Box welding method, and box welded joint

Abstract

Provided are a box welding method and a box welded joint. The present invention provides a box welding method for joining an upright plate 2 to a main plate 1 by box welding, the method including: first, forming a first welding bead 3 along the periphery of a rectangular contacting surface 2a where the upright plate 2 comes into contact with the main plate 1; next, disposing a weld metal damming member 9 on the main plate 1 so as to be in contact with the short side of the first welding bead 3; and next, forming a second welding bead 4 extending onto the main plate 1 so as to follow the weld metal damming member 9, the second welding bead having an overlapping portion 5 formed covering the long side of the first welding bead and an extending portion 6 formed extending from the overlapping portion 5 onto the main plate 1.

Description

Rotation welding method and rotation welding joint

[0001] The present invention relates to a box welding technique for welding a main plate to a vertical plate such as a gusset, which is widely used in the construction of steel structures. In particular, the present invention relates to a box welding method and a box welded joint suitable for welding steel structures (such as steel bridges and ships) that require excellent fatigue properties.

[0002] Generally, steel structures have many boxing welded joints, in which the periphery of a vertical plate is welded to a main plate (so-called "boxing weld"). In boxing welded joints, the vertical plate is surrounded by a weld bead. 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 overlap, causing fatigue cracks, which then propagate and lead to fatigue failure. Note that the external forces are loads repeatedly acting on the steel structure from the outside. For example, in the case of a steel bridge, these loads are caused by natural weather conditions (e.g., wind) and vehicle traffic, while in the case of a ship, these loads are caused by wind and waves.

[0003] In recent years, as steel structures age, there have been increasing reports of fatigue-related damage. To prevent such damage, steel structures must be inspected regularly to monitor the progression of damage and take appropriate measures as the damage progresses. When fatigue-related damage occurs in steel bridges, it is possible to reduce the external forces acting on the bridge by restricting vehicle traffic. However, this can cause traffic congestion and delays in logistics, significantly impacting social activity. Therefore, technologies to improve the fatigue properties of boxing welded joints in steel structures are being investigated.

[0004] In conventional box welding of vertical plates, the weld bead surrounds the vertical plate, and if defects (such as cracks) occur in the weld bead and the shape of the weld toe is not smoothly formed, stress concentration is likely to occur at the weld toe. As a result, the welding residual stress caused by the box welding and the repeated stress caused by external forces overlap, causing fatigue cracks, which then propagate and lead to fatigue failure.

[0005] In response to this, Patent Document 1 discloses a technique for preventing the occurrence of gaps associated with the above-mentioned weld bead defects using conventional welding equipment and welding materials to improve fatigue properties. In this technique, a narrow side weld bead (i.e., the first weld bead) is first welded, and then long side weld beads (i.e., the second and third weld beads) are welded, thereby covering the narrow side weld bead with the long side weld bead. The long side weld bead is welded so that it extends beyond the already welded narrow side weld bead. This prevents the occurrence of the above-mentioned gaps and, ultimately, the occurrence of fatigue cracks regardless of the shape of the weld toe. Furthermore, the narrow side weld bead is welded so that its length does not exceed the long side weld bead, thereby more significantly preventing the occurrence of the above-mentioned gaps. The reason for this length is as follows. If the short side weld bead is too long and extends from below the two long side weld beads onto the main plate, a gap is likely to form between the main plate, the short side weld bead, and the long side weld bead (specifically, one of the two long side weld beads), which makes fatigue cracks more likely to occur.

[0006] JP 2018-158380 A

[0007] However, when considering actual construction, repair, or reinforcement, the technology of Patent Document 1 above needs to be implemented during welding of the vertical plate, and there is a problem in that it is difficult to improve the fatigue characteristics of box welded joints that have already been constructed.

[0008] Furthermore, in actual welding work, differences in the skill of the worker, the performance of the welding machine, etc. can cause variations in the width and straightness of the long side weld beads, resulting in the distance between the extensions of the long side weld beads being narrower than the intended distance. Another problem is that welding spatter and other factors can cause geometric discontinuities within the distance between the long side weld beads, which can cause stress concentrations at these locations and reduce fatigue strength.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a boxing welding method and a boxing weld joint that can easily repair already constructed boxing weld joints by simply performing additional welding, and that can improve fatigue strength inexpensively and stably, taking into account actual welding procedures.

[0010] The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, discovered that forming an additional weld bead (i.e., a second weld bead) that covers the weld bead that is box-welded to the upright plate on the main plate (i.e., the first weld bead), runs along the long side of the rectangular abutment surface of the upright plate, and extends further onto the main plate is effective in preventing fatigue cracks.

[0011] Furthermore, when welding an already constructed boxing weld joint, different welding positions are required, such as vertical, horizontal, or upward welding positions, rather than always facing downward. In welding positions other than downward, it is difficult to control the length of the second weld bead and the spacing between the extensions of the two second weld beads. Therefore, a new welding method has been discovered in which a welding guide is placed to control the length and spacing of the extensions of the second weld bead even in welding positions other than downward, and a weld bead is formed.

[0012] In addition, since this guide has the function of blocking the weld metal formed by welding, it will be referred to as a "weld metal blocking member" hereinafter.

[0013] The present invention was made based on the above findings and further studies, and is summarized as follows: [1] A boxing welding method for joining a standing plate to a main plate by box welding, comprising: first, forming a first weld bead along the periphery of a rectangular contact surface where the standing plate abuts against the main plate; then, using a weld metal blocking member having a rectangular bottom surface that abuts against the main plate, disposing the weld metal blocking member on the main plate so that the member abuts against a short side of the first weld bead; and then, extending a second weld bead onto the main plate along the weld metal blocking member, the second weld bead having an overlapping portion that covers a long side of the first weld bead and an extension portion that extends from the overlapping portion onto the main plate. [2] A box welding method for joining a standing plate to a main plate by box welding, wherein a first weld bead is formed in advance along the periphery of a rectangular contact surface where the standing plate abuts against the main plate, and a weld metal blocking member having a rectangular bottom surface that abuts against the main plate is first used to arrange the weld metal blocking member on the main plate so that the member abuts against a short side of the first weld bead, and then a second weld bead having an overlapping portion formed by covering the long side of the first weld bead and an extension portion extending from the overlapping portion onto the main plate is formed by extending the second weld bead onto the main plate along the weld metal blocking member. [3] The box welding method according to [1] or [2], wherein the length N from the tip of the extension portion to the toe of the short side of the rectangular abutment surface of the first weld bead is 5.0 mm to 100.0 mm, and the spacing M between the toes of the extension portion is 2.0 mm or more. [4] The shape of the weld metal retaining member is such that the length N in the longitudinal direction of the rectangular bottom surface is T The shape of the front and rear sides, which are cross sections perpendicular to the longitudinal direction of the rectangular bottom, is an inverted trapezoid, and the length of the short side of the rectangular bottom is a bottom width M T is 0.2 mm or more, and the bottom width M T[5] The boxing welding method according to any one of [1] to [4], wherein a shape of a region where a lateral side surface of the weld metal damming member contacts the second weld bead in a cross section perpendicular to the longitudinal direction of the rectangular bottom surface of the weld metal damming member is a curve or a line with an elevation angle θ of 60° or less from the rectangular bottom surface. [6] A boxing welded joint formed by boxing welding a standing plate to a main plate, the boxing welded joint comprising: a first weld bead formed along the periphery of a rectangular abutment surface where the standing plate abuts against the main plate; and a second weld bead having an overlapping portion formed to cover a long side of the first weld bead and an extension portion formed by extending from the overlapping portion onto the main plate, wherein in a cross section perpendicular to the longitudinal direction of the extension portion, an elevation angle θ from the main plate in a region where the extension portion and the main plate contact each other is 60° or less. [7] The boxing welded joint according to [6], wherein a length N from a tip of the extension portion to a toe on a short side of the rectangular abutment surface of the first weld bead is 5.0 mm to 100.0 mm, and a spacing M between the toes of the extension portion 6 is 2.0 mm or more.

[0014] According to the present invention, by using a weld metal retaining member as a guide to extend the weld bead onto the main plate in boxing welding, it becomes easy to control the spacing between the extensions of the weld bead and the length of the extensions to predetermined dimensions, and as a result, it becomes possible to improve fatigue strength. Furthermore, if the present invention is used not only when constructing a new steel structure but also when repairing or strengthening an aging steel structure, it becomes possible to inexpensively and stably improve the fatigue strength of the resulting boxing welded joint, which is of great industrial benefit.

[0015] FIG. 1 is a plan view schematically illustrating an example of a procedure for performing a box welding method according to the present invention. FIG. 2 is a perspective view schematically illustrating an example of a weld metal blocking member used in the box welding method according to the present invention. FIGS. 3(a) to 3(c) are cross-sectional views schematically illustrating different cross-sectional shapes (three examples) of a weld metal blocking member used in the box welding method according to the present invention. FIG. 4 is a cross-sectional view schematically illustrating the state before and after removal of a weld metal blocking member (specifically, (a) during welding and (b) after removal). FIG. 5 is a perspective view schematically illustrating the appearance of an example of a welded joint obtained by the box welding method according to the present invention. FIG. 6 is a plan view schematically illustrating the shape of one side of an example of a welded joint obtained by the box welding method according to the present invention.

[0016] Representative embodiments of the 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.

[0017] [Box Welding Method] FIG. 5 is an external view of an example of a welded joint obtained by the box welding method according to the present invention, and FIG. 6 is a plan view schematically showing the shape of one side of the example of the welded joint.

[0018] The box welding method according to the present invention is a box welding method in which a weld metal damming member (hereinafter also simply referred to as "damming member") 9, which can be removed after welding, is placed on main plate 1 and used as a guide. Specifically, in order to reinforce weld bead 3 (i.e., first weld bead) that joins standing plate 2, such as a gusset, placed on main plate 1, second weld bead 4 is extended along damming member 9. This makes it possible to improve the dimensional accuracy of the shape of the extended weld bead (hereinafter also referred to as "extended bead" or "extended portion") and further improve the fatigue strength of the welded joint.

[0019] As described above, the boxing welding method of the present invention can be applied not only to the construction of new steel structures but also to the repair and reinforcement of boxing welded joints that have already been constructed. In the former case, the welding can be performed from the first step in the welding procedure described below, and in the latter case, the welding can be performed from the second step in the same welding procedure.

[0020] [Welding Procedure] The procedure for implementing the box welding method according to the present invention will be described with reference to FIG.

[0021] In FIG. 1, the rectangular contact surface 2a where the standing plate 2 contacts the main plate 1 coincides with the shape surrounded by a rectangular line when the standing plate 2 is projected onto the main plate 1.

[0022] First, in the first step, the upright plate 2 is placed on the main plate 1, and box welding is performed along the periphery of the rectangular abutment surface 2a where the upright plate 2 abuts against the main plate 1. As shown in Figure 1(a) , the box welding method according to the present invention is performed under welding conditions described below to obtain a box welded joint. Here, a first weld bead 3 is formed around the periphery of the rectangular abutment surface 2a on the main plate 1 where the upright plate 2 abuts.

[0023] Next, in the second step, as shown in FIG. 1B, a damming member 9 is installed so as to contact the first weld bead 3 on the short side 2c side of the rectangular contact surface 2a (i.e., so as to contact the short side of the first weld bead 3). In FIG. 1B, the damming member 9 is shown with a rectangular bottom surface 9a that contacts the main plate 1. The damming member 9 is disposed so that the center line X of the rectangular bottom surface 9a is aligned with the thickness center line Y of the standing plate 2 and contacts the first weld bead 3. Here, aligning the center lines X and Y means that a deviation of 20% of the thickness of the standing plate 2 is acceptable. Furthermore, the damming member 9 contacting the first weld bead 3 means that the short side of the rectangular bottom surface 9a is either in direct contact with the weld toe of the first weld bead 3 or is acceptable even if it is spaced apart by approximately 1 to 2 mm.

[0024] Next, in the third step, as shown in FIG. 1B , a second weld bead having an overlapping portion and an extension portion, as described below, is formed. Specifically, the first second weld bead 4a is first welded from the middle of one long side 2b of the rectangular abutting surface 2a so as to overlap the first weld bead 3, forming an overlapping portion 5a of the first second weld bead 4a. Here, the reason why the first second weld bead 4a may start welding from the middle of the long side 2b is that it is not necessary to pass through the entire long side 2b. As shown in FIG. 6 , the length L of the overlapping portion 5a from the welding start point of the first second weld bead 4a (i.e., the welding start end 8a) to the short side 2c of the rectangular abutting surface 2a is preferably 5.0 mm or more. This length L is more preferably 10.0 mm or more. Furthermore, this length L is preferably 100.0 mm or less, and more preferably 50.0 mm or less.

[0025] Next, the first second weld bead 4a is placed over the first weld bead 3 on the short side 2c of the rectangular abutment surface 2a. The first second weld bead 4a is then extended onto the main plate 1 along the rectangular bottom surface 9a of the installed dam member 9, forming an extension 6a of the first second weld bead 4a. Figure 6 shows the length N (hereinafter also referred to as the "extension length") from the tip of the extension 6a (i.e., the weld end point 7a), which serves as the welding end point, to the weld toe 3a on the short side 2c of the first weld bead 3. This length N may be 5.0 mm or more, but considering workability, it should be at most approximately 100.0 mm. Extending the extension 6a onto the main plate 1 distributes stress concentrated in the boxing weld to the extension bead, thereby reducing the stress concentration in the boxing weld and suppressing the occurrence of fatigue cracks. This length N is preferably 10.0 mm to 30.0 mm.

[0026] 1(c), the second second weld bead 4b is formed on the other long side 2d of the rectangular abutment surface 2a, forming an overlapping portion 5b and an extension 6b of the first second weld bead 4b. It is preferable to form the overlapping portion 5b and the extension 6b so that the second second weld bead 4b also has the same bead length and bead shape as the first second weld bead 4a.

[0027] 6, the distance M between the extensions 6a and 6b of two adjacent second weld beads 4a and 4b is preferably 2.0 mm or more from the viewpoint of the fatigue strength improvement effect described above. More preferably, the distance M is equal to or less than the length of the short side 2c of the rectangular abutment surface 2a (i.e., equal to or less than the thickness of the standing plate 2). More preferably, the distance M is equal to or greater than 5.0 mm and equal to or less than the thickness of the standing plate.

[0028] 1(a) to 1(c), the construction procedure for one short side of the vertical plate 2 has been described, but the other short side can be constructed in the same manner. In that case, two more second weld beads 4c and 4d are welded. Therefore, the boxing welded joint according to the present invention is a welded joint in which two or four second weld beads 4 are formed.

[0029] Furthermore, when forming two or four second weld beads 4, it is not necessary for the lengths and shapes of the above-described portions to be the same for all two or all four second weld beads 4. As long as the extension length N is within the range of 5.0 mm to 100.0 mm and the interval M is 2.0 mm or more, the same effect can be obtained.

[0030] The blocking member 9 is removed after the welding is completed.

[0031] [Weld Metal Guarding Member] Here, a description will be given of the weld metal guarding member, which is an auxiliary member for forming an extended bead in the box welding method according to the present invention.

[0032] An example of the damming member 9 is shown in FIG. 2. The shape of the damming member 9 is composed of six flat surfaces. The lower surface of the six flat surfaces is a rectangular bottom surface 9a, and the upper surface is a rectangular top surface 9b. The rectangular bottom surface 9a is the surface that contacts the main plate 1, and its longitudinal length N T is a length corresponding to the length N of the extension portion of the second weld bead 4 formed by extending on the main plate 1. This longitudinal length N T It is preferable that the length N is 5.0 mm to 200.0 mm. T It is more preferable that the length N is 5.0 mm to 100.0 mm. TIt is more preferable that the length N is 5.0 mm to 50.0 mm. T is preferably set to be larger than the target dimension of the length N of the extension portion of the weld bead described above.

[0033] The length of the short side of the rectangular bottom surface 9a that contacts the main plate 1 (i.e., the bottom width) M T is 0.2 mm or more and is a length that matches the distance M between the toes of the extension parts. T is preferably set and prepared for each welding operation so as to match the aforementioned distance M between extension 6 a of first second weld bead 4 a and extension 6 b of second second weld bead 4 b. Here, this distance M is a target value.

[0034] Next, one of the two side surfaces perpendicular to the longitudinal direction of the rectangular bottom surface 9 a is a front side surface 9 c, the opposite side surface is a rear side surface 9 d, and the two side surfaces along the longitudinal direction of the rectangular bottom surface 9 a are lateral side surfaces 9 e. It is preferable that the cross-sectional shape perpendicular to the longitudinal direction (i.e., the shapes of the front side surface 9 c and the rear side surface 9 d) is a substantially inverted trapezoid.

[0035] Examples of cross-sectional shapes (three examples here) are shown in Figure 3. As shown in Figures 3(a) and 3(b), the shape of the region where the lateral side surface 9e contacts the weld bead in a cross section perpendicular to the longitudinal direction is preferably formed as a curve with an elevation angle (i.e., rise angle) θ from the rectangular bottom surface 9a of 60° or less. Alternatively, as shown in Figure 3(c), a straight line with an elevation angle θ from the rectangular bottom surface 9a of 60° or less may be used instead of the curve. It is more preferable that θ be 5° or more and 60° or less. If the elevation angle θ from the rectangular bottom surface 9a exceeds 60°, stress concentration at the weld toe will result in poor fatigue strength of the resulting welded joint. Therefore, by using such a curve or straight line with an elevation angle θ of 60° or less, the shape of the weld bead extensions 6a, 6b tends to approximate a semi-ellipse, as shown in Figure 4. As a result, stress concentration in the extensions can be reduced or avoided.

[0036] Here, the cross-sectional shapes shown in Figures 3(a) to 3(c) are referred to as inverted trapezoids. This inverted trapezoid includes shapes in which the lower region of each lateral side surface 9e (i.e., the region on the rectangular bottom surface 9a side) is curved, and both lateral side surfaces 9e are either straight or flared upward, as shown in Figures 3(a) and 3(b). It also includes shapes in which the lower region of each lateral side surface 9e is linear, and both lateral side surfaces 9e are flared upward, as shown in Figure 3(c).

[0037] Here, the relationship between the shape of the lower portion of the damming member 9 and the weld bead will be described with reference to Fig. 4. The cross section shown in Fig. 4 is a cross section in the plate thickness direction taken along line A-A shown in Fig. 1(c).

[0038] The shape of the damming member 9 shown in Fig. 4(a) is the same as the shape shown in Fig. 3(a), i.e., the lower region of the lateral side surface 9e is curved and both lateral side surfaces 9e are flared upward. Fig. 4(a) is a cross-sectional view when the damming member 9 is placed on the main plate 1 so as to contact the short-side toe 3a of the first weld bead, and the extensions 6a and 6b of the second weld bead 4 are formed along the longitudinal lateral side surfaces 9e of the damming member 9. Fig. 4(b) is a cross-sectional view after the damming member 9 has been removed. As shown in Fig. 4(b), the shape of the weld bead is formed in the same shape as the lower part of the damming member 9. In other words, the width M of the short side of the rectangular bottom surface 9a of the damming member 9 is T is equal to the distance M between the extension beads, and the weld toes on the inside of the two weld beads have a rising shape according to the elevation angle θ. Therefore, when welding is performed using the damming member 9 of the present invention, the weld toes have a smooth shape and the distance M between the extension beads is kept constant, so that stress concentration in the extension parts can be reduced or avoided. Note that the shape of the rectangular upper surface 9b of the damming member 9 does not have to be flat. Furthermore, the height H of the damming member 9 T is not particularly limited, but is determined appropriately depending on ease of handling, and is preferably set to 20.0 mm to 60.0 mm. The elevation angle θ of the damming member 9 and the elevation angle θ of the weld bead of the weld joint may be measured by the method described in the examples.

[0039] Next, the damming member 9 is preferably made of a material that does not bond with the weld metal. By using a material that does not bond with the weld metal, the damming member 9 can be easily removed from its installed position after bead welding. Examples of such a material include copper and ceramics. Note that examples of ceramics include those containing silica, zirconia, alumina, etc. as a main component.

[0040] [Boxing Welded Joint] Next, a boxing welded joint obtained by the box welding method according to the present invention will be described.

[0041] The boxing welded joint of the present invention is a boxing welded joint formed by joining a standing plate 2 to a main plate 1 by boxing welding. The boxing welded joint of the present invention includes at least a main plate 1 and a standing plate 2, and has a weld bead at the joint between them. This boxing welded joint has a first weld bead 3 and a second weld bead 4 as weld beads. Preferably, there are two or four second weld beads 4. When referring to two second weld beads as shown in FIG. 1 or FIG. 6, they are referred to as 4a and 4b, respectively, and when referring to four second weld beads as shown in FIG. 5, they are further referred to as 4c and 4d.

[0042] The first weld bead 3 is formed along the periphery of a rectangular contact surface 2 a where the upright plate 2 contacts the main plate 1 .

[0043] 6, second weld beads 4a and 4b, which are important in the present invention, have overlapping portions 5a and 5b and extensions 6a and 6b, respectively. Overlapping portions 5a and 5b are formed by covering two long sides 2b and 2d of rectangular abutment surface 2a of first weld bead 3, and extensions 6a and 6b are formed by extending linearly from overlapping portions 5a and 5b onto main plate 1.

[0044] Here, the length N from the tip 7a of the extension 6a (or the tip 7b of the extension 6b) to the short-side toe 3a of the rectangular abutment surface 2a of the first weld bead 3 is preferably in the range of 5.0 mm to 100.0 mm. If the length N is less than 5.0 mm, the effect of improving fatigue strength is poor, and if it exceeds 100.0 mm, a long period of time is required for construction. The length N is more preferably 10.0 mm to 30.0 mm.

[0045] Furthermore, the distance M between the opposing weld toes of the extensions 6a and 6b, i.e., the width of the space surrounded by the adjacent extensions 6a and 6b, is preferably 2.0 mm or more. If the distance M is less than 2.0 mm, the beads are likely to connect to each other, and the fatigue strength improvement effect is not achieved. In addition, if the distance M exceeds the length of the short side 2c of the rectangular abutment surface 2a, i.e., the thickness of the standing plate 2, the fatigue strength improvement effect cannot be achieved, so the distance M is preferably equal to or less than the thickness of the standing plate. More preferably, the distance M is equal to or greater than 5.0 mm and equal to or less than the thickness of the standing plate.

[0046] Furthermore, the length L of the overlapping portion 5a or 5b (i.e., the length from the weld start end 8a or 8b of the second weld bead to the short side 2c of the rectangular abutment surface 2a) is preferably 5.0 mm or more. This is because a length less than 5.0 mm increases the likelihood of weld defects occurring at the corners of the vertical plate. More preferably, it is 10.0 mm or more. There is no particular upper limit to the length L, and the maximum length L is when the overlapping portion 5a or 5b contacts the second weld beads 4c and 4d formed on the other short side of the rectangular abutment surface 2a. In other words, this is when the weld bead continuously covers the entire long side 2b of the rectangular abutment surface 2a, and the effects of the present invention can be obtained even in such cases.

[0047] In addition, in a cross section perpendicular to the longitudinal direction of the extension portions 6 a and 6 b, the elevation angle θ from the main plate 1 in the region where the extension portions 6 a and 6 b contact the main plate 1 is 60° or less. Note that the explanation regarding the elevation angle θ is omitted here as it is the same as that described above.

[0048] The spacing M and length N of the extension portion of the second weld bead and the length L of the overlapping portion of the second weld bead were measured with a vernier caliper. The measurement method may be the method described in the examples.

[0049] [Box Welding Means and Welding Object] In the present invention, the plate thickness of the main plate 1 is not particularly limited, but is preferably 5.0 mm to 100.0 mm.

[0050] The thickness of the vertical plate 2 is preferably 5.0 mm to 30.0 mm. A thickness of less than 5.0 mm is not practically used in construction, while a thickness of more than 30.0 mm is disadvantageous in terms of improving fatigue properties. More preferably, it is 5.0 mm to 15.0 mm.

[0051] Furthermore, the present invention is effective regardless of the material of the main plates and upright plates used. For example, the main plates may be made of steel materials such as SM400, SM490, SM520, SM570, etc., with a yield stress of 245 MPa to 560 MPa.

[0052] The welding means for performing the box 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. Either manual welding or automatic welding can be used.

[0053] Furthermore, the welding position can be vertical, horizontal, or upward, in addition to downward. When the welding position is vertical, horizontal, or upward, the box welding method according to the present invention can be easily carried out by fixing the weld metal blocking member with adhesive tape or the like to prevent the blocking member from falling when the member is installed.

[0054] [Repair Method Using Box Welding Method of the Present Invention] The present invention can be applied not only to the construction of new steel structures, but also to the repair of deteriorated steel structures.

[0055] In the case of repair, the welding method is the same as in the explanation of the construction procedure in FIG. 1 above, where first weld bead 3 in FIG. 1(a) has already been formed, and repair work can be performed by carrying out construction similar to the construction procedures in FIG. 1(b) and (c) for forming second weld bead 4 (4a, 4b).

[0056] 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.

[0057] First, a main plate (plate thickness: 14 to 25 mm, plate width: 80 mm, length: 500 mm) and a vertical plate (plate thickness: 14 to 25 mm, plate width: 75 mm, height: 50 mm) were prepared.

[0058] Next, the boxing welding method of the present invention was performed on the main plate and the vertical plate using a gas metal arc welding method with a flux-cored wire or a solid wire, and using the weld metal damming member. The "Cross-sectional shape" column in Table 2 shows the shapes of the damming members selected from Figures 3(a) to 3(c) above. Note that Nos. 2, 6, 11, 12, 14, and 16 in Table 2 are intended for cases in which the above-mentioned deteriorated steel structure is to be repaired.

[0059] Next, the resulting box welded joints (see FIG. 5) were subjected to the fatigue test described below.

[0060] Here, the flux-cored wire used for all box welded joints was MX-Z200 (wire diameter 1.2 mm) manufactured by Kobe Steel, Ltd. The composition of the wire (mass %) was as follows: C: 0.04%, Si: 0.07%, Mn: 1.22%, P: 0.010%, S: 0.011%, the balance being Fe and unavoidable impurities.

[0061] The solid wire used for the horizontal and overhead box welded joints was DW-Z100 (wire diameter 1.2 mm) manufactured by Kobe Steel, Ltd. The wire composition (mass %) was as follows: C: 0.05%, Si: 0.45%, Mn: 1.35%, P: 0.013%, S: 0.009%, with the balance being Fe and unavoidable impurities.

[0062] The welding conditions were a welding current of 240 A, a welding voltage of 32 V, a welding speed of 30 cm / min, and a leg length of approximately 8 mm by turn welding. Note that the vertical plate was placed in the center of the main plate, so the rectangular abutment surface was located in the center of the main plate.

[0063] For the main plates and vertical plates, steel plates A to C having the chemical compositions shown in Table 1 were used. The fatigue tests were carried out at room temperature in the atmosphere under axial load control, a stress ratio of 0.1, and a frequency of 10 Hz. In addition, tensile test specimens (parallel portion diameter 6 mmΦ) were taken 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).

[0064] For the obtained boxing welded joint, the dimensions of the second weld bead were measured as follows.

[0065] First, the spacing M of the extension portions of the second weld beads was measured at three locations, the average value (actual measured value) was calculated, and the difference between the average value and the target value was calculated. The results are shown in the "Spacing M of extension portions" column of Table 2.

[0066] The length N of the extension portion of the second weld bead was measured with a vernier caliper, and the measured value was also shown in the "Extension length N" column of Table 2.

[0067] The length L of the overlapping portion of the second weld bead was measured with a vernier caliper, and the measured value was also shown in the "Overlapping portion length L" column of Table 2.

[0068] The elevation angle θ of the extension of the second weld bead was measured by observing the cross section of the weld bead separately, and the measured value was also listed in the "Extension angle θ" column of Table 2.

[0069]

[0070] The measured bead spacing, stress range of the fatigue test, and test results for the boxing welded joints are shown in Table 2. The test results refer to the fatigue life, which is the number of load cycles until fatigue failure. Here, the fatigue life is expressed as the number of load cycles until fatigue failure.

[0071]

[0072] As is clear from Table 2, in all of the inventive examples, as a result of using a damming member, the extension interval M was 2.0 mm or more and smaller than the thickness of each of the upright plates, the extension length N was 5.0 to 100.0 mm, and the overlap length L was 5.0 mm or more, and they had a good fatigue life. This good fatigue life means that the fracture life was more than twice that of the comparative example under the same stress condition.

[0073] On the other hand, in none of the comparative examples was a damming member used, so the target extension interval M was greater than the thickness of each of the vertical plates, and the fatigue life was less than half that of the invention examples.

[0074] REFERENCE SIGNS LIST 1 Main plate 2 Standing plate 2a Rectangular abutment surface 2b Long side of rectangular abutment surface 2c Short side of rectangular abutment surface 2d Long side of rectangular abutment surface 3 First weld bead 3a Short side toe of first weld bead 4 (4a, 4b, 4c, 4d) Second weld bead 5 (5a, 5b) Overlapping portion of second weld bead 6 (6a, 6b) Extension portion of second weld bead 7 (7a, 7b) Tip of extension portion of second weld bead (welding end end) 8 (8a, 8b) Welding start end of second weld bead 9 Weld metal damming member 9a Rectangular bottom surface of weld metal damming member 9b Rectangular top surface of weld metal damming member 9c Front side surface of weld metal damming member 9d Rear side surface of weld metal damming member 9e Lateral side surface of the weld metal blocking member L Length of the overlapping portion from the welding start end of the second weld bead to the short side of the rectangular abutment surface M Spacing between extensions N Length of the extension portion from the short side toe of the first weld bead to the tip of the extension portion of the second weld bead M T Length of the short side of the rectangular bottom of the weld metal damming member (bottom width) N T Length of the rectangular bottom surface of the weld metal damming member in the longitudinal direction H T Length (height) between the rectangular top surface and rectangular bottom surface of the weld metal damming member X: Center line (in the longitudinal direction) of the rectangular bottom surface of the weld metal damming member Y: Center line of the thickness of the upright plate θ: Elevation angle (rise angle) from the rectangular bottom surface of the weld metal damming member

Claims

1. A box welding method for joining a standing plate to a main plate by box welding, comprising: first, forming a first weld bead along the periphery of a rectangular contact surface where the standing plate abuts against the main plate; then, using a weld metal blocking member with a rectangular bottom surface that abuts against the main plate, disposing the weld metal blocking member on the main plate so that the member abuts against the short side of the first weld bead; then, extending a second weld bead onto the main plate along the weld metal blocking member, the second weld bead having an overlapping portion that covers the long side of the first weld bead and an extension portion that extends from the overlapping portion onto the main plate.

2. A box welding method for joining a standing plate to a main plate by box welding, wherein a first weld bead is formed in advance along the periphery of a rectangular contact surface where the standing plate abuts against the main plate, and a weld metal blocking member having a rectangular bottom surface that abuts against the main plate is first used to arrange the weld metal blocking member on the main plate so that the member abuts against the short side of the first weld bead, and then a second weld bead having an overlapping portion formed by covering the long side of the first weld bead and an extension portion extending from the overlapping portion onto the main plate is formed by extending the second weld bead onto the main plate along the weld metal blocking member.

3. A box welding method according to claim 1 or 2, wherein the length N from the tip of the extension portion to the toe of the shorter side of the rectangular abutment surface of the first weld bead is 5.0 mm to 100.0 mm, and the spacing M between the toes of the extension portions is 2.0 mm or more.

4. The shape of the weld metal blocking member is such that the longitudinal length N of the rectangular bottom surface is T The shape of the front and rear sides, which are cross sections perpendicular to the longitudinal direction of the rectangular bottom, is an inverted trapezoid, and the length of the short side of the rectangular bottom is a bottom width M T is 0.2 mm or more, and the bottom width M T The box welding method according to any one of claims 1 to 3, wherein the length of the extension is equal to the distance M between the toes of the extension.

5. A box welding method according to claim 4, wherein the shape of the area where the lateral side surface of the weld metal damming member comes into contact with the second weld bead in a cross section perpendicular to the longitudinal direction of the rectangular bottom surface of the weld metal damming member is a curve or a line with an elevation angle θ from the rectangular bottom surface of 60° or less.

6. A box weld joint formed by box welding a standing plate to a main plate, the box weld joint comprising: a first weld bead formed along the periphery of a rectangular contact surface where the standing plate contacts the main plate; and a second weld bead having an overlapping portion formed to cover the long side of the first weld bead and an extension portion formed by extending from the overlapping portion onto the main plate; and in a cross section perpendicular to the longitudinal direction of the extension portion, the angle of elevation θ from the main plate in the region where the extension portion and the main plate contact is 60° or less.

7. A boxing welded joint as set forth in claim 6, wherein the length N from the tip of the extension portion to the toe of the shorter side of the rectangular abutment surface of the first weld bead is 5.0 mm to 100.0 mm, and the spacing M of the toes of the extension portions is 2.0 mm or more.

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