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Title:
MULTI-LAYERED PIPE FOR STRUCTURAL CABLE
Document Type and Number:
WIPO Patent Application WO/2018/196966
Kind Code:
A1
Abstract:
The invention relates to a multi-layered pipe (1) for structural cable, a system and a method thereof, comprising a tubular shaped wall (25), the pipe (1) comprises at least a first layer (10) and a second layer (20), wherein the first layer (10) has a thermal resistance higher than the second layer (20), wherein the pipe (1) further comprises at least one heat-generated heating element (30). The present invention combines a passive and an active ice and snow removal system in order to remove ice and snow accreted on structural cables in a cost- effective and efficient manner while minimal consumption of energy is required.

Inventors:
ANNAN, Rachid (Hauptstrasse 107, 3255 Rapperswil, 3255, CH)
EGGER, Philipp (Quellenstrasse 34, 8005 Zürich, 8005, CH)
SCHWARZ, Andreas (Diesbachstrasse 12, 3012 Bern, 3012, CH)
Application Number:
EP2017/059937
Publication Date:
November 01, 2018
Filing Date:
April 26, 2017
Export Citation:
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Assignee:
VSL INTERNATIONAL AG (Wankdorfallee 5, 3014 Bern, 3014, CH)
International Classes:
E01D11/00; D07B1/14; E01D19/16
Domestic Patent References:
WO2014001514A12014-01-03
WO2014001515A12014-01-03
WO2014001514A12014-01-03
WO2014001515A12014-01-03
Foreign References:
JP2008190194A2008-08-21
CN105862591A2016-08-17
JP2006322177A2006-11-30
JPH08296206A1996-11-12
Attorney, Agent or Firm:
BOVARD AG (Optingenstrasse 16, 3013 Bern, 3013, CH)
Download PDF:
Claims:
Claims

1 . A multi-layered pipe (1 ) for structural cable, comprising a tubular shaped wall (25), the pipe (1 ) comprises at least a first layer (10) and a second layer (20), wherein the first layer (10) and the second layer (20) are made of at least one material, wherein the first layer (10) has a thermal resistance higher than the second layer (20), the pipe (1 ) further comprises at least one heat- generating heating element (30).

2. The pipe (1 ) according to claim 1 , wherein one or more channels (35) are provided to the first layer (10) and/or the second layer (20) of the pipe (1 ) or there between for accommodating the heat-generating heating element (30).

3. The pipe according to claim 1 or claim 2, the first layer (10) is completely encircled by the second layer (20), in which the heating element (30) is provided to the first layer (10), the second layer (20) or there between, or the heating element (30) is embedded into the wall (25) of the pipe (1 ).

4. The pipe (1 ) according to any one of the preceding claims, further comprising a third layer (50), wherein each layer is completely encompassed by another layer, forming an innermost layer, a middle layer and an outermost layer, wherein the innermost and the outermost layer are made of the same or different material, for instance High Density Polyethylene (HDPE) whereas the middle layer is provided with for instance a polyurethane foam, wherein the heating element (30) is provided in the middle layer close to the outermost layer.

5. The pipe (1 ) according to any one of the preceding claims, wherein the heating element (30) is provided longitudinally at least partially along the pipe (1 ), wherein the heating element (30) is a heating wire or a band heater.

6. The pipe (1 ) according to any one of the preceding claims, wherein the heating element (30) has a heating power of less than 100 W/m, preferably less than 50 W/m, preferably less than 30 W/m or more preferably around 20 W/m.

7. The pipe (1 ) according to any one of the preceding claims, wherein the heating element (30) has a diameter of between 1 to 50 mm, preferably between 2 to 30 mm, between 3 to 10 mm or more preferably around 5 mm.

8. The pipe (1 ) according to any one of the preceding claims, wherein one or more channels (35) are provided longitudinally at least partially along the pipe (1 ) for accommodating the heat-generating heating element (30), wherein the channels (35) comprises a heating wire or heating band or heated air and/or liquid, in such a way that the heat is transferred efficiently towards the outer surface of the wall (25) and that the heat generating heating element (30) can be replaced.

9. The pipe (1 ) according to any one of the preceding claims, wherein the heating element (30) is provided for ice shedding having a shedding differential temperatures of less than 100 K, preferably less than 50 K, less than 15 K, less than 10 K or less than 5 K.

10. The pipe (1 ) according to any one of the preceding claims, wherein the tubular shaped wall (25) has an outer surface (28) and an inner surface (27), wherein the outer surface (28) is provided with one or more strakes (40) or grooves or dimples.

1 1 . The pipe (1 ) according to claim 10, wherein the groove or dimple is in form of a circular shape, an oval shape, a mixture of predetermined shapes or a channel, whereas the strake (40) forms a protrusion for reducing rain and wind induced vibrations, wherein the strake (40) has a height being a distance from a strake root part connected to the outer surface (28) of the pipe and a strake end part terminating the strake outwards away from the pipe (1 ), the strake (40) having a width being transverse to the height, the width decreasing in the direction from the strake root part towards the strake end part, wherein the height is less than 5 percent of the diameter of the pipe (1 ), wherein the strakes (40) are arranged to form a helical pattern, a periodic pattern or a predetermined pattern.

12. The pipe (1 ) according to any one of the claims 10 to 1 1 , wherein the strake (40) has a length transverse to the height and the width and along which length the strake is connected to the pipe, the length of each strake (40) being equal or less than the circumference of the outer surface (28) of the pipe (1 ), or less than half of the circumference of the outer surface (28) of the pipe, wherein the strake (40) comprises a first strake surface portion facing away from the pipe, the first strake surface portion being concave or straight.

13. The pipe (1 ) according to any one of the claims 10 to 12, wherein the longitudinal direction of the strake (40) extends in a direction substantially orthogonal to the longitudinal direction of the pipe (1 ).

14. A thermal de-icing system comprising the multi-layered pipe (1 ) for structural cable according to any one of the claims 1 to 13, further comprising for instance a thermostat, a remote control and/or a monitoring device.

15. A method of manufacturing a multi-layered pipe (1 ) for structural cable, the pipe (1 ) comprises a tubular shaped wall (25), comprising the steps of: a. Providing at least a first layer (10) and a second layer (20), forming the wall (25) of the multi-layered pipe (1 ), wherein the first layer (10) and the second layer (20) are made of at least one material, b. Providing a heat-generating heating element (30) on or within the wall (25) of the pipe (1 ).

Description:
Multi-Layered Pipe for Structural Cable

Technical field of the invention

The present invention relates to the technical field of structural cables. In particular, the present invention relates to pipes for housing strand bundles such as tensile members used in constructions comprising high strength steel cables that are applicable to masts, towers, bridges, footbridges, roofs for stadiums or other similar structures, wherein the pipe is suitable to prevent ice and snow accretion and for efficient ice/snow removal.

Background of the invention

Bridge cables are particularly prone to ice (glaze or rime type) and snow (wet snow) accretion due to their inclined arrangement and cylindrical shape. Depending on the weather conditions, the thickness of the ice layer may exceed 15 mm in case of glaze ice or even 40 mm for wet snow accretions in extreme cases, hence posing a serious threat to users and the public when falling.

Large ice accretion can either occur from precipitation icing when super-cooled water droplets freeze on impact with the cable surface or when wet snow deposits consolidate and freeze in dropping ambient temperatures or from in-cloud icing when moist air freezes to the cable surfaces. These conditions are typically characterized by a change in ambient temperatures combined with high humidity and precipitation as they often occur in winter storms during with a rapid succession of cold and warm fronts.

Moreover, more frequent and more extreme winter storms due to climate change have also caused havoc recently across many countries which have led to some high profiles incidents. Such incidents have been reported among others on Port Mann and Alex Fraser Bridges in Vancouver, Margaret Hunt Hill Bridge in Dallas and Uddevalla Bridge in Sweden.

For this reason, atmospheric icing of bridges and bridge cables can result in financial losses for a bridge operator since in most cases, most if not all traffic on a bridge has to be suspended until the snow or ice removal operation is completed. More importantly, when ambient temperatures increase or when the surface of the bridge cable under the ice gets heated by solar radiation, human safety and the safety of road vehicles may be placed at risk due to the risk of being hit by the falling ice blocks whilst passing over the bridge or through areas adjacent to the bridge. Typically, accidents occur when large ice fragments strike the windscreens of passing cars either resulting in direct injury or damage (fracturing of glass or damage to car body) or in consequential damage following an accident caused by the driver's reaction. Bridges are therefore either closed preventative^ as a safety measure or have to be closed following an accident. This inevitably leads to high direct costs to repair the damage as well as high cost of non-availability to the bridge users as well as to the bridge operators.

Similarly to the ice accretion process, mass reduction of ice requires certain conditions to be initiated. Different atmospheric conditions and

rheological limits of ice are the decisive factors for three physical phenomena of ice shedding: ice melting, ice sublimation and mechanical ice breaking. Ice melting and ice sublimation are relatively slow processes which reduce the mass of the ice at the cable surface gradually whereas mechanical ice breaking is a sudden process resulting in shedding of solid ice particles. Bridge cables are most commonly affected by a combination of these three effects. Depending on the thickness of the ice, the evolution of the ambient temperature over time, wind conditions, and mechanical impact or cable vibration, one of the three mechanisms becomes controlling and ice shedding occurs sooner or later with larger or smaller particle sizes.

Ice or snow prevention and removal systems can generally be classified into two categories, namely passive and active. While passive ice/snow prevention and removal systems utilise natural forces such as the wind, gravity, incidental radiation and temperature variations, active systems utilise external forces.

Various ideas and designs for different de- and anti-icing techniques have been developed in the passive systems.

A first, simple known passive risk mitigation strategy has been used to equip bridges with external ice-monitoring devices, using cameras and sensors to monitor weather and icing conditions and to allow shut-down when there is a risk of ice shedding.

Other passive ice removal system such as surface coatings on bridge cables have also been applied. Such surface coatings are designed to minimize the adhesion between the cable surface and the ice or snow particles such as to prevent build-up and to facilitate early shedding by loss of adhesion.

Such coatings are however not robust enough considering the long life span of a bridge and could easily be peeled off. Furthermore, they are costly to apply to the surface of bridge cables.

On another hand, active ice and snow removal systems which resort to the use of external mechanisms have also been utilised for the prevention and/or the removal of ice and snow on bridge cables. One example of a mechanical ice removal system has been realised in Port Mann Bridge, where chain rings are released from the top of the bridge to be slid down along the bridge cables. Accreted ice and snow on the cables can thus be scrapped off through the sliding movement of the chain rings by the gravity force. However, the chain rings need to be brought up manually to the top of the bridge in their standby positions. For this reason, operation costs are inevitably high as additional workers need to be employed for this specific purpose. Moreover, these chain rings also cause wear and damages to bridge cables and pipes due to the high abrasive effects of the chain rings on the cable surface and their impact with the protrusions of strake profiles (which are known to be essential to control the risk of rain-wind-induced vibrations) on the outer surface of the cables/pipes. An alternative to the chain rings active system could be a mechanical scraper system, wherein a plurality of brush devices are provided onto each and every bridge cable. These brush devices are capable of moving up and down along the cables in order to scrape off the ice or snow formed on the bridge cables. Such solution appears to be non-economical, as each and every bridge cable requires such a brush device to be installed and operated.

Other non-typical active ice and snow removal systems include the use of helicopters to blow off snow and the use of hot water cannons for the removal of ice and snow. These solutions obviously are non-economical and impractical.

In addition, other examples of active ice and snow removal systems are inductive pulse de-icing where high electric impulses are used to shock heat and vaporize interface layer, or for instance the use of an inflation system for the expansion of pipe by air pressure or other solutions to break-off ice.

However these methods have their disadvantages, as excessive electrical power is required for the inductive pulse de-icing method whereas the inflation systems are not easy to be integrated into the bridge cables and are not robust enough. Furthermore, consistent results are hard to be obtained from these methods, thus rendering these methods unreliable.

All these methods and systems require an activation immediately when a critical snow or ice built-up is observed in order to minimize the risk of un-controlled ice shedding over traffic. This requires at least partial closure of the bridge and leads to unwanted interruptions to traffic. Several icing events have occurred during peak traffic hours and these systems do not allow to schedule ice removal operations in advance.

Therefore, there remain needs to find a cost-effective, more reliable and a safer solution for ice and snow removal and prevention on bridge cables, in particular stay cables. In addition, an active de-icing system which allows for a controlled and scheduled intervention to remove the ice and snow from the bridge cables during off-peak traffic times is particularly sought after. Summary of the invention

The inventors of the present invention have found out an effective solution for the above-discussed problems by introducing a new pipe as presently claimed. Thanks to the heating system provided to the multi-layered pipe, wherein one layer of the pipe has a lower thermal resistance to another layer of the pipe, the multi-layered pipe according to the present invention is configured in such a way to provide for a cost-effective and a reliable solution to the existing problems. The proposed active sytem of ice and snow prevention and removal is achieved through the use of a heating element with a multi- layered pipe which allows to minimize the consumption of electrical energy.

This allows ice and snow accreted on structural cables of a bridge, in particular stay cables, to be removed in a controlled manner, thereby reducing the number of interventions needed for ice and snow removal. The present invention allows to schedule ice removal operations in a more reliable manner making use of the improved ice retention. The time needed for the ice and snow removal can thus be calculated and timed. The present invention also reduces significantly the risk of having to close the entire bridge during removal by minimizing the size of the ice particles and allowing targeted de-icing of the cables in a defined sequence. The proposed active system also allows the ice and snow to be removed at a specific schedule in a certain duration of time, for instance during off-peak time.

According to a first aspect of the invention, there is provided a multi- layered pipe for bridge cable as recited in claim 1 . More specifically, the first aspect of the invention relates to a multi-layered pipe for bridge cable for de- icing and/or snow removal, wherein the pipe comprises a tubular shaped wall, the pipe comprises at least a first layer and a second layer, wherein the first layer and the second layer are made of at least one material, wherein the first layer has a thermal resistance higher than the second layer, wherein the pipe further comprises at least one heating element. The multi-layered pipe is configured in such a way that the pipe is provided with a heating element to remove accreted ice and snow in an active manner. For instance, the pipe having a lower thermal resistance is provided as an outer layer such that heat can be efficiently transmitted to the outer surface of the wall. The pipe having a higher thermal resistance is provided on the inside such as to prevent heat losses by insulating the heating element against the steel mass of the cable. Hence, ice and snow can be prevented or removed while minimizing energy consumption.

According to a second aspect of the invention, there is provided a thermal de-icing system as recited in claim 14. The new system allows the proposed pipe to be integrated into different structures, thereby the new system is applicable in different constructions.

According to a third aspect of the invention, there is provided a method of manufacturing a multi-layered pipe for bridge cable, comprising the steps of (a) providing at least a first layer and a second layer, forming the wall of the multi-layered pipe, wherein the first layer and the second layer are made of at least one material; (b) providing a heat-generating heating element on or within wall of the pipe.

In a first embodiment of the present invention, the first layer is completely encircled by the second layer, in which the heating element is provided to the first layer, the second layer or there between, or the heating element is embedded into the wall of the pipe. Such configuration allows the multi-layered pipe to have a lower thermal conductivity or a higher thermal resistance on one side of the pipe, thus allowing the heat to be radiated to the opposite side, thereby reducing the amount of heat required for preventing ice formation on cables and/or removing ice and snow on cables. For instance the layer having a lower thermal conductivity or a higher thermal resistance is provided closer to the strand bundles that are housed within the pipe whereas the layer having a higher thermal conductivity or a lower thermal resistance is arranged at the outer periphery of the wall of the pipe. Such configuration ensures that heat generated by the heating element can be efficiently

transmitted to the outer surface of the pipe whereas the strand bundles housed within the pipes are not being heated. In a second embodiment of the present invention, the pipe further comprises a third layer, wherein each layer is completely encompassed by another layer, forming an innermost layer, a middle layer and an outermost layer, wherein the innermost and the outermost layer are made of the same or different material, for instance High Density Polyethylene (HDPE), whereas the middle layer is provided with for instance a polyurethane foam, wherein the heating element is provided in the middle layer close to the outermost layer. Such configuration allows the heat generated by the heating element to be transferred more efficiently to the outer surface of the wall such that the ice and snow can be removed while less heat is transmitted to the internal components of the pipe such as tendons comprising strand bundles. Such configuration may be easier to be manufactured, as the heating element can be first inserted into the pipe before filling up with filling material, for instance the polyurethane foam or polyethylene foam.

In a third embodiment of the present invention, the heating element is provided longitudinally at least partially along the pipe, wherein the heating element is a heating wire or a band heater. Such heating element is cost- efficient, light weight, easily replaceable and can be configured such that only certain regions of the cables are being heated.

In one preferred embodiment, one or more channels are provided to the first layer and/or the second layer of the pipe or there between for accommodating the heat-generating heating element. This allows the heating element to be replaceable or installed easily in the pipe. Moreover, the heat generated by the heating element can also be transferred and radiated outwards efficiently thanks to these channels.

In another embodiment, the heating element has a heating power of less than 100W/m, preferably less than 50W/m, preferably less than 30W/m or more preferably around 20W/m. Such heating power values allow different ranges of heat to be generated accordingly by the heating element.

According to one embodiment, the heating element has a diameter of between 1 to 50 mm, preferably between 2 to 30 mm, between 3 to 10 mm or more preferably around 5 mm. Such diameters of the heating elements has the advantage of ensuring that the diameter of the multi-layered pipe of the present invention does not become significantly larger than for a conventional structural cable. Preferably the diameter of the pipe of the present invention does not exceed 50 %, 30 %, 15 % or 10 % compared to the conventional structural cables which typically have a diameter in the range of from 80mm to 600mm.

According to another embodiment, one or more channels are provided longitudinally at least partially along the pipe for accommodating the heat-generating heating element, wherein the channels comprises air and/or liquid, wherein the air and/or liquid is heated by the heating element in such a way that the heat is transferred efficiently towards the outer surface of the wall. The heated air or liquid generated by the heating element can circulate through the channels provided to the multi-layered pipe via for example a high pressure system. Through this indirect heating method, the whole cable strand can be kept at temperatures above freezing. Nevertheless, total energy demand may be exceptionally high with this heating method.

In a further embodiment, the heating element is provided for ice shedding having a shedding differential temperatures of less than 100 K, preferably less than 50 K, 15 K, 10 K or 5 K. Such differential temperatures are sufficient to provide for an efficient active system of ice shedding on structural or bridge cables.

In a yet further embodiment, the tubular shaped wall has an outer surface and an inner surface, wherein the outer surface is provided with one or more strakes, grooves or dimples. Such surface features provided on the outer surface of the wall not only show an improved behaviour against rain-wind induced vibrations, they also allow ice layers to be retained longer on the pipe which allow some initial melting before the ice drops. Such profiles also break up the structure of the ice into sections of different thickness which causes fragmentation of the ice. Such profiles reduce the weight of the ice fragments that eventually drop. Similar effects have been demonstrated whether dimples, grooves or strakes are provided on the outer surface of the wall. In another embodiment of the present invention, the groove is in form of a circular shape, an oval shape, a mixture of predetermined shapes or a channel, whereas the strake forms a protrusion for reducing rain and wind induced vibrations, wherein the strake has a height being a distance from a strake root part connected to the outer surface of the pipe and a strake end part terminating the strake outwards away from the pipe, the strake having a width being transverse to the height, the width decreasing in the direction from the strake root part towards the strake end part, wherein the height is less than 5 percent of the diameter of the pipe. Such strakes have the advantage of efficiently reducing rain-wind induced vibrations as the aerodynamic properties of the cable are improved significantly. At the same time, cable drag is not increased significantly despite the presence of the strakes. The reason is that the stream-wise vorticity generated by the strake is increased. This is desirable as it reduces the wake formed leeward relative to the cable, which reduces cable drag. Moreover, such strakes avoid accreting too much snow and ice on the pipe. Further, such strake profiles cause uneven thickness to ice layer formed on the structural or bridge cable.

In a further embodiment, the strake is arranged to form a helical pattern, a periodic pattern or a predetermined pattern. Predetermined patterns of strakes can be customised into different profiles such that the strakes are used according to different needs. A helical pattern is easy to manufacture compared to a periodic pattern, while a periodic pattern can be more efficient in removing ice chunks in smaller pieces.

In another embodiment, the strake has a length transverse to the height and the width and along which length the strake is connected to the pipe, the length of each strake being equal or less than the circumference of the outer surface of the pipe, or less than half of the circumference of the outer surface of the pipe. Such strakes also allow smaller pieces of ice to be melted and dropped from the pipe as they melt.

According to one embodiment, the strake comprises a first strake surface portion facing away from the pipe, the first strake surface portion being concave. The concave surface improves the aerodynamic properties of the pipe or cable, whereby rain and wind induced vibrations are minimized by ramping any water present on this outer surface of the pipe away from the surface and eventually spraying the water off at the tip of the strake. This can reduce the amount of water that can freeze to the cable surface. Instead of being concave, the strake may also be straight for easy manufacturing.

According to a further embodiment, the longitudinal direction of the strake extends in a direction substantially orthogonal to the longitudinal direction of the pipe. This allows ice fragments to be retained longer due to the strake profiles and arrangements.

In one further embodiment, the method further comprises the step of (a) providing a third layer, wherein each layer is completely encompassed by another layer, forming an innermost layer, a middle layer and an outermost layer; (b) providing the heating element in the middle layer close to the outermost layer.

Brief description of the drawings

The following drawings are not necessarily drawn to scale, emphasis instead is generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings:

Figure 1 is a schematic cross section overview of the pipe according to a first embodiment of the present invention.

Figure 2 is a schematic cross section overview of the pipe according to a second embodiment of the present invention.

Figure 3 is a schematic cross section overview of the pipe according to a third embodiment of the present invention. Figure 4 is a perspective overview of the pipe according to a fourth embodiment of the present invention.

Figure 5 is a schematic cross section overview of the pipe according to the fourth embodiment of the present invention.

Detailed description of the preferred embodiment

Several preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and

configurations incorporated herein has been omitted for conciseness.

Figure 1 illustrates a schematic cross-section overview of a multi- layered pipe 1 for structural cable according to a first embodiment of the present invention. The multi-layered pipe 1 comprises a tubular shaped wall 25, wherein a plurality of strand bundles 22 are contained therein. In this embodiment, the wall 25 is made up of two layers, namely a first layer 10 and a second layer 20. The first layer 10 is completely encircled by the second layer 20, wherein a plurality of heating elements 30 are provided in between the first 10 and the second layer 20. More specifically, the heating elements 30 are provided at the first layer 10 which is the innermost layer, within a plurality of voids or channels 35 which are provided for accommodating the heating elements 30. However, it can be foreseen that the heating elements 30 can also be embedded within the first layer 10. The first layer 10 is located closer to the strand bundles 22 housed within the pipe 1 and it has a lower thermal conductivity or a higher thermal resistance compared to the second layer 20. Such configuration ensures that the strand bundles 22 are being shielded from the heat generated by the heating elements 30. In other words, the heat can thus be efficiently radiated outwards such that accreted ice and snow on structural cables/pipes can be removed in a controlled and a timed manner through heat flow.

It is noted that the multi-layered pipe 1 of the present invention comprises at least a first layer 10 and a second layer 20, wherein the first and second layers 10, 20 can be made of different materials with different thermal conductivities/thermal resistance; or of the same material but with different wall thicknesses. For instance when the first layer and the second are made of the same material, the first layer having a higher thermal resistance than the second layer can be realised through for example having a thickness higher than the second layer.

Figure 2 shows a schematic cross-section overview according to the second embodiment of the present invention. The second embodiment is largely similar to the first embodiment with the exception that a plurality of heating elements 30 are provided at the second layer 20 of the wall 25 which has a lower thermal resistance compared to the first layer 10. In particular, a plurality of channels 35 or voids can be provided around the periphery of the wall 25 within the second layer 20 of the multi-layered pipe 1 in order to accommodate the heating elements 30. Such configuration maybe a preferred embodiment as unnecessary heat loss can be avoid through the first layer 10 having a higher thermal resistance or a lower thermal conductivity. Therefore, heat flows towards the second layer 20 and thereby reduces the heat transmission towards strand bundles 22 which are housed within the pipe 1 . It can also be foreseen that the heating element 30 can be embedded directly into the second layer 20, wherein channels or voids are not being provided.

To this end, the channels 35 or voids may be provided at any layer or locations of the multi-layered pipe 1 such that the heating element 30 can be accommodated therein to heat the pipe 1 directly (for instance with heating wires) or indirectly (for example with warm air and/or liquid). In this connection, it is noted that the heating wire in the channels 35 can be replaceable easily when the heating wire is placed in the channels 35 or voids and not being embedded.

Figure 3 shows another embodiment according to the present invention, wherein a further third layer 50 is provided to the multi-layered pipe 1 . As can be seen in this embodiment, each layer is completely encompassed by another layer, thereby forming an innermost layer, a middle layer and an outermost layer. It can also be foreseen that not the entire layer is encircled by another layer but such example also gives the same technical effect of transmitting heat efficiently towards the outer surface of the wall.

In this embodiment, the first layer 10 forms an innermost layer, the second layer 50 forms a middle layer whereas the third layer 20 forms an outermost layer. All three layers may be made of a similar material. However, it is preferable that the innermost and the outermost layers 10, 20 are made of the same material, for instance High Density Polyethylene (HDPE) whereas the middle layer 50 is provided with for instance a polyurethane foam, wherein the heating elements 30 are provided in the middle layer 50 close to the outermost layer 20. The middle layer 50 may have a larger thickness compared to the other two layers. The heating elements 30 provided in the middle layer 50 close to the outermost layer 20 has the advantage that outer surface 28 or the pipe 1 can be heated more easily compared to the strand bundles 22 housed within the pipe 1 . However, it is reiterated that all three layers may be made of different materials or different thicknesses.

In these embodiments, a total number of six heating elements 30 are provided on the periphery circumference of the wall 25. However, it can be foreseen that any number of the heating elements 30 are provided to the pipe 1 , for instance ranging from 2, 4, 8, 10, 20 or more. Furthermore, the heating element 30 can also be provided at only a certain region of the circumference of the wall (for instance arc sector positions where ice and snow tend to

accumulate on the structural cables) or provided at a certain length of the longitudinal direction of the pipe 1 in order to actively remove the ice or snow at a specific time while allowing minimal amount of consumption of electrical power. In this connection, it can be foreseen that each and every heating element 30 can be individually controlled and their outputs can be varied from each other.

Figure 4 shows a perspective view according to a further embodiment of the present invention. As can be seen in this figure, the multi- layered pipe 1 comprises a tubular shaped wall 25 having an inner surface 27 and an outer surface 28, wherein a plurality of strake elements 40 are provided on the outer surface 28 of the wall 25. In this embodiment, all strakes 40 are arranged orthogonally to the longitudinal direction of the pipe 1 , wherein the plurality of strakes are arranged in a way to resemble helical shape, as can be seen in the Figure 4.

In this specific embodiment, a combination of a passive system (ice retention mechanism having a plurality of strake elements 40) and an active system (heating elements 30) are provided to the pipe for structural

cables/pipes of the present invention. The strake profiles 40 gives an improved retention of ice and snow, thus targeted lane closures can be achieved while minimally affecting the traffic flows. Furthermore, the heating element 30 can be a heating wire or a band heater placed between or on the multi-layered pipe 1 or embedded within the multi-layered pipe 1 .

Such arrangement of the strakes 40 was found by the present inventors to be an effective solution for the problem of how to reduce the size of the falling ice. The Figure 4 shows an example where a passive system is combined with an active system to provide a synergistic effect to the problem. Specifically, the strakes 40 which are in form of protrusions provided on the outer surface 28 of the wall 25 enable ice and snow to be retained longer at the pipe outer surface 28. Due to the geometries and arrangements of the strakes 40, a series of stronger and weaker areas (or uneven thickness) of the frozen ice and snow are created on the pipe. When the heating elements 30 are activated, smaller pieces of ice fragments are thus created and are shed from the multi-layered pipe 1 .

The features of the strakes as incorporated herein have been well described in the patent specifications of WO2014/001514 and WO2014/001515. Said patent applications described outer surface of a cable being provided with the said strake profiles. According to those patent applications, the strake profiles 40 can be provided in different forms as well as can be arranged extending along the longitudinal direction of the pipe or orthogonally to the longitudinal direction of the pipe. Such patterns and arrangements provided on the outer surface of the structural or bridge cables are advantageous as they show an improved behaviour against rain-wind induced vibrations, which is an effect where cable starts to vibrate due to oscillation of the water rivulets formed on a plain cylinder at the top and bottom of the cross section.

However, the inventors of the present invention surprisingly found out that despite the advantages provided by the aforementioned strakes for reducing the rain-wind induced vibrations, the solution is not sufficient to overcome the problem posed for ice and snow accretion on structural cables. Although these protrusions or strakes indirectly allow more ice and snow to be retained on the outer surface of the cables, the bridge has to be closed at a point for ice and snow removal when the accumulation reaches a maximum level or could pose a danger to the road users.

Therefore, the active system espoused in the present invention in combination with the strake profiles 40 provides for a cost-effective, reliable and safe solution for a problem that has not yet been solved by the profession in the art. Ice shedding through the present invention can be controlled and scheduled accordingly, for example ice shedding can be performed during low traffics hours or in a more controllable fashion, since the active system of the present invention allows such procedure to be carried out according to the needs.

Furthermore, thanks to the strake profiles 40 provided on the outer surface 28 of the pipe 1 , particularly the plurality of orthogonally arranged strakes 40 as shown in Figures 4 and 5, ice layer is particularly weakened by the presence of these protrusions 40 which results in a reduction of the size and mass of the ice particles that drop once ice-shedding occurs. This effect is especially pronounced compared to other conventional strake profiles such as a single or a double helical shape or a ring shape. The strake elements 40 arranged in such a manner as shown in Figures 4 and 5 surprisingly shed ice into smaller fragments, when the heating element 30 is activated.

To this end, it is mentioned that in certain embodiments, heat insulating blanket can be used to wrap around the strand bundles 22 and compliment or replace the innermost pipe layer whereas the heating element 30 such as the heating wires are provided in between or on the multi-layered pipe 1 . Such wrapping ensures less heat can be transferred to the strand bundles in order to minimize heat loss. Such heat insulating blanket ensures a smaller thickness (hence lighter weight) of the pipe can be realised. Such pipe not only reduces cost but also allows easier construction in case cables are prefabricated.

The currently proposed active de-icing system can entirely be controlled remotely. Hence, contrary to the other active de-icing system where chain rings are required to be brought back to the top of the bridge by rope access technicians, such risk does not exist in the present invention. Moreover, due to the existence of the strake elements 40 which may be provided on the outer surface 28 of the wall 25, other active systems involving the mechanical removing mechanisms are not suitable to be combined with the passive system.

In this case, present invention provides an ingenious solution to overcome the formulated problem, whereby a heating element 30 is provided to the pipe 1 such that the active system can be combined with the passive system (strakes) in order to provide for a synergistic effect.

It is reiterated that the heating element 30 used in the present invention can either be used to produce heat continuously or intermittently for example through the heating wire or band heater during periods of high icing risk to prevent any accretion of snow or ice in the first place. The heating element 30 may be provided on the outer surface 28 of the pipe 1 , or on the inner surface 27 of the pipe 1 , or housed within the channels 35 provided on/in the pipe 1 , or embedded within the multi-layered pipe 1 .

Alternatively, heat can be introduced either by blowing hot air into the available void between the high tensile steel strands and the outer pipe enclosing the cable or by embedding heating wires directly into the pipe.

However, this solution may be too costly and inefficient due to the high amount of energy consumed. Most of the energy is lost by heating up the steel mass of the cable and by convection losses inside the pipe rather than targeted heating of the ice interface at the pipe surface. Therefore, the channels 35 or voids provided within the first layer 10, the second layer 20 or there between 10, 20 can be used to provide a good solution for the circulation of heated air and/or liquid within the pipe 1 .

Figure 5 is a schematic cross-section overview of the Figure 4. As can be seen in this figure, the multi-layered pipe 1 appears to be similar to the Figure 1 but with the only difference is that a plurality of strake elements 40 are provided on the outer surface 28 of the pipe 1 . It can be easily foreseen that despite providing the heating elements 30 in the first layer 10 as shown in the Figure 5, the heating element 30 can of course be provided in any layers or anywhere or embedded within the wall of the pipe 1 .

By "about" or "around" or "substantially" in relation to a given numerical value for unit, amount, temperature or a period of time, it is meant to include numerical values within 25% of the specified value.

By "comprising" it is meant including, but not limited to, whatever follows the word "comprising". Thus, the use of the term "comprising" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present. The terms "comprising" and

"including" as used herein are interchangeable with each other.

By "consisting of" it is meant including, and limited to, whatever follows the phrase "consisting of". Thus, the phrase "consisting of" indicates that the listed elements are required or mandatory, and that no other elements may be present.

By "completely" or "entirely" it is meant totally and utterly. Thus, the use of the term "completely" or "entirely" as used herein indicates that the layer is totally and utterly (almost 100 %) encircled or encompasssed by another layer which has a larger diameter.

The terms "at least one" and "one or more" as used herein are interchangeable and relate to at least 1 and include 1 , 2, 3, 4, 5, 6, 7, 8, 9 and more. The invention has been described broadly and generically herein. Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.