Unit reinforcing bars

Abstract

We provide unit reinforcing bars that offer superior strength and durability. [Solution] The unit reinforcement of the present invention is formed by joining a plurality of structural reinforcements 2 arranged parallel to each other and a plurality of fixed reinforcements 4 that intersect with the structural reinforcements at the intersection. The intersection of the structural reinforcements 2 and the fixed reinforcements 4 is heated to below a predetermined temperature by energizing, and then an external stress equal to or greater than the yield strength of both reinforcements 2 and 4 is applied to form a joint 6. The entire unit, including the joint 6, has a strength within the standard range of both reinforcements.

Description

Technical Field

[0001] The present invention relates to unit reinforcing bars.

Background Art

[0002] In recent years, in the construction of buildings and the like, it has been desired to simplify on-site work and uniformize quality by transporting and using unit reinforcing bars that have been processed and assembled in a factory in advance to the site. Conventionally, resistance spot welding has been widely used for joining metal materials. Resistance spot welding sandwiches the overlapping metal materials with electrodes from above and below, and melts the base material (metal material) by Joule heat generated by passing a large current through the metal material from the electrodes, thereby welding the metal materials together.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When resistance spot welding is used for joining reinforcing bars, it is extremely difficult to sufficiently ensure the strength and toughness of the welded part because it is impossible to suppress the formation of the fusion-solidification structure and the heat-affected zone associated with welding. In addition, cracks and fractures are likely to occur in the welded part due to fusion-solidification, resulting in poor durability and fatigue resistance. For this reason, the welding of reinforcing bars, which are structural materials, is prohibited or restricted.

[0005] In this regard, for example, Patent Document 1 discloses a resistance spot welding method in which the mechanical properties of the welded part are improved to some extent by the heat history and the like. Further, for example, Patent Document 2 discloses a unit reinforcing bar that suppresses heat deterioration occurring at the outer edge of the welded part by dissipating the heat generated by resistance spot welding.

[0006] However, resistance spot welding inherently requires the melting of the base material (metal), and the resulting decrease in the mechanical properties of the weld is unavoidable. Therefore, as mentioned above, welding of reinforcing bars is prohibited or restricted. [Means for solving the problem]

[0007] This invention addresses the current situation described above and aims to provide a unit reinforcing bar that joins reinforcing bars without relying on resistance spot welding.

[0008] The present invention relates to a unit reinforcement comprising a plurality of structural reinforcements arranged parallel to each other and a plurality of fixed reinforcements intersecting the structural reinforcements, joined at the intersection. The intersection of the structural reinforcements and the fixed reinforcements is formed as a joint by heating to below a predetermined temperature by applying an electric current and then applying an external stress equal to or greater than the yield strength of both reinforcements. The entire unit, including the joint, has a strength within the standard range of both reinforcements.

[0009] The material, shape, and size of the structural reinforcement and fixing reinforcement according to the present invention are not particularly limited, and round steel or various deformed steel bars can be used. The shape of the structural reinforcement may be straight, rectangular, U-shaped, L-shaped, or any other shape. The shape of the fixing reinforcement may be any shape other than straight, as long as it can be in contact with the structural reinforcement. In addition, the shapes of reinforcement commonly used in the construction of buildings, etc. (for example, vertical reinforcement, horizontal reinforcement, stirrups, etc.) may be adopted as they are.

[0010] The unit reinforcement of the present invention has a strength within the standard range for both reinforcements, including the joint. In other words, it is sufficient that the entire unit reinforcement, including the joint, has a strength within the standard range that is usable in the construction of buildings and the like (for example, a strength within the JIS standard range). Furthermore, it is preferable to use various types of round steel or deformed steel bars that have a strength within the standard range for the structural reinforcement and fixing reinforcement that make up the unit reinforcement.

[0011] The predetermined temperature (joining temperature) at which the joint is heated by current is below the eutectoid temperature of both reinforcing bars, specifically, it should be approximately 723°C (point A1) or lower. The heating of the joint in this invention raises the temperature of the joint and does not melt the base material of the joint, as in conventional resistance spot welding. Generally, the melting temperature of reinforcing bars is very high, at approximately 1500°C, and heating to approximately 723°C or lower only softens the base material to the extent that it forms a softened region, and does not melt. Because the unit reinforcing bars of this invention are joined at a low temperature (723°C or lower) without melting the joint, the main structure of the entire reinforcing bar unit, including the joint, does not undergo transformation, and is joined in a non-transformed (solid phase) state.

[0012] The method of energization can be a direct method, an indirect method, or a series method, or a similar method. It is not particularly limited as long as it does not impair the effects of the present invention, and other methods are also acceptable.

[0013] After heating by energization, deformation is initiated at a low temperature by applying an external stress exceeding the yield strength of both reinforcing bars to the softened region of the joint, forming a new surface and achieving a joint. Since the amount of deformation of the joint depends on the amount of pressure applied to the pressing portion, increasing the amount of pressure applied can promote the formation of the new surface. The external stress may be applied continuously at a constant pressure, instantaneously, or in a pulsed manner.

[0014] The external stress applied to both reinforcing bars is preferably the fluid stress of the reinforcing bars at the joining temperature. By using the fluid stress of the reinforcing bars at the joining temperature as the external stress, continuous deformation at the joint is initiated at the set joining temperature, allowing for stable joining of the newly formed surfaces with minimal pressure. Furthermore, by pressing the outer circumference of the joint after applying the external stress, the gap between the reinforcing bars can be further reduced.

[0015] By controlling the current density by increasing the current value in accordance with the increase in the contact area of ​​the joint, the joint can be heated to a desired temperature quickly and uniformly. Furthermore, by controlling the external stress by increasing the external load in accordance with the increase in the contact area of ​​the joint, the desired joint temperature can be controlled more precisely. The specific methods for controlling the current density and external stress are not particularly limited; for example, the current value and external load can be set in multiple stages.

[0016] The unit reinforcing bar according to the present invention has a ferrite-pearlite structure as its main structure, including the joints. In this invention, since the heating temperature of the joints by energization is low, below the eutectoid temperature (approximately 723°C), retained austenite and martensite do not form. In other words, the main structure of the entire unit reinforcing bar, including the joints, is a ferrite-pearlite structure that is highly strong and durable, rather than an unstable retained austenite or a highly brittle martensite structure, making it suitable for reinforcing bar units where long-term structural stability is required. [Effects of the Invention]

[0017] Unlike conventional reinforcing bars joined by resistance spot welding, the unit reinforcing bars of the present invention are joined without melting the bars, and the reduction in strength due to the joining process is controlled very efficiently. As a result, they have higher strength, durability and fatigue resistance than those joined by resistance spot welding, and the risk of cracks or breakage during use is low, so they can be used with confidence at construction sites. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram illustrating a unit reinforcement according to Example 1 of the present invention, where (A) is a diagram illustrating the unit reinforcement viewed from the longitudinal direction of the structural reinforcement, and (B) is a diagram illustrating the unit reinforcement viewed from a direction perpendicular to the longitudinal direction of the structural reinforcement. [Figure 2]It is a schematic explanatory diagram of the unit reinforcing bar according to Example 2. (A) is an explanatory diagram of the unit reinforcing bar seen from the longitudinal direction of the structural reinforcing bar, and (B) is an explanatory diagram of the unit reinforcing bar seen from the direction orthogonal to the longitudinal direction of the structural reinforcing bar. [Figure 3] It is a schematic explanatory diagram of the unit reinforcing bar according to Example 3. (A) is an explanatory diagram of the unit reinforcing bar seen from the longitudinal direction of the structural reinforcing bar, and (B) is an explanatory diagram of the unit reinforcing bar seen from the direction orthogonal to the longitudinal direction of the structural reinforcing bar. [Figure 4] It is a schematic diagram of the unit reinforcing bar according to Example 4 seen from the longitudinal direction of the fixing reinforcing bar. [Figure 5] It is a schematic diagram of the unit reinforcing bar according to Example 5 seen from the longitudinal direction of the fixing reinforcing bar. [Figure 6] It is a schematic diagram of the unit reinforcing bar according to Example 6 seen from the longitudinal direction of the fixing reinforcing bar. [Figure 7] It is a schematic diagram of the unit reinforcing bar according to other examples. [Figure 8] It is an explanatory diagram of a joining method using energization by the direct method. (A) is an explanatory diagram of the preparation process before joining, and (B) is an explanatory diagram of the heating process by energization. [Figure 9] It is an explanatory diagram of the external stress application process of the joining method using energization by the direct method.

Modes for Carrying Out the Invention

[0019] Hereinafter, examples of the unit reinforcing bar of the present invention will be described with reference to the drawings. The present invention is not limited only to these examples. In the following description, the same or corresponding parts may be given the same reference numerals, and duplicate descriptions may be omitted. Also, each drawing is for conceptually explaining the present invention, and the dimensions of each component may be different from those in practice.

[0020] <Example 1> A wall unit reinforcing bar 100, which can be used as a vertical reinforcement during wall construction according to Embodiment 1 of the present invention, will be described with reference to Figure 1. Figure 1(A) is a schematic explanatory diagram of the wall unit reinforcing bar 100 as viewed from the longitudinal direction of the structural reinforcement bar 2. Figure 1(B) is a schematic explanatory diagram of the wall unit reinforcing bar 100 as viewed from a direction perpendicular to the longitudinal direction of the structural reinforcement bar.

[0021] The wall unit reinforcement 100 is composed of multiple structural reinforcements 2 and fixed reinforcements 4. The structural reinforcements 2 are straight bars, arranged parallel to each other, forming a virtual layout plane as a whole. The fixed reinforcements 4 are straight bars, arranged perpendicular to the multiple structural reinforcements 2. The wall unit reinforcement 100 is formed by joining the structural reinforcements 2 and the fixed reinforcements 4 at their intersections, which are joints 6, without melting.

[0022] The method for joining the joints 6 using a direct current supply method will be explained with reference to Figures 8 and 9. First, as shown in Figure 8(A), the structural reinforcement 2 and the fixed reinforcement 4 are placed on top of each joint 6 and fixed by being sandwiched between electrodes 8 and 10 from above and below. In Figure 8(A), both reinforcement bars 2 and 4 are sandwiched between electrodes 8 and 10, but they may also be temporarily fixed using, for example, reinforcement clips.

[0023] Next, as shown in Figure 8(B), current is passed from electrode 8 to electrode 10, for example, to heat the joint 6. The arrows in Figure 8(B) indicate the direction of current flow. The heating temperature (joining temperature) should be less than the eutectoid temperature of both reinforcing bars 2 and 4 (approximately 723°C). Note that electrodes 8 and 10 are used to raise the temperature near the joint 6 by current to form a softened region 20, and do not melt the joint 6 like general welding electrodes.

[0024] The upper and lower electrodes 8 and 10 are equipped with movable pressing parts 12. Finally, as shown in Figure 9, the pressing parts 12 are pushed forward and pressed into the softened region 20 of the joint 6, thereby applying an external stress greater than the yield strength of both reinforcing bars 2 and 4 to the softened region 20 and joining them. By pushing forward and pressing in the pressing parts 12, the vicinity of the joint 6 is locally deformed, and the newly formed surfaces come into contact, resulting in a non-transformed joining. The pressing parts 12 only need to be pressed in once, and the pressing time can be, for example, about 1 second. In Figure 9, the pressing parts 12 on both electrodes 8 and 10 press the joint 6 from above and below, but for example, the pressing parts 12 may be provided on only one electrode. A recess 30 is formed on the surface of both reinforcing bars 2 and 4 where the pressing parts 12 have been pressed in.

[0025] Since the joint 6 is joined at a temperature below the eutectoid temperature of both reinforcing bars 2 and 4 without melting, there is no deterioration in functional properties due to thermal degradation. Furthermore, no retained austenite or martensite is formed, and the main structure of the entire unit reinforcement, including the joint 6, is composed of a ferrite-pearlite structure that is highly strong and durable. In other words, since the unit reinforcement is joined at the joint 6 in an untransformed state, there is no singularity where the hardness of the joint 6 differs significantly from that of the two reinforcing bars 2 and 4, and the uniformity of the entire unit reinforcement, including the joint 6, is maintained.

[0026] As described above, the wall unit reinforcement 100 according to this embodiment has high strength, durability, and fatigue resistance throughout, including the joint 6. Unlike unit reinforcement using resistance spot welding, there is a low risk of cracking or damage occurring during use, and it can be used with confidence at construction sites. Furthermore, the joint 6 can be joined simply by heating it with an electric current and applying external stress for about 1 second at a time, making it quick and easy to manufacture.

[0027] <Example 2> A wall unit reinforcing bar 200, which can be used as a vertical reinforcement during wall construction according to Embodiment 2 of the present invention, will be described with reference to Figure 2. Figure 2(A) is a schematic explanatory diagram of the wall unit reinforcing bar 200 viewed from the longitudinal direction of the structural reinforcement bar 2. Figure 2(B) is a schematic explanatory diagram of the wall unit reinforcing bar 200 viewed from a direction perpendicular to the longitudinal direction of the structural reinforcement bar 2. The wall unit reinforcing bar 200 is constructed in the same manner as in Embodiment 1, except that the end of the structural reinforcement bar 2 is bent in a J shape.

[0028] <Example 3> A wall unit reinforcing bar 300, which can be used as a vertical reinforcement during wall construction according to Embodiment 3 of the present invention, will be described with reference to Figure 3. Figure 3(A) is a schematic explanatory diagram of the wall unit reinforcing bar 300 viewed from the longitudinal direction of the structural reinforcement bar 2. Figure 3(B) is a schematic explanatory diagram of the wall unit reinforcing bar 300 viewed from a direction perpendicular to the longitudinal direction of the structural reinforcement bar 2. The wall unit reinforcing bar 300 is constructed in the same manner as in Embodiment 1, except that the end of the structural reinforcement bar 2 is bent in an L-shape.

[0029] <Example 4> A beam unit reinforcing bar 400, which can be used as a stirrup during beam construction according to Embodiment 4 of the present invention, will be described with reference to Figure 4. Figure 4 is a schematic explanatory diagram of the beam unit reinforcing bar 400 viewed from the longitudinal direction of the fixed reinforcing bar 4. The beam unit reinforcing bar 400 is constructed in the same manner as in Embodiment 1, except that the structural reinforcing bar 2 is bent into a rectangular shape, similar to the shape of a general stirrup. The beam unit reinforcing bar 400 can also be used as a stirrup during column construction by changing the orientation of its arrangement during construction.

[0030] <Example 5> A beam unit reinforcing bar 500, which can be used as a stirrup during beam construction according to Embodiment 5 of the present invention, will be described with reference to Figure 5. Figure 5 is a schematic explanatory diagram of the beam unit reinforcing bar 500 as viewed from the longitudinal direction of the fixed reinforcing bar 4. The beam unit reinforcing bar 500 is formed in the same manner as Embodiment 1, except that both upper ends of the structural reinforcing bar 2 are bent inward into a U-shape (hook shape), similar to the shape of a general stirrup.

[0031] <Example 6> A foundation unit reinforcing bar 600, which can be used as reinforcing bar when constructing a raft foundation for a building according to Embodiment 6 of the present invention, will be described with reference to Figure 6. Figure 6 is a schematic explanatory diagram of the foundation unit reinforcing bar 600 viewed from the longitudinal direction of the fixed reinforcing bar 4. The foundation unit reinforcing bar 600 is the same as in Embodiment 1, except that the structural reinforcing bar 2 is configured as a continuous unit in the order of vertical section, first horizontal section, inclined section, and second horizontal section.

[0032] The overall shape of the unit reinforcement of the present invention is not limited to Examples 1 to 6, and may be other shapes (see Figure 7). It is not particularly limited as long as the effectiveness of the unit reinforcement of the present invention is not impaired, and can accommodate various shapes required at actual construction sites. [Explanation of Symbols]

[0033] 1 unit rebar 2. Structural reinforcement 4. Fixed reinforcing bars 6 Joint 8 electrodes 10 electrodes 12 Pressing part 20 Softening region 30 recesses

Claims

1. A unit reinforcement is formed by joining together multiple structural reinforcements arranged parallel to each other and multiple fixed reinforcements that intersect with the structural reinforcements at the intersection, The intersection of the structural reinforcement and the fixed reinforcement is formed as a joint by heating it to below a predetermined temperature by applying an external stress equal to or greater than the yield strength of both reinforcements. The entire structure, including the joint, has a strength within the specified range for both reinforcing bars. Unit reinforcing bars.

2. The predetermined temperature is below the eutectoid temperature of both reinforcing bars. The unit reinforcement according to claim 1.

3. The main structure of the entire area, including the aforementioned joint, is a ferrite-pearlite structure. The unit reinforcing bar according to claim 1 or 2.

Images