Buckling stress estimation device, buckling stress estimation method, and buckling stress estimation program

Abstract

To provide an estimation device of buckling stress intensity, which estimates buckling stress intensity of an H-shaped section member receiving only compressive force without convergence calculation.SOLUTION: An estimation device 50 of buckling stress intensity has a pair of flanges and a web, and estimates buckling stress intensity of an H-shaped section member on which only compressive force along a member axis direction acts as external force. The estimation device also includes an estimation section 52 for estimating the buckling stress intensity on the basis of a width-thickness ratio of the web in consideration of a buckling restraint effect on the web by the pair of flanges. The buckling restraint effect is represented by a first ratio as a ratio of a plate thickness center distance of the pair of flanges and each width of the pair of flanges and a second ratio as a ratio of each thickness of the pair of flanges and a thickness of the web.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a device for estimating buckling stress, a method for estimating buckling stress, and a program for estimating buckling stress. [Background technology]

[0002] Conventionally, for H-shaped steel (H-shaped cross section members) subjected to compressive forces, a buckling stress estimation device is known that estimates the buckling stress by considering coupled buckling between the web and flange (see, for example, Patent Document 1). In this buckling stress estimation device, the out-of-plane displacement W of the web is used. w The out-of-plane displacement W of the pair of flanges is estimated using equation (1), and the out-of-plane displacement W of the pair of flanges is also estimated. f1 ,W f2 This is estimated using equations (2) and (3).

[0003]

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[0004] However, the axial direction of the H-beam is defined as the x-axis. The web is defined as extending along the x-axis and the y-axis, respectively. The thickness direction of the web is defined as the z-axis. The distance between the centers of a pair of flanges in the direction along the y-axis is defined as b w It is defined as follows: The half-wavelength of the wavy displaced web is defined as a. Then, the buckling stress is calculated using these out-of-plane displacements W. w ,W f1 ,W f2 , and determined in accordance with the Energy Law. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-006789 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in the buckling stress estimating device of Patent Document 1, a convergence (focusing) calculation is required to obtain the buckling stress. In the convergence calculation, if the initial value of an appropriate variable or the setting of the step width is incorrect, it is conceivable that the obtained buckling stress may change or the calculation may take time.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a buckling stress estimating device, a buckling stress estimating method, and a buckling stress estimating program that estimate the buckling stress of an H-shaped cross-sectional member that receives only a compressive force without performing a convergence calculation.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention proposes the following means. (1) Aspect 1 of the present invention is a buckling stress estimating device for estimating the buckling stress of an H-shaped cross-sectional member having a pair of flanges and a web, and being subjected to only a compressive force along the material axis direction as an external force, the device comprising an estimating unit that estimates the buckling stress based on the width-thickness ratio of the web in consideration of the buckling restraint effect of the pair of flanges on the web, wherein the buckling restraint effect is the ratio of the distance b between the centers of the plate thicknesses of the pair of flanges w to the width B of each of the pair of flanges, which is a first ratio, and the thickness t f of each of the pair of flanges <​​​​​​The first ratio is the ratio of the width B of each of the pair of flanges, and the thickness t of each of the pair of flanges. f and the thickness t of the web w This is a method for estimating buckling stress, expressed using the second ratio, which is the ratio of [the two factors].

[0010] (3) A third aspect of the present invention is a buckling stress estimation program for an estimation device that estimates the buckling stress of an H-shaped cross section member having a pair of flanges and a web, wherein only a compressive force along the axial direction of the material acts as an external force, wherein the estimation device functions as an estimation unit that estimates the buckling stress based on the width-to-thickness ratio of the web, taking into account the buckling constraint effect of the pair of flanges on the web, and the buckling constraint effect is the distance between the center thicknesses of the pair of flanges b w The first ratio is the ratio of the width B of each of the pair of flanges, and the thickness t of each of the pair of flanges. f and the thickness t of the web w This is a program for estimating buckling stress, expressed using the second ratio, which is the ratio of [the two factors].

[0011] In these inventions, the inventors, after careful consideration, have taken into account the buckling restraint effect of a pair of flanges on the web, expressed using the first ratio and the second ratio. And the web width-to-thickness ratio (b w / t w Based on this, we found that the buckling stress can be estimated for H-shaped cross-section members subjected only to compressive forces without performing convergence calculations. Therefore, for H-shaped cross-section members subjected only to compressive forces, the buckling stress can be estimated without performing convergence calculations.

[0012] (4) Aspect 4 of the present invention is that the estimation unit calculates the variable X using the first ratio and the second ratio by formula (5), the variable X and the width-to-thickness ratio (b w / t w The buckling stress σ is obtained by equation (6) using ). cr The buckling stress estimation device described in (1) may be used to estimate the buckling stress. Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants.

[0013]

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[0014] (5) Embodiment 5 of the present invention is an estimation step in which the variable X is calculated using the first ratio and the second ratio, by formula (7), the variable X and the width-to-thickness ratio (b w / t w The buckling stress σ is obtained by equation (8) using ). cr The method for estimating buckling stress described in (2) may also be used. Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants.

[0015]

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[0016] (6) Aspect 6 of the present invention is that the estimation unit calculates the variable X using the first ratio and the second ratio by formula (9), the variable X and the width-to-thickness ratio (b w / t w The buckling stress σ is obtained by equation (10) using ). cr The program used to estimate the buckling stress may be the program described in (3). Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants.

[0017]

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[0018] Here, equation (5) is identical to equations (7) and (9), and equation (6) is identical to equations (8) and (10). In these inventions, the variable X calculated by equation (5) using the first ratio and the second ratio, and this variable X and the width-to-thickness ratio (b w / t w Equation (6) using ) gives the buckling stress σ cr This is estimated. In this way, using equations (5) and (6), the buckling stress can be accurately estimated for an H-shaped cross section member subjected only to compressive force without performing convergence calculations.

[0019] (7) Embodiment 7 of the present invention may be the buckling stress estimation device described in (4), wherein the constant a1 is 0.685 or more and 0.715 or less, the constant a2 is 1.498 or more and 1.698 or less, the constant b1 is -0.437 or more and -0.287 or less, and the constant b2 is 4.012 or more and 4.512 or less. (8) Embodiment 8 of the present invention may be the method for estimating buckling stress described in (5), wherein the constant a1 is 0.685 or more and 0.715 or less, the constant a2 is 1.498 or more and 1.698 or less, the constant b1 is -0.437 or more and -0.287 or less, and the constant b2 is 4.012 or more and 4.512 or less. (9) Embodiment 9 of the present invention may be the buckling stress estimation program described in (6), wherein the constant a1 is 0.685 or more and 0.715 or less, the constant a2 is 1.498 or more and 1.698 or less, the constant b1 is -0.437 or more and -0.287 or less, and the constant b2 is 4.012 or more and 4.512 or less.

[0020] In these inventions, the buckling stress σ is determined using constants a1, a2, b1, b2 within a narrowed range. cr This allows for a more accurate estimation. [Effects of the Invention]

[0021] The buckling stress estimation device, buckling stress estimation method, and buckling stress estimation program of the present invention can estimate the buckling stress for an H-shaped cross section member subjected only to compressive force without performing convergence calculations. [Brief explanation of the drawing]

[0022] [Figure 1] This is a perspective view of a building equipped with H-shaped steel to which a buckling stress estimation device according to one embodiment of the present invention is applied. [Figure 2] This figure shows an overview of the device for estimating the same buckling stress. [Figure 3] This is a schematic perspective view showing an H-shaped steel beam buckling under compressive force. [Figure 4] This is a cross-sectional view of the H-shaped steel beam perpendicular to the material axis. [Figure 5] This flowchart shows a method for estimating buckling stress according to one embodiment of the present invention. [Figure 6] This figure shows the relationship between buckling stress σcr,cal and buckling stress σcr,FEM. [Modes for carrying out the invention]

[0023] Hereinafter, an embodiment of the buckling stress estimation device, buckling stress estimation method, and buckling stress estimation program according to the present invention will be described with reference to Figures 1 to 6.

[0024] [1. Structure of buildings equipped with H-shaped steel] This buckling stress estimation device (hereinafter simply referred to as the estimation device) is used, for example, to estimate the buckling stress of an H-shaped steel beam (H-shaped cross section member) 10 used as a steel beam in building 1 shown in Figure 1. The H-shaped steel beam 10 comprises a first flange 11, a second flange 12, and a web 13. In Figure 1, the floor slab 20, which will be described later, is shown by a dashed line. The first flange 11, the second flange 12, and the web 13 are each formed from steel plates.

[0025] The H-shaped steel beam 10 extends, for example, in a direction along a horizontal plane. The first flange 11 is formed in a flat plate shape and is positioned such that the thickness direction of the first flange 11 is aligned with the vertical direction. The second flange 12 is formed in a flat plate shape and is positioned above the first flange 11. The thickness direction of the second flange 12 is aligned with the vertical direction. The web 13 is formed in a flat plate shape that exhibits a rectangular shape when viewed in the thickness direction of the web 13. The web 13 is positioned so that its thickness direction aligns with the horizontal plane. The web 13 is joined to the center in the width direction on the upper surface of the first flange 11 and to the center in the width direction on the lower surface of the second flange 12, respectively.

[0026] The ends of the H-shaped steel beam 10 in the direction of the material axis are fixed to columns 15, etc. The H-shaped steel beam 10 supports the floor slab 20 from below. Shear connectors 21, such as headed studs, are provided on the second flange 12 of the H-shaped steel beam 10. The shear connectors 21 are embedded in the floor slab 20. Building 1 is used by installing equipment (not shown) on the floor slab 20, etc.

[0027] [2. Configuration of the estimation device] Figure 2 shows the estimation device 50 of this embodiment. The estimation device 50 is a computer and includes a CPU (Central Processing Unit) 51, a main memory 55, an auxiliary storage device 60, an input / output interface (IO / I / F) 65, and a recording / playback device 70. The CPU 51, main memory 55, auxiliary storage device 60, input / output interface 65, and recording / playback device 70 are connected to each other by a bus 75. The main memory 55 is RAM (Random Access Memory) or the like, which serves as the work area for the CPU 51. The input / output interface 65 is connected to an input device 66 such as a keyboard or mouse, and a display device 67. The recording and playback device 70 records and plays back data to and from a recording medium 71 such as a USB (Universal Serial Bus) memory.

[0028] The auxiliary storage device 60 is a hard disk drive or the like that stores various data and programs. The auxiliary storage device 60 stores a buckling stress estimation program (hereinafter simply referred to as the estimation program) 61 for making the computer function as an estimation device 50, as well as various other programs such as the OS program. The estimation program 61 and other programs are imported from the recording medium 71 to the auxiliary storage device 60 via the recording and playback device 70. The estimation program 61 and the like are stored on the recording medium 71. These programs may also be imported into the auxiliary storage device 60 from an external device via a disc-type recording medium such as a CD or DVD, or via a communication device (not shown).

[0029] The CPU 51 performs various calculations. Functionally, the CPU 51 includes an estimation unit 52. The processing performed by the estimation unit 52 will be described in detail later. The estimation unit 52, a functional component of the CPU 51, functions when the CPU 51 executes an estimation program 61, etc., stored in the auxiliary storage device 60. The estimation program 61, etc., is a program for the estimation device 50. The estimation program 61 causes the estimation device 50 to function as the estimation unit 52.

[0030] [3. Processing details of the estimation device and estimation unit] As shown in Figure 3, the estimation device 50 estimates the buckling stress of an H-shaped steel beam 10 when only a compressive force F1 (pure compression) acting as an external force along the material axis direction (longitudinal direction) of the H-shaped steel beam 10 is applied. Figure 3 shows the state in which the H-shaped steel beam 10 is buckled. The compressive force F1 acts on each end face 10a of the H-shaped steel beam 10 in the material axis direction.

[0031] Here, as shown in Figure 4, the dimensions of the H-shaped steel beam 10 in a cross section perpendicular to the material axis direction are defined. The thickness of flanges 11 and 12 is t f (mm) is specified. The width of flanges 11 and 12 is specified as B (mm). Half the width of flanges 11 and 12 is specified as b f (mm) is specified. The thickness of web 13 is t wThe width of the web 13 is defined as d(mm). The depth of the H-beam 10 is defined as H(mm). The distance between the center thicknesses of flanges 11 and 12 is b w (mm) is specified. Distance between the centers of the plate thickness b w This refers to the distance between the center of the first flange 11 in the thickness direction and the center of the second flange 12 in the thickness direction, in the direction in which flanges 11 and 12 face each other. In this case, the distance between the centers of the plate thickness is b. w (Ht f ) is equal to . The value of H is (d+2t f It is equal to ). The Young's modulus of the H-shaped steel beam 10 is defined as E (N / mm). The Poisson's ratio of the H-shaped steel beam 10 is defined as ν (-). The width-to-thickness ratio of web 13 is (b w / t w ) is defined as follows: The first ratio is defined as the distance between the centers of the plate thickness b w The ratio of width B (b w The second ratio is defined as the thickness t. f and thickness t w The ratio (t f / t w ) is stipulated.

[0032] In the H-shaped steel beam 10, the preferred range of dimensions is as follows: • Width-to-thickness ratio of flanges 11 and 12 (b f / t f ): 20 or less • Web width-to-thickness ratio of web 13 (b w / t w ): 300 or less • Aspect ratio (dB): 1.0 or higher, 10 or lower ·Plate thickness ratio (t f / t w ):1.0 or more and 5.0 or less

[0033] In the estimation device described in Patent Document 1, convergence calculations are required to determine the buckling stress. As a result of diligent research, the inventors have investigated a method to explicitly determine the buckling stress without using convergence calculations. Then, the estimation unit 52 considers the buckling restraint effect of the flanges 11 and 12 on the web 13 and calculates the width-to-thickness ratio of the web 13 (bw / t w We proposed a method to estimate buckling stress based on the first ratio (b). Specifically, the estimation unit 52 uses the first ratio (b w / B) and the second ratio (t f / t w Equation (21) calculates the variable X using the variable X and the width-to-thickness ratio (b w / t w Equation (22) using ) gives the buckling stress σ cr (N / mm 2 We estimate the following. Here, a1, a2, b1, and b2 are real constants.

[0034]

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[0035] Note that the first term "4.0" on the right-hand side of equation (22) is the buckling coefficient of a flat plate that is simply supported on two sides and subjected only to compressive force. In the second term on the right-hand side of equation (22), (a1X / (X+a2)) is added to 1. Since the value of (a1X / (X+a2)) is positive, the buckling coefficient corresponding to the H-shaped steel 10, (4.0+(a1X / (X+a2)) is greater than 4.0. This (a1X / (X+a2)) is the term in equation (22) that takes into account the buckling restraint effect on the webs of flanges 11 and 12. The buckling restraint effect is expressed as the first ratio (b) in equation (21). w / B) and the second ratio (t f / t w It is expressed using ).

[0036] Buckling stress σ estimated by FEM (Finite Element Method) cr,FEM Assuming this is the true value, this buckling stress σ cr,FEM The buckling stress σ was determined to be σ. cr,FEM The maximum error in the buckling stress estimated by the estimation device described in Patent Document 1 is approximately 7%. Buckling stress degree σ cr,FEM The buckling stress σ estimated by the estimation device 50 for this purpose crThe constants a1, a2, b1, and b2 were determined so that the maximum error would be approximately 7%. In this case, it is preferable that the constants a1, a2, b1, and b2 are within the following ranges: Constant a1 is between 0.685 and 0.715; Constant a2 is between 1.498 and 1.698; Constant b1 is between -0.437 and -0.287; and Constant b2 is between 4.012 and 4.512. Furthermore, the constants a1, a2, b1, and b2 are most preferably given the following values. The constant a1 is 0.7. The constant a2 is 1.548, the constant b1 is -0.337, and the constant b2 is 4.312 (hereinafter referred to as the optimal values ​​of constants a1, a2, b1, and b2).

[0037] Taking a safety factor into account, the first term on the right-hand side of equation (22) may be set to 4.0 or less. That is, equation (22) may be modified to look like equation (24) using a coefficient α (0 < α ≤ 1.0) that is greater than 0 and less than or equal to 1.0.

[0038]

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[0039] However, σ cr ’ The buckling stress σ is calculated considering the safety factor. cr This is the buckling stress of the H-shaped steel beam 10, calculated as a smaller value than the given value. In equations (21) and (22), the distance between the centers of the plate thickness is b. w Instead, the internal dimensions of web 13 b w '(=b w -t f ), you may also use H.

[0040] [4. Method for estimating buckling stress] Next, the method for estimating buckling stress in this embodiment (hereinafter simply referred to as the estimation method) will be described. Figure 5 is a flowchart of the estimation method S1. In estimation method S1, the buckling stress of an H-shaped steel beam 10 is estimated when only a compressive force F1 along the axial direction of the material acts as an external force. In the estimation method S1, an estimation step S5 is performed. In the estimation step S5, considering the buckling restraint effect on the webs of the flanges 11 and 12, based on the width-thickness ratio (b w / t w ) of the web 13, the buckling stress σ cr is estimated. In the estimation step S5, the buckling stress σ cr is estimated by equations (21) and (22). When the estimation step S5 ends, all steps of the estimation method S1 end, and the buckling stress σ cr of the H-shaped steel 10 is estimated.

[0041] 〔5. Estimation Results by the Estimation Device〕 Fig. 6 shows the estimation results by the estimation device 50. In Fig. 6, the horizontal axis represents the buckling stress σ cr (σ cr,cal )(N / mm 2 ) estimated by the estimation device 50, and the vertical axis represents the buckling stress σ cr,FEM (N / mm 2 ) estimated by the buckling eigenvalue analysis of FEM. The closer the buckling stress σ cr,cal is to the buckling stress σ cr,FEM , the higher the accuracy of the estimation of the buckling stress is considered to be. The round (〇) marks in Fig. 6 represent the relationship between the vertical axis and the horizontal axis in each analysis case for the H-shaped steel 10 in which the buckling eigenvalue analysis was performed. Also, the line L1 in Fig. 6 represents the state where the buckling stress σ cr,cal is equal to the buckling stress σ cr,FEM .

[0042] Note that for the shell model of the H-shaped steel 10 with a material axis direction length 50 times the self-weight, an analysis model with a mesh division of about 20 mm square was used for the buckling eigenvalue analysis of FEM. Here, the material axis direction of the analysis model is defined as the x-axis direction, the self-weight direction is defined as the y-axis direction, and the width direction of the flanges 11 and 12 is defined as the z-axis direction. At this time, the nodes at both ends in the x-axis direction of the analysis model were rigidly coupled to the representative nodes at the cross-section centers of both ends respectively. Then, the following restraint conditions (1) to (3) were given to the analysis model as geometric boundary conditions. Constrain the displacement in the z-axis direction at the nodes on the joint line between the flanges 11, 12 and the web 13. At one of the representative nodes at both ends of the H-shaped steel 10 in the x-axis direction, constrain the displacements in the y-axis and z-axis directions, and the rotations about the x-axis, y-axis, and z-axis. At the other representative node at both ends of the H-shaped steel 10 in the x-axis direction, constrain the displacements in the y-axis, z-axis, and x-axis directions, and the rotations about the x-axis, y-axis, and z-axis. Then, an analysis was performed by applying a uniform compressive force in the x-axis direction as a mechanical boundary condition to the analysis model.

[0043] In the H-shaped steel 10, the thickness t f etc. were changed, and for 2440 cases, the buckling stress σ cr,cal and the buckling stress σ cr,FEM were compared. The values of the constants a1, a2, b1, and b2 at this time were the optimal values of the constants a1, a2, b1, and b2 (constant a1 is 0.7, constant a2 is 1.548, constant b1 is -0.337, and constant b2 is 4.312). The buckling stress σ cr,FEM with respect to the buckling stress σ cr,cal had a maximum error of about 3.0%. It was found from FIG. 6 that the buckling stress σ cr,cal could be estimated with sufficient accuracy for practical use.

[0044] 〔6. Effects of this embodiment〕 As described above, in the estimation device 50, estimation method S1, and estimation program 61 of this embodiment, as a result of intensive studies by the inventors, the buckling restraint effect of the flanges 11, 12 on the web 13, which is represented by the first ratio and the second ratio, is considered. And based on the width-thickness ratio (b w / t w ) of the web 13, by estimating the buckling stress, it was found that the buckling stress σ cr of the H-shaped steel 10 that only receives the compressive force F1 can be estimated without performing a convergence calculation. Therefore, for the H-shaped steel 10 on which only the compressive force F1 acts, the buckling stress σ crIt is possible to estimate this.

[0045] Furthermore, the estimation unit 52 (in estimation step S5) uses the first ratio and the second ratio to calculate the variable X by equation (21), and this variable X and the width-to-thickness ratio (b w / t w Equation (22) using ) gives the buckling stress σ cr This is estimated. Thus, using equations (21) and (22), the buckling stress σ for the H-shaped steel 10 subjected only to compressive force F1 can be estimated without performing convergence calculations. cr It is possible to estimate this accurately. The constant a1 may be between 0.685 and 0.715, the constant a2 between 1.498 and 1.698, the constant b1 between -0.437 and -0.287, and the constant b2 between 4.012 and 4.512. In this case, the buckling stress σ may be calculated using the narrowed ranges of constants a1, a2, b1, and b2. cr This allows for a more accurate estimation.

[0046] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and modifications, combinations, deletions, etc., of the configuration are also included without departing from the spirit of the present invention. For example, in the above embodiment, equations (21) and (22) do not need to be used when estimating the buckling stress. The H-shaped cross-sectional member is assumed to be an H-shaped steel beam 10. However, the H-shaped cross-sectional member is not limited to an H-shaped steel beam 10; it may have a pair of flanges and a web. [Explanation of Symbols]

[0047] 10 H-shaped steel (H-shaped cross-section member) 11. First flange 12. Second flange 13 Web 50 Estimation device (device for estimating buckling stress) 52 Estimation part 61. Estimation Program (Program for estimating buckling stress) F1 Compression Force S1 Estimation method (Estimation method of seat bending strength) S5 Presumed Project

Claims

1. A buckling stress estimation device for estimating the buckling stress of an H-shaped cross section member having a pair of flanges and a web, where only a compressive force along the axial direction of the material acts as an external force, The system includes an estimation unit that estimates the buckling stress based on the width-to-thickness ratio of the web, taking into account the buckling restraint effect of the pair of flanges on the web. The buckling restraint effect is due to the distance b between the center thicknesses of the pair of flanges. ｗ The first ratio is the ratio of the width B of each of the pair of flanges, and the thickness t of each of the pair of flanges. ｆ and the thickness t of the web ｗ It is expressed using the second ratio, which is the ratio of , The estimation unit is a buckling stress estimation device that estimates the buckling stress σ cr by formula (1) which calculates the variable X using the first ratio and the second ratio, and formula (2) which uses the variable X and the width-to-thickness ratio. Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants. [Math 1]

2. constant a １ is between 0.685 and 0.715, and the constant a ２ is between 1.498 and 1.698, and the constant b １ is between -0.437 and -0.287, and the constant b ２ The buckling stress estimation device according to claim 1, wherein the value is 4.012 or more and 4.512 or less.

3. A method for estimating the buckling stress of an H-shaped cross section member having a pair of flanges and a web, and subjected only to a compressive force along the axial direction of the material as an external force, Considering the buckling restraint effect of the pair of flanges on the web, an estimation step is performed to estimate the buckling stress based on the width-to-thickness ratio of the web. The buckling restraint effect is the distance b between the centers of the plate thicknesses of the pair of flanges ｗ and the first ratio, which is the ratio of the width B of each of the pair of flanges, and the thickness t of each of the pair of flanges ｆ and the thickness t of the web ｗ is represented using the second ratio, which is the ratio thereof, A method for estimating buckling stress, wherein the estimation step involves estimating the buckling stress σcr by equation (3), which calculates the variable X using the first ratio and the second ratio, and equation (4), which uses the variable X and the width-to-thickness ratio (b w / t w). Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants. [Math 2]

4. constant a １ is between 0.685 and 0.715, and the constant a ２ is between 1.498 and 1.698, and the constant b １ is between -0.437 and -0.287, and the constant b ２ The method for estimating buckling stress according to claim 3, wherein the value is 4.012 or more and 4.512 or less.

5. A buckling stress estimation program for an estimation device that estimates the buckling stress of an H-shaped cross section member having a pair of flanges and a web, and subjected only to a compressive force along the axial direction of the material as an external force, The estimation device is configured to function as an estimation unit that estimates the buckling stress based on the width-to-thickness ratio of the web, taking into account the buckling restraint effect of the pair of flanges on the web. The buckling restraint effect is due to the distance b between the center thicknesses of the pair of flanges. ｗ The first ratio is the ratio of the width B of each of the pair of flanges, and the thickness t of each of the pair of flanges. ｆ and the thickness t of the web ｗ It is expressed using the second ratio, which is the ratio of , The estimation unit is a buckling stress estimation program that estimates the buckling stress σcr by formula (5), which calculates the variable X using the first ratio and the second ratio, and by formula (6), which uses the variable X and the width-to-thickness ratio (b w / t w). Here, E is the Young's modulus of the H-shaped cross-section member, ν is the Poisson's ratio of the H-shaped cross-section member, and a1, a2, b1, and b2 are constants. [Math 3]

6. constant a １ is between 0.685 and 0.715, and the constant a ２ is between 1.498 and 1.698, and the constant b １ is between -0.437 and -0.287, and the constant b ２ The buckling stress estimation program according to claim 5, wherein the value is 4.012 or more and 4.512 or less.

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