Welded assembled box-shaped cross-sectional member and its design method

Abstract

To provide a welded assembly box-shaped cross-sectional member and a method for designing the same, which can suppress a decrease in member strength and occurrence of breakage in corner welding even when corner welding is partial penetration welding.SOLUTION: In a welded assembly box-shaped cross-sectional member consisting of four skin plates joined to each other by corner welding, the thickness t and yield strength σy of the skin plate, the weld depth tw of the corner weld and the strength σyw of the weld metal satisfy the relationship (tw.σyw) / (t.σy)≥1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding and a design method thereof.

Background Art

[0002] For column members of buildings, square steel pipes such as cold-rolled formed square steel pipes, cold-pressed formed square steel pipes, and welded assembled box-shaped cross-sectional members are often used. For column members of mid-rise and high-rise buildings, relatively inexpensive cold-rolled formed square steel pipes and cold-pressed formed square steel pipes are often used. On the other hand, for column members of super high-rise buildings, since the required rigidity and strength are very large, welded assembled box-shaped cross-sectional members that can be made larger in cross-section, thicker, and higher in strength are often used.

[0003] Here, the welded assembled box-shaped cross-sectional member has a higher manufacturing cost than cold-rolled formed square steel pipes and cold-pressed formed square steel pipes. The factors include that, along with the increase in the strength of the member, in addition to the high cost of the steel plates constituting the skin plates of the welded assembled box-shaped cross-sectional member itself, a large number of man-hours and manufacturing periods are required for welding construction management during the manufacture of the welded assembled box-shaped cross-sectional member.

[0004] In particular, when the wall thickness of the welded assembled box-shaped cross-sectional member is extremely thick, the welding depth when joining the skin plates of the welded assembled box-shaped cross-sectional member to each other by fillet welding becomes large. The fillet welding of the welded assembled box-shaped cross-sectional member is often performed by CO 2 welding or submerged arc welding, but in either case, when the welding depth of the fillet welding becomes large, the fillet welding cannot be performed in one pass and the number of welding passes increases. Therefore, the fillet welding becomes multi-layered, the manufacturing cost of the welded assembled box-shaped cross-sectional member increases, and the manufacturing period becomes longer.

[0005] In the case of multi-layer submerged arc welding, for example, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, in order to prevent the weld metal from prematurely breaking at a low level and falling below the base material standard strength, it is necessary to perform thermal management such as the inter-pass temperature and its holding time, as well as the post-weld heat treatment temperature and its holding time.

[0006] In submerged arc welding, the weld depth that can be achieved in one pass is approximately up to 60 mm at maximum. Therefore, when manufacturing a welded fabricated box-shaped cross-sectional member with a wall thickness of 60 mm or more by submerged arc welding, the fillet weld becomes a multi-layer submerged arc weld. Then, thermal management as described above is required, and the manufacturing period of the welded fabricated box-shaped cross-sectional member is drastically prolonged.

[0007] In response to such problems, for example, in Patent Document 1, a method for manufacturing a box column in which the corner portions of a welded fabricated box-shaped cross-sectional member are fillet welded from the inside has been proposed. However, welding work inside the welded fabricated box-shaped cross-sectional member places a high workload on the welder and may also be a dangerous operation.

[0008] Therefore, for example, as disclosed in Non-Patent Document 3, making the fillet weld of the welded fabricated box-shaped cross-sectional member a partial penetration weld has been considered.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Non-Patent Documents

[0010]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0011] However, as disclosed in Non-Patent Document 3, when the fillet weld of the welded fabricated box-shaped cross-sectional member is a partial penetration weld, in the column-beam joint panel portion where a large shear force acts, shear deformation concentrates on the fillet weld, and the member strength decreases in the column-beam joint panel portion. In particular, when the strength of the weld metal of the fillet weld is low compared to the base material strength and the penetration depth of the partial penetration weld is small, fracture may occur in the fillet weld due to the shear deformation of the column-beam joint panel portion, and destruction unintended by the designer may occur.

[0012] And since a simple strength evaluation formula for the structure in which the fillet weld of the welded fabricated box-shaped cross-sectional member is a partial penetration weld has not been proposed, such a structure is not used very much at present.

[0013] In view of the above problems, an object of the present invention is to provide a welded fabricated box-shaped cross-sectional member and a design method thereof that can suppress a decrease in member strength and the occurrence of fracture in the fillet weld even when the fillet weld is a partial penetration weld.

Means for Solving the Problems

[0014] To solve the above problems, the present invention has the following features.

[0015] [1] A welded fabricated box-shaped cross-sectional member in which four skin plates are joined to each other by fillet welds, wherein the plate thickness t and yield strength σ of the skin plates y , and the penetration depth t of the fillet weld w and the strength σ of the weld metal yw satisfy t w < t and the relationship of the following formula (1), a welded fabricated box-shaped cross-sectional member.

[0016] (t w ·σ yw ) / (t · σ y ) ≧ 1......(1) [2] A welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding, which is used as the column member in a structure having column members and beam members. At least in the column-beam joint panel portion where the beam member is attached, the plate thickness t and yield strength σ of the skin plate y , and the welding depth t of the fillet welding w and the strength σ of the weld metal yw satisfy t w < t and satisfy the relationship of the following formula (1). A welded assembled box-shaped cross-sectional member.

[0017] (t w ·σ yw ) / (t·σ y ) ≥ 1......(1) [3] The welded assembled box-shaped cross-sectional member according to [1] or [2], wherein the groove depth of the fillet welding is 60 mm or more.

[0018] [4] A design method for a welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding, wherein the plate thickness t and yield strength σ of the skin plate y , and the welding depth t of the fillet welding w and the strength σ of the weld metal yw satisfy t w < t and satisfy the relationship of the following formula (1). A design method for a welded assembled box-shaped cross-sectional member.

[0019] (t w ·σ yw ) / (t·σ y ) ≥ 1......(1)

Effect of the Invention

[0020] According to the welded assembled box-shaped cross-sectional member and its design method of the present invention, even when the fillet weld 13 is a partial penetration weld where the welding depth t w is smaller than the plate thickness t of the skin plates 11 and 12 (t w < t), the strength σ of the weld metal of the fillet weld 13 ywBy increasing it and performing overmatch welding that satisfies the relationship of the above formula (1), shear strength equivalent to that of the column-beam joint panel part of a welded assembled box-shaped cross-sectional member where fillet welding is full penetration welding and overmatch welding can be obtained.

[0021] That is, within the range that satisfies the above formula (1), by reducing the welding depth t of fillet welding to make it partial penetration welding, it becomes possible to perform fillet welding in one pass even when the plate thickness t of the skin plate of the welded assembled box-shaped cross-sectional member is large. Thus, even when fillet welding is made into partial penetration welding, it is possible to suppress a decrease in member strength and the occurrence of fracture in fillet welding. Therefore, without reducing the member strength of the welded assembled box-shaped cross-sectional member, the welding workability of fillet welding can be significantly improved, and the manufacturing cost and manufacturing period of the welded assembled box-shaped cross-sectional member can be significantly reduced. w

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0023] Hereinafter, with reference to the drawings, embodiments of the welded and assembled box-shaped cross-sectional member of the present invention and its design method will be described in detail.

[0024] FIGS. 1(a) and 1(b) show a cross-sectional view and a side view of the welded and assembled box-shaped cross-sectional member of the present embodiment.

[0025] As shown in FIG. 1(a), the welded and assembled box-shaped cross-sectional member 1 of the present embodiment is formed by joining four skin plates 11 and 12 to each other by fillet welding 13. And the plate thickness t and yield strength σ of the skin plates 11 and 12 y , as well as the welding depth t of the fillet welding 13 w and the strength σ of the weld metal yw satisfy t w <t and the relationship of the following formula (1).

[0026] (t w ·σ yw ) / (t·σ y )≧1 ……(1) The welded and assembled box-shaped cross-sectional member 1 has, over its entire length, the plate thickness t and yield strength σ of the skin plates 11 and 12 y , as well as the welding depth t of the fillet welding 13 w and the strength σ of the weld metal yw satisfy the relationship of the above formula (1). Alternatively, among the welded and assembled box-shaped cross-sectional members 1 used as column members, at least in the panel part of the column-beam joint where the beam member is attached, the plate thickness t and yield strength σ of the skin plates 11 and 12 y , as well as the welding depth t of the fillet welding 13 wand the strength σ of the weld metal yw is t w <Satisfy the relationship of t < t and the above formula (1). With such a configuration, as will be described later, even when the fillet weld 13 is a partial penetration weld, a decrease in the member strength of the welded assembled box-shaped cross-sectional member 1 and breakage at the fillet weld 13 can be suppressed.

[0027] Further, in the welded assembled box-shaped cross-sectional member 1 of the present embodiment, the groove depth of the fillet weld 13 is preferably 60 mm or more. With such a configuration, even when the fillet weld 13 is a partial penetration weld, the welding depth t of the fillet weld 13 w is sufficiently ensured, and the member strength of the welded assembled box-shaped cross-sectional member 1 can be more reliably ensured.

[0028] Further, the design method of the welded assembled box-shaped cross-sectional member of the present embodiment is a design method of the welded assembled box-shaped cross-sectional member 1 in which the four skin plates 11 and 12 are joined to each other by the fillet weld 13. And the plate thickness t and yield strength σ of the skin plates 11 and 12 y , and the welding depth t of the fillet weld 13 w and the strength σ of the weld metal yw is t w <Satisfy the relationship of t < t and the above formula (1), and by designing the welded assembled box-shaped cross-sectional member 1, it is realized.

[0029] The inventors examined the shear strength of the panel part of the column-beam joint of the welded assembled box-shaped cross-sectional member used as a column member as follows. And through this examination, at least in the panel part of the column-beam joint, the plate thickness t and yield strength σ of the skin plates 11 and 12 of the welded assembled box-shaped cross-sectional member 1 y , and the welding depth t of the fillet weld 13 w and the strength σ of the weld metal yw If the relationship of the above formula (1) is satisfied, it was confirmed that even when the fillet weld 13 is a partial penetration weld, a decrease in the member strength of the welded assembled box-shaped cross-sectional member 1 and breakage at the fillet weld 13 can be suppressed.

[0030] First, as shown in FIGS. 1(c) and 1(d), in the welded assembled box-shaped cross-sectional member 1, the plate thickness t of the skin plates 11 and 12 and the welding depth t of the fillet weld 13 w are sufficiently small with respect to the plate width of the skin plates 11 and 12. Assuming that the skin plates 11 and 12 are concentrated at the plate thickness center, a mechanical model is set up by ignoring the shear stress generated in the plate thickness direction of the skin plates 11 and 12.

[0031] And when a shear force acts on the welded assembled box-shaped cross-sectional member 1, it is assumed that shear deformation and bending deformation occur in each part of the welded assembled box-shaped cross-sectional member 1 as follows.

[0032] First, as shown in FIGS. 2(a) and 2(b), when the direction of the shear force acting on the welded assembled box-shaped cross-sectional member 1 is parallel to one of the width directions of a pair of opposing skin plates 11 and another pair of opposing skin plates 12 (hereinafter referred to as "when applying force in the 0° direction"), the following assumptions are made. That is, a pair of skin plates 11 parallel to the shear force undergo shear deformation in the region of the width (d c -X) mm at the center of the width direction, and bending deformation occurs at the upper and lower ends of the panel part of the column-beam joint in the regions of the width (X / 2) mm at both ends of the width direction. However, d c is the distance between the centers of the plate thicknesses of the skin plates 11 and 12 of the welded assembled box-shaped cross-sectional member 1, and d c = D - t with respect to the width D of the welded assembled box-shaped cross-sectional member 1, and the range of X is 0 ≦ X ≦ d c / 2. Furthermore, it is assumed that shear deformation occurs in all fillet welds 13.

[0033] And in the mechanical model as described above, the value of X is 0 ≦ X ≦ d cWhile varying within the range of / 2, the shear strengths of the column-beam joint panel portions of the welded assembled box-shaped cross-sectional member 1 were calculated respectively. Then, the minimum value among these shear strengths was taken as the shear strength of the column-beam joint panel portion of the welded assembled box-shaped cross-sectional member 1. Specifically, the above calculations were performed with reference to the calculation methods described in Non-Patent Document 4 and Non-Patent Document 5. In this way, the shear strength p M pa of the column-beam joint panel portion of the welded assembled box-shaped cross-sectional member 1 was obtained, and it was as shown in the following formulas (2) to (7).

[0034] When applying force in the 0° direction, (1) When 1 ≤ (t w ·σ yw ) / (t·σ y ),

[0035]

Equation

[0036] (2) When 1 - √3(d c / d b ) ≤ (t w ·σ yw ) / (t·σ y ) ≤ 1,

[0037]

Equation

[0038] (3) When (t w ·σ yw ) / (t·σ y ) ≤ 1 - √3(d c / d b ),

[0039]

Equation

[0040] However, d in the above formulas (2) to (4) bis the height of the column-beam joint panel part. Also, the " p M p0 guidelines" in the above formulas (2) to (4) are values calculated as shown in the following formula (5).

[0041]

Equation

[0042] Here, the " p M p0 guidelines" shown in the above formula (5) is the shear strength evaluation formula of the column-beam joint panel part described in Non-Patent Document 6, and is the value of the bending moment acting on the column-beam joint panel part when the entire column-beam joint panel part undergoes shear deformation and reaches the full plastic strength. This " p M p0 guidelines" is currently the most widely used shear strength evaluation formula for the column-beam joint panel part of a welded built-up box-section member constructed such that the fillet weld 13 is a full penetration weld and the strength of the weld metal of the fillet weld exceeds the strength of the base material, i.e., an overmatch weld.

[0043] The shear strength p M pa of the column-beam joint panel part of the welded built-up box-section member 1 obtained by the above formulas (2) to (4) w ·σ yw depends on the ratio (t y ) of the shear strength of the weld metal of the fillet weld to the shear strength of the base material (t·σ w ·σ yw ) / (t·σ y ) and the aspect ratio d b / d c of the column-beam joint panel part. This will be explained below.

[0044] In Fig. 4, when the ratio (t w ·σ yw ) / (t·σ y ) of the shear strength of the fillet weld to the shear strength of the base material is changed in the range of 0.0 to 1.2, the shear strength p Mpa The ratio of the value of p M p0 "pointer" p M pa / ( p M p0 "pointer") with respect to the aspect ratio d of the column-beam joint panel part b / d c is shown in a graph for the cases where d / d is 1.0, 1.5, and 2.0.

[0045] As shown in FIG. 4, the smaller the ratio (t w ·σ yw ) of the yield strength of the weld metal of the fillet weld 13 to the yield strength of the base material (t·σ y ), the lower the yield strength of the column-beam joint panel part. Also, the larger the aspect ratio d w ·σ yw ) / (t·σ y ) of the column-beam joint panel part, the greater the decrease in the yield strength of the column-beam joint panel part. And if the ratio (t b / d c ) of the yield strength of the weld metal of the fillet weld 13 to the yield strength of the base material (t·σ w ·σ yw ) is 1.0 or more, that is, if the relationship of the above formula (1) is satisfied as in the welded and assembled box-shaped cross-sectional member 1 of the present embodiment, regardless of the aspect ratio d y ) of the column-beam joint panel part of the welded and assembled box-shaped cross-sectional member 1 calculated by the above formulas (2) to (4) w ·σ yw ) / (t·σ y ) is 1.0 or more, that is, if the relationship of the above formula (1) is satisfied as in the welded and assembled box-shaped cross-sectional member 1 of the present embodiment, regardless of the aspect ratio d b / d c of the column-beam joint panel part, the shear yield strength p M pa of the column-beam joint panel part of the welded and assembled box-shaped cross-sectional member 1 calculated by the above formulas (2) to (4) p M p0 "pointer" described in Non-Patent Document 6 is confirmed to be almost equal.

[0046] Furthermore, the inventors numerically analyzed the shear yield strength of the column-beam joint panel part of the welded and assembled box-shaped cross-sectional member by the finite element method, and the shear yield strength p M paBy comparing with the value of , the validity of the above equations (2) to (4) was verified.

[0047] Figures 5(a) to 5(d) show the shapes of the analysis models targeted in this numerical analysis. In this numerical analysis, the analysis model of the column-beam joint panel alone shown in Figure 5(a) was taken as the analysis target. Specifically, the cross-sectional size of the welded fabricated box-section member 1 was set as an outer dimension of 150 mm × 150 mm, a wall thickness of 16 mm, and the height of the panel member composed of the welded fabricated box-section member 1 was 250 mm. Also, as shown in Figures 5(b) to 5(d), the weld depth of the fillet weld 13 was set to three types: 5 mm, 10 mm, and 16 mm, and numerical analysis was performed for each of these.

[0048] Figure 6 shows the material properties set for the skin plates 11 and 12 of the welded fabricated box-section member 1 and the fillet weld 13. As shown in Figure 6, for the skin plates 11 and 12 of the welded fabricated box-section member 1, the yield strength was set to 412 N / mm 2 of the material properties. Also, for the fillet weld 13 with a weld depth of 5 mm shown in Figure 5(b), the yield strength was 510 N / mm 2 of the material properties (weld metal B). For the fillet weld 13 with a weld depth of 10 mm shown in Figure 5(c), the yield strength was 383 N / mm 2 (weld metal A), 714 N / mm 2 (weld metal C) of two types of material properties. Also, for the fillet weld 13 with a weld depth of 16 mm shown in Figure 5(d), the yield strength was 383 N / mm 2 (weld metal A), 510 N / mm 2 (weld metal B) of two types of material properties were set, and numerical analysis was performed for each of these.

[0049] Then, as shown in Figure 5(a), while restraining the rotation at the axial ends of the member, anti-symmetric shear forces were input, and numerical analysis was performed under the condition of gradually increasing these shear forces.

[0050] The shear strength of the beam-to-column joint panel of a welded box section member calculated by this numerical analysis is plotted in Figure 7. Based on the load-deformation relationship obtained from this numerical analysis, the 0.35% offset strength when a force is applied in the 0° direction and the 0.5% offset strength when a force is applied in the 45° direction were calculated and plotted in Figure 7 as well.

[0051] As shown in Fig. 7, the shear strength of the beam-column joint panel of the welded box section member calculated by the above numerical analysis is calculated by the above formulas (2) to (4). p M pa The values ​​were almost the same, confirming the validity of the above formulas (2) to (4).

[0052] In this manner, as in the welded box section member 1 of this embodiment, the plate thickness t and the yield strength σ y , and the weld depth t of the corner weld 13 w and the strength of the weld metal σ yw If the relationship of the above formula (1) is satisfied, that is, the yield strength (t w σ yw ) and base material yield strength (t σ y ) and the ratio (t w σ yw ) / (t σ y ) is 1.0 or more, p M pa / ( p M p It can be seen that the value of the guideline (index) approaches 1.0, and the decrease in the component strength of the welded box section component 1 can be suppressed.

[0053] In other words, in the welded box section member 1, the corner welds 13 are welded to a weld depth t w Even when partial penetration welding is performed in which the thickness of the skin plates 11 and 12 is smaller than the plate thickness of the skin plates 11 and 12, the strength of the weld metal of the corner weld 13, σ yw By increasing the weld length and performing an overmatch weld that satisfies the relationship in equation (1) above, it is possible to obtain a shear strength equivalent to that of the column-beam joint panel of a welded box section member in which the corner welds 13 are full penetration welds and overmatch welds.

[0054] Here, as described above, in submerged arc welding, the maximum welding depth that can be achieved in one pass is about 60 mm. Therefore, when manufacturing a welded built-up box-shaped cross-sectional member with a wall thickness of 60 mm or more by submerged arc welding with overmatch welding and full penetration welding, the fillet welding becomes multi-layer submerged arc welding, and post-heat management is required, so the manufacturing period of the welded built-up box-shaped cross-sectional member is drastically prolonged.

[0055] On the other hand, in the welded built-up box-shaped cross-sectional member 1 of the present embodiment, within the range that satisfies the relationship of the above formula (1), the welding depth t of the fillet welding 13 w is made smaller to perform partial penetration welding, so that even when the plate thickness t of the skin plates 11 and 12 of the welded built-up box-shaped cross-sectional member 1 is large, the fillet welding 13 can be welded in one pass. Therefore, post-heat management such as in the case of constructing a welded built-up box-shaped cross-sectional member with a wall thickness of 60 mm or more by full penetration multi-layer submerged arc welding is not required, so the welding workability of the fillet welding 13 is significantly improved, and the manufacturing cost and manufacturing period of the welded built-up box-shaped cross-sectional member 1 can be significantly reduced. Further, in the welded built-up box-shaped cross-sectional member 1 of the present embodiment, by satisfying the relationship of the above formula (1), even when the fillet welding 13 is partial penetration welding, a decrease in the member strength of the welded built-up box-shaped cross-sectional member 1 due to the influence can be suppressed.

[0056] Note that when the fillet welding 13 does not satisfy the relationship of the above formula (1), the member strength of the welded built-up box-shaped cross-sectional member 1 is mainly affected by the column-beam joint panel part. Even if the relationship of the above formula (1) is not necessarily satisfied at parts other than the column-beam joint panel part of the column member, the member strength of the welded built-up box-shaped cross-sectional member 1 does not significantly decrease. Therefore, at least in the column-beam joint panel part of the welded built-up box-shaped cross-sectional member 1 used as a column member where the beam member is attached, the relationship of the above formula (1) should be satisfied.

Example

[0057] Specific examples of the welded built-up box-shaped cross-sectional member 1 of the present invention will be described below.

[0058] In the welded and assembled box-shaped cross-sectional member 1 of this embodiment, the yield strength σ of the skin plates 11 and 12 y is 385 N / mm 2 , and the plate thickness t is 85 mm. Also, the root depth of the fillet weld 13 is 60 mm, and the fillet weld 13 was constructed by single-pass submerged arc welding.

[0059] Then, when the welded and assembled box-shaped cross-sectional member 1 of this embodiment was fabricated, it was confirmed that the welding depth t of the fillet weld 13 w could be ensured to be 70 mm or more due to penetration and reinforcement.

[0060] At this time, in order to satisfy the relationship of the above formula (1), the strength σ of the weld metal of the fillet weld 13 yw needs to be 467.5 N / mm 2 or more. That is, if the welding material is selected so that the strength σ of the weld metal of the fillet weld 13 yw is 467.5 N / mm 2 or more and the fillet weld 13 is constructed, it was confirmed that even if the fillet weld 13 of the welded and assembled box-shaped cross-sectional member 1 is a partial penetration weld, the reduction in the strength of the panel part of the column-beam joint of the welded and assembled box-shaped cross-sectional member 1 and the occurrence of fracture at the fillet weld 13 can be suppressed.

Explanation of Reference Numerals

[0061] 1 Welded and assembled box-shaped cross-sectional member 11, 12 Skin plates 13 Fillet weld

Claims

1. A welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding, The plate thickness t and yield strength σ of the skin plate ｙ , as well as the welding depth t of the fillet weld ｗ and the strength σ of the weld metal ｙｗ satisfy t > 60 mm, t w ≤ 60 mm, t ｗ < t and the relationship of the following formula (1), a welded assembled box-shaped cross-sectional member. (t ｗ ·σ ｙｗ ) / (t·σ ｙ ) ≥ 1......(1)

2. A welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding, which is used as the column member in a structure having a column member and a beam member, At least in the column-beam joint panel portion to which the beam member is attached, the plate thickness t and yield strength σ of the skin plate ｙ , as well as the welding depth t of the fillet weld ｗ and the strength σ of the weld metal ｙｗ are such that t > 60 mm, t w ≤ 60 mm, t ｗ < t and satisfy the relationship of the following formula (1), a welded fabricated box-shaped cross-section member. (t ｗ ·σ ｙｗ ) / (t · σ ｙ ) ≥ 1......(1)

3. A design method for a welded assembled box-shaped cross-sectional member formed by joining four skin plates to each other by fillet welding, The plate thickness t and yield strength σ of the skin plate ｙ , as well as the welding depth t of the fillet weld ｗ and the strength σ of the weld metal ｙｗ are such that t > 60 mm, t w ≤ 60 mm, t ｗ < t and satisfy the relationship of the following formula (1), a design method for a welded assembled box-shaped cross-sectional member. (t ｗ ·σ ｙｗ ) / (t·σ ｙ ) ≥ 1......(1)

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