upper end of said joined base structure and connector portion; and   driving the joined base structure and connector portion into the supporting surface of the earth using force applied to the rim at said upper end of said joined base structure.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]    The disclosure will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0054]      FIG. 1  is a perspective view of part of a wind turbine tower and supporting base structure according to the prior art; 
           [0055]      FIG. 2  is a view of three different wind and water turbines each of which comprises a connector assembly according to an embodiment of the disclosure; 
           [0056]      FIG. 3  is a side view in more detail of the connector assembly of  FIG. 2  showing how this assembly comprises a first connector portion joined to the base support and a second connector portion joined to the main tower; 
           [0057]      FIG. 4  is a cross-section view of the connector assembly, taken along lines IV-IV of  FIG. 3 , showing how an abutment at the lower end of the second connector portion rests on a seat formed by a first side surface of a lip that extends around the first connector portion, and how a clamping mechanism is used to clamp the main tower to the base support; and 
           [0058]      FIGS. 5 to 7  are enlarged views of the clamping mechanism of  FIG. 4 , showing how the clamping mechanism includes sliding blocks that are driven radially inwards by the axial movement of a drive block to engage with a second side of the lip so that the lip is held tightly between the abutment and sliding blocks. 
       
    
    
     DETAILED DESCRIPTION 
       [0059]      FIG. 1  shows a prior art wind turbine tower  1  having a main tower  2  with a hollow tubular body  4 , the lower end  6  of which has a flange  8  to which is welded a tubular transition piece  10  that extends downwards from the tubular body for connection to a tubular base  12  of a lower supporting structure  14 . The lower supporting structure is in this example a single tubular pile  14  driven into the bed of a relatively shallow body of water. An upper end  16  of the pile then provides the tubular base  12 . 
         [0060]    When the main tower  2  is to be connected to the tubular base  12  of the lower supporting structure  14 , the tubular transition piece  10 , which has an inner diameter greater than the outer diameter of the tubular base  12 , is inserted over the tubular base. Typically, the drilled or driven pile is installed with its axis aligned to within 0.5° of vertical. 
         [0061]    To permit the axial alignment between the tubular body  4  of the main tower  2  and the tubular base  12  to be adjusted, a clearance gap  18  is provided between the outer tubular transition piece  10  and the inner tubular base  12 . The gap  18  allows a certain degree of movement between the tubular body of the main tower  2  and the tubular base  12  prior to these being fixed in place with respect to each other, and also accommodates the fact such tubular members may be slightly oval. 
         [0062]    With the main tower  2  suspended by a crane (not shown), the orientation of the tower is adjusted until this is sufficiently close to vertical. The orientation and spacing of the transition around the tubular base is then set by internal pads (not shown) inside the gap at the top of the pile  14  and then fixed in place with a high quality epoxy grout (not shown) inserted between the outer wall of the pile and the inner wall of the tubular transition piece. 
         [0063]    As mentioned above, a number of problems have been noted with this alignment and setting procedure. 
         [0064]    As shown in  FIG. 2 , the disclosure is applicable to wind turbine towers standing in water, as well as to submerged tide turbines. In both cases, the lower base structure stands in a body of water, for example supported on piles driven into the seabed or lakebed. Although not illustrated, the disclosure is also applicable to wind turbines on dry land. 
         [0065]    The disclosure therefore provides a connector assembly  20  for affixing a main tower  102 ,  202 ,  302  to a lower base structure  114 ,  214 ,  314 . The disclosure is suitable for use in a variety of situations, for example: a shallow water wind turbine  101 , where a main tower  102  having a hollow tubular body  104  is supported by supporting base support  112  formed from the top of a single tubular pile  114 ; a deeper water turbine  201  supported by a lower base structure formed from a base support  212  on a lattice framework structure  22  and four piles  23 , the lattice structure being terminated at an upper end by a tubular member that forms a tubular base for the turbine tower; or a submerged tide turbine  301  supported on a base support  312  mounted on a triangular base frame  24  held down by three tubular piles  123 . 
         [0066]      FIGS. 3 to 7  show the connector assembly  20  in more detail. The connector assembly is formed in steel and has a first connector portion  26  that is welded  28  at an upper end  116  of the lower base support  112  and also a second connector portion  27  welded  30  at a lower end  106  of a main tower  102 . In some instances, the weld could be facilitated by a flange or some other features at the weld interface. 
         [0067]    The first connector portion  26  is preferably formed from a forged or cast tubular section with an outer profile that provides a connector interface. As will be described in more detail below, this connector interface includes an annular top radius profile. The second connector portion interfaces with and sits down on the top radius profile to provide for angular adjustment between the first and second connector portions to provide accurate adjustment for levelness/verticality. 
         [0068]    The first connector portion  26  has a generally circular ring  31  and the second connector portion has a generally circular collar  32 . Both the ring and collar have a cylindrical symmetry and so the ring defines a ring axis  33 , while and the collar defines a collar axis  34 . The collar also has an opening  35  at a lower end for receiving the ring  31 . The connector portions  26 ,  27  include clamping means  40  for clamping engagement of the ring  31  within the collar  32 . 
         [0069]    As shown in  FIGS. 3 to 5 , the ring axis  33  and collar axis  34  may be collinear, however, the connector assembly  20  includes means to allow the alignment of these two axes to be varied within about 1.5° of each other in two orthogonal directions so that any tilt of the base support  112  away from vertical within these limits can be accommodated to achieve a vertical orientation of the main tower  102 . 
         [0070]    The ability to compensate for this amount of misalignment is provided by a pivot interface between the first and second connector portions  26 ,  27 . The ring  31  has an annular seat  37  with a convex annular surface that is centered at a point  39  on the ring axis  33  near the top end  116  of the base support. This spherical surface therefore faces both radially away from the ring axis  33  and axially away from the ring  31  and towards the second connector portion  27 . 
         [0071]    The collar  32  has an abutment  35  with an annular concave surface  36  that is centered on the same point  39  on the ring axis  33  as that of the seat  37 . This concave spherical surface therefore faces both radially towards the ring axis  33  and axially away from the collar  32  and towards the first connector portion  26 . 
         [0072]    Until clamped by the clamping means  40 , which will be described in more detail below, the contact between the seat  37  and the abutment  35  is therefore along an interface which acts similarly to that of a ball and socket joint and which permits tilt adjustment of the ring axis  33  and collar axis  34 . 
         [0073]    As shown in the drawings, the abutment  35  is in contact with the seat  37  and serves in use to transfer the weight of the main tower  102  to the base structure  112 . Once adjusted for the correct tilt alignment, the angular orientation of the ring  31  within the collar  32  is set using the clamping means  40 . The clamping means comprises a plurality of clamps  41 , preferably between about ten and twenty clamps, spaced evenly around the circumference of the collar  32  together with a corresponding clamping surface  43  on the ring  31 . Each clamp  41  has an axially extending bore  45  and an intersecting radially extending bore  46  machined in the steel material of the collar  32 . The inner and outer walls  42 ,  44  are therefore integrally formed. The bores  45 ,  46  define an outer wall  44  that is radially outwards from the axial bore  45  and an inner wall  42  that is radially inwards from the axial bore  45 . Each of the radial bores  46  therefore passes through the inner wall  42  between the axial bore  45  and a cylindrical inner surface  47  of the collar  32 . 
         [0074]    Each clamp  41  has a moveable clamping block, or dog,  48 , each of which acts as a clamping member against the clamping surface  43  and which is slideable within each of the bores  46  in the radial direction towards or away from the ring axis  33 . Each radial bore  46  has a rectangular cross-section that is defined on four sides by the surfaces machined in the inner wall  42 . The moveable clamping block  48  closely matches this profile. 
         [0075]    The axial bore  45  also has a rectangular cross-section and holds a second movable block which is a drive block, or drive dog,  49  that has a flat radially outer surface  53  that is in sliding contact with a radially inner surface  54  of the outer wall  44 . The axial bore  45  and drive block  49  each have a rectangular shape such that the drive block  49  moves with close sliding fit up and down in the axial bore depending on the turn of a drive bolt  50  with which the drive block is threaded. The drive block  49  has on a radially inwards side a flat inclined surface  51  which is in contact with an oppositely inclined surface  52  of the movable block  48 , so that the drive block functions as cam block to move the movable clamping block  48  radially inwards when the drive block is driven upwards by the bolt  50 . 
         [0076]    Both the movable block  48  and drive block  49  are machined from steel and have a rectangular shape as viewed in a radially extending cross-section. With reference now also to  FIGS. 6 and 7 , because the contacting surfaces  51 ,  52  of the drive block and movable block are oppositely inclined with respect to each other, when the drive block  49  is moved in an upwards axial direction, the movable block  48  is forced outwards through the bore  46  in a radially inwards direction. During this process, the inner surface  54  of the outer wall  44  prevents the drive block  49  from moving in an outwards radial direction and so provides a restoring force to any resistance encountered by the movement of the driven movable block  48  when this contacts the clamping surface  43  of the ring  31 . The movable block  48  therefore acts as a dog and the driven block  49  acts as a drive dog. 
         [0077]    The driven block  49  is actuated by means of the threaded bolt  50  that engages with a similarly threaded bore  55  in the driven block  49 . The bolt  50  extends through a plain bore  56  in the collar above the axial bore  45  in a direction parallel with the collar axis  34  such that when the bolt is turned, the driven block is pulled or pushed in one or the other of the axial directions, while the axis of the bolt remains fixed. The bolt  50  has a hexagonal head  58  that is seated in recess  59  in a conically shaped section  60  of the collar  32 , the recess being sized so that suitable tools may turn the bolt. During assembly, each bolt is individually actuated and tightened so that the collar is evenly clamped to the ring. 
         [0078]    This is achieved by supporting the majority of the tower weight using an installation crane (not shown) and then actuating previously identified high and low side clamping blocks  48  to initially move the connection over on the top radius of the ring seat  37  until verticality is achieved. The clamping blocks  48  may then be clamped into position. The remaining clamping blocks are then actuated to provide a pre-loaded and structural connection to the pile. It is worth noting that the external clamping surface  43  is engineered to accept the various positions of the clamping blocks on this surface. 
         [0079]    Although in this example actuation is mechanical through a bolt arrangement, it would also be possible to use a hydraulic running tool and then mechanically lock each clamping block using, by way of example, threaded bolts, studs and or nuts. 
         [0080]    Each clamp  41  is designed mainly for single use, and for long lifetime in salty conditions. Each axial bore  45  within the collar  32  may be packed with grease to ensure smooth movement of the sliding blocks and to minimize the rate of corrosion. The number of parts in the moving mechanism is kept to a minimum to ensure reliability, both when the clamping connection is made, and when the connection is to be released when the tower is to be disassembled, which could be after a period as long as 50 years. 
         [0081]    Although the clamping connector described above has no spring or hydraulic mechanism to control the movement of the blocks  48 ,  49  or to provide a retraction force to push the movable block  48  to a retracted orientation, such features could be provided if necessary. 
         [0082]    As can be seen from  FIGS. 5 to 7 , the clamping surface  43  is oppositely inclined with respect to the curved surface  38  of the seat  37 , which together form a projection or lip  65  that extends fully around the circumference of the ring  31 . The movable block therefore has a chamfer  62 , with a circumferentially curved profile, to match the circumferentially curved and inclined shape of the clamping surface  43 . The clamping force is therefore directed normal to the inclined clamping surface with components both in a radial direction and an axial direction, while the weight of the main tower  102  also generates a force on the seat  37  with both radial and axial components. The effect with the movable blocks  48  each fully tightened is that the lip  65  of the ring  31  is securely gripped on opposite inclined sides, thereby securely fixing the main tower to the base support at the desired tilt angle between the ring and collar axes  33 ,  34 . 
         [0083]    The first connector  26  may have a groove  66  or other features for the attachment of other necessary features to the assembled turbine tower, for example a deck, an access platform, a boat landing, an access ladder or J tubes for power cables. Although not illustrated, the second connector may also have similar attachment features. 
         [0084]    In use, each connector assembly  20  can support the weight of a typical wind turbine, currently up to 1,400 tonnes, when clamped to a tubular supporting member such as a pile  114  that is approximately 6 m in diameter. The connector assembly  20  can also accommodate a deviation from circularity in such a tubular supporting of up to about ±1.5% and with a tolerance on nominal diameter of about ±1.0%. 
         [0085]    The disclosure described above provides the ability to adjust the angle between the main tower and support structure and hence the verticality of the tower without relying on a grouted interface. The predicted lifetime of the connector assembly is also much greater than that of a grouted interface. The disclosure therefore provides a convenient, safe and speedy connector assembly for making a structural connection that lends itself to offshore turbine towers both above and below the waterline, but is not necessarily limited to these applications. 
         [0086]    One additional benefit of the disclosure is that the larger cross-section profile of the first connector portion, as compared with that of the supporting tubular structure, can provide a useful handling means for the pile via a running tool and a larger and more efficient drive face that would be less prone to piling damage. 
         [0087]    It should be noted that although the disclosure is particularly applicable to cases in which the assembled tower is in a substantially vertical orientation, but is also applicable to other structures where the axial alignment of neighbouring tubular members needs to be adjustable or in which an assembled structure is at an angle to vertical, for example when used as an arch or brace as part of a larger structure. 
         [0088]    It should also be noted that although the disclosure has been described in detail with the first connection portion (i.e. the connector portion that is affixed at the upper end of the lower base structure) as having the ring, and the second connector portion (i.e. the connector portion that is affixed at the lower end of the tower) as having the collar, the disclosure is also applicable to the case where the first connector portion has the collar and the second connector portion has the ring. 
         [0089]    It is to be recognized that various alterations, modifications, and/or additions may be introduced into the constructions and arrangements of parts described above without departing from the spirit or scope of the present disclosure, as defined by the appended claims.