Elongated steel pipe

Abstract

To provide a structure in which elongated steel pipes used for reinforcing natural ground or the like can stably maintain the nested state until the elongated steel pipes arranged in a nested manner are stretched.SOLUTION: An elongated steel pipe comprises a connecting portion which is provided between a rear end of a first steel pipe that makes up part of the elongated steel pipe and a front end of a subsequent steel pipe, and which engages a rear end of the first steel pipe with the front end of the subsequent steel pipe when the elongated steel pipe is elongated, and a temporary fixing portion which temporarily fixes the rear end of the first steel pipe with the rear end of the subsequent steel pipe with a force weaker than the tensile force applied to the connecting portion when the first steel pipe and the subsequent steel pipe are not elongated.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an elongated steel pipe that can be combined to form a long steel pipe, and is used in civil engineering, architecture, steel towers, scaffolding, supports, and other structures. In particular, the present invention relates to an elongated steel pipe that is suitable for pouring concrete into natural ground. [Background technology]

[0002] Steel pipes are widely used as supports placed inside buildings to support the structure of the building, as scaffolding installed around buildings during construction, maintenance, and inspection, and as steel pipes for reinforcing the ground. The length of steel pipe required for these applications varies depending on the application, but for large structures, lengths exceeding 10 meters are used. Since it is difficult to manufacture such long steel pipes with precision, i.e., with a uniform thickness and without axial deformation, for applications requiring long lengths, relatively short steel pipes, for example, approximately 3 meters, are usually joined together at the site where they are to be used.

[0003] Conventionally, steel pipes have been joined by welding, screwing, or using joint members, but these operations require the steel pipe to be joined to be brought close to a single laid steel pipe, then centered and joined, which is a significant burden.In response to this, a drawn steel pipe has been proposed in which multiple steel pipes of different diameters are nested and sequentially drawn out, starting with the larger-diameter steel pipe or the smaller-diameter steel pipe, to form a long pipe (for example, Patent Documents 1 and 2).

[0004] Such drawn steel pipes are provided with a connecting section in which the rear end of a leading steel pipe is connected to the front end of a following steel pipe when the leading steel pipe is in an elongated state, and by successively stretching the steel pipes, a long steel pipe can finally be produced whose length is close to "the length of one steel pipe" x "the number of steel pipes." Various proposals have also been made for the structure of the connecting section of such drawn steel pipes (for example, Patent Document 3). Patent Document 3 discloses a mechanism in which an elastic ring is fitted onto the outer periphery of the front end of the following steel pipe, and a recess is provided on the inner surface of the rear end of the leading steel pipe into which this ring engages, so that the two steel pipes are automatically connected when the leading steel pipe is in a fully elongated state, by which the ring engages with the recess on the rear end.

[0005] Furthermore, Patent Document 2 discloses a mechanism for preventing the two steel pipes that make up an elongated steel pipe from returning to their original retracted state after they have been stretched and connected. These technologies make it possible to eliminate the need for time-consuming joining work by continuing the work of stretching the elongated steel pipe, thereby significantly improving the work of joining multiple steel pipes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-6961 [Patent Document 2] Japanese Patent Publication No. 2022-94158 [Patent Document 3] Japanese Patent Application Publication No. 09-42239 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0007] When driving the above-mentioned elongated steel pipes into the natural ground, for example, a driving bit is attached to the leading steel pipe (referred to as the lead pipe), a rotating rod that passes through the inside of the steel pipe is attached to the bit, and the bit is driven by rotating the bit. The elongated steel pipe is stretched by the driving force of the bit. During this stretching, the elongated steel pipe is placed on a predetermined support means called a guide shell. Here, when placing the elongated steel pipe on the guide shell or when positioning the lead pipe at the driving position and starting driving, external vibrations or tilting of the elongated steel pipe may cause the pipe or the steel pipe following the lead pipe to slide in the opposite direction to the direction of stretching of the elongated steel pipe due to its own weight. If the steel pipe moves in the opposite direction and is stretched, it cannot be returned to its original position by hand, making the process of placing it on the guide shell and starting driving extremely difficult, potentially making it impossible to position the lead pipe at the driving position or start driving.

[0008] The present invention aims to provide a structure that can maintain a stable nested state of elongated steel pipes arranged in a nested manner until they are stretched, thereby improving work efficiency from setting the elongated steel pipes to the start of stretching (start of pouring). [Means for solving the problem]

[0009] In order to solve the above problems, the drawn steel pipe of the present invention has a temporary fixing portion provided on multiple steel pipes arranged in a nested manner, which temporarily fixes the steel pipes together with a force weaker than the load applied during stretching.

[0010] In other words, the drawn steel pipe of the present invention is a drawn steel pipe in which a plurality of steel pipes of different diameters are nested together so that they can slide axially relative to each other, and the nested steel pipes are drawn sequentially, starting from the front end of the plurality of steel pipes, while being stretched, and is characterized by having: a connecting portion provided at the rear end of one of the plurality of steel pipes and the front end of the subsequent steel pipe, which engages the rear end of the first steel pipe with the front end of the subsequent steel pipe when the drawn steel pipe is drawn; and a temporary fixing portion which temporarily fixes the rear end of the first steel pipe with the rear end of the subsequent steel pipe with a force weaker than the tensile force applied to the connecting portion when the first steel pipe and the subsequent steel pipe are not drawn.

[0011] The terms "front end" and "rear end" used in this specification are for convenience only and should be interpreted as being interchangeable depending on the direction in which the drawn steel pipe is stretched. [Effects of the Invention]

[0012] According to the present invention, by providing a temporary fixing means for the steel pipes of an elongated steel pipe that are arranged so that they can slide relative to each other in their stored state, it is possible to facilitate the handling and positioning of the elongated steel pipe until the actual stretching operation begins. [Brief explanation of the drawings]

[0013] [Figure 1] Overall view of the drawn steel pipe [Figure 2] FIG. 1 is a diagram showing a connection portion of a steel pipe according to a first embodiment. [Figure 3] A diagram showing the entire elongated steel pipe used for concrete pouring into the ground [Figure 4] FIG. 1 is a diagram showing one steel pipe (intermediate pipe) constituting the drawn steel pipe of embodiment 1. [Figure 5] 10A and 10B are diagrams showing a temporary fixing portion, illustrating examples of arrangements of through holes provided in a socket and examples of pins that engage with the through holes; [Figure 6] Diagram explaining the structure and function of the joint [Figure 7] FIG. 10 shows a modified example of the temporary fixing portion. [Figure 8]1 is a diagram illustrating an example of a casting method using an elongated steel pipe according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the elongated steel pipe of the present invention will be described with reference to the drawings.

[0015] Figure 1 shows an elongated steel pipe in which multiple steel pipes are nested. Here, as an example, elongated steel pipe 1 consisting of four steel pipes 1A, 1B, 1C, and 1D is shown, but the number of steel pipes is not particularly limited as long as it is two or more. The upper diagram in Figure 1 shows the nested state (referred to as the stored state), and the lower diagram shows the maximally stretched state (referred to as the stretched state).

[0016] The multiple steel pipes 1A-1D that make up the drawn steel pipe 1 are all similar cylindrical pipes, but each has a different outer diameter. The outer diameter of steel pipe 1D, which has the smallest outer diameter, is smaller than the inner diameter of steel pipe 1C, which has the second smallest outer diameter, and steel pipe 1C has the outer diameter smaller than the inner diameter of steel pipe 1B, which has the largest outer diameter. They are arranged so that they can slide axially relative to each other, and steel pipes 1B-1D can be nested inside steel pipe 1A, which has the largest outer diameter. A flange 15 is fixed to the end of steel pipe 1D with the smallest diameter, and connecting parts (not shown) are provided between steel pipe 1A and steel pipe 1B, between steel pipe 1B and steel pipe 1C, and between steel pipe 1C and steel pipe 1D, so that the steel pipes will not fall out even when they slide.

[0017] The material and size of each steel pipe vary depending on the application. For example, steel pipes used to reinforce natural ground are made of materials such as stainless steel or steel pipes, and although not limited to these, a combination of steel pipes with a total length of approximately 3 m, a wall thickness of 3.5 mm to 6.0 mm, and an outer diameter of approximately 114 mm to 76 mm can be used. Commonly available STK400 and STK490 steel pipes can also be used, but it is preferable to use high-tensile steel pipes such as STK700. Furthermore, the shape of the steel pipe can be any shape, such as cylindrical, elliptical, or rectangular, depending on the application.

[0018] The ends of the steel pipes are provided with connecting portions for connecting adjacent steel pipes when converting multiple steel pipes from a retracted state to an extended state. As shown in Fig. 2, the connecting portion 20 is composed of a pair of sockets including a connecting portion (rear-end socket 21) provided at the end of one of two adjacent steel pipes (e.g., steel pipe 1B) and a connecting portion (front-end socket 22) provided at the end of the other (e.g., steel pipe 1C). When the outer steel pipe and the inner steel pipe are extended, this pair of sockets engage with each other as shown in the lower part of Fig. 2, thereby connecting the adjacent steel pipes.

[0019] The connecting portion 20, as will be described in detail later, is provided with a return prevention mechanism that prevents the steel pipe from returning in the opposite direction from the extended state, and a temporary fixing portion that temporarily fixes the connecting portions of adjacent steel pipes together when the steel pipes are in the stored state.

[0020] An elongated steel pipe having such a configuration is stored in a nested state in which multiple steel pipes 1A-1D are stored, and by, for example, fixing the smallest diameter steel pipe 1D and pulling the largest diameter steel pipe 1A, each steel pipe is successively pulled out and connected at their connecting parts 20. When finally stretched to its maximum length, the steel pipes become steel pipes that are roughly the length of one steel pipe multiplied by the length of the number of steel pipes (minus the length of the overlapping parts at the connecting parts).

[0021] Among the steel pipes that make up the drawn steel pipe 1, the ends of the largest diameter steel pipe (steel pipe 1A in FIG. 1) and the smallest diameter steel pipe (steel pipe 1D in FIG. 1) that do not have the connecting portion 20 are fixed with components required depending on the application of the drawn steel pipe. When a drawn steel pipe is used for driving concrete into the natural ground, for example, when the largest diameter steel pipe 1A is driven into the natural ground as the lead pipe, a driving bit 50 is attached to the tip of the steel pipe 1A as shown in FIG. 3, and a rod 70 or the like is attached to this bit 50 for imparting driving force. In addition, a flange 15 or the like is attached to the rear end of the steel pipe 1D, which is the terminal pipe, for fixing to a guide cell or a face (the surface of the natural ground where concrete is poured), as shown in FIG. 1.

[0022] Next, the return prevention mechanism and temporary fixing portion of the connecting portion 20 will be described.

[0023] When the leading pipe is poured into the ground, a force (ground resistance) acts on the leading pipe against the thrust, i.e., a force acting in the opposite direction to the stretching direction, but the return prevention mechanism is a mechanism that prevents the steel pipe from being retracted from its stretched state due to this force acting in the opposite direction to the stretching direction. In other words, the return prevention mechanism locks the connection between the steel pipes, preventing them from returning in the retracting direction.

[0024] The temporary fixing portion secures the nested steel pipes together until the drawn steel pipe is positioned in the natural ground, preventing the steel pipes from sliding and losing their nested position before concrete pouring begins. In other words, the temporary fixing portion prevents the rearmost steel pipe in the stretching direction from moving in the opposite direction to the leading steel pipe due to its own weight or external forces when the drawn steel pipe 1 is stretched. The fixing force of the temporary fixing portion is weaker than the load applied to the leading pipe when stretching the drawn steel pipe, or the driving force (tensile force) of the leading pipe during concrete pouring, but is greater than the aforementioned own weight and external forces. The temporary fixing portion is configured to be released when the pipe is stretched and stretched. The fixing force of the temporary fixing portion depends on the weight of the steel pipe, the tensile force applied to the steel pipe, etc., and cannot be specifically specified. However, for example, in the case of an drawn steel pipe for concrete pouring in the natural ground (a steel pipe consisting of three steel pipes), the tensile force applied to the leading pipe is approximately 9 kN, so a force less than this is sufficient.

[0025] By providing such a temporary fixing portion at the connecting portion of the drawn steel pipe of this embodiment, when the drawn steel pipe 1 is fixed to the installation location or when the leading steel pipe of the drawn steel pipe 1 is positioned at the pouring position, the steel pipe at the rear end can be prevented from sliding backward due to its own weight and interfering with the work. In addition, since the fixing force of the temporary fixing portion is smaller than the tensile force received from the steel pipe at the front end, when a force (tensile force) that stretches the steel pipe at the front end is applied to the connecting portion, the fixation between the connecting portions by the temporary fixing portion is released, and the steel pipe at the rear end is stretched by the tensile force and can move toward the front end.

[0026] Next, a specific embodiment of the connecting portion 20 will be described.

[0027] <Embodiment 1> In this embodiment, an elongated steel pipe for ground reinforcement, in which the leading pipe is a steel pipe 1A with the largest diameter and the terminal pipe is a steel pipe 1D with the smallest diameter, is taken as an example, as shown in Fig. 1. The overall view of this elongated steel pipe, as shown in Fig. 1, has a structure in which a plurality of steel pipes of different diameters are arranged so that they can slide relative to each other, and a connecting part 20 consisting of a pair of sockets (rear end socket 21, front end socket 22) for connecting adjacent steel pipes is attached to the end (at least one of the rear end and the front end) of each steel pipe.

[0028] Figure 4 shows a steel pipe (intermediate pipe) 1B having a rear end socket 21 at one end and a front end socket 22 at the other end. Below, details of the connecting portion 20 will be explained using Figure 4 and the above-mentioned Figure 2.

[0029] The rear-end socket 21, which is fixed to the rear end of the steel pipe 1B, is made of a tubular member. Its outer diameter is uniform along its axial direction, but its inner surface is formed with a stepped portion 210 that protrudes inward. The socket has two tubular portions, a first tubular portion 211 and a second tubular portion 212, sandwiching the stepped portion 210. The first tubular portion 211 is fixed to the outer periphery of the rear end of the steel pipe body so that a predetermined gap is provided between the rear end surface of the steel pipe body and the stepped portion 210 of the rear-end socket 21. The gap between the rear end surface of the steel pipe body and the stepped portion 210 of the rear-end socket 21 forms a recess 40 between the steel pipe and the connecting portion. The stepped portion 210 and the second tubular portion 212 protrude axially outward from the rear end of the steel pipe body.

[0030] Furthermore, the pipe portions (211, 212) of the rear-end socket 21 are formed with a structure that functions as a temporary fixing portion 30 that temporarily fastens the rear-end socket of the following steel pipe when the rear-end socket 21 is in the stored state. In this embodiment, the temporary fixing portion is formed with a pin (not shown) that temporarily connects two adjacent steel pipes together, and this pin penetrates the first pipe portion 211 of the rear-end socket 21, and a through hole 31 is formed that penetrates at least a portion of the second pipe portion 212. In the case of a leading pipe, the through hole 31 that functions as the temporary fixing portion 30 may be provided only in the second pipe portion 212, and in the case of a terminal pipe, it may be provided only in the first pipe portion 211. Furthermore, as shown in FIG. 4, in the case of an intermediate pipe 1B having a leading steel pipe and a trailing steel pipe at the front and rear, the through hole 31 is provided in both the first pipe portion 211 and the second pipe portion 212.

[0031] The diameter of the through hole 31 is approximately the same as or slightly smaller than the outer diameter of the pin, and the pin passes through the through hole 31 in the first pipe section of one steel pipe and fits into the through hole in the first pipe section of the other steel pipe, thereby securing the steel pipes together. The circumferential position of the through hole 31 may be one or more locations around the circumference of the tubular member. This can be adjusted appropriately, taking into account the strength of the pin and the fixing force required for temporary fixation. Figure 5 shows an example cross section of a rear-end socket 21 with a through hole 31 located at one location around the circumference.

[0032] On the other hand, the front socket 22 fixed to the front end of the steel pipe (for example, steel pipe 1B) is a tubular member with a processed front end, and its outer diameter is smaller than the inner diameter of the preceding steel pipe 1B and the inner diameter of the second pipe portion of the rear socket 21, and it is fixed to the outer periphery of the front end of the steel pipe 1C. An elastic ring 45 is fitted in a reduced diameter state to the rear end (on the steel pipe main body side) of the front socket 22. That is, when steel pipe 1C is housed inside steel pipe 1B (in an unstretched state), elastic ring 45 is contracted and in contact with the inner surface of outer steel pipe 1B, but when steel pipe 1B is stretched and moves in the direction shown by the arrow in Fig. 2 (upper diagram) and the gap (recess 40) between the rear end of steel pipe 1B and step portion 210 of rear-end socket 21 reaches the position of elastic ring 45 (lower diagram in Fig. 2), elastic ring 45, which had been contracted, expands and enters the gap (recess 40), connecting steel pipe 1B and steel pipe 1C and preventing steel pipe 1B from returning. In other words, it acts as a return prevention mechanism.

[0033] With this connection, the tensile force that was applied to steel pipe 1B is applied to steel pipe 1C, and the stretching operation of steel pipe 1C begins. Thereafter, in the same manner, steel pipe 1C is stretched to its maximum extent, and when rear-end socket 21 fixed to the rear end of steel pipe 1C engages with front-end socket 22 of the following steel pipe 1D, elastic ring 45 at the rear end of front-end socket 22 fits into recess 40 of the front-end socket, achieving connection and preventing return.

[0034] Next, details of the temporary fixing portion 30 will be described with reference to Figure 6 and the aforementioned Figure 5. Figure 6 shows the temporary fixing portion 30 in a state in which four steel pipes are nested (stored state). As described above, each of the steel pipes 1A to 1C has a pin through hole 31 formed in the rear-end socket 21 (pipe portion). In the stored state, the steel pipes that make up the elongated steel pipe are arranged so that the through hole 31 formed in the first pipe portion 211 of steel pipe 1A and the through hole 31 formed in part of the first pipe portion 211 of steel pipe 1B overlap in the radial direction of the steel pipes. In this state, a pin 35 is inserted into the through holes 31 of the two steel pipes. This forms a structure that functions as the temporary fixing portion 30.

[0035] As mentioned above, the pins 35 are used with a strength (the total strength of each pin if there are multiple pins) that is strong enough to withstand the weight of the steel pipe and break under the tensile force applied to the leading pipe. Specifically, as shown in Figure 5, grooved spring pins made of rolled spring steel with a shear load (kN) of about 6 (JIS B 2808 general load pins or light load pins) can be used. When selecting pins 35, one with an appropriate shear load is selected depending on the number of pins (number of through holes).

[0036] If the rear-end socket 21 is not fixed to the rear end of the terminal tube 1D, a protector 13 as shown in Fig. 6 may be fixed by screwing or the like, and the rear-end socket 21 of the intermediate tube 1C may be temporarily fixed to this protector 13. For example, as shown in Fig. 6, the inner surface of the rear-end socket 21 (first tube portion 211) of the intermediate tube 1C adjacent to the terminal tube 1D may be threaded onto the outer circumferential surface of the tip of the protector 13, and then connected by screwing. Alternatively, through holes corresponding to the through holes formed in the first tube portion 211 of the rear-end socket 21 of the intermediate tube 1C may be formed in the protector 13, and pins 35 may be inserted into these through holes.

[0037] With the steel pipes nested in this manner, by inserting a pin into the through hole of the rear end socket 21 fixed to the rear end of each steel pipe, the movement of the steel pipes in the sliding direction is restricted, and the nested state can be maintained until the stretching operation is performed.

[0038] In the elongated steel pipes configured as described above, the movement of each steel pipe in the sliding direction is restricted by the temporary fixing portion 30 (pin 35) until a tensile force is applied to the leading pipe. When a tensile force is applied to the leading pipe, the pin 35 breaks, the temporary fixing is released, and the pipe becomes extendable. By pulling the leading pipe in this state, a long steel pipe is formed. When the pipes are fully extended, the connection state is locked by the anti-return mechanism, preventing them from returning to the contracted state.

[0039] <Modification> In embodiment 1, a combination of a through hole 31 provided in the socket and a pin 35 is used as a means for temporarily fixing the steel pipes in a stored state, but the temporary fixing means may be any means that connects the steel pipes with a relatively weak force. For example, as shown in Figure 7, it is possible to fix the overlapping portion of the rear end socket 21B of one steel pipe and the rear end socket 21C of the other steel pipe (the tip of the first pipe portion of one rear end socket 21B and the tip of the second pipe portion of the other rear end socket 21C) using metal brazing, welding, or a joining material 60 such as an adhesive.

[0040] When arranging steel pipes with fixed sockets in a nested manner, temporary fixing portions using such a joining material can be achieved by applying a spot of joining material to the inner or outer surface of one of the sockets where the two sockets overlap, storing the two sockets so that they overlap, and then heating the outer surface of the outer socket to join and temporarily fix the two sockets.

[0041] Next, an example of a construction method (casting method) using the above-described steel pipe for ground reinforcement will be described with reference to Fig. 8, taking as an example an elongated steel pipe consisting of four steel pipes with the leading pipe having the largest diameter.

[0042] First, as a preparation step, an elongated steel pipe 100 is prepared with a bit 50 attached to the tip of the leading pipe. A rod 70 is inserted into this elongated steel pipe and attached to the bit 50. In this state, the elongated steel pipe 100 is set in a guide shell 81 installed near the casting site. The guide shell 81 is a long device equipped with a drifter 80, which is the drive source for the bit 50. The guide shell 81 is provided with a pair of steel pipe receiving jigs (centralizer / subcentralizer) 82 to align the core of the steel pipe with the drilling direction, and the drifter 80 is mounted behind it. The rod 70 is connected to the drifter 80. The system is now ready for casting.

[0043] Next, the guide shell 81 is set so that the bit 50 abuts the desired casting position, and the drifter 80 is driven to start excavating with the bit 50 (Figure 8: Casting begins). As the bit 50 rotates, excavation progresses, and rock chips and soil created by the excavation are expelled from inside the steel pipe. Initially, the entire drawn steel pipe 100 advances into the ground. Once the entire drawn steel pipe 100 advances and the flange 15 of the terminal pipe 1D is fixed by the steel pipe receiving jig 82 or the face, the steel pipe is pulled out from the drawn steel pipe 100 (Figure 8: Casting in progress).

[0044] With the flange 15 of the terminal pipe 1D fixed at the steel pipe receiving jig 82 or the working face, a second rod is connected to the rear end of the first rod, and excavation continues with the bit. When the leading pipe 1A is stretched from the drawn steel pipe, the front socket 22 of the following intermediate pipe 1B fits into the rear end socket 21 fixed to the rear end of the leading pipe 1A, and at that time, the elastic ring 45 fits into the recess 40 formed in the rear end socket 21 of the leading pipe 1A, connecting the leading pipe and the intermediate pipe.

[0045] As excavation progresses, the second intermediate pipe 1B is also pulled out and advances into the ground as the leading pipe moves. Even after the second intermediate pipe 1B has been pulled out to its maximum extent and connected to the third intermediate pipe 1C, excavation continues, causing the third intermediate pipe 1C to advance into the ground in the same manner. During this series of pulling-out operations (sliding of the steel pipe), the flange 15 of the end pipe is caught on the steel pipe receiving jig 82 or the face, allowing for smooth, continuous pulling-out operations to be performed using this as a fulcrum.

[0046] After casting, the rod is rotated in the reverse direction to remove it from the bit and pull it out of the steel pipe, and reinforcing anchoring material is injected into the end of the terminal pipe, which is the same as a general casting method, so a description will not be given here.

[0047] As described above, according to the construction method for ground reinforcement using elongated steel pipes of the present invention, by providing a means for temporarily fixing the steel pipes to each other before starting the stretching work of the elongated steel pipes, it is possible to stably move the elongated steel pipes and position them at the installation location, thereby greatly improving the workability of laying and pouring elongated steel pipes. [Explanation of symbols]

[0048] 1: elongated steel pipe, 1A to 1D: steel pipe, 13: protector, 15: flange, 20: connecting portion, 21: rear end socket, 22: front end socket, 210: step portion, 211: first pipe portion, 212: second pipe portion, 30: temporary fixing portion, 31: through hole, 35: pin, 40: recess, 45: elastic ring (return prevention mechanism), 100: steel pipe for ground reinforcement, 50: bit, 55: inner guide, 60: joining material (welded portion or adhesive portion), 70: rod, 80: drifter, 81: guide shell, 82: steel pipe receiving jig (centralizer / sub-centralizer).

Claims

1. A stretched steel pipe is a steel pipe in which a plurality of steel pipes having different diameters are nested so as to be slidable relative to each other in the axial direction, and the nested steel pipes are successively stretched from the leading steel pipe of the plurality of steel pipes, a connecting portion provided at the rear end of one steel pipe constituting the plurality of steel pipes and the front end of a subsequent steel pipe, which engages the rear end of the one steel pipe with the front end of the subsequent steel pipe when the drawn steel pipe is stretched; a temporary fixing portion that temporarily fixes the rear end portion of the first steel pipe and the rear end portion of the subsequent steel pipe with a force that is weaker than the tensile force applied to the connecting portion when the first steel pipe and the subsequent steel pipe are not stretched; An elongated steel pipe comprising:

2. The drawn steel pipe according to claim 1, The connecting portion includes a rear end socket and a front end socket that can be engaged with each other, the rear end socket being provided at the rear end of a steel pipe having a subsequent steel pipe among the plurality of steel pipes, and the front end socket being provided at the front end side of a steel pipe having a preceding steel pipe among the plurality of steel pipes, The temporary fixing portion is an elongated steel pipe that temporarily fixes the rear end sockets of two adjacent steel pipes together when the two adjacent steel pipes each have the rear end socket.

3. The drawn steel pipe according to claim 2, the rear end socket is a tubular member having a convex stepped portion on its inner surface, and includes a first tubular portion fixed to the outer periphery of the rear end of the steel pipe, and a second tubular portion located outside the rear end of the steel pipe with the stepped portion sandwiched therebetween; When the two adjacent steel pipes are not stretched, the first pipe portion of the rear-end socket portion fixed to the trailing steel pipe is fitted into the second pipe portion of the rear-end socket portion fixed to the preceding steel pipe, An elongated steel pipe characterized in that the temporary fixing portion temporarily fixes the second pipe portion of the rear end socket of the preceding steel pipe and the first pipe portion of the rear end socket of the following steel pipe.

4. The drawn steel pipe according to claim 3, the rear-end socket is provided with a hole penetrating at least a part of the first pipe portion and the second pipe portion at a position where the first pipe portion of the rear-end socket of the leading steel pipe and the second pipe portion of the rear-end socket of the trailing steel pipe overlap in the radial direction of the rear-end socket when the two adjacent steel pipes are not stretched, The elongated steel pipe is characterized in that the temporary fixing portion is made of a temporary fixing member installed by passing through the hole.

5. The drawn steel pipe according to claim 4, The elongated steel pipe is characterized in that the fixing member is a pin that deforms or breaks due to the tensile force when the elongated steel pipe is stretched.

6. The drawn steel pipe according to claim 3, The elongated steel pipe is characterized in that the connecting portion is provided with a slip-out prevention portion that prevents the front end socket from slipping out of the rear end socket when the rear end socket and the front end socket are engaged.

7. The drawn steel pipe according to claim 6, The slip-out prevention portion includes an elastic ring provided on the outer periphery of the steel pipe having the tip socket in the vicinity of the tip socket, the rear end socket is fixed to the rear end of the steel pipe with a gap between its step portion and the rear end face of the steel pipe, An elongated steel pipe characterized in that, when the rear end socket and the front end socket are engaged, the elastic ring fits into the gap between the stepped portion of the rear end socket and the rear end face of the steel pipe, preventing the steel pipe from coming loose.

8. The drawn steel pipe according to claim 2, The elongated steel pipe is characterized in that the temporary fixing portion is a welded portion or adhesive portion that joins the rear end sockets of two adjacent steel pipes.

9. The drawn steel pipe according to claim 1, A concrete driving bit fixed to the tip of the steel pipe with the largest diameter among the plurality of steel pipes; a flange fixed to a rear end portion of the rear end of the plurality of steel pipes with the smallest diameter, An elongated steel pipe for ground reinforcement configured to be driven into the ground while stretching the elongated steel pipe from the steel pipe with the largest diameter by the driving force applied to the driving bit.

Images