Improvement of a strand guiding device and deviation pad

Abstract

Present application relates to a plurality of deviation pads (10) for use to support and / or deviate stressed tension members, wherein each of the deviation pad (10) comprises multiholes for receiving strands (100) and its use. Present invention also relates to a strand guiding device (900) and a method for use to support and / or deviate stressed tension members, comprising a plurality of deviation pads according to the deviation pads of the present invention housed within at least one guide tube (300).

Description

[0001] Improvement of a Strand Guiding Device and Deviation Pad TECHNICAL FIELD The invention relates to a new deviation pad for use to support and / or deviate stressed tension members. The deviation pad can be provided to a strand guiding device to be used for instance in deviators of tendons used in construction, wind towers, post-tensioned cable stabilized structures. More specifically, the invention relates to a new concept in strand guiding devices and a method to protect strands in deviation elements. The invention likewise relates to constructions comprising the aforementioned guiding device for strands and to methods to install it in the structures. BACKGROUND OF THE INVENTION The invention applies more specifically, but not exclusively, to guiding devices for tension members, such as strands of cables which, made up of a multiplicity of strands, are used in civil engineering and building activities. Numerous structures and notably bridges comprise cables which are used in particular to support elements of these structures. Such cables are stressed in traction between their opposite ends, but frequently deviators, also known as guiding devices, are used for holding the cables in such a manner as to deviate them in whatever way in the direction in which they must extend. The function of a deviator of the type cited above is thus to permit lateral and / or longitudinal and local holding of a cable and transfer of the stress caused by this deviation to a support, such as a bridge pylon or a diaphragm, provided for this purpose. A deviator of the aforementioned type is intended to be interposed between the support and the cable such as inside a pylon for stay cables or a bridge girder diaphragm for external tendons. Conventional deviators used one simple steel pipe for all strands, i.e. the bundle of strands placed inside one common pipe. In some solutions individual steel tubes were provided for the strands. More recently, deviators with holes or channels (obtained by so-called void formers which are removed after the grouting) for each individual strand were developed. In some solutions adopted for saddles, the holes have a V shape to improve the clamping effect. Deviators with individual tubes or channels are conceived to allow individual local support of each strand of a cable. To this end, a recent deviator comprises at least one bearing area for guiding a strand of a cable, and preferably a plurality of bearing areas for deviation, each permitting the individual support of one of the strands of a cable. In known deviator solutions, the deviator is composed of a round or rectangular or otherwise shaped solid box filled, after strand installation, with a high-strength cement grout. The box may be formed by a steel structure or by any other material, such as polymeric tube embedded in the concrete structure. Strands are arranged to traverse the deviator longitudinally inside the solid box. In such solutions, the strands can be unsheathed to increase friction between the strands and some parts of the deviator. In the case of fully grouted and bonded strands, the cement mortar can also protect the unsheathed strands from corrosion. However, the disadvantage in this case is that the strands are tightly in place in the solidified cement mortar, and for this reason the strands cannot be move relatively to the steel box, as it is required to tension the tendon passing through the deviator. In addition, the strands cannot be replaced individually. In the context of this application, the term corrosion is used to mean any process, for example chemical or electrolytic, which can have a deleterious effect on the chemical integrity, and hence the mechanical properties, of the strands. It is also possible to insert in the deviator curved tubes or channels for holding the strands in place in the saddle. The deviator conventionally comprises at least as many tubes as the guy cable, also known as tendon or stay cable, comprises strands. Each strand is then arranged to traverse one tube longitudinally. The inside part of each individual tube may be filled with a flexible corrosion protection compound. This solution does not require subsequently filling the saddle with cement mortar. An advantage of this solution is that it allows the replacement of the strands individually. A disadvantage of this solution is, however, that the deviator structure is onerous, complex to fabricate and difficult to install in a sufficient accurate manner. A further disadvantage is that the full tendon formed by multiple strands cannot be prefabricated and threaded inside the deviator in one single operation. On the contrary, each strand must be inserted individually inside its corresponding tube. It is the aim of the present invention to provide an improved deviator concept so that the shortcomings of the prior art can be overcome. SUMMARY OF THE INVENTION According to a first aspect of the invention, it relates to one or more deviation pads for use to support or deviate stressed tension members, wherein each of the deviation pad comprises multiholes for receiving strands. The deviation pad is capable of taking lateral forces due to deviation even when only a single is provided. For instance, a strand guiding device is provided, the strand guiding device being formed by one or an arrangement of deviation pads supporting the transversal forces created by the deviation of the strands. According to a second aspect of the invention, it relates to strand guiding device for use to support and / or deviate stressed tension members, comprising a plurality of deviation pads according to the present invention housed within at least one guide tube. According to a third aspect of the invention, it relates to the use of a plurality of deviation pads to support or deviate stressed tension members in a guide tube, wherein each of the deviation pad comprises multiholes for receiving strands. According to a fourth aspect of the invention, it relates to a method of installing and de-installing tendons used for instance in construction, wind tower, post-tensioned cable stabilized structures, comprising the Option (I) comprising the steps of a. Providing a plurality of deviation pads according to the present invention b. Link the deviation pads with positioning ties; c. Threading each hole of the deviation pads with a conduit to form a strand guiding device; d. Inserting the strand guiding device inside a guide tube; e. Threading each of the conduit with a strand; f. Stressing the plurality of strands which formed a tendon; Or the Option (II) comprising the steps of: a. Providing a plurality of deviation pads according to any one of the aforementioned claims; b. Link the deviation pads with positioning ties; c. Threading each hole of the deviation pads with a conduit to form a strand guiding device; d. Threading each of the conduit with a strand; e. Attaching the strand guiding device onto the strands; f. Inserting the bundle of strands and the strand guiding device inside a guide tube; g. Stressing the plurality of strands which formed a tendon. The Option (II) has the advantage that strand guiding device can be installed on the tendon before inserting in the structure. The deviation pad or pads according to the present invention may be used to guide monostrand, that is individual strand covered by a polymeric sheath and filled with a corrosion protection compound such as grease or wax and allowing the relative displacement between the sheath and the strand. According to a variant of the invention, the deviation pad or pads may provide support to flexible channels extending from the first end to the second end inside the strand guiding device, the channels being arranged to be traversed longitudinally by a strand of a cable, and further arranged to hold the strand in place when under tension, characterized in that the body of the strand guiding device comprises protective material arranged to protect the strand from corrosion and allowing later removal of the strand. The above-proposed solution offers several advantages. The strands that traverse the guiding device can be replaced individually. Furthermore, the injected protective material protects the strands from corrosion, and also reduces fretting corrosion risk. If needed, the protective filling material can also be replaced easily. According to an embodiment of the invention, the deviation pads are designed to withstand the lateral forces due to the deviation of the stressed tension members. The deviator pad has the advantage that it acts not only as a deviator (takes lateral forces due to deviation once the tensile member takes the load) but also acts as a support. According to an embodiment of the invention, the hole that accommodate each strand has a cross-section in the shape of an inverted rain drop or V shape to improve clamping effect. According to an embodiment of the invention, the deviation pads comprise smaller holes in its periphery for installing positioning ties. According to an embodiment of the invention, the multiholes comprise one or more chamfered edges. This prevents damaging the strands. According to a variant of the invention, each or most of the multiholes from the deviation pad (10) form a bell mouth at one or both sides of the multiholes extremity with a flaring angle between 0.5° to 45°, preferably between 1° to 15°, more preferably between 2° to 5°. This is advantageous as it not only capable to hold or support the stressed tension members, but it also prevents damaging them. Moreover, it allows for easier threading of the tension members. In a further embodiment, the deviation pad is most ideal to support deviation where the change in angle is not more than 3°. According to an embodiment of the invention, the deviation pad is made of a steel, an alloy material, a cementitious material, or a polymeric material. The chosen material would be able to serve as a deviator pad. According to an embodiment of the invention, the plurality of deviation pads is arranged in a same interval along the entire length of the strand guiding device, or is arranged at smaller intervals in the curved sections of the guide tube. The advantage is that the deviation pads can withstand the lateral forces due to the deviation of stressed tension members. Since these forces increase with the angles, it is therefore recommended to place more of these pads in the areas with big curvature. For instance, if the change in angle is 20º and the pad is designed to withstand a force corresponding to 2º, a total of 10 pads are required to be placed in this area. According to an embodiment of the invention, the plurality of deviation pads is provided to support conduits extending from a first longitudinal end to a second longitudinal end of the guide tube housed in a structure, wherein the conduit being arranged to be traversed longitudinally at least a strand of a tendon. According to an embodiment of the invention, it comprises a protective material provided therein for protecting the strand from corrosion and replacement of the strand. According to an embodiment of the invention, at least one sealing device is provided to at least one of the first longitudinal end or the second longitudinal end of the guide tube, or at least one sealing device is provided to at least one of the first longitudinal end or the second longitudinal end of the conduit. According to an embodiment of the invention, it further comprises a step of injecting cementitious grout fill interstices between the conduits. According to an embodiment of the invention, it further comprises a step of injecting a flexible filler inside the conduits to fill the interstices between the conduit and the sheathed strand. According to a variant of the invention, sealing means can also be provided at both ends of the body to further protect the interior of the body and to prevent the protective material from escaping from the body. According to a variant of the invention, the sealing device may be installed on the tendon before its installation inside the area of the deviator, allowing to thread the full tendon in the structure. The deviation pads may be arranged at regular distances from each other and provide individual support to withstand the deviation forces, while the space between the deviation pads provide the necessary flexibility for its installation through the deviator. An advantage of the above-proposed solution is that the strands of the tendon itself allow to obtain the desired curved geometry of the flexible channels. A further advantage of this solution is that the cost and the complexity may be significantly reduced. According to another variant of the invention, it is provided a method for protecting strands from corrosion in a strand guiding device comprising a body having a first end and a second end, the guiding device comprising at least one channel extending from the first end to the second end inside the strand guiding device, the channel being arranged to be traversed longitudinally by a strand of a cable, and further arranged to hold the strand in place when under tension, characterized in that the method comprises injecting into the body of the strand guiding device protective material for protecting the strand from corrosion and allowing later removal of the strand. Other aspects of the invention are recited in the dependent claims attached hereto. According to the present invention, the term “traversal” is used interchangeably with other terms having similar meaning such as “lateral”. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention being not limited to the disclosed embodiment. Other embodiments and variants are understood and can be achieved by those skilled in the art when carrying out the claimed invention, based on a study of the drawings, the disclosure and the appended claims. The word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention. The term “strands” as used herein is interchangeably and could equally apply to any other type of tensile member, such as wires or fibers, and vice versa. For example, it can be understood that a plurality of strands form one or more tensile members. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will become apparent from the following description of a non-limiting exemplary embodiment, with reference to the appended drawings, in which: - Figure 1A is a simplified perspective view of a strand guiding device formed by one deviation pad inserted in a concrete structure. - Figure 1B is a close-up view of the previous figure 1A showing the detail of the deviation pad and a bundle of monostrand. - Figure 2A is a cross section of a deviator formed by a curved guide tube and an arrangement of multiple deviation pads supporting a bundle of conduits that house the individual sheathed strands. - Figure 2B is a perspective view of the same arrangement shown in figure 2A, depicting an in-situ fabricated deviator or saddle for deviating a tendon made out of individually adherent sheathed strands, also known as tightly extruded strands. - Figure 2C is a perspective view of the arrangement of conduits and multiple pads linked by positioning ties. - Figure 3A is a cross section of a deviator formed by a curved guide tube and an arrangement of multiple deviation pads supporting a bundle of conduits that house the individual non adherent sheathed strands, also known as monostrand or unbonded monostrand. - Figure 3B is a perspective close-up view of the same arrangement shown in figure 3A, depicting the exit of a deviator, the external tendon and the in-situ fabricated deviator or saddle formed by multiple deviation pads supporting the conduits that house the individual monostrand. A general filler, usually a cementitious grout is injected to fill the interstices between the conduits, providing a protective barrier against corrosion and mechanical protection. - Figure 3C is a perspective view of the arrangement of conduits and multiple pads linked by positioning ties once the elements are inserted inside the guide tube in the concrete structure. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION An embodiment of the present invention will be described in the following in more detail with reference to the attached figures. Figure 1A shows a strand guiding device 900 comprises at least one deviation pad 10 (illustrated). A tendon 800 formed by a multiplicity of sheathed strands 100 is installed in a concrete structure 400 and anchored in one of its extremities by a tendon anchorage 820. Figure 1B is a close-up view of the previous figure 1A. The bottom part of the tendon 800 may have a different alignment from its top portion. When the tendon 800 is under tension, this creates deviation forces that have to be transmitted from the steel strands 120 to the individual sheath 110 (which together formed sheathed strand 100) and then to the deviation pad 10. These forces are transferred to the concrete structure 400 through the guide tube 300. The deviation pad 10 has individual holes to receive the sheathed strands 100 and transfer the lateral forces created by the angular deviation. For this reason, the deviation pad 10 has to be designed to support those loads and is usually metallic, either machined or made out of cast steel. The exit of the individual holes has to be accommodated with a deviation angle and may preferably have chamfered edges in order not to damage the individual sheath 110. The deviation pad 10 may have also smaller holes in its periphery to install positioning ties 500. As an alternative the deviation pad 10 can also be connected to the tendon 800 and held in position by additional devices (not shown in the picture) such as heat shrinkable sleeves, or a stuffing box formed by a drilled neoprene layer and a compression plate. Each sheathed strand 100 is formed by a steel strand 120, an individual sheath 110 and a corrosion protection compound, usually grease or wax (not depicted in the drawing). If the quantity of corrosion protection compound and the interstice left between the steel strand 120 and the individual sheath 110 are increased, these two elements can slide relatively to each other. It is customary to speak of monostrand or unbonded monostrand if movement between strand 120 and sheath 110 is possible with limited force. If the individual sheath 110 is tightly extruded on the steel strand 120 and the quantity corrosion protection compound is smaller, both elements cannot have relative movements and the sheathed strand 100 is usually identified as adherent or tightly extruded strand. Depending on the type of sheathed strand 100, the steel strand 120 will move independently of (in the case of monostrand) or together with its individual sheath 110. In order to stress the tendon, the tensile element, that is the steel strands 120, have to move relatively to the structure. The same need appears in case of replacement of the tensile element when the steel strand 120 has to be extracted completely from the concrete structure 400 before being replaced by a new tensile element. Since most of the tendons 800 are embedded in concrete or protected by the injection of a cementitious grout 600, a bond is created between the said structure 800 and all sheaths that are in contact with the filler, such as the individual sheaths 100 or the global tendon sheath 810. In the case of adherent strands, it will be necessary to provide an additional element to allow for the relative movement of movement of the sheathed strand 100 and the structure 400. This additional element may be a polymeric or metal conduit 200 covering the individual sheath 100. In this description we will refer to sheathed strands 100 to encompass both possible types, either monostrand or tightly extruded strands. Figure 2A and 2B show a strand guiding device 900 formed by an arrangement of multiple deviation pads 10 supporting a bundle of conduits 200 that house the individual sheathed strands 100. Figure 2C is showing the strand guiding device 900 comprises deviation pads 10 and conduits 200 before the insertion of the sheathed strands 100.The multiple deviation pads 10 are linked by positioning ties 500 in order to maintain its relative distance. The deviation pads 10 receive the conduits 200, that in turn receive the sheathed strands 100. Moreover, according to the present inventions, the strand guiding device 900 relates to the element or set of elements that are assembled and that will support or deviate the tension members. The strand guiding device 900 may comprise deviation pad 10 and guide tube 300, and optionally with conduit 200, positioning ties 500 and sheathed strand 100. The guide tube as used herein may refer to traditional steel guide tubes and the internal surface of the concrete structures formed by extractable formworks. Noteworthy, in most cases the curved guide tube 300 (a deviator) may be inserted in the concrete. However, the guide tube 300 may also be removed once it gives the shape to the concrete. In other words, an inflatable form or an extractable formwork may be provided. It should be noted that according to the present inventions it is possible to insert the strand guiding device 900 shown in figure 2C as a prefabricated assembly inside the structure 400 before or after the installation of the sheathed strands 100. Once the strand guiding device 900 in position inside the concrete structure 400 and after installation of the sheathed strands 110, the guide tube 300 may be filled with a rigid cementitious filler 600 or a flexible filler 700. In case the guide tube 300 is filled with a rigid cementitious filler 600, the filler may be used to transfer the lateral deviation forces or a part of them, allowing to make the deviation pads 10 with a softer material such as a polymeric compound, usually polyethylene. A sealing device 610 for injection (not depicted on the drawings) will be installed in that case at the exit of the guide tube 300. The interstice between the conduits 200 and the sheathed strands 100 may also be filled with an additional flexible filler 700. In that case, it will be necessary to provide an additional sealing device 710 for the flexible filler. Figure 3A shows an arrangement of multiple deviation pads 10 supporting a bundle of conduits 200 that house the individual sheathed strands 110. Figure 3B shows a detail of the same arrangement shown in figure 3A at the exit of the guide tube 300 in the area of the diabolo 310, that has a bell mouth shape to provide for installation tolerances and a smooth transition. Figure 3B depicts an external tendon 800 formed by a bundle of sheathed strands 100 inserted in the individual conduits 200. In the area outside of the concrete structure 400, the configuration shown in figures 3A and 3B corresponds to individual monostrand, that is non adherent sheathed strands 100 that are inserted into a polymeric tendon sheath 810, that is filled with cementitious filler 700 after stressing the tendon 800. In the area inside the concrete structure 400, the position of the conduits 200 is maintained by the deviation pads 10. Before the interstices are filled with cementitious filler 600, the arrangement of sheathed strands 100, conduits 200 and pads 10 is flexible and can be threaded inside the guide tube 300 of the concrete structure 400. The angular deviation of the full deviator can be obtained by incremental deviations at each of the deviation pads 10, thus defining a polygonal line formed by the conduits 200 that are supported by the deviation pads. It is also possible to adopt more rigid conduits 200 (using for instance, metal or rigid polymers instead of polyethylene tubes) or to insert the sheathed strands 100 in the conduits 200, allowing to obtain a smoother curved transition between the deviation pads 10. It is also possible to fill the interstices between the conduits 200 and the sheathed strands by a flexible filler 700. In case of replacement of the tensile elements, it is possible to pull the sheathed strands 100 (if they are of the adherent type) from its conduits 200 or alternatively to extract the steel strand 120 from its individual sheath 110 (if they are of the unbonded type). Figure 3C shows a strand guiding device 900 formed by conduits 200 and multiple pads 10 linked by positioning ties 500, once the elements are inserted inside the curved guide tube 300 in the concrete structure 400. The shape of the conduits 200 is shown circular on the drawings, but it is also possible to give it an inverted drop cross section in order to enhance friction, causing the steel strands 120 or the sheathed strands 100 to be clamped in the bottom V shape of the conduits 200. This solution can be advantageously adopted to increase the friction between the tensile element and the saddles installed on top of the pylon of cable stay bridges, avoiding or limiting possible sliding movements of the tensile elements in case of imbalance of forces on both sides of the pylon.

[0002] Reference List deviation pad strand (sheathed) individual strand sheath steel strand conduit first end of the conduit second end of the conduit guide tube first end of the guide tube second end of the guide tube diabolo (of guide tube) concrete structure positioning ties cementitious filler sealing device (for cementitious filler) flexible filler sealing device (for flexible filler) tendon (polymeric) tendon sheath tendon anchorage strand guiding device

Claims

Claims 1. One or more deviation pads (10) for use to support and / or deviate stressed tension members, wherein each of the deviation pad (10) comprises multiholes for receiving strands (100).

2. The deviation pads (10) according to claim 1 that are designed to withstand the lateral forces due to the deviation of the stressed tension members.

3. The deviation pads (10) according to claim 1 or claim 2, wherein the hole that accommodate each strand (100) has a cross-section in the shape of an inverted rain drop or V shape to improve clamping effect.

4. The deviation pads (10) according to claim 1 or claim 2 or claim 3, comprising smaller holes in its periphery for installing positioning ties (500).

5. The deviation pads (10) according to any one of the preceding claims, wherein the multiholes comprise one or more chamfered edges.

6. The deviation pads (10) according to any one of the preceding claims, wherein each or most of the multiholes from the deviation pad (10) form a bell mouth at one or both sides of the multiholes extremity with a flaring angle between 0.5° to 45°, preferably between 1° to 15°, more preferably between 2° to 5°.

7. The deviation pads (10) according to any one of the preceding claims, wherein the deviation pad is made of a steel, an alloy material, a cementitious material, or a polymeric material.

8. A strand guiding device (900) for use to support and / or deviate stressed tension members, comprising a plurality of deviation pads according to any one of the preceding claims 1 to 7 housed within at least one guide tube (300).

9. The strand guiding device (900) according to claim 8, wherein the plurality of deviation pads (10) is arranged in a same interval along the entire length of the strand guiding device (900), or is arranged at smaller intervals in the curved sections of the guide tube (300).

10. The strand guiding device (900) according to claim 8 or claim 9, wherein the plurality of deviation pads (10) is provided to support conduits (200) extending from a first longitudinal end (303) to a second longitudinal end (305) of the guide tube (300) housed in a structure (400), wherein the conduit (200) being arranged to be traversed longitudinally at least a strand (100) of a tendon (800).

11. The strand guiding device (900) according to any one of the preceding claims 8- 10, comprising a protective material provided therein for protecting the strand (100) from corrosion and replacement of the strand (100).

12. The strand guiding device (900) according to any one of the preceding claims 8- 11, wherein at least one sealing device is provided to at least one of the first longitudinal end (303) or the second longitudinal end (305) of the guide tube (300), or at least one sealing device is provided to at least one of the first longitudinal end (203) or the second longitudinal end (205) of the conduit (200).

13. Use of a plurality of deviation pads (10) according to any one of the preceding claims 1-7 to support or deviate stressed tension members in a guide tube (300), wherein each of the deviation pad (10) comprises multiholes for receiving strands (100).

14. A method of installing and de-installing tendons used for instance in construction, wind tower, post-tensioned cable stabilized structures, comprising the Option (I) comprising the steps of a. Providing a plurality of deviation pads (10) according to any one of the aforementioned claims 1 to 6; b. Link the deviation pads (10) with positioning ties (500); c. Threading each hole of the deviation pads (10) with a conduit (200) to form a strand guiding device (200); d. Inserting the strand guiding device (200) inside a guide tube (300); e. Threading each of the conduit (200) with a strand (100); f. Stressing the plurality of strands (100) which formed a tendon (800); Or the Option (II) comprising the steps of a. Providing a plurality of deviation pads (10) according to any one of the aforementioned claims 1 to 6; b. Link the deviation pads (10) with positioning ties (500); c. Threading each hole of the deviation pads (10) with a conduit (200) to form a strand guiding device (200); d. Threading each of the conduit (200) with a strand (100); e. Attaching the strand guiding device (200) onto the strands (100); f. Inserting the bundle of strands (100) and the strand guiding device (200) inside a guide tube (300); g. Stressing the plurality of strands (100) which formed a tendon (800).

15. The method of installing and de-installing tendons according to the claim 14, further comprising a step of injecting cementitious grout fill interstices between the conduits (200).

16. The method of installing and de-installing tendons according to the claim 14 or 15, further comprising a step of injecting a flexible filler (700) inside the conduits (200) to fill the interstices between the conduit (200) and the sheathed strand (100).