Abstract:
The device has two supports ( 15, 16 ) which can be moved in relation to each other in a transverse direction to the axis ( 2 ) of the traction element ( 1 ). Several clamping jaws ( 19, 20 ) are displaceably mounted in pairs opposite each other on said supports. The clamping jaws ( 19, 20 ) have surfaces which grasp the traction element ( 1 ). When strain is placed on the traction element, the clamping jaws are displaced linearly at increasing distances except for the rear pair, in such a way that the clamping force can be evenly distributed over a great length, despite the extension of the traction element ( 1 ). This allows, for example, steel cables with a high traction force to be tensioned without damaging the cable.

Description:
The present application is the national stage under 35 U.S.C. §371 of International Appln. PCT/CH00/00177 which designated the United States, and was not published in English. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The invention is directed to a device for fixing, tensioning or pulling an extendable traction element, in particular a cable. 
     2. Prior Art 
     Besides grouting heads, clamp heads and bollards, for end fixtures or intermediate fixtures of steel cables also so-called cable clamps are used. The necessary gripping force is produced by clamp jaws which are pressed against the cable with e.g. bolts, springs or wedges. This solution is suitable for relatively small forces where the cable elongation over the clamp length during the tension build-up is negligible. For the tensioning of thicker cables with elevated traction forces, however, the clamps known at present are less suitable, as they can damage the cable and harbour some uncertainties in the frictional force transmission. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to provide a device with which extensible traction elements can be tensioned, fastened and pulled without damage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following figures an embodiment of the invention is shown: 
     FIG. 1 a side view of the device according to the invention, 
     FIG. 2 is a cross-section along section A—A of FIG. 1, 
     FIG. 3 is a cross section through a second embodiment and 
     FIG. 4 is a detail of the stroke limitation of the jaws. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The device serves to fix, tension or pull a longitudinally elastic or extensible traction element. A favoured field of application is the tensioning of steel cables for suspended structures, e.g. for suspended large-area roofs. Here the tensioned length of the cable plays a great role in its function and form stability. New cables have the unfortunate tendency to grow in length during the first few weeks of being put under load. The unpleasant result of this elongation is that after being put into service the freshly built suspended structure must be closed again for a few weeks in order to re-tension the cables. 
     This shut-down shortly after opening a plant, and subsequently also when installing cables in need of periodic renewal, is of course inconvenient for the operators of such plants. Under some circumstances a re-tensioning is no longer possible after installation. Similar problems arise with the carrier cables of suspended bridges and suspended railways, where cables must likewise be re-tensioned, shifted and periodically renewed. Also, other traction elements such as tie-rods, belts or plastic ropes are difficult to tension for high loads without damaging them. 
     On applying the tractive force using clamping jaws, the traction element slips, starting from the tractive side of the traction element, as the frictional adhesion is overcome, until it grips over the whole length of the clamping jaw. In practice, however, it is not determinable how much force is transmitted per unit length. If the clamping jaw material is hard, at least the surface of the traction elements will be damaged. If the material is soft, it will be rubbed off at least on the side facing the drawn cable. 
     The embodiment described hereinafter avoids these deficiencies. Acting on a steel cable  1  with axis  2  is a tractive force in the axial direction Z. The cable is clamped in the device  10 . The device  10  has a frame  11  with two frame parts  12 ,  13  arranged symmetrically about the axis  2 . The components  12 ,  13  have mutually facing wedge surfaces  14  converging in the direction of traction Z. Sliding on the surfaces  14  are two mutually opposing wedges  15 ,  16 . These save rectilinear mutually facing slide surfaces  17 ,  18 , e.g. in the form of dovetail guideways, on each of which a row of clamping jaws  19 ,  20  are displaceably located. Except for the rearmost jaw pair viewed in the direction of traction Z, the clamping jaws are displaceable out of their basic position shown in FIG. 1 by an amount limited by stops  21  formed on slide surfaces  17 ,  18  in the direction of traction Z. The possible amount of displacement  22  of the jaws  19 ,  20  out of their basic position increases linearly in the direction of traction Z. It is adjustable in order to adapt the device  10  to cables  1  of different moduli of elasticity (for steel cables between about 70,000 and 160,000 N/mm2). The jaws  19 ,  20  all have the same length. They are attached interchangeably on the slide surfaces  17 ,  18  in order to adapt the device  10  to other cross-sections of the cable  1  or other traction elements. The jaws  19  are restored to their basic position by springs  23 . 
     Fitted to the frame  11  are two hydraulic cylinders  29 ,  30 , the pistons  31  of which are attached to the wedges  15 ,  16  and actuate these latter. 
     Two further hydraulic cylinders  33 ,  34  anchored in a foundation  32  pull the frame  11  in the opposite direction to the traction Z via non-depicted drawbars and transverse bolts  35 , which latter are stuck through the components  12 ,  13 . 
     As shown in FIG. 2, the two frame components  12 ,  13  are pivotably connected together on one side of the cable only. In the simplified representation the connection is via connecting parts  42 ,  43  fixed to the components  12 ,  13  and a shaft  44 , the axis  45  of which intersects the axis  2  at right angles roughly in the longitudinal center of the row of jaws  19 ,  20 . 
     It is thus achieved that under linearly increasing elongation of the cable  1  in the direction of traction Z and hence approximately linear reduction in cable diameter, the same radial force nevertheless acts on the cable  1  over the entire length of the row of jaws  19 ,  20 . This effect can, however, also be approximately achieved without pivot action, but instead with relatively long strain bolts which press the components  12 ,  13  towards each other. 
     The clamping jaws  19 ,  20  have semi-cylindrical recesses with inserts  46  of a material which is softer than the traction element to be tensioned or fastened. For steel cables  1 , suitable “soft”materials for the inserts  46  are e.g. bearing metal, tin, plastic etc. With the contact pressure between clamping jaw  19 ,  20  and the cable  1  equal to that between the jaw  19 ,  20  and slide surface  17 ,  18 , the adhesion between the jaw  19 ,  20  and the cable  1  is greater than that between the jaw  19 ,  20  and slide surface  17 ,  18 . Depending on the nature of the surface of traction element  1  and the material selected for the inserts  46 , “adhesion” means either a frictional grip (smooth cable surface) or an at least partial positive grip (rough surface with impressions in the inserts  46 ). 
     To apply tension, the cable  1  is placed between the jaw pairs  19 ,  20  from the side, and the wedges  15 ,  16  applied via the cylinders  29 ,  30 . Then the cylinders  33 ,  34  are actuated. The rearmost, fixed, jaw pair  19 ,  20  relative to the direction of traction Z, pull (together with the other jaws) the cable  1  up to the limit of their frictional adhesion with the slide surfaces  17 ,  18 , thereby elongating the cable  1 . Due to the elongation increasing from the rear to the front, the front clamping jaws  19 ,  20  slip first and then immediately afterwards the others. The graduation of the stroke limits  22  is designed such that all jaws  19 ,  20  bear against their stops  21  when the specified tensioning force for the cable  1  has been attained via the cylinders  33 ,  34 . Thereby the very strong force to be applied especially to thick cables can be transmitted to the cable over a great length in spite of the cable elongation, which due to the damage to the cable caused by slip or crushing was as yet not possible with conventional tensioning clamp devices. 
     This offers the opportunity e.g. to pre-stretch steel cables for suspended structures prior to installation, so that shut-downs for re-tensioning shortly after installation can be largely avoided. When the device  10  is employed for fixing a traction element  1 , the tensioning cylinders  33 ,  34  can be omitted and the frame  11  anchored directly. The cylinders  29 ,  30  are only needed for installation purposes in this case. The device is also suitable for the continuous dragging of extensible traction elements  1  by rigging two of these devices  10  one behind the other and performing intermittent drag steps alternating. 
     The abutments or stops  21  of the displacements of the clamping jaws  19 ,  20  in the direction of traction Z is not absolutely necessary, but convenient, so that when the diameter of the cable  1  varies along the clamped length the tractive force is nevertheless roughly evenly distributed over the clamped length. 
     Instead of via the wedge surfaces  14 , the radial pressing of the supports  15 ,  16  can also be applied via cylinders arranged radially to the axis  2 , or via a parallelogram linkage, the dead point of which is close to the maximum clamped length of the cable  1 . Like the wedges  15 ,  16 , such parallelogram linkages can also be connected together on components  12 ,  13 , which are pivotable relative to each other about the axis  45 . The pivot facility about the axis  45  is not absolutely necessary, however. If, e.g. a pre-loading via stain bolts acts on the components  12 ,  13 , the pre-elongation of the bolts (several mm) is quite adequate to compensate for the diameter reduction of the cable  1 , in order to attain a uniform force distribution. 
     FIG. 3 shows the embodiment in which the two frame components  12 + 13  are not pivotable, but are rigidly connected together by strain bolts  50 . The strain bolts  50  bear on plates  52 , which are held apart by a row of rectangular.pipes  53 . The strain bolts  50  are located immediately alongside the side wall  54  of the pipes  53  directed towards the axis  2 . Due to the eccentric loading of the pipes  53  by the strain bolts  50 , the pipes bend slightly. When the cable is tensioned, the frame components  12 ,  13  are forced apart by the wedges  15 ,  16 . Due to the elastic pre-elongation of the strain bolts  50 , which amounts to several times the difference between the diameter of the cable  1  in its tensioned and non-tensioned states, the radial pressure of the jaws  19 ,  20  on the cable  1  is distributed roughly evenly over the whole clamping length in spite of the diameter diminishing with increasing tensile stress. 
     FIG. 4 depicts diagrammatically along section IV—IV of FIG. 3 a device for the automatic adjustment of the stops  21  for the displacement of the clamping jaws  19 ,  20 . The wedge (or support)  15  is omitted in FIG. 4 for reasons of clarity. Firmly bolted to the foremost clamping jaw  19   a  with reference to the direction of traction Z is a control rod  58 . The rearmost jaws  19 ,  20  (or the last two or three rear jaws) are attached rigidly to the wedges  15 ,  16 . At every jaw  19  except the rearmost and foremost a triangular control piece  59  projects from the control rod  58  towards the axis  2 . As shown in FIG. 4, the wedge angles α of the control pieces  59   b ,  59   c  diminish with increasing distance from the front jaw  19   a . Abutting against the two flanks  60  of the control pieces  59   b ,  59   c  is one stop piece  61   b ,  61   c  each. The stop pieces  61   b ,  61   c  abut against surfaces  62  of stops  63  rigidly connected to the relevant wedge  15 . The surfaces  62  are perpendicular to the axis  2 . On the side of every stop piece  61   b ,  61   c  opposite the flanks  60  and inclined to the axis  2  is a wedge-shaped surface  64 , which mates with a corresponding counterpart surface  65  of the relevant jaw  19   b ,  19   c . By way of non-depicted springs, the control rod  58  is pre-loaded counter to the direction of traction Z to the basic position shown in FIG. 4, in which the stop pieces  61   b ,  61   c  bear with their front and rear faces against the flanks  60 , the surface  62  and the counterpart surface  65 . 
     When the cable  1  is now pulled in the direction Z, the foremost jaw  19  a moves further away from the rearmost jaw  19  n due to the cable elongation, taking the rod  58  with it. The control pieces  59   b ,  59   c  thereby move away from the stop pieces  61   b ,  61   c . Since the following jaws  19   b  and  19   c  are likewise put under load by tension Z, they push via the wedge surfaces  65  the opposing stop pieces  61   b ,  61   c  towards each other until they once more rest against control pieces  59   b ,  59   c  . As the wedge angle α diminishes with increasing distance from the foremost jaw  19   a , the displacement of the stop pieces  61   b ,  61   c  towards each other also diminishes with increasing distance. The angles ax are so selected that the displacement stroke limited by stops  21  is subject to a linear increase starting from the rearmost jaw pair  19   n . On relieving the tension on the cable  1 , the spring pulls the control rod  58  back to the basic position, and the control pieces  59   b ,  59   c  drive the opposing stop pieces  61  apart again into the basic positions accordingly. The chief advantage of the automatic stop setting described is that a uniform traction force distribution among the individual jaw pairs is achieved without having to previously determine the modulus of elasticity of the cable  1 . The same device can be employed for various kinds of cable without modification.