Abstract:
A bridge for crossing a passage of a navigation channel includes a section in the form of a single span, which may be displaced by vertical translation between a base position spanning the passage, in which the span rests on fixed support sections of the bridge, and a raised position, for opening the passage, and a support structure for the span on displacement of the span, and a drive for lifting the span. The bridge has only one support structure, with the drive, located on one side of the passage to be spanned.

Description:
FIELD OF INVENTION 
   The invention relates to a bridge intended in particular for crossing a channel of a waterway and having a part in the form of a span, which can be moved by vertical translation between a low position for crossing the channel, in which the span rests on stationary support parts of the bridge, and a high position for opening the channel, and a support structure for the span during its movement as well as some means for lifting the span. 
   BACKGROUND 
   Bridges of this type that are known have the major disadvantage of having a complex structure requiring much space, inasmuch as they have, on each side of the channel, a support structure that requires extensive installation work particularly when the structure is in the water, and that must be equipped with lifting means that must be powered and perfectly coordinated, which requires sophistication in the design of these means. 
   SUMMARY OF THE INVENTION 
   The present invention provides a bridge that does not have the disadvantages just set forth. 
   To attain this aim, a bridge according to the invention has only one support structure, provided with lifting means, which is arranged on just one side of the channel to be crossed. 
   According to one characteristic of the invention, the lifting means entails a traction cable, one end of which is attached to the span and the other end of which is connected to a traction device, running over pulleys that are part of the support structure. 
   According to another characteristic of the invention, the two lifting cables are attached to each side of the span and run over a pulley mounted on the support structure in a vertical plane passing through the middle of the span. 
   According to yet another characteristic of the invention, the support structure has two girder support pylons each provided at its free end with a pulley over which cables for lifting the span run. 
   According to yet another characteristic of the invention, the pylons and the girders are provided with reinforcement elements such as girders or stay cables. 
   According to yet another characteristic of the invention, the means for lifting the span entail a balance arm mounted to pivot on a support structure from one end of which the span is suspended, whereas some pivoting actuation means are connected at the other end. 
   According to yet another characteristic of the invention, the span is a self-supporting structure suspended from the end of the balance arm by suspension cables. 
   According to yet another characteristic of the invention, the span has a lightened structure, borne by a multiple of stay cables, in a low position for crossing the channel as well as in a high position for opening the channel, the stay cables being suspended from end of the balance arm. 
   According to yet another characteristic of the invention, a balance arm includes two levers with two arms that are both mounted to pivot on a pylon while being connected, if necessary, by a crosspiece. 
   According to yet another characteristic of the invention, the weight of the span is at least partially counterbalanced by counterweights. 

   
     BRIEF DESCRIPTION OF DRAWING FIGURES 
     The invention will be better understood, and other aims, characteristics, details and advantages of it will appear more clearly in the course of the following explanatory description in reference to the appended drawings given only as examples illustrating two embodiments of the invention and in which: 
       FIGS. 1 and 2  are perspective views of a first embodiment of a bridge according to the invention, the bridge occupying its low position for crossing the channel of a waterway; 
       FIGS. 3 and 4  are perspective views of the embodiment according to  FIGS. 1 and 2  but show this bridge in its high position for opening the channel; 
       FIGS. 5 and 6  are perspective views of two different versions of the bridge according to  FIGS. 1-4 ; 
       FIGS. 7 and 8  are perspective views illustrating a second embodiment of a bridge according to the invention in its position for crossing the channel; 
       FIG. 9  is a perspective view of the bridge according to  FIGS. 7 and 8  but shows the bridge in its high position for opening the channel; 
       FIG. 10  is a perspective view of a bridge with two spans according to  FIGS. 7-9   
       FIGS. 11 and 12  are perspective views of another version of the second embodiment of a bridge according to the invention, illustrating the bridge in its position for crossing the channel; 
       FIG. 13  is a perspective view of the bridge according to  FIGS. 11 and 12  but illustrating the bridge in its high position for opening the channel; 
       FIG. 14  is a perspective view of a version of the second embodiment of a bridge according to the invention, which has two mobile spans, one of which is represented in its position for crossing the channel and the other of which is represented in its high position for opening the channel; 
       FIG. 15  is a top view of the bridge according to  FIG. 14 , but where the two spans occupy their position for crossing the channel, and 
       FIG. 16  is a diagrammatic side view of yet another embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   As illustrated by the figures, a lifting bridge  1  according to the invention, intended for enabling one to cross channel  2  of a maritime waterway, has a roughly horizontal mobile part in the form of span  3 , which can be moved by translation roughly vertically between a low position for crossing channel  2  and a high position for opening the channel, and stationary parts  4 ,  5  on both sides of span  3  and on which the latter is supported at  7  and  8  by its two ends  9  and  10  in position for crossing. The bridge also has structure  12  for support of span  3  during its movement between its two positions for crossing the channel and for opening the channel, and some means  14  controlling the movement of the span, hereafter called lifting means. 
   As seen in the figures, lifting bridge  1  according to the invention has just one support structure  12  and just one lifting control device  14 , which are mounted on just one side of channel  2  to be crossed, namely, in the example represented, on stationary part  5 . This stationary support part, in the examples represented, is on one of the banks of the waterway but could also be provided in the waterway. 
   According to a first embodiment represented in  FIGS. 1-6 , support structure  12  is stationary and essentially includes, on each lateral side of span  3 , vertical pylon  16  anchored at its lower end in stationary bank part  5  and which bears, at its upper end, girder  17  extending from the pylon, inclined upward, up to approximately the middle of span  2 , and girder  18  extending upward at approximately a right angle with respect to girder  17 . 
   Span  3  is suspended mainly during lifting from the free end of each girder  17  by the intermediary of two lifting cables  20 ,  21  fastened through an end of span  3  and running over pulley  23  mounted on the end of girder  17 , along this girder, over another pulley  24  situated at the top of the pylon, and then inside of pylon  16  to traction device  25  arranged at the foot of this pylon. This device could be a winch for winding or unwinding of lifting cables  20 ,  21 , or any other suitable traction device such as a jack. In order to ensure the horizontal position of span  3 , each lifting cable  20 ,  21  is attached to span  3  at one end of the span. 
   Given that the span is thus suspended from the free ends of girders  17 , the end of each girder is held by stay cable  27  that extends between this end and the free end of holding girder  18 , on one hand, and between these ends and stationary part  5  of the bridge on which it is attached at  28  an appropriate distance from the foot of pylon  16  in the plane formed by this pylon and suspension girder  17  and holding girder  18 . In order to reinforce the support structure of the span, the upper end of each pylon  16  is held in position by reinforcing leg  30  that extends between the upper end of the pylon and the stationary part in the above-mentioned plane, as seen in  FIGS. 1-4 , or by two stay cables  32  according to  FIG. 5 .  FIG. 6  shows yet another version of the device for reinforcing the support structure, which, in the extension of the suspension girder  17 , beyond pylon  16 , has girder part  36  whose end is held to stationary part  5  by stay cables  37  and which also serves as anchoring place for stay cable  27  for holding the free end of suspension girder  17 . Of course, girders could also be used in place of stay cables  27  and  37 . 
   It is observed that support structure  12  can possibly consist of framing members situated on the side of span  3 , which are independent or connected by any type of connection. In general, any geometry can be applied to this structure. 
   The weight of span  3  suspended from support structure  12  can be 1  to varying degrees balanced by counterweights acting continually or only during lifting. These counterweights, such as those indicated at  39 , for example, are placed in the traction cables and, like these cables, are thus inside the pylons. Of course, any other suitable solution for the counterweights and traction cables can be considered. The counterweights could in particular be “disengaged” and the cables relaxed when the span is in position for crossing the channel. 
   Span  3  can be a self-supporting structure of the lattice, box, Warren girder or Bow string type or the like. 
   It should also be noted that the span, during its movement, is held at its corresponding end in contact with pylons  16  and is thus guided at just one end. 
     FIGS. 7-15  illustrate several versions of a second embodiment of a bridge according to the invention. 
   This second embodiment is characterized by the fact that the lifting of span  3  is ensured by the tilting of balance arm  42  mounted so as to pivot at the top of pylons  16 . The pivoting of the balance arm takes place on rotational bearings, pivot pins, hard bearing or any other tilting mechanism. This balance arm is formed by two two-armed levers  43  connected together, for example, by crosspiece  45  at the ends of front arms  44 , from which span  3  is suspended by suspension cables  46 , whereas at each free end of rear arm  44 ′, whose length can be different from that of the front arm, traction cables  48  are connected, actuated by a traction device of any appropriate nature such as winches or jacks  50 . This traction device can be associated with a device for anchoring of the balance arm in stationary part  5 , such as cables, bars, or portals, which immobilizes the tilting of the balance arm when the span is in position for crossing the channel and which does not hinder the action of the traction device during lifting. In order to counterbalance the weight of the span at least partially, counterweight  52  can be inserted between the end of the edge of lever  44 ′ and each cable  48 . Each two-armed lever  43  has, at the site of the tip of support pylon  16 , transverse girder  54  that projects upward and makes it possible to prevent bending of the lever due to stay cables  56  and  57  attached between the end of girder  54  and the ends of suspension arm  44  and traction arm  44 ′ of levers  43 . 
   Given that during its movement under the effect of the tilting of balance arm  42 , between its two positions for crossing channel  2  and for opening the channel, the span describes a slight arc of circle in the vertical plane, each pylon  16  has guide path  59  consequently curved on which the adjacent end of span  3  rests. A device for horizontal movement of the mechanism for pivoting the balance arm during lifting could enable one to avoid the curvature of this guide path. 
     FIG. 10  shows a bridge structure that has two separate and independently lifted spans  3 ,  3 ′. Each span is suspended from balance arm  42  as described in the preceding. The two balance arms could be mounted on two pairs of pylons  16  or on a device with three pylons of which the central pylon indicated by  16 ′ in  FIG. 10  would then be shared by the two balance arms. 
   In reference to  FIGS. 11-15 , a particularly advantageous implementation version of the embodiment of the bridge, with lifting of the spans by tilting of a balance arm, will be described hereafter. In this implementation version, span  3  is a cable-stayed structure, that is to say borne by multiple stay cables  62  in position of operation, that is to say in its position for crossing represented in  FIGS. 11 and 12 , as well as in lifting position according to  FIG. 13 , which allows simplification of the structure of the span, and particularly lightening of the weight, as emerges from the FIGS. since the span no longer needs to be self-supporting. A reduction of the weight of the span is thus obtained. 
   As illustrated by  FIG. 14 , this implementation version of the span in the form of a cable-stayed span can also be applied to a bridge with two spans, according to  FIG. 9 . 
   Another very advantageous embodiment is represented in  FIG. 16 . In this embodiment, the span is suspended from balance arm  42  by the intermediary of the suspension device indicated by  64  not at its center of gravity symbolized by arrow  65 , but rather from a site offset from center  65  in the direction of pylons  16 , so that when the span is lifted, it has a tendency to tilt in the direction of arrow  66 . The amplitude of this offsetting identified in the figure by the letter “a” is determined as a function of the maximum wind effects that can possibly act on the system, 
   Rotation thus brought about by the span, when it is lifted, in the direction of arrow  66 , is prevented by pulling the span downward on its end on the pylon side  68  by means of a pair of cables  69  each of which can be wound on winch  70  or unwound from the winch. Each winch  70  arranged at the foot of pylon  16  unwinds its cable as the lifting of the span progresses in order to follow its position and to ensure its stability regardless of the wind conditions. During the lifting, the span is thus stabilized in all directions both by its suspension from the balance arm and by the follower cable that regulates the rotation of the suspension/span assembly under the balance arm while preventing any untimely pendular motion. For this purpose, the unwinding or winding movements of winches  50  are under the control of the tilting of the balance arm. 
   It should be noted that the tilting in the direction of arrow  66  could also be occasioned by a weight added at the end of the span away from the pylons, as diagrammatically indicated at  71 . This version has the advantage that the suspension of the span can take place at its center of gravity. 
   Of course, multiple modifications can be made to the bridge as represented in the figures. Thus, the support structures can be designed differently, while taking care that the constitutive elements of these structures are preferably acted upon by traction or compression. The counterweights could be placed differently, integrated or not in the support structures, for example, integrated in the balance arms. In this way also, any type of arrangement for the sheets of stay cables and particularly their number can be considered. 
   It should be noted that the invention allows the execution of bridges with very long spans whose length can possible reach 100 m or more.