Beam, beam-column junction structure, building, and construction and design method of beam

Abstract

To provide a beam that is joined to a column and highly capable of plastic deformation.SOLUTION: A beam 21 is a steel-framed beam with a first flange 22, a second flange 23, and a web 24 joined to the first flange and the second flange, and satisfies formulas, in which at at least one end part of the beam in the material axis direction Z, the first flange, the second flange, and the web are respectively joined to a column 11, and no stiffeners for stiffening the web are attached to the end parts.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a beam, a beam-column joint structure, a building, a beam construction method, and a beam design method. [Background technology]

[0002] In buildings with earthquake-resistant or vibration-damping structures, horizontal loads such as earthquakes act on beams (girders) connected to columns. Generally, the position where the beam is connected to the column, i.e., the end of the beam, bears the greatest stress, and it is therefore believed that plastic deformation progresses from the end of the beam. Therefore, the beams are required to have the plastic deformation capacity to stably resist horizontal loads such as earthquakes. On the other hand, when the beams used in a building are small beams, studies are being conducted to further reduce the weight without impairing the performance of the building and thereby reduce the cost of the building (see, for example, Patent Documents 1 and 2). Also, beams that can reduce the weight while maintaining bending rigidity and the like are being studied (see, for example, Patent Documents 3 to 6).

[0003] Furthermore, when H-shaped steel beams are used, the width-thickness ratio of the web of the H-shaped steel must be equal to or less than the width-thickness ratio specified in the Ministry of Construction Notification in order to ensure stable plastic deformation capacity against horizontal loads such as earthquakes. Specifically, the ratio must satisfy the constraints shown in formula (1) (see, for example, Non-Patent Document 1).

[0004]

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[0005] Here, the left side of equation (1) (d / t w ) is the width-thickness ratio of the web, F on the right side of equation (1) is the standard strength of the allowable stress of the steel material that forms the beam. d is the inner depth of the beam, t w is the thickness of the web. On the other hand, it is possible to apply the design to a range exceeding the range of formula (1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6003526 [Patent Document 2] Patent No. 6003527 [Patent Document 3] Patent No. 7172779 [Patent Document 4] Patent No. 7207054 [Patent Document 5] Patent No. 7207055 [Patent Document 6] Patent No. 7207056 [Non-patent literature]

[0007] [Non-Patent Document 1] "2020 Edition: Commentary on the Structural Technical Standards for Buildings," edited by the Building Administration Information Center and the Japan Building Disaster Prevention Association, National Official Gazette Sales Cooperative, November 2020 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the range exceeding the value of equation (1), plastic deformation capacity cannot be expected. In this case, the design penalty is large and the design becomes uneconomical, so unreinforced beams without stiffeners attached to the web are not generally used. In some cases, stiffeners are welded to the web to prevent local buckling, but this increases processing costs and labor.

[0009] The present invention has been made in consideration of these problems, and aims to provide a beam that is joined to a column and is capable of exhibiting plastic deformation capacity, a column-beam joint structure that includes this beam, a building, a construction method for this beam, and a design method for this beam. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention proposes the following means. (1) Aspect 1 of the present invention is a steel beam having a first flange, a second flange, and a web joined to the first flange and the second flange, which satisfies equations (11) and (12). At least one end of the beam in the material axis direction is joined to a column, and no stiffener for stiffening the web is attached to the end. Here, F w is the standard strength of the allowable stress of the steel material forming the web, d is the inner depth of the beam, t w is the thickness of the web.

[0011]

number

[0012] In this invention, the inventors have conducted extensive research and found that in a beam in which the first flange, the second flange, and the web are each joined to a column at at least one end in the material axis direction, if equations (11) and (12) are satisfied, the beam can exhibit plastic deformation capacity even if no stiffener is attached to the end of the beam to stiffen the web. Therefore, the beam connected to the column can exhibit plastic deformation capacity.

[0013] (2) A second aspect of the present invention may be the beam according to (1) that satisfies the formulas (13) to (16). Here, F f is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t f is the thickness of each of the first flange and the second flange, b is half the length of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam.

[0014]

number

[0015] In this invention, the plastic deformation capacity can be more reliably exhibited.

[0016] (3) Aspect 3 of the present invention may be a beam as described in (1) or (2), in which the first flange, the second flange, and the web are respectively joined to the two columns at both ends of the beam in the material axis direction, and satisfy equation (18). Here, L is the length of the beam, H is the width of the beam, Z is the pf is the sum of the plastic section modulus of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (18) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in equation (18) w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0017]

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[0018] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at both ends of the beam, the plastic deformation capacity can be more reliably exerted.

[0019] (4) A fourth aspect of the present invention may be a beam as described in (1) or (2), in which the first flange, the second flange, and the web are each joined to the column at only one end of the beam in the material axis direction, and satisfy equation (19). Here, L is the length of the beam, H is the width of the beam, Z is the pf is the plastic section modulus of each of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (19) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in equation (19) w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0020]

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[0021] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at only one end of the beam, the plastic deformation capacity can be more reliably exerted.

[0022] (5) A fifth aspect of the present invention is a beam described in any one of (1) to (3), in which a plasticized region occurs at least in the range from the end to the end of the beam at least at one end of the beam in the material axis direction. (6) A sixth aspect of the present invention is the beam according to (4), wherein a plasticized region is generated at least in a range from one end of the beam in the material axis direction to the width of the beam. In this invention, the beam joined to the column can exhibit plastic deformation capacity.

[0023] (7) Aspect 7 of the present invention is a reference strength F of allowable stress of the steel material forming the first flange and the second flange. f is the reference intensity F w The beam according to any one of (1) to (6), which is larger than Generally, the external force acting on a steel beam is dominated by bending moment, and there is a margin of strength against shear force. In this invention, the reference strength F w By reducing the size, it is possible to rationally configure the web in accordance with the required performance, increase the availability of steel materials for forming the web, and reduce the manufacturing cost of the web.

[0024] (8) Aspect 8 of the present invention is a beam-column joint structure comprising the beam according to any one of (1) to (7) and the column. In this invention, a beam-column joint structure can be constructed by providing a beam that can exhibit plastic deformation capacity in the beam that is joined to the column.

[0025] (9) A ninth aspect of the present invention is a building that includes, in part, the column-beam joint structure described in (8). In this invention, a building can be constructed by providing beams that are joined to columns and that are capable of exhibiting plastic deformation capacity.

[0026] (10) Aspect 10 of the present invention is a method for constructing a steel beam having a first flange, a second flange, and webs joined to the first flange and the second flange, wherein the beam is constructed to satisfy equations (11-1) and (12-1), and the first flange, the second flange, and the web are each joined to a column at at least one end of the beam in the material axis direction, and no stiffener for stiffening the web is attached to the end. Here, F w is the standard strength of the allowable stress of the steel material forming the web, d is the inner depth of the beam, tw is the thickness of the web.

[0027]

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[0028] In this invention, the inventors have conducted extensive research and found that in a beam in which the first flange, the second flange, and the web are each joined to a column at at least one end in the material axis direction, if equations (11-1) and (12-1) are satisfied, the beam can exhibit plastic deformation capacity even if no stiffener is attached to the end of the beam to stiffen the web. Therefore, the beam connected to the column can exhibit plastic deformation capacity.

[0029] (11) An eleventh aspect of the present invention may be the beam construction method described in (10), in which construction is performed so as to satisfy the formulas (13-1) to (16-1). Here, F f is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t f is the thickness of each of the first flange and the second flange, b is half the length of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam.

[0030]

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[0031] In this invention, the plastic deformation capacity can be more reliably exhibited.

[0032] (12) Aspect 12 of the present invention is a beam construction method described in (10) or (11), in which the first flange, the second flange, and the web are constructed so as to be joined to the two columns at both ends of the beam in the material axis direction, respectively, and construction is performed so as to satisfy equation (18-1). Here, L is the length of the beam, H is the width of the beam, Z is thepf is the sum of the plastic section modulus of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (18-1) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in Equation (18-1) w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0033]

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[0034] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at both ends of the beam, the plastic deformation capacity can be more reliably exerted.

[0035] (13) Aspect 13 of the present invention is a beam construction method described in (10) or (11), in which the first flange, the second flange, and the web are constructed so as to be joined to the column at only one end of the beam in the material axis direction, and the construction is performed so as to satisfy equation (19-1). Here, L is the length of the beam, H is the width of the beam, Z is the pf is the sum of the plastic section modulus of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (19-1) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in Equation (19-1) w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0036]

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[0037] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at only one end of the beam, the plastic deformation capacity can be more reliably exerted.

[0038] (14) Aspect 14 of the present invention is a method for designing a steel beam having a first flange, a second flange, and webs joined to the first flange and the second flange, respectively, wherein the beam is designed to satisfy equations (11-2) and (12-2), and at least one end of the beam in the material axis direction is designed so that the first flange, the second flange, and the web are each joined to a column, and no stiffener for stiffening the web is attached to the end. Here, F w is the standard strength of the allowable stress of the steel material forming the web, d is the inner depth of the beam, t w is the thickness of the web.

[0039]

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[0040] In this invention, the inventors have conducted extensive research and found that in a beam in which the first flange, the second flange, and the web are each joined to a column at at least one end in the material axis direction, if equations (11-2) and (12-2) are satisfied, the beam can exhibit plastic deformation capacity even if no stiffener is attached to the end of the beam to stiffen the web. Therefore, the beam connected to the column can exhibit plastic deformation capacity.

[0041] (15) A fifteenth aspect of the present invention may be the beam design method according to (14), in which the beam is designed to satisfy the formulas (13-2) to (16-2). Here, F f is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t f is the thickness of each of the first flange and the second flange, b is half the length of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam.

[0042]

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[0043] In this invention, the plastic deformation capacity can be more reliably exhibited.

[0044] (16) Aspect 16 of the present invention may be a beam design method described in (14) or (15), in which the first flange, the second flange, and the web are designed to be joined to the two columns at both ends of the beam in the material axis direction, respectively, and are designed to satisfy equation (18-2). Here, L is the length of the beam, H is the width of the beam, Z is the pf is the sum of the plastic section modulus of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (18-2) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in Equation (18-2) w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0045]

number

[0046] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at both ends of the beam, the plastic deformation capacity can be more reliably exerted.

[0047] (17) Aspect 17 of the present invention may be a beam design method described in (14) or (15), in which the first flange, the second flange, and the web are designed to be joined to the column at only one end of the beam in the material axis direction, and are designed to satisfy equation (19-2). Here, L is the length of the beam, H is the width of the beam, Z is the pf is the sum of the plastic section modulus of the first flange and the second flange, Z pw is the plastic section modulus of the web, A w is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (19-2) pf F f and Z pw F w is the value calculated for the cross section perpendicular to the material axis direction at the end of the beam, and A in Equation (19-2)w F w is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam.

[0048]

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[0049] In this invention, when the first flange, the second flange, and the web are respectively joined to two columns at only one end of the beam, the plastic deformation capacity can be more reliably exerted. [Effects of the Invention]

[0050] The beam, beam-column joint structure, building, beam construction method, and beam design method of the present invention enable the beam joined to the column to exhibit plastic deformation capacity. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a perspective view of a main part of a building according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a front view of a beam provided in the building. [Figure 3] FIG. 10 is a diagram illustrating the boundary conditions of an analytical model of a column-beam joint structure. [Figure 4] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 1. [Figure 5] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 2. [Figure 6] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 3. [Figure 7] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 4. [Figure 8] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 5. [Figure 9] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 6. [Figure 10] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 7. [Figure 11] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 8. [Figure 12] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 9. [Figure 13] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 10. [Figure 14] FIG. 11 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 11. [Figure 15] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 12. [Figure 16] FIG. 11 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 13. [Figure 17] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 14. [Figure 18] This is a diagram showing the bending moment acting on a beam when a horizontal force such as an earthquake force is applied, when both ends of the beam are rigidly connected to two columns. [Figure 19] This figure shows the bending moment acting on a beam when a horizontal force such as an earthquake force is input, in a case where the first end of the beam is rigidly connected to a column and the second end is pin-connected to another beam arranged in a direction intersecting the beam. [Figure 20] FIG. 10 is a perspective view of a main part of a beam-column joint structure according to a second embodiment of the present invention. [Figure 21] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 21. [Figure 22] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 22. [Figure 23] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 23. [Figure 24]FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 24. [Figure 25] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 25. [Figure 26] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 26. [Figure 27] FIG. 10 is a diagram showing the change in M / Mp with respect to the rotation angle θ in Case No. 27. DETAILED DESCRIPTION OF THE INVENTION

[0052] (First embodiment) Hereinafter, a first embodiment of a beam, a beam-column joint structure, a building, a beam construction method, and a beam design method according to the present invention will be described with reference to FIGS.

[0053] [1. Building composition] 1, for example, a building 1 of this embodiment includes a column-beam joint structure 10, a floor slab (not shown), and a wall. That is, the building 1 includes the column-beam joint structure 10 in a part thereof. The beam-column joint structure 10 has two columns 11, a beam (first beam) 21 of this embodiment, and a joint 26. Note that only one of the two columns 11 is shown in FIG. There is no limitation on the configuration of the column 11. For example, the column 11 includes a column body 12, a diaphragm 13, and a gusset plate 14.

[0054] The column body 12 is formed of a square steel pipe and extends in the vertical direction X. In this example, the pillar 11 has two diaphragms 13. The diaphragms 13 are formed in a rectangular ring shape and are fixed to the outer circumferential surface of the pillar body 12 by welding or the like. The two diaphragms 13 are arranged at an interval from each other in the vertical direction X. The gusset plate 14 is formed in a flat plate shape. The gusset plate 14 is arranged so that the thickness direction of the gusset plate 14 is along a horizontal plane. A plurality of through holes (not shown) are formed in the gusset plate 14. The plurality of through holes are arranged at intervals from one another in the up-down direction X.

[0055] The gusset plate 14 is disposed between the two diaphragms 13. The gusset plate 14 is fixed to the outer peripheral surface of the column body 12 and the two diaphragms 13 by welding or the like. The two pillars 11 are spaced apart from each other along a horizontal plane. The columns may be made of H-section steel, reinforced concrete, reinforced steel concrete, etc.

[0056] The beam 21 extends along a horizontal plane in the material axis direction Z. The beam 21 is made of a steel frame. The beam 21 has an upper flange (first flange) 22, a lower flange (second flange) 23, and a web 24. The upper flange 22, the lower flange 23, and the web 24 are each formed in a flat plate shape. The upper flange 22 and the lower flange 23 face each other in the vertical direction X. Here, a width direction Y of the beam 21 is defined, which is perpendicular to the vertical direction X and the material axis direction Z. The upper flange 22 is disposed above the lower flange 23 . The web 24 is disposed between the upper flange 22 and the lower flange 23. The web 24 is joined to the middle portion of the upper flange 22 in the width direction Y and the middle portion of the lower flange 23 in the width direction Y, respectively. The arrangement of the upper flange 22 and the lower flange 23 is not limited to this. The beam 21 may be a rolled H-shaped steel or a welded and assembled H-shaped steel.

[0057] For example, the end of the first side Z1 (hereinafter simply referred to as the first side Z1) in the material axis direction Z of the beam 21 means a range from the end of the first side Z1 of the beam 21 in the material axis direction Z that is 0.25 times the length L (mm) of the beam 21 in the material axis direction Z. Here, the side opposite to the first side Z1 in the material axis direction Z is defined as a second side Z2 in the material axis direction Z (hereinafter simply referred to as the second side Z2). The range of the end portion of the second side Z2 of the beam 21 is the same as the range of the end portion of the first side Z1 of the beam 21. The central portion of the beam 21 in the material axis direction Z means the portion of the beam 21 other than the end portion of the first side Z1 of the beam 21 and the end portion of the second side Z2 of the beam 21. The range of the end of the first side Z1 of the web 24 is the same as the range of the end of the first side Z1 of the beam 21, and the range of the end of the second side Z2 of the web 24 is the same as the range of the end of the second side Z2 of the beam 21.

[0058] A plurality of through holes (not shown) are formed in the end portion of the first side Z1 of the web 24. The plurality of through holes are arranged in the up-down direction X at intervals from one another. Similarly, a plurality of through holes (not shown) are formed at the end of the web 24 on the second side Z2.

[0059] The joint 26 includes a plurality of bolts 27, nuts (not shown), and welds 28 and 29. The shaft portion (not shown) of the bolt 27 is passed through the through-hole of the gusset plate 14 and the through-hole of the web 24. The head portion (reference numeral omitted) of the bolt 27 contacts the gusset plate 14 from a first side Y1 (hereinafter simply referred to as the first side Y1) in the width direction Y relative to the gusset plate 14. The nut is in contact with the web 24 from a second side Y2 (hereinafter simply referred to as the second side Y2) opposite to the first side Y1 in the width direction Y with respect to the web 24. The nut is fitted onto the shank of the bolt 27. The head and nut of the bolt 27 fasten the gusset plate 14 and the web 24 in the width direction Y.

[0060] The weld 28 joins the end of the first side Z1 of the upper flange 22 of the beam 21 to the diaphragm 13 above the column 11. The weld 29 joins the end of the first side Z1 of the lower flange 23 of the beam 21 to the diaphragm 13 below the column 11. As described above, at the end of the first side Z1 of the beam 21, the upper flange 22, the lower flange 23, and the web 24 are joined to the column 11 by the joints 26, respectively. Similarly, although not shown, at the end of the second side Z2 of the beam 21, the upper flange 22, the lower flange 23, and the web 24 are joined to the column 11 by joints 26, respectively.

[0061] As described above, the beam 21 is a main girder in which the upper flange 22, the lower flange 23, and the web 24 are respectively joined to the two columns 11 at both ends in the material axis direction Z. The main girder here refers to a beam whose end is joined to a column. On the other hand, the sub-beam refers to a beam whose end is joined to a main girder. The joints between both ends of the beam 21 and the column 11 are rigid joints.

[0062] At the end of the second side Z2 of the beam 21, the upper flange 22, the lower flange 23, and the web 24 do not have to be joined to the column 11. No stiffeners for stiffening the web 24 are attached to the end of the first side Z1 and the end of the second side Z2 of the beam 21. The stiffeners referred to here mean members attached to at least the web 24 among the upper flange 22, the lower flange 23, and the web 24, and are not members connecting the beam 21 to other beams or other members as stiffeners to prevent lateral buckling of the beam 21.

[0063] The floor slab is supported from below by beams 21. The walls separate the spaces defined in the vertical direction X by the floor slab.

[0064] [2. Beam specifications] Here, the specifications of the beam 21 are defined as shown in FIG. The thickness of each of the upper flange 22 and the lower flange 23 is t f (mm). The thickness of the web 24 is t wThe height of the beam 21 is defined as H (mm). The width of the beam 21 (length in the width direction Y) is defined as B (mm). The length (B / 2) of half the width of each of the upper flange 22 and the lower flange 23 is defined as b (mm). Inside dimension of beam 21 (H-2t f The cross-sectional area of ​​the web 24 taken along a plane perpendicular to the material axis direction Z is defined as A w (mm 2 ) is stipulated.

[0065] The reference strength of the allowable stress of the steel material forming the upper flange 22 and the lower flange 23 is F f (N / mm 2 The reference strength of the allowable stress of the steel material forming the web 24 is defined as F w (N / mm 2 The sum of the plastic section modulus of the upper flange 22 and the lower flange 23 is defined as Z pf (mm 3 The plastic section modulus of the web 24 is defined as Z pw (mm 3 ) is stipulated. The coefficient α(-) represents the degree of strain hardening of the plastic hinge portion generated at the end of the beam 21 in the material axis direction Z. The coefficient α is preferably 1.3 or more.

[0066] [3. Consideration of plastic deformation capacity] [3.1. First installment] As shown in Figure 3, an elastic-plastic analysis was performed using a model of a beam-column joint structure 10 in which only the end of the first side Z1 of the beam 21 is joined to the column 11. In other words, the beam 21 was assumed to be a cantilever beam. The end of the first side Z1 of the beam 21 is rigidly connected to the column 11, and the end of the second side Z2 of the beam 21 is set as the loading point. A forced downward displacement δ is applied to this loading point. The deformed beam 21 is shown by the dotted line L1. As shown in FIG. 3, the rotation angle θ of the beam 21 is defined as (δ / L).

[0067] In addition, the following conditions (1) to (3) were added to the analysis. (1) Beam 21 is made of 490N grade steel (F = 325 (N / mm 2 )), 550N class steel (F=385(N / mm 2 The analysis was performed by applying the stress-strain relationship of the following formula: where the flanges 22, 23 and the web 24 were given the same stress-strain relationship. (2) In order to consider the preferable range of coefficient α, the length L of beam 21 was calculated as a value between 1.2 and 1.5 in increments of 0.1 using the value of coefficient α as a variable, or as the lower limit value of 4.0H (L / H = 4.0), which is the condition under which the shear force of beam 21 is most prominent. (3) The initial imperfection of the beam 21 was set as the primary mode of the buckling eigenvalue analysis, and the smaller of (H / 150) and 4 mm, which are the maximum manufacturing control tolerances, was entered.

[0068] Cases No. 1 to 14 used in the analysis are shown in Table 1.

[0069] [Table 1]

[0070] For example, the cross-sectional shape of Case No. 1 is H-1200 x 600 x 9 x 40. The reference strength F of the upper flange 22, the lower flange 23, and the web 24 is 325 N / mm 2 The value of H / B is 2.0. f The value of d / t is 7.5. w The value of t is 124.4. f / t w The value of the coefficient α for calculating L / H is 4.4. The value of the coefficient α is 1.2 or more and 1.5 or less in increments of 0.1. Here, the following equations (21) to (23) are defined.

[0071]

number

[0072] In addition, the thickness ratio t f / tw It is desirable that the value be greater than 22 / 9 and less than 40 / 9, taking into account the range of expected practical use. Table 1 also shows the upper limits of the inequalities in equations (21) to (23) for cases 1 to 14. Cases 1 to 8 have a reference strength F of 325 N / mm 2 The results are for cases 9 to 14, where the reference strength F is 385N / mm 2 This is the result in the case where For example, in Case No. 1, the upper limit of the inequality in Equation (21) is 125. Similarly, the upper limit of the right-hand side of Equation (22) is 7.7, and the upper limit of the right-hand side of Equation (23) is 13.3.

[0073] The analysis results are shown in Figures 4 to 17. In Figures 4 to 17, the horizontal axis represents the rotation angle θ, and the vertical axis represents M / M p M is the bending moment (Nmm) acting on the end (fixed end) of the first side Z1 of the beam 21. M p is the total plastic moment of the beam 21 (Nmm). In Case No. 1 shown in FIG. 4 and Case No. 9 shown in FIG. 12, the analysis was performed by changing the coefficient α that determines the length of the beam 21 in several ways. For Cases No. 2 to No. 8 shown in Figures 5 to 11 and Cases No. 10 to No. 14 shown in Figures 13 to 17, analysis was performed only when L / H was 4, where shear force is thought to be most dominant.

[0074] In Figs. 4 to 17, M / M p When the value of the moment M exceeds 1, the beam 21 exceeds the yield strength and undergoes strain hardening. p However, if buckling (local buckling) occurs in the beam 21, the strength of the beam 21 will exceed M / M p decreases. When the beam 21 is long enough, the shear force does not prevail against the bending moment, and the beam 21 is less likely to buckle in shear. At this time, the beam 21 is in a state where its performance is determined by its resistance to the bending moment, that is, by the buckling at the end of the beam 21.

[0075] In Case No. 1 shown in Figure 4, as the coefficient α increases, the rotation angle θ gradually increases, and the M / M p When the coefficient α is less than 1.0, the rotation angle θ increases. This tendency is evident when the coefficient α is 1.3 or greater, as the change in the rotation angle θ due to the change in the coefficient α becomes small, demonstrating stable plastic deformation capacity. In order to ensure the plastic deformation capacity of the beam 21, it is preferable that the coefficient α is 1.3 or more.

[0076] It was found that in cases No. 1 to 14, in which the beam 21 satisfies equations (26) and (27), a certain level of plastic deformation capacity can be exerted.

[0077]

number

[0078] In the cases of cases Nos. 1 to 3, 6, 7, 9 to 11, 13, and 14 in which the beam 21 satisfies equations (22), (30) to (33) in addition to equations (26) and (27), the plastic deformation capacity of the beam 21 can be more reliably exerted.

[0079]

number

[0080] In addition, in equation (31), t f0 / t w0 means the ratio of the plate thickness of the upper flange 22 or the lower flange 23 to the thickness of the web 24, and is a constant value of 22 / 9. In the cases of Cases No. 1 to 14 in which the beam 21 satisfies Equation (35) in addition to Equations (26) and (27), the plastic deformation capacity can be more reliably exhibited. Here, Q pis the full plastic shear strength (N). max[A,B] means the value of A or B, whichever is not the smaller. If the cross section or steel type of the beam 21 changes between the end of the beam 21 in the material axis direction Z and the center of the beam 21 in the material axis direction Z, Z in equation (35) pf F f and Z pw F w is a value calculated for a cross section perpendicular to the material axis direction Z at the end of the beam 21. w F w is the smaller of the values ​​calculated at the end of the beam 21 and the central part of the beam 21. Equation (35) can be simply expressed as equation (36).

[0081]

number

[0082] In the cases of Cases No. 1 to 14 in which the beam 21 satisfies Equation (39) in addition to Equations (26) and (27), the plastic deformation capacity can be more reliably exhibited. Here, when the cross section or steel type of the beam 21 changes between the end portion of the beam 21 in the material axis direction Z and the center portion of the beam 21 in the material axis direction Z, Z in the formula (39) pf F f and Z pw F w is a value calculated for a cross section perpendicular to the material axis direction Z at the end of the beam 21. w F w is the smaller of the values ​​calculated at the end of the beam 21 and the central part of the beam 21. Incidentally, equation (39) can be simply expressed as equation (40).

[0083]

number

[0084] Generally, the bending moment M acting on a beam that does not satisfy equation (1) is the full plastic moment M p Exceeds (M / M pIt is believed that if the load exceeds 1, the beam's plastic deformation capacity cannot be expected, or buckling will occur in the beam within the elastic range. However, by limiting the range of the cross-sectional shape of the beam 21 and the length L of the beam 21, the total plastic moment M p It was found that the strength exceeded

[0085] 18 shows the bending moment M acting on the beam 21 when a horizontal force such as an earthquake force is applied, in the case where both ends of the beam 21 are rigidly joined to two columns 11. The bending moment M acts on the end of the beam 21 on the first side Z1 and the end of the beam 21 on the second side Z2 in the opposite directions. 19 shows the bending moment M acting on the beam 21 when a horizontal force such as an earthquake force is applied, in a case where the end of the beam 21 on the first side Z1 is rigidly joined to the column 11 and the end of the beam 21 on the second side Z2 is pin-joined to a second beam 21A different from the column 11 and the beam 21. In this example, the beam 21 is rigidly joined to the column 11 at only one end of the beam 21 in the material axis direction Z. The end of the beam 21 on the second side Z2 in the material axis direction Z is not joined to the column 11. The bending moment M does not act on the end of the beam 21 on the second side Z2.

[0086] At least one end of the beam 21 in the material axis direction Z, when it is joined to a column, a plasticized region due to bending moment is generated in the range from the end to the beam.

[0087] [3.2. Part 2] Here, in the study conducted in [3.1], we reconfirmed equations (36) and (40). The dimension of the left side of equation (36) (L / H) is dimensionless (-). On the other hand, the dimension of the right side of equation (36) is α(-), Z pf (mm 3 ), F f (N / mm 2 ), Z pw (mm 3 ), F w (N / mm 2 ), A w (mm 2), so it is "mm". Therefore, in equation (36), the dimensions of the left side and the right side do not match. Similarly, the dimension of the left side (L / H) of equation (40) is dimensionless (-). In contrast, the dimension of the right side of equation (40) is "mm." Therefore, the dimension of the left side and the right side of equation (40) do not match.

[0088] In [3.1], using Figure 18, a state in which the upper flange 22, the lower flange 23, and the web are joined to two columns 11 at both ends of the beam 21 in the material axis direction Z is described. Also, using Figure 19, a state in which the upper flange 22, the lower flange 23, and the web are joined to the columns 11 at only the end of the first side Z1 (one side in the material axis direction Z) of the beam 21 is described. 18 and 19, the bending moment M changes linearly, so the shear force Q acting on the beam 21 is a constant value. Therefore, the relationship between the length L of the beam 21, the bending moment M, and the shear force Q is expressed by equation (51) for the beam 21 shown in FIG. 18, and by equation (52) for the beam 21 shown in FIG. 19.

[0089]

number

[0090] Furthermore, in the transformation of equation (35), the relationship between equations (53) and (54) is shown.

[0091]

number

[0092] As mentioned above, Z pf F f and Z pw F w is a value calculated for the cross section perpendicular to the material axis direction Z at the end of the beam 21, and by equation (53), the total plastic moment M p is "Z pf F f +Zpw F w ". Thus, the total plastic moment M p It has been explained that the calculation is performed for the cross section of the end of the beam 21, which corresponds to the end of the beam 21 where the bending moment M is maximum in FIGS. Also, as mentioned above, A in equation (35) w F w is defined as the smaller of the values ​​calculated at the end of the beam 21 and the center of the beam 21, and the full plastic shear strength Q p is "A w F w / √3". Therefore, the full plastic shear strength Q p Regarding this, the part of the beam 21 with the smallest total plastic shear strength will be used.

[0093] Based on these contents and equation (51), equation (35-1), which is an excerpt of equation (35), shows that for the bending moment distribution shown in Figure 18, the bending moment acting on both ends of the beam 21 in the material axis direction Z is a full plastic moment M p When the shear force Q acting on the beam 21 is α times the total plastic shear strength Q p It can be said that this represents the length L of the beam 21 at the time when the beam reaches the point where the two ends are joined (hereinafter referred to as the time when both ends are joined). p The smallest part of the beam 21 is used.

[0094]

number

[0095] This is because the shear force Q is constant over the entire length of the beam 21, and the shear yield is determined by the cross section with the smallest full plastic shear strength.

[0096] Similarly, based on these contents and equation (52), equation (39-1), which is an excerpt of equation (39), indicates that for the bending moment distribution shown in FIG. 19, the bending moment acting on one end of the first side Z1 of the beam 21 is a full plastic moment M p When the shear force Q acting on the beam 21 is α times the total plastic shear strength Q p It can be said that this represents the length L of the beam 21 at the time when the beam reaches the point where the end joint is reached (hereinafter referred to as the time when the end joint is reached). p The smallest part of the beam 21 is used.

[0097]

number

[0098] Both sides of equation (35-1) and both sides of equation (39-1) have the dimension of length (mm).

[0099] Equations (35-1) and (39-1) have the dimension of length and can be said to represent the "length L of the beam 21 at the time when both ends are joined and at the time when one end is joined" when the bending moment distributions in Figures 18 and 19 are assumed. Therefore, if the length L of the left side of equation (36) and the length L of the left side of equation (40) are non-dimensionalized by the length H, then, like equations (36-1) and (40-1), equations (35-1) and (39-1) also need to be non-dimensionalized by the length H. Therefore, equations (35) and (39) are non-dimensionalized as in equations (35-2) and (39-2).

[0100]

number

[0101] As discussed above, equations (36) and (40) are modified so that the dimensions of the left and right sides of the equations match, resulting in equations (36-1) and (40-1).

[0102] [4. Beam construction method] The beam construction method involves the following steps: Construction should be carried out so as to satisfy equations (26) and (27). The beam 21 is constructed so that the upper flange 22, the lower flange 23, and the web 24 are each joined to the column 11 at least at one end in the material axis direction Z. No stiffener is attached to at least one end of the beam 21 in the material axis direction Z. The beam construction method is to satisfy equations (22), (30), (31), and (33). The beam construction method may also be to satisfy equation (36-1). The beam construction method may also be to satisfy equation (40-1).

[0103] [5. Beam design method] The beam design method involves the following steps: It is designed to satisfy equations (26) and (27). The beam 21 is designed so that the upper flange 22, the lower flange 23, and the web 24 are each joined to the column 11 at at least one end in the material axis direction Z. No stiffener is attached to at least one end of the beam 21 in the material axis direction Z. The beam design method involves designing to satisfy equations (22), (30), (31), and (33). The beam design method may involve designing to satisfy equation (36-1). The beam design method may involve designing to satisfy equation (40-1).

[0104] 6. Effects of this embodiment As described above, in the beam 21, beam construction method, and beam design method of this embodiment, the inventors have conducted extensive research and found that in a beam 21 in which the upper flange 22, the lower flange 23, and the web 24 are respectively joined to the column 11 at least at the end of the first side Z1, if equations (26) and (27) are satisfied, the beam 21 can exhibit plastic deformation capacity even if no stiffening material is attached to the end of the beam 21 to stiffen the web 24. Therefore, the beam 21 joined to the column 11 can exert plastic deformation capacity.

[0105] The beam 21, the beam construction method, and the beam design method may satisfy the formulas (22), (30), (31), and (33). In this case, the plastic deformation capacity can be more reliably exhibited. The beam 21, the beam construction method, and the beam design method may satisfy equation (36-1). In this case, when the upper flange 22, the lower flange 23, and the web 24 are joined to the two columns 11 at both ends of the beam 21 in the material axis direction Z, the beam 21 can more reliably exert its plastic deformation capacity. In addition, as a general range of use for beams where performance around the strong axis is important, it is desirable that the beam satisfy equation (32). In addition, the plate thicknesses used in general buildings are distributed discretely (6 mm, 9 mm, 12 mm, etc.), with 6 mm being the lower limit. Therefore, when using beams with a large web width-thickness ratio based on this invention, a range of 600 mm or more for a relatively large beam depth is desirable, as this is the range in which the effect of reducing steel weight through thinning is significant.

[0106] The beam 21, the beam construction method, and the beam design method may satisfy the formula (40-1). In this case, when the upper flange 22, the lower flange 23, and the web 24 are respectively joined to the two columns 11 at the ends of only the first side Z1 of the beam 21, the plastic deformation capacity can be more reliably exhibited. Furthermore, in the beam 21 of this embodiment, the beam 21 joined to the column 11 can exhibit plastic deformation ability. Furthermore, in the building 1 of this embodiment, the building can be constructed by providing the beams 21 joined to the columns 11 with beams 21 that can exert plastic deformation capacity.

[0107] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. 20. The same components as those in the previous embodiment are designated by the same reference numerals, and their description will be omitted. Only the differences will be described. As shown in FIG. 20, a column-beam joint structure 30 of this embodiment includes two columns 31, a beam 41 of this embodiment, and a joint 61. The pillar 31 has a pillar body 12 and two diaphragms 13 . The beam 41 has a beam member 42, two brackets 47, and two connecting members 52. Note that only one of the two brackets 47 and only one of the two connecting members 52 are shown in Fig. 20.

[0108] The beam member 42 has an upper flange member 43, a lower flange member 44, and a web member 45. The upper flange member 43, the lower flange member 44, and the web member 45 are configured in the same manner as the upper flange 22, the lower flange 23, and the web 24. The bracket 47 has an upper bracket piece 48, a lower bracket piece 49, and a central bracket piece 50. The upper bracket piece 48, the lower bracket piece 49, and the central bracket piece 50 are configured by shortening the upper flange 22, the lower flange 23, and the web 24 in the material axis direction Z. The connecting members 52 connect the upper flange member 43 and the upper bracket piece 48, the lower flange member 44 and the lower bracket piece 49, and the web member 45 and the central bracket piece 50, respectively.

[0109] The upper flange member 43, the upper bracket piece 48, and a part of the connecting member 52 form a first flange 55. Similarly, the lower flange member 44, the lower bracket piece 49, and another part of the connecting member 52 form a second flange 56, and the web member 45, the central bracket piece 50, and another part of the connecting member 52 form a web 57. The joint 61 has welds 62, 63, and 64. Weld 62 joins upper bracket piece 48 of beam 41 to diaphragm 13 above column 11. Weld 63 joins lower bracket piece 49 of beam 41 to diaphragm 13 below column 11. Weld 64 joins center bracket piece 50 of beam 41 to column body 12 of column 11. As described above, at the end of the first side Z1 of the beam 41, the first flange 55, the second flange 56, and the web 57 are joined to the column 31 by the joints 61, respectively.

[0110] For example, the length of the beam 41 is the length of the beam member 42 and the two brackets 47 as a whole in the material axis direction Z.

[0111] The column-beam joint structure 30 of this embodiment configured as described above can also achieve the same effects as the column-beam joint structure 10 of the first embodiment.

[0112] (Third embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. In the beam 21 of this embodiment, the reference strength F of the allowable stress of the steel material forming the upper flange 22 and the lower flange 23 in the beam 21 of the first embodiment is f is the reference strength F of the allowable stress of the steel material forming the web 24. w is greater than.

[0113] In the following, the analysis was carried out under the conditions (2) and (3) of the first embodiment. Furthermore, flanges 22 and 23 are made of 550N class steel (F f =385(N / mm 2 )), 490N grade steel (F w =325(N / mm 2 The stress-strain relationship was given as follows:

[0114] Cases No. 21 to 27 used in the analysis are shown in Table 2.

[0115] [Table 2]

[0116] For example, the cross-sectional shape of Case No. 21 is H-1100 x 550 x 9 x 40. The reference strength F of the flanges 22 and 23 f is 385 (N / mm 2), the reference strength F of the web 24 w is 325 (N / mm 2 ) The value of H / B is 2.0. b / t f The value of d / t is 6.9. w The value of t is 113.3. f / t w The value of the coefficient α for calculating L / H is 4.4. The value of the coefficient α is 1.2 or more and 1.5 or less in increments of 0.1.

[0117] The analysis results are shown in Figures 21 to 27. In Figures 21 to 27, the horizontal axis represents the rotation angle θ, and the vertical axis represents M / M p M is the bending moment (Nmm) acting on the end (fixed end) of the first side Z1 of the beam 21. M p is the total plastic moment of the beam 21 (Nmm). In Case No. 21 shown in FIG. 21, the coefficient α that determines the length of the beam 21 was changed in several ways to perform the analysis. In Case No. 21, M / M p In the range of 1 or more, when the coefficient α is 1.3 or more and 1.5 or less, M / M p is almost constant, but when the coefficient α is 1.2, M / M p Therefore, it is preferable that the coefficient α is 1.3 or more in order to ensure the plastic deformation capacity.

[0118] Cases 21 to 23 shown in Figures 21 to 23 satisfy formula (36-1). On the other hand, cases 24 and 25 shown in Figures 24 and 25 do not satisfy formula (36-1). Although cases 24 and 25 have a certain degree of plastic deformation capacity, cases 21 to 23, which satisfy formula (36-1), have a higher plastic deformation capacity.

[0119] As described above, the beam 21, column-beam joint structure, building, beam construction method, and beam design method of this embodiment enable the beam 21 joined to the column 11 to exhibit plastic deformation capacity. Furthermore, in general, the external force acting on a steel beam is dominated by bending moment, and the beam has a sufficient strength against shear force. w By reducing the size, the web 24 can be configured rationally according to the required performance, and the availability of steel material for forming the web 24 can be increased, thereby reducing the manufacturing cost of the web 24.

[0120] Even in steel beams 21, which have traditionally been thought to be unable to maintain plastic deformation capacity after reaching full plastic moment or to buckle within the elastic range, by limiting the range of the cross-sectional shape and length L of the beam 21, it is possible to maintain a strength exceeding full plastic moment while exhibiting stable plastic deformation capacity exceeding 1 / 50 to 1 / 25 rad at the member angle (rotation angle θ) of the beam 21 alone.

[0121] Although the first to third embodiments of the present invention have been described above in detail with reference to the drawings, the specific configurations are not limited to these embodiments, and the present invention also includes modifications, combinations, deletions, etc. of the configurations within the scope of the gist of the present invention. Furthermore, it goes without saying that the configurations shown in each embodiment can be used in appropriate combinations. [Explanation of symbols]

[0122] 1 Building 10,30 Column beam joint structure 11 pillars 21 Beam 22 Upper flange (first flange) 23 Lower flange (second flange) 24,57 Web 55 First flange 56 Second flange Z Material axis direction

Claims

1. A first flange; A second flange; a web joined to each of the first flange and the second flange; A steel beam comprising: Formulas (1) and (2) are satisfied, At least one end of the beam in the material axis direction is joined to a column, and the first flange, the second flange, and the web are joined to a column, A beam in which no stiffeners are attached to the ends to stiffen the web. Here, F ｗ is the standard strength of the allowable stress of the steel material forming the web, d is the inner diameter of the beam, t ｗ is the thickness of the web. [Equation 1]

2. The beam according to claim 1 , which satisfies the following equations (3) to (6): Here, F ｆ is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t ｆ is the thickness of each of the first flange and the second flange, b is half the width of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam. [Equation 2]

3. At both ends of the beam in the material axis direction, the first flange, the second flange, and the web are respectively joined to the two columns; The beam according to claim 1 or 2, which satisfies the formula (8). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the central portion of the beam in the material axis direction, Z in the formula (8) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (8) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [Equation 3]

4. At only one end of the beam in the material axis direction, the first flange, the second flange, and the web are respectively joined to the column, The beam according to claim 1 or 2, which satisfies the formula (9). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (9) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (9) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [Equation 4]

5. The beam according to claim 1 or 2, wherein a plasticized region is generated at least in a range from the end to the end of the beam at least at one end in the material axis direction of the beam.

6. The beam according to claim 3 , wherein a plasticized region is generated at least in a range from the end to the end of the beam at least at one end in the material axis direction of the beam.

7. The beam according to claim 4 , wherein a plasticized region is generated at least in a range from one end of the beam in the material axis direction to the end of the beam.

8. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam according to claim 1 or 2, wherein the beam is greater than

9. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam of claim 3 , wherein the beam is greater than

10. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam of claim 4 , wherein the beam is greater than

11. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam of claim 5 , wherein the beam is greater than

12. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam of claim 6 , wherein the beam is greater than

13. The reference strength F of the allowable stress of the steel material forming the first flange and the second flange ｆ is the reference intensity F ｗ The beam of claim 7 , wherein the beam is greater than

14. A beam according to claim 1 or 2; The pillar; A column-beam joint structure comprising:

15. A beam according to claim 3; The pillar; A column-beam joint structure comprising:

16. A beam according to claim 4; The pillar; A column-beam joint structure comprising:

17. A beam according to claim 5; The pillar; A column-beam joint structure comprising:

18. A beam according to claim 6; The pillar; A column-beam joint structure comprising:

19. A beam according to claim 7; The pillar; A column-beam joint structure comprising:

20. A building comprising, as a part thereof, the column-beam joint structure according to claim 14.

21. A building comprising, as a part thereof, the column-beam joint structure according to claim 15.

22. A building comprising, as a part thereof, the column-beam joint structure according to claim 16.

23. A building comprising, as a part thereof, the column-beam joint structure according to claim 17.

24. A building comprising, as a part thereof, the column-beam joint structure according to claim 18.

25. A building comprising, as a part thereof, the column-beam joint structure according to claim 19.

26. A method for constructing a steel beam comprising a first flange, a second flange, and a web joined to the first flange and the second flange, The construction is carried out so as to satisfy the formulas (11) and (12), At least one end of the beam in the material axis direction is constructed so that the first flange, the second flange, and the web are each joined to a column, A beam construction method in which no stiffeners for stiffening the web are attached to the ends. Here, F ｗ is the standard strength of the allowable stress of the steel material forming the web, d is the inner diameter of the beam, t ｗ is the thickness of the web. [Equation 5]

27. A beam construction method according to claim 26, wherein construction is carried out so as to satisfy equations (13) to (16). Here, F ｆ is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t ｆ is the thickness of each of the first flange and the second flange, b is half the width of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam. [Equation 6]

28. At both ends of the beam in the material axis direction, the first flange, the second flange, and the web are constructed so as to be joined to the two columns, respectively; 28. A beam construction method according to claim 26 or 27, wherein construction is carried out so as to satisfy formula (18). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the central portion of the beam in the material axis direction, Z in the formula (18) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (18) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [Equation 7]

29. At only one end of the beam in the material axis direction, the first flange, the second flange, and the web are constructed so as to be joined to the column, The beam construction method according to claim 26 or 27, wherein construction is carried out so as to satisfy formula (19). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the central portion of the beam in the material axis direction, Z in the formula (19) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (19) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [Equation 8]

30. A method for designing a steel beam including a first flange, a second flange, and a web joined to the first flange and the second flange, the method comprising: Designed to satisfy equations (21) and (22), At least one end of the beam in the material axis direction is designed so that the first flange, the second flange, and the web are joined to a column, A beam design method in which no stiffeners for stiffening the web are attached to the ends. Here, F ｗ is the standard strength of the allowable stress of the steel material forming the web, d is the inner diameter of the beam, t ｗ is the thickness of the web. [Equation 9]

31. The beam design method according to claim 30, wherein the beam is designed to satisfy equations (23) to (26). Here, F ｆ is the reference strength of the allowable stress of the steel material forming the first flange and the second flange, t ｆ is the thickness of each of the first flange and the second flange, b is half the width of each of the first flange and the second flange, H is the height of the beam, and B is the width of the beam. [Equation 10]

32. At both ends of the beam in the material axis direction, the first flange, the second flange, and the web are designed to be joined to the two columns, respectively; The beam design method according to claim 30 or 31, wherein the beam is designed to satisfy equation (28). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (28) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (28) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [0011]

33. At only one end of the beam in the material axis direction, the first flange, the second flange, and the web are designed to be joined to the column, The beam design method according to claim 30 or 31, wherein the beam is designed to satisfy equation (29). Here, L is the length of the beam, H is the width of the beam, and Z ｐｆ is the sum of the plastic section moduli of the first flange and the second flange, Z ｐｗ is the plastic section modulus of the web, A ｗ is the cross-sectional area of ​​the web taken along a plane perpendicular to the axial direction, and α is a coefficient representing the degree of strain hardening of the plastic hinge portion occurring at the end of the beam in the axial direction. In addition, when the cross section or steel type of the beam changes between the end portion of the beam in the material axis direction and the center portion of the beam in the material axis direction, Z in the formula (29) ｐｆ F ｆ and Z ｐｗ F ｗ is a value calculated for a cross section perpendicular to the material axis direction at the end of the beam, and A in equation (29) ｗ F ｗ is the smaller of the values ​​calculated for the end portion of the beam and the central portion of the beam. [0012]

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