EP3555369B1 - Method for installing a tensioning element in an anchor block, holder, in particular for carrying out the method and combination of a holder with a prestressing element - Google Patents

Description

The invention relates to a method for installing a tensioning element in an anchor block already fastened to a structure according to the preamble of claim 1.

Such a method is used, for example, in the erection of structures, such as cable-stayed bridges, which have a plurality of tendons, each of which in turn comprises a plurality of tensioning elements that are accommodated in a common jacket tube made, for example, of high-density polyethylene (HDPE) can. The method is used to pull the tensioning elements into the duct and then anchor them in the anchor block.

As is known per se from the prior art, the tensioning elements used according to the invention can each comprise a strand formed from a plurality of wires. For example, the strand can be formed from seven steel wires. In order to be able to provide an initial protection against corrosion, the strands can be galvanized and / or coated with epoxy resin. As a further corrosion protection measure, the strands can be encased in a protective sheath made, for example, of plastic, in particular polyethylene (PE). Before sheathing the stranded wire with the protective jacket, the stranded wire can be coated with a corrosion protection material, for example wax or grease, which preferably essentially completely fills the space between the stranded wire and the protective jacket.

To install a tensioning element, the bracket is usually attached to the free end of the tensioning element. For this purpose, for example, the central wire of the braid can be exposed and a so-called central wire clamp can be attached to it. Alternatively, the free end of the central wire can also be plastically deformed to form an upsetting head on which the holder can engage in a form-fitting manner while the outer wires adjacent to the holder are removed. Then a pull rope attached to the bracket is hauled in by means of a winch, so that the tensioning element is moved to the anchor block together with the bracket. When you arrive at the anchor block, there are two alternatives:
Either the pull rope already runs through the passage opening of the anchor block in which the tensioning element is to be anchored. In this case, the tensioning element together with the bracket attached to it must still be pulled through the through opening and then the tensioning element must be attached to the anchor block. With this procedure, the size of the bracket is limited, since it has to fit through the through opening of the anchor block together with the tensioning element. It is easy to see that this entails restrictions with regard to the stability of the fastening. In addition, the pull rope has to be threaded through the respective passage opening again for each installation process, which makes the process more complex overall.

Or the tensioning element is transferred to another winch, the pull rope of which has been pulled through the associated passage opening in the anchor block, while the tensioning element is moved to the anchor block at the same time. However, this procedure requires a further winch and is also subject, at least in the last section of the installation process, to the same restrictions with regard to the stability of the connection of holder and tensioning element as the procedure described above.

document DE 25 49 299 A1 , which is the closest prior art discloses a method of installing a tensioning element in an anchor block, wherein the tensioning element is connected to a bracket to move the tensioning element toward the anchor block.

Also refer to the documents US 2005/055974 A1 , U.S. 5,461,743 A and DE 21 03 192 A1 pointed out.

It is therefore the object of the present invention to simplify the installation of clamping elements.

This object is achieved according to the invention by a method according to claim 1.

In this way, it is possible to insert the tensioning element into the through-opening of the anchorage without having to loosen the bracket for hanging the tensioning element onto another winch, and without having to re-insert the bracket and the associated pulling rope through the associated through-opening during each installation process the anchor block to have to pass. In addition, the holder does not need to be designed taking into account the dimensions of the through openings of the anchor block, since according to the invention only the section of the tensioning element arranged on the other side of the holder, i.e. the protrusion of the tensioning element, is passed through the through opening. This simplifies the installation process both in terms of the time required for its implementation and in terms of the personnel required for its implementation as well as in terms of the equipment required for its implementation.

According to the invention it can also be provided that the holder is moved to the anchor block by means of a pull rope.

Advantageously, both at the end facing the anchor block the holder and at the end of the holder facing away from the anchor block each have a pull rope, wherein a separate winch can preferably be assigned to both pull ropes. This development enables a controlled back and forth movement of the bracket between a tensioning element starting position, which can be located, for example, on the deck of the cable-stayed bridge or at the level of the foundation of a tower, and the anchor block, which is located, for example, in the pylon of the cable-stayed bridge or at level the spire can be located, for example a controlled back and forth movement in the duct of the tendon. It is also advantageous if the winch assigned to the tensioning element starting position is operated in such a way that the tension ropes are essentially constantly under tension while the holder is moved to the anchor block.

A problem that often arises in the course of the movement of the tensioning element to the anchor block, for example, but not exclusively due to the tensile load on the tension ropes, is twisting of the tensioning element connected to the holder about its longitudinal direction. Since tendons in practice often include a large number of tensioning elements, for example more than one hundred tensioning elements, the ducts have an inside diameter that is significantly larger than the diameter of the individual tensioning elements. Therefore, the twisting of the tensioning element that has just moved to the anchor block, especially at the beginning of the installation of the tensioning element, when a few tensioning elements are still in the cladding tube, can result in the free end of the tensioning element, in particular the free end of the protrusion, in the already caught in the cladding tube clamping elements. In order to be able to prevent this problem, it is proposed in a further development of the invention that a guide unit be attached to the free end of the tensioning element, at least while the holder is being moved to the anchor block. The mere fact that the guide unit is attached to the free end of the tensioning element and is thus transverse to the longitudinal direction of the tensioning element extends beyond this, it makes it difficult for the tensioning element to get caught in other tensioning elements received in the cladding tube. This applies all the more if the dimensions of the guide unit transversely to the direction of longitudinal extension of the tensioning element are more than twice as large as those of the tensioning element itself.

In addition or as an alternative to this, it can also be provided that the guide unit is connected to the pull rope, for example is detachably connected. The connection can be formed, for example, by an eyelet which loosely surrounds the pull rope, so that it can be moved relative to the pull rope. The releasability can for example be provided in the manner of a snap hook or the like. However, it is also conceivable that the connection is formed by means of a clamp which can be fixed to the pull rope so that it cannot move relative thereto.

In order to be able to carry out the installation of the clamping elements even more effectively, it is proposed that the holder be designed for attaching at least two clamping elements. In this way, several tensioning elements can be moved from the tensioning element starting position to the anchor block in one operation. Care only has to be taken to ensure that each of the tensioning elements is inserted into the respectively assigned passage opening of the anchor block. However, this can be ensured, for example, by simple numbering or colored marking of the clamping elements.

In principle, it is conceivable that the projections of the at least two clamping elements are of different lengths. This would make it possible to insert the tensioning elements one after the other into the associated through holes. This can be particularly advantageous in confined spaces. In order to achieve the shortest possible installation time, however, it is preferred according to the invention that the overhangs of the at least two clamping elements are of essentially the same length are. This makes it possible to simultaneously introduce the tensioning elements into the through openings of the anchor block and anchor them therein.

• einen Basiskörper mit einer länglichen Ausnehmung zur Aufnahme des Spannelements,
  • wobei die Ausnehmung an ihren beiden Längsenden jeweils eine Austrittsöffnung aufweist, welche dazu ausgelegt und bestimmt sind, das Spannelement in den Basiskörper ein- und aus diesem wieder austreten zu lassen, und
  • wobei die Ausnehmung an einer ihrer Längsseiten eine längliche Öffnung aufweist, welche einen im Wesentlichen geradlinig verlaufenden Abschnitt aufweist, der sich über die gesamte Länge des Basiskörpers erstreckt, und
• eine Haltekrafterzeugungseinrichtung, welche dazu bestimmt ist, eine Haltekraft zu erzeugen, welche das Spannelement gegen eine Begrenzungswand der Ausnehmung andrückt.

A holder for a tensioning element is described below, which is particularly suitable for carrying out the method according to the invention, comprising:

• a base body with an elongated recess for receiving the clamping element,
  • wherein the recess has an outlet opening at each of its two longitudinal ends, which are designed and intended to allow the clamping element to enter and exit the base body, and
  • wherein the recess has an elongated opening on one of its longitudinal sides which has a substantially rectilinear section which extends over the entire length of the base body, and
• a holding force generating device which is intended to generate a holding force which presses the clamping element against a boundary wall of the recess.

The bracket also helps simplify installation of the tensioning elements. You only need to insert the respective tensioning element into the recess from above through the substantially straight section of the upper opening of the recess and then to actuate the holding force generating device. The protrusion of the clamping element required for carrying out the method according to the invention can emerge from the holder through one outlet opening, while the remaining length of the clamping element emerges from the other outlet opening. As a result of its actuation, the holding force generating device generates a holding force which holds the clamping element securely in the holder while the holder is moved together with the clamping element to the anchor block.

In a further development of the holder, it is proposed that the holding force generating device comprises an engagement element which is adjustable relative to the base body and which is designed and intended to come into abutment engagement with the clamping element and to press it into abutment against a stationary wall section of the recess of the base body. In this case, the engagement element can be formed, for example, by a stamp which is adjustable relative to the base body and which, in particular with the aid of a tool, can be adjusted by hand or by means of a power device. Alternatively, however, it is also conceivable that the engagement element is formed by a surface section of a flexible element, for example a hose or a balloon, which can be filled and emptied hydraulically and / or pneumatically.

While the tensioning element is pressed against a stationary wall section of the recess of the base body in abutment, an at least partial displacement of the tensioning element in the recess can also occur. For example, the holding force generating device can be designed to deflect the tensioning element from its straight course. Thus, according to one embodiment of the holder, it is conceivable that a length section of the tensioning element located between the two outlet openings is bent into an essentially double-S-shaped course. If the simple double-S-shaped course is not sufficient to generate the required holding force, a multiple double-S-shaped course can also be used. For this purpose, a corresponding number of engagement elements can be provided.

In a further development of the holder, it is proposed that the base body further comprise a ceiling wall which covers the recess at least in sections, for example adjacent to the stationary wall section. This ceiling wall can secure the clamping element positively against it, in an unintentional manner automatically from the Stepping out recess.

In order to be able to move more than one tensioning element to the anchor block by means of the bracket, it is further proposed that the bracket comprise at least two recesses. For example, the holder can comprise two such recesses, which are arranged essentially mirror-symmetrically with respect to the longitudinal direction of the holder. A common holding force generating device can be assigned to the two recesses.

The common holding force generating device can comprise two engagement elements, each of which is intended to come into contact with one of the clamping elements, and which can be adjusted by means of a common adjusting device. However, it is also possible for the common holding force generating device to comprise an engagement unit which can be pivoted or rotated on the base body about an axis running parallel to its height direction. Two sections of the engagement unit can each form an engagement element which is intended to come into contact engagement with one of the clamping elements.

As far as the holding force is concerned, it goes without saying that the engagement between the holding force generating device and the tensioning element must be accomplished in a manner that prevents or prevents the risk of damage to the tensioning element or a part of the tensioning element, for example the protective jacket surrounding the strand This completely excludes danger, regardless of whether the holding force is generated by frictional engagement and / or by positive engagement.

With regard to a portion of the holding force generated by frictional engagement, care must be taken that the clamping force, ie the portion of the holding force generated by frictional engagement, the tensioning element, in particular the protective sheath of the strand forming the actual tensioning element, is essentially only elastic deformed. In particular, plastic deformation of the protective jacket could lead to crack formation, which could endanger the protection of the strand from corrosion due to the penetration of moisture through the cracks.

If a form-fit component of the holding force is generated by holding elements penetrating the protective sheath of the strand that forms the actual tensioning element, care should be taken to ensure that these holding elements do not permanently damage the protective sheath. The openings in the protective sheath resulting from such damage could namely penetrate into the protective sheath, which could lead to corrosion on the stranded wire. For example, the surface of the engagement element provided for abutment engagement with the tensioning element could be formed at least in sections with a rough surface, with the individual retaining projections forming the surface roughness protruding from the base of the surface by a distance that is smaller than the thickness of the protective jacket.

Since the protective sheath usually hugs the stranded wire, for example in the manner of a shrink tube, the positive-locking component of the holding force can also be generated in that the surface of the engagement element provided for contact engagement with the tensioning element is provided with a coating which is adapted to the Surface of the clamping element is designed. Additionally or alternatively, however, it is also possible for the cover to be designed to be elastically deformable, so that it can adapt to the surface shape of the tensioning element. Furthermore, in order to increase the frictional contribution to the holding force, the coating can have a coefficient of static friction which is greater than that of the material from which the stamp is formed.

The surface of the base body, against which the tensioning element is pressed by means of the stamp, can also be provided with a coating of at least one of the above-explained for the coating of the stamp Has properties.

Figur 1

eine schematische Ansicht einer Schrägseilbrücke, bei deren Errichtung das erfindungsgemäße Verfahren und die Halterung zum Einsatz kommen;

Figur 2

eine schematische Ansicht zur Erläuterung des Zusammenwirkens der Spannelemente mit der Halterung, den Zugseilen und der Ankerplatte;

Figur 3

eine Draufsicht auf eine erste Ausführungsform der Halterung; und

Figur 4

eine Draufsicht auf eine zweite Ausführungsform der Halterung.

The invention will be explained in more detail below on the basis of an exemplary embodiment with reference to the accompanying drawing. It shows:

Figure 1

a schematic view of a cable-stayed bridge, in the construction of which the method according to the invention and the bracket are used;

Figure 2

a schematic view to explain the interaction of the tensioning elements with the holder, the pull cables and the anchor plate;

Figure 3

a plan view of a first embodiment of the holder; and

Figure 4

a plan view of a second embodiment of the holder.

In Figure 1 is a cable-stayed bridge in which the method according to the invention can be used, generally designated 100. It comprises a bridge deck 102 on which, for example, traffic routes for motor vehicles and / or other vehicles and / or pedestrians can be arranged, and at least one pylon 104. A stay cable 110 runs between an anchor point 106 of the pylon 104 and an anchor point 108 of the bridge deck 102.

Although in Figure 1 only a single stay cable 110 is shown, it goes without saying that the stay cable bridge 100 can comprise a plurality of such stay cables and in the majority of cases also comprises. For the sake of simplicity, Figure 1 only a single stay cable 110 is shown.

The stay cable 110 in turn comprises a plurality of strands, of which in Figure 1 For the sake of clarity, only three are shown, namely the strands 112, 114 and 116.

The strand 112 is already fully installed, i.e. it is anchored both in an anchor block 118 of the anchor point 106 and in an anchor block 120 of the anchor point 108. For this purpose, it penetrates through bores 118a and 120a of anchor blocks 118 and 120 and is held in them by means of wedges 122 and 124, respectively.

In contrast to this, the strands 114 and 116 are in the process of being transported from an initial position 126, which is arranged in the vicinity of the anchor point 108, to the anchor point 106. For this purpose, the two strands 114 and 116 are placed in a holder 128 and fastened to it by clamps (see also Figure 3 ). How the attachment of the strands 114 and 116 to the bracket 128 is accomplished is discussed below with reference to FIG Figure 3 will be explained in detail. At the two longitudinal ends 128a and 128b of the holder 128, traction cables 130 and 132 are attached, which run over pulleys 134 to a first winch 136 and a second winch 138. By appropriately activating the two winches 136 and 138, a controlled back and forth movement of the holder 128 between the starting position 126 and the anchor point 106 can be achieved.

The fastening of the pull cords 130 and 132 to the longitudinal ends 128a and 128b of the holder 128 can be done, for example, by means of so-called swivels which have an axial joint.

Essential to the invention is the location at which the holder 128 is attached relative to the free ends 114a, 116a of the strands 114, 116. This location is chosen such that the distance d between the bracket 128 and the free ends 114a, 116a of the strands 114, 116 is greater than a free strand length, which is required to pass the strands through the through-holes 118b and 118c of the anchor block 118 (see Figure 2 ) and be able to anchor there by means of the wedges 122. In this way, the two strands 114 and 116 can be transported to the anchor point 106 until their free ends 114a and 116a are arranged directly in front of the anchor block 118. The transport speed of the strands 114 and 116 is then reduced by appropriate control of the winches 136 and 138 in such a way that their free ends 114a and 116a can be threaded into the through-bores 118b and 118c by hand. If the free ends 114a and 116a protrude sufficiently from the rear of the anchor block 118, the winches 136 and 138 are stopped in order to enable the assembly personnel to anchor the strands 114 and 116 in the anchor block 118 by means of the wedges 122. After anchoring, the clamping engagement between the bracket 128 and the strands 114 and 116 can be released so that the bracket 128 can be moved back to the starting point 126 by appropriately controlling the winches 136 and 138 in order to pick up the next pair of strands there.

It should also be added that guide units 140 and 142 are arranged at the free ends 114a and 116a of the strands 114 and 116 (see FIG Figure 2 ). These guide units 140 and 142 have the task of preventing the free ends 114a and 116a of the strands 114 and 116 from getting caught between already installed strands during transport to the anchor point 106 due to their protrusion 114b and 116b beyond the bracket 128. This danger is all the more so since the strands 112, 114 and 116 are received in a tube 144 which is arranged between the two anchor points 106 and 108 in order to protect the strands from external influences, in particular from corrosion.

The two guide units 140 and 142 are advantageously releasably connected to the pull rope 130, the corresponding connection points in FIG Figure 2 are only indicated schematically at 140a and 142a.

When using such guide units 140 and 142, it is also advantageous if the transport of the strands 114 and 116 to the anchor point 106 is interrupted when the free ends 114a and 116a of the strands 114 and 116 are located directly in front of the anchor block 118 in order to allow the assembly personnel to enable the guide units 140 and 142 to be removed from the strands 114 and 116.

In Figure 3 a first embodiment of a bracket 128 is shown. It comprises a base body 150 that is mirror-symmetrical with respect to a longitudinal axis A and has two elongated, upwardly open recesses 152 and 154, which are designed and intended to receive the strands 114 and 116.

The recesses 152 and 154 are delimited towards the longitudinal axis A by delimiting walls 152a and 154a and on their side facing away from the longitudinal axis A by webs 152b and 154b and by surfaces 152c and 154c, which are formed on punches 156 and 158. Furthermore, the strands 114 and 116 received in the recesses 152 and 154 rest on a surface 150a of the base body 150. Finally, the recesses 152 and 154 have front openings 152d and 152e or 154d and 154e on their two longitudinal ends. The delimitation walls 152a and 154a, as well as the webs 152b and 154b, are attached to the base body 150 or formed in one piece with it in the illustrated embodiment.

The openings through which the strands 114 and 116 can be inserted into the recesses 152 and 154 are shown in FIG Figure 3 with 153 or 155, their rectilinear section with 153a or 155a.

As in Figure 3 is indicated by the arrows 160 and 162, the holder 128 further comprises holding force generating means, by means of which the punches 156 and 158 act on the strands 114 and 116 in order to press them against the boundary wall in 152a and 154a. In this way, the strands 114 and 116 are clamped between the boundary walls 152a and 154a on the one hand and the punches 156 and 158 on the other hand with a force that enables the strands 114 and 116 to be transported to the anchor point 106 by means of the holder 128 without the Litz wires 114 and 116 inadvertently detach themselves from the holder 128. The holding force generating means 160 or 162 together with the respective punch 156 or 158 form holding force generating devices in the sense of the claims.

The holding force generating means 160 and 162 can be designed as mechanically or / and electromotive and / and electromagnetic and / or pneumatically and / or hydraulically actuated actuating units. Regardless of the type of actuating force generation, a transmission can also be provided which reduces an input movement of the respective actuating unit into an actuating movement of the punches 156 and 158.

For example, the holding force generating means 160 and 162 can be formed by screw bolts, which are received in a threaded hole in the base body 150 and press against the punches 156 and 158. The thread of the screw bolt serves the just mentioned reduction of the rotational input movement of the screw bolt into a translational adjusting movement of the screw bolt and thus acts as the gear. However, it is also possible that the holding force generating means 160 and 162 are designed as inflatable tube elements, the surface sections of which acting on the strands 114 and 116 act as the punches 156 and 158.

It is also conceivable that a common actuating unit is assigned to both rams 156 and 158. For example, the punches 156 and 158 could be designed as cams which are arranged on the outer circumference of a disk, which is rotatably mounted on the base body 150 about an axis Z running orthogonally to the longitudinal axis A and to the transverse direction Q. In this case, a single setting unit is sufficient to press both punches 156 and 158 simultaneously against the strands 114 and 116 by rotating the disk.

As in Figure 3 is shown, both the boundary walls 152a and 154a and the surfaces 152c and 154c of the punches 156 and 158 are curved. In particular, the delimitation walls 152a and 154a have a double-S-shaped profile as seen in the direction of the longitudinal axis A. In this case, the lateral offset, ie the offset in the transverse direction Q, in the exemplary embodiment shown is essentially the same size as the diameter D of the strands 114 and 116. Furthermore, the base body 150 comprises a top wall 164, which in FIG Figure 3 is shown in dashed lines and is arranged in such a way that it covers those portions of the boundary walls 152a and 154a which are at the smallest distance from the longitudinal axis A.

In this way, the strands 114 and 116 can be attached to the bracket 128 as follows:
First, as shown in Figure 3 for the strand 114 is shown, running in a straight line into the associated recess, here the recess 152 is inserted until they rest on the surface 150a of the base body 150. The strand 114 enters the recess 152 through the opening 152d and exits it again at the other end of the holder 128 through the opening 152e. The holding force generating means 160 are then actuated in such a way that the punch 156 is placed laterally against the strand 114 and this begins to press against the boundary wall 152a. As a result, the straight course of the strand in the immediate vicinity of the punch is bent into a double-S-shaped course, which corresponds to the double-S-shaped course of the associated boundary wall. This is in Figure 3 for the example of the strand 116. In In this state, the strand 116 engages under the top wall 164, so that it is enclosed on all sides by the boundary wall 154a of the bottom surface 150a, the surface 154c of the punch 158 and the top wall 164 and is thus held in a form-fitting manner on the holder 128.

In Figure 4 a second embodiment of a holder is shown, which is essentially according to the first embodiment Figure 3 corresponds. Therefore, in Figure 4 Similar parts are provided with the same reference numerals as in Figure 3 , but increased by the number 100. In addition, the bracket 228 according to Figure 4 are only described below insofar as they differ from the holder 128 according to FIG Figure 3 differs, the description of which is otherwise expressly referred to.

The holder 228 differs from the holder 128 mainly in that a single holding force generating unit 260 is provided, which is rotatably mounted on the base body 250 about an axis X running parallel to the vertical axis Z. The holding force generation unit 260 has two cams 260a and 260b which interact with the punches 256 and 258. Because of this arrangement, the punches 256 and 258 do not act as in the embodiment according to FIG Figure 3 from the outside to the inside, but from the inside to the outside. Therefore, the boundary walls 252a and 254a of the recesses 252 and 254, against which the punches 256 and 258 press the strands 214 and 216, are formed on parts of the base body 250 which are arranged on the side of the strands 214 and 216 facing away from the longitudinal axis A. . In an analogous manner, the webs 252b and 254b are arranged on the side of the strands 214 and 216 facing the longitudinal axis A. Finally, the top wall 264 is also divided into two parts.

The rotation of the holding force generating unit 260 can be brought about in a manner known per se to the person skilled in the art. For this reason, a detailed description is not given here.

In Figure 4 the state of the holding force generating unit 260, which enables the braid 216 to be inserted into the recess 254, is shown below the longitudinal axis A. For this purpose, the two cams 260a and 260b are aligned on the longitudinal axis A. In Figure 4 Above the longitudinal axis A, on the other hand, the holding state is shown, according to which the strand 214 is pressed by the punch 256 against the delimitation wall 252a and thus under the top wall 264. This is made possible by rotating the holding force generating unit 260 by 90 ° about the axis X, so that the cam 260a assumes the position 260a '.

Claims (7)

1. Method for installing a tensioning element (114) in an anchor block (118) that has already been fastened to a structure, comprising the steps of:

   • attaching the tensioning element (114) to a mount (128),

   • moving the mount (128) towards the anchor block (118),

   • inserting the tensioning element (114) into a through-opening (118b) in the anchor block (118), and

   • subsequently fastening the tensioning element (114) to the anchor block (118),

   characterised in that the tensioning element (114) is guided through the through-opening (118), in that the tensioning element is fastened to the anchor block by means of wedges, and in that the mount (128) is attached to the tensioning element (114) at a spacing (d) from a free end (114a) of the tensioning element (114) to be fastened to the anchor block that is selected such that the length of the projection (114b) of the tensioning element (114), which is created by this spacing (d), on the side of the mount (128) that is nearer to the anchor block (118) is greater than the length of a portion of the tensioning element (114) that is required in order to insert the tensioning element (114) into the through-opening (118b) in the anchor block (118) and to fasten the tensioning element (114) to the anchor block (118).
2. Method according to claim 1, characterised in that the tensioning element (114) comprises a strand, which is made up of a plurality of wires and is preferably sheathed by a protective cover.
3. Method according to either claim 1 or claim 2, characterised in that the mount (128) is moved towards the anchor block (118) by means of a traction rope (130, 132).
4. Method according to any of claims 1 to 3, characterised in that a guide unit (140) is attached to the free end (114a) of the tensioning element (114), at least whilst the mount (128) is being moved towards the anchor block (118).
5. Method according to claim 3 and claim 4, characterised in that the guide unit (140) is connected, for example releasably connected (at 140a), to the traction rope (130).
6. Method according to any of claims 1 to 5, characterised in that the mount (128) is designed for the attachment of at least two tensioning elements (114, 116).
7. Method according to claim 6, characterised in that the projections (114b, 116b) of the at least two tensioning elements (114, 116) are substantially the same length.

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