Patent Publication Number: US-2013230350-A1

Title: Reinforcement bar coupler

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This patent application is a National Phase application under 35 U.S.C. §371 of International Application No. PCT/KR2011/008203, filed Oct. 31, 2011, which claims priority to Korean Patent Application Nos. 10-2010-0109388 filed Nov. 4, 2010, and 10-2011-0007910 filed Jan. 26, 2011, entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a reinforcement bar coupler. 
     2. Background Art 
     In general, a reinforcement bar is used a manner in which it is buried inside concrete when constructing a steel-reinforced concrete structure in order to reinforce the strength of the concrete structure. In particular, a large number of reinforcement bars are used for reinforcement in large buildings, special structures, and engineering work structures such as bridges. 
     However, since reinforcement bars are manufactured to be standardized regular lengths, it is required to connect those reinforcement bars that are manufactured at limited lengths to each other when using such reinforcement bars in large buildings, special structures, and engineering work structures such as bridges. 
     Typically, methods that have been used up to now to couple reinforcement bars include lap jointing, welding, screw-machining, mechanical jointing and the like. 
     Lap jointing is a method of coupling reinforcement bars by overlapping the reinforcement bars at a predetermined length and tying them with a wire or a steel wire. A large portion of the reinforcement bars are lost, and the reinforcement bars are easily detached due to the weak strength of jointed portions. Also, a working time is increased due to poor constructability, which is problematic. The welding has problems in that construction is difficult and the strength of the portions of the reinforcement bars adjacent to the welded portions is remarkably weakened because of the heat generated when the welded portions are heated. 
     In order to overcome the foregoing problems, a mechanical coupling technology was developed. As an example, a reinforcement bar coupling device is disclosed in Korean Laid-Open Patent Publication No. 10-2009-0009578 (published Jan. 23, 2009). Referring to this device, as shown in  FIG. 1 , a pair of reinforcement bars  1  and  2  which have joint protrusions  1   a  and  2   a  at predetermined intervals on the outer circumference thereof and rib protrusions  1   b  and  2   b  in the longitudinal direction are disposed such that they face each other. The ends  1   c  and  2   c  of the reinforcement bars  1  and  2  which face each other are wrapped in first and second couplers  10 ′ and  20 ′. Both ends of the first and second couplers  10 ′ and  20 ′ are clamped via screw clamping using clamping nuts  31 ′ and  33 ′. Afterwards, fastening pins  35 ′ are fitted into fastening holes  31   a ′ and  33   a ′ of the clamping nuts  31 ′ and  33 ′. 
     However, in the foregoing technologies, when the reinforcement bars are connected to each other at work sites, a great deal of manual labor of craftsmen is required, i.e. the first and second couplers  10 ′ and  20 ′ are butted against each other, the clamping nuts  31 ′ and  33 ′ are clamped, and the fastening pins  35 ′ are fitted. Accordingly, a long time and a large cost are spent on construction. 
     In addition, Korean Patent No. 10-0837113 (published Jun. 13, 2008) was disclosed as another mechanical coupling method of the related art. As shown in  FIG. 2 , one end of each reinforcement bar  100 ″ is machined into the shape of a wedge, thereby forming a connecting portion  101 ″. The connecting portions  101 ″ of a pair of reinforcement bars  100 ″ are connected and fixed to each other using a pair of coupler members  11 ″ and  21 ″, a pair of coupler connecting pins  30 ″, a pair of rubber bands  40 ″ and the like. 
     However, this approach of the related art has a significant drawback in that ends of the reinforcement bars  100 ″, which are manufactured at standardized sizes, must be machined before use in order to form the connecting portions  101 ″. In addition, the coupler members  11 ″ and  21 ″, the coupler connecting pins  30 ″, the rubber bands  40 ″ and the like must be individually and manually fastened to the reinforcement bars  100 ″, thereby leading to the problems of increased construction time and cost. 
     SUMMARY 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and is intended to provide a reinforcement bar coupler, in which a female thread having an inclined taper plane is formed on the inner surface of a coupler cap, and a clamping spring is formed such that it is inserted into and fastened to the female thread. When a reinforcement bar is inserted into the clamping spring, the clamping spring is closely abutted to the bottom of the female thread and is increased in diameter so that the reinforcement bar slips. In the state in which the reinforcement bar is inserted, when an external force is applied in the direction opposite to the direction in which the reinforcement bar is inserted, the clamping spring moves along the inclined taper plane and is decreased in diameter, thereby holding the reinforcement bar. It is therefore possible to easily connect and couple the reinforcement bar with one touch based on a change in the diameter of the clamping spring using a relatively simple configuration. 
     The present invention is also intended to provide a reinforcement bar coupler, in which a base spring which is machined from the outside is used without directly machining the inner surface of the coupler cap in order to form the bottom and the inclined taper plane of the female thread, thereby facilitating machining and manufacture. One-touch connecting means allows the clamping spring to be fitted into and fastened to the base spring in the state in which the clamping spring is twisted in the direction in which its diameter is increased. The one-touch connecting means also allows the diameter of the clamping spring to be restored when the insertion of the reinforcement bar is completed. Accordingly, even if there is a difference in the diameter between reinforcement bars due to characteristics of the manufacturing process of the reinforcement bars, the reinforcement bars can be properly coupled to each other irrespective the difference. 
     In an aspect, the present invention provides a reinforcement bar coupler with which a reinforcement bar is connected and fixed. The reinforcement bar coupler includes a hollow coupler cap having an open outer end through which the reinforcement bar is to be inserted into the coupler cap; a spiral female thread circumferentially recessed on an inner surface of the coupler cap, the female thread having an inclined taper plane which is inclined and protrudes from a recessed bottom in a direction toward the outer end; and a clamping spring having a spiral shape that corresponds to the female thread, the clamping spring being made of a material that can be twisted and changed in diameter under an external force and be elastically restored, and being fitted into and fastened to the female thread. When the reinforcement bar is inserted, the clamping spring is closely abutted to the recessed bottom of the female thread and is unwound so that a diameter thereof is increased so that the reinforcement bar slips. When an external force in a direction opposite to a direction in which the reinforcement bar is inserted is applied in a state in which the reinforcement bar is inserted, the clamping spring moves in the direction toward the outer end of the coupler cap along the inclined taper plane due to a frictional force exerted onto the reinforcement bar and is wound on the reinforcement bar so that the diameter thereof is gradually decreased, thereby holding the reinforcement bar. 
     The reinforcement bar coupler according to the present invention is characterized in that the female thread includes a base spring fitted into the coupler cap. The base spring is spirally wound so as to have an outer diameter corresponding to an inner diameter of the coupler cap, and has bottoms which are formed on an inner surface of the base spring, are spirally wound, and are spirally recessed in a circumferential direction at positions where adjacent joints meet, and inclined taper planes which are inclined and protrudes from the recessed bottoms in a direction toward the outer end. The reinforcement bar coupler further includes an anti-dislodgement unit having a reinforcement bar passage hole in a central portion thereof, the reinforcement bar passage hole having a predetermined diameter through which the reinforcement bar can pass. The anti-dislodgement unit is fastened to the outer end of the coupler cap in order to prevent the base spring from being dislodged in the direction toward the outer end of the coupler cap in a state in which the base spring is fitted into the coupler cap. 
     The reinforcement bar coupler according to the present invention is characterized in that the base spring has a rounded portion which is roundly machined along each corner of upper edges of the joints such that, when the clamping spring is moved in the direction toward the outer end of the coupler cap along the inclined taper plane, an upper edge of each of the joints overlaps an inner portion of a lower edge of an adjacent joint and an inner diameter of the base spring is decreased under an external force. 
     The reinforcement bar coupler according to the present invention is characterized in that the clamping spring has clamping taper planes, which correspond to the inclined taper planes such that the clamping spring is slideable and movable along the inclined taper plane, and an angled corner portion, a part of which thrusts into the reinforcement bar when the diameter of the clamping spring is decreased. 
     The reinforcement bar coupler according to the present invention is characterized by further including a one-touch connecting means which prevents the clamping spring from interfering with insertion of the reinforcement bar while the reinforcement bar is being inserted into the coupler cap, and causes the clamping spring to hold the reinforcement bar when the insertion of the reinforcement bar into the coupler cap is completed. The one-touch connecting means includes a hook portion provided adjacent to the outer end of the coupler cap. The hook portion supporting one end of the clamping spring, a support plate provided inside the coupler cap, and a leaf spring supported by the support plate, the leaf spring having a protrusion protruding from the support plate between the hook portion and the leaf spring such that the other end of the clamping spring is supported in a state in which the clamping spring is twisted in a direction in which the diameter there is increased. When the reinforcement bar is inserted into the coupler cap and presses against the protrusion, the protrusion is recessed due to elasticity and no longer supports the other end of the clamping spring, so that the diameter of the clamping spring is restored due to elasticity. 
     According to the reinforcement bar coupler of the present invention having the above-described configurations, it is possible to easily connect and couple reinforcement bars with one touch based on a change in the diameter of the clamping springs caused by twisting using a relatively simple configuration. Since the bottom and the inclined taper plane are formed without machining the female thread, it is easy to machine and manufacture the reinforcement bar coupler. Since the cross-section of the clamping spring has a triangular shape, the reinforcement bar can be more securely fixed based on the sliding movement of the clamping spring and the thrust of the angled end portions into the reinforcement bar. Since the one-touch connecting means allows the clamping spring to be fitted into and fastened to the base spring in the state in which the clamping spring is twisted in the direction in which its diameter is increased and the diameter of the clamping spring to be restored when the insertion of the reinforcement bar is completed, the reinforcement bars can be properly coupled to each other irrespective the difference even if there is a difference in the diameter between reinforcement bars due to characteristics of the manufacturing process of the reinforcement bars. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view showing a reinforcement bar coupler of the related art; 
         FIG. 2  is an exploded perspective view showing another reinforcement bar coupler of the related art; 
         FIG. 3  are example views showing the states in which reinforcement bar couplers according to the present invention are used; 
         FIG. 4  is an exploded perspective view showing a reinforcement bar coupler according to a first embodiment of the present invention; 
         FIG. 5  is a perspective view showing a part of the reinforcement bar coupler according to the first embodiment of the present invention which is partially cut away; 
         FIG. 6  is an exploded perspective view showing a reinforcement bar coupler according to a second embodiment of the present invention; 
         FIG. 7  is a perspective view showing a part of the reinforcement bar coupler according to the second embodiment of the present invention which is partially cut away; and 
         FIG. 8  to  FIG. 10  are side cross-sectional views showing the state in which the reinforcement bar coupler according to the second embodiment of the present invention is used. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to a reinforcement bar coupler according to the present invention, embodiments of which are illustrated in the accompanying drawings. 
       FIG. 3  is example views showing the states in which reinforcement bar couplers according to the present invention are used,  FIG. 4  is an exploded perspective view showing a reinforcement bar coupler according to a first embodiment of the present invention, and  FIG. 5  is a perspective view showing a part of the reinforcement bar coupler according to the first embodiment of the present invention which is partially cut away. 
     Referring to the figures, the reinforcement bar coupler according to the first embodiment of the present invention includes a coupler cap  10 , female threads  20 , a clamping spring  30  and one-touch connecting means  50 . 
     The coupler cap  10  is configured such that the reinforcement bars  1  which are to be connected and fixed to each other are inserted into the coupler cap  10  through the open outer ends. As shown in  FIG. 3 , the coupler cap  10  may have a variety of shapes, such as (a) an anchor type, (b) a linear type, (c) a T type, (d) a cross type, and so on. 
     As shown in the figures, each of the reinforcement bars  1  which are referred to herein may include a reinforcement bar having a typical shape in which the joint protrusions  1   a  and the rib protrusions  1   b  are formed, as well as a bolt having a male thread on the outer circumference thereof and a bar type member having a predetermined length. 
     According to the first embodiment of the present invention, the coupler cap  10  is illustrated as a linear type which is most frequently used on work sites. The coupler cap  10  is configured as a hollow cylindrical pipe which is symmetrical about the longitudinal axis such that the pair of reinforcement bars  1  are connected to each other in the longitudinal direction. 
     The female threads  20  defines spaces into which the clamping springs  30  are fitted into and fastened to. According to the first embodiment of the present invention, the female threads  20  are spirally recessed along the circumferential direction on the inner surface of the coupler cap  10 . 
     In the meantime, the female threads  20  have inclined taper planes  22  which protrude from recessed bottoms  21  in the direction toward the outer ends, such that the clamping spring  30  can slide and move along the female threads  20 . 
     As a machining process of forming the female threads  20  on the inner surface of the coupler cap  10 , a cutting tap which spirally cuts the inner surface may be used. It is preferable to use a rolled tap which forms the female threads  20  by plastically deforming the inner surface of the coupler cap  10  during heating in order to save processing costs. 
     The clamping springs  30  are components which hold the reinforcement bars  1  inserted into the coupler cap  10 . The clamping springs  30  have a spiral shape that corresponds to the female threads  20 , and are made of a material such as a spring steel that can be twisted and changed in diameter under an external force and be elastically restored. The clamping springs  30  are fitted into and fastened to the female threads  20 . That is, the clamping springs  30  are a type of torsion spring which is changed in diameter in response to the twisted direction and is elastically restorable. 
     The clamping springs  30  can be rotated in one direction along the female threads  20  from the outer ends of the coupler cap  10 , and be fitted into and fastened to the female threads  20  inside the coupler cap  10 . 
     The clamping springs  30  are configured such that they are closely abutted to the recessed bottoms  21  of the female threads  20  and are unwound so that their diameter is increased, thereby enabling the reinforcement bars  1  to slip, when the reinforcement bars  1  are inserted into the clamping springs  30 . Specifically, when the reinforcement bars  1  are inserted into the clamping springs  30 , the clamping springs  30  are pushed in the direction toward the recessed bottoms  21  of the female threads  20  and are unwound so that their diameter is increased, due to a force under which the reinforcement bars  1  are inserted and a frictional force exerted onto the reinforcement bars  1 , thereby enabling the reinforcement bars  1  to slip. 
     Furthermore, according to the first embodiment of the present invention, in the initial state before the reinforcement bars  1  are inserted by the one-touch connecting means  50 , the clamping springs  30  are fastened into the female threads  20  of the coupler cap  10  in the state in which they are twisted in the direction in which their diameter is increased. Accordingly, the clamping springs  30  are minimally influenced by the diameter of the reinforcement bars  1 , and allow the reinforcement bars  1  to be properly inserted irrespective of the types of the reinforcement bars  1 . A detailed description thereof will be given with respect to a second embodiment of the present invention which will be described later. 
     In addition, in the state in which the reinforcement bars  1  are inserted, when an external force is applied in the direction opposite to the direction in which the reinforcement bars  1  are inserted, the clamping springs  30  are wound while moving in the direction toward the outer ends of the coupler cap  10  along the inclined taper planes  22  due to the frictional force exerted onto the reinforcement bars  1  so that the diameter of the clamping springs  30  is gradually decreased, thereby holding the reinforcement bars  1 . 
     The one-touch connecting means  50  prevent the clamping springs  30  from interfering with the insertion of the reinforcement bars  1  in the process in which the reinforcement bars  1  are being inserted into the coupler cap  10 . When the insertion of the reinforcement bars  1  into the coupler cap  10  is completed, the one-touch connecting means  50  allow the clamping spring  30  to hold the reinforcement bars  1 . Each of the one-touch connecting means  50  includes a hook portion  51 , a support plate  52  and a leaf spring  53 . A detailed description thereof will be given with respect to the second embodiment of the present invention which will be described later. 
     The reinforcement bar coupler according to the first embodiment of the present invention has been described hereinabove, and a detailed description will be given below of a reinforcement bar coupler according to the second embodiment of the present invention. 
       FIG. 6  is an exploded perspective view showing the reinforcement bar coupler according to the second embodiment of the present invention,  FIG. 7  is a perspective view showing a part of the reinforcement bar coupler according to the second embodiment of the present invention which is partially cut away, and  FIG. 8  to  FIG. 10  are side cross-sectional views showing the state in which the reinforcement bar coupler according to the second embodiment of the present invention is used. 
     Referring to the figures, the reinforcement bar coupler according to the second embodiment of the present invention includes a coupler cap  10 , base springs  20   a,  clamping springs  30 , anti-dislodgement units  40  and one-touch connecting means  50 . 
     When compared with the first embodiment of the present invention, the reinforcement bar coupler according to the second embodiment of the present invention further includes the anti-dislodgement units  40 , with the base springs  20   a  substituting the female threads  20 . 
     The coupler cap  10  is a hollow cylindrical pipe which serves as a housing of the reinforcement bar coupler according to the second embodiment of the present invention which connects and couples a pair of reinforcement bars  1  to each other in the longitudinal direction. The coupler cap  10  is configured such that both ends are symmetrical to each other about the longitudinal axis such that the pair of reinforcement bars  1  are respectively inserted into the coupler cap  10  through the outer ends thereof. The base springs  20   a  are inserted into and disposed in the coupler cap  10 . 
     The base springs  20   a  are components which are fitted into the coupler cap  10 , and to which the clamping springs  30  are fitted and fastened. The base springs  20   a  are spirally wound such that they have an outer diameter corresponding to the inner diameter of the coupler cap  10 , and have bottoms  21  on the inner circumference thereof. The bottoms  21  are spirally wound, and are spirally recessed in the circumferential direction at positions where adjacent joints  20   a ′ and  20   a ″ meet each other. 
     That is, the clamping springs  30  having the spiral shape are fitted into and fastened to the bottoms  21  of the base springs  20   a  which are spirally recessed. 
     In addition, the method of forming the female threads  20  directly on the inner surface of the coupler cap  10  as in the first embodiment of the present invention may be regarded as a method of forming the bottoms  21 . However, this method is complicated and the cost of manufacture is increased, which is problematic. Therefore, according to the second embodiment of the present invention, the configuration of the base springs  20   a,  which can be more easily manufactured than the threads  20 , is employed. 
     In addition, each base spring  20   a  has an inclined taper plane  22  which protrudes from the recessed bottom  21  in the direction toward the outer end. 
     Specifically, in the process of manufacturing the base springs  20   a,  the base springs  20   a  are formed such that their cross-section has a substantially triangular shape, so that the inclined taper planes  22  are naturally formed. As clamping taper planes  31  of the clamping springs  30  are meshed with the inclined taper planes  22 , the clamping springs  30  can slide and move. 
     In addition, each base spring  20   a  has rounded portions  23  which are machined along the corners of the upper edge of the joints  20   a ′ and  20   a ″ such that they have a round shape. Consequently, when the clamping spring  30  moves in the direction toward the outer end of the coupler cap  10  along the inclined taper plane  22 , due to the external force, the upper edge of the joint  20   a ″ overlaps the inner portion of the lower edge of the adjacent joint  20   a ′ so that the inner diameter is decreased. 
     Specifically, in the state in which the reinforcement bars  1  are inserted, when the external force is applied to the reinforcement bars  1  in the direction opposite to the direction in which the reinforcement bars  1  are inserted, the clamping springs  30  are wound while moving in the direction toward the outer ends of the coupler cap  10  along the inclined taper planes  22  due to the frictional force exerted onto the reinforcement bars  1  so that their diameter is gradually decreased, thereby holding the reinforcement bars  1 . In this case, like the clamping springs  30 , the base springs  20   a  are subjected to an external force in the direction opposite to the direction in which the reinforcement bars  1  are inserted. Since each base spring  20   a  has the rounded portion  23  which is machined in the longitudinal direction along each corner of the upper edges of the joints  20   a ′ and  20 ″, the upper edge of one joint  20   a ″ overlaps the inner portion of the lower edge of the adjacent joint  20   a ′ and the inner diameter of the base springs  20   a  is also decreased, so that the reinforcement bar  1  can be more reliably held. 
     Table 1 and Table 2 below represent results of tensile strength tests for reinforcement bar couplers according to KS D 0249: 2003 (regulated Mar. 4, 2003), a test method for a mechanical coupling of steel bars for steel-reinforced concrete published by the Korean Standards Association. 
     First, Table 1 below represents the result of the tensile strength test for a reinforcement bar coupler in which no rounded portions  23  are formed in the base springs  20   a,  i.e. the adjacent joints  20   a ′ and  20   a ″ of the base springs  20   a  do not overlap each other so that the inner diameter of the base springs  20   a  is not changed when the reinforcement bars  1  are pulled in the direction toward the both ends of the coupler cap  10 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Test item 
                 Unit 
                 Classification 
                 Result 
                 Test method 
               
               
                   
               
             
            
               
                 Tensile strength 
                 N/mm 2   
                 1 
                 582 
                 KS D 0249: 2003 
               
               
                 Tensile strength 
                 N/mm 2   
                 2 
                 581 
                 KS D 0249: 2003 
               
               
                 Tensile strength 
                 N/mm 2   
                 3 
                 476 
                 KS D 0249: 2003 
               
               
                   
               
            
           
         
       
     
     Table 2 below represents the result of the tensile strength test for a reinforcement bar coupler in which the rounded portions  23  are formed in the base springs  20   a,  i.e. the adjacent joints  20   a ′ and  20   a ″ of the base springs  20   a  overlap each other so that the inner diameter of the base springs  20   a  is decreased when the reinforcement bars  1  are pulled in the direction toward the both ends of the coupler cap  10 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Test item 
                 Unit 
                 Classification 
                 Result 
                 Test method 
               
               
                   
               
             
            
               
                 Tensile strength 
                 N/mm 2   
                 1 
                 621 
                 KS D 0249: 2003 
               
               
                 Tensile strength 
                 N/mm 2   
                 2 
                 601 
                 KS D 0249: 2003 
               
               
                   
               
            
           
         
       
     
     In Table 2 above, the reinforcement bar used in the secondly repeated test was fractured, failing to withstand the tensile force of a test device, and thus no further tests were carried out. 
     However, based on the above test results, it can be appreciated that the upper edge of each joint  20   a ″ overlaps the inner portion of the lower edge of the adjacent joint  20   a ′ so that the inner diameter of the base spring  20   a  is decreased when the rounded portion  23  is formed in the base spring  20   a.  This shows that the force of holding the reinforcement bars  1  is further enhanced. It can be appreciated that the tensile strength of the reinforcement bar coupler according to the second embodiment of the present invention is greater than the tensile strength of the reinforcement bars  1 . 
     The clamping springs  30  are components which hold the reinforcement bars  1  inserted into the coupler cap  10 . The clamping springs  30  have a spiral shape that corresponds to the bottoms  21  of the base springs  20 , and are made of a material such as a spring steel that can be twisted and changed in diameter under an external force and be elastically restored. The clamping springs  30  are fitted into and fastened to the base springs  20 . That is, the clamping springs  30  are a type of torsion spring which is changed in diameter in response to the twisted direction and is elastically restorable. 
     The clamping springs  30  can be rotated in one direction along the bottoms  21  of the base springs  20  from the outer ends of the coupler cap  10 , and be fitted into and fastened to the bottoms  21  of the base springs  20  inside the coupler cap  10 . 
     The clamping springs  30  are configured such that they are closely abutted to the recessed bottoms  21  of the base springs  20  and are unwound so that their diameter is increased, thereby enabling the reinforcement bars  1  to slip, when the reinforcement bars  1  are inserted into the clamping springs  30 . Specifically, when the reinforcement bars  1  are inserted into the clamping springs  30 , the clamping springs  30  are pushed in the direction toward the recessed bottoms  21  of the base springs  20  and are unwound so that their diameter is increased due to a force under which the reinforcement bars  1  are inserted and a frictional force exerted onto the reinforcement bars  1 , thereby enabling the reinforcement bars  1  to slip. 
     Furthermore, according to the second embodiment of the present invention, as shown in  FIG. 8 , in the initial state before the reinforcement bars  1  are inserted by the one-touch connecting means  50 , the clamping springs  30  are fastened into the recessed bottoms  21  of the base springs  20  in the state in which they are twisted in the direction in which their diameter is increased. Accordingly, the clamping springs  30  are minimally influenced by the diameter of the reinforcement bars  1 , and allow the reinforcement bars  1  to be properly inserted irrespective of the types of the reinforcement bars  1 . A detailed description thereof will be given later. 
     In addition, as shown in  FIG. 10 , in the state in which the reinforcement bars  1  are inserted, when an external force is applied in the direction opposite to the direction in which the reinforcement bars  1  are inserted, the clamping springs  30  are wound while moving in the direction toward the outer ends of the coupler cap  10  along the inclined taper planes  22  due to the frictional force exerted onto the reinforcement bars  1  so that the diameter of the clamping springs  30  is gradually decreased, thereby holding the reinforcement bars  1 . 
     Although the clamping springs  30  may have a circular cross-section like typical springs, the clamping springs  30  according to the first embodiment of the present invention have the clamping taper planes  31  that correspond to the inclined taper planes  22  such that the clamping springs  30  can slide and move along the inclined taper planes  22 . As shown in  FIG. 10 , the cross-section has a triangular shape such that angled corner portions  32  are formed which partially thrust into the reinforcement bars  1  when the diameter is decreased. 
     The anti-dislodgement units  40  are components which prevent the base springs  20   a  from being dislodged in the direction toward the outer ends of the coupler cap  10  in the state in which the base springs  20   a  are inserted into the coupler cap  10 . Each of the anti-dislodgement units  40  has a reinforcement bar passage hole  41  through which a corresponding reinforcement bar  1  can pass. The anti-dislodgement units  40  are fastened to the outer ends on both sides of the coupler cap  10 . 
     In the meantime, according to the second embodiment of the present invention, a hook portion  51  is formed in each lower end of the anti-dislodgement units  40  as components of the one-touch connecting means  50  which can support one end of each of the clamping springs  30 . In addition, as shown in the figures, when the anti-dislodgement units  40  are configured so as to have threads such that they are fixed to the coupler cap  10  via rotation, the hook portion  51  can twist the clamping springs  40  in the direction in which their diameter is increased so that the initial state before the insertion of the reinforcement bar  1  can be naturally realized. 
     The one-touch connecting means  50  are components that prevent the clamping springs  30  from interfering with the insertion of the reinforcement bars  1  while the reinforcement bars  1  are being inserted into the coupler cap  10  and allow the clamping springs  30  to hold the reinforcement bars  1  when the insertion of the reinforcement bars  1  into the coupler cap  10  is completed. Each of the one-touch connecting means  50  includes the hook portion  51 , a support plate  52  and a leaf spring  53 . 
     The hook portion  51  is a component that supports one end  30   a  of the clamping spring  30  between the hook portion  51  and the protrusion  531  of the leaf spring  53  in the state in which the clamping spring  30  is twisted in the direction in which its diameter is increased. The hook portion  51  is provided adjacent to each outer end of the coupler cap  10 . Although each hook portion  51  may be formed on one end of the base spring  20   a,  the hook portion  51  is formed on each of the anti-dislodgement units  40  according to the second embodiment of the present invention. In the meantime, the hook portion  51  can have any shapes which belong to the scope of protection of the present invention as long as they can hold the rotation of one end  30   a  of the clamping spring  30 . 
     The support plate  52  is a component that is provided at the inner center of the coupler cap  10 . The support plate  52  can rotate along the bottom  21  of the base spring  20   a  before fastening of the clamping spring  30 , and be fixed to the inner central portion of the coupler cap  10  integrally with the leaf spring  53  which is supported by the support plate  52 . 
     The leaf spring  53  is a component that selectively supports the other end  30   b  of the clamping spring  30 , and is fixed to the support plate  52  using a coupling bolt  533 . As shown in  FIG. 8 , the leaf spring  53  has a protrusion  531  which protrudes from the support plate  52  between the hook portion  51  and the leaf spring  53  so as to support the other end of the clamping spring  30  in the state in which the clamping spring  30  is twisted in the direction in which its diameter is increased. As shown in  FIG. 9 , when the reinforcement bar  1  presses against the protrusion  531  while being inserted into the coupler cap  10 , the protrusion  531  is recessed due to elasticity and no longer supports the other end  30   b  of the clamping spring  30 , so that the diameter of the clamping spring  30  is restored due to elasticity. 
     In the meantime, it is preferred that a guide portion  532  be formed at the opposite side of the protrusion  531  of the leaf spring  53 . The guide portion  532  guides the clamping spring  30  so as to be positioned inside by decreasing the diameter of the other end portion of the clamping spring  30  so that the other end  30   b  of the clamping spring  30  is supported by the protrusion  531 . 
     In addition, the head of the coupling bolt  533  which protrudes a predetermined height from the support plate  52  serves as a stopper which restricts insertion of the reinforcement bar  1 . The head of the coupling bolt  533  also serves to provide a buffering space between the support plate  52  and the reinforcement bar  1  which is inserted. Otherwise, the leaf spring  53  may be pressed flat due to an insertion force resulting from the insertion of the reinforcement bar  1  and thus be permanently damaged. 
       FIG. 8  to  FIG. 10  show the state in which the reinforcement bar coupler according to the second embodiment of the present invention is used.  FIG. 8  shows the process in which the reinforcement bars  1  are inserted into the coupler cap  10 . The clamping springs  30  are supported and are closely abutted to the bottoms  21  of the base springs  20   a  by the hook portions  51  and the protrusions  531  of the leaf springs  53  in the state in which the clamping springs  30  are twisted in the direction in which their diameter is increased, so that a predetermined gap “t” is formed between the reinforcement bars  1 . Consequently, even if there is a difference in the diameter between the reinforcement bars  1  due to characteristics of the manufacturing process of the reinforcement bars  1 , the reinforcement bars  1  can be properly inserted without interfering with the clamping springs  30 . 
       FIG. 9  shows the state in which the insertion of the reinforcement bars  1  into the coupler cap  10  is completed. Since one end of each of the reinforcement bars  1  presses against the protrusions  531  of the leaf springs  53 , the other end  30   b  of the clamping springs  30  which has been supported by the protrusions  531  of the leaf springs  53  is no longer supported, so that the clamping springs  30  are elastically restored. Consequently, the clamping springs  30  are closely abutted to the reinforcement bars  1 . 
       FIG. 10  shows the case in which the reinforcement bars  1  are subjected to an external force in the direction opposite to the direction in which the reinforcement bars  1  are inserted, i.e. an external force in the direction toward the outer ends of the coupler cap  10 , in the state in which the insertion of the reinforcement bars  1  into the coupler cap  10  is completed. Consequently, the clamping taper planes  31  of the clamping springs  30  slide and move along the inclined taper planes  22  due to the frictional force between the clamping springs  30  and the reinforcement bars  1  so that the diameter of the clamping springs  30  is gradually decreased, and portions of the angled corner portions  32  of the clamping springs  30  thrust into the reinforcement bars  1 , so that the clamping springs  30  securely fix the reinforcement bars  1 . 
     In the meantime, each reinforcement bar  1  has the opposing rib protrusions  1   b  and  2   b  on both sides of the body, which is typically cylindrical, in the longitudinal direction thereof. The joint protrusions  1   a  are circumferentially formed on both sides of the rib protrusions  1   b  at predetermined intervals. The portions of the reinforcement bars  1  into which the angled corner portions  32  of the clamping springs  30  thrust will be the joint protrusions  1   a  and the rib protrusions  1   b  of the reinforcement bars  1  rather than the cylindrical bodies of the reinforcement bars  1 . 
     In addition, as described above with respect to the rounded portions  23  of the base springs  20   a,  in the state in which the reinforcement bars  1  are inserted, when the reinforcement bars  1  are subjected to an external force in the direction opposite to the direction in which the reinforcement bars  1  are inserted, the clamping springs  30  are wound while being moved in the direction toward the outer ends of the coupler cap  10  along the inclined taper planes  22  under the frictional force exerted onto the reinforcement bars  1  so that their diameter is gradually decreased, thereby holding the reinforcement bars  1 . In this case, like the clamping springs  30 , the base springs  20  are also subjected to an external force in the direction opposite to the direction in which the reinforcement bars  1  are inserted, and the base springs  20   a  have the rounded portions  23 , which are rounded in the longitudinal direction along the corners of the upper edges of the joints  20   a ′ and  20   a ″. Consequently, the upper edges of each joint  20   a ″ overlap the inner portions of the lower edges of the adjacent joint  20   a ′, and the diameter of the base springs  20   a  is also decreased, so that the reinforcement bars  1  can be more reliably held. 
     Based on the systematic coupling relationship of the above-described components, it is possible to easily connect and couple the reinforcement bars to each other using the reinforcement bar coupler according to the first embodiment of the present invention with one touch based on a change in the diameter of the clamping springs  30  caused by the twisting, even though the reinforcement bar coupler has a relatively simple configuration including the coupler cap  10 , the base springs  20   a,  the clamping springs  30  and the anti-dislodgment devices  40 . Since the bottoms  21  and the inclined taper planes  22  are formed on the base springs  20   a  without machining the female threads  20  on the inner surface of the coupler cap  10 , the reinforcement bar coupler can be easily machined and manufactured. 
     Since the cross-section of the clamping springs  30  has a triangular shape, the reinforcement bars  1  can be more securely fixed based on the sliding movement of the clamping springs  30  and the thrust of the angled end portions into the reinforcement bars  1 . Since the one-touch connecting means  50  are provided, the clamping springs  30  can be inserted into and fastened to the base springs  20   a  in the state in which the clamping springs  30  are twisted in the direction in which their diameter is increased, and the diameter of the clamping springs  30  is restored due to elasticity when the insertion of the reinforcement bars  1  is completed. Consequently, even if there is a difference in the diameter between the reinforcement bars  1  due to characteristics of the manufacturing process of the reinforcement bars  1 , the reinforcement bars  1  can be properly inserted without interfering with the clamping springs  30 . 
     The reinforcement bar coupler that has been set forth above and shown in the drawings is merely a certain embodiment of the present invention, and it should not be construed that the foregoing embodiment limits the technical principle of the present invention. The scope of protection of the present invention is defined by only the description of the appended claims. It is apparent to a person having ordinary skill in the art that modifications and changes can be made to the embodiments without departing from the scope of the present invention, and such modifications and changes shall belong to the scope of protection of the present invention. 
     The present invention having the above-described configuration can easily connect and fix reinforcement bars with one touch based on a change in the diameter of the clamping springs by twisting even if it has a simple configuration, and thus is industrially useful.