Cable System for a Structural- and Tensioning Element and a Method for Replacing the Tensile Elements and the Use Thereof

TECHNICAL FIELD OF THE INVENTION

[0001]Present invention relates to the field of civil engineering involving structural elements e.g., building, or tensioning elements e.g., bridge cable. The invention can be applied to the load-bearing structures or elements. The invention also relates to a method of installing said system on the load bearing structural- and tensioning element.

BACKGROUND OF THE INVENTION

[0002]Cables for stayed bridges, footbridges or suspension bridges are used to safely support bridge loads and traffic loads. Similarly, the cables are applicable in extended roofs for stadium or arena.

[0003]In the examples of bridges, the vertical loads are transferred through the cables in tension to the towers, which carry them by vertical compression to the ground through the anchorages, which must resist the inward and sometimes vertical pull of the cables. A suspension bridge can be viewed as an upside-down arch in tension with only the towers in compression. Because the deck is hung in the air, care must be taken to ensure that it does not move excessively under loading. The deck therefore must be either heavy or stiff or both.

[0004]The deck of a suspended bridge is supported by a main cable by use of intermediate connecting hangers. A conventional suspension bridge comprises pylons, decks, main cables, hangers and clamps for hanging the hanger to the main cable. The hangers can be either vertically arranged or inclined (cf. FIGS. 1A and 1B, respectively).

[0005]The main cable is typically anchored at each end to the ground. It is generally made up of a plurality of tensile elements which are closely arranged next to each other. Depending on its purpose, a main cable may have a mean diameter of a few centimetres to a few metres.

[0006]Due to its indispensable function in the entire bridge system, the replacement of a main cable has to overcome a myriad of difficulties. It is often the case that the traffic flow must be reduced or even stopped completely when a main cable is to be replaced. Nevertheless, most of the main cables to date are either not replaceable, or when its replacement is necessary and possible, it may be extremely cumbersome, costly, and usually cause a massive disruption to the traffic flows.

[0007]Moreover, as the clamps in the state of the art are usually connected directly to the tensile elements of the main cable, such connection induces rapid aging and degradation of the bridge components, or known as fatigue corrosion fretting.

[0008]It is therefore envisaged to provide a new cable system, a method, and a use of the cable system to overcome at least part of the aforementioned problems.

SUMMARY OF THE INVENTION

[0009]The inventors of the present invention have found out effective remedies for the above-discussed problems with the current engineering and architecture knowledge and thereby proposed a new cable system and a method thereof. The cable system proposed herein is more durable as the tensile elements are not directly and radially compressed by a friction clamp which tends to increase wear.

[0010]In a first aspect, present invention relates to a cable system for a tensioning elements such as suspension bridges and/or structural elements such as extended roofs of buildings, comprising main cables, hangers, and clamps, wherein the main cable comprises a pipe as a housing, one or more tensile elements provided within the pipe for carrying longitudinal tensile force along the main cable, preferably the tensile elements are replaceable easily when needed; and a compressing element provided surrounding at least partly the tensile elements for taking radial compression and possibly longitudinal compression, wherein the hanger is connected to the main cable through the clamp, configured in such a way that the hanger force is introduced only into the compressing element and is further transferred radially from the compressing element to the tensile elements.

[0011]According to the second aspect of the invention, it relates to a method of providing a cable system for a structural element and/or tensioning element according to the claimed cable system, comprising the steps of a) Providing tensile elements within a pipe of a main cable; b) Providing a compressing element to surround at least partly the tensile elements for taking radial compression and possibly longitudinal compression

[0012]According to the third aspect of the invention, it relates to the use of the cable system according to the claims for accommodating one or more tensile elements located within a pipe of a main cable.

[0013]In one preferred embodiment, one or more cavities and/or ducts are provided to accommodate the tensile elements. The said ducts can be formed by e.g., cavities; the cavities may comprise ducts and other voids for accommodating components or elements related to the cable system. The cavities and/or ducts are provided within the pipe of the main cable for housing the tensile elements, and possibly other components and elements related to the cable system. The cavities can also be created by tubing elements, either acting as inner formwork inside the compressing element and/or retired before introducing the tensile elements or left in place. The tensile elements can be replaced easily whenever needed as they are not “buried” or “cemented” to the main cable. The proposed cable system according to this variant allows an easy replacement of the main cable (e.g., the tensile elements). Thanks to the cavities and/or ducts provided within the pipe of the main cable, tensile elements can be positioned inside their cavities or individual duct. This allows for an easy replacement of the main cable as each single tensile element can be detensioned separately and be replaced, not needing to replace the entire main cable at once. Consequently, this ensures a lower maintenance cost as well as minimizes the disturbance on the traffic.

[0014]In this connection, it is disclosed that the compressing element is provided to surround at least partly the tensile elements for taking radial compression and possibly longitudinal compression. This means that, as an example, the compressing elements are provided peripherally around the tensile elements to a certain part (or section) of the main cable and not necessarily extended in the entire length of the tensile elements (and main cable).

[0015]In one embodiment, tubing elements are provided for the introduction of cavities and/or ducts, or one or more tubing elements are provided inside the main cable for acting as removable formworks for the introduction of the compressing element in between the tubing elements, thereby forming one or more cavities and/or ducts for accommodating the tensile elements. In other words, such tubing elements can be used to maintain their shape for the installation of the compressing element. Such tubing elements can furthermore advantageously contribute to the compressing element as a compressing component. For example, in one variant, tubing elements are left in place and maintaining the shape inside the compressing element, then used as cavities to introduce ducts or tensile elements. In another variant, tubing elements acting as removable formwork and extracted once the compressing element has set. In this case, the created cavity in the concrete is used to introduce duct or tensile element. In some instances when the tubing elements are made out of metal, they could contribute and serve as additional function of the compressing element.

[0016]According to yet another embodiment, tubing elements are provided for the introduction of cavities and/or ducts, or one or more tubing elements are provided inside the main cable for acting as removable formworks for the introduction of the compressing element in between the tubing elements, thereby forming one or more cavities and/or ducts for accommodating the tensile elements. As an example, the cavities may be left void to provide for inspection ports to be accessed by endoscopes or other inspection equipment.

[0017]According to an embodiment, the tensile elements and the compressing element are arranged coaxially within the pipe. That is, they are arranged such that the respective centres of gravity of their cross sections are coincident.

[0018]In another embodiment of the invention, a filler material is provided to the cavities, or is provided to a space between the tensile element and the tube, wherein the filler material is preferably a soft or a liquid filler material. This allows the filler material to be introduced to the main cable easily.

[0019]In yet a further embodiment, the compressing element comprises a rigid filler matrix such as mortar, concrete, polymer-concrete, ashcrete or timbercrete.

[0020]In a further variant of the invention, the compressing element has a compressive strength of at least about 5 MPa or between about 10 MPa and 100 MPa, preferably about 50 MPa.

[0021]In another embodiment of the invention, the compressing element is provided only to a corresponding part of the main cable e.g., where the clamps are located or on the deviation areas on top of the towers. This advantageously reduces the weight of the main cable while maintaining its function. Moreover, preferably, a plug and a sealing device are provided, wherein the filler material provided to the duct is confined by the plug with a sealing device, creating a leak-tight joint between the individual ducts and the duct. In some cases, compressing element may be provided in the zones of the clamps and also on top of the towers.

[0022]In a preferred embodiment, at least a part of the remaining part of the main cable is provided with a non-structural void filler material such as soft matrix, liquid, foam, air, expanded polymer and etc.

[0023]In a further embodiment of the invention, the filler material provided to a space within the pipe and between the duct is confined by a plug with a sealing device, creating a leak-tight joint between the individual ducts.

[0024]According to a variant of the invention, a part of the clamp comprises a first part, comprising a substantially ring shape for encasing or attaching to the main cable, wherein its diameter is slightly larger than the pipe of the main cable; and/or the clamp comprises a second part which is a lug plate where the hangers can be attached thereto. Such clamp not only avoids the hanger to be permanently fixed to the clamp (which causes problems such as rapid aging and degradation of the bridge components, or known as fatigue corrosion fretting), it also allows the hangers to be replaced easily.

[0025]In a further embodiment, the main cable is provided with several sections having injection vents and sealed ends for the injection of grout. This allows the filler material to be introduced to the main cable.

[0026]In yet another embodiment, the tensile elements are installed in the ducts before providing the compressing element to the main cable.

[0027]According to a variant of the invention, one or more tubing elements are provided inside the main cable to act as removable inner formworks, leaving cavities for the introduction of the compressing element.

[0028]In a further embodiment, one or more cavities and/or ducts are provided to the pipe for accommodating the tensile elements, preferably prior to the step of providing tensile elements within a pipe of a main cable. In a further variant, providing tubing elements serving as removable formworks for creating the cavities and/or ducts.

[0029]In yet another embodiment, the tensile elements are installed in the cavities and/or ducts prior to providing the compressing element to the pipe of the main cable.

[0030]According to one embodiment, the cable system is used for replacing existing tensile element of the main cable, wherein the existing tensile element is detached from its anchoring termination and is removed from its individual cavity prior to being replaced by a new tensile element, followed by anchoring at their extremities.

[0031]By “about” or “approximately” in relation to a given numerical value, it is meant to include numerical values within 10% of the specified value. All values given in the present disclosure are to be understood to be complemented by the word “about” unless it is clear to the contrary from the context.

[0032]The indefinite article “a” or “an” does not exclude a plurality, thus should be treated broadly.

[0033]The term “structural element” as used herein refers to a basic component of a building structure which forms a structural frame building structure such as beams, pillars, roof terraces, slabs, columns, girders and/or other structural members and connections.

[0034]The term “tensioning element” as used herein refers to an element which carries tension and no compression. The tensioning element may be provided to a structural element in order to support the load. The tensioning element described herein may for instance be used in a bridge cable, comprising tensile elements (or known as tendon).

[0035]The term “compressing element” as used herein refers to an element which is subject to axial compressive forces, and that the element is being pushed, or carry a load. Compression force occurs when a physical force presses inward on an object, causing it to become compacted.

[0036]The term “clamp” as used herein refers a structural item, designed to transfer the force F_Ed from the hanger to the main cable.

[0037]To this end, it is reiterated that according to the present invention, it is not necessarily limited to only main cables but theoretically can also be applied to all kinds of cables including hangers.

BRIEF DESCRIPTION OF THE FIGURES

[0038]FIG. 1A shows a schematic view of a suspension bridge having vertical hanger arrangement.

[0039]FIG. 1B shows a schematic view of a suspension bridge having inclined hanger arrangement.

[0040]FIG. 2 shows a schematic view of tensile elements of a main cable according to prior art.

[0041]FIG. 3 shows an embodiment of the main cable according to the present invention.

[0042]FIG. 4A shows a clamp according to an embodiment of the present invention in the case of connecting main cable and hanger in a vertical hanger arrangement.

[0043]FIG. 4B illustrates the mechanism of force transfer according to an embodiment of the present invention in the case of connecting main cable and hanger in a vertical hanger arrangement.

[0044]FIG. 4C shows a clamp installed on the main cable according to an embodiment of the present invention in the case of connecting the main cable and hanger in a vertical hanger arrangement.

[0045]FIGS. 5A, 5B and 5C show respectively a clamp, the mechanism of force transfer and a clamp installed on the main cable according to an embodiment of the present invention for connecting main cable and hanger in an inclined hanger arrangement.

[0046]FIG. 6 shows an example of a plug with sealing device to be installed at the extremity of the portion of the main cable.

DETAILED DESCRIPTION OF THE INVENTION

[0047]The inventors of the present invention propose a cable system, a method, and a more durable usage as the tensile elements are not directly compressed by a friction clamp radially which tends to increase wear. Moreover, according to a preferred variant of the invention, it allows easy replacement of the tensile elements of a cable. The cables are able to be replaced in a more effective manner, thereby ensuring lower maintaining cost. Moreover, the current method also ensures a minimal traffic disturbance.

[0048]FIGS. 1A and 1B show two different suspension bridges having main cables 12, piers 21, hangers 22, towers 23, a deck 30 and anchorages 33. The main cables 12 are placed over the towers 23 and anchored at their extremities with the anchorages 33. The weight of the deck 30 and the traffic loads are supported predominantly through the main cables 12 by using intermediate connecting hangers 22. These hangers 22 can either be vertically arranged (as illustrated in the FIG. 1A) or inclined (as shown in the FIG. 1B), wherein the former is more prevalent than the latter.

[0049]Typically, one or more main cables 12 are provided on the left and right sides of the bridge and the main span length can range from several metres to several hundred metres. However, small suspension bridges often use single cables as their main cables 12, either a single cable on each side or a monocable. The cables themselves, also known as tendons, are formed predominantly by many tensile elements (which comprised of a plurality of wires or strands). These tensile elements are usually highly redundant as they are designed in such a way that the failure of a limited number of individual strands or wires will not reduce the overall safety of the bridge. A commonly used tensile element can be formed by a plurality of wires or by 7-wire steel strands which are standard tensile elements for cables. Because of their high strength and widespread use, they are probably the cheapest means to carry a given tension load.

[0050]FIG. 2 demonstrates an example of a main cable 12 in the prior art where the individual tensile elements 15 are tightly arranged next to each other, forming a main cable 12 which is suitable to be used in a structural element or tensioning element. In this example, the tensile elements 15 are arranged in a parallel pattern, covered by an external wrapping 31 and tightly held by steel bands 32. The hangers 22 are connected to the main cable 12 by means of a clamp 24 that transfers the loads to the main cable 12. Such main cables 12 are difficult to be replaced and often the hangers 22, clamps 24 and bridge deck 30 have to be removed before the main cables 12 can be replaced.

[0051]In order to overcome the difficulties of replacing the main cables, a new type of cable is proposed, which is illustrated in the FIG. 3 and the following figures. The main cable 12 comprises a pipe 11 as a housing. Within the pipe 11, a plurality of cavities 17, which are arranged substantially parallel to the longitudinal direction of the main cable 12, are provided within the pipe 11. The configuration generally proposed in the present invention is a channel like structure which is suitable for accommodating an object e.g., tensile elements in the present case. In this example, the ducts 18 are provided within the pipe 11, creating individual cavities 17 before introducing the tensile elements 15. Then, the space between the ducts 18 and the pipe 11 can be filled up with a compressing element 16, which is predominantly made up of as cement-comprising mortar. As each of the tensile elements 15 is located within its own cavity 17, it can be replaced individually without compromising the primary function of the main cable 12. In this connection, it is disclosed that the individual tensile elements 15 shown on FIG. 3 are bare strands with or without galvanization, but the invention is also applicable to polyethylene sheathed strands, providing an additional layer of corrosion protection.

[0052]To this end, it is disclosed that the compressing element 16, which is usually provided initially in form of a grout, is only injected into the main cable 12 once the individual ducts 18 and preferably all of the tensile elements 15 have been installed inside the pipe 11. This allows the compressing element to be hardened according to the shapes of the ducts 18 as well as the tensioned main cable 12 before the tensile elements 15 are tensioned and anchored.

[0053]Moreover, the compressing element 16 can be filled up throughout the entire length of the main cable 12. As the compressing element 16 is a rigid (solid) filler material such as mortar, this unavoidably increases the weight of the main cable 12. Alternatively, it may be possible in some situations to introduce the compressing element 16 only to some sections of the main cable 12, such as the areas where clamps 24 are being placed for attaching the hangers 22 to the main cable 12 or the cable deviation areas on top of the towers 23. In this embodiment, the remaining part of the main cable, instead of compressing element 16, can be left void without filler or alternatively filled up with other lighter-weight material such as foam material in order to fill up the space and maintain the parallel pattern of the individual ducts 18.

[0054]FIG. 4A shows an example of the clamps 24 that can be provided to connect the main cable 12 and the hangers 22 (cf. FIG. 4B). The clamp 24 according to this invention is a structural item, designed to transfer the force F_Ed from the hanger 22 to the main cable 12.

[0055]To this end, it is reiterated that the main cable 12 comprises two main components arranged longitudinally. The first component being tensile elements 15, serves to carry longitudinal tensile force. The second component being a compressing element 16 serves to carry compressing force. In other words, the compressing element 16 is made of a rigid material. It is disclosed herein that the two components are not directly linked, for instance in the longitudinal direction. Nevertheless, they may transfer the forces on the transverse direction, for instance at the position where the clamps 24 are situated. The compressing element 16 may be a cement mortar, comprising standard or ultra-high-performance concrete (UHPC).

[0056]FIGS. 4A, 4B and 4C demonstrate an embodiment of the present invention how the hanger 22 may be attached to the main cable 12 through a clamp 24 in a vertical hanger arrangement.

[0057]The clamp 24 comprises a first part 24a having a substantially cylindrical shape, wherein its diameter is slightly larger than the pipe 11 of the main cable 12. This first part 24a of the clamp 24 is a structural tube 24e for encasing the pipe 11 and transfer the transverse component of the force F_Ed,⊥ by bearing to the compression component of the main cable 12.

[0058]The clamp 24 further comprises a second part 24b which may be a lug plate 24f where hangers 22 can be attached thereto. Thanks to this configuration of the clamp 24, the connection between the hanger 22 and the main cable 12 is capable of transferring longitudinal and transverse loads.

[0059]Moreover, a transverse plate 24c may be provided to the first part 24a in order to stiffen the structural tube 24e and transferring the longitudinal component of the load F_Ed,∥ by bearing to the compression component of the main cable, as shown in the FIG. 4A.

[0060]Alternatively, a transverse plate 24d having a plurality of holes may be provided in the clamp 24 for threading the ducts 18 and maintaining the parallel pattern of tensile elements 15 within the main cable 12 (FIG. 4A).

[0061]According to one embodiment, the clamp 24 may be encased on a pipe 11, as shown in the FIG. 4C. According to another embodiment, the clamp 24 having a transverse plate 24c may be used to join longitudinally two sections of the pipe 11. In this example, a transverse plate 24c or a transverse plate having a plurality of holes 24d according to the FIG. 4A may be provided to the clamp 24.

[0062]In addition, a transverse plate 24d can be firstly placed transversally to the main cable 12 in a certain location of the free length of the said main cable 12 (that is, in the part of the main cable 12 between two consecutive clamps 24 or between a clamp and the deviation areas on top of the towers 23). The transverse plate 24d comprises a plurality of holes to allow the ducts 18 to be placed longitudinally along the main cable 12. Multiple transverse plates 24d can be placed at different location of the main cable 12 to support the placement of the ducts 18. Then tensile elements 15 can be placed inside the ducts 18, and followed by the injection of a compressing element 16 within the space between the ducts 18 and the pipe 11, whereby the compressing element 16 is usually being injected in the form of a grout comprising cement material. Once the compressing element 16 has reached the necessary strength, the tensile elements 15 can be stressed and locked at the anchorages 33.

[0063]In addition, the cavities 17 can furthermore be filled up with a soft filler material 19, for instance liquid injection such as wax or grease. This liquid injection serves to improve the corrosion protection of the tensile elements 15.

[0064]FIGS. 5A, 5B and 5C demonstrate another embodiment of the present invention how the hanger 22 may be attached to the main cable 12 through a clamp 24′ in an inclined hanger arrangement.

[0065]The clamp 24′ according to this embodiment comprises a first part 24a′ having a raindrop transversal section which serves to encase the pipe 11. This first part 24a′ of the clamp 24′ is a structural tube 24e′ which has a slightly larger diameter than the pipe 11.

[0066]The clamp 24′ further comprises a second part 24b′ which has a connection component where hangers 22 can be attached thereto. Due to this configuration of the clamp 24′, the connection between the hanger 22 and the main cable 12 is capable of transferring only transverse loads and not longitudinal loads.

[0067]FIG. 6 shows an example of a plug with sealing device 25 to be installed at the extremity of the portion of the main cable 12 that is injected with a compressing element 16 to fill the space between the ducts 18 (part of the inside of the pipe 11). The FIG. 6 shows a possible configuration of the plug with sealing device 25 that can be made out of elastic material creating a leak-tight joint with the ducts 18 and the inside of pipe 11. Alternatively, the plug with sealing device 25 can be made out of rigid polymeric material and be equipped with watertight seals on its external part and with individual sealing rings around each duct 18 and tensile element 15. Alternatively, the plug with sealing device 25 can be made by a stuffing box formed by two cylindrical layers of polymeric material such as UHMW polyethylene, polyamide, etc. equipped with bolts that allow to compress a deformable cylindrical layer of highly deformable material such as neoprene.

[0068]As disclosed above, it may be possible in some cases to introduce compressing element 16 only in some areas of the main cable 12, such as the areas of deviation of top of the towers 23 and the areas of connection of the clamps 24. The free length of the main cable 12 can be then injected with a lighter material or left void. In this case, it is also possible to prefabricate the injected portions of the main cable 12 (deviation on top of the towers 23 and clamps 24), introducing tubing elements 20 with the required pattern before the injection of the compressing element 16. It is foreseen that the tubing element 20 may be able to be removed in order to create cavities 17 or introduce the ducts 18. Alternatively, the tubing elements 20 may be left intact to guide the ducts 17 when the injection of the compressing element has hardened.

[0069]To this end, it is reiterated that thanks to the compressing element 16 and the clamp 24 of the present invention, the main cable 12 has a higher durability as the tensile elements are not compressed directly by the clamp. Moreover, the compressing element 16 provides a hydrophobic environment to the tensile elements 15, thereby reducing the corrosion rate of the tensile elements 15.