METHOD FOR TRANSFORMING A CABLE SUPPORTED BRIDGE FROM A FIRST BRIDGE STATE INTO A SECOND BRIDGE STATE AND CABLE SUPPORTED BRIDGE

Description

FIELD OF THE INVENTION

According to a first aspect, the present invention relates to a method for transforming a cable supported bridge comprising a bridge deck, a support structure and a plurality of stay cables extending between a bridge deck side anchorage located at said bridge deck and a support structure side anchorage located at said support structure, from a first bridge state in which at least one of said stay cables extends according to a first catenary into a second bridge state in which said at least one stay cable or at least one new stay cable replacing said at least one stay cable extends according to a second catenary.

BACKGROUND OF THE INVENTION

Well-known examples of cable supported bridges are cable stayed bridge, arch bridges, extradosed bridges and the like bridges in which said stay cable extends between a bridge deck side anchorage located at a bridge deck of said cable supported bridge and a support structure side anchorage located at a support structure of said cable supported bridge. While cable stayed bridge and extradosed bridges usually have pylons as support structures, arches constitute the support structures of arch bridges.

Usually, said bridge deck side anchorage and said support structure side anchorage each having an anchor unit for receiving and holding an allocated end of said stay cable, and a fastening unit for fastening said anchor unit to said bridge deck and said support structure, respectively. In this context, it is important to note that, due to its weight, the stay cable does not extend along the direct and straight connection line between the two anchorages, usually referred to as “chord”, but rather along a curved line, usually referred to as “catenary”, extending below this direct and straight connection line. Depending on the length, the weight and the tensioning force of the stay cable, the orientation of the tangents to the catenary at the respective positions of the anchorages may considerably deviate from the orientation of the direct and straight connection line.

Fastening units of stay cables usually comprise a recess pipe, at the free end of which the stay cable emerges from the anchorage and extends freely toward the respective other anchorage. Due to imprecise work during the manufacture and/or positioning of the fastening unit on the bridge deck and/or the support structure, and/or differences between design assumptions (forces, weight and the like) and actual values, the specified tolerance angles for the alignment of the recess pipe are not seldomly exceeded. This results in a permanent angle break of the stay cable at the exit of the recess pipe. This permanent angle break poses a major problem for the service life of the stay cable because of the bending moment related thereto and permanently acting on the stay cable.

Further it is to be noted that the above problem of a permanent angle break does not only occur due to manufacturing tolerances being exceeded, but can also occur in the following further situations.

If, according to a first further situation, an old and, for example due to grout injection or improved material properties, heavy stay cable is replaced by a new, lighter stay cable during a renovation of the cable supported bridge, the new, lighter stay cable will run along a completely different catenary than the old, heavy stay cable, while carrying the same load. In this case, too, the directions of the recess pipes on the bridge deck and on the support structure do no longer match the course of the new catenary, thus resulting in a permanent angle break.

And according to a second further situation, it may be intended to raise the bridge deck of the cable supported bridge, for example to increase the clearance for container ships. In this case, too, the catenary of the stay cable changes. And this is even more true if, at the same time, the heavy old stay cables are also replaced by new lightweight stay cables.

EP 4 124 750 A1 proposes to arrange two shim plates between the anchor head and the fastening unit at the actual anchor point of the strands of the stay cable. By rotating the shim plates relative to each other, the orientation of the actual anchor point can be changed. This solution, however, only addresses the problem of a potential angle break at the actual anchor point, but not the problem of angle break at the exit of the recess pipe, i.e. at the exit of the anchor unit.

Although WO 2013/004350 A1 and WO 2021/180298 A1 are addressing the problem of the angle break at the exit of the recess pipe, the solutions provided merely distribute the angle break over a larger length section of the stay cable, so that locally lower bending moments act on the stay cable.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to at least reduce, if not completely eliminate, the risk of a permanent bending moment acting on the stay cable.

According to the present invention, this object is solved by a method for transforming a cable supported bridge comprising a bridge deck, a support structure and a plurality of stay cables extending between a bridge deck side anchorage located at said bridge deck and a support structure side anchorage located at said support structure, from a first bridge state in which at least one of said stay cables extends according to a first catenary into a second bridge state in which said at least one stay cable or at least one new stay cable replacing said at least one stay cable extends according to a second catenary, said bridge deck side anchorage and said support structure side anchorage each having an anchor unit for receiving and holding an allocated end of said at least one stay cable, and a fastening unit for fastening said anchor unit to said bridge deck and said support structure, respectively, said method comprising at least one of the steps of

- a) providing at a predetermined position of a first building part, namely said bridge deck or said support structure, a further anchorage for receiving and holding an end of said at least one stay cable previously received and held by a first anchorage, namely said bridge deck side anchorage or said support structure side anchorage, and or an end of said at least one new stay cable, and
- b) displacing said anchor unit of said first anchorage or said further anchorage relative to the allocated fastening unit of said first anchorage or said further anchorage to said predetermined position,
  
  said predetermined position being located closer to or further away from a respective other building part, namely said support structure or said bridge deck, than said first anchorage or said anchor unit of said first anchorage or said further anchorage, respectively, and being determined such that a tangent to the second catenary of said at least one stay cable or said at least one new stay cable at an entrance to said anchor unit of a second anchorage, namely said support structure side anchorage or said bridge deck side anchorage, located at said respective other building part is substantially parallel to an axis of a recess pipe of said anchor unit of said second anchorage.

Applying this method, the catenary of the (new) stay cable may be adjusted to an anchorage, in particular the recess pipe of an anchorage, already existing at the respective other building part, namely said support structure or said bridge deck. Consequently, an angle break at the existing anchorage can be avoided or at least reduced. Furthermore, the method according to the invention allows avoiding the necessity of rebuilding all anchorages of the cable supported bridge, but limits the rebuilding to the anchorages of one building part, preferably to the bridge deck side anchorages, which are easier to access.

According to a second aspect, the present invention further relates to a cable supported bridge, comprising

- a bridge deck,
- a support structure, and
- at least one stay cable extending between a bridge deck side anchorage located at said bridge deck and a support structure side anchorage located at said support structure
  
  said bridge deck side anchorage and said support structure side anchorage each having an anchor unit for receiving and holding a respective free end of said stay cable, and a fastening unit for fastening said anchor unit to said bridge deck and said support structure, respectively, said anchor unit and said fastening unit of a first anchorage of said bridge deck side anchorage and said support structure side anchorage allocated to a first building part, namely said bridge deck or said support structure, being adapted and configured to allow displacement of said anchor unit relative to said fastening unit to a predetermined position, said predetermined position being located closer to or further away from a respective other building part, namely said support structure or said bridge deck, than a previous position of said anchor unit of said first anchorage, and being predetermined such that a tangent to the catenary of said stay cable at an entrance to said anchor unit of a second anchorage of said bridge side anchorage and said support structure side anchorage located at said respective other building part is substantially parallel to a recess pipe of said anchor unit of said second anchorage.

In order to avoid angle break problems at the first anchorage in both, the method and the cable supported bridge according to the present invention, said anchor unit of said first anchorage may be pivotably mounted to said allocated fastening unit. Due to the pivotability, the anchor unit can automatically adjust to the catenary. Consequently, an additional adaptation of the orientation of the anchor unit can be avoided while displacing the anchor unit.

Although the afore-mentioned pivotability could be provided by using a spherical bearing plate, a simple solution in terms of construction for putting the pivotability into practice may implement an anchor unit having a pivoting axis which may be displaceable relative to said predetermined position.

As an alternative, an element receiving said pivoting axis could be displaceable relative to said allocated fastening unit. For example, the element receiving said pivoting axis could be constituted by a gusset plate.

According to both alternatives, the anchor unit having the pivoting axis can be designed as a clevis anchor unit. Although clevis anchors as such are known in the art, the provide an advantageous design for a pivotable mounting.

In order to allow displacement of the pivoting axis or the element receiving the pivoting axis, it is suggested that said fastening unit comprises a plurality of holes having different distances from the respective other building part. In addition or as an alternative, said fastening unit may include at least one elongated hole extending at least partially towards the respective other building part.

A simple and effective constructional design of said fastening unit may be achieved, if said fastening unit comprises two separate substantially U-shaped fastening sub-units. Both U-shaped sub-units can be arranged lying on their sides, with the base legs of the U-shapes facing each other, such that, for example, the gusset plate can be received between them.

Conventional stay cables including a plurality of strands made from a plurality of, preferably seven, wires encased by a PE (polyethylene) sheath can be used in a plurality of applications of the method according to the invention. For other applications, however, it is preferred if at least one strand of said stay cable is designed as an epoxy coated strand. In this case removing the PE sheath is not necessary, as the fastening wedges of the anchor units can bite through the epoxy coating into the strand. The latter solution is particularly advantageous in situations where the final length of the stay cable is difficult to predict. For example, if the purpose of the method according to the invention is to raise the bridge deck in order to increase the clearance for container ships, it cannot be predicted whether the intended overall raising of the bridge deck can be achieved, as the properties thereof cannot 100% be predicted and measured.

It should be noted that in the case of a mere adjustment of the stay cables intended to optimize tolerances, the displacement may occur in both directions, i.e. in the direction closer to or the direction further away from the respective other building part.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail referring to a specific embodiment shown in the attached drawings, in which

FIGS. 1a and 1b show two schematic diagrams explaining the problem underlying the invention;

FIG. 2 shows a view explaining the difference between the terms “chord” and “catenary”;

FIGS. 3a and 3b show two schematic diagrams explaining the solution to the problem underlying the invention;

FIGS. 4a to 4c show illustrations explaining the structure of a Clevis anchor used in accordance with the invention; and

FIG. 5 shows a schematic side view explaining the anchoring of an epoxy-coated strand.

DETAILED DESCRIPTION OF AN EMBODIMENT

In FIGS. 1a and 1b, a cable stayed bridge 100 is shown as an example of a cable suspended bridge. The cable stayed bridge 100 includes a bridge deck 102 and two pylons 104, with the pylons 104 representing examples of a support structure of the cable suspended bridge.

The bridge deck 102 is suspended from the pylons 104 by means of stay cables 106, 108. Although FIGS. 1a and 1b show only two inner stay cables 106 and two outer stay cables 108 for the sake of simplicity, it is understood that the bridge deck 102 may be suspended from the pylons 104 by means of a large number of stay cables. Each of the stay cables 106, 108 is anchored to the bridge deck 102 by means of a bridge deck side anchorage 110 and anchored to the pylon 104 by means of a pylon side anchorage 112.

In the illustrated example, the cable stayed bridge 100 spans a body of water W, such as a river or a harbor entrance. In practice, for example, the problem may arise that the bridge deck 102 must be permanently raised (see FIG. 1b) to increase the clearance for container ships. For this purpose, at least inner stay cables 106 have to be shortened to give the bridge deck 102 a higher course at least in its center. In FIG. 1b, the new, higher course is shown by solid lines, while the old, lower course, also shown in FIG. 1a, is shown by dashed lines.

It can be seen in FIG. 1b that the shortening of the stay cables 106 also changes their orientation, in particular the angle α at which the stay cables 106 exit the pylon side anchorage 112. In this context, the change in angle α may well reach values in the order of 2° to 3°. Taking into account that the tolerances for the angle α that usually have to be respected in the construction of a cable suspended bridge 100 are only 0.2° to 0.3°, it is easy to see that the angle break resulting from the elevation of the bridge deck 102 can no longer be tolerated because the bending moment that accompanies it, acting on the stay cable 106, affects the structural integrity of the stay cable 106 and, consequently, the service life of the stay cable 106.

Although the path of the stay cables 106, 108 is shown as a straight line in FIGS. 1a and 1b and also later in FIGS. 3a and 3b for the sake of simplicity, it is understood that the stay cables 106, 108 do not actually extend along the straight line designated as “chord CH” (see FIG. 2), but rather, due to the weight of the stay cable, along a curved line below the chord designated as “catenary CAT”.

FIG. 2 further illustrates the anchorages 110, 112 in somewhat greater detail. In particular, each of the anchorages 110, 112 includes an anchor unit 114 for receiving and holding a respective free end of the stay cable 106, and a fastening unit 116 for fastening said anchor unit 114 to the bridge deck 102 or the pylon 104, respectively. The anchor unit 114 is further associated with a recess pipe 118 within which the strands of the stay cable 106, 108 are fanned out for actual anchoring in the anchor unit 114. Thus, the end 118a of the recess pipe 118 provides an entrance to the anchor unit 114.

As shown in FIGS. 3a and 3b, in the embodiment shown, the solution to the problem explained above according to the invention is to relocate the bridge deck side anchorage 110 towards the pylon 104 before lifting the bridge deck 102 or to provide a new bridge deck side anchorage 120 at a position P2 closer to the pylon 104 compared to the previous position P1 of the former bridge deck side anchorage 110. This does create an angle break for a short time, as shown in FIG. 3a by comparing the solid and dashed lines for the stay cable 106. However, the new position P2 is selected in such a way that the stay cable 106 enters the pylon side anchorage 112 again at the same angle α after the bridge deck 102 has been raised as it did before in the non-displaced state of the bridge deck side anchorage 110 and the non-raised state of the bridge deck 102 (see FIG. 3b). This can prevent an angle break permanently acting on the stay cable 106.

Furthermore, when determining the new position P2, it can be taken into account if, in addition to lifting the bridge deck 102, a heavy old stay cable with a weight-related low catenary is replaced by a light new stay cable with a correspondingly higher catenary. And it goes without saying that the method according to the invention can also be used if the bridge deck 102 is not to be lifted, but heavy stay cables are nevertheless to be replaced by light stay cables.

As indicated in FIGS. 3a and 3b, the new bridge deck side anchorages 120 may be mounted on the top surface 102a of the bridge deck 102 for ease of work and to avoid compromising the structural integrity of the bridge deck 102 extensively.

Further, clevis anchors may preferably be used as new bridge deck side anchorages 120. These have the advantage of automatically assuming the correct orientation due to their pivotable mounting. With reference to FIGS. 4a to 4c, the design of such clevis anchors will be explained in more detail.

As shown in particular in FIG. 4c, the actual anchor unit 114 also in the case of the clevis anchor essentially corresponds to the conventional structure of an anchor unit. Rather, the particular details of the formation of a clevis anchor relate to the fastening unit 116 and the connection of the actual anchor unit 114 to the fastening unit 116.

A base member 122 of the clevis anchor is substantially U-shaped, with a base leg 122a of the U-shape for supporting and holding the anchor unit 114, while both side legs 122b of the U-shape are used for supporting the ends of a pivoting bolt 124. A central portion of the pivoting bolt 124 passes through a hole 126a provided in a gusset plate 126, and is thereby pivotally supported in the gusset plate 126.

In the embodiment shown in FIG. 4a, the hole 126a of the gusset plate 126 is formed as an elongated hole. Filler pieces 128a and/or 128b may be inserted into the elongated hole 126a in front of and/or behind the pivoting bolt 124. In particular, the pivoting bolt 124 can bear against the filler piece 128a in a force-transmitting manner when the stay cable 106 is tensioned.

Further, the gusset plate 126 may be received between two U-shaped fastening sub-units 130, the two “U”s being arranged with their respective base legs 130a facing each other. The connection between the gusset plate 126 and the fastening sub-units 130 is made by a plurality of bolts 132 passing through a grid of holes provided in both the gusset plate 126 and the fastening sub-units 130.

Thus, a final adjustment of the position P2 of the new bridge deck side anchorage 120 can be made, on the one hand, by relocating the pivoting bolt 124 in the elongated hole 126a and, on the other hand, by fixing the gusset plate 126 to the fastening sub-units 130 accordingly by means of the respective hole grids.

Finally, the fastening sub-units 130 may be attached to the bridge deck 102 via a plurality of bolts 134 that penetrate the bridge deck 102. This provides a means of attachment to the bridge deck 102 that is reliable and that places minimal stress on the structural integrity of the bridge deck 102.

Since, in the case of lifting the bridge deck 102, this lifting takes place step by step, the stay cable 106 must be shortened step by step. In the case of a stay cable 106 whose individual strands 136 are enclosed in a PE sheath (PE=polyethylene), this would mean that a corresponding length of PE sheath would have to be removed from the strand before each shortening step. It is important to note that it is not possible to immediately free the entire strand length required for the planned uplift from the PE sheath, since in view of the structural integrity of the bridge deck 102 it cannot be predicted whether the planned uplift can be fully achieved. However, the protection of the strands 136 by the PE sheath is important with respect to the corrosion resistance of the stay cable 106. On the other hand, the stepwise removal of the PE sheath is very costly and time-consuming due to the large number of strands 136.

Therefore, according to the invention, it is preferred (see FIG. 5) to use strands 136 which do not have a PE sheath as corrosion protection, but rather are epoxy-coated. The wedge elements 138 of the anchor unit 114 are designed in such a way that their teeth 138a can easily penetrate the epoxy layer 136b and bite into the steel wires 136a of the strand 136 and thus hold them. This eliminates the need for laborious removal of the PE sheath.

Claims

1. A method for transforming a cable supported bridge comprising a bridge deck, a support structure and a plurality of stay cables extending between a bridge deck side anchorage located at said bridge deck and a support structure side anchorage located at said support structure, from a first bridge state in which at least one of said stay cables extends according to a first catenary into a second bridge state in which said at least one stay cable or at least one new stay cable replacing said at least one stay cable extends according to a second catenary, said bridge deck side anchorage and said support structure side anchorage each having an anchor unit for receiving and holding an allocated end of said at least one stay cable, and a fastening unit for fastening said anchor unit to said bridge deck and said support structure, respectively, and said method comprising at least one of the steps of a) providing at a predetermined position of a first building part, namely said bridge deck or said support structure, a further anchorage for receiving and holding an end of said at least one stay cable previously received and held by a first anchorage, namely said bridge deck side anchorage or said support structure side anchorage, and or an end of said at least one new stay cable, andb) displacing said anchor unit of said first anchorage or said further anchorage relative to the allocated fastening unit of said first anchorage or said further anchorage to said predetermined position,
2. The method according to claim 1, wherein said anchor unit of said first anchorage is pivotably mounted to said allocated fastening unit.
3. The method according to claim 2, wherein a pivoting axis of said anchor unit is displaceable relative to said predetermined position.
4. The method according to claim 2, wherein an element receiving said pivoting axis is displaceable relative to said allocated fastening unit.
5. The method according to claim 2, wherein the anchor unit is designed as a clevis anchor unit.
6. The method according to claim 1, wherein said fastening unit comprises a plurality of holes having different distances from the respective other building part.
7. The method according to claim 1, wherein said fastening unit comprises at least one elongated hole extending at least partially towards the respective other building part.
8. The method according to claim 1, wherein said fastening unit comprises two separate substantially U-shaped fastening sub-units.
9. The method according to claim 1, wherein at least one strand of said stay cable is designed as an epoxy coated strand.
10. A cable supported bridge, comprising a bridge deck,a support structure, andat least one stay cable extending between a bridge deck side anchorage located at said bridge deck and a support structure side anchorage located at said support structuresaid bridge deck side anchorage and said support structure side anchorage each having an anchor unit for receiving and holding a respective free end of said stay cable, and a fastening unit for fastening said anchor unit to said bridge deck and said support structure, respectively,said anchor unit and said fastening unit of a first anchorage of said bridge deck side anchorage and said support structure side anchorage allocated to a first building part, namely said bridge deck or said support structure, being adapted and configured to allow displacement of said anchor unit relative to said fastening unit to a predetermined position,said predetermined position being located closer to or further away from a respective other building part, namely said support structure or said bridge deck, than a previous position of said anchor unit of said first anchorage, and being predetermined such that a tangent to the catenary of said stay cable at an entrance to said anchor unit of a second anchorage of said bridge side anchorage and said support structure side anchorage located at said respective other building part is substantially parallel to a recess pipe of said anchor unit of said second anchorage.
11. The cable supported bridge of claim 10, wherein said anchor unit of said first anchorage is pivotably mounted to said allocated fastening unit.
12. The cable supported bridge of claim 11, wherein a pivoting axis of said anchor unit is displaceable relative to said predetermined position.
13. The cable supported bridge of claim 11, wherein an element receiving said pivoting axis is displaceable relative to said allocated fastening unit.
14. The cable supported bridge of claim 11, wherein the anchor unit is designed as a clevis anchor unit.
15. The cable supported bridge of claim 10, wherein said fastening unit comprises a plurality of holes having different distances from the respective other building part.
16. The cable supported bridge of claim 10, wherein said fastening unit comprises at least one elongated hole extending at least partially towards the respective other building part.
17. The cable supported bridge of claim 10, wherein said fastening unit comprises two separate substantially U-shaped fastening sub-units.
18. The cable supported bridge of claim 10, wherein at least one strand of said stay cable is designed as an epoxy coated strand.

METHOD FOR TRANSFORMING A CABLE SUPPORTED BRIDGE FROM A FIRST BRIDGE STATE INTO A SECOND BRIDGE STATE AND CABLE SUPPORTED BRIDGE

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