Patent Publication Number: US-2023142377-A1

Title: Cable bending limiting arrangement and combination of a cable bending limiting arrangement with a cable, an anchorage, a compacting clamp unit and a recess pipe

Description:
The invention relates to a cable bending limiting arrangement for an anchoring unit comprising an anchorage, a cable including a plurality of wires and/or strands extending in a tensioned manner from the anchorage, a compacting clamp unit adapted and intended for compacting the wires and/or strands to a side-by-side arrangement and located at a predetermined distance from the anchorage, and a recess pipe surrounding the cable in at least a portion of the predetermined distance. 
     Such cables may, for example, be used for suspending and/or supporting structural units of super-ordinate structures, e.g. buildings, towers, bridges, and the like. 
     A well-known, but in no way limiting example of a cable in connection with which the cable bending limiting arrangement according to the present invention may be used is a stay cable, e.g. used for suspending the deck of a cable stayed bridge. In this case, the cable extends between a lower anchorage located close to the bridge deck and an upper anchorage located close to the top of a pylon suspending the bridge deck via the stay cables. The cable usually comprises a plurality of strands, each strand typically including seven steel wires, namely a central wire and six outer wires helically twisted around the central wire, covered in a plastic tube, e.g. made from HDPE (high density polyethylene). Conventionally, the strands of the cable widen from the compacting clamp unit towards the anchorage, as each of the strands is individually fixed to the anchorage. 
     In use, the cables are subject to movements, in particular lateral movements, namely dynamic movements, e.g. induced by wind and rain, vibrations of the bridge deck due to heavy traffic, earth quakes and the like, and quasi-stationary movements, e.g. induced by temperature, a traffic jam on the bridge, the exchange of a neighboring stay cable and the like. As a consequence of such lateral movements, bending stress of the strands occurs near the anchorage, which in the worst case may result in damage, e.g. wire rupture, of the strands. 
     In order to reduce the amplitude of dynamic lateral movements, i.e. the bending angle of the strands, and thus the bending stress acting on the cables, it has been suggested to laterally attach a damping device to the cable. Usually such damping devices are located at a distance from the anchorage which corresponds to between 2% and 3% of the overall length of the stay cable. However, it turned out that nevertheless the bending angle of the strands may exceed a critical value beyond which it becomes relevant to the design, such that the steel cross section of the wires had to be increased. 
     In order to avoid excessive bending angles at the anchorage, it has further been suggested to arrange so-called cable guide constructions at a certain distance from the anchorage. In this case, however, the damping devices had to be placed far away from the anchorage to be effective which in particular unnecessarily increased their size resulting i.a. in increased costs and a deteriorated appearance of the stay cables, which are often used by architects as design elements. 
     In view of the above, it is the object of the present invention to provide a solution to the afore-discussed problems. 
     According to the present invention, the cable bending limiting arrangement comprises a cable bending limiting device adapted and intended for being located axially inside the recess pipe and radially between an outer surface of the cable and an inner surface of the recess pipe leaving an annular gap of a predetermined radial width if the longitudinal axis of the cable extends substantially orthogonal to the anchorage. 
     Based on this design, the cable may move in the lateral direction, as long as the bending angle doesn&#39;t exceed a predetermined value defined by the predetermined radial width of the annular gap. As soon as the cable bending limiting device enters into contact with both, the cable and the recess pipe, the bending of the cable strands at the anchorage is stopped, and a second bending location is created at a distance from the anchorage resulting in a local distribution of the bending stress. Furthermore, as the recess pipe doesn&#39;t extend up to the compacting clamp unit, and as the cable bending limiting device is located inside the recess pipe, the strands of the cable are not fully compacted at the location of the cable bending limiting device and may be elastically deflected, thus further reducing the pressure exerted on the individual strands. 
     In this context, it should be noted that the damping effect of the damping device is decreased as soon as the stay cable enters into contact with the cable bending limiting device, as the damping effective length in this case is determined by the distance between the location of the damping device and the contact point. In practice, however, this effect occurs only in extreme situations, e.g. the exchange of a neighboring stay cable as an example of an extreme quasi-stationary situation or an earth-quake as an example of an extreme dynamic situation, or in situations of accumulated quasi-stationary and/or dynamic effects. 
     In view of the load-bearing capacity of the strands it is suggested that said predetermined radial width corresponds to a bending angle of not more than 40 mrad, preferably not more than 25 mrad. Based on a recess pipe having a length of 4 m, the predetermined radial width should amount to not more than 160 mm, preferably not more than 100 mm, as beyond these values, the steel cross-section of the strand wires would have to be increased. 
     According to a further embodiment, the cable bending limiting device may have a substantially cylindrical surface on its radially outer surface and a surface of a predetermined maximum curvature at its radially inner surface. In this embodiment, the surface of predetermined maximum curvature, i.e. predetermined minimum radius, allows to further limit the bending stress exerted on the strands. Advantageously, the radius of the predetermined curvature may amount to at least 2 m, preferably to at least 4 m, even more preferably to at least 4.3 m. 
     Although it is in principle also conceivable to attach the cable bending limiting device to the cable, it is suggested that the cable bending limiting device is attached to the inner surface of the recess pipe, as this alternative may easily be put into practice. In other words, the cable bending limiting device may be formed as a ring element having an outer diameter substantially equal to the inner diameter of the recess pipe. 
     In order to enhance the local distribution of the bending stress, it is further suggested that the cable bending limiting device is located closer to the free end of the recess pipe than to the opposite end thereof, preferably adjacent to the free end of the recess pipe. 
     According to a further embodiment of the invention, the cable bending limiting device may be made from polyethylene, e.g. HDPE, or a rubber material, e.g. chloroprene rubber, and/or the material of the cable bending limiting device may have an elasticity modulus of at least 700 MPa or a hardness of at least 60° Shore A, respectively, in order not to jeopardize the limitation of the bending stress due to compression of the cable bending limiting device. 
     In order to limit lateral movement of the cable, the cable bending limiting device may further include a damping device adapted and intended for damping lateral movement of the cable and adapted for being laterally attached to the cable. 
     According to an advantageous embodiment, the damping device may include a fluidic, preferably hydraulic, damper or friction damper or rubber damper. 
     In order to limit the size of the damping device, one end thereof may be connected to the compacting clamp unit 
     Although the other end of the damping device may be connected to the super-ordinate structure, e.g. the bridge deck of a cable stayed bridge, it may be advantageous, if the respective other end of the damping device is connected to a transition pipe which in turn is connected to the recess pipe. As the recess pipe and thus also the transition pipe is rigidly connected to the super-ordinate structure, the damping device may be of limited size. 
     According to a further aspect, the invention relates to a combination of a cable bending limiting arrangement according to the afore-discussed first aspect with a cable, an anchorage, a compacting clamp unit and a recess pipe. With respect to further embodiments of this combination and the technical effects which may be used when using this combination, it is referred to the above discussion of the cable bending limiting arrangement. 
    
    
     
       In the following, the present invention will be explained in more detail referring to the attached drawing, in which 
         FIG.  1    shows a schematic sectional side view of a cable bending limiting arrangement according to the present invention in cooperation with a cable and other components of an anchoring arrangement; 
         FIG.  2    shows an enlarged sectional view of the anchoring section of the anchoring arrangement; and 
         FIGS.  3  and  4    show enlarged sectional views of the cable bending limiting arrangement according to the present invention in a neutral state ( FIG.  3   ) and in a state, in which it becomes active by being in contact with both, the cable and the recess pipe ( FIG.  4   ). 
     
    
    
     In  FIG.  1    an anchoring arrangement is generally designated by reference to numeral  100 . In the embodiment shown in  FIG.  1   , the anchoring arrangement  100  serves for anchoring a stay cable  102  of a cable stayed bridge to a merely schematically indicated bridge deck  104  of the cable stayed bridge via an anchorage  106  abutting against an anchor plate  104   a  of the bridge deck  104 . 
     The stay cable  102  comprises a plurality of strands  108  which, as may be seen in more detail from  FIG.  2   , are individually fixed to an anchor block  110  of the anchorage  106  by means of conical wedges  112 . A ring nut  114  is screwed onto the anchor block  110  and is pressed against the anchor plate  104   a  by the tension of the stay cable  102 . Furthermore, a watertight and adjustable sealing unit  116  is provided which interacts with the sheathing  108   a  surrounding the wires  108   b  of the strands  108  up to the wedges  112 . With respect to the constructional and functional details of the anchorage  106  reference is made to US 2016/0168855 A1 filed by the present applicant and relating to such an anchorage. The disclosure of US 2016/0168855 A1 relating to the design of the anchorage is hereby incorporated in to the present application by way of reference. 
     Referring back to  FIG.  1   , the strands  108  of the stay cable  102  are bundled together by a compacting clamp unit  118  in order provide a minimum cross-section to environmental forces, such as wind and rain induced forces. Seen from another perspective, the strands widen from the compacting clamp unit  118  towards the anchorage  106  in order to allow their individual fixation to the anchor block  110 . The compacting clamp unit  118  is located at a predetermined distance d from the anchor block  110  in order not to exert too much bending stress onto the strands  108 . Of course, the bending stress focusses at the anchor block  110 , and in particular at the location of the conical wedges  112 , while at least some bending stress is relieved by the design of the sealing unit  116 . 
     In order to protect the stay cable  102  from external influences, it is surrounded by a recess pipe  120  and a transition pipe  122 . While the recess pipe  120  is embedded in the concrete of the bridge deck  104  close to the anchor plate  104   a  (see  FIG.  2   ), and thus is rigidly connected to the bridge deck  104 , the transition pipe  122  is releasably connected to the recess pipe  120 . In order to allow attaching the compaction clamp unit  118  to the stay cable  102 , the recess pipe  120  has a length l 1  which is smaller than the predetermined distance d, while the transition pipe  122  has a length l 2  which in combination with the length of the recess pipe  120  allows to cover the compaction clamp unit  118 . 
     As already mentioned at the outset, the stay cables  102  are subject to movements, in particular lateral movements, namely dynamic movements, e.g. induced by wind and rain, vibrations of the bridge deck due to heavy traffic, earth quakes and the like, and quasi-stationary movements, e.g. induced by temperature, a traffic jam on the bridge, the exchange of a neighboring stay cable and the like. As a consequence of such lateral movements, dynamic bending stress of the strands  108  of the stay cables  102  occurs near the anchorage  106 , and in particular close to the conical wedges  112 . 
     For reducing the amplitude of such lateral movements, i.e. the bending angle of the strands  108 , and thus the bending stress exerted on the cables  102 , a damping device  124  is laterally attached to the stay cable  102 . One end of the damping device  124  is connected to the compacting clamp unit  118  while the respective other ends thereof is connected to the bridge deck  104 . The damping device  124  may, for example, include a hydraulic damper. 
     As a further measure for reducing the bending stress exerted on the strands  108 , a cable bending limiting device  130  is provided inside the recess pipe  120 , advantageously adjacent to the free end  120   a  thereof. 
     According to the embodiment shown in  FIGS.  1 ,  3  and  4   , the cable bending limiting device  130  may be formed by a ring element having an outer diameter substantially equal to the inner diameter of the recess pipe  120 . Advantageously, the ring element  130  has a cylindrical surface  130   a  on its radially outer side and a curved surface  130   b  of a predetermined maximum curvature at its radially inner side. In particular, the surface of predetermined maximum curvature, i.e. predetermined minimum radius, allows to further limit the bending stress exerted on the strands. Advantageously, the radius R (see  FIG.  3   ) of the predetermined curvature may amount to at least 2 m, preferably to at least 3.5 m, even more preferably to at least 4.3 m. 
     As may be seen from  FIG.  3   , an annular gap  132  having a radial width w exists between the cable bending limiting device  130  and the strands  108  of the stay cable  102 , if the central axis A of the stay cable  102  is in alignment with the central axis B of the anchorage  106 . However, the central axis A of the stay cable  102  may be deflected from this aligned state due to environmental forces. Due to the spacing between the cable bending limiting device  130  and the strands  108  of the stay cable  102 , the stay cable  102  may freely move in the lateral direction, as long as its bending angle doesn&#39;t exceed a predetermined threshold angle. In this context, the term “freely” refers to the fact that there is no contact between the cable bending limiting device  130  and the strands  108  of the stay cable  102 , while taking the action of the damping device  124  into account. 
     As soon as the stay cable  102  abuts against the cable bending limiting device  130  (see  FIG.  4   ), the bending of the strands  108  at the anchorage  106  is stopped, and a second bending location is created at the contact point/area with the cable bending limiting device  130  resulting in a local distribution of the bending stress. Furthermore, the radius R of the curved surface  130   b  makes sure that the bending stress exerted on the strands  108  by the cable bending limiting device  130  doesn&#39;t exceed their respective design limit. 
     As a consequence, the cable bending limiting device  130  according to the present invention reliably prevents the stay cable  102  or its strands  108 , respectively, from being subjected to excessive bending stress.