WO2020090939A1

WO2020090939A1 - Square steel pipe and method of welding square steel pipe

Info

Publication number: WO2020090939A1
Application number: PCT/JP2019/042691
Authority: WO
Inventors: 毅萩野; 前嶋　匡; 佐藤　誠
Original assignee: 旭化成建材株式会社
Priority date: 2018-10-31
Filing date: 2019-10-30
Publication date: 2020-05-07
Also published as: KR20210066877A; KR102485533B1; JPWO2020090939A1; JP7252249B2

Abstract

Provided is a square steel pipe having a rectangular cross section and comprising: a plurality of steel sheets thicker than a plate thickness of a steel pipe constituting a rectangular steel pipe column; and a welded metal (32) bonded by welding side edges of the steel sheets. The welded metal (32) is formed at a corner of the square steel pipe, and comprises a multilayer structure in which different types of material are stacked. The yield point of a material forming an inner material layer (321) located on the inside of multiple layers is higher than the yield point of a material forming an outer material layer (322) located on the outside of the multiple layers.

Description

Welding method for square steel pipe and square steel pipe

The present invention relates to a square steel pipe and a method for welding a square steel pipe.

Conventionally, in the joint portion of the rectangular steel pipe column used for the column member of the steel structure and the H-shaped steel used for the beam member, the diaphragm type (for example, through diaphragm type, inner diaphragm type, outer diaphragm type, etc.) is used. Has been adopted. In recent years, a non-diaphragm type column-beam joint structure has been adopted in which a H-shaped steel can be directly welded to the pipe wall surface by using a column-beam joint core made of a short, thick rectangular steel pipe without providing this diaphragm. (For example, Patent Document 1).

As the thick-walled rectangular steel pipe applied to the above non-diaphragm type beam-column joint structure, for example, it is known that cast steel or shaped steel is welded. In Patent Document 1, four rectangular steel plates are combined in a box shape, and side edge portions of the steel plates are welded to each other to form a thick-walled rectangular steel pipe having a quadrangular shape in cross section. In detail, four steel plates with the groove formed on both side edges are arranged in a box shape, the side edges of the respective steel sheets are adjacent to each other, and a welding torch is arranged between the side edges, respectively. Patent Document 1 describes a method in which a torch is moved upward from below the steel sheet and the side edges of the steel sheet are welded at the same time.

JP, 2014-024092, A

By the way, the thick-walled square steel pipe applied to the non-diaphragm type beam-column joint structure has a structure in which the H-section steel is directly joined to the side surface thereof as described above, and therefore has a strength capable of withstanding such a structure. Desired. When such a thick-walled rectangular steel pipe is constructed by welding the side edge portions of the steel sheets to each other as in Patent Document 1, stress is likely to concentrate particularly on the joint portion, and the strength as designed can be obtained. Sometimes there is not. Although Patent Document 1 describes that the work efficiency is improved by simultaneously welding the side edge portions of each steel sheet, it is possible to improve the strength of the thick-walled rectangular steel pipe formed by welding. Was not considered and needed improvement.

Therefore, an object of the present invention is to provide a technique capable of improving the strength of a square steel pipe used for a beam-column joint structure.

A square steel pipe according to one aspect of the present invention is a square steel pipe used for a column-beam joint portion between a column and a beam, and is a welded joint formed by welding a plurality of steel plates and side edges of the steel plates. It is a steel pipe having a quadrangular cross-sectional view and a welded part has a multilayer structure in which different kinds of materials are laminated, and the yield point of the material forming the inner material layer located inside the multilayer is It is higher than the yield point of the material forming the outer material layer located on the outer side.

According to the present invention, it is possible to provide a technology capable of improving the strength of a rectangular steel pipe used in a beam-column joint structure.

It is a perspective view for explaining the important section of a steel frame structure. It is a perspective view showing a schematic structure of a thick square steel tube concerning this embodiment. It is a side view which shows schematic structure of the thick-walled square steel pipe which concerns on this embodiment. It is a top view showing a schematic structure of a thick-walled square steel pipe concerning this embodiment. It is an enlarged view which expands and shows the weld metal formed between the adjacent steel plates. It is a figure for demonstrating the modification of the backing metal applied to a thick-walled square steel pipe. It is a figure for demonstrating the modification of the steel plate in a thick-walled square steel pipe.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings. In addition, in each of the drawings, components denoted by the same reference numerals have the same or similar configurations.

First, the configuration of the beam-column joint structure to which the rectangular steel pipe according to the present embodiment is applied will be described. When constructing a steel frame structure using a rectangular steel tube column and an H-shaped steel beam, a structure is used in which a rectangular steel tube column is erected and the H-shaped steel beam is attached to the rectangular steel tube column. When connecting the H-shaped steel beam to the rectangular steel tube column, a non-diaphragm type is adopted as the structure of the column-beam joint portion (column-beam joint structure). FIG. 1 shows a main part of a steel frame structure that adopts this non-diaphragm type beam-column joint structure. In FIG. 1, a rectangular steel pipe column 10 a joined to the upper side of the thick-walled rectangular steel pipe 30 in the beam-column joining structure 1 is shown separated from the thick-walled rectangular steel pipe 30. In addition, in FIGS. 1 to 7 described below, for convenience of illustration, a portion that is not a cross section may be hatched. FIG. 1 shows a main part of a steel frame structure that adopts a non-diaphragm type beam-column joint structure, but the beam-column joint structure in the present embodiment is not limited to this mode, and for example, a thick-walled prism A mode in which a hole is opened in the steel pipe 30 and the beam 20 is bolted is also included.

As shown in FIG. 1, a column-beam joint structure 1 includes upper and lower rectangular

steel pipe columns

10a and 10b extending in the vertical direction and a thick-walled rectangular steel pipe disposed between the upper and lower square steel pipe columns 10a and 10b. 30 (square steel pipe), and a beam 20 whose one end is fixed to the side surface of the thick-walled square steel pipe 30 and which is extended in the horizontal direction.

The beam 20 is made of H-shaped steel, and is composed of two flat plate-like flanges 20a facing each other and a web 20b formed between the facing flanges 20a. The beam 20 is welded to the thick-walled rectangular steel pipe 30 such that the flanges 20a are vertically opposed to each other and one end surface of the web 20b is in contact with the side surface of the thick-walled rectangular steel pipe 30.

The square

steel pipe pillars

10a and 10b are long pillar steel pipes that are pillars of the steel frame structure and have a substantially square cross section. The lower end of the thick-walled rectangular steel pipe 30 is joined to the upper end of the rectangular steel pipe column 10b (lower floor column) extending to the lower side, and the thick-walled prism is attached to the lower end of the rectangular steel pipe column 10a (upper column) extending to the upper side. The upper end of the steel pipe 30 is joined. Hereinafter, when the respective square

steel pipe columns

10a and 10b are not individually distinguished and are collectively expressed, they are simply referred to as "square steel pipe columns 10".

The thick-walled rectangular steel pipe 30 is a short rectangular steel pipe having a substantially quadrangular shape in cross section, which is disposed at a connecting portion (column-beam joint portion) between the upper and lower rectangular steel pipe columns 10 and the beam 20. In the beam-column joint structure 1, the upper and lower rectangular steel pipe columns 10 and the thick-walled rectangular steel pipe 30 are arranged so as to be linearly positioned. Since the non-diaphragm type thick square steel pipe 30 capable of directly joining the beam 20 made of H-shaped steel to the side surface is used in the beam-column joint structure 1 in the present embodiment, the plate thickness of the thick square steel pipe 30 The t _c is formed to be thicker than the plate thickness t _p of the square steel tubular column 10. The plate thickness t _c is, for example, 22 to 50 mm, and the plate thickness t _p is, for example, 6 to 25 mm. The length of the thick-walled rectangular steel pipe 30 in the longitudinal direction is longer than the height of the beam 20 joined to the side surface of the thick-walled rectangular steel pipe 30 (the height between the flanges 20a).

The configuration of the thick-walled rectangular steel pipe 30 will be further described with reference to FIGS. 2 to 5. FIG. 2 is a perspective view showing a schematic configuration of the thick-walled rectangular steel pipe 30. FIG. 3 is a side view showing a schematic configuration of the thick-walled rectangular steel pipe 30. FIG. 4 is a plan view showing a schematic configuration of the thick-walled rectangular steel pipe 30. FIG. 5 is an enlarged view for explaining the weld metal 32 (weld portion) formed at the corner of the thick-walled rectangular steel pipe 30.

As shown in FIG. 2, the thick-walled rectangular steel pipe 30 is formed by welding four

rectangular steel plates

31a, 31a, 31b, 31b thicker than the steel pipes constituting the square steel pipe column 10 to each other by welding. It is molded by. Hereinafter, a process of welding the edges of the

steel plates

31a, 31a, 31b, 31b to each other to form the weld metal 32 will be described. In the present specification, when the

steel plates

31a, 31a, 31b, 31b are not individually distinguished but are collectively expressed, they are simply referred to as "steel plates 31".

First of all, four steel plates 31 are arranged in a box shape so as to face each other. A groove G having an inclination of a predetermined angle is formed on the side edges of the steel plates 31 arranged in a box shape adjacent to each other. In this embodiment, a groove G having an inclination of a predetermined angle is formed at both widthwise edges of the

steel plates

31b, 31b arranged to face each other. Then, a predetermined welding device (for example, a welding torch (not shown)) is arranged in the groove G between the adjacent steel plates 31, and the steel plates 31 are arranged along the vertical direction (the vertical direction in FIG. 3) of the steel plates 31. The adjacent steel plates 31 are joined by welding from one end to the other end (as shown in FIG. 3, from the upper end to the lower end of the steel plate). In this way, the weld metal 32 is formed on the side edge portions (inside the corner portions of the steel plates 31) of the adjacent steel plates 31 to join the steel plates 31 to each other to manufacture a steel pipe having a substantially rectangular cross section.

In the present embodiment, the weld metal 32 obtained by multi-layer welding is formed in the groove G formed between the adjacent steel plates 31. FIG. 5 is an enlarged view showing the periphery of the weld metal 32 in an enlarged manner. The weld metal 32 is formed at the corners (near the four corners of the substantially square cross section) of the thick-walled rectangular steel pipe 30 and has a multilayer structure in which a plurality of types of materials are laminated.

In the step of forming the weld metal 32 having the multilayer structure shown in FIG. 5, in the welding forming step of the first layer, the backing metal is provided on the groove G backside (the inner surface side of the steel sheet 31) formed between the adjacent steel sheets 31. 35 is applied and welding is performed by CO ₂ semi-automatic welding to form the inner material layer 321.

After forming the inner material layer 321, welding is performed by submerged arc welding to form the outer material layer 322. In this way, the multi-layered weld metal 32 including the inner material layer 321 and the outer material layer 322 is formed. In the present embodiment, in the welding of the first layer, welding is performed by CO ₂ semi-automatic welding to form one inner material layer 321, and in the welding of the second and subsequent layers, welding is performed by submerged arc welding and the outer material layer 322. Are formed in multiple layers. With submerged arc welding, there is the aspect that welding of steel materials with relatively long welding areas, such as long members, can be performed continuously without human intervention, but since there is a large heat input at one time, the base metal However, there are some aspects that have a large thermal effect, such as impairing toughness. In this respect, as in the present embodiment, if the welding of the columnar four-sided box-shaped cross section that is desired to be continuously welded in a long area without manpower is performed in multiple layers, the heat input once is suppressed to a low level, and The heat effect of can be reduced. In the present specification, of the weld metal 32 having a multi-layer structure, the material layer located on the inner side (the inner surface side of the thick-walled rectangular steel pipe 30 (the lower side of the weld metal 32 in FIG. 5)) is the inner material layer. The material layer located on the outer side (the outer surface side of the thick-walled rectangular steel tube 30 (the upper side of the weld metal 32 in FIG. 5)) is referred to as an outer material layer 322.

Of the weld metal 32 having a multilayer structure as described above, a high-strength material is used for the inner material layer 321 formed by welding the first layer. Specifically, the yield point measured according to the tensile test specified in JIS Z 2241 of the material used for the inner material layer 321 is the tensile test specified in JIS Z 2241 of the material used for the steel plate 31. The yield point is higher than the yield point measured according to JIS standard and is higher than the yield point measured according to the tensile test specified in JIS Z 2241 of the material forming outer material layer 322.

More specifically, the inner material layer 321 is a yield point is measured according to the tensile test defined in JIS Z 2241 is 460N / mm ² or more and a tensile strength of 550 N / mm ² or more numbers It is formed using a range of materials. Furthermore, in addition to satisfying the numerical values of the yield point and the tensile strength measured according to the tensile test specified in JIS Z 2241, the shock absorption energy in the Charpy impact test specified in JIS Z 2242 It is preferable to form the inner material layer 321 using a material of 70 J or more at 0 ° C. As the welding material used for the inner material layer 321, for example, YGW18 or the like can be adopted. The welding material in the first layer should have a strength (yield point, tensile strength) higher than that of the base material, and in order to ensure that the welding material has a lower limit value higher than the upper limit value of the base material standard. However, from the viewpoint of cost, it is more preferable to use a welding material having a standard lower limit value that stochastically exceeds the upper and lower median values of the base material standard.

The outer material layer 322 has a yield point of 390 N / mm ² or more measured according to the tensile test specified in JIS Z 2241 and is compliant with the tensile test specified in JIS Z 2241 of the inner material layer 321. A material having a tensile strength lower than the yield point measured and a tensile strength in the numerical range of 490 N / mm ² or more is used. As a welding material for the outer material layer 322 satisfying such a condition, for example, EH12K, EH14, S502-H or the like can be adopted.

For the steel plate 31, the yield point measured according to the tensile test specified in JIS Z 2241 is in the numerical range of 325 to 445 N / mm ² , and the tensile strength is in the range of 490 to 610 N / mm ² . A range of steel materials is used. As such a steel material, for example, rolled steel material SN490B for building structure, TMCP steel plate TMCP325B for building structure, etc. can be adopted.

As described above, the inner material layer 321 formed by welding the first layer has a high-strength material (steel sheet 31, measured according to the tensile test stipulated in JIS Z 2241 of the material used for the outer material layer 322). By using a material having a yield point higher than the yield point), the joint strength of the inner side (the inner surface side of the thick rectangular steel tube 30) of the weld metal 32 formed by welding the side edge portions of the steel plate 31 can be improved. Can be improved. Since the beam 20 is directly joined to the side surface of the thick-walled rectangular steel pipe 30 as shown in FIG. 1, a direction in which the inner corner of the thick-walled rectangular steel pipe 30 opens due to tensile stress from the beam 20 (see FIG. 5). Force acts on the inner corner of the thick-walled rectangular steel tube 30, especially at the end of the gap between the backing metal 35 and the steel plate 31 on the side of the weld metal 32, in the present embodiment. Since the inner material layer 321 is formed to improve the inner joint strength of the weld metal 32, it is possible to enhance the proof stress against the stress concentration. Further, by using a material (for example, YGW18 or the like) whose impact absorption energy is 70 J or more at 0 ° C. in the Charpy impact test specified in JIS Z2242 described above for the inner material layer 321, the toughness can be improved. Even if the tensile stress acts, the possibility of fracture in the weld metal 32 can be suppressed. As one of preferable combinations, the inner material layer 321 can be composed of YGW18, the outer material layer 322 of S502-H, and the steel plate 31 of SN490B.

As described above, in the step of forming the weld metal 32, the inner material layer 321 made of a material having a higher yield point than the yield point measured according to the tensile test of JIS 2241 of the material used for the steel plate 31 is formed. And after forming the inner material layer 321, an outer material layer 322 made of a material having a lower yield point measured in accordance with a tensile test specified in JIS Z 2241 of the material of the inner material layer 321 is formed. And a step of performing. In the step of forming the outermost layer in the weld metal 32 forming step (that is, the step of forming the last layer of the outer material layer 322 including a plurality of layers), the welding voltage value and the welding current in the welding operation in the submerged arc welding. It is preferable to adjust the value and the welding speed value. That is, in the step of forming the outer material layer 322, only in the step of welding the outermost layer of the outer material layer 322, the welding voltage value, the welding current value, and the welding current value when welding the layers other than the outermost layer of the outer material layer 322 are welded. It is preferable to weld at different speed values. By adjusting and welding only the stage of welding the outermost layer in this way, it is possible to suppress the extra metal generated when the weld metal 32 is formed. Preferably, the welding voltage value and welding current value at the stage of forming the outermost layer of the weld metal 32 so that the height h of the extra metal (FIG. 5) falls within the range of 0 to 1 mm from the outer surface of the steel plate 31. It is preferable to adjust the welding speed value. By suppressing the surplus as described above, it is possible to eliminate the step of mechanically scraping the surface in order to smooth the surplus, and it is possible to reduce the manufacturing cost.

In addition, considering the case of joining a beam to a rectangular steel pipe with a weld surplus, it is difficult to join the beam as it is if the joint surface is not smooth. Although the beam has been joined since then, the column-beam joint structure 1 or the welding method as in the present embodiment reduces the excess by suppressing the height of the excess within a predetermined value. It is possible to join a beam to a square steel pipe without any problem. Moreover, at the inner corner of the thick-walled rectangular steel pipe 30, stress concentration occurs when a force that deforms the tube wall (steel plate) of the thick-walled rectangular steel pipe outward is transmitted from the beam at the time of an earthquake, etc. Of the relatively high material to form the inner material layer 321 to improve the inner joint strength of the weld metal 32 and increase the proof stress against stress concentration. Therefore, even if the height of the welding excess is reduced, In other words, even if the cross section of the welded part is reduced, it is possible to secure strength exceeding a predetermined level.

In the first place, in the case of post-joining, it is general that the post-joining portion is designed to have higher strength than the base metal in consideration of defects due to welding (“base metal strength ≦ welding strength”). In this respect, in the beam-column joint structure 1 or the welding method of the present embodiment, after that, the strength at the post-joined portion by welding is set to “inner material layer ≧ outer material layer” and further “inner material layer ≧ outer material layer”. By designing the stress concentration portion (inner material layer) with a relatively high strength by setting “≧ base material”, it is possible to reduce the cross-sectional expansion that is secured by the reinforcement, that is, the reinforcement.

The thick-walled rectangular steel pipe 30 manufactured through the above-described welding process has a backing metal 35 having a rectangular shape in plan view arranged inside the corner of the thick-walled rectangular steel pipe 30 and formed outside the backing metal 35. The inclined groove G thus formed is welded to form the weld metal 32. As shown in FIG. 2, the backing metal 35 has a prismatic shape extending along the inside of the corner of the thick-walled rectangular steel tube 30, but is not limited to this shape and various other shapes. Can be changed to.

For example, as shown in FIG. 6 (A), it is possible to form the backing metal 35B arranged inside the corner portion of the thick-walled rectangular steel pipe 30 into an L-shape in plan view. The backing metal 35B having an L-shape in plan view shown in FIG. 6A extends from the upper end to the lower end of the thick-walled rectangular steel pipe 30 along the inside of the corner of the thick-walled rectangular steel pipe 30. As another modified example, as shown in FIG. 6 (B), the backing metal 35C arranged inside the corner of the thick-walled rectangular steel tube 30 can be formed in a triangular shape in plan view. The backing metal 35C having a triangular shape in plan view also extends from the upper end to the lower end of the thick-walled rectangular steel pipe 30 along the inside of the corner of the thick-walled rectangular steel pipe 30. By arranging

such backing plates

35B and 35C, a direction in which the steel plate 31 opens due to tensile stress from the beam 20 (FIG. 1) welded to the outer side of the thick-walled rectangular steel tube 30 (broken line arrow F in FIG. 6). When a force is applied in the direction (shown in FIG. 3), the

backing plates

35B and 35C can be easily followed. It is possible to relieve the stress concentration generated at the inner corner of the thick-walled rectangular steel pipe 30 and at the end of the gap between the backing metal 35 and the steel plate 31 on the side of the weld metal 32.

In the embodiment described above, the groove G shape between the adjacent steel plates 31 in which the weld metal 32 is formed has a shape that widens from the inside to the outside of the thick rectangular steel tube 30. The inclination angle θ (FIG. 5) of the groove G shape is set in the range of 20 ° to 40 °, for example. If the inclination angle θ is 40 ° or more, the welding amount increases, so that the economical efficiency decreases, and if it is 20 ° or less, it becomes difficult to secure the quality. In this way, by forming the groove shape of the adjacent steel plates 31 into a shape that widens from the inner side to the outer side of the thick-walled rectangular steel pipe 30, the amount of material used for the inner material layer 321 in the weld metal 32. Can be suppressed. As described above, it is preferable to use a material having high strength and high toughness for the inner material layer 321, but it is possible to reduce the material cost by suppressing the usage amount of the material having such characteristics. it can.

In addition, in the present embodiment, an example in which the shape of the groove G formed between the adjacent steel plates 31 is the shape that widens from the inside to the outside of the thick-walled square steel pipe 30 is shown. The groove shape is not limited to such a groove shape, and the groove shape can be transformed into various other shapes.

Further, in the embodiment described above, the side edges of four flat steel plates 31 are welded and joined to each other to manufacture the thick-walled rectangular steel pipe 30 having a substantially quadrangular cross-sectional shape. It is not limited to manufacturing the thick-walled rectangular steel pipe 30 using the flat plate-shaped steel plate 31.

For example, as shown in FIG. 7 (A), a cross section in which two steel plates 31d having a substantially L-shape in plan view are used and the groove Gd between the edges of the steel plate 31d is welded to be welded metal 32d. It is also possible to manufacture the thick-walled rectangular steel pipe 30D having a substantially rectangular shape as viewed. Further, as shown in FIG. 7B, two steel plates 31e having a substantially U-shape in plan view are used, and the groove Ge between the edges of the steel plate 31e is welded to be welded metal 32e. It is also possible to manufacture the thick-walled rectangular steel pipe 30E having a substantially square cross section. Further, as shown in FIG. 7C, a thick rectangular steel tube 30F may be formed by combining an H-shaped steel 31f and two flat steel plates 31g. Specifically, first, an H-section steel 31f including two flat plate-shaped flanges 31f1 facing each other and a web 31f2 formed between the facing flanges 31f1 is prepared. In the H-shaped steel 31f, a flat plate-shaped steel plate 31g having grooves Gf formed at both widthwise edges is arranged so as to connect between the facing flanges 31f1. The groove Gf formed at both edges of the steel plate 31g is welded to form a weld metal 32f, and the flange 31f1 of the H-shaped steel 31f and the steel plate 31g are joined. In this way, it is also possible to manufacture the thick-walled rectangular steel pipe 30F (that is, a rectangular steel pipe having a quadrangular cross-section) by combining the H-shaped steel 31f and the steel plate 31g with each other.

The embodiments described above are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention.

For example, in the embodiment described above, the inner material layer 321 is composed of a single layer, and the outer material layer 322 is composed of a plurality of layers made of the same material. 321 may be formed in two or more layers. In addition, more layers of the inner material layer 321 may be formed than layers of the outer material layer 322. The steps described in the embodiment, each element included in the embodiment, and the arrangement, material, condition, shape, size, and the like are not limited to those illustrated, and can be appropriately changed. Further, the configurations shown in different embodiments can be partially replaced or combined.

DESCRIPTION OF SYMBOLS 1 ... Column-beam connection structure, 10 ... Square steel pipe column, 20 ... Beam (H-shaped steel beam), 30 ... Thick wall square steel pipe (square steel pipe), 31 ... Steel plate, 32 ... Weld metal (welded part), 35 ... Back Gold, 321 ... Inner material layer, 322 ... Outer material layer

Claims

A rectangular steel pipe used for a column-beam joint between a column and a beam,
The square steel pipe is
A steel pipe having a quadrangular cross-section, comprising a plurality of steel plates and a welded part formed by welding the side edges of the steel plates to each other,
The weld comprises a multi-layer structure in which different kinds of materials are laminated,
The rectangular steel pipe, wherein a yield point of a material forming an inner material layer located inside of the multilayer is higher than a yield point of a material forming an outer material layer located outside of the multilayer.
The rectangular steel pipe according to claim 1, wherein the yield point of the material forming the outer material layer is equal to or higher than the yield point of the material forming the steel sheet.
The rectangular steel pipe includes four flat steel plates,
The groove formed in the side edge portion of the flat plate-shaped steel plate has a shape that expands from the inside to the outside of the square steel pipe,
The inner material layer is a layer located on the innermost side of the weld formed by welding the groove portion,
The rectangular steel pipe according to claim 1 or 2.
The material forming the inner material layer has a shock absorption energy of 70 J or more at 0 ° C. in a Charpy impact test,
The rectangular steel pipe according to any one of claims 1 to 3.
The inner material layer is composed of a single layer,
The outer material layer is composed of a plurality of layers made of the same material,
The rectangular steel pipe according to any one of claims 1 to 4.
The material constituting the inner material layer, yield point 460N / mm 2 or more, and the tensile strength is at 550 N / mm 2 or more,
The material constituting the outer material layer, yield point 390 N / mm 2 or more, and is the tensile strength of 490 N / mm 2 or more,
The rectangular steel pipe according to any one of claims 1 to 5.
A backing metal is arranged on the inner surface side of the corner portion of the square steel pipe,
The backing metal has a substantially L shape in cross section or a substantially triangular shape in cross section,
The rectangular steel pipe according to any one of claims 1 to 6.
An upper end of a lower floor pillar is joined to a lower end of the rectangular steel pipe according to any one of claims 1 to 7,
The lower end of the upper floor pillar is joined to the upper end of the rectangular steel pipe,
A beam-column joint structure in which a beam is joined to a side surface of the rectangular steel pipe.
A welding method for a rectangular steel pipe having a rectangular cross section used for a column-beam joint between a column and a beam,
A step of preparing a plurality of steel plates,
A welding step of welding the edge portions of the steel sheet to each other,
The welding process is
An inner material layer forming step of forming an inner material layer made of a material higher than the yield point of the material used for the rectangular steel pipe;
An outer material layer forming step of forming an outer material layer made of a material having a material lower than a yield point of the inner material layer after the inner material layer forming step, the welding method for a rectangular steel pipe.
In the inner material layer forming step, one inner material layer is formed by CO 2 semi-automatic welding.
The method for welding a rectangular steel pipe according to claim 9.
In the outer material layer forming step, a plurality of outer material layers are formed by submerged arc welding,
The method for welding a rectangular steel pipe according to claim 9 or 10.