JP7513007B2 - Welded joint for box-shaped section member and welding method thereof - Google Patents

Description

The present invention relates to a welded joint for a box-shaped cross-section member constructed by combining multiple steel plates to form a rectangular cross-section, and to a welding method for the same.

Square steel pipes, such as cold roll-formed square steel pipes, cold press-formed square steel pipes, and welded assembled box section members, are often used for column members in buildings and other structures. In low- to mid-rise buildings and high-rise buildings, relatively inexpensive cold roll-formed square steel pipes and cold press-formed square steel pipes are often used for column members. On the other hand, in high-rise buildings, the rigidity and strength required for column members is very high, so welded assembled box section members, which can be made larger in cross section, thicker, and stronger, are often used for column members.

The four steel plates (skin plates) that make up a welded box section member generally have the same strength and thickness for ease of design. In contrast, Patent Documents 1 and 2 disclose technology for changing the strength and thickness of one pair of opposing steel plates from those of the other pair of steel plates. This increases the freedom in designing the welded box section member and reduces the amount of corner welding required to join the steel plates together.

Japanese Patent Application Laid-Open No. 4-366257 JP 2017-179723 A

Tetsuya Fujita and six others, "Welding materials and welding conditions applicable to 550N/mm2 and 590N/mm2 class steel materials (Part 3: Setting of heat input and interpass temperature control conditions)", Proceedings of the Architectural Institute of Japan Annual Meeting (Hokkaido), August 2013, pp. 1151-1152 Masanori Ishida and 7 others, "Study on welding construction method of high-strength 780N/mm2 steel for architectural structures (part 6) Mechanical test results of welded parts", Proceedings of the Architectural Institute of Japan Annual Meeting (Hokuriku), September 2019, pp. 1099-1100

Column-to-column welded joints using welded-assembled box-section members are generally welded horizontally with a R-shaped groove as shown in Figure 2, and full penetration welds are often formed using overmatch welding, which makes the strength of the weld material greater than that of the base metal. The groove preparation for welded joints between welded-assembled box-section members is often done by a steel frame fabricator using machining, gas cutting, plasma cutting, etc. In particular, for large welded-assembled box-section members, the groove preparation is done using gas cutting and plasma cutting.

Here, in a welded joint between welded box sections formed by combining four steel plates of the same thickness and strength, the shape of the R-shaped groove formed in each steel plate constituting the welded box section member may be the same. However, in a welded joint between welded box sections as disclosed in Patent Documents 1 and 2, the shape of the R-shaped groove formed in each steel plate differs depending on the differences in plate thickness and strength between the steel plates. For this reason, the welding conditions and welding lamination method differ for each steel plate with a different plate thickness and strength, making the welding method complicated. In addition, if the shape of the R-shaped groove formed in each steel plate differs depending on the differences in plate thickness and strength between the steel plates, the groove processing at the steel frame fabricator also becomes complicated.

Furthermore, the steel plates used in welded box sections tend to be relatively high strength. For this reason, the welding materials for the welded joints between welded box sections also need to be relatively high strength, and heat input and interpass temperatures need to be strictly controlled to avoid welding defects and insufficient strength. In addition, horizontal welding performed on column-to-column joints using welded box sections is more difficult than downward welding, etc., and is more susceptible to problems such as welding defects and insufficient strength.

In view of the above problems, the present invention aims to provide a welded joint for a box-shaped cross-section member, which is made by combining steel plates of different thicknesses, and which can be made rational and sound with a relatively simple structure, and a welding method for the same.

To solve the above problems, the present invention has the following features:

[1] A welded joint for a box- _{shaped cross-section member, in which a first steel plate having a plate thickness t1 and} a second steel plate having a plate thickness _t2 smaller than the plate thickness t1 are arranged on a pair of opposing surfaces, and the second steel plate is arranged on the other pair of opposing surfaces to form a rectangular cross-section, is joined in the longitudinal direction of the box-shaped cross-section member, and in the welded joint, the first steel plates are joined to each other and the second steel plates are joined to each other, no groove is formed in the first steel plate and the second steel plate of one of the box-shaped cross-section members joined by the welded joint, a square groove is formed in the first steel plate and the second steel plate of the other box-shaped cross-section member joined by the welded joint, and the groove angle _θ1 of the square groove formed in the first steel plate, the root gap _r1 of the joint between the first steel plates, and the groove angle _θ2 of the square groove formed in the second steel plate and a root gap _r2 at the joint between the second steel plates satisfies the relationships _θ1 = _θ2 and _r1 = _r2 .

[2] The welded joint of a box section member according to [1], wherein the yield strength σ _y1 of the first steel plate and the yield strength σ _y2 of the second steel plate satisfy the relationship σ _y1 ≠ σ _y2 .

[3] The welded joint of a box section member according to [1], wherein the yield strength σ _y1 of the first steel plate and the yield strength σ _y2 of the second steel plate satisfy the relationship σ _y1 < σ _y2 .

[4] The welded joint of a box section member according to claim 3, wherein the joining of the first steel plates together at a portion of thickness _t2 from the inside of the cross section of the box section member and the joining of the second steel plates together are performed using a first welding material, and the joining of the first steel plates together at a portion of thickness ( _t1 - _t2 ) from the outside of the cross section of the box section member is performed using a second welding material, and the yield strength _σywa of the first welding material, the yield strength _σywb of the second welding material, the yield strength _σy1 of the first steel plate, and the yield strength _σy2 of the second steel plate satisfy the relationship _σy1 ≦ _σywb ≦ _σy2 ≦ _σywa .

[5] A welding method for forming a welded joint of a box-shaped cross-section member according to [4], comprising: continuously rotating-welding a portion of the first steel plate, the portion being at a thickness _t2 from the inside of the cross-section of the box-shaped cross-section member, to the second steel plate using the first welding material.

According to the welded joint for box section members and the welding method thereof of the present invention, the groove angles _θ1 , _θ2 of the R-groove formed in the first steel plate and the second steel plate are equal to each other, and the root gap _r1 of the joint between the first steel plates is equal to the root gap _r2 of the joint between the second steel plates. Therefore, even if the plate thicknesses of the first steel plate and the second steel plate are different from each other, the groove processing of the first steel plate and the second steel plate can be easily performed.

In addition, the cross-sectional shape of the L-shaped groove formed in the first steel plate at a thickness _t2 from the inside of the cross section of the box-shaped cross-section member is the same as the cross-sectional shape of the L-shaped groove formed in the second steel plate, so that both can be continuously welded. Therefore, when forming a column-to-column welded joint using a welded assembly box-shaped cross-section member by horizontal welding, the difficulty of welding is reduced and the heat input and interpass temperature can be easily controlled. As a result, a sound welded joint can be formed with a relatively simple configuration, which is rational and prevents problems such as welding defects and insufficient strength.

FIG. 1 is a schematic diagram showing a cross section of a welded box section member. 2(a) and 2(b) are diagrams showing the groove shape in a welded joint of a box cross-section member of the present invention. 3(a) and 3(b) are diagrams showing the main part of a welded joint of a box section member of the present invention. 4(a) to 4(d) are diagrams showing the state of the weld joint of the box section member of the present invention before welding is performed. 5(a) to 5(d) are diagrams showing the initial stages of welding a welded joint of a box section member of the present invention. 6(a)-6(d) are diagrams showing stages nearing completion of welding of a weld joint in a box section member of the present invention.

Below, we will explain in detail an embodiment of the welded joint for a box section member and the welding method thereof with reference to the drawings.

The welded joint of the box section member of this embodiment is formed by joining together welded assembled box section members 1 as shown in Fig. 1 in the longitudinal direction. As shown in Fig. 1, the box section member 1 is formed by combining a first steel plate having a plate thickness _t1 and a second steel plate having a plate thickness _t2 smaller than the plate thickness _t1 to form a rectangular cross section and joining them together by corner welds 13. Specifically, a first steel plate 11 is disposed on a pair of opposing surfaces, and a second steel plate 12 is disposed on the other pair of opposing surfaces.

In the welded joint of the box-shaped cross-section member of this embodiment, the box-shaped cross-section members 1 are joined in the length direction so that the first steel plates 11 are joined and the second steel plates 12 are joined. As shown in FIG. 1, an erection piece 18 is provided at the end of the box-shaped cross-section member 1, and the box-shaped cross-section members 1 are butt-welded in a state in which they are positioned by the erection piece 18.

2(a) and 2(b) show the groove shape of the welded joint of the box-shaped section member of this embodiment. As shown in FIG. 2(a) and FIG. 2(b), the first steel plate 11 and the second steel plate 12 of the box-shaped section member 1 on one side (lower side of FIG. 2(a) and FIG. 2(b)) joined by the welded joint are not formed with a groove. In contrast, the first steel plate 11 and the second steel plate 12 of the box-shaped section member 1 on the other side (upper side of FIG. 2(a) and FIG. 2(b)) joined by the welded joint are formed with a V-shaped groove 11a with a groove angle θ ₁ and a groove angle θ ₂ , respectively.

In addition, root gaps _r1 and _r2 are provided at the innermost portions of the R-shaped groove 11a of the first steel plate 11 and the R-shaped groove 12a of the second steel plate 12, respectively, to ensure that full penetration welding is formed. The back sides of the root gaps _r1 and _r2 are closed by a backing metal 16. The backing metal 16 is attached by being welded to the back side of the first steel plate 11 or the second steel plate 12 in a state where it is placed on an end plate 17 that closes the end of one of the box section members 1 (the lower side in Figs. 2(a) and 2(b)) joined by the weld joint.

As shown in Figures 2(a) and 2(b), the groove width of the welded portion between the first steel plates 11 is _r1 + _t1 ·tan _θ1 , and the groove width of the welded portion between the second steel plates 12 is _r2 + _t2 ·tan _θ2 .

In the welded joint of the box-shaped cross-section member of this embodiment, the groove angle θ ₁ of the R-shaped groove 11a formed in the first steel plate 11 and the groove angle θ ₂ of the R-shaped groove 12a formed in the second steel plate 12 satisfy the relationship of θ ₁ = θ _2. In addition, the root gap r ₁ of the joint between the first steel plates 11 and the root gap r ₂ of the joint between the second steel plates 12 satisfy the relationship of r ₁ = r _2. In this way, the groove processing can be performed so that the root gap and the groove angle are constant over the entire end of the box-shaped cross-section member 1. This groove processing can be performed by normal gas cutting or plasma cutting.

3(a) and 3(b) show a main portion of a welded joint of the box section member 1 of this embodiment. In the box section member 1 of this embodiment, the yield strength σ _y1 of the first steel plate 11 and the yield strength σ _y2 of the second steel plate 12 satisfy the relationship σ _y1 < σ _y2 .

Here, in welded joints between welded assembled box section members, it is common to use overmatch welding, in which the strength of the weld material is made greater than the strength of the base material. To achieve this, it is necessary to make the strength of the weld material that joins the first steel plates 11 of this embodiment greater than the strength of the first steel plates 11, and the strength of the weld material that joins the second steel plates 12 greater than the strength of the second steel plates 12.

Here, in the welded joint of the box section member 1 of this embodiment, as shown in Figures 3(a) and 3(b), the joining of the first steel plates 11 together in a portion of thickness _t2 from the inside of the cross section of the box section member 1 is performed using a first welding material 14 having a yield strength _σywa greater than _σy2 . The joining of the second steel plates 12 together is also performed using the first welding material 14. The joining of the first steel plates 11 together in a portion of thickness ( _t1 - _t2 ) from the outside of the cross section of the box section member 1 is performed using a second welding material 15 having a yield strength _σywb greater than _σy1 and smaller than _σywa . That is, the yield strength σ _ywa of the first welding material 14, the yield strength σ _ywb of the second welding material 15, the yield strength σ _y1 of the first steel plate 11, and the yield strength σ _y2 of the second steel plate 12 satisfy the relationship σ _y1 < σ _ywb < σ _y2 < σ _ywa .

The heat input and interpass temperature must be controlled more strictly when welding with the high-strength first welding material 14 than when welding with the second welding material 15. In other words, welding with the second welding material 15 is easier to perform than welding with the first welding material 14. For this reason, it is easier to control the heat input and interpass temperature by minimizing the amount of welding using the first welding material 14 and increasing the amount of welding using the second welding material 15.

Therefore, in the welded joint of the box section member 1 of this embodiment, of the V-shaped groove 11a formed in the first steel plate 11, only a portion of thickness _t2 from the inside of the cross section of the box section member 1 is welded using a first welding material 14. Then, the remaining portion of the V-shaped groove 11a formed in the first steel plate 11, i.e., a portion of thickness ( _t1 - _t2 ) from the outside of the cross section of the box section member 1, is welded using a second welding material 15.

In this way, as described later, the portion of the V-shaped groove 11a formed in the first steel plate, which is a thickness _t2 from the inside of the cross section of the box-shaped cross-section member, and the V-shaped groove 12a formed in the second steel plate can be continuously welded by using the same first welding material 14. Therefore, even when forming a column-to-column welded joint using a welded assembly box-shaped cross-section member by horizontal welding, the difficulty of welding is reduced and the heat input and interpass temperature can be easily controlled, which is preferable.

The welding method for the weld joint of the box section member 1 in this embodiment is a welding method for forming the weld joint of the box section member 1 described above, and can be performed using various procedures, but it is preferable to perform it using the following procedure, for example.

Figures 4(a) to 4(d) show the state of the weld joint of the box section member of this embodiment before welding is performed. Figure 4(a) is a vertical cross-sectional view of the second steel plate 12, Figure 4(b) is a perspective view of the corner of the box section member 1 viewed from the outside, Figure 4(c) is a vertical cross-sectional view of the first steel plate 11, and Figure 4(d) is a horizontal cross-sectional view of the weld joint portion of the box section member 1. Figures 4(a) to 4(d) also show the mutually orthogonal X-axis, Y-axis, and Z-axis to make it easier to understand the relationship of the orientation between the figures.

Figures 5(a) to 5(d) show the initial stage of welding of the welded joint of the box section member of this embodiment. Figures 5(a) to 5(d) correspond to Figures 4(a) to 4(d), respectively.

5(a) to 5(d), in the initial stage of welding of the welded joint of the box section member of this embodiment, a first welding material 14 having a yield strength σ _ywa is used to perform box welding continuously from a portion of the first steel plate 11 having a thickness _t2 from the inside of the cross section of the box section member 1 to the second steel plate 12, using the first welding material 14. Specifically, welding is started from the flat portion of the first steel plate 11, 90° box welding is performed at the corner where the first steel plate 11 and the second steel plate 12 intersect at right angles, and welding is terminated halfway through the flat portion of the second steel plate 12.

At this time, by using the first welding material 14 having the yield strength σ _ywa , overmatch welding is performed for both the yield strengths σ _y1 and σ _y2 of the first steel plate 11 and the second steel plate 12. The portion of the R-shaped groove 11a formed in the first steel plate 11 with a thickness t ₂ from the inside of the cross section of the box-shaped cross-section member has the same cross-sectional shape as the R-shaped groove 12a formed in the second steel plate 12, so that the same first welding material 14 can be used to perform lamination of the same shape from the first steel plate 11 to the second steel plate 12 without changing the welding conditions. Therefore, even when forming a welded joint between columns using a welded assembly box-shaped cross-section member by horizontal welding, the difficulty of welding is reduced and the heat input and interpass temperature are easily controlled. If such lamination is continued, the welding of the entire cross section of the second steel plate 12, which has a plate thickness smaller than that of the first steel plate 11, is completed first.

Figures 6(a) to 6(d) show the stages nearing completion of welding of the weld joint of the box section member of this embodiment. Figures 6(a) to 6(d) correspond to Figures 4(a) to 4(d), respectively.

6(a) to 6(d), after welding of the entire cross section of the second steel plate 12 is completed, welding of only the flat plate portion of the first steel plate 11, which has not yet been completed, is continued using the second welding material 15 having the yield strength σ _ywb . This finally completes a full penetration welded joint in the entire cross section of the box section member 1. At this time, by using the first welding material 14 having the yield strength σ _ywb , overmatch welding is performed with respect to the yield strength σ _y1 of the first steel plate 11.

In the above embodiment, the yield strength σ _ywa of the first welding material 14, the yield strength σ _ywb of the second welding material 15, the yield strength σ _y1 of the first steel plate 11, and the yield strength σ _y2 of the second steel plate 12 are set to satisfy the relationship σ _y1 < σ _ywb < σ _y2 < σ _ywa . However, the welded joint between the welded assembled box section members of the present invention is not limited to this configuration. For example, some or all of the yield strength σ _ywa of the first welding material 14, the yield strength σ _ywb of the second welding material 15, the yield strength σ _y1 of the first steel plate 11, and the yield strength σ _y2 of the second steel plate 12 may be equal to each other.

In the following, a specific example of the welded joint of the box section member of this embodiment will be described. In this example, the outer shape of the welded assembled box section member 1 is 800 mm x 800 mm. The first steel plate 11 is made of 550 N/mm ² class steel plate (design strength 385 N/mm ² ) and has a plate thickness t ₁ of 80 mm. The second steel plate 12 is made of 780 N/mm ² class steel plate (design strength 630 N/mm ² ) and has a plate thickness t ₂ of 50 mm. In this case, for example, the groove angles θ ₁ and θ ₂ of the square grooves 11a and 12a formed on the first steel plate 11 and the second steel plate 12 can be set to θ ₁ = θ ₂ = 30°. In addition, the root gap _r1 of the joint between the first steel plates 11 and the root gap _r2 of the joint between the second steel plates 12 can be set to _r1 = _r2 = 7 mm. For the backing metal 16, for example, a steel plate having a cross-sectional size of 9 mm x 25 mm can be used.

In the horizontal _CO2 welding of the 550 N/mm ² -class steel plate constituting the first steel plate 11, a 550 N/mm ^2- class welding material, for example, YGW18 defined in the Japanese Industrial Standard JIS Z3312 "MAG and MIG welding solid wires for mild steel, high-tensile steel and low-temperature steel", can be used. Therefore, a 550 N/mm ^2- class welding material such as YGW18 can be used as the second welding material 15. Welding using the 550 N/mm ² -class second welding material 15 can be performed without preheating, with a heat input of 30 kJ/cm or 20 kJ/cm or less, and an interpass temperature of 250 ° C. or less, as described in Non-Patent Document 1, for example.

In addition, in horizontal _CO2 welding of the 780 N/mm ² -class steel plate constituting the second steel plate 12, a 780 N/mm ^2- class welding material, for example, G78A2UCN4M4T defined in the Japanese Industrial Standards JISZ, can be used. Therefore, a 780 N/mm ^2- class welding material, such as G78A2UCN4M4T, can be used as the first welding material 14. Welding using the 780 N/mm ^2- class first welding material 14 can be performed with preheating at 75°C or higher, heat input at 20 kJ/cm or lower, and interpass temperature at 200°C or lower, as described in Non-Patent Document 2, for example.

REFERENCE SIGNS LIST 1 box-shaped cross-section member 11 first steel plate 12 second steel plate 11a, 12a bevel groove 13 corner weld 14 first welding material 15 second welding material 16 backing metal 17 end plate 18 erection piece t ₁ thickness of first steel plate t ₂ thickness of second steel plate θ ₁ groove angle of bevel groove formed on first steel plate θ ₂ groove angle of bevel groove formed on second steel plate r ₁ root gap at joint between first steel plates r ₂ root gap at joint between second steel plates

Claims (5)

A welded joint for a box-shaped cross-section member is formed by combining a first steel plate having a plate thickness _t1 and a second steel plate having a plate thickness _t2 smaller than the plate thickness _t1 , the first steel plate being disposed on a pair of opposing surfaces, and the second steel plate being disposed on another pair of opposing surfaces, so as to form a rectangular cross-section, and the welded joint is formed by joining two box-shaped cross-section members in the longitudinal direction of the box-shaped cross-section member,
In the welded joint, the first steel plates are joined to each other and the second steel plates are joined to each other,
The first steel plate and the second steel plate of one of the box-shaped cross-section members joined by the weld joint are not formed with a groove, and the first steel plate and the second steel plate of the other box-shaped cross-section member joined by the weld joint are formed with a V-shaped groove,
A welded joint of a box section member, in which the groove angle θ ₁ of the R-shaped groove formed in the first steel plate, the root gap r ₁ of the joint between the first steel plates, the groove angle θ ₂ of the R-shaped groove formed in the second steel plate, and the root gap r ₂ of the joint between the second steel plates satisfy the relationships θ ₁ = θ ₂ and r ₁ = r ₂ . The welded joint of a box section member according to claim 1 , wherein the yield strength σ _y1 of the first steel plate and the yield strength σ _y2 of the second steel plate satisfy the relationship σ _y1 ≠ σ _y2 . The welded joint of a box section member according to claim 1 , wherein the yield strength σ _y1 of the first steel plate and the yield strength σ _y2 of the second steel plate satisfy the relationship σ _y1 < σ _y2 . Among the joining between the first steel plates, the joining of a portion having a thickness of _t2 from the inside of the cross section of the box section member and the joining of the second steel plates are performed using a first welding material, and among the joining between the first steel plates, the joining of a portion having a thickness of ( _t1 - _t2 ) from the outside of the cross section of the box section member is performed using a second welding material,
The welded joint of a box section member _as described in claim 3, wherein the yield strength σ _ywa of the first welding material, the yield strength σ _ywb of the second welding material, the yield strength σ _y1 of the first steel plate, and the yield strength σ y2 of the second steel plate satisfy the relationship σ _y1 ≦ σ _ywb ≦ σ _y2 ≦ σ _ywa . 5. A welding method for forming a welded joint of a box-shaped cross-section member according to claim 4, comprising the steps of: continuously rotating-welding a portion of the first steel plate having a thickness _t2 from an inside of a cross-section of the box-shaped cross-section member to the second steel plate using the first welding material.

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