Box welded joint and box welding method with excellent fatigue life

Abstract

To provide a boxing joint having fatigue strength which can be stably and inexpensively improved even if short bead occurs, considering actual welding work, and a boxing method.SOLUTION: A boxing joint is provided which is obtained by boxing a gusset 2 to a main plate 1, the boxing joint has a first weld bead 3 and a second weld bead 4. The first weld bead is formed along the other long side via from one long side to a short side of a rectangular contact surface 2a where the gusset contacts the main plate, and the second weld bead has a long side weld portion 9, an overlapped portion 5 and an extending portion 6. The long side weld portion is formed along the long side of the rectangular contact surface, the overlapped portion is formed by covering a weld portion of the first weld bead, and the extending portion is formed by being drawn from the overlapped portion onto the main plate. A length L from a distal end of the first weld bead to the short side of the rectangular contact surface is 5 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a boxing welding technique for main plates and gussets that is widely used when constructing steel structures, and in particular to a boxing welded joint and a boxing welding method that are suitable for steel structures (such as steel bridges and ships) that require excellent fatigue properties. [Background technology]

[0002] Generally, steel structures have many boxing welded joints, in which the periphery of a gusset is welded to the main plate (so-called "boxing weld"). In boxing welded joints, the weld bead surrounds the gusset. If the weld bead has defects (e.g., cracks) that prevent the weld toe from being smoothly shaped, stress concentration at the weld toe is likely to occur. As a result, the welding residual stress caused by the boxing weld and the repeated stress caused by external forces combine to generate fatigue cracks, which then propagate and cause fatigue failure. Note that an external force refers to a load repeatedly acting on a steel structure from the outside. For example, if the steel structure is a steel bridge, this load would be repeatedly generated by natural weather conditions (e.g., wind) or vehicle traffic, while if the steel structure is a ship, this load would be repeatedly generated by wind and waves.

[0003] In recent years, as steel structures age, there have been an increasing number of reports of fatigue-related damage. To prevent such damage, it is necessary to regularly inspect steel structures, monitor the progression of damage, and take appropriate measures as the damage progresses. In particular, when fatigue-related damage occurs in steel bridges, it is possible to reduce the external forces acting on the steel bridge by restricting vehicle traffic, but this can cause traffic congestion and delays in logistics, resulting in significant adverse effects on social activity. Therefore, technologies to improve the fatigue properties of box-welded joints in steel structures are being investigated.

[0004] For example, Patent Document 1 discloses a technique for reliably increasing joint fatigue strength by fillet-welding the long sides of the rectangular abutment surface (hereinafter also referred to as the "rectangular abutment surface") where the gusset abuts the main plate to the main plate, cooling the abutment to room temperature, and then box-welding the short sides from the corners of the rectangular abutment surface. In this technique, a weld bead formed along the short sides of the rectangular abutment surface (hereinafter also referred to as the "short side weld bead") is placed over a weld bead formed along the long sides (hereinafter also referred to as the "long side weld bead"), and the short side weld bead extends beyond the long side weld bead onto the main plate. In this way, welding the long side weld bead first and then placing and welding the short side weld bead over it tends to create a gap (i.e., a space surrounded by the main plate, long side weld bead, and short side weld bead) where the weld beads overlap. This facilitates fatigue cracking due to stress concentration, making it difficult to prevent the fatigue crack from propagating. In other words, the technology disclosed in Patent Document 1 cannot be expected to significantly improve the fatigue strength of boxing welded joints.

[0005] In response to this, Patent Document 2 discloses a technique for preventing the occurrence of the above-mentioned gap using ordinary welding equipment and welding materials in order to suppress increases in boxing welding costs. In this technique, a narrow side weld bead (first weld bead) is first welded in a straight line parallel to the narrow side, and then long side weld beads (second and third weld beads) are welded to cover the narrow side weld bead. The long side weld bead is then welded so that it extends beyond the already welded narrow side weld bead. This prevents the occurrence of the above-mentioned gap and, ultimately, the occurrence of fatigue cracks regardless of the shape of the weld toe. Furthermore, the patent document discloses that welding the narrow side weld bead so that its length does not exceed the long side weld bead further significantly prevents the occurrence of the above-mentioned gap. The patent document states that the reason for welding the narrow side weld bead so that its length does not exceed the long side weld bead is that if the narrow side weld bead is too long and extends onto the main plate from below the two long side weld beads, the above-mentioned gap is likely to occur, which makes fatigue cracks more likely to occur. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-19860 [Patent Document 2] JP 2018-158380 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, when considering actual welding, performing welding so that the narrow side weld bead does not extend beyond the wide side weld bead according to the technique of Patent Document 2 can cause problems in welding management. In other words, in actual welding, the end position of the narrow side weld bead, which is formed in a straight line parallel to the narrow side, can vary due to differences in worker skill and welding machine performance, resulting in the actual length of the narrow side weld bead being 5 to 10 mm shorter than the target length. This phenomenon is called a short bead of the narrow side weld bead. In this case, if a gap (a gap of 10% or more compared to the bead width of the wide side weld bead) occurs where the narrow side weld bead overlaps with the wide side weld bead, stress concentration occurs due to bead discontinuity, which poses a problem of reduced fatigue strength.

[0008] In view of the above circumstances, the present invention takes into consideration actual welding construction and has an object to provide a boxing welded joint and a boxing welding method that can inexpensively and stably improve fatigue strength even if short beads occur. [Means for solving the problem]

[0009] The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that if the narrow side weld bead is not formed in a straight line parallel to the narrow side, but is formed starting from the long side, passing along the short side, and ending on the opposite long side, excellent fatigue strength can be obtained regardless of whether short beads are formed in the narrow side weld bead. Furthermore, they discovered that if the length of the overlapping portion between the narrow side weld bead that covers the long side of the narrow side weld bead and the narrow side weld bead is 5 mm or more, fatigue strength is effectively improved.

[0010] The present invention was made based on the above findings and further studies, and the gist of the present invention is as follows. [1] A boxing weld joint obtained by joining a gusset to a main plate by box welding, The box weld joint has a first weld bead and a second weld bead; the first weld bead is formed along one long side, via one short side, and along the other long side of a rectangular abutment surface where the gusset abuts against the main plate, the second weld bead has a long side weld portion, an overlap portion, and an extension portion; The long side weld is formed along a long side of the rectangular abutment surface, the overlapping portion is formed to cover the weld portion of the first weld bead, the extension portion is formed by extending from the overlap portion onto the main plate, The length L1 from the welding start end of the first weld bead to the short side of the rectangular abutment surface is 5 mm or more, The length L2 from the short side of the rectangular abutment surface to the welding end end of the first weld bead is 5 mm or more. A turn weld joint characterized by: [2] The boxing weld joint according to [1], characterized in that the first weld beads and the second weld beads each have two beads. [3] In the above [1] or [2], The length N (N1, N2) between the tip of the extension portion and the short side toe of the rectangular abutment surface of the first weld bead is 5 mm to 50 mm, The distance M between the toes of the extension is 2 mm or more. A turn weld joint characterized by: [4] In any one of [1] to [3], the thickness T of the main plate S A boxing welded joint characterized in that the gap is 5mm to 20mm. [5] In any one of [1] to [4], the length T of the short side of the rectangular contact surface G A boxing welded joint characterized in that the gap is 5mm to 20mm. [6] In a turn welding method for joining a gusset to a main plate by turn welding, a first weld bead is formed along one long side, via one short side, and along the other long side of a rectangular abutment surface where the gusset abuts against the main plate; Next, a second weld bead is formed, the second weld bead having a long side weld portion formed along the long side of the rectangular abutment surface, an overlap portion formed by covering the weld portion of the first weld bead, and an extension portion formed by extending from the overlap portion onto the main plate; The length L1 from the welding start end of the first weld bead to the short side of the rectangular abutment surface is 5 mm or more, The length L2 from the short side of the rectangular abutment surface to the welding end end of the first weld bead is 5 mm or more. A turn welding method characterized by the above. [7] In the above [6], the first weld beads are formed in two on both short side sides of the rectangular abutment surface, and then the second weld beads are formed in two on both long side sides of the rectangular abutment surface. [8] In the above [6] or [7], the length N (N1, N2) between the tip of the extension portion and the short side toe of the rectangular abutment surface of the first weld bead is set to 5 mm to 50 mm, The distance M between the toes of the extension is 2 mm or more. A turn welding method characterized by the above. [9] In any one of [6] to [8], the thickness T of the main plate S The method of box welding is characterized in that the distance is 5 mm to 20 mm.

[10] In any one of [6] to [9], the length T of the short side of the rectangular contact surface G The method of box welding is characterized in that the distance is 5 mm to 20 mm. [Effects of the Invention]

[0011] According to the present invention, when constructing a new steel structure or repairing an aging steel structure, even if a short bead occurs in the narrow side weld bead during boxing, it is possible to inexpensively and stably improve the fatigue strength of the boxing welded joint, which is an industrially significant advantage. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view schematically showing an example of a boxing weld joint according to the present invention. FIG. [Figure 2] 1 is a plan view schematically showing an example of a procedure for performing a box welding method according to the present invention. FIG. [Figure 3] FIG. 3 is an enlarged schematic plan view of FIG. 2(c). DETAILED DESCRIPTION OF THE INVENTION

[0013] Representative embodiments of the box weld joint and box welding method according to the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these. Furthermore, since the drawings are intended to conceptually explain the present invention, the dimensions and ratios of the various components shown may differ from the actual dimensions.

[0014] Fig. 1 is a perspective view that schematically shows an example of a box welded joint according to the present invention, Fig. 2 is a plan view that schematically shows an example of the procedure for performing a box welding method to obtain the box welded joint, and Fig. 3 is an enlarged view of Fig. 2(c). In Fig. 2, the rectangular abutment surface 2a where the gusset 2 abuts against the main plate 1 coincides with the shape enclosed by the rectangular line when the gusset 2 is projected onto the main plate 1, and is composed of a long side 2b and a short side 2c. Figs. 2 and 3 show the procedure for performing a box welded joint and box welding method on one short side of the rectangular abutment surface 2a.

[0015] [Box weld joint] The boxing weld joint according to the present invention has a first weld bead 3 and a second weld bead 4. Preferably, there are two first weld beads 3 and 3' and two second weld beads 4a and 4b.

[0016] First weld bead 3 is formed from one long side, via one short side, to the other long side of rectangular contact surface 2a where gusset 2 contacts main plate 1. First weld bead 3' is symmetrical to first weld bead 3, and is formed from one long side, via the other short side, to the other long side of rectangular contact surface 2a.

[0017] Next, second weld beads 4 (4a, 4b) are formed along the long sides of rectangular abutment surface 2a, and are formed by continuously covering two first weld beads 3 and 3' and extending onto main plate 1. Therefore, second weld beads 4 (4a, 4b) have long side weld portions 9 (9a, 9b), overlapping portions 5 (5a, 5b), and extension portions 6 (6a, 6b). Long side weld portions 9 (9a, 9b) are formed along long side 2b of rectangular abutment surface 2a. Overlapping portions 5 (5a, 5b) are formed by covering the long side 2b portions of rectangular abutment surface 2a of first weld beads 3 and 3'. Extension portions 6 (6a, 6b) are formed by extending from overlapping portions 5 (5a, 5b) onto main plate 1.

[0018] It is preferable that long side welds 9 (9a, 9b) are formed continuously at first weld beads 3 and 3', but they may be interrupted midway. When first weld bead 3 is formed only on one short side of rectangular abutting surface 2a, second weld bead 4a is formed from the middle of the long side of rectangular abutting surface 2a so as to cover weld start end 10a of first weld bead 3. Similarly, second weld bead 4b is formed from the middle of the other long side of rectangular abutting surface 2a so as to cover weld end end 10b of first weld bead 3.

[0019] Here, the length L of the overlapping portion 5 (5a, 5b), i.e., the length L1 from the weld start end 10a of the first weld bead 3, 3′ to the short side 2c of the rectangular abutment surface 2a and the length L2 from the short side 2c of the rectangular abutment surface 2a to the weld end end 10b of the first weld bead 3, 3′, should be 5 mm or more. If these lengths L1 and L2 are less than 5 mm, fatigue strength may decrease regardless of whether a short bead is formed. Note that if the length L exceeds 20 mm, unnecessary welding man-hours for forming the first weld bead increase, so it is preferably 5 mm to 20 mm. More preferably, it is 10 mm to 15 mm.

[0020] Furthermore, the length N (N1, N2) between the tip 7 (7a, 7b) of the extension 6 (6a, 6b) of the second weld bead 4 (4a, 4b) and the short side toe 3a of the rectangular abutment surface 2a of the first weld bead 3, 3' is preferably in the range of 5 mm to 50 mm. If it is less than 5 mm, there is no effect in improving fatigue strength, and if it exceeds 50 mm, construction takes a long time. More preferably, it is 10 mm to 20 mm.

[0021] Furthermore, the distance M between the toes of the extensions 6 of the second weld beads 4 (4a, 4b), i.e., the width of the space surrounded by the extensions 6a and 6b, is preferably 2 mm or more. If it is less than 2 mm, the beads are likely to be connected to each other, and the fatigue strength improvement effect is not achieved. More preferably, it is 5 mm to 10 mm.

[0022] Next, the plate thickness T of the main plate in the present invention S Although there is no limitation, it is preferably 5 mm to 20 mm.

[0023] In addition, the thickness of the gusset in the present invention, i.e., the length T of the short side of the rectangular contact surface G is not particularly limited, but is preferably 5 mm to 20 mm from the viewpoint of improving fatigue properties. G If the distance is less than 5 mm, it is difficult to form a second weld bead with a distance M of 0 mm or more, while if the distance exceeds 20 mm, it is disadvantageous in terms of improving the fatigue properties.

[0024] [Rotation welding method (construction procedure)] Next, the procedure for performing the box welding method for obtaining a box welded joint according to the present invention will be described with reference to FIG.

[0025] 2(a), using a welding method and welding conditions described below, a first weld bead 3 is formed from the middle of one long side 2b of a rectangular abutment surface 2a that abuts a gusset 2 on a main plate 1, via one short side 2c, and along the other long side 2b. The long side from which welding starts when forming this first weld bead 3 may be any of the long sides.

[0026] Here, the welding start point of the first weld bead 3 may be a location where the length L1 from the weld start end 10a of the first weld bead 3 to the short side 2c of the rectangular abutting surface 2a is 5 mm or more. The welding end point of the first weld bead 3 may be a location where the length L2 from the short side 2c of the rectangular abutting surface 2a to the weld end end 10b of the first weld bead 3 is 5 mm or more. As mentioned above, if the lengths L1 and L2 are less than 5 mm, fatigue strength may decrease regardless of whether a short bead is formed. Note that if the lengths L1 and L2 exceed 20 mm, unnecessary welding man-hours for forming the first weld bead increase. Therefore, the lengths L1 and L2 are preferably 5 mm to 20 mm. More preferably, they are 10 mm to 15 mm. Note that it is not necessary for the lengths L1 and L2 to be the same; equivalent effects can be achieved as long as each length is 5 mm or more.

[0027] Next, as shown in FIG. 1, when forming a second first weld bead 3' on the other short side that is symmetrical to the short side on which the above-mentioned first weld bead 3 is formed, it is preferable to form the first first weld bead 3 and then form the second bead using the same procedure as the first bead.

[0028] Next, as shown in FIG. 2( b), a second weld bead 4a is formed along one long side 2b of the rectangular abutment surface 2a, covering the weld bead on the long side 2b side of the first weld bead 3, and extending onto the main plate. This second weld bead 4a is preferably formed by continuously covering the first first weld bead 3 formed on one short side of the rectangular abutment surface with the second first weld bead 3' formed on the other short side. The formed second weld bead 4a has a long side weld portion 9a that extends over the long side of the rectangular abutment surface and does not overlap the first weld beads 3 and 3', an overlap portion 5a that overlaps the first weld bead 3, and an extension portion 6a that extends onto the main plate 1.

[0029] Here, the length N1 between the tip 7a of the extension 6a of the second weld bead 4a and the short side toe 3a of the rectangular abutting surface 2a of the first weld bead 3 is preferably in the range of 5 mm to 50 mm. If it is less than 5 mm, there is no effect in improving fatigue strength, and if it exceeds 50 mm, construction takes a long time. More preferably, it is 10 mm to 20 mm.

[0030] Finally, as shown in FIG. 2(c), a second second weld bead 4b is formed along the other long side 2b of the rectangular abutment surface 2a, covering the weld bead on the long side 2b side of the first weld bead 3 and extending onto the main plate. Similar to the first second weld bead 4a, this second weld bead 4b also has a long side weld 9b, an overlapping portion 5b, and an extension 6b. Furthermore, the spacing M (the spacing between the toes of the extensions), which is the width of the space surrounded by the extensions 6a and 6b of the second weld beads 4a and 4b, is preferably 2 mm or greater. If it is less than 2 mm, the beads are likely to connect to each other, and the fatigue strength improvement effect will not be achieved. A spacing M of 5 mm to 10 mm is more preferable.

[0031] It is preferable that long side welds 9 (9a, 9b) are formed continuously on first weld beads 3 and 3', but they may be formed segmented along the way. When first weld bead 3 is formed only on one short side of rectangular abutting surface 2a, second weld bead 4a is formed from the middle of the long side of rectangular abutting surface 2a so as to cover weld start end 10a of first weld bead 3. Similarly, second weld bead 4b is formed from the middle of the other long side of rectangular abutting surface 2a so as to cover weld end end 10b of first weld bead 3.

[0032] In the above description, second weld bead 4a is formed first and second weld bead 4b is formed later, but which is formed first or last is not particularly limited.

[0033] Furthermore, when forming the second weld bead, if two weld beads are formed, the lengths and shapes of the above-mentioned portions do not need to be the same for both beads.

[0034] [Rotation welding method and welding object] The welding means for performing the rotation welding are mainly the shielded metal arc welding method and the gas metal arc welding method, but other means can also be used as appropriate, and either manual welding or automatic welding may be employed.

[0035] The present invention can be applied not only to the construction of new steel structures, but also to the reinforcement and repair of deteriorated steel structures.

[0036] [Fatigue resistance] The present invention is effective regardless of the material of the main plates and gussets used to construct the steel structure. Examples of the material for the main plates include steel types such as SM400, SM490, SM520, and SM570, with a yield stress of 245 MPa to 560 MPa. [Example]

[0037] The present invention will be further described below with reference to examples. However, the following examples are merely intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention.

[0038] Main plate (thickness T S :14mm, plate width:80mm, length:500mm) with gusset (plate thickness T G The specimens (diameter: 14 mm, width: 75 mm, height: 50 mm) were box-welded by gas metal arc welding using a flux-cored wire, and fatigue tests were conducted on the box-welded joints obtained. The procedure is explained below.

[0039] For the main plate and gusset, steel plates having the chemical composition (mass%) shown in Table 1 were used. Furthermore, tensile test specimens (parallel portion diameter 6 mmΦ) were taken from the steel plates in accordance with the provisions of JIS Z 2241, and tensile tests were carried out to measure the yield stress (MPa) and tensile strength (MPa).

[0040] [Table 1]

[0041] The flux-cored wire used was MX-Z200 (wire diameter: 1.2 mm) manufactured by Kobe Steel, Ltd., a material conforming to JIS Z 3313. The wire had the following composition (mass%): C: 0.04%, Si: 0.07%, Mn: 1.22%, P: 0.010%, S: 0.011%, with the balance being Fe and unavoidable impurities.

[0042] The welding conditions for the gas metal arc welding were welding current: 240A, welding voltage: 32V, welding speed: 30cm / min, and the leg length was targeted to be approximately 8mm for both the first and second weld beads. Note that the gusset was positioned in the center of the main plate, so the rectangular abutment surface was located in the center of the main plate.

[0043] The fatigue tests were carried out under axial load control, stress ratio of 0.1, and frequency of 10 Hz in room temperature and air.

[0044] The measured bead spacing (L1, L2, N1, N2, M) of the obtained boxing welded joints, the stress range as the fatigue test conditions, and the fatigue test results are shown in Table 2. Here, the fatigue life is expressed as the number of load repetitions (cycles) until fatigue fracture occurs.

[0045] [Table 2]

[0046] As is clear from Table 2, all of the inventive examples had lengths L1 and L2 of 5 mm or more and had good fatigue lives, whereas all of the comparative examples had lengths L1 and L2 of less than 5 mm, and had fatigue lives that were half or less of those of the inventive examples. [Explanation of symbols]

[0047] 1 Main plate 2 gussets 2a: rectangular contact surface; 2b: long side of rectangular contact surface; 2c: short side of rectangular contact surface 3, 3' First weld bead 3a Toe of the short side of the first weld bead 4(4a, 4b) Second weld bead 5 (5a, 5b) Second weld bead overlap 6(6a, 6b) Extension of second weld bead 7 (7a, 7b) Tip of extension of second weld bead 9(9a, 9b) Long side weld of second weld bead 10a Weld start end of first weld bead 10b Welding end portion of first weld bead L (L1, L2) Length from the tip of the first weld bead to the short side of the rectangular contact surface M Spacing between extensions N (N1, N2) Length from the short side toe of the first weld bead to the tip of the extension

Claims

1. A box weld joint obtained by joining a gusset to a main plate by box welding, The box weld joint has a first weld bead and a second weld bead; the first weld bead is formed along one long side, via one short side, and along the other long side of a rectangular abutment surface at which the gusset abuts against the main plate, the second weld bead has a long side weld portion, an overlap portion, and an extension portion; The long side weld is formed along a long side of the rectangular abutment surface, the overlapping portion is formed to cover the weld portion of the first weld bead, the extension portion is formed by extending from the overlap portion onto the main plate, The length L1 from the welding start end of the first weld bead to the short side of the rectangular abutment surface is 5 mm or more, The length L2 from the short side of the rectangular abutment surface to the welding end end of the first weld bead is 5 mm or more. A turn weld joint characterized by:

2. The boxing weld joint according to claim 1, wherein the first weld beads and the second weld beads each have two weld beads.

3. a length N (N1, N2) between the tip of the extension portion and the short side toe of the rectangular abutment surface of the first weld bead is 5 mm to 50 mm, The distance M between the toes of the extensions is 2 mm or more.

3. The box weld joint according to claim 1 or 2.

4. The thickness T of the main plate Ｓ 4. The boxing weld joint according to claim 3, wherein the distance is 5 mm to 20 mm.

5. The length T of the short side of the rectangular contact surface Ｇ 5. The boxing weld joint according to claim 4, wherein the distance is 5 mm to 20 mm.

6. In a turn welding method for joining a gusset to a main plate by turn welding, a first weld bead is formed along one long side of a rectangular abutment surface where the gusset abuts against the main plate, passing through one short side and along the other long side; Next, a second weld bead is formed, the second weld bead having a long side weld portion formed along a long side of the rectangular abutment surface, an overlap portion formed by covering the weld portion of the first weld bead, and an extension portion formed by extending from the overlap portion onto the main plate; The length L1 from the welding start end of the first weld bead to the short side of the rectangular abutment surface is 5 mm or more, The length L2 from the short side of the rectangular contact surface to the welding end portion of the first weld bead is set to 5 mm or more. A turn welding method characterized by the above.

7. 7. The box welding method according to claim 6, wherein after two first weld beads are formed on both short side sides of the rectangular abutment surface, two second weld beads are formed on both long side sides of the rectangular abutment surface.

8. a length N (N1, N2) between the tip of the extension portion and the short side toe of the rectangular abutment surface of the first weld bead is set to 5 mm to 50 mm; The distance M between the toes of the extension is set to 2 mm or more.

8. The box welding method according to claim 6 or 7.

9. The thickness T of the main plate Ｓ 9. The box welding method according to claim 8, wherein the distance is 5 mm to 20 mm.

10. The length T of the short side of the rectangular contact surface Ｇ 10. The box welding method according to claim 9, wherein the distance is 5 mm to 20 mm.

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