[0001] The present invention relates to a deicing device for a duct. The present invention also relates to a structural cable with such a deicing device, and a method for deicing a duct with such a deicing device.

[0002] The duct may be a sheath for structural cables. Structural cables are used in civil engineering, for instance in cable-stayed bridges. It is applicable, in particular, to the sheath of such cables used for supporting, stiffening or stabilizing structures.

BACKGROUND

[0003] Stay cables are widely used to support suspended structures such as bridge decks or roofs. They can also be used to stabilize erected structures such as towers or masts.

[0004] A typical stay cable includes a bundle of tendons, for example wires or strands, housed in a collective duct, or sheath. The sheath is intended to protect the metallic tendons of the bundle.

[0005] The sheath is in contact with the surrounding environment. As such, it is susceptible to the formation of frost, rime, ice or snow thereon.

[0006] Addressing this phenomenon is important, as the presence of frost, rime, ice or snow on the sheath may significantly alter the aerodynamic properties of the stay cable, which in turn may lead to vibrations of the cable. Ice chunks falling from the cables may also cause problems.

[0007] Several approaches have been developed to address this, such as an approach relying on a metallic collar configured to break ice and frost by being moved along the sheath. However, this is not fully satisfactory, as it tends to erode the sheath, and it may become unusable in certain circumstances.

[0008] Another approach is known from WO 2019/064042 A1 wherein the sheath comprises heating components. However, the solution disclosed in that document is not applicable to example to cables already mounted on bridges. [0009] WO 2018/142174 A discloses a sheath with a cavity that may receive a vibration module to break superficial ice or frost deposits.

[00010] US 10,113,278 B1 discloses a module for deicing a cable sheath with a mass and a vibrator. In this solution, the module is placed in the interstitial space that is left accessible by the tendons arranged within the sheath. The module causes vibrations along the cable that are expected to remove the ice or snow covering the cable. However, this solution is not satisfactory because the vibrating mass may hit the tendons of the cable and damage them and because such solution requires a lot of power. Also, this solution is not appropriate when the interstitial space is not large enough or almost nonexistent to receive such module.

[00011] In recent years, new types of structural cable have been developed, where the interstitial space is injected with filler material such as epoxy or wax. In these structural cables, there is no available place to insert a deicing module within the sheath.

SUMMARY

[00012] An object of the present invention is to propose a deicing device for a duct that can remove ice, frost, rime or snow therefrom in an improved manner. To that end, the invention relates to a deicing device for a duct, the deicing device comprising: a frame disposed around an outer surface of the duct; and a plurality of bearing units inserted at different angular positions between the outer surface of the duct and the frame, at least one of the bearing units comprising an actuator for compressing the duct when powered.

[00013] The frame firmly supports the actuator around the duct. In addition, the pressure exerted on the duct causes a local deformation of the duct which can then cause a temporary and reversible shape change of the cross-section of the duct which may detach ice chunks from the duct.

[00014] In an embodiment, the actuator comprises a vibrator configured to generate vibrations on the duct.

[00015] In another embodiment, the vibrations are in a frequency range of 50 to 5000 Hz. [00016] In another embodiment, the actuator is configured to apply compression pulses to the duct.

[00017] In another embodiment, at least one of the bearing units has a first part for contacting the frame and a second part for contacting the outer surface of the duct, the second part being movable with respect to the first part in a direction perpendicular to the outer surface of the duct.

[00018] In another embodiment, the second part is movable with respect to the first part in the direction with a stroke in a range of 10 to 150 mm.

[00019] In another embodiment, the first part is attached to the frame.

[00020] In another embodiment, at least one of the bearing units comprises a shoe maintained against the outer surface of the duct, the shoe having a contact surface with a curvature smaller than a curvature of the outer surface of the duct.

[00021] In another embodiment, the shoe comprises a soft material at the contact surface. [00022] In another embodiment, the deicing device further comprises a system for displacing the frame and the plurality of bearing units along a longitudinal direction of the duct.

[00023] In another aspect, there is proposed a structural cable comprising: a duct; tendons extending in the duct and having ends anchored to respective parts of a construction work; and at least one deicing device as detailed above, arranged around the duct.

[00024] In another aspect, there is proposed a method for deicing a sheath, the method comprising: placing, around an outer surface of the duct, a deicing device comprising a frame and a plurality of bearing units, the plurality of bearing units being arranged at different angular positions between the outer surface of the duct and the frame; powering an actuator provided in at least one of the bearing units for compressing the duct. [00025] In another embodiment, the method comprises controlling the actuator to apply vibrations or compression pulses to the duct.

[00026] In another embodiment, the method further comprises: bringing the deicing device to a first position along the duct; controlling the actuator to apply pressure to the duct at the first position; displacing the deicing device from the first position to a second position along the duct; and controlling the actuator to apply pressure to the duct at the second position.

BRIEF DESCRIPTION THE DRAWINGS

[00027] Other features and advantages of the deicing device disclosed herein will become apparent from the following description of non-limiting embodiments, with reference to the appended drawings, in which:

- Fig. 1 is a schematic side view of a stay cable;

- Fig. 2 is a cross-sectional view of a stay cable;

- Figs. 3 and 4 are cross-sectional views of the stay cable shown in Fig. 2 fitted with an embodiment of a deicing device;

- Figs. 5 and 6 are views in a longitudinal cross-section of the stay cable and the deicing device shown in Fig. 4 with illustrative displacement systems.

DESCRIPTION OF EMBODIMENTS

[00028] In the present description, the deicing device is described in relation with a sheath of a structural cable such as a stay cable 10. However, the device may be suitable for deicing any type of duct exposed to cold and humid environment, provided that the outer surface of such a duct is accessible for installation of the deicing device.

[00029] Fig. 1 shows a stay cable 10 equipped with a sheath 20 and extending along an oblique path between first and second parts 12, 14 where it is anchored using respective anchoring devices 16, 18. The stay cable is used to suspend the second part 14 (e.g., a bridge deck) from the first part 12 (e.g., a pylon), or to stabilize a tall structure forming the first part 12 from the ground or some lower structure forming the second part 14. [00030] The structural cable 10 comprises tendons 22 disposed parallel to each other (Fig. 2) and contained in a collective sheath 20. For example, the tendons may be steel strands each protected by a substance such as grease or wax and individually contained in a respective plastic sleeve.

[00031] The collective sheath 20 forms a protective cover for the tendons 22. It is in the form of a duct which internally defines a cavity 24 running along the length of the cable 10 and within which the tendons 22 are arranged. Optionally, a filler material 26 is injected into the cavity 24 to fill the spaces not occupied by the tendons.

[00032] The cross-section of the sheath 20 is typically circular. Other shapes, e.g. polygonal, elliptical, etc., are possible. The sheath 20 comprises an inner surface facing the tendons 22 and an outer surface 28 opposite to the inner surface.

[00033] The cable 10 may have a length of up to several hundred meters. The bundle may include a few tens of tendons 22.

[00034] The sheath 20 is typically made of plastic material such as high-density polyethylene (HDPE).

[00035] Figures 3 and 4 show an embodiment of a deicing device. The deicing device acts locally from the outside of the sheath 20 to deform it so as to remove the potentially accumulated ice, frost, rime or snow on its outer surface. It should be understood the deicing device is not limited to removing a specific form of ice: the word “deicing” is meant to cover the removal of any kind of frozen water.

[00036] The deicing device is disposed around the outer surface 28 of the sheath 20. It comprises a frame 60 and a plurality of bearing units 34, 42.

[00037] The frame 60 surrounds the sheath 20 and maintains the other components of the deicing device against or close to the sheath 20. The frame 60 provides rigidity to the deicing device, necessary to the deicing action.

[00038] The frame 60 may be in the form of a hoop, as shown in Figs. 3-6. Alternatively, it may be in the form of a sleeve having some longitudinal extension. Transversely to the stay, the frame may have a circular shape (Figs. 3-4), though other shapes are possible such as square shape, elliptical, etc. To increase its rigidity, the frame 60 preferably has a closed shape surrounding the cable sheath 20. A closed shape also prevents the deicing device to fall from the sheath, for example in case of a strong vibration, acceleration or a shock which the cable would be subject to. If, however, its structure is strong enough, it may have an open shape such as a C shape, which can facilitate its placement around the sheath.

[00039] In the embodiments of Figs. 3-6, the deicing device comprises two bearing units in contact with the sheath 20. A first bearing unit 42 and a second bearing unit 34 are thus inserted between the outer surface 28 of the duct 20 and the frame 60, at different angular positions around the sheath. For example, the two bearing units are diametrically disposed above and under the sheath 20, as shown.

[00040] Other arrangements of the bearing units around the sheath 20 may be considered. Alternatives include having four bearing units arranged at 90° from each other, three bearing units at 120° from each other, etc.

[00041] In the embodiment of Fig. 3, the first bearing unit 42 disposed under the stay cable comprises a base 32 and a shoe 31. The base 32, for example a metallic part, is attached to the frame 60. The shoe 31 has a surface 33 for contacting the outer surface 28 of the sheath 20. The surface 33 is concave, with a cylindrical shape to conform to the outer surface 28 of the portion of the sheath 20 with which the shoe 31 is in contact.

[00042] The second bearing unit 34 disposed above the stay cable comprises a first part 36 in contact with the frame 60 and a second part 35 in contact with the outer surface 28 of the sheath 20. The first part is formed by a support 36 which may be attached to the frame 60 while the second part is a shoe 35 movable with respect to the support 36 in a radial direction Y, i.e. in a direction perpendicular to the outer surface 28 of the sheath 20. The shoe 35 has a surface 38 for contacting the outer surface 28 of the sheath 20.

[00043] A mechanism 37 is disposed between the support 36 and the shoe 35 to move the shoe 35 between a rest position (Fig. 4) and a bearing position (Fig. 3) in which the deicing device is firmly clamped on the sheath 20. In the bearing position, the shoe 35 is farther from the inside of the frame 60 than in the rest position. The mechanism 37 can include a jack, a solenoid, a scissors or pantograph mechanism, an eccentric cam driven by a motor, or any kind of mechanism suitable to provide a linear displacement perpendicularly to the stay cable. Thus, the second bearing unit 34 can be used as a lifting system to press the shoes 31, 35 on both sides of the sheath 20.. The linear stroke of the mechanism 37 is in a range of 10 to 150 mm, for example, depending on the clearance between bearing units 34, 42 and the sheath 20. [00044] One or both of the bearing units 34, 42 includes an actuator arranged to compress the sheath 20 when it is powered, so as to facilitate separation of ice deposits from the outer surface 28 of the sheath.

[00045] In an embodiment, the actuator comprises the above-mentioned mechanism 37 of the second bearing unit 34. The pressure applied by activation of the mechanism 37 in the bearing position provides some deformation of the sheath 20 which tends to reduce the adherence of any ice layer formed on the sheath due to the difference of stiffness between the plastic wall of the sheath 20 and the ice. Furthermore, the mechanism 37 may be controlled to apply pressure pulses to deform the plastic wall and thus shake the accumulated ice off the sheath 20. The deformation results in part from flattening of the upper part of the plastic wall between the tendons of the upper layer of the bundle and the shoe 35 and, to a larger extent, from transmission of the pressure pulse to the first bearing unit 42 via the support 36 and the rigid frame 60.

[00046] As an alternative or a complement, the actuator may comprise a vibrator provided in the first bearing unit 42. In the illustration of Figs. 3-4 the vibrator comprises an eccentric cam 39 mounted between the base 32 and the shoe 31 and driven by a motor (not shown) when the second bearing unit 34 is in the bearing position. In the bearing position (Fig. 3), powering the vibrator 39 causes vibratory changes of the shape of the sheath 20 which is less rigid than the frame 60. In alternative embodiments, the vibrator includes an electromagnetic loudspeaker, with a power in a range of 50 to 500 W, or a piezoelectric element.

[00047] The vibrator generates vibrations in a range of 50 to 5000 Hz, for example, and preferably in a range of 100 to 1000 Hz. When it uses an eccentric cam 39, it can be rotated by the motor at a speed in a range of 5000 to 35000 rpm, and preferably of 10000 rpm to 30000 rpm to have a vibration frequency of 166 Hz to 500 Hz.

[00048] Alternatively, several vibrators are provided to distribute the mechanical effect on the periphery of the sheath. In particular, there can be a vibrator in the first bearing unit 34.

[00049] Circuitry to control and power the actuator(s) and the mechanism 37 of the second bearing unit may be carried by the frame 60. The circuitry may include a radiofrequency unit configured to allow an operator to supervise the deicing process using a remote controller.

[00050] In addition, the deicing device may be displaced along the sheath 20, by sliding on the outer surface 28. [00051] The surface 33 of the shoe 31 and the surface 38 of the shoe 35 advantageously has a curvature smaller than that of the outer surface 28 of the sheath, to avoid puncturing the sheath when the actuator is activated. Furthermore, the surfaces 33 and 38 can be made of soft material, to avoid damaging the sheath when the deicing device is displaced longitudinally, for example an elastomeric material such as polyurethane. A deformable coating can accommodate surface irregularities on the outer surface 28 of the sheath 20, e.g. between two adjacent sheath sections or due to helical ribs or other formations provided on the outer surface 28 to mitigate rain/wind-induced vibrations, when the deicing device is displaced along the sheath 20.

[00052] The deicing device is displaced along the sheath 20 while the first bearing unit 42 is in the rest position (Fig. 4). Then, the shoe 31 of the first bearing unit 42 under the stay cable is not pressed onto the sheath 20, due to the weight of the deicing device.

[00053] The deicing device may be connected to a displacement system 70 for moving it along the longitudinal direction of the sheath 20.

[00054] In the example shown in Fig. 5, the displacement system comprises a rope 70 connected to the high and the low ends of the base 32 of the first bearing unit 42. The rope is used for pulling the deicing device along the sheath 20. It is connected to a pulling system located in the vicinity of the anchoring devices 16, 18 of the cable 10.

[00055] In the case of a cable- stayed bridge, the pulling system may comprise one or more winches with a capacity between 50 and 500 kg, which are installed at the bottom of the cable 10 on the deck, and at the head of cable on or in the pylon. Alternatively, the pulling system is mounted on the deicing device. For example, the hoisting system comprises wheels driven by a motor and engaging a rope 70 serving as a guide and support for the displacement of the deicing device along the sheath.

[00056] Alternatively, the displacement system may be part of a vehicle on which the deicing device is mounted (Fig. 6). A motor 71 on the vehicle is then used to drive wheels or rollers 72 contacting the outer surface 28 of the sheath 20, in order to move the deicing unit up or down along the stay cable. The wheels or rollers 72 may be provided with a lining/covering made of soft material to have both a sufficient grip onto sheath surface 28 and to avoid damaging the sheath when the vehicle is rolling onto it. The soft material may be for example an elastomeric material such as polyurethane. [00057] In another embodiment, displacement of the deicing device includes separating the frame 60 from the cable 10 and taking it to another location along the sheath 20 when it is necessary to change the position of the deicing device.

[00058] One stay cable may be equipped with more than one deicing devices distributed along the longitudinal direction of the sheath 20. For example, the deicing devices may be spaced from each other in a range of 10 m to 50 m.

[00059] A method for deicing a sheath 20 as disclosed herein uses the above-described deicing device. It comprises placing the deicing device around the sheath 20 and powering the actuator 37 and/or 39 to compress the sheath 20.

[00060] At a first position along the stay cable where deicing is performed, the mechanism 37 of the second bearing unit 34 is used to push the shoe 35 in the direction Y perpendicular to the outer surface 28 of the sheath 20, i.e. to bring the second bearing unit 34 from the rest position to the bearing position. This causes the frame 60 to be lifted and the shoe 31 of the other bearing unit to be applied against the lower part of the outer surface 28 of the sheath 20. It also applies a first compression effort across the section of the sheath 20.

[00061] In the case of a vehicle with a displacement system provided with drive wheels or rollers 72, the first and the second bearing units 34, 42 may be at a distance of the outer surface 28 when in rest position. The bearing units 34, 42 are then coming into contact with the sheath 20 when the mechanism 37 is activated.

[00062] Then, the vibrator 39 of the first bearing unit 42 can be powered to generate vibrations. The vibrations may be generated during 1 to 15 seconds in the frequency range of 50 to 5000 Hz. This causes the release of the ice accumulated on the sheath over an estimated length of 20 cm to 2 m, depending on the thickness and the stiffness of the ice.

[00063] Then the mechanism 37 of the second bearing unit 34 is deactivated to bring it into the rest position, and the displacement system is activated to pull the deicing device along the cable 10 to a second position where the deicing device will be used in the same manner. The stroke of the mechanism 37 (or the flexibility given to the drive wheels or rollers axles) allows sufficient clearance to accommodate some thickness of ice on the outer surface of the sheath when the deicing device is moved. If the ice layer is too thick, the deicing device can be brought up to a second position that is the position where it becomes an obstacle. At such position, the deicing device is powered again in order to locally shake the ice off the sheath 20. Then the operator can proceed to move the deicing device to successive position where it is powered.

[00064] All these actions are conveniently controlled by using a remote controller so as to avoid the use of lifting systems or cranes. The remote controller can be combined with an automated and/or smart system provided with sensors and a computer to generate instructions for the deicing device.

[00065] It will be appreciated that the embodiments described above are illustrative of the invention disclosed herein and that various modifications can be made without departing from the scope as defined in the appended claims.