Design methods for steel beams

Abstract

To provide a steel beam design method that can design a stiffening length of a stiffener and a rational cross section of the stiffener with considerations of increasing yield strength of a steel beam by stiffening with a horizontal stiffener.SOLUTION: A design step of the stiffening length of a stiffener designs the length of a stiffening part in such a way that the yield strength Ma0 at a non-stiffening part of a web where no horizontal stiffener is installed to is greater than the bending moment M2 caused on the web at the end part on the center side along the web-length direction in the stiffening part. A design step of the cross section of a horizontal stiffener designs the cross section profile of a horizontal stiffener in such a way that: an equation satisfies that the moment of inertia Ish of a horizontal stiffener is greater than the value that the product of the square of a required radius of gyration reqish of the horizontal stiffener and the section area Ash of the horizontal stiffener is multiplied by 0.7; and an equation satisfies that the ratio δsh of the section area Ash of the horizontal stiffener to the section area Aw of the web is 0.1 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a design method for steel girders.

Background Art

[0002] There is known a method of stiffening a thin web by using stiffeners only for the web near the hinge formation position at the beam end for a steel girder with a large web width-to-thickness ratio, thereby reducing the amount of steel used while ensuring the required plastic deformation performance (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the design of a steel girder in such a thin web stiffener stiffening method, it is necessary to design the length of the web stiffened by the stiffener (stiffener stiffening length) and the cross-section of the horizontal stiffener for stiffening the web. Regarding the design of the stiffener stiffening length, a design that appropriately evaluates the increase in the ultimate strength of the steel girder stiffened by the stiffener is required, but it has not been established at present. Also, regarding the design of the cross-section of the horizontal stiffener, a method of designing the cross-section of the horizontal stiffener with respect to the required rigidity has been proposed, but in such a method, since it is a design formula on the safe side, there is a case where the horizontal stiffener has an excessive cross-sectional shape.

[0005] Therefore, an object of the present invention is to provide a design method for a steel girder that can design a stiffener stiffening length considering the increase in the ultimate strength of the steel girder due to the stiffening of the horizontal stiffener and a reasonable cross-section of the horizontal stiffener.

Means for Solving the Problem

[0006] To achieve the above object, the design method of the steel beam according to the present invention is a steel beam provided with a stiffener reinforcement part joined with a horizontal stiffener extending horizontally in a predetermined length range from the end in the longitudinal direction of the web toward the center, and includes a stiffener reinforcement length design step of calculating the length dimension of the stiffener reinforcement part in the steel beam, and a horizontal stiffener cross-section design step of calculating the cross-sectional shape of the horizontal stiffener. In the stiffener reinforcement length design step, the bending moment M2 generated at the position of the end on the center side in the longitudinal direction of the web in the stiffener reinforcement part is greater than the allowable strength M of the non-reinforced part where the horizontal stiffener is not provided on the web. sh The length dimension of the stiffener reinforcement part is designed so that the allowable strength M of the non-reinforced part a0 is calculated by the following formulas (1.1) and (1.2), the bending moment M2 is calculated by reducing the bending moment M1 generated at the end position in the longitudinal direction of the web by the ratio of the length of the non-reinforced part to the inner legal length of the steel beam, the bending moment M1 is calculated by the following formula (1.3). In the horizontal stiffener cross-section design step, in the stiffener reinforcement part, the region from the position where the horizontal stiffener is joined to the upper end of the web, the region from the position where the horizontal stiffener is joined to the lower end of the web, and when a plurality of horizontal stiffeners are provided at intervals in the vertical direction, the regions between the horizontally arranged horizontal stiffeners are each referred to as a sub-panel, and the second moment of area I of the horizontal stiffener sh is not less than the value obtained by multiplying the square of the required radius of gyration of the horizontal stiffener req i sh by the cross-sectional area A of the horizontal stiffener and multiplying by 0.7, and the ratio δ sh between the cross-sectional area A of the horizontal stiffener and the cross-sectional area A of the web sh satisfies the following formula (2.2) such that δ is not less than 0.1, and the second moment of area I of the horizontal stiffener w is calculated from the following formula (2.1a), and the required radius of gyration of the horizontal stiffener sh The cross-sectional shape of the horizontal stiffener is designed so as to satisfy the following formula (2.1), and the second moment of area I of the horizontal stiffener sh is calculated from the following formula (2.1a), and the required radius of gyration of the horizontal stiffenerreq i sh This is calculated using the following formulas (2.1b) and (2.1c).

[0007]

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[0008] In this invention, the bending moment M2 generated at the central end of the stiffener stiffening section in the longitudinal direction, i.e., at the boundary with the unstiffened section, is greater than the yield strength M of the unstiffened section. a0 If it is small, the bending moment M2 generated at the boundary between the stiffened section and the unstiffened section is equal to the yield strength M of the unstiffened section. a0 When this is reached, a plastic hinge is formed at the boundary between the stiffened and unstiffened sections, resulting in a double-hinged state and a deformation state in which the plastic deformation capacity rapidly decreases. In contrast, in the present invention, the yield strength M of the unstiffened section is greater than the bending moment M2 generated at the boundary between the stiffened and unstiffened sections. a0 Because the length of the stiffener stiffening section is designed to increase the load-bearing capacity, there is no risk of the deformation described above occurring, and it is possible to design the stiffener stiffening length to take into account the increase in load-bearing capacity due to the stiffening of the horizontal stiffener. Furthermore, compared to conventional design methods for the cross-section of horizontal stiffeners, the present invention enables a more rational cross-sectional design while ensuring a stiffening effect.

[0009] In the steel beam design method according to the present invention, the horizontal stiffener may be provided on only one side of the web.

[0010] This approach facilitates the design and fabrication of steel beams and reduces the amount of steel used. [Effects of the Invention]

[0011] According to the present invention, it is possible to design a stiffener stiffening length that takes into account the increase in the load-bearing capacity of the steel beam due to the stiffening of horizontal stiffeners, and a rational cross-section of the horizontal stiffener. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view of a steel beam according to an embodiment of the present invention. [Figure 2] This is a side view of a steel beam according to an embodiment of the present invention, as seen from the width direction. [Figure 3] This graph shows the maximum load-bearing capacity approximation formula according to Reference 1 and the load-bearing capacity of the un-rigidified section of the steel beam in the design method of this embodiment. [Figure 4] This diagram shows the design bending stress for a steel beam with stiffener reinforcements. [Figure 5] This graph shows the approximate formula for the maximum load-bearing capacity according to Reference 1 and the approximate formula for the assumed load-bearing capacity at the beam end in the steel beam design method of this embodiment. [Figure 6] This table shows the specifications of the analysis case used to verify the design formula for stiffener stiffening length using FEM analysis. [Figure 7] This is a graph showing the analysis results for Case 1. [Figure 8] This is an image showing the analysis results for Case 1. [Figure 9] This is a graph showing the analysis results for Case 2. [Figure 10] This is an image showing the analysis results for Case 2. [Figure 11] This diagram shows the arrangement of stiffeners and the definitions of each dimension. [Figure 12] This is a diagram showing the sub-panel. [Figure 13] This is the location for calculating the second moment of area of ​​the horizontal stiffener. [Figure 14] This table shows the specifications of the analysis case used to verify the cross-sectional design formula for the horizontal stiffener. [Figure 15] This figure shows the analysis model for Case 1. [Figure 16] This is a table showing the analysis results. [Modes for carrying out the invention]

[0013] The design method for steel beams according to embodiments of the present invention will be described below with reference to Figures 1-16. As shown in Figures 1 and 2, the steel beam 1 in this embodiment is an H-shaped steel beam. The steel beam 1 has an upper flange 2, a lower flange 3, and a web 4. The steel beam 1 extends horizontally, and both ends are joined to the column 12. Hereinafter, the horizontal direction in which the steel beam 1 extends will be referred to as the length direction. The horizontal direction perpendicular to the length direction will be referred to as the width direction. In the description of the steel beam 1, the vertical direction will be referred to as the height direction. Figures 1 and 2 show the vicinity of one end 1a in the length direction of the steel beam 1.

[0014] A stiffener 5 is joined to a predetermined region of the web 4 of the steel beam 1, extending from the longitudinal end 4a toward the longitudinal center. The web 4 of the steel beam 1 is stiffened by the stiffener 5. The stiffener 5 is joined to only one face of the web 4. In this embodiment, the stiffener 5 consists of two horizontal stiffeners 51, 52 and one vertical stiffener 53.

[0015] The area in web 4 where stiffener 5 is joined and stiffened is referred to as the "stiffener stiffening section 6," and the length dimension of the stiffener stiffening section 6 in the longitudinal direction is referred to as the "stiffener stiffening length L." st It is written as "Stiffener stiffening length L st This corresponds to the "length dimension of the stiffener stiffening portion" of the present invention. The stiffener stiffeners 6 are provided near both ends of the web 4 in the longitudinal direction. The area of ​​the web 4 other than the stiffener stiffeners 6 is referred to as the "unstiffened area 7". The unstiffened area 7 is provided in the middle of the web 4 in the longitudinal direction. The end of the stiffener stiffener 6 that is closest to the column 12 is referred to as the first end 6a. The end of the stiffener stiffener 6 that is further away from the column 12, i.e., the end on the side of the unstiffened section 7, is referred to as the second end 6b. The first end 6a is located at the end 4a of the web 4 in the longitudinal direction.

[0016] The two horizontal stiffeners 51 and 52 are each long, flat steel plates with their surface horizontal and joined to the web 4 in a direction extending in the longitudinal direction. The two horizontal stiffeners 51 and 52 are identical in shape and strength. The two horizontal stiffeners 51 and 52 are spaced apart in the height direction. The distance between the upper horizontal stiffener 51 and the upper flange 2, and the distance between the lower horizontal stiffener 52 and the lower flange 3 are the same dimension.

[0017] In the stiffener stiffening section 6, the area from where the upper horizontal stiffener 51 is joined to the upper end of the web 4 and the area from where the lower horizontal stiffener 52 is joined to the lower end of the web 4 are referred to as outer panels 41, 41, respectively, and the area from where the upper horizontal stiffener 51 is joined to where the lower horizontal stiffener 52 is joined is referred to as inner panel 42. The outer panels 41, 41 and inner panel 42 are each referred to as sub-panels 43.

[0018] Of the longitudinal ends of the two horizontal stiffeners 51 and 52, the end closest to the column 12 is denoted as the first end 51a and 52a, and the end further away from the column 12 is denoted as the second end 51b and 52b. The first ends 51a and 52a of the two horizontal stiffeners 51 and 52 are located at the position of the longitudinal end 4a of the web 4, that is, at the position of the first end 6a of the stiffener stiffener section 6. The second ends 51b and 52b of the two horizontal stiffeners 51 and 52 are located at the position of the second end 6b of the stiffener stiffener section 6.

[0019] The vertical stiffener 53 is a flat steel plate, joined to the web 4 with its plate surface facing the length direction and extending in the height direction. The vertical stiffener 53 is positioned at the second end 6b of the stiffener stiffener portion 6.

[0020] In the steel beam design method according to this embodiment, the stiffener stiffening length L st The system includes a stiffener stiffening length design process for calculating the stiffener stiffener length and a horizontal stiffener cross-sectional design process for calculating the cross-sectional shape of the horizontal stiffeners 51 and 52.

[0021] (Stiffener stiffening length design process) In the stiffener stiffening length design process, the required stiffener stiffening length L st Design it as follows: Stiffener stiffening length L st The yield strength M of the unstiffened section 7 is greater than the bending moment M2 generated at the second end 6b of the stiffened section 6. a0 Design it so that it becomes larger. The load-bearing capacity M of the unreinforced section 7. a0 This is calculated using the following formulas (1.1) and (1.2). The width-to-thickness ratio of web 4 increases, and the maximum load-bearing capacity (W) of steel beam 1 increases. F0 The load-bearing capacity of the un-rigidified section M max ) is the full plastic moment M of the un-rigidified section. p Even when the value falls below a certain level, an appropriate load-bearing capacity assessment is possible.

[0022]

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[0023] The bending moment M2 generated at the second end 6b of the stiffener stiffening section 6 is the bending moment M1 at the end 1a of the steel beam 1 multiplied by the length of the unstiffened section 7 of the steel beam 1 (internal length L0 of the steel beam 1 - stiffener stiffening length L0). st The calculation is performed assuming that the reduction is calculated by multiplying by 2) and the ratio of the internal length L0 of the steel beam 1. Here, the stiffener stiffening length L st The bending moment M1 at the end 1a of the design steel beam 1 is given by the width-to-thickness ratio index W according to the following reference 1. F The maximum load-bearing capacity is calculated using the evaluation formula that employs [the specified method / method]. Reference 1: Kikuo Igarashi, Ryota Suekuni, Takuma Shinohara, and Tao Wang: Novel width-to-thickness ratio index and width-to-thickness ratio classification for evaluating the load-bearing capacity and plastic deformation capacity of steel H-shaped beams, Journal of Structural Engineering, Architectural Institute of Japan (668), pp. 1865-1872, 2011.10) Stiffener stiffening length L st In calculating this, in order to overestimate end stresses and design on the safe side, the maximum load-bearing capacity evaluation formula from Reference 1, which was derived by taking the lower limit of the maximum load-bearing capacity, is modified to take the upper limit of the maximum load-bearing capacity, and is calculated using the following formula (1.3).

[0024]

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[0025] Figure 3 shows a graph comparing the maximum load-bearing capacity approximation formula according to Reference 1 with the load-bearing capacity of the un-rigidified section of the steel beam in the design method of this embodiment. Figure 4 shows the design bending stress of the steel beam 1 with the stiffener stiffening section 6. Note that in the above-mentioned reference 1, the maximum load-bearing capacity approximation formula is expressed as shear strength, but in the design method for the steel beam of this embodiment, it is converted to bending moment by multiplying both sides by the shear span and then expressed. Figure 5 shows the approximate formula for the maximum load-bearing capacity according to Reference 1 and the approximate formula for the assumed load-bearing capacity at the beam end in the steel beam design method of this embodiment.

[0026] (Stiffener stiffening length L determined by FEM analysis) st Verification of the design formula) The stiffener stiffening length L according to the steel beam design method described above. st To verify the validity of the design formula, a large deformation nonlinear analysis (FEM analysis) was performed, and the stiffener stiffening length L st We examined the relationship between this and plastic deformation capacity. Figure 6 shows the analysis cases. In all cases, the steel beam is an H-shaped steel. The beam cross section was set to H-650×200×6×13, and the shear span was set to 4000 mm. In this analysis, the stiffener stiffening length L st We conducted an analysis using the following parameters.

[0027] Analysis Case 1 is the longitudinal dimension of the area where stiffening is actually performed by horizontal stiffeners 51 and 52 (hereinafter referred to as the stiffener stiffening length l). st The stiffener stiffening length L (as indicated above) is calculated according to the steel beam design method described above. st (The following is the required stiffener stiffening length L) st This is an analysis case assuming a shorter length than (as indicated by the notation). Required stiffener stiffening length L st The stiffener stiffening length l st Ratio (stiffener stiffening length l)st Required stiffener length: L st ) is 0.69. Analysis Case 2 is about stiffener stiffening length l st Required stiffener length L st This is an analysis case assuming a scenario exceeding [a certain value]. Required stiffener stiffening length L st The stiffener stiffening length l st The ratio is 1.00.

[0028] Figures 7-10 show the load-deformation relationship and deformation characteristics of the analysis results. As shown in Figures 7 and 8, the stiffener stiffening length l st Required stiffener length L st In the shorter Case 1, coupled buckling of the flange and web occurs at the boundary between the stiffened and unstiffened sections. On the other hand, as shown in Figures 9 and 10, the stiffened length l st Required stiffener length L st In Case 2, which exceeds [a certain value], it can be confirmed that failure at the beam ends is dominant. As the load-bearing capacity of the beam end increases, when the bending moment acting at the boundary between the stiffened section 6 and the unstiffened section 7 reaches the full plastic load-bearing capacity, a plastic hinge is formed at the boundary between the stiffened section 6 and the unstiffened section 7, resulting in a two-hinged state. This can lead to a deformation state like Case 1, where the plastic deformation capacity decreases rapidly. To prevent such failure, the stiffened length L described above is used to ensure that the horizontal stiffeners 51 and 52 are secured to a position where the existing stress falls below the full plastic load-bearing capacity, taking into account the increased stress at the end. st The design (the design method for steel beams in this embodiment) can be confirmed to be effective.

[0029] (Horizontal stiffener cross section design process) In the horizontal stiffener cross-section design process, the cross-sections of horizontal stiffeners 51 and 52 are designed as follows. Figure 11 shows the arrangement of stiffener 5 and the definition of various dimensions. Figures 12 and 13 show the calculation locations for the second moment of area of ​​the horizontal stiffeners.

[0030] Second moment of area I of horizontal stiffeners 51, 52 shThe required radius of gyration of the horizontal stiffener req i sh The square of and the cross-sectional area A of the horizontal stiffener sh The following equation (2.1) is satisfied, and the cross-sectional area A of the horizontal stiffeners 51 and 52 is greater than or equal to the product of the two multiplied by 0.7. sh and the cross-sectional area A of the web w The ratio δ sh Design it so that it satisfies equation (2.2) below, where is 0.1 or greater. Second moment of area I of a horizontal stiffener sh The required radius of gyration of the horizontal stiffener is calculated using the following formula (2.1a). req i sh This is calculated using the following formulas (2.1b) and (2.1c).

[0031] As described above, the subpanels in equation (2.2) refer to the following regions within the stiffener stiffening section: the region from where the upper horizontal stiffener is joined to the upper end of the web, the region from where the lower horizontal stiffener is joined to the lower end of the web, and the region between the upper and lower horizontal stiffeners.

[0032] The calculation of the second moment of area shall conform to the "Steel Structure Allowable Stress Design Standards (S Standard)" (see Reference 2 below). The ratio of the cross-sectional area of ​​horizontal stiffeners 51 and 52 to the cross-sectional area of ​​web 4 shall conform to References 3 and 4 below. Reference 2 Architectural Institute of Japan: Allowable stress design standards for steel structures 1st edition October 2019 Reference 3: Kikuo Igarashi, Yoshihiro Yanagishita: Elastic buckling behavior and optimal stiffening rigidity of a stiffened plate subjected to bending shear force, Journal of Structural Engineering, Architectural Institute of Japan, Vol. 80, No. 708, pp. 321-331, 2015.2 Reference 4: Kikuo Igarashi, Naohiro Igawa, Yoshihiro Yanagishita, Kazuya Mitsui: Buckling behavior of webs stiffened with horizontal stiffeners and design method of horizontal stiffeners, Journal of Structural Engineering, Architectural Institute of Japan, Vol. 85, No. 773, pp. 957-967, 2020.1

[0033] The rotation center of the radius of gyration i of the cross-sectional area, where horizontal stiffeners 51 and 52 are positioned on one side, is calculated using the surface 44 of the web 4 as the principal axis (see Figure 13).

[0034]

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[0035] (Verification of the design formula for the cross-section of the horizontal stiffener using FEM analysis) To verify the validity of the design formulas for the cross-sections of horizontal stiffeners 51 and 52 using the steel beam design method described above, a large deformation nonlinear analysis (FEM analysis) was performed. Figure 14 shows the analysis cases. In all cases, the steel beam is an H-shaped steel. The beam cross section was set to H-650×200×8×11, and the shear span was set to 1550 mm.

[0036] The horizontal stiffener cross-section in analysis case 1 is a shape that is approximately the lower limit of the horizontal stiffener cross-section calculated by the steel beam design method described above. Figure 15 shows the analysis model for Case 1. The cross-section of the horizontal stiffener in analysis case 2 is a more conservative cross-sectional shape than the cross-section of the horizontal stiffener calculated using the steel beam design method described above.

[0037] Figure 16 shows a table of plastic deformation ratios, which are evaluation indices representing the deformation performance of the beam in the analysis results. From the table in Figure 16, it can be confirmed that even in Case 1, which is the lower limit of the design conditions, the deformation capacity is equal to or greater than that of Case 2. Therefore, it can be confirmed that by reinforcing with horizontal stiffeners that satisfy the cross-section of the horizontal stiffeners calculated by the above steel beam design method, it is possible to design a more rational cross-section of horizontal stiffeners while ensuring the deformation performance of the steel beams.

[0038] The vertical stiffeners 53 shown in Figures 1 and 2 are positioned at the second end 6b of the stiffener stiffening section 6, thereby confining the shear buckling waveform generated in the web 4 of the stiffener stiffening section 6 within the stiffener stiffening section 6 and preventing it from affecting the unstiffened section 7. The required stiffness of the vertical stiffener 53 is calculated using different formulas in the Architectural Institute of Japan's "Standards for Allowable Stress Design of Steel Structures," depending on whether the side length ratio β of the subpanel is less than 1 or greater than 1. In this embodiment, by specifying the length of the horizontal stiffener to be 1.2 times or more the beam depth (3.3 Applicable Range), it is clear that the side length ratio β of the subpanel will be greater than 1. Therefore, the formula for calculating the required stiffness when β≧1 (Formula 4.18 in the Architectural Institute of Japan's "Standards for Allowable Stress Design of Steel Structures," see below) is applied mutatis mutandis. Vertical stiffeners can also be used in combination with gusset plates on joists that satisfy the required rigidity.

[0039] The vertical stiffener 53 is designed to have a second moment of area greater than or equal to that shown in the following formula, and the stiffener plate thickness and stiffener width are determined so that the width-to-thickness ratio of the stiffener cross-section is 16 or less.

[0040]

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[0041] Next, the operation and effects of the steel beam design method according to this embodiment will be described. The bending moment M2 generated at the second end 6b of the stiffener stiffener 6, i.e., at the boundary with the unstiffened section, is greater than the yield strength M of the unstiffened section. a0 If it is small, the bending moment M2 generated at the boundary between the stiffened part 6 and the unstiffened part 7 is equal to the yield strength M of the unstiffened part 7. a0 When this is reached, a plastic hinge is formed at the boundary between the stiffened portion 6 and the unstiffened portion 7, resulting in a double-hinged state, which may lead to a deformation state in which the plastic deformation capacity rapidly decreases. In contrast, in this embodiment, the yield strength M of the unstiffened portion 7 is greater than the bending moment M2 generated at the boundary between the stiffened portion 6 and the unstiffened portion 7. a0 The stiffener stiffening length L will increase st Because it is designed in such a way that there is no risk of the deformation described above, the stiffener length L takes into account the increase in load-bearing capacity due to stiffener stiffening. st This design is possible. Furthermore, in this embodiment, compared to conventional design methods for the cross-section of horizontal stiffeners, a more rational cross-sectional design is possible while ensuring the stiffening effect. As a result, the amount of steel used in the horizontal stiffeners 51 and 52 can be reduced by about 20%.

[0042] In this embodiment, the horizontal stiffeners 51 and 52 are joined to only one side of the web 4. This facilitates the design and fabrication of the steel beam 1 and reduces the amount of steel material used.

[0043] Although embodiments of the steel beam design method according to the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the invention. For example, in the above embodiment, a vertical stiffener 53 is provided at the boundary between the stiffened portion 6 and the unstiffened portion 7, but the vertical stiffener 53 may not be provided. In the above embodiment, two horizontal stiffeners 51 and 52 are provided in one stiffener stiffener section 6, but the number of horizontal stiffeners provided in one stiffener stiffener section 6 may be set as appropriate.

[0044] In the above embodiment, the stiffeners 5 (horizontal stiffeners 51, 52, vertical stiffener 53) are joined to only one side of the web 4, but they may be joined to both sides of the web 4, taking rigidity into consideration. [Explanation of symbols]

[0045] 1. Steel beam 4 Web 5 Stifle 6. Stiffener stiffening section 7 Unstiffened part 43 Subpanel 51 Horizontal stiffener 52 Horizontal stiffener

Claims

1. A stiffener stiffening length design process for a steel beam provided with a stiffener stiffening section, in which horizontal stiffeners extending horizontally are joined to a predetermined length range from the end of the web in the longitudinal direction toward the center, and The process includes a horizontal stiffener cross-sectional design step for calculating the cross-sectional shape of the horizontal stiffener, In the stiffener stiffening length design process, The bending moment M generated at the central end of the web in the longitudinal direction in the stiffener stiffening portion ２ The load-bearing capacity M of the un-rigidified section where the horizontal stiffener is not provided on the web is greater than that of the web. ａ０ The length dimension of the stiffener stiffening section is designed to increase the size of the stiffener stiffening section. The load-bearing capacity M of the unreinforced section ａ０ This is calculated using the following formulas (1.1) and (1.2): The aforementioned bending moment M ２ This is the bending moment M generated at the end of the web in the longitudinal direction. １ The bending moment M is calculated by reducing it by the ratio of the length of the un-rigidified section to the inner length of the steel beam. １ This is calculated using the following formula (1.3): In the aforementioned horizontal stiffener cross-section design process, In the stiffener stiffening section, the region from the position where the horizontal stiffener is joined to the upper end of the web, the region from the position where the horizontal stiffener is joined to the lower end of the web, and, if multiple horizontal stiffeners are provided at intervals in the vertical direction, the region between the vertically arranged horizontal stiffeners are each referred to as a subpanel. The second moment of area I of the horizontal stiffener ｓｈ is the required radius of gyration of the horizontal stiffener ｒｅｑ i ｓｈ squared and the cross-sectional area A of the horizontal stiffener ｓｈ satisfies the following formula (2.1) which is a value obtained by multiplying the product by 0.7 and is greater than or equal to that value, Cross-sectional area A of the horizontal stiffener ｓｈ and the cross-sectional area A of the web ｗ The ratio δ ｓｈ The cross-sectional shape of the horizontal stiffener is designed to satisfy the following equation (2.2) such that the value is 0.1 or greater. The second moment of area I of the horizontal stiffener ｓｈ This is calculated using the following formula (2.1a): Required cross-sectional radius of gyration of the horizontal stiffener ｒｅｑ i ｓｈ This is a design method for steel beams calculated from the following equations (2.1b) and (2.1c). [Math 1]

2. The design method for a steel beam according to claim 1, wherein the horizontal stiffener is provided on only one side of the web.

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