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

The invention relates to a method for transforming a cable supported bridge from a first bridge state in which at least one of said stay cables extends according to a first catenary to 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, comprising at least one of the steps of          a) providing at a predetermined position of said bridge deck a further anchorage for an end of said at least one stay cable previously received and held by said bridge deck side anchorage or for an end of at least one new stay cable, and     b) displacing an anchor unit of said bridge deck side anchorage or said further anchorage relative to an allocated fastening unit of said bridge deck side anchorage or said further anchorage to said predetermined position, said predetermined position being located closer to or further away from a support structure od said cable supported bridge than said bridge deck side anchorage or said anchor unit of said bridge deck side 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 support structure side anchorage is substantially parallel to an axis of a recess pipe of said anchor unit of said support structure side anchorage.

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 ofa) 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,
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, comprisinga 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 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.

DETAILED DESCRIPTION OF AN EMBODIMENT

InFIGS.1aand1b, a cable stayed bridge100is shown as an example of a cable suspended bridge. The cable stayed bridge100includes a bridge deck102and two pylons104, with the pylons104representing examples of a support structure of the cable suspended bridge.

The bridge deck102is suspended from the pylons104by means of stay cables106,108. AlthoughFIGS.1aand1bshow only two inner stay cables106and two outer stay cables108for the sake of simplicity, it is understood that the bridge deck102may be suspended from the pylons104by means of a large number of stay cables. Each of the stay cables106,108is anchored to the bridge deck102by means of a bridge deck side anchorage110and anchored to the pylon104by means of a pylon side anchorage112.

In the illustrated example, the cable stayed bridge100spans a body of water W, such as a river or a harbor entrance. In practice, for example, the problem may arise that the bridge deck102must be permanently raised (seeFIG.1b) to increase the clearance for container ships. For this purpose, at least inner stay cables106have to be shortened to give the bridge deck102a higher course at least in its center. InFIG.1b, the new, higher course is shown by solid lines, while the old, lower course, also shown inFIG.1a, is shown by dashed lines.

It can be seen inFIG.1bthat the shortening of the stay cables106also changes their orientation, in particular the angle α at which the stay cables106exit the pylon side anchorage112. 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 bridge100are only 0.2° to 0.3°, it is easy to see that the angle break resulting from the elevation of the bridge deck102can no longer be tolerated because the bending moment that accompanies it, acting on the stay cable106, affects the structural integrity of the stay cable106and, consequently, the service life of the stay cable106.

Although the path of the stay cables106,108is shown as a straight line inFIGS.1aand1band also later inFIGS.3aand3bfor the sake of simplicity, it is understood that the stay cables106,108do not actually extend along the straight line designated as “chord CH” (seeFIG.2), but rather, due to the weight of the stay cable, along a curved line below the chord designated as “catenary CAT”.

FIG.2further illustrates the anchorages110,112in somewhat greater detail. In particular, each of the anchorages110,112includes an anchor unit114for receiving and holding a respective free end of the stay cable106, and a fastening unit116for fastening said anchor unit114to the bridge deck102or the pylon104, respectively. The anchor unit114is further associated with a recess pipe118within which the strands of the stay cable106,108are fanned out for actual anchoring in the anchor unit114. Thus, the end118aof the recess pipe118provides an entrance to the anchor unit114.

As shown inFIGS.3aand3b, in the embodiment shown, the solution to the problem explained above according to the invention is to relocate the bridge deck side anchorage110towards the pylon104before lifting the bridge deck102or to provide a new bridge deck side anchorage120at a position P2closer to the pylon104compared to the previous position P1of the former bridge deck side anchorage110. This does create an angle break for a short time, as shown inFIG.3aby comparing the solid and dashed lines for the stay cable106. However, the new position P2is selected in such a way that the stay cable106enters the pylon side anchorage112again at the same angle α after the bridge deck102has been raised as it did before in the non-displaced state of the bridge deck side anchorage110and the non-raised state of the bridge deck102(seeFIG.3b). This can prevent an angle break permanently acting on the stay cable106.

Furthermore, when determining the new position P2, it can be taken into account if, in addition to lifting the bridge deck102, 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 deck102is not to be lifted, but heavy stay cables are nevertheless to be replaced by light stay cables.

As indicated inFIGS.3aand3b, the new bridge deck side anchorages120may be mounted on the top surface102aof the bridge deck102for ease of work and to avoid compromising the structural integrity of the bridge deck102extensively.

Further, clevis anchors may preferably be used as new bridge deck side anchorages120. These have the advantage of automatically assuming the correct orientation due to their pivotable mounting. With reference toFIGS.4ato4c, the design of such clevis anchors will be explained in more detail.

As shown in particular inFIG.4c, the actual anchor unit114also 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 unit116and the connection of the actual anchor unit114to the fastening unit116.

A base member122of the clevis anchor is substantially U-shaped, with a base leg122aof the U-shape for supporting and holding the anchor unit114, while both side legs122bof the U-shape are used for supporting the ends of a pivoting bolt124. A central portion of the pivoting bolt124passes through a hole126aprovided in a gusset plate126, and is thereby pivotally supported in the gusset plate126.

In the embodiment shown inFIG.4a, the hole126aof the gusset plate126is formed as an elongated hole. Filler pieces128aand/or128bmay be inserted into the elongated hole126ain front of and/or behind the pivoting bolt124. In particular, the pivoting bolt124can bear against the filler piece128ain a force-transmitting manner when the stay cable106is tensioned.

Further, the gusset plate126may be received between two U-shaped fastening sub-units130, the two “U”s being arranged with their respective base legs130afacing each other. The connection between the gusset plate126and the fastening sub-units130is made by a plurality of bolts132passing through a grid of holes provided in both the gusset plate126and the fastening sub-units130.

Thus, a final adjustment of the position P2of the new bridge deck side anchorage120can be made, on the one hand, by relocating the pivoting bolt124in the elongated hole126aand, on the other hand, by fixing the gusset plate126to the fastening sub-units130accordingly by means of the respective hole grids.

Finally, the fastening sub-units130may be attached to the bridge deck102via a plurality of bolts134that penetrate the bridge deck102. This provides a means of attachment to the bridge deck102that is reliable and that places minimal stress on the structural integrity of the bridge deck102.

Since, in the case of lifting the bridge deck102, this lifting takes place step by step, the stay cable106must be shortened step by step. In the case of a stay cable106whose individual strands136are 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 deck102it cannot be predicted whether the planned uplift can be fully achieved. However, the protection of the strands136by the PE sheath is important with respect to the corrosion resistance of the stay cable106. On the other hand, the stepwise removal of the PE sheath is very costly and time-consuming due to the large number of strands136.

Therefore, according to the invention, it is preferred (seeFIG.5) to use strands136which do not have a PE sheath as corrosion protection, but rather are epoxy-coated. The wedge elements138of the anchor unit114are designed in such a way that their teeth138acan easily penetrate the epoxy layer136band bite into the steel wires136aof the strand136and thus hold them. This eliminates the need for laborious removal of the PE sheath.