Box welded joint, box welding method, and method for manufacturing welded joint

Abstract

To provide a boxing weld joint and a boxing method which can dramatically improve fatigue strength with simple means.SOLUTION: There is provided a boxing weld joint obtained by boxing and joining a gusset to a main plate, wherein one side or both sides of an end face of the gusset vertical to the main plate are chamfered, and a length (t) of a short side of a contact surface contacting the main plate of the gusset is within a range of 0.2 times or more and 0.8 times or less of a plate thickness (t0) of the gusset. There is provided a boxing method for joining a gusset to a main plate by boxing, wherein when one side or both sides of an end face of the gusset vertical to the main plate are chamfered, and the gusset is brought into contact with the main plate, a length (t) of the short side of a contact surface is within a range of 0.2 times or more and 0.8 times or less of a plate thickness (t0) of the gusset.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Generally, in steel structures, there are many boxing welded joints in which the periphery of a gusset 2 is welded to a main plate 1 (so-called boxing weld) as shown in Figure 2. In a boxing welded joint, a weld bead 3 surrounds the gusset 2, and stress concentration occurs at the toe of the weld bead 3. As a result, the welding residual stress caused by the boxing weld and the repeated stress caused by an external force are superimposed, causing fatigue cracks, which then propagate and cause fatigue failure. Note that an external force is a load that repeatedly acts on a steel structure from the outside. For example, if the steel structure is a steel bridge, it is a load that repeatedly occurs due to natural weather conditions (such as wind) or vehicle traffic. If the steel structure is a ship, it is a load that repeatedly occurs due to vibration caused by power or wind and waves.

[0003] In recent years, reports of fatigue-induced damage have been increasing as steel structures age. To prevent such damage, it is necessary to periodically inspect steel structures, manage the progress of the damage, and take measures according to the progress of the damage. In particular, when fatigue-induced damage occurs in steel bridges, it is possible to reduce the external forces acting on the steel bridge by restricting vehicle traffic, but this causes traffic congestion and delays in logistics, which has a significant negative impact on social activities. Therefore, various technologies have been proposed to improve the fatigue properties of boxing welded joints in steel structures.

[0004] For example, Patent Document 1 describes that fatigue life is improved by forming an extension bead on the upper surface of the main plate from each of both longitudinal ends of the gusset.

[0005] In addition, in the technology disclosed in Patent Document 2, a first weld bead is formed along the short side of a rectangular abutment surface where the gusset abuts against the main plate. The first weld bead is then formed by extending from both sides of the short side of the rectangular abutment surface onto the main plate. Next, a second weld bead and a third weld bead are formed along the long side of the rectangular abutment surface. The second weld bead and the third weld bead are then formed by covering the first weld bead and extending beyond the first weld bead onto the main plate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-233747 A [Patent Document 2] JP 2018-158380 A [Non-patent literature]

[0007] [Non-Patent Document 1] Satoshi Iki et al.: “High-performance steel for shipbuilding - JFE Steel's life cycle cost reduction technology”, JFE Technical Report, No. 5, August 2004, pp. 13-18 [Non-Patent Document 2] Satoshi Iki et al.: “Effect of Microstructure on Fatigue Crack Propagation Rate”, JFE Technical Report, No. 33, February 2014, pp. 55-61 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional technology has the following problems. The technology of Patent Document 1 requires the formation of an extended bead in a shape that covers the welded turn, which results in a long welding time and poor workability. The technology described in Patent Document 2 also requires a long welding time and poor workability.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a box welded joint, a box welding method, and a method for manufacturing a welded joint that can dramatically improve fatigue strength using simple means. [Means for solving the problem]

[0010] The box welded joint of the present invention, which advantageously solves the above-mentioned problems, is a box welded joint obtained by box welding a gusset to a main plate, characterized in that one or both sides of an end face of the gusset perpendicular to the main plate are chamfered, and the length (t) of the short side of the abutment surface of the gusset that abuts against the main plate is in the range of 0.2 to 0.8 times the plate thickness (t0) of the gusset.

[0011] In addition, the box welded joint according to the present invention is (a) the chamfered range of the end face of the gusset is equal to or greater than the height of the weld bead in a direction perpendicular to the main plate; (b) the main plate is made of fatigue-resistant steel; This may be a more preferable solution.

[0012] The box welding method of the present invention, which advantageously solves the above-mentioned problems, is a box welding method for joining a gusset to a main plate by box welding, characterized in that one or both sides of an end face of the gusset perpendicular to the main plate are chamfered, and when the gusset is abutted against the main plate, the length (t) of the short side of the abutting surface is in the range of 0.2 to 0.8 times the plate thickness (t0) of the gusset.

[0013] The turning welding method according to the present invention is as follows: (a) The chamfered range of the end face of the gusset is set to a length, in a direction perpendicular to the main plate, equal to or greater than the height of the weld bead in a direction perpendicular to the main plate; (b) using fatigue-resistant steel for the main plate; This may be a more preferable solution.

[0014] The method for manufacturing a welded joint according to the present invention, which advantageously solves the above-mentioned problems, is a method for manufacturing a welded joint obtained by joining a gusset to a main plate by turn welding, and is characterized in that one or both sides of an end face of the gusset perpendicular to the main plate are chamfered, and when the gusset abuts against the main plate, the length (t) of the short side of the abutting surface is in the range of 0.2 to 0.8 times the plate thickness (t0) of the gusset. Effect of the Invention

[0015] According to the boxing welded joint, boxing welding method, and welded joint manufacturing method of the present invention, it is possible to provide a boxing welded joint that dramatically improves the fatigue strength of the weld bead in the boxing welding of the gusset by a simple means. At the same time, it is possible to avoid the deterioration of the performance and trouble of the steel structure due to fatigue fracture from the welded part. [Brief description of the drawings]

[0016] [Figure 1] 1A is a schematic diagram showing a boxing welded joint according to one embodiment of the present invention, in which (a) is a perspective view, (b) is a top view, and (c) is a cross-sectional view showing a fatigue fracture surface of a main plate. [Diagram 2] 1A is a schematic diagram showing a boxing welded joint according to a conventional technique, in which (a) is a perspective view, (b) is a top view, and (c) is a cross-sectional view showing a fatigue fracture surface of a main plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the embodiments of the present invention will be described in detail. Note that the drawings are schematic and may differ from the actual ones. The following embodiments are merely examples of equipment and methods for embodying the technical idea of ​​the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims.

[0018] The inventors considered that it is important to suppress both the initiation and propagation of fatigue cracks in order to increase the fatigue strength of boxing welded joints. As a result of examining the mechanism by which fatigue cracks occur in boxing welded joints, it was clarified that fatigue cracks occur by the following mechanism. Figure 2 shows a conventional boxing welded joint. Figure 2(a) shows a perspective view of a boxing welded joint in which a gusset 2 is box-welded to a main plate 1a of conventional steel with a weld bead 3. Figure 2(b) shows a top view. Figure 2(c) is a cross-sectional view showing a fatigue fracture surface 4a of the main plate 1a near the weld bead toe 31 of the gusset end surface 23. As shown in Figure 2(c), on the short side 23a side of the approximately rectangular abutment surface where the gusset 2 abuts against the main plate 1a, the toe of the weld bead 3 becomes a stress concentration source, and fatigue cracks occur from there. In many cases, multiple small cracks occur at the toe of the weld bead 3. It was found that these microcracks grow and merge to form a fatigue fracture surface 4a, which then forms a large fatigue crack. This is because the shape of the weld bead toe 31 is inevitably not uniform, and the degree of local stress concentration varies. In addition, after a fatigue crack initiates from the weld bead toe 31, the crack propagates to the main plate, causing fatigue failure. At this time, the length b of the region where cracks can initiate is approximately equal to the gusset plate thickness t0.

[0019] An example of a boxing welded joint developed based on the above-mentioned study is shown in FIG. 1. FIG. 1(a) shows a perspective view of a boxing welded joint in which a gusset 2 is box-welded to a main plate 1 made of fatigue-resistant steel with a weld bead 3. FIG. 1(b) shows a top view. FIG. 1(c) is a cross-sectional view showing a fatigue fracture surface 4 of the main plate 1 near a weld bead toe 31 of a gusset end face 22. As shown in FIG. 1, by making the length of the short side 22a of the contact surface of the gusset that contacts the main plate smaller than the plate thickness t0 of the gusset, the range in which microcracks can occur before coalescence can be limited and the number of microcracks before coalescence can be reduced. Therefore, it was found that it is possible to prevent cracks from suddenly growing large due to coalescence. If the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 is larger than 0.8 times the plate thickness t0 of the gusset, the effect of suppressing crack coalescence cannot be obtained. For this reason, the length t of the short side 22a of the abutment surface of the gusset 2 that abuts against the main plate 1 is set to 0.8 times or less the plate thickness t0 of the gusset. More preferably, the length t of the short side 22a of the abutment surface of the gusset 2 that abuts against the main plate 1 is set to 0.7 times or less the plate thickness t0 of the gusset. Here, the short side 22a of the abutment surface of the gusset 2 refers to a surface that is perpendicular to the wide surface of the surfaces perpendicular to the main plate surface of the gusset 2 that is erected perpendicular to the main plate 1. In the example of Fig. 1, it refers to a surface that is chamfered from both sides of the gusset end surface 23 in Fig. 2 and has a narrower width in the plate thickness direction.

[0020] On the other hand, if the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 is made too short, stress concentration increases. It has also been found that although crack coalescence is suppressed, the formation of fatigue cracks may be accelerated due to the action of excessive stress. If the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 is smaller than 0.2 times the plate thickness t0 of the gusset 2, the fatigue life reduction due to the large stress concentration may exceed the fatigue life extension effect due to the crack coalescence suppression. Therefore, the overall fatigue life extension effect cannot be obtained. Therefore, the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 is set to 0.2 times or more the plate thickness t0 of the gusset 2. More preferably, the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 is set to 0.3 times or more the plate thickness t0 of the gusset 2.

[0021] From the above, the fatigue life of a box-welded structure can be improved by controlling the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 within an appropriate range, such as 0.2 to 0.8 times the plate thickness t0 of the gusset 2.

[0022] In order to make the length t of the short side 22a of the contact surface of the gusset 2 that contacts the main plate 1 smaller than the plate thickness t0 of the gusset, the edge of the end surface 23 of the gusset 2 perpendicular to the main plate 1 can be chamfered as a simple method. The chamfered surface 21 may be one side of the end surface of the gusset 2, or both sides of the end surface of the gusset 2. The chamfered shape may be either flat or curved. It is sufficient as long as it has a shape that can reduce the length a of the region where cracks can occur. In addition, it is preferable that the chamfered surface 21 has a length from the end that contacts the main plate 1 in a direction perpendicular to the main plate, which is equal to or greater than the height h of the weld bead in a direction perpendicular to the main plate. In addition, the angle that the chamfered edge 21a makes with the short side 22a of the contact surface on the surface where the gusset 2 contacts the main plate 1 is preferably in the range of 15° to 75°, and more preferably in the range of 30° to 60°.

[0023] In this embodiment, the effect can be achieved regardless of the material of the main plate 1 and the gusset 2. Since the size of the crack front on the main plate 1 side at the early stage of fatigue crack initiation can be limited, a further longer life can be expected by applying a main plate 1 with a low fatigue crack propagation rate (fatigue cracks are less likely to propagate). It is preferable to use a fatigue-resistant steel for the main plate 1. A fatigue-resistant steel is a steel material that improves the fatigue crack propagation resistance of the base material, improves the fatigue crack initiation resistance of the welded joint, or improves both properties to extend the fatigue life of a welded steel structure. In general, a slab having an appropriate chemical composition is manufactured through an optimal cooling and rolling process. For example, a steel material with a fatigue crack propagation speed about half that of a conventional material, as described in Non-Patent Document 1 and Non-Patent Document 2, can be used. EXAMPLES

[0024] Steel types having the chemical composition shown in Table 1 were used for the main plate and gusset, and boxing welded joints were fabricated. The repeated stresses shown in Table 2 were applied and the life until fracture, that is, the number of repeated stresses, was evaluated. The plate thickness t0 of the main plate and gusset was the same. The chamfering of the gusset end surface was a 45° flat surface. Steel types A to C are conventional steels. Steel type D is a fatigue-resistant steel.

[0025] Test No. 5 in Table 2 is a boxing welded joint produced by the conventional method shown in Figure 2, and those with a longer fracture life (more repeated stresses) were considered to be preferable. All of the inventive examples had a preferable fracture life.

[0026] [Table 1]

[0027] [Table 2] [Industrial Applicability]

[0028] INDUSTRIAL APPLICABILITY The box welded joint, box welding method, and welded joint manufacturing method of the present invention are industrially useful because they can avoid performance degradation and problems of steel structures due to fatigue fracture from welds. [Explanation of symbols]

[0029] 1 Main plate (fatigue-resistant steel) 1a Main plate (conventional steel) 2 Gusset 21 Chamfered surface 21a Chamfered edge 22 Gusset end face 22a Contact surface short side 23 Gusset end face 23a Contact surface short side 3 Weld Bead 31 Area where cracks can occur (toe of weld bead) 4. Fatigue fracture 4a Fatigue fracture surface (crack coalescence) t Contact surface short side length t0 gusset plate thickness a, b Length of region where cracks can occur h Weld bead height

Claims

1. A box weld joint obtained by joining a gusset to a main plate by box welding, One or both sides of the end face of the gusset perpendicular to the main plate are chamfered, The length (t) of the short side of the contact surface of the gusset that contacts the main plate is the plate thickness (t ０ ) in the range of 0.2 to 0.8 times the normalized joint ...

2. 2. The box welded joint according to claim 1, wherein the chamfered range of the end face of the gusset has a length in a direction perpendicular to the main plate that is equal to or greater than the height of the weld bead in the direction perpendicular to the main plate.

3. 3. The boxing welded joint according to claim 1, wherein the main plate is made of fatigue resistant steel.

4. A method of joining a gusset to a main plate by turn welding, comprising the steps of: One or both sides of the end face of the gusset perpendicular to the main plate are chamfered; When the gusset is brought into contact with the main plate, the length (t) of the short side of the contact surface is set to the thickness (t) of the gusset. ０ ) in the range of 0.2 to 0.8 times the welding temperature.

5. 5. The box welding method according to claim 4, wherein the chamfered range of the end face of the gusset is set to a length in a direction perpendicular to the main plate that is equal to or greater than the height of the weld bead in the direction perpendicular to the main plate.

6. 6. The box welding method according to claim 4 or 5, wherein the main plate is made of fatigue resistant steel.

7. A method for manufacturing a boxing welded joint obtained by boxing welding a gusset to a main plate, comprising: One or both sides of the end face of the gusset perpendicular to the main plate are chamfered; When the gusset is brought into contact with the main plate, the length (t) of the short side of the contact surface is set to the thickness (t) of the gusset. ０ ) in the range of 0.2 to 0.8 times.

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