Patent Publication Number: US-2002000075-A1

Title: Lattice girder supporting frame having oblique cut truss braces

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to lattice girder supporting frames. In particular, the present invention is directed to lattice girder supporting frames for mine and tunnel lining, in which boom members are connected to brace members and cross-ties to provide a high load-bearing capacity.  
       [0002] This application is based on German Patent Application 100 20 006.0, which is incorporated herein by reference.  
       BACKGROUND  
       [0003] Lattice girders are described in DE 19711627 C/2, wherein bracing elements have braces connected to boom members. The braces are bent in the area where the boom members connect to the boom members. This is disadvantageous because the braces have a limited diameter with this arrangement.  
       [0004] EP 0073 733 A1, FR-PS 1.098003, DE 82 06 277, and DE 40 03 525 A1 also describe similar lattice girders. Each of these girders suffers from the same problem as above.  
       SUMMARY OF THE INVENTION  
       [0005] A lattice girder supporting frame is provided in which three or four boom members are arranged in parallel to each other, so that a side view of the boom members forms the comers of a triangle or square. The boom members are spatially connected to each other by means of bracing elements. Each of the bracing elements includes a plurality of straight truss braces arranged in a pyramid shape. The straight truss braces are arranged along the edge of the pyramid shape, extending between lower and upper boom members.  
       [0006] The straight truss braces have ends that are bevel cut, or chamfered, so as to conform to the pyramid angle and the bevel cut ends contact with the boom members. Also, the ends of the truss braces are obliquely cut, and these oblique surfaces are welded to the boom members. In the area of the pyramid base, the straight truss braces are fixedly secured by cross-ties connecting the boom members to each other.  
       [0007] With the present invention, increased bearing loads and rigidity are possible due to the greater cross-sections of the ends of the braces connected to the boom members. Bends are generally avoided altogether, or at least reduced, because the straight truss braces, which are arranged along the edges of a pyramid between the boom members, are in contact with the surfaces of the boom members through an oblique and beveled cut conforming to the pyramid angle and are welded to the boom members in the area of these miter cuts, and the truss braces are fixedly secured in their position by means of cross-ties in the base area and at the top of the truncated pyramid and the cross-ties simultaneously connect the lower boom members in the base area of the pyramid. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
     [0009]FIG. 1 a  shows a detailed cross-sectional view of a four-boom lattice girder frame of the present invention along line  1   a - 1   a  of FIG. 1B;  
     [0010]FIG. 1 b  shows a lateral view of the four-boom lattice girder frame shown in FIG. 1 a ;  
     [0011]FIG. 2 a  shows a cross-sectional view of a three-boom lattice girder frame along line  2   a - 2   a  of FIG. 2 b ;  
     [0012]FIG. 2 b  shows a lateral view of the three-boom lattice girder frame shown in FIG. 2 a ;  
     [0013]FIG. 2 c  shows a cross-sectional view of a four-boom lattice girder frame along line  2   c - 2   c  of FIG. 2 d ;  
     [0014]FIG. 2 d  shows a lateral view of the four-boom lattice girder frame shown in FIG. 2 c ;  
     [0015]FIG. 3 shows a top view of the three-boom lattice girder frame; and  
     [0016]FIG. 4 shows a top view of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0017] A lattice girder supporting frame for mine and tunnel lining is provided with boom members  2  arranged in parallel to each other as shown in FIGS. 1 a - 2   d.    
     [0018]FIGS. 1 a  and  1   b  show welds between boom members  2 , truss braces  3 , and cross-ties  4 . Specifically, a welded connection  1  is provided between boom member  2  and truss brace  3 , a welded connection  6  is provided between the truss brace  3  and the cross-tie  4 , and a welded connection  5  is provided between the boom member  2  and the cross-tie  4 .  
     [0019] As illustrated in FIGS. 2 a - 2   d , three or four boom members  2  may be provided. A bracing element, consisting of four straight truss braces  3  and two or three cross-ties  4  which are arranged between the boom members  2 , is discussed below.  
     [0020] The boom members  2  are arranged in parallel to each other so as to form a triangle (see FIGS. 2 a  and  2   c ). The boom members  2  may also be arranged to form a square (not shown). The boom members  2  are spatially connected to each other by means of bracing elements, which include four straight truss braces  3  arranged in such a manner to form a pyramid shape. The truss braces  3  are disposed along the edges of the pyramid, and are each welded, by the welded connection  1 , to upper and lower boom members  2  at contact faces of the truss braces  3 . A longitudinal axis of each of the truss braces  3  is disposed along a plane P extending from the axes of the upper and lower boom members  2 , as shown in FIGS. 1 a ,  2   a  and  2   c.    
     [0021] The truss braces  3  are located in the plane P connecting the upper and lower boom axis, so that no additional moments can occur.  
     [0022] The truss braces  3  at the truncated pyramid top are fixedly secured in a similar manner by cross-ties  4  arranged on an interior side of the pyramid. A plane of symmetry S of the outer pyramid surface, and thus also of each truss brace axis, lies in the plane extending from the axes of the upper boom to a plane on which the lower booms lie.  
     [0023] Each truss brace  3  has a beveled cut end so as to have chamfered surfaces  3   a . Also, the ends of each truss brace  3  are obliquely cut so as to have an oblique surface  3   b . The chamfered and oblique surfaces  3   a ,  3   b  are welded to the boom members at the weld connections  1 .  
     [0024] This structure provides a substantially increased load-bearing capacity and rigidity due to the selection of greater material cross-sections of the truss braces. The load-bearing capacity in the conventional girder arrangement is limited by the radii at the bends of the truss braces  3  in the area of the boom members  2 , which conform to the standards and increasing diameters of required truss braces, as well as by the problems of dimensioning and arranging the welds according to the greater brace cross-sections in such a manner that the load bearing capacity of the welds corresponds to the forces acting out from the diagonals of the structure.  
     [0025] With the structure of the present invention, the bracing element of the lattice girder is laid out so as to generally avoid bends. The straight truss braces  3  which are arranged along the edges of the pyramid in the area of the boom members  2 , are in contact with the surfaces of the boom members  2  through an oblique surface  3   b  conforming to the pyramid angle and are welded to the surfaces in the area of the mitre cuts, and the truss braces  3  are fixedly secured in their position by means of cross-ties  4  in the base area and the cross-ties  4  simultaneously connect the lower boom members  2  in the base area of the pyramid. In FIGS. 2 c  and  2   d , the cross-tie  4  may also be provided at the top of the truncated pyramid.  
     [0026] Fabrication of the straight truss braces  3  from tube, round bar or structural steel is most easily achieved by cutting to length with a bevel cut, which is required as a result of the V-shape arrangement conforming to the pyramid edge. The four straight truss braces  3 , that are welded together by the three cross-ties  4  to form a bracing element, are identical.  
     [0027] With the present invention, the pyramid structure of the bracing elements forms a truss. The pyramid angle of the bracing elements in the girder axis may be chosen depending on the stress. The oblique surfaces  3   a  of the ends of the truss braces  3  are angled in accordance with the pyramid angle. The trusses are positioned between the boom members  2  in series at varying spacings Z, Z′ (for example, as shown in FIGS. 2 b  and  2   d ) depending on project-specific requirements, and welded to the boom members  2  accordingly. The lattice arches that are used in mine and tunnel lining are fabricated in segments which are then fitted together to form an arch. The segments are provided at their ends with connections which transfer the cutting forces.  
     [0028]FIG. 3 illustrates a three-boom girder lattice frame embodiment from a top view. In particular, the bracing element imparting rigidity to the girder consists of four straight truss braces  3  and three cross-ties  4 , which have been welded to the boom members  2  at the welded connections  1  and  5  in the manner described above. By arranging several bracing elements in series, a truss structure is created.  
     [0029]FIG. 4 is an embodiment of a bracing element welded in the manner described for FIGS. 1 a  and  1   b , consisting of four straight truss braces  3  to which the three cross-ties  4  have been welded at the welded connections  6  to impart rigidity.  
     [0030] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.