Method for designing steel frame beam

Abstract

To provide a method for designing a steel frame beam, which enables rationalization by enabling the design of a stiffened beam corresponding to target performance.SOLUTION: A method for designing a steel frame beam, the steel frame beam being provided with a stiffner stiffening portion to which a horizontal stiffener extending in a horizontal direction is joined in a predetermined length range from an end portion of a web in a length direction toward a center of the web, the method comprising: calculating a width-thickness ratio index WFa by Expression (1); and confirming that a stiffner stiffened beam has a target member rank (deformation performance) by a section of the width-thickness ratio index WFa.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for designing a steel beam. [Background technology]

[0002] A thin-walled web stiffener stiffening method has been proposed for steel beams with a large web width-thickness ratio, which reduces the amount of steel used by stiffening only the web near the hinge formation position at the beam end, while ensuring the necessary plastic deformation performance (see Patent Documents 1 and 2 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-183782 [Patent Document 2] Japanese Patent Publication No. 2020-094339 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the qualitative stiffening effect of stiffeners has been confirmed in this construction method, the quantitative stiffening effect has not been demonstrated.Furthermore, there is a problem in that no quantitative evaluation method has been proposed for the plastic deformation performance of beams stiffened with stiffeners.

[0005] The present invention has been made in consideration of the above circumstances, and provides a method for designing a steel beam that enables the design of a stiffener-stiffened beam in accordance with target performance and enables rationalization. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention employs the following means. The design method for a steel beam according to the present invention is a method for determining the width-thickness ratio index W from the formula (1) in a steel beam provided with a stiffener stiffening portion in which a horizontal stiffener extending horizontally is joined within a predetermined length range from the end of the web in the longitudinal direction toward the center. Fa Calculate the width-thickness ratio index W Fa By checking the above section, it is confirmed that the stiffener-stiffened beam is of the target member rank.

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[0007] The steel beam design method configured in this way allows stiffener-stiffened beams to be designed according to the target performance, enabling rationalization. [Effects of the Invention]

[0008] According to the design method of a steel beam of the present invention, it is possible to design a stiffener-stiffened beam according to the target performance, thereby enabling rationalization. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a steel beam that is the subject of a steel beam design method according to an embodiment of the present invention. [Figure 2] 1 is a side view of a steel beam, which is the subject of a steel beam design method according to one embodiment of the present invention, viewed from the width direction. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] This is a diagram showing horizontal stiffeners of a steel beam arranged unequally (ho≠hi). [Figure 5] This is a diagram showing horizontal stiffeners of a steel beam arranged at equal intervals (ho=hi). [Figure 6] FIG. 10 is a diagram showing α (web compressive stress distribution coefficient) when the stiffener is equally divided. [Figure 7] FIG. 10 is a diagram showing α (web compressive stress distribution coefficient) when two stiffeners are unequally divided at a ratio of 1:2:1. [Figure 8] This figure shows the equivalent flange width when calculating WF after widening the beam end. [Figure 9] FIG. 10 is a diagram showing the relationship between target deformation performance and WF. [Figure 10] FIG. 1 is a diagram showing a setting procedure for a steel beam design method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for designing a steel beam according to one embodiment of the present invention will be described with reference to the drawings. The method for designing a steel beam according to this embodiment is a quantitative design technique that focuses on the plastic deformation performance of a beam stiffened with stiffeners.

[0011] First, the structure of a steel beam that is the subject of the steel beam design method will be described. Fig. 1 is a perspective view of a steel beam that is the subject of a steel beam design method according to one embodiment of the present invention, and Fig. 2 is a side view of the steel beam that is the subject of a steel beam design method according to one embodiment of the present invention, viewed from the width direction. As shown in Figures 1 and 2, the steel beam 1 that is the subject of the steel beam design method according to this embodiment is an H-shaped steel. The steel beam 1 has an upper flange 11, a lower flange 12, and a web 13. The steel beam 1 extends horizontally, and both ends are joined to columns 2. 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 explanation of the steel beam 1, the vertical direction will be referred to as the height direction.

[0012] The column 2 is a square steel pipe with its axis aligned along its height. A steel beam 1 is joined to each of the four sides of the column 2.

[0013] The upper flange 11 and the lower flange 12 are formed in a plate shape. The plate surfaces of the upper flange 11 and the lower flange 12 face in the height direction. The upper flange 11 is disposed above the lower flange 12. The web 13 is formed in a plate shape. The plate surface of the web 13 faces in the width direction. The upper and lower ends of the web 13 are joined to the upper flange 11 and the lower flange 12, respectively. Figures 1 and 2 show the vicinity of one end 1a of the steel beam 1 in the longitudinal direction.

[0014] Stiffeners 3 are joined to a predetermined region of the web 13 of the steel beam 1 from the longitudinal end 13a toward the center in the longitudinal direction. The web 13 of the steel beam 1 is stiffened by the stiffeners 3. The stiffeners 3 are joined to only one side of the plate surface of the web 13. In this embodiment, the stiffeners 3 are two horizontal stiffeners 31, 32 and one vertical stiffener 33.

[0015] The area of ​​the web 13 where the stiffener 3 is joined and stiffened is referred to as the "stiffener stiffening portion 4."

[0016] The stiffener-stiffened portions 4 are provided near both longitudinal ends of the web 13. The areas of the web 13 other than the stiffener-stiffened portions 4 are referred to as "unstiffened portions 5." The unstiffened portions 5 are provided in the middle of the web 13 in the longitudinal direction.

[0017] Of the longitudinal ends of the stiffener stiffening part 4, the end closest to the column 2 is referred to as the first end 4a. Of the longitudinal ends of the stiffener stiffening part 4, the end away from the column 2, i.e., the end on the non-stiffened part 5 side, is referred to as the second end 4b. The first end 4a is located at the longitudinal end 13a of the web 13.

[0018] The horizontal stiffeners 31, 32 are each a long, flat steel plate. The plate surfaces of the horizontal stiffeners 31, 32 face in the height direction. The horizontal stiffener 31 is arranged above the horizontal stiffener 32. The length direction of the horizontal stiffeners 31, 32 is aligned with the length direction of the steel beam 1. The width direction ends of the horizontal stiffeners 31, 32 are joined to the web 13. The horizontal stiffeners 31, 32 have the same shape and strength. The horizontal stiffeners 31, 32 are arranged at an interval in the height direction.

[0019] 2, in the stiffener stiffening part 4, the region from the lower surface of the upper flange 11 to the center in the height direction of the horizontal stiffener 31, and the region from the center in the height direction of the horizontal stiffener 32 to the upper surface of the lower flange 12 are referred to as outer panels 41, 41, respectively. In the stiffener stiffening part 4, the region from the center in the height direction of the horizontal stiffener 31 to the center in the height direction of the horizontal stiffener 32 is referred to as inner panel 42.

[0020] FIG. 3 is a cross-sectional view taken along line III-III in FIG. As shown in FIG. 3, the length between the upper flange 11 and the lower flange 12 is expressed as the inner height d (mm) of the web. The length from the lower surface of the upper flange 11 to the center of the horizontal stiffener 31 in the height direction is expressed as the outer panel component h. o The length dimension from the center of the horizontal stiffener 31 in the height direction to the center of the horizontal stiffener 32 in the height direction is expressed as the inner panel component h i The length dimension from the center of the horizontal stiffener 32 in the height direction to the top surface of the lower flange 12 is expressed as (mm). o The length dimension from the lower surface of the upper flange 11 to the center in the height direction of the horizontal stiffener 31 and the length dimension from the center in the height direction of the horizontal stiffener 32 to the upper surface of the lower flange 12 are the same dimension.

[0021] Of the longitudinal ends of the horizontal stiffeners 31, 32, the ends closest to the column 2 are referred to as first ends 31a, 32a. Of the longitudinal ends of the horizontal stiffeners 31, 32, the ends away from the column 2 are referred to as second ends 31b, 32b. The first ends 31a, 32a of the horizontal stiffeners 31, 32 are located at a position on the end 13a side of the longitudinal direction of the web 13, i.e., on the side of the first end 4a of the stiffener stiffening portion 4. The first ends 31a, 32a of the horizontal stiffeners 31, 32 are located a short distance away from the column 2. The second ends 31b, 32b of the horizontal stiffeners 31, 32 are located at a position on the side of the second end 4b of the stiffener stiffening portion 4.

[0022] The vertical stiffener 33 is a flat steel plate. The plate surface of the vertical stiffener 33 faces the longitudinal direction of the steel beam 1. The ends of the vertical stiffener 33 in the width direction are joined to the web 13. The vertical stiffener 33 is disposed at the position of the second end 4b of the stiffener stiffening part 4. The vertical stiffener 33 is disposed slightly spaced from the second ends 31b, 32b of the horizontal stiffeners 31, 32.

[0023] Next, the design method for steel beams will be explained. 1. Design Policy The shear buckling stress of the stiffened steel beam (steel beam 1) web (web 13) is calculated, and the increase in shear buckling strength from the unstiffened (original cross section) section is assumed to be equivalent to that of a steel beam cross section with an apparently larger web thickness, and an equivalent width-thickness ratio is calculated. The calculated equivalent width-thickness ratio is used to calculate the width-thickness ratio index WF, and it is confirmed that the target performance is met.

[0024] 2. Shear buckling stress of stiffener reinforcement The shear buckling stress of the stiffener-stiffened girder is calculated as the smaller of the shear buckling stress of the outer panel (outer panel 41) and the inner panel (inner panel 42) using the following equations (1) to (3). The shear buckling strength and buckling coefficient of the outer panel are shown in equation (2). The shear buckling strength and buckling coefficient of the inner panel are shown in equation (3).

[0025]

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[0026]

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[0027]

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[0028] Figure 4 shows the horizontal stiffeners 31 and 32 of the steel beam 1 in unequal (h o ≠h i) is arranged. FIG. 5 shows the horizontal stiffeners 31 and 32 of the steel beam 1 arranged in equal intervals (h o =h i ) is arranged. Figure 6 is a diagram showing α (web compressive stress distribution coefficient) when the stiffeners are equally divided. Figure 7 is a diagram showing α (web compressive stress distribution coefficient) when two stiffeners are unequally divided in a ratio of 1:2:1. Note that when the horizontal stiffener plates (horizontal stiffeners 31, 32) are equally arranged, the shear buckling stress of the outer panel is smaller, so only the outer panel is calculated.

[0029] 3.Equivalent width-thickness ratio The equivalent width-thickness ratio of stiffened beams is calculated using the following formulas (4) and (5). The equivalent width-thickness ratio is shown in formula (4). The shear buckling stress of the unstiffened (original cross section) and the buckling coefficient of the outer panel are shown in formula (5).

[0030]

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[0031]

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[0032] 4. Confirmation of target performance The target performance is the width-thickness ratio index W, which uses the equivalent width-thickness ratio of the stiffened girder. Fa This is done by W Fa By this classification, it is confirmed that the stiffener-stiffened beam has the target member rank (deformation performance). W Fa is calculated using the following formula (6), and W is shown in Table 1. Fa The relationship between the member rank according to the classification and the plastic deformation magnification is shown. Note that 0.01 in equation (6) is the safety factor set based on the experimental results. Figure 8 shows the equivalent flange width when calculating the width-thickness ratio index with the beam end widened. Figure 9 shows the relationship between the target deformation capacity and WF.

[0033]

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[0034] [Table 1]

[0035] The setting procedure for the steel beam design method of this embodiment is summarized in FIG. Each part is designed (S1), then the allowable stress is calculated (S2).

[0036] If there are no problems in S2, the stiffener placement and stiffener stiffening length are determined (S3). As a result, as shown in Figure 9, any structure that does not meet the required stiffener stiffening length is excluded from the scope of application. The stiffener stiffening length is explained in the specification of Japanese Patent Application No. 2022-128689.

[0037] Next, the stiffener cross section is determined (S4). Next, the required stiffness of the stiffener is confirmed (S5). If the required stiffness is met, the beam member is ranked according to the equivalent width-thickness ratio (S6). If there is a problem in S2, the member cross section and span are reviewed (S11). If the required stiffness is not met in S5, return to S4. If it is outside the applicable range in S6, return to S3.

[0038] The steel beam design method configured in this way makes it possible to design stiffener-stiffened beams that meet the target performance, thereby enabling rationalization of steel beams.

[0039] The shapes and combinations of the components shown in the above-described embodiment are merely examples, and various modifications can be made based on design requirements, etc., within the scope of the present invention.

[0040] For example, in the embodiment shown above, the vertical stiffener 33 is provided at the boundary between the stiffener-stiffened portion 4 and the non-stiffened portion 5, but the vertical stiffener 33 does not have to be provided.

[0041] Furthermore, in the embodiment shown above, two horizontal stiffeners 31, 32 are provided in one stiffener stiffening portion 4, but the number of horizontal stiffeners provided in one stiffener stiffening portion 4 can be set appropriately.

[0042] Furthermore, in the embodiment shown above, the stiffeners 3 (horizontal stiffeners 31, 32, vertical stiffener 33) are joined to only one side of the web 13, but they may also be joined to both sides of the web 13 in consideration of rigidity.

[0043] The Sustainable Development Goals (SDGs) are 17 international goals adopted at the United Nations Summit in September 2015. The steel beam design method according to this embodiment can contribute to achieving one of the 17 SDGs, for example, goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation." [Explanation of symbols]

[0044] 1 Steel beam 3 Stiffener 4 Stiffener reinforcement part 13. Web 31,32 Horizontal stiffener WFa width-thickness ratio index

Claims

【Request Item 1】 In a steel beam provided with a stiffener stiffening portion in which a horizontal stiffener extending horizontally is joined within a predetermined length range from the longitudinal end of the web toward the center, the width-thickness ratio index W is calculated from the formula (1). Ｆａ is calculated, and the width-thickness ratio index W Ｆａ A design method for steel beams that checks whether stiffener-stiffened beams meet the target member rank based on the section. [Equation 1]

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