Combination of a Guiding Device with at least one Strand

Description

According to a first aspect, the invention relates to a guiding device for at least one strand, the guiding device comprising a curved body in which a correspondingly curved channel is formed, said channel having a cross- section comprising a first portion located towards the convex side of the curved channel and a second portion located towards the concave side of the curved channel, said first portion being dimensioned so as to allow threading the strand through the channel, and said second portion being shaped so as to allow clamping the strand between two side walls of the second portion.

Such guiding devices are, for example, used at cable-stayed bridges and extra-dosed bridges for deviating individual strands of a multi-strand stay cable through a friction-type saddle including such a guiding device. This allows the construction of slender pylons without hollow cross-section which would be required for placing cable anchorages inside the pylon. A friction- type saddle also has significant cost advantages compared to solutions with anchorages.

The challenge, however, is to provide a high friction between the strands and the guiding device in order to ensure a transfer of differential forces from one side of the pylon to the other, as well as a high fatigue performance, a high durability and to have the possibility to exchange single strands.

A guiding device of the afore-mentioned type is, for example, known from WO 2007/121782 A1. According to this prior art, the second portion of the cross-section of the channel has two V-shaped sidewalls forming an angle between them in order to provide a phenomenon of wedging the strand when the strand is tensioned between its two ends. This wedging phenomenon is disadvantageous as the inclined surfaces create high splitting forces onto the concrete forming the body of the guiding device.

Furthermore, WO 2012/076815 A2 discloses a guiding device, in which the surface of the second portion has a circular cross-section, the radius of the circle being substantially equal to the radius of the strand. This embodiment is disadvantageous as well, as it merely provides for a contact friction of a round strand in a round hole.

The same is true for the embodiments known from US 6,880,193 B2 and US 7,003,835 B2.

In view of the above, it is the object of the invention to provide an improved guiding device.

According to the present invention, this object is achieved by a guiding device of the afore-mentioned type in which said two side walls of said second portion extend parallel to each other.

According to the invention the two parallel side walls provide an improved friction behavior by geometrically clamping the strand instead of wedging it. It also allows to exchange single strands and provides a high durability and fatigue resistance.

According to a second aspect, the invention relates to a combination of a guiding device according to the present invention with at least one strand, in which the effective outer diameter of the strand is equal to or greater than the effective distance between the two parallel side walls. Although in principle, any type of strand can be used in combination with the guiding device of the present invention, advantageously a conventional 7- wire strand may be used, i.e. a strand in which six external wires are helically wound around one internal wire, said external wires preferably having a diameter of about 5.2mm and said internal wire preferably having a diameter of about 5.3mm. Furthermore, the seven wires may be surrounded by a protective plastic sheath, e.g. a polyethylene (PE) sheath. Moreover, a corrosion-inhibiting material, e.g. wax, may be provided for filling any hollow space between the plastic sheath and the wires and/or between the external wires and the internal wire.

According to an embodiment, inside the channel, the strand may be free from any protective plastic sheath. In other words, if a strand having a protective plastic sheath is used, the sheath has to be peeled off from the wires at least in that strand section which is received within the channel. Where applicable, furthermore the wax may be removed from the wires. In this case, the effective diameter of the strand is the maximum diameter of the strand in the peeled section, i.e. the sum of the diameters of two external wires and the one internal wire.

It is, however, also conceivable that the strand including its protective sheath is located in the second portion of the channel’s cross-section. For example, by filling the hollow spaces between the plastic sheath and the wires and/or between the external wires and the internal wire with resin instead of wax, the internal friction of the strand may be increased, such that the strand can be used in this unpeeled state. For example, the strand could be coated with epoxy guaranteeing the corrosion protection. Optionally the epoxy coated strand could further have a plastic sheath, preferably a polyethylene sheath. In this case, the effective diameter of the strand is the maximum diameter of the strand in its unpeeled state, i.e. the sum of the diameters of two external wires and the one internal wire plus the double of the thickness of the sheath wall. If the strand is in direct contact with the side walls, the effective distance of the two side walls is equal to the geometrical distance of the two side walls. For example, when designed for a conventional 7-wire strand, the effective distance of the two side walls may amount to 15.5mm.

In order to increase the friction between the strand and the side walls, it is, however, also conceivable that at least one of the side walls is at least partially covered by a friction-increasing layer. Furthermore, a bottom wall of the second portion of the channel’s cross-section may be at least partially covered by a friction-increasing layer. Advantageously, the friction-increasing layer covering the bottom wall and at least one of the friction-increasing layers covering the side walls may be integrally formed. Furthermore, said friction-increasing layer preferably may be made from a high-friction rubber.

According to a further embodiment, at least a predetermined length section of an interior wall of the channel is covered by a friction-increasing layer along its entire circumference, thus constituting a hollow profile serving as a lost formwork. Said hollow profile may be made, for example, from plastic material, e.g. from polyethylene (PE), polypropylene (PP), polyamide (PA), of from rubber, preferably high-friction rubber.

The wall thickness of the hollow profile, in particular the wall thickness of the two side walls of the second portion of the cross-section of the channel may be chosen such that the plastic material of the hollow profile is plastically deformed by the strand, in case of a dismantled strand, or that the plastic material of the hollow profile and/or the material of the protective sheath of the strand is/are plastically deformed, in the case of a strand including the protective sheath. In particular, the outer dimension of the strand (with or without the protective sheath) may be chosen to be larger than the inner dimension of the hollow profile, but smaller than the outer dimension of the hollow profile. In this way a plastic deformation of the plastic material providing effective friction may be obtained, while direct contact with the concrete may be avoided.

According to a further embodiment, the hollow profile is form as a corrugated tube including a plurality of clamping portions having a cross-section as discussed before and a plurality of non-clamping portions having a larger cross-section, said clamping portions and non-clamping portions being arranged in an alternating sequence in the longitudinal direction of the hollow profile. This design may safeguard that the tensioning force of the strand is always sufficiently strong for pulling the strand from the first portion of the channel’s cross-section to the second portion of the channel’s cross-section, while ensuring a sufficiently pronounced plastic deformation of the hollow profile in order efficiently clamp the strand. To this purpose, the ratio of the sum of the lengths of the clamping portions and the sum of the lengths of the non-clamping portions may be varied. In other words, the clamping portions and the non-clamping portions may be of equal or different lengths.

Advantageously, a plurality of clamping portions, preferably all clamping portions, may have the same length, and/or a plurality of non-clamping portions, preferably all non-clamping portions, may have the same length.

Furthermore, it is advantageous that a periodic length of the clamping and non-clamping portions is different from the periodic length of the twist of the strand.

According to a further embodiment, the bottom wall of the second portion of the channel’s cross-section may extend substantially orthogonal to the two side walls. In order to allow to thread the strand through the channel, the minimum dimension of the first portion may be equal to or greater than the diameter of the strand including the protective plastic sheath. After threading the strands in the first portion, they may be transferred to the second portion by tensioning the strand from its two ends.

If the first portion has a circular shape, an overall keyhole-like shape of the cross-section may be obtained together with a substantially rectangular second portion.

In order to create a dry environment inside the channel (dehumidification) and thus to avoid corrosion and not to change the friction behavior of the strands, a hygroscopic material may be provided at least in the first portion of the channel’s cross-section and/or in a chamber which is in gas-exchange connection with the channel. For example, the hygroscopic material may be a granulate of Silicagel. In addition or as an alternative, the air inside the channel may be actively dried, e.g. by an electrical dehumidifier. Either the air inside the entire cable or only the air inside the sealed guiding device may be dried. In addition or as a further alternative, the channel may be filled with inert gas, e.g. a noble gas or nitrogen.

In order to be able to monitor the humidity state in the channel, and thus to identify the risk of corrosion at an early stage, a humidity sensor may be provided in the first portion of the channel’s cross-section and/or in the chamber.

In order to allow easy access to the chamber, in particular access from outside, the chamber may be formed in the pylon and may have a door. In order to avoid ingress of humidity, the door may be sealed. In addition to or as an alternative for the hygroscopic material, after having installed the strand, the hollow profile may be filled with a hardening foam, e.g. an adhesive foam, preferably a polyurethane foam. Hereby the friction between the strand and the hollow profile may be increased. For strand replacement, however, the strand can be pulled out of the hollow profile together with the foam, if a predetermined friction threshold is exceeded.

According to a further embodiment, the body of the guiding device is made from hardened grout.

Finally, sealings and/or bending filters, analogous to those known from the applicant’s DYNA Grip® anchorages may be provided at the exit points of the channel.

In the following, the present invention will be explained in more detail referring to specific embodiments shown in the attached drawing, in which

Figure 1 shows a schematic view of a stay cable bridge equipped with three friction-type saddles including guiding devices according to the present invention;

Figure 2 shows a partially sectional view of a friction-type saddle including a guiding device according to the present invention;

Figure 3 shows a cross-sectional view of Figure 2 taken along lines Ill-Ill in Figure 2;

Figures 4a to 41 show cross-sections of the channel of the guiding device according to the invention;

Figure 5 shows a view similar to Figure 2 of another embodiment of the guiding device according to the present invention; and Figure 6 shows a perspective, partially cut-away view of a hollow profile serving as a lost formwork for forming the channel. In Figure 1 a cable-stayed bridge is generally denoted by reference numeral 100. The cable-stayed bridge 100 comprises a pylon 102, a bridge deck 104 and a plurality of stay cables 106 for supporting the bridge deck 104 at the pylon 102. To this end, the free ends 106a of the stay cables 106 are fixed to the bridge deck 104 by anchors 108, while friction-type saddles 110 are used to redirect the stay cables 106 at the pylon 102.

The present invention focuses on the construction of the friction-type saddles 110, and in particular the guiding devices 120 thereof (see Figure 2). Figure 2 shows a sectional view of a friction-type saddle 110 including a guiding device 120 according to the present invention. The friction-type saddle 110 is mounted on or inside the pylon 102 and serves for redirecting one of the stay cables 106, or to be precise for redirecting a plurality of strands 112 forming the stay cable 106.

To this end, the guiding device 120 comprises a curved body 122 in which a plurality of correspondingly curved channels 124 is formed. Each of these curved channels 124 accommodates one of the strands 112 of the stay cable 106.

For forming the curved channels 124 in the curved body 122, the curved body 122 comprises a housing 126, e.g. made from steel plates 126a (see Figure 3), and a plurality of separator plates 128 including a plurality of through holes (not shown), the positions of the through holes corresponding to the positions of the curved channels 124 (see Figure 3). The separator plates 128 serve for guiding flexible channel forming elements (not shown) along the length of the housing 126. After the channel forming elements have been installed in place, the remaining empty space inside the housing 126 is filled with grout 130. As soon as the grout is hardened, the channel forming elements are removed from the housing 126 resulting in the plurality of curved channels 124 formed by the grout 130 inside the housing 126.

As may be seen from Figure 3 and Figures 4a to 4I, the curved channels 124 have a keyhole-shaped cross-section 132 including a substantially circular first portion 132a and a substantially rectangular or square second portion 132b, the first portion 132a being located towards the convex side 124a of the curved channel 124 and the second portion 132b being located towards the concave side 124b of the curved channel 124.

Due to the substantially rectangular or square shape of the second portion 132b, the side walls 132b1 and 132b2 of the second portion 132b extends substantially parallel to each other (see Figure 4a). Due to the parallelism of the side walls 132b1 and 132b2 any wedging effect on the strands 112 may be avoided. Nevertheless, the strands 112 may be clamped in the second portion 132b by appropriately dimensioning the second portion 132b in dependence upon the dimensions of the strand 112 and the circumstances of its accommodation in the second portion 132b. Some conceivable scenarios of such circumstances of accommodation will be discussed in the following.

The first step of mounting a strand 112 in a curved channel 124 is to thread the strand 112 through the curved channel 124. To this end, the first portion 132a of the keyhole-shaped cross-section 132 has a diameter which is greater than the outer diameter of the strand 112 including its protection sheath 112a (see Figure 4b). In order to avoid that the strand 112 is inadvertently transferred from the first portion 132a to the second portion 132b, a mounting supporting element 134 may be placed in the second portion 132b (see Figure 4c).

As a next step, the protection sheath 112a may be removed from the section of the strand 112 which will be accommodated in the curved channel 124, in order to increase the friction between the actual strand 112 and the curved channel 124, in particular by eliminating the internal friction between the actual strand 112, i.e. between the unit formed by the six outer wires 112b helically wound around the center wire 112c, on the one side, and the protection sheath 112a, on the other side. The resulting state is shown in Figure 4d.

After removal of the mounting supporting element 134, the dismantled strand 112 may be transferred to the second portion 132b of the keyhole-shaped cross-section 132, e.g. by tensioning the strand between its two ends in the anchors 108, and clamped between the two side walls 132b1 and 132b2 thereof (see Figure 4e). To this end, the diameter D1 of the dismantled strand 112, i.e. the sum of the diameters of two outer wires 112b and the center wire 112c, is equal to or preferably greater than the distance D2 (see Figure 4a) of the two side walls 132b1 and 132b2 (D1 >= D2).

In order to increase the friction between the grout forming the side walls 132b1 and 132b2 and the steel of the dismantled strand 112, a friction- increasing element 136, e.g. made from a high-friction rubber, may be arranged between the strand 112 and the side walls 132b1 and 132b2 and/or a bottom wall 132b3 of the second portion 132b, as may be seen from Figure 4f. In this context, it should be noted that although the friction-increasing element 136 shown in Figure 4f has two side walls 136a and 136b and a bottom wall 136c, which are integrally formed, they may also be provided as separate elements. Furthermore, they do not necessarily all have to be present.

Of course, the thickness of the two side walls 136a and 136b has to be taken into account, when calculating the width D2 of the second portion 132b.

Although the strand 112, according to Figures 4d, 4e and 4f was dismantled, this needs not necessarily be the case. Usually, the strand 112 is dismantled in order to avoid internal friction between the wires 112b, 112c and the protection sheath 112c caused by wax which is used as an internal corrosion protection material. Nevertheless, if, for example, a resin is used as an internal corrosion protection material, it is conceivable to clamp the strand 112 including its protection sheath 112a in the second portion 132b (see Figure 4g). In this case, the double thickness of the protection sheath 112a has to be taken into account when calculating the diameter of the strand 112. Figures 4i to 41 show embodiments, according to which hollow profiles 160 made from plastic material are used as channel forming elements, namely as lost formwork, for forming the channel 124. In particular, Figures 4i and 4j show an embodiment including a dismantled strand 112, while Figures 4k and 4I show an embodiment including a strand 112 covered in a protection sheath 112a.

As may be seen from Figures 4i and 4j, the distance D3 between the inner surfaces of the two side walls 160a and 160b is substantially equal to or less than the smallest diameter D1’ of the dismantled strand 112 (see Figure 4i), while the distance D4 between the outer surfaces of the two side walls 160a and 160b is greater than the largest diameter D1 of the dismantled strand 112 (see Figure 4j). Flereby, it can be ensured that the plastic material of the hollow profile 160 is plastically deformed by the strand 112. Analogously, as may be seen from Figures 4k and 4I for the case of a non- dismantled strand 112, the distance D3’ between the inner surfaces of the two side walls 160a and 160b is substantially equal to or less than the smallest diameter D5’ of the non-dismantled strand 112 (see Figure 4k), while the distance D4’ between the outer surfaces of the two side walls 160a and 160b is greater than the largest diameter D5 of the non-dismantled strand 112 (see Figure 4I). Flereby, it can be ensured that the plastic material of the hollow profile 160 and/or the material of the protective sheath 112a of the strand 112 is/are plastically deformed.

Although the hollow profile 160 may have a constant cross-section throughout its length, Figure 6 shows an advantageous embodiment in which the hollow profile 160 is formed as a corrugated tube having length sections 160c of the afore-discussed cross-section and length sections 160d of larger cross-section. In particular, the distance D1’ or D5’ (see Figures 4i or 4k, respectively) in these length sections 160d is larger than the largest diameter D1 or D5 (see Figures 4j or 4I, respectively) of the dismantled or non- dismantled strand 112, respectively, such that the hollow profile 160 may not exert any clamping force on the strand 112.

By appropriately choosing the distance D3 or D3’, respectively, and the length and number of the length sections 160c inside the guiding device 100 in relationship to the dimensions of the dismantled or non-dismantled strand 112, the clamping force exerted by the hollow profile 160 on the strand 112, and the force required for pulling the strand 112 from the first portion 132a of the channel’s cross-section to the second portion 132b of the channel’s cross-section may be chosen independently from each other.

One problem encountered with friction-type saddles is corrosion of the dismantled sections of the strands 112. In order to reduce the risk of such corrosion, measures may be taken for reducing the degree of humidity in the curved channels 124. To this end, a hygroscopic material 138, e.g. a Silicagel granulate, may be provided at least in the first portion 132a of the channel’s cross-section 132 (see Figure 4h).

As may be seen from Figure 5, in addition or as an alternative, a hygroscopic material 140, e.g. provided in the form of pads, may be placed in a chamber 142, which is formed in the pylon 102 and is in gas-exchange connection with the channels 124, e.g. via a passage 144 opening into an end section 126b of the housing 126. Preferably, the chamber 142 has a door 146 by which it is accessible from the outside, in order to allow exchange of the hygroscopic material 140.

In order to monitor the degree of humidity in the channels 124, a humidity sensor 148 may be provided in at least one of the channels 124 (see Figure 2) and/or the chamber 142 (see Figure 5).

Furthermore, it should be noted that a sealing unit 150 including a bending filter may be provided in both end sections 126b of the housing 126 of the guiding device 120 of all friction-type saddles 110. These sealing units 150 may be designed similar to those known from the applicant’s DYNA Grip® anchorages which are well-known to those skilled in the art.