Patent Publication Number: US-2022220669-A1

Title: A deicing device for a sheath of a structural cable and a method for deicing a structural cable

Description:
The present invention relates to a deicing device for a sheath of a structural cable. The present invention also relates to a method for deicing a sheath with such a deicing device. 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 
     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. 
     A typical stay cable includes a bundle of tendons, for example wires or strands, housed in a collective sheath. The sheath is intended to protect the metallic tendons of the bundle. 
     By design, the sheath is destined to be in contact with the surrounding environment. As such, it is susceptible to the formation of frost, rime, ice or snow thereon. 
     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. 
     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. 
     Another approach is known from document 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. 
     Document WO 2018/142174 A discloses a sheath with a cavity that may receive a vibration module to break superficial ice or frost deposits. 
     In addition, document U.S. Pat. No. 10,113,278 B1 discloses a module for deicing a cable sheath with a mass and a vibrator. This solution causes vibrations along the cable that removes the ice or snow covering the cable. However, the vibrating mass may hit the tendons of the cable and damage them. Also, such solution requires a lot of power. 
     SUMMARY 
     An object of the present invention is to propose a deicing device for a sheath of a structural cable 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 sheath of a structural cable, the structural cable comprising tendons housed in the sheath, the deicing device comprising a base, a bearing element, and a power system configured to press the bearing element against the tendons while the base is in contact with an inner surface of the sheath. 
     It results that the deicing device is firmly supported on the tendons. In addition, the pressure exerted on the tendons causes a local deformation of the sheath which can then cause a temporary and reversible shape change of the section of the sheath which may lead of local detachment of the ice for ejection. 
     The deicing device thus prevents damage to the tendons by clamping the movements of the base before activation of the vibrator. Furthermore, the vibrations are transmitted optimally to the sheath through the base with low energy dissipation. 
     In an embodiment, the deicing device includes a power system is further configured to generate vibrations between the bearing element and the base. 
     In another embodiment, the bearing element is movable in a direction perpendicular to the inner surface of the sheath, with a stroke in a range of 3 to 75 mm. 
     The power system may comprise an actuator for the movement of the bearing element in the perpendicular direction, the actuator being fixed to the base and to the bearing element. 
     In another embodiment, the base has a convex surface facing the inner surface of the sheath, the convex surface having a curvature larger than a curvature of the inner surface of the sheath. 
     In another embodiment, the power system comprises a vibrator generating vibrations in a range of 50 to 5000 Hz. 
     In another aspect, there is proposed a structural cable comprising a sheath, tendons housed in the sheath, and at least one deicing device. 
     In another aspect, there is proposed a method for deicing a sheath of a structural cable of a construction work, the structural cable comprising tendons housed in the sheath. The method comprises inserting a deicing device within the sheath of the structural cable, the deicing device comprising a base and a bearing element, pressing the bearing element against the tendons while the base is in contact with an inner surface of the sheath. 
     Pressing the bearing element against the tendons may comprise moving the bearing element in a direction perpendicular to an inner surface of the sheath. 
     The method for deicing may also comprise generating vibrations in the deicing device during 1 to 15 seconds. 
     Pressing the bearing element against the tendons may comprise applying a pressure pulse by the bearing element. 
     The method for deicing may also comprise displacing the deicing device along the sheath, and pressing again the bearing element against the tendons while the base is in contact with an inner surface of the sheath at another position along the sheath. 
     When the method for deicing comprises displacing the deicing device along the sheath, and pressing again the bearing element against the tendons while the base is in contact with an inner surface of the sheath at another position along the sheath, the deicing device may be displaced over a distance greater than a length of the deicing device. 
    
    
     
       BRIEF DESCRIPTION THE DRAWINGS 
       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; 
         FIG. 3  is a cross-sectional view of the stay cable shown in  FIG. 2  and an example of a deicing device arranged within the stay cable, the bearing element being in a bearing position; 
         FIG. 4  is a view in a longitudinal cross-section of the stay cable and the deicing device shown in  FIG. 3 ; 
         FIG. 5  is the cross-sectional view of the  FIG. 3 , the bearing element being in a rest position; 
         FIG. 6  is a perspective view of the stay cable with a deicing device arranged within the bearing element being in a bearing position; 
         FIG. 7  is a cross-sectional view of the stay cable as in  FIG. 3  provided with another example of a deicing device; 
         FIG. 8  is the cross-sectional view of the  FIG. 7 , the bearing element being in a rest position. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a structural cable  10  that may be equipped with a sheath  20  according to the invention. 
     The cable  10  is, for example, a stay 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 . 
     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. 
     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. 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  28  facing the tendons  22 . The inner surface  28  may be circular like the cross-section of the sheath  20 . 
     The tendons  22  are arranged within the cavity  24  so that an interstitial space  26  is left accessible. The interstitial space  26  has a height H in range of 20 to 120 mm, for example of 30 to 100 mm. The interstitial space  26  extends within the sheath  20  and over the entire length of the sheath  20 . Since the tendons  22  normally support the sheath  20 , the interstitial space  26  is generally located below the tendons  22  within the sheath  20 . 
     The cable  10  may have a length of up to several hundred meters. The bundle may include a few tens of tendons  22 . 
     The sheath  20  is typically made of plastic material such as high-density polyethylene (HDPE). 
       FIGS. 3 and 4  show the deicing device  30 . The deicing device  30  acts locally from within the sheath  20  to remove the potentially accumulated ice, frost, rime or snow on its outer surface. Therefore, it should be understood the deicing device is not limited to remove ice: the word “deicing” is meant to cover the removal of any kind of frozen water. 
     The deicing device  30  is located in the interstitial space  26 , between the inner surface  28  of the sheath  20  and the bottom side of the tendons  22 . The deicing device has a length L 32  which is in a range of 50 to 500 mm, and preferably in a range of 50 to 300 mm. The deicing device  30  comprises a base  32 , a bearing element  34  and a power system  36 . 
     The base  32  is the support of the deicing device  30 . The base  32  is intended to lay on the inner surface  28  of the sheath  20 . The base  32  is for example a metal part. Typically, the base  32  has a convex surface  33  that is in contact with the inner surface  28  of the sheath  20 . The convex surface  33  faces the inner surface  28  of the sheath  20 . In other words, the convex surface  33  may be concave with respect to bearing element  34  side, while being convex with respect to the inner surface  28  of sheath  20  side. 
     The convex surface  33  has a curvature larger than the curvature of the inner surface  28 . In that way, the deicing device  20  is adapted to be displaced along the sheath  20 , on the inner surface  33 . More precisely, the base  32  is curvilinear and forms the convex surface  33 . The width of the base  32  is defined by the curvilinear length of the base  32 . The width of the base  32  depends on the height H of the interstitial space  26  available under the tendons  22 . The curvilinear length is as long as possible without blocking the movement of the base  32  along the sheath  20 , and to prevent the base  32  from turning over. 
     In addition, the base  32  may be connected to a displacement system. The displacement system may be a hoisting system connected to the high and the low ends of the base  32  and that can pull the deicing device  30  along the sheath  20 . The hoisting system may be located in the vicinity of the anchoring devices  16 ,  18  of the cable  10 . Alternatively, the hoisting system is directly integrated to the deicing device  30 . For example, the hoisting system comprises rollers surrounding a guiding rope/cable, the guiding rope serves as a guide and support for the displacement of the deicing device  30  along the sheath. The rollers may be motor-driven with motor integrated to the deicing device. In the case of a cable-stayed bridge, the hoisting system may comprise 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. In addition, the displacement system may comprise a guide wire provided along the sheath  20  and connected to the deicing device  30  to prevent the deicing device  30  from turning over in the interstitial space. 
     The bearing element  34  is intended to contact one or more tendons  22 . For example, the bearing element  34  is a shoe with an external surface  38 . The shoe is pressed against the tendons  22 . More precisely, the external surface  38  is in contact with the tendons  22 . The external surface  38  is for example made of plastic. In another example, the external surface  38  is made of rubber or any other material that can prevent damage to the tendons  22 . Actually, the bearing element  34 , when contacting tendons  22 , exerts a pressing force on the tendons  22  so that the deicing device  30  is firmly supported on the bundle of tendons  22 . By “pressing force” it should be understood that the bearing element  34  exerts on the tendons  22  a non-zero force (i.e. different from zero). For example, the force applied on the tendons is more than 10N, and preferably in a range of 100N to 10 kN. The applied force may be measured for example with a dynamometer integrated in the deicing device  30 . If the force applied is more than a threshold value corresponding to a sufficient pressing force applied on the tendons  22 , a vibrator  42  of the deicing device  30  may be activated. 
     The bearing element  34  is movable between a rest position ( FIG. 5 ) and a bearing position ( FIG. 3 ). In the rest position, the bearing element  34  does not contact or barely contacts the tendons  22 . In other words, in the rest position, the bearing element  34  does not exert a pressing force on the tendons  22 . In the bearing position, the bearing element  34  contacts tendons  22  and it exerts a pressing force on the tendons  22 . The movement of the bearing element  34  between the rest position and the bearing position is according a direction Y, the direction Y being perpendicular to the inner surface  28  of the sheath. The movement of the bearing element  34  is radial (and transversal) with respect to the longitudinal direction of the tendons  22  and the sheath  20 . More precisely, regarding the deicing device  30 , the bearing element  34  can move with respect to the base  32 , perpendicularly to the convex surface  33 . The bearing element  34  can thus move away and towards the base  32 . There is therefore a relative movement between the bearing element  34  and the base  32 . The movement of the bearing element  34  is actuated by the power system  36 , as detailed here below. 
     The power system  36  is configured to press the bearing element  34  against the tendons  22  while the base  32  is in contact with the inner surface  28  of the sheath  20 . In an embodiment, it is further configured to generate vibrations between the bearing element  34  and the base  32 . For this purpose, the power system  36  comprises an actuator  40  for the movement of the bearing element  34 . The actuator  40  may be for example a cylinder. The cylinder is preferably electric, or hydraulic or pneumatic. The actuator  40  may also be a scissor or pantograph mechanism, an elliptical cam rotated by a low speed motor or any other mechanical system causing a translation. 
     The stroke U of the actuator  40  is in a range of 3 to 75 mm, and preferably in a range of 5 to 30 mm. 
     The power system  36  may be powered by a remote power source at the end of the cable  10 . In that configuration, the power cable may be wound with the hoisting system, in the case where a hoisting system is provided. According to another embodiment, the power system  36  may be powered by a battery embedded in the deicing device  30 . In that case, the base  32  can hold the embedded circuitry for control and power supply. Alternatively, the deicing device  30  may be controlled by a remote control, for example from a control station next to the construction. 
     The actuator  40  is firmly attached to the bearing element  34  and the base  32 . The actuator  40  allows pressing the bearing element  34  against the tendons  22 . Since the base  32  is in contact with the sheath  20  the exerted pressure on the tendons  22  causes a local deformation of the sheath  20 . More precisely, the actuator  40  produces a radial force against the tendons  22 , preferably vertical, up to a slight deformation of the sheath  20 , which can then cause a temporary and reversible shape change of the circular section S 1  of the sheath  20  to a substantially elliptical or oval section S 2 , illustrated in  FIG. 6 . Given the difference in stiffness between the ice and the sheath  20 , some lamella of air can be created on the contacting surface between the cable and the ice, thereby the adhesion of ice on the cable is broken. Therefore, this deformation may be a first step of local detachment of the ice for ejection. 
     In addition, the actuator  40 , when the power system  36  comprises additionally a vibrator  42  (which will be detailed below), clamps the movements of the base  32  before activation of the vibrator  42  to prevent damage to the tendons  22  under the effect of movement of the base  32  under vibrations. The clamping of the base  32  and the bearing element  34  may be optimally obtained for example thanks to a dynamometer as detailed above. In this clamping position, the deicing device  30  and the sheath  20  contact each other with a high rigidity. In other words, the rigidity is controlled by the force applied on the tendons  22 . The vibrator  42  is thereby rigidly connected with the sheath  20 , allowing an optimal transmission of the vibrations to the snow, frost or ice which covers the cable through the base  32  and the sheath  20  with low energy dissipation. 
     The power system  36  may also comprise a vibrator  42 . The vibrator  42  generates vibrations, for example in a range of 50 to 5000 Hz, and preferably in a range of 100 to 1000 Hz. The vibrator  42  is for example an electromagnetic loudspeaker with a power of preferably between 50 and 500 W. The vibrator  42  may also be a piezoelectric element. In another example, the vibrator  42  is an eccentric or cam rotated at a speed in a range of 5000 to 35000 rpm, and preferably of 10000 rpm to 30000 rpm (i.e. 166 Hz to 500 Hz). 
     In addition, the assemblies of the vibrator  42  and the actuator  40  with the base  32  have a significant stiffness so as to minimize the energy dissipation during the activation of the vibrator. 
     The deicing device is not limited to the features detailed here above. Indeed, the deicing device may comprise others features, taken alone or in combination:
         the base  32  may comprise a plurality of supporting points along its length L 32 , i.e. the base  32  contacts the inner surface  28  of the sheath  20  by these supporting points;   the deicing device  30  may comprise a plurality of bases  32 , and a bearing element  34 ;   the deicing device  30  may comprise a plurality of bearing elements  34 , and a base  32 ;   the deicing device may comprise a plurality of power system  36 .       

     In addition, the deicing device may be connected to other deicing devices aligned along a longitudinal direction of the sheath  20 , i.e. aligned behind each other along the longitudinal direction of the sheath  20 . In another example, the deicing devices may be arranged in the interstitial space  26 , but each deicing device having a different radial position. 
       FIGS. 7 and 8  illustrate another example of the deicing device  30 . In this example, the bearing element  34  differs from the one of the deicing device  30  previously described. Indeed, in this configuration, the base  32  and the bearing element  34  are identical: so as the base  32 , the bearing element  34  as a curvilinear shape that allows to the base  32  and the bearing element  34  to be indifferently placed against the inner surface  28  or the tendons  22 . Preferably, the bearing element  34  and the base  32  are made in the same material, such as plastic, for example polyamide. Therefore, the deicing device  30  can be placed within the interstitial space  26  without having to match the base  32  on the inner surface  28  and the bearing element  34  on the tendons  22 . In this configuration, the bearing element  34  and the base  32  can be defined as such only relative to the position of the deicing device  30  in the interstitial space  26 . 
     In the following description, a method for deicing a sheath  20  is described. The method uses the above-described deicing device  30 . In an embodiment, it comprises the following steps:
         inserting the deicing device  30  within the sheath  20  of the structural cable  10 ;   bringing the deicing device  30  at a first required position along cable  10  and sheath  20 ;   pressing the bearing element  34  against the tendons  22  while the base  32  is in contact with the inner surface  28  of the sheath  20 . The pressing step can be done by moving the bearing element  34  in the direction Y, for example by applying a pressure to the bearing element  34 ;   alternatively, generating vibrations in the deicing device  30  during 1 to 15 seconds;   releasing the pressure applied on the tendons  22 ;   displacing the deicing device  30  along the sheath  20 , for example over a distance greater than the length L 32  of the deicing device  30 ; and   pressing again the bearing element  34  against the tendons  22  at another position along the sheath  20 .       

     Alternatively, while the bearing element  34  is pressed against the tendons  22 , the method comprises applying a pressure pulse by the bearing element  34 . The pressure pulse is applied as a pressure force variation, possibly fast, to be transmitted to the ice or snow covering the cable sheath, useful for example in a first step of local detachment of the ice for ejection. The pressure pulse is actually a variation of the pressing force on the tendons  22 . The pressing force is therefore always above the threshold value corresponding to a sufficient pressing force applied on the tendons  22 , so that the power system  36  permanently presses the bearing element  34  against the tendons  22 . For example, the pressing force minimum value is above 10N, and its maximum value remains within the range of 100N to 10 kN. In addition, one or more pressure pulse may be applied to the cable while the bearing element  34  is pressed against the tendons  22 . 
     For example, the method consists of first placing the deicing device  30  at one position along the sheath  20 . More precisely, the deicing device is placed in the interstitial space  26  of the sheath  20 , for example apart from the tendons  22 , with the base  32  of the deicing device  30  laying on the inner surface  28  of the sheath  20 . In an inactive state of the device  30 , the bearing element  34  is in a rest position. When deicing (or the removing of snow, frost or rime) is needed, the deicing device  30  is activated. Beforehand, when the deicing device is not in the appropriate location for the deicing action, the deicing device  30  is displaced along the inner surface  28  of the sheath  20 . By its activation, the actuator  40  moves the bearing element  32  in the perpendicular direction Y, from the base  32  to the tendons  22 . The bearing element  34  is thus pressed against the tendons  22  while the base  32  is in contact with the inner surface  28  of the sheath  20 . The bearing element  32  is therefore in the bearing position. The actuator  40  thus presses the bearing element  34  against the tendons  22  such that the deicing device  30  is firmly maintained against the sheath  20  and the tendons  22 . 
     Once the deicing device  30  is placed between the tendons  22  and the inner surface  28  of the sheath  20  (and therefore while the bearing element  34  presses the tendons  22 ), the vibrator  42  may be activated for a few seconds, for example 1 to 15 seconds, and preferably 1 to 10 seconds. Activation of the vibrator  42  results in fragmentation of the ice over a length of 20 cm to 200 cm of the sheath  20  and up to several meters, for instance 5 meters. 
     To cover the entire length of the sheath  20 , the deicing device  30  may be moved step by step along the sheath  20  via the displacement system preferably automated and remotely controllable. Before moving the deicing device  30  along the sheath  20 , the actuator  40  stops the pressure of the bearing element  34  against the tendons  22  by moving the bearing element  32  in the perpendicular direction Y, from the tendons  22  to the base  32 . The bearing element  32  is therefore back in the rest position. The deicing device  30  is then moved in another place along the sheath  20  where deicing is needed. 
     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.