Abstract:
A modular bridge section including one or more box girders, wherein at least one box girder 1, 1&#39; is equipped with at least one lower chord structure 5, 5&#39;, which is mounted floatingly at or in the box girder 1, 1&#39; in the loaded state only between the end stops 6, 6&#39;, 6&#34;, 6&#39;&#34;, which are arranged in the vicinity of the coupling elements 7, 7, 7&#34;, 7&#39;&#34;.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a modular bridge section for a floating bridge according to the preamble of the principal claim. 
     BACKGROUND OF THE INVENTION 
     A bridge section with one detachable lower chord structure each in the area of a side wall of a box girder has been known from WO 93/21390. The arrangement is designed in this way in order for the lower chord structure to be able to be detached in a simple manner from the box girder by pulling out laterally the short horizontal connecting pin. 
     It is disadvantageous that the lower chord structure is subject not only to tension, but also to bending. In addition, the connecting pins of the lower chord structure are subject to both horizontal and vertical forces. The horizontal forces are generated from the tensile forces, which are introduced into the coupling elements. The vertical forces are generated from the difference in height between the connections at the box girder and the positions of the coupling holes. These vertical forces are superimposed by transverse forces arising from the load on the bridge. 
     In addition, it must be pointed out that this bridge section has a detachable lower chord structure for a bridge on two supports and also an integrated lower chord structure. When this bridge section is used for a floating bridges, the first-named lower chord structure shall be removed in order to reduce the redundant weight. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The primary object of the present invention is to design a lower chord structure, specially for bridge sections of floating bridges, such that the connections of such a lower chord structure at the box girder are designed optimally. 
     The lower chord structure shall always remain in the bridge section and shall not be detachable, as in the bridge module according to the above-described state of the art. 
     The object described is accomplished according to the claims in a lower chord structure of the type described in the introduction by the lower chord structure being mounted floatingly, i.e., flexibly, in the loaded state only between the end stops, which are arranged in the vicinity of the coupling elements. 
     The advantages achieved by the present invention are mainly that only the difference between the two tensile forces in the lower chord structure are introduced into the box girder via one of the two end stops. 
     This end stop transmitting the differential force is located at the end of the lower chord structure, namely, at the opposite end, where the stronger tensile force is introduced into the lower chord structure. 
     Furthermore, provisions are made according to one embodiment of the present invention for the end stop 
     to be arranged vertically, 
     to be able to be designed as a cylindrical bolt, 
     or to have a square shaft with two round pins, 
     and for it to be preferably mounted in both blind holes in the box girder 
     and in a clamp, wherein the clamp is rigidly connected to the box girder. 
     It is achieved as a result that 
     1. the lower chord structure is not subject to bending, because the force is transmitted in the end stops via a double-shear connection; 
     2. no water can enter the interior of the box girder via a bolt clearance and pin clearance that may have developed when the bridge section is used in a floating bridge, and 
     3. the clamps have not only a load transmission function, but they also secure the cylindrical end stop against falling out at the same time. 
     It is preferably also provided according to the present invention that the broad side of the rectangular beam tie is arranged in the plane of the bottom of the box girder. 
     The present invention offers a possibility of designing the bottom of the box girder such that the tensile forces introduced by the vertical end stops are locally transmitted in the area of the coupling elements only in the case of the arrangement of a lower chord structure between the longitudinal side walls. These tensile forces are weaker than the maximally occurring tensile forces in the lower chord structure. The rest of the area of the box girder bottom now has only the task of keeping the box girder water-tight when it is used as a floating bridge section and no additional fillings are arranged in the interior of the box girder. 
     The use of the modular bridge section according to the present invention is not limited to the use in floating bridges. It may, of course, also be used for bridges on supports while maintaining the features according to the present invention. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a view of a longitudinal section of a box girder with cylindrical end stops for the lower chord structure; 
     FIG. 2 is a horizontal view along the box girder bottom on the lower chord structure according to FIG. 1; 
     FIG. 3 is a longitudinal sectional view of a box girder with square, shaft-like stops for the lower chord structure; 
     FIG. 4 is a horizontal view along the box girder bottom on the lower chord structure according to FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, FIG. 1 shows a vertical longitudinal section of a box girder 1 with a deck 2 that is load-bearing for vehicular travel, with side walls 3 and with a lower chord structure 5 under the bottom 4 of the box girder 1. The chord structure having means in the material of the chord structure for transmitting tensile forces. 
     Cylindrical end stops 6, 6&#39; are arranged in the vicinity of the coupling elements 7, 7&#39; of the lower chord structure 5. The rectangular beam tie 8, which connects the coupling elements 7, 7&#39; to one another, has one or more elongated holes 9, 9&#39; in the area of the coupling elements 7, 7&#39;. A cylindrical end stop 6, 6&#39; is passed through each elongated hole 9, 9&#39;. The end stops 6, 6&#39; are mounted in the box girder 1 and in a clamp 11, 11&#39; fastened to the box girder 1, preferably in blind holes 13, 13&#39; in the box girder 1 and in holes 14, 14&#39; in the clamp 11, 11&#39;. It is achieved as a result that no bending moments develop in the lower chord structure 5 due to the double-shear connection and the wall of the hole in the connection structure is kept low. 
     The blind holes 13, 13&#39; have a larger diameter than the hole 14, 14&#39; in the clamp 11, 11&#39;. The cylindrical stop 6, 6&#39; is mounted captively as a result. 
     An intended clearance between the box girder 1 and the clamps 11, 11&#39;, which makes possible a free longitudinal movement of the rectangular beam tie 8 in the loaded state, is recognizable. 
     To make possible a horizontal displacement of the coupling elements 7, 7&#39;, which is equal to the elongation of the beam tie 8, the horizontal bolts 12, 12&#39; are arranged above the coupling elements 7, 7&#39; in the longitudinal direction of the beam tie 8. The bolts 12, stops 6, holes 13 and clamps 11 form a mounting means for creating a floating or sliding connection between the chord structure and the box girder in a loaded state of the chord structure. The mounting means transmits a difference in tensile forces at ends of said chord to the box girder. 
     FIG. 2 shows a horizontal view along the box girder bottom 4 on the lower chord structure 5 in the unloaded state. It can be recognized how the cylindrical end stops 6, 6&#39; are now in contact with the inner surfaces 10, 10&#39; of the elongated holes 9, 9&#39;. The elongated holes 9, 9&#39; are at least as long as the maximum elongation of the beam tie 8 at the maximally occurring tensile force in the lower chord structure 5. 
     FIG. 3 shows a vertical longitudinal section of a box girder 1&#39; with a deck 2&#39; that is load-bearing for vehicular travel, with side walls 3&#39; and with a lower chord structure 5&#39; under the bottom 4&#39; of the box girder 1&#39;. 
     End stops 6&#34;, 6&#39;&#34; are arranged at the transition point 15, 15&#39; between the coupling element 7&#34;, 7&#39;&#34; and the beam tie 8&#39; in the vicinity of the coupling elements 7&#34;, 7&#39;&#34; of the lower chord structure 5&#39;. 
     The broad side B z  of the preferably rectangular beam tie 8&#39; is smaller than the broad side B k  of the coupling elements 7&#34;, 7&#39;&#34;. In the unloaded state of the lower chord structure 5&#39;, the projecting surfaces 18, 18&#39; of the two coupling elements 7&#34;, 7&#39;&#34; are in contact with the square shafts 16 of the end stops 6&#34;, 6&#39;&#34;, which shafts are located on both sides of the beam tie 8&#39;. Each square shaft 16 has two round pins 17, 17&#39;, which are mounted in the box girder 1&#39; as well as in a clamp 11&#34;, 11&#39;&#34; connected to the box girder 1&#39;. The advantage of this mounting of the pins is that the end stops 6&#34;, 6&#39;&#34; are always in contact with the projecting surfaces 18, 18&#39; and thus they generate weak contact pressures. 
     The round pins 17 of the end stops 6&#34;, 6&#39;&#34; are mounted in respective blind holes 13&#34;, 13&#39;&#34; of the box girder 1&#39;, and the round pins 17 are mounted in holes 14&#34;, 14&#39;&#34; of the clamps 11&#34;, 11&#39;&#34;. The end stop 6&#34;, 6&#39;&#34; is secured against falling out by the square shaft 16. 
     An intended clearance between the box girder 1&#39; and the clamps 11&#34;, 11&#39;&#34;, which makes possible a free longitudinal movement of the rectangular beam tie 8&#39; in the loaded state, is clearly recognizable. 
     Horizontal displacement of the coupling elements 7&#34;, 7&#39;&#34;, which is equal to the elongation of the beam tie 8&#39;, is possible due to the arrangement of the horizontal bolts 12&#34;, 12&#39;&#34; above the coupling elements 7&#34;, 7&#39;&#34; in the longitudinal direction of the beam tie 8&#39;. 
     FIG. 4 shows a horizontal view along the box girder bottom 4&#39; on the lower chord structure 5&#39; in the unloaded state. It can be recognized that each of the two end stops 6&#34;, 6&#39;&#34; arranged on both sides of the beam tie 8&#39; is arranged in the immediate vicinity of the transition point 15, 15&#39; of the coupling element 7&#34;, 7&#39;&#34; with the beam tie 8&#39;. 
     The two projecting surfaces 18, 18&#39; of the coupling element 7, 7&#39; are in contact with the square shafts 16, 16&#39; of the end stops 6&#34;, 6&#39;&#34; in the unloaded state of the lower chord structure 5&#39;. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.