Patent Publication Number: US-2012023858-A1

Title: Truss-type shear reinforcement material having double anchorage functions at both top and bottom thereof

Description:
TECHNICAL FIELD 
     The present invention relates to a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, and more particularly, to such a truss-type shear reinforcement device of a reinforced concrete structure, which is installed in a reinforced concrete structure to increase resistance against shear failure. The truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof is configured by installing double anchorage at the upper and lower sides of a truss, which is formed by connecting an upper chord member with a lower chord member through connection members such as vertical members or diagonal members, thereby improving shear resistance, shear reinforcement and ductility and improving construction quality while making construction of a concrete structure more convenient. 
     BACKGROUND ART 
     In a reinforced concrete structure constructed through application of reinforcing bars and concrete, particularly, slabs, girders or beams, columns, walls, corbels, and the like needs increased shear resistance, and thus, a shear reinforcement device for reinforcement of shear performance is constructed. For example, a shear force greatly acts on a joint (i.e., a column head portion) between the slab and the column along the circumference of the column in the reinforced concrete structure. Thus, if the joint does not have a sufficient shear resistance, there is a great risk of occurrence of shear failure. In particular, in case of the joint between the slab and the column in a flat slab structure in which a large girder or a small beam are not installed but the slab is directly supported by the columns, an excessive stress is intensively concentrated on the slab surrounding the column unlike a general joint between the beam and the column to induce a bidirectional shear failure (or punching shear failure) forming a reversed trapezoidal shape as disclosed in Korean Patent Laid-Open Publication No. 10-2007-0053836 entitled “SHEAR REINFORCEMENT DEVICE FOR COLUM-SLAB JOINTS AND ITS MENUFACTURING METHOD” and Korean Patent Registration No. 10-0676627 entitled “SHEAR REINFORCEMENT DEVICE FOR SLAB-COLUMN JOINTS AND SHEAR REINFORCEMENT STRUCTURE USING THE DEVICE”. Since such a shear failure is very brittle unlike other types of failure patterns, it is greatly critical to stability of the slab-column joints, so that a special attention must be paid to the joints in the structure design and a sufficient measure must be taken to prevent the shear failure from being occurring. 
       FIG. 1  shows perspective views of shear reinforcement devices used to increase the shear performance of the joints between slabs and columns in a reinforced concrete structure, and  FIG. 2  shows views for explaining problems occurring at the time of installation and stress reversal of the shear reinforcement devices shown in  FIG. 1 . 
     In this case,  FIGS. 1(   a ) and  2 ( a ) are views for explaining a method which applies a typical stirrup  100  as the shear reinforcement device, and  FIGS. 1(   b ) and  2 ( b ) are views for explaining a method which applies a shear stud  200  as the shear reinforcement device as disclosed in Korean Patent Laid-Open Publication No. 10-2004-0076644 entitled “REINFORCED CONCRETE REINFORCEMENT DEVICE AND METHOD FOR CONSTRUCTING REINFORCED CONCRETE STRUCTURE INCLUDING THE SAME”. In addition,  FIGS. 1(   c ) and  2 ( c ) are views for explaining a method which applies a shear band  300  as the shear reinforcement device as disclosed in Korean Patent Laid-Open Publication No. 10-2007-0053836 entitled “SHEAR REINFORCEMENT DEVICE FOR COLUM-SLAB JOINTS AND ITS MENUFACTURING METHOD” and Korean Patent Registration No. 10-0676627 entitled “SHEAR REINFORCEMENT DEVICE FOR SLAB-COLUMN JOINTS AND SHEAR REINFORCEMENT STRUCTURE USING THE DEVICE”. 
     Referring to  FIGS. 1 and 2 , a conventional shear reinforcement method entails a problem in that since the shear reinforcement device (i.e., stirrup  100 , shear stud  200  and shear band  300 ) is deformed at the time of stress reversal, the shear performance is remarkably lowered upon the repeated exertion of the shear stress. Further, the concrete coating thickness during construction must be necessarily taken into consideration, but is difficult to precisely control actually, thus resulting in a problem in that construction defects occur or the performance of the structure is deteriorated. Moreover, since the conventional shear reinforcement devices are difficult for field workers with repetitive motion tasks to install, careful attention must be paid to installation of the shear reinforcement devices and satisfaction of the required design conditions is difficult. 
     The problems associated with the conventional prior arts will be described hereinafter in more detail. First, the method for using the stirrup  100  as the shear reinforcement device will be described hereinafter in more detail. 
     Lower main reinforcing bars  5  and upper main reinforcing bars  4  are installed. In this case, although not shown, the upper and lower sub reinforcing bars may be installed in the vicinity of the upper and lower portions of a concrete layer. Then, the upper and lower main reinforcing bars  4  and  5  are surrounded by the stirrup  100  and both ends of the stirrup  100  are tied together on any one of the upper and lower main reinforcing bars  4  and  5 . Thus, this makes it difficult to work as well as much working time is spent. As shown in  FIG. 2(   a ), if an upper stress is expanded, there occurs a phenomenon in which the both ends of the stirrup  100  tied together on the main reinforcing bar are widened in a direction of an arrow, and thus the shear performance is remarkably lowered upon the repeated exertion of the shear stress. In addition, as shown in  FIG. 2(   a ), concrete coating thicknesses L 1  and L 2  are specified from a top surface  2  and an underside surface of a slab  1 . Since such a method of using the stirrup  100  requires that the thickness of the stirrup  100  should be taken into consideration, it is difficult to actually satisfy the specified concrete coating thicknesses L 1  and L 2  due to an error of work. Besides, since the upper and lower main reinforcing bars  4  and  5  and the upper and lower portions of the slab adjacent to the main reinforcing bars  4  and  5  are moved from the top surface  2  and the underside surface  3  of the slab  1 , the moment resistance performance of the structure is deteriorated. 
     Next, the method for using the shear stud  200  as the shear reinforcement device will be described hereinafter in more detail. 
     The shear stud  200  is configured such that stud bodies are vertically installed on the rail  210  at regular intervals and heads  230  are disposed on the tops of the stud bodies. Thus, the installation work of the shear stud  200  can be expected to be relatively improved as compared to the method for using the stirrup  100  as the shear reinforcement device. The method for using the shear stud  200  as the shear reinforcement device, however, still encounters a problem. That is, as shown in  FIG. 2 , if an upper stress is expanded, the stud bodies are widened in a direction of the heads  230 , and thus the shear performance is lowered upon the repeated exertion of the shear stress. Also, a worker must pay a special attention to satisfy the specified concrete coating thicknesses L 1  and L 2 , and the upper or lower reinforcing bars are moved from the top surface  2  or underside surface  3  of the slab  1 , and thus the performance of the structure is deteriorated. 
     Last, the method for using the shear band  300  as the shear reinforcement device will be described hereinafter in more detail. 
     As shown in  FIG. 1(   c ), the shear band  300  is configured such that a sheet as disclosed in Korean Patent Laid-Open Publication No. 10-2007-0053836 entitled “SHEAR REINFORCEMENT DEVICE FOR COLUM-SLAB JOINTS AND ITS MENUFACTURING METHOD” or a wire rod as disclosed in Korean Patent Registration No. 10-0676627 entitled “SHEAR REINFORCEMENT DEVICE FOR SLAB-COLUMN JOINTS AND SHEAR REINFORCEMENT STRUCTURE USING THE DEVICE” is bent in a concavo-convex shape. Thus, the installation work of the shear band  300  can be expected to be relatively improved as compared to the method for using the stirrup  100  as the shear reinforcement device. The method for using the shear band  300  as the shear reinforcement device, however, still encounters a problem in that in case of applying the sheet, there occurs an interference between the sheet and the placement of the upper and lower reinforcing bars, making the construction difficult, and in that in case of the sheet, the shear band  300  blocks concrete at the time of pouring of concrete for the slab, thus resulting in defective filling of concrete. In particular, in case of the shear band  300  to which the sheet is applied, there is caused a problem in that the shear band  300  isolates concrete being poured, and thus the strength of the joints between slabs and columns is rather weakened due to isolation of concrete. In addition, the method for using the shear band  300  as the shear reinforcement device still involves a drawback in that it has the same problems as those occurring in the above-mentioned stirrup  100  and shear stud  200 , as well as the shear band  300  is widened transversely at the upper and lower sides thereof and upon the expansion of the stress as shown in  FIG. 2(   c ). 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Accordingly, the present invention has been made in an effort to solve the problems occurring in the prior art and it is an object of the present invention to provide a novel truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which can stably secure the shear performance through a structure for preventing deformation of the shear reinforcement device at the time of stress reversal thereof. 
     Another object of the present invention is to provide a novel truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, in which the concrete coating thickness can be conformed to a specified value even without taking into consideration the concrete coating thickness at the time of installation of the shear reinforcement device by a worker so that the time required for field workers to install the shear reinforcement device can be reduced and the specified design conditions can be easily satisfied during construction, thereby minimizing construction defects due to installation of the shear reinforcement device and effectively increasing the performance of the structure. 
     Still another object of the present invention is to provide a novel truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which is installed in a reinforced concrete structure, particularly at joints where slabs and columns are joined to each other or is installed as a substitute for a stirrup of a beam, a column, a wall, a foundation, and the like to increase resistance against shear failure. 
     Yet another object of the present invention is to provide a novel truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which can be installed in a reinforced concrete structure, particularly at joints where slabs and columns are joined to each other or can be installed as a substitute for a stirrup of a beam, a column, a wall, a foundation, and the like, thereby effectively preventing an interference between the shear reinforcement device and the reinforcing bars during the reinforcing bar placement, and maximizing the shear reinforcement range to effectively prevent shear failure occurring at the joints between slabs and columns. 
     Particularly, a further object of the present invention is to provide a novel truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which is configured to have a double anchorage structure at upper and lower sides thereof unlike the conventional prior arts, thereby ensuring reliability of strength and ductility against an allowable shear stress of a concrete structure being poured, particularly the joints between slabs and columns even at the time of occurrence of repeated stress reversal due to exertion of a lateral load such as earthquake, and the like, and enhancing lateral load resistance. more effectively. 
     Technical Solution 
     To achieve the above objects, according to the features of the present invention, there is provided a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which is installed in a reinforced concrete structure to increase resistance against shear failure, characterized in that the truss-type shear reinforcement device includes: a truss  20  including an upper chord member  24 , a lower chord member  26 , and one or more connection members  21  for interconnecting the upper chord member  24  and the lower chord member  26 ; one or more upper anchor heads  34  fixedly connected with the upper chord member  24  of the truss  20  at the upper side of the truss  20 ; and one or more lower anchor heads  44  fixedly connected with the lower chord member  26  of the truss  20  at the lower side of the truss  20 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the connection members  21  may include any one of a vertical member  22  and a diagonal member  23 . The vertical member  22  may be formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the vertical member  22  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the vertical member  22  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the vertical member  22  are vertically aligned. In addition, the diagonal member  23  may be formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the diagonal member  23  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the diagonal member  23  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the diagonal member  23  are diagonally aligned. 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the connection members  21  may include an upper spacer  32  protrudingly extending upwardly from the top of the upper chord member  24  by a predetermined distance, and a lower spacer  42  protrudingly extending downwardly from the bottom of the lower chord member  26  by a predetermined distance. In addition, each of the upper anchor heads  34  may be joined to the upper spacer  32  so that it is installed spaced apart by the predetermined distance from the upper chord member  24 , and each of the lower anchor heads  44  may be joined to the lower spacer  42  so that it is installed spaced apart by the predetermined distance from the lower chord member  26 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the upper anchor heads  34  may be installed spaced apart by the predetermined distance from the upper chord member  24  by the upper spacer  32  fixed at a lower side thereof to the upper chord member  24  and fixed at an upper side thereof to the upper anchor head  34 . In addition, each of the lower anchor heads  44  may be installed spaced apart by the predetermined distance from the lower chord member  26  by the lower spacer  42  fixed at an upper side thereof to the lower chord member  26  and fixed at a lower side thereof to the lower anchor head  44 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, the upper spacer  32  may be fixed to the upper panel point  31  where the upper chord member  24  and the connection member  21  are joined to each other, and the lower spacer  42  may be fixed to the lower panel point  41  where lower chord member  26  and the connection member  21  are joined to each other. 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, the horizontal cross-sectional area of each of the upper anchor heads  34  may be formed to be equal to 7-14 times that of the upper spacer  32 , and the horizontal cross-sectional area of each of the lower anchor heads  44  may be formed to be equal to 7-14 times that of the lower spacer  42 . 
     Advantageous Effects 
     The truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention has a structure in which upper and lower anchor heads  34  and  44  are mounted at the upper and lower sides of a truss  20  including an upper chord member  24  and a lower chord member  26  which are connected with each other by the connection members  21 . Thus, the upper anchor head  34  and the upper chord member  24  perform a double anchorage function at the upper side of the shear reinforcement device, and the lower anchor head  44  and the lower chord member  26  perform a double anchorage function at the lower side of the shear reinforcement device, so that shear resistance and ductility of the inventive shear reinforcement device is further improved as compared to the conventional prior art. Particularly, the conventional shear reinforcement device has a limitation in that a shear reinforcement range must be reduced by the coating thickness of the shear reinforcement device and the thickness of the members, thereby deteriorating the reinforcement performance. On the other hand, the inventive truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof has an advantage in that since a vertical shear reinforcement range is covered up to the entire range except the concrete coating thickness, the shear reinforcement performance can be maximized. In addition, the inventive truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof can further achieve a confining effect in the longitudinal direction, i.e., in the direction of an X axis through the truss, and is excellent in its own bending resistance. Moreover, the upper side of the shear reinforcement device in which the upper anchor heads  34  are mounted and the lower side of the shear reinforcement device in which lower anchor heads  44  are mounted are in a symmetrical relationship, so that the shear reinforcement device has a very stable reinforcement performance against the stress reversal of the shear reinforcement portion due to an earthquake load, and the like. Besides, the inventive shear reinforcement device does not produce any interference with the reinforcing bars placed in concrete, thereby further improving constructionability. In addition, the function of the spacers  32  and  42  for adjusting the placement position and distance of the reinforcing bars is performed automatically, and thus the reinforcing bars can be placed at more accurate positions through the height adjustment of the truss  20 , thereby shortening the construction period while effectively improving construction quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows perspective views of shear reinforcement devices used to increase the shear performance of the joints between slabs and columns in a reinforced concrete structure. 
         FIG. 2  shows views for explaining problems occurring at the time of installation and stress reversal of the shear reinforcement devices shown in  FIG. 1 . 
         FIG. 3  is a view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a technical spirit of the present invention. 
         FIG. 4  shows views illustrating applicable forms of a truss in the shear reinforcement device of  FIG. 3 . 
         FIG. 5  shows views for explaining the confining effect of a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention. 
         FIG. 6  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention. 
         FIG. 7  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to another preferred embodiment of the present invention. 
         FIG. 8  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to still another preferred embodiment of the present invention. 
         FIG. 9  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to yet another preferred embodiment of the present invention. 
         FIG. 10  shows views for explaining various examples of an anchor head in a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention. 
         FIG. 11  is a view illustrating an example in which a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention is typically applied to a reinforced concrete structure. 
         FIG. 12  is a view illustrating an example in which a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention is applied to a joint where a slab and a column are joined to each other. 
         FIGS. 13 to 15  are views illustrating examples of prefabrication of reinforcing bars using a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
       FIG. 3  is a view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a technical spirit of the present invention, and  FIG. 4  shows views illustrating applicable forms of a truss in the shear reinforcement device of  FIG. 3 . 
     Referring to  FIG. 3 , a shear reinforcement device  10  according to a technical spirit of the present invention includes double anchorage functions at upper and lower sides thereof and is installed in a reinforced concrete structure to increase resistance against shear failure. That is, the shear reinforcement device  10  according to the present invention is configured such that a plurality of upper anchor heads  34  and a plurality of lower anchor heads  44  are mounted at the upper and lower sides of a truss  20  including an upper chord member  24  and a lower chord member  26  which are connected with each other by a plurality of connection members  21 . Thus, the respective anchor heads  34  and  44  serves as a primary anchorage means, and the upper chord member  24  and the lower chord member  26  serves as a secondary anchorage means to perform double anchorage functions at the upper and lower sides of the shear reinforcement device  10 . 
     In such a shear reinforcement device  10  according to the present invention, the truss  20  includes the upper chord member  24 , the lower chord member  26 , and a plurality of connection members  21  for interconnecting the upper chord member  24  and the lower chord member  26 . 
     The truss  20  has a function of a bar-support which enables upper and lower main reinforcing bars and sub reinforcing bars to be tied on the upper chord member  24  or the lower chord member  26  by tie wires within a concrete structure in which the truss is installed together at a joint between a slab and a column. In addition, the truss  20  has a function of a structure device capable of supporting a load when lifting the prefabricated re-bars in the prefabrication of reinforcing bars. For this reason, the shear reinforcement device  10  according to the present invention enables the prefabrication of reinforcing bars as shown in  FIG. 13  showing an example of prefabrication of reinforcing bars for a column and  FIG. 14  showing an example of prefabrication of reinforcing bars for a beam so that it is possible to expect an effect of reducing the construction period. 
     In this case, as shown in  FIGS. 3 and 4 , each of the connection members  21  of the truss  20  may be configured in such a fashion as to selectively apply the vertical member  22  and the diagonal member  23 . The vertical member  22  is formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the vertical member  22  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the vertical member  22  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the vertical member  22  are vertically aligned. In addition, the diagonal member  23  is formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the diagonal member  23  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the diagonal member  23  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the diagonal member  23  are diagonally aligned. 
     The connection member  21  preferably is configured to include the vertical member  22  and the diagonal member  23  simultaneously, but may be configured to include any one of the vertical member  22  and the diagonal member  23  depending on the need of designers and users as in a preferred embodiment of the present invention. The structure of the connection member  21  may be modified and applied in various forms through application of relevant techniques in the art to which the present invention pertains without departing from the technical spirit of the present invention. For example, the truss refers to a structure in which one or more members are arranged in a triangular shape, and is a framework of completely performing a function of the structure. The truss can be classified into a simple truss, a compound truss, and a complex truss depending on its shape. The truss  20  according to the present invention may be configured in various forms without departing from the technical spirit of the present invention. In addition, as shown in  FIG. 4(   c ), in the case where the truss is composed of only the upper chord member  24 , the lower chord member  26 , and the vertical member  22 , it is called a referred to as a Vierendeel truss. The Vierendeel truss, which is commonly used in Europe, is connected with rigid panel points, and thus is a Rahmen structure rather than the truss. Nevertheless, the Vierendeel truss is treated to be included in a range of the truss in the present invention. 
     Meanwhile, in the shear reinforcement device  10  according to the present invention, each of the upper anchor heads  34  is fixedly connected with the upper chord member  24  of the truss  20  at the upper side of the truss  20 , and each of the lower anchor heads  44  is fixedly connected with the lower chord member  26  of the truss  20  at the lower side of the truss  20 . The upper anchor head  34  and the lower anchor head  44  are installed spaced apart by the predetermined distance from the upper anchor member  24  and the lower anchor member  26  by means of upper and lower spacers  32  and  42  as in the preferred embodiments shown in  FIGS. 6 to 8 . In this case, the predetermined distance is preferably a distance which allows the upper and lower anchor heads  34  and  44  to be placed at the positions of the upper and lower main reinforcing bars  4  and  5 , i.e., the positions of satisfying the specified concrete coating thicknesses L 1  and L 2  within a concrete structure, specifically a slab  1  as shown in  FIGS. 3 and 10 . Of course, the upper anchor head  34  and the lower anchor head are preferably formed integrally with the truss  20  together with the spacers  32  and  42 , but may be configured in various forms to provide diversity and convenience of its manufacture as in the preferred embodiments of the present invention. 
     The upper and lower spacers  32  and  42 , which allow the upper and lower anchor heads  34  and  44  to be fixed to the upper chord member  24  and the lower chord member  26  at the predetermined distance, function to secure spaces for accommodating the placement of the upper and lower main reinforcing bars  4  and  5  and the upper and lower sub reinforcing bars  4 ′ and  5 ′. In addition, the upper and lower spacers  32  and  42  function to adjust the outermost positions of the reinforcing bars, i.e., the positions of satisfying the specified concrete coating thicknesses L 1  and L 2  and the outermost positions of the anchor heads at the same time. Thus, the lengths of the upper and lower spacers  32  and  42  to which the upper and lower anchor heads  34  and  44  are joined are adjusted depending on the depth needed for placement of the upper and lower reinforcing bars. That is, the upper spacer  32  is adjusted in length to correspond to a sum of the diameters of the two upper main and sub reinforcing bars  4  and  4 ′ to facilitate the accommodation of the upper main reinforcing bar  4  and the upper sub reinforcing bar  4 ′. In addition, the lower spacer  42  is adjusted in length to correspond to a sum of the diameters of the two lower main and sub reinforcing bars  5  and  5 ′ to facilitate the accommodation of the lower main reinforcing bar  5  and the lower sub reinforcing bar  5 ′. By virtue of the configuration of the upper and lower spacers  32  and  42 , the ends of the upper and lower anchor heads  34  and  44  and the ends of the upper and lower outermost reinforcing bars are placed side by side, so that uniform construction quality can be easily secured. 
     In the shear reinforcement device  10  according to the present invention, the upper and lower anchor heads  34  and  44 , and the upper and lower spacers  32  and  42  are preferably installed in a symmetrical pattern with respect to their central axes. That is, if the upper and lower anchor heads  34  and  44 , or the upper and lower spacers  32  and  42  are biased with respect to their central axes, a bending stress may occur excessively, thereby resulting in a deterioration of the entire performance of the shear reinforcement device  10 . In this case, the central axes of the upper and lower anchor heads  34  and  44 , or the upper and lower spacers  32  and  42  coincide with the central axes of the panel points  31  and  31  (see  FIG. 3 ) where the upper chord member  24  and the lower chord member  26  are connected with the connection members  21 . In addition, the upper and lower spacers  32  and  42  are preferably joined to the panel points  31  and  41  (see  FIG. 3 ) of the upper chord member  24  and the lower chord member  26  of the truss  20 . If the upper and lower spacers  32  and  42  are not joined to the panel points  31  and  41  of the upper chord member  24  and the lower chord member  26  of the truss  20 , an additional bending stress occurs to deteriorate the structure performance of the truss. 
       FIG. 5  shows views for explaining the confining effect of a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention. In  FIG. 5 , the dotted lines indicate the schematic compressive stress trajectories of the concrete structure against the shear reinforcement device. 
     Referring to  FIG. 5 , it can be seen that the truss-type shear reinforcement device  10  having double anchorage functions at upper and lower sides thereof according to the present invention confines the concrete in a direction of Y axis, i.e., in an arrow direction as shown in  FIG. 5(   a ). That is, in the truss-type shear reinforcement device  10  having double anchorage functions at upper and lower sides thereof according to the present invention, since the truss  20  confines the behavior of the concrete occurring in the direction of Y axis, an additional concrete shear reinforcement effect is generated. Particularly, it can be seen that this confinement of the shear reinforcement device  10  produces a larger shear reinforcement effect when the diagonal member  23  is applied as the connection member  21  as shown in  FIG. 5(   c )&lt; 
     In addition, it can be seen that the truss-type shear reinforcement device  10  having double anchorage functions at upper and lower sides thereof according to the present invention confines the concrete in a direction of X axis, i.e., in an arrow direction as shown in  FIG. 5(   b ). That is, since the truss-type shear reinforcement device  10  having double anchorage functions at upper and lower sides thereof according to the present invention includes a first and secondary anchorage means in the direction of X axis, the shear resistance performance is improved. In this case, the primary anchorage means includes the upper and lower anchor heads  34  and  44 , and the secondary anchorage means includes the upper chord member  24  and the lower chord member  26 . In particular, since ductility is improved to greatly alleviate the brittle behavior of concrete in shear failure, stability of the concrete structure against the shear failure is enhanced. 
     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to  FIGS. 6 to 15 . 
     Meanwhile, the illustration and detailed description of the constitution, operation and effects that can be easily understood from a typical related technique in the art, including a general shear reinforcement device for a reinforced concrete structure and a related technical constitution and action, a construction technique of slabs and columns using the shear reinforcement device, and the like will be made briefly or omitted and only portions related with the present invention will be shown and described. 
       FIG. 6  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention,  FIG. 7  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to another preferred embodiment of the present invention,  FIG. 8  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to still another preferred embodiment of the present invention,  FIG. 9  is a perspective view illustrating a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to yet another preferred embodiment of the present invention, and  FIG. 10  shows views for explaining various examples of an anchor head in a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention. 
     Referring to  FIGS. 6 to 9 , the truss-type shear reinforcement device  10  having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention is configured such that a plurality of upper anchor heads  34  and a plurality of lower anchor heads  44  are mounted at the upper and lower sides of a truss  20  including an upper chord member  24  and a lower chord member  26  which are connected with each other by a plurality of connection members  21  according to a technical spirit of the present invention. Thus, the respective anchor heads  34  and  44  serves as a primary anchorage means, and the upper chord member  24  and the lower chord member  26  serves as a secondary anchorage means to perform double anchorage functions at the upper and lower sides of the shear reinforcement device  10 . In this case, the truss  20 , the upper and lower anchor heads  34  and  44 , and the upper and lower spacers  32  and  42  allowing the upper and lower anchor heads  34  and  44  to be fixedly connected to the truss  20  may be configured in various forms as shown in  FIGS. 6 to 9 . 
     Referring to  FIG. 6 , the shear reinforcement device  10  shown in this embodiment applies the vertical member  22  and the diagonal member  23  as the connection member  21  of the truss  20 , and the vertical member  22  and the diagonal member  23  are fastened to each other by bolts. Of course, fastening structures of various forms such as welding, riveting, and the like may be applied. In this case, the upper and lower spacers  32  and  42  allowing the upper and lower anchor heads  34  and  44  to be fixedly connected to the truss  20  are formed integrally with the vertical member  22  as the connection member  21 . That is, the upper and lower spacers  32  and  42  have the functions of the vertical member  22  of the truss  20  and the upper and lower spacers  32  and  42  using a sheet. The upper spacer  32  is formed in such a fashion as to protrudingly extend upwardly from the top of the upper chord member  24  by a predetermined distance, and the lower spacer  42  is formed in such a fashion as to protrudingly extend downwardly from the bottom of the lower chord member  26  by a predetermined distance. Thus, the upper anchor head  34  is joined to the upper spacer  32  so that it is installed spaced apart by the predetermined distance from the upper chord member  24 , and the lower anchor head  44  is joined to the lower spacer  42  so that it is installed spaced apart by the predetermined distance from the lower chord member  26 . In this embodiment, there is shown an example of the joining by welding. 
     In the meantime, the shear reinforcement devices  10  according to this embodiment and other embodiments which will be described later include through-holes  22   a  formed at arbitrary positions thereof to increase the bonding force with concrete. In this embodiment, the through-holes formed on the vertical members  22 , the diagonal members  21 , the upper and lower chord members  24 ,  26  and the upper and lower anchor heads  34  and  44  are used as holes for assembly, but through-holes except the assembly purpose and the through-holes formed on the upper and lower anchor heads  34  and  44  perform the functions of the through-holes  21   a . Of course, such a configuration for increasing the bonding force with concrete may have the shape of protrusions (e.g., embossing) used variously in the art as well as the shape of the through-holes. Such a configuration may be selectively applied depending on the need. 
     Further, in  FIG. 9 , a non-explained reference numeral  70  is another spacer, which functions to automatically adjust the concrete coating thickness when placing the shear reinforcement device  10  on a concrete form at the time of installation of the shear reinforcement device  10  a as shown in  FIG. 11(   a ). Thus, a head  71  of the spacer  70  is set to have the same height as the concrete coating thickness L 2  (see  FIG. 2) . 
     Referring to  FIG. 7 , the shear reinforcement device  10  shown in this embodiment applies the vertical member  22  and the diagonal member  23  as the connection member  21  of the truss  20 , and the vertical member  22  and the diagonal member  23  are fastened to each other by welding. Of course, fastening structures of various forms such as bolts, rivets, and the like may be applied. In addition, although it is shown in this embodiment that the upper chord member  24 , the lower chord member  26 , and the vertical members  22  apply a pipe, the present invention is not limited thereto. The shear reinforcement device  10  according to this embodiment is configured such that the upper anchor head  34  is joined to the upper spacer  32  so that it is installed spaced apart by the predetermined distance from the upper chord member  24 , and the lower anchor head  44  is joined to the lower spacer  42  so that it is installed spaced apart by the predetermined distance from the lower chord member  26  like the above-mentioned embodiment. Thus, the upper spacer  32  is fixed at a bottom thereof to the upper chord member  24 , and is fixed at a top thereof to the upper anchor head  34 . In addition, the lower spacer  42  is fixed at a top thereof to the lower chord member  26 , and is fixed at a bottom thereof to the lower anchor head  44 . Of course, the configurations of the upper anchor head  34  and the upper spacer  32 , and the lower anchor heads  44  and the lower spacer  42  may be implemented in various forms. In this embodiment, the shear reinforcement device  10  is configured such that the upper anchor head  34  is formed integrally with the upper spacer  32 , and the lower anchor head  44  is formed integrally with the lower spacer  32 . 
     Referring to  FIG. 8 , the shear reinforcement device  10  shown in this embodiment applies only the vertical member  22  as the connection member  21  of the truss  20 , and has a structure in which the upper chord member  24  and the lower chord member  26  of the truss  20  are joined to the vertical member  22  in such a fashion as to inserted into through-holes  22   b  formed on the vertical member  22 . Herein, the upper chord member  24  and the lower chord member  26  may be configured to be fixed to the vertical member  22  by means of welding. In addition, in this embodiment, the upper anchor heads  34 , the upper spacer  32 , the vertical member  22 , the lower spacer  42 , and the lower anchor head  44  are formed integrally with each other. 
     Referring to  FIG. 9 , the shear reinforcement device  10  shown in this embodiment applies a wire  23   a  and a turnbuckle  23   b  as the diagonal member  23  used as the connection member  21  of the truss  20  while having a basic structure of the shear reinforcement device shown in  FIG. 7 . That is, such a configuration of the diagonal member  23  may be configured in other forms besides fastening means such as weld, bolts, and the like. 
     Like the various technical configurations shown in  FIGS. 6 to 9 , the shear reinforcement device  10  according to the present invention may be configured in various forms without departing from the technical spirit of the present invention. 
     In the meantime, the shear reinforcement device  10  according to a preferred embodiment of the present invention may apply the cross-sectional shapes of the upper and lower anchor heads  34  and  44 , and the upper and lower spacers  32  and  42  in various manner as shown in  FIG. 10 . For example,  FIG. 10(   a ) shows an example in which the upper and lower anchor heads  34  and  44 , and the upper and lower spacers  32  and  42  adopt a quadrilateral plate to have the same length in one direction, and  FIG. 10(   b ) shows an example in which the upper and lower spacers  32  and  42  adopt a square bar having a relatively small cross-sectional area as compared to the upper and lower anchor heads  34  and  44  having the quadrilateral plate. In addition,  FIG. 10(   c ) shows an example in which the upper and lower spacers  32  and  42  adopt a circular bar having a relatively small cross-sectional area as compared to that of the upper and lower anchor heads  34  and  44  while the upper and lower anchor heads  34  and  44 , and the upper and lower spacers  32  and  42  have a circular cross-sectional area. 
     In this case, preferably, the horizontal cross-sectional area of the upper anchor head  34  is formed to be equal to 7-14 times that of the upper spacer  32 , and the horizontal cross-sectional area of the lower anchor head  44  is formed to be equal to 7-14 times that of the lower spacer  42  in order to secure a sufficient anchorage effect. Limitation of the cross-sectional area of the upper anchor head  34  is based on the proportional relationships of the cross-sectional area which is the most suitable for the stud and the stem, which has been proposed by Abdel-Salam Mokhtar, Amin Ghali and Walter Dilger, et al., in “Stud Shear Reinforcement For Flat Concrete Plates” ACI Structural Journal (technical paper), Title no. 82-60. 
       FIG. 11  is a view illustrating an example in which a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention is typically applied to a reinforced concrete structure, and  FIG. 12  is a view illustrating an example in which a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention is applied to a joint where a slab and a column are joined to each other. 
     Referring to  FIGS. 11 and 12 , the shear reinforcement device  10  according to the preferred embodiments of the present invention is installed at a joint where a slab and a column of a reinforced concrete structure are joined to each other or is installed as a substitute for a non-reinforced portion or a stirrup reinforced portion such as a beam, a column, a wall, a foundation, and the like in order to increase resistance against shear failure. 
     Referring to  FIG. 11 , a method in which the shear reinforcement device  10  according to the preferred embodiment of the present invention is used in a concrete structure (slab) will be described hereinafter. First, a concrete form is first constructed prior to construction of the slab. In  FIG. 11 , the details necessary for construction of the slab concrete form are recognized by general technicians, and thus their description will be omitted and only a state in which the sheet of a final sub concrete form is installed is shown. 
     Next, the lower main reinforcing bar  5  and the lower sub reinforcing bar  5 ′ are installed. At this time, a plurality of spacers  70 ′ is typically embedded at regular intervals below the lower main reinforcing bar  5  to secure the concrete coating thickness L 2  (see  FIG. 3 ) of the reinforcing bars. In this case, the concrete coating thickness L 2  is required to be equal to more than 2 cm in case of the slab. Of course, the shear reinforcement device  10  according to the present invention can secure the concrete coating thickness through installation of the dedicated spacers  70  to improve convenience of the work as described above. 
     In addition, as shown in  FIGS. 11(   a ) and  11 ( b ), the shear reinforcement device  10  according to the preferred embodiment of the present invention is installed above the lower reinforcing bars. In this case, for the shear reinforcement device  10  according to the preferred embodiment of the present invention, since the lower chord member  26  may be placed on the lower reinforcing bars, there occurs no interference the shear reinforcement device  10  and the reinforcing bars, and the requirements of the concrete coating thickness can be easily satisfied during the construction of the shear reinforcement device  10 . 
     Subsequently, the upper main reinforcing bar  4  and the upper sub reinforcing bar  4 ′ are installed. In this case, when the upper reinforcing bar is placed on the upper chord member  24  of the shear reinforcement device  10  installed at the previous step, the upper chord member  24  coincides with the placement height of the upper reinforcing bar, so that a worker need not do any other work to secure the concrete coating thickness L 1  (see  FIG. 3 ) of the upper reinforcing bar. 
     The construction method performed by using the shear reinforcement device  10  according to the present invention is significantly excellent in constructionability and has a high accuracy in bar placement as compared to the conventional shear reinforcement device, thereby improving construction quality. That is, the shear reinforcement device  10  according to the present invention is intended to first construct the lower reinforcing bars (including the main reinforcing bar and the sub reinforcing bar: the embedded spacer) on the concrete form. On the other hand, the conventional shear reinforcement device (i.e., the shear stud shown in  FIG. 1  ( b )) is first required to be placed on the concrete form, and then requires that the lower reinforcing bars (i.e., the main reinforcing bar and the sub reinforcing bar) are placed thereon. At this time, the conventional shear reinforcement device entails a problem in that a worker suffers from an inconvenience of having of paying a special attention to the shear reinforcement device to prevent the shear reinforcement device from falling down or being displaced in the placement of the shear reinforcement device. Further, such a conventional shear reinforcement device has a disadvantage in that since the placement position of the lower reinforcing bar  5  is higher than that in shear reinforcement device  10  according to the present invention by the lower thickness of the shear reinforcement device (see  FIG. 2(   b )), the bending performance of the structure cured later is relatively deteriorated as compared to that of the shear reinforcement device  10  according to the present invention. Moreover, in the construction method using the conventional shear reinforcement device according to the prior art, since the placement height of the upper reinforcing bars (i.e., the main reinforcing bar and the sub reinforcing bar) cannot be confirmed, separate spacers for placing the upper reinforcing bars are required to be installed. On the other hand, since the shear reinforcement device  10  according to the present invention has its own function of the spacers, its construction is performed in a convenient and rapid manner, and accurate bar placement quality is secured. 
     Referring to  FIG. 12 , the placement of the shear reinforcement device at the slab-column joints does not cause interference between the shear reinforcement device and the column since it doe not pass through the column. In addition, as described above, there also occurs no interference between the shear reinforcement device  10  according to the present invention and the reinforcing bars in the slab. The shear reinforcement device  10  according to the present invention also serves as the spacer with respect to the slab reinforcing bars, thereby providing convenience of construction. 
     As such, the shear reinforcement device  10  according to the preferred embodiment of the present invention allows the upper and lower reinforcing bars placed to be disposed at the outermost position where the concrete coating thickness is secured, and simultaneously performs a shear reinforcement, so that the bending resistance of the reinforced concrete structure can be secured maximally. Further, there occurs a stress reversal phenomenon in which a tensioned portion and a compressed portion are reversed upon the exertion of a lateral load such as earthquake, and the like on the reinforced concrete structure. However, the shear reinforcement device  10  according to the preferred embodiment of the present invention can always maintain a uniform shear reinforcement function by virtue of symmetricity of elements in the vertical direction, thereby resulting in improved stability of the shear reinforcement performance. 
       FIGS. 13 to 15  are views illustrating examples of prefabrication of reinforcing bars using a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to a preferred embodiment of the present invention, in which  FIG. 13  shows an example of prefabrication of reinforcing bars for a column formed by joining a plurality of shear reinforcement device  10  to each other,  FIG. 14  shows an example of prefabrication of reinforcing bars for a beam joined with the concrete form, and  FIG. 15  shows an example of prefabrication of reinforcing bars using wires and turnbuckles. 
     Referring to  FIGS. 13 to 15 , the shear reinforcement device  10  according to the preferred embodiment of the present invention has an its own excellent bending stiffness by virtue of the features of the truss and a further excellent bending stiffness in a state of being tied with the reinforcing bars. As a result, the inventive shear reinforcement device  10  enables prefabrication of reinforcing bars by joining a plurality of shear reinforcement devices in the form of a column or a beam. Therefore, the shear reinforcement device  10  according to the present invention is used as a substitute for a stirrup used in an existing traditional prefabrication of reinforcing bars so as to prefabricate the main reinforcing bars together, which makes it possible to be utilized as a novel prefabrication of reinforcing bars 
     While the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the preferred embodiments of the present invention has been described and illustrated in connection with specific exemplary embodiments with reference to the accompanying drawings, it will be readily appreciated by those skilled in the art that it is merely illustrative of the preferred embodiments of the present invention and various modifications and changes can be made thereto within the technical spirit and scope of the present invention. 
     MODE FOR INVENTION 
     In one exemplary embodiment of the present invention, there is provided a truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof, which is installed in a reinforced concrete structure to increase resistance against shear failure, characterized in that the truss-type shear reinforcement device includes: 
     a truss  20  including an upper chord member  24 , a lower chord member  26 , and one or more connection members  21  for interconnecting the upper chord member  24  and the lower chord member  26 ; 
     one or more upper anchor heads  34  fixedly connected with the upper chord member  24  of the truss  20  at the upper side of the truss  20 ; and 
     one or more lower anchor heads  44  fixedly connected with the lower chord member  26  of the truss  20  at the lower side of the truss  20 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the connection members  21  may include any one of a vertical member  22  and a diagonal member  23 . The vertical member  22  may be formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the vertical member  22  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the vertical member  22  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the vertical member  22  are vertically aligned. In addition, the diagonal member  23  may be formed at an upper portion thereof with an upper panel point  31  where the upper chord member  24  and the diagonal member  23  are joined to each other, and are formed at a lower portion thereof with a lower panel point  41  where the lower chord member  26  and the diagonal member  23  are joined to each other, in such a fashion that the upper panel point  31  and the lower panel point  41  of the diagonal member  23  are diagonally aligned. 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the connection members  21  may include an upper spacer  32  protrudingly extending upwardly from the top of the upper chord member  24  by a predetermined distance, and a lower spacer  42  protrudingly extending downwardly from the bottom of the lower chord member  26  by a predetermined distance. 
     In addition, each of the upper anchor heads  34  may be joined to the upper spacer  32  so that it is installed spaced apart by the predetermined distance from the upper anchor member  24 , 
     and each of the lower anchor heads  44  may be joined to the lower spacer  42  so that it is installed spaced apart by the predetermined distance from the lower chord member  26 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, each of the upper anchor heads  34  may be installed spaced apart by the predetermined distance from the upper chord member  24  by the upper spacer  32  fixed at a lower side thereof to the upper chord member  24  and fixed at an upper side thereof to the upper anchor head  34 . 
     In addition, each of the lower anchor heads  44  may be installed spaced apart by the predetermined distance from the lower chord member  26  by the lower spacer  42  fixed at an upper side thereof to the lower chord member  26  and fixed at a lower side thereof to the lower anchor head  44 . 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, the upper spacer  32  may be fixed to the upper panel point  31  where the upper chord member  24  and the connection member  21  are joined to each other, 
     and the lower spacer  42  may be fixed to the lower panel point  41  where lower chord member  26  and the connection member  21  are joined to each other. 
     In the truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention, the horizontal cross-sectional area of each of the upper anchor heads  34  may be formed to be equal to 7-14 times that of the upper spacer  32 , 
     and the horizontal cross-sectional area of each of the lower anchor heads  44  may be formed to be equal to 7-14 times that of the lower spacer  42 . 
     INDUSTRIAL APPLICABILITY 
     The truss-type shear reinforcement device having double anchorage functions at upper and lower sides thereof according to the present invention is installed at a foundation of a reinforced concrete structure, a slab, and a portion where a wall and a slab column are joined to each other so that applicable examples of various forms proposed in the preferred embodiments of the present invention can be applied either alone or combinedly to increase resistance against shear failure.