JP2024021553A - Beam design method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve design and inhibit bearing strength from reducing.

SOLUTION: A beam design method is for a beam that has flanges to be connected to a column. The aforesaid flange, in a specific range extending from the part to be connected to the aforesaid column along the longitudinal direction of the aforesaid beam, comprises a first widening part in which the flange width of one side in the width direction crossing the aforesaid longitudinal direction is widened, and a second widening part in which the flange width of the other side in the aforesaid width direction is widened. Where a shearing span ratio that is a ratio between a shear span and a beam depth takes a certain value, the relation between the proportion of the aforesaid first widening part to the sum value of the width of the aforesaid first widening part and the width of the aforesaid second widening part and the yield strength of the aforesaid beam is computed by an analysis to determine a value of the aforesaid proportion with which the analyzed value of the aforesaid yield strength surpasses a design value of a yield strength when the end part opposite to the aforesaid connection part of the aforesaid specific range is considered to be the dangerous cross section.

SELECTED DRAWING: Figure 6

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a beam design method.

The joints between beams and columns (hereinafter also referred to as beam end joints) are at risk of breaking due to large stress generated by external forces such as earthquakes. There are known devices that reduce stress at the mouth. Usually, beams with widened parts of the same width on the left and right sides (hereinafter also referred to as haunch beams of the same width) are joined to the columns so that their axes are aligned.

Also, for structural planning reasons, beams may be connected eccentrically to columns. In this case, if a haunch beam of the same width is applied, widening parts are provided on both sides of the beam, so even if the beam is eccentric, a large amount of space will be required between the beam and the outer wall, which is not desirable in terms of design. do not have. Therefore, a beam in which a widened portion is provided only on one side (hereinafter also referred to as a one-sided haunch beam) has been proposed (see, for example, Patent Document 1).

JP2017-61837A

Since single-sided haunch beams are susceptible to twisting, the yield strength can be significantly reduced depending on the dimensions of the beam. In order to ensure the same yield strength as a haunch beam of the same width, the cross section of the flange needs to be larger than that of a haunch beam of the same width, and more steel frames are required.

The present invention has been made in view of these problems, and its purpose is to improve the design and suppress the decline in yield strength.

The main invention for achieving the above object is a method of designing a beam having a flange joined to a column, wherein the flange is arranged in a predetermined range along the longitudinal direction of the beam from the joint with the column. The first widened part has a flange width widened on one side in the width direction intersecting the longitudinal direction, and the second widened part has a flange width widened on the other side in the width direction, and has a shear span. When the shear span ratio, which is the ratio to the beam width, is a certain value, the ratio of the width of the first widened part to the sum of the width of the first widened part and the width of the second widened part, and The relationship between the yield strength of the beam and the yield strength of the beam is determined by analysis, and the ratio by which the analytical value of the yield strength of the beam exceeds the design value of the yield strength with the end of the predetermined range opposite to the joint as a critical cross section. This is a method of designing beams characterized by the following.

Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

According to the present invention, it is possible to improve the design and suppress the decrease in yield strength.

FIG. 1A is a top view of the beam-column joint structure of this embodiment, and FIG. 1B is a perspective view of the beam-column joint structure. FIG. 3 is an explanatory diagram of the shape of the widened portion (haunch share ratio). It is an explanatory diagram of an analysis model. It is a figure showing an example of stress distribution by analysis. 5A to 5E are diagrams showing the relationship between load Q and deformation δ. 6A to 6E are diagrams showing the relationship between the ratio of the analytical value aQy of the yield strength to the calculated value cQy (aQy/cQy) and the haunches share x. FIG. 3 is an explanatory diagram of a range in which an analytical value of yield strength exceeds a calculated value.

At least the following matters will become clear from this specification and the accompanying drawings.

A method for designing a beam having a flange to be joined to a column, wherein the flange is arranged in a predetermined range along the longitudinal direction of the beam from the joint with the column on one side in the width direction intersecting the longitudinal direction. a first widened part in which the flange width on the other side in the width direction is widened, and a second widened part in which the flange width on the other side in the width direction is widened, and the shear span ratio, which is the ratio of the shear span to the beam width, is In the case of a certain value, the relationship between the ratio of the width of the first widened part to the sum of the width of the first widened part and the width of the second widened part and the yield strength of the beam is determined by analysis. , determining the ratio by which the analytical value of the yield strength of the beam exceeds the design value of the yield strength with an end opposite to the joint in the predetermined range as a critical cross section. Method.

According to such a beam design method, it is possible to improve the design and suppress a decrease in proof strength.

In this beam design method, when the shear span ratio is different from the certain value, the relationship between the ratio and the yield strength of the beam is determined by analysis, and the yield strength of the beam is calculated. It is desirable to find the ratio by which the analytical value exceeds the design value.

According to such a beam design method, it is possible to determine the percentage of yield strength exceeding the design value for each shear span ratio.

Such a beam design method, wherein the ratio at a value between the certain value and the another value, the ratio when the shear span ratio is the certain value, and the ratio when the shear span ratio is the other value. It is desirable to find it by interpolation with the above-mentioned ratio.

According to such a beam design method, it is possible to determine the ratio when the shear span ratio is between a certain value and another value.

In this method of designing a beam, it is preferable that the yield strength of the beam is a load when the tangential stiffness in the load-deformation relationship is reduced to 1/3 of the initial stiffness.

According to such a beam design method, if the load-deformation relationship is obtained, the yield strength can be determined, so a unified evaluation can be performed.

In this method of designing a beam, it is desirable that the beam be designed such that the joint portion yields after the end portion yields.

According to such a beam design method, the joint can be protected.

A method of designing such a beam, the beam being designed such that the load at which the total plastic bending strength of the joint part is reached is 1.2 times or more the load at which the total plastic bending strength of the end part is reached. It is desirable to do so.

According to such a beam design method, after the end portion yields, the joint portion can yield under a load that is 1.2 times or more greater than the load at that time.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

===This embodiment===
<About column-beam joint structure>
FIG. 1A is a top view of the column-beam joint structure of this embodiment, and FIG. 1B is a perspective view of the column-beam joint structure, both of which show a state in which a part of the frame consisting of columns and beams is taken out.

The column-beam joint structure of this embodiment includes a column 10 and a beam 20. In addition, among the directions (horizontal direction) intersecting the vertical direction, the direction along the longitudinal direction of the beam 20 is defined as the beam longitudinal direction (equivalent to the longitudinal direction), and the direction along the width direction of the beam 20 is defined as the beam width direction ( (equivalent to the width direction).

The pillar 10 is a vertical structural member that supports floors, beams, etc. in a structural building. As shown in the figure, the pillar 10 of this embodiment is a square steel pipe. Further, the pillar 10 has a diaphragm 12.

The diaphragm 12 is a steel plate that increases the rigidity of the joint of the pillar 10. The diaphragm 12 of this embodiment is a so-called through diaphragm, and is made by cutting a square steel pipe that constitutes the column 10, and sandwiching the cut square steel pipes between the two and welding them together. Further, the diaphragm 12 protrudes outward around the pillar 10. In other words, the diaphragm 12 increases the width of the column 10 (column width). A pair of upper and lower diaphragms 12 are provided at positions corresponding to the flanges 24 of the beam 20.

The beam 20 is a structural member that horizontally connects columns in a structural building. Furthermore, in this embodiment, the beam 20 is eccentrically joined to one side in the beam width direction (specifically, the side on which the widened portion 24a described later is formed) with respect to the center of the column 10.

As shown in FIGS. 1A and 1B, the length (shear span) of the beam 20 in the beam longitudinal direction is L, and the beam depth of the beam 20 is D. Furthermore, in the following description, the ratio between the shear span L and the beam depth D is referred to as a shear span ratio L/D.

Note that the shear span L is the length of a member that can be considered to have a constant shear force, and is the distance from the beam end joint to the recursion point (not shown) of the beam 20.

As shown in the figure, the beam 20 is made of iron and has an H-shaped cross section perpendicular to the longitudinal direction of the beam (so-called H-shaped steel), and has a web 22 and a flange 24 .

The web 22 is a plate-like member that connects the upper and lower flanges 24, and is orthogonal to the upper and lower flanges 24. Additionally, the web 22 is joined to the column 10. Note that a gusset plate (not shown) may be provided on the column 10 and the gusset plate and the web 22 may be joined using bolts and nuts. The web 22 allows shear forces to be borne. Further, the web 22 is provided at the center of the flange width (flange width B described later) of the flange 24. This makes it easier to evaluate the influence of the widened portions 24a and 24b, which will be described later. Further, the thickness of the web 22 is assumed to be _tw .

The flanges 24 are plate-like members arranged at the upper and lower edges of the beam 20, respectively. The end of the flange 24 in the beam longitudinal direction is joined to the face of the diaphragm 12 of the column 10 by welding. This joint (here, the joint with the diaphragm 12) is also referred to as a beam end joint (or haunch base end). As described above, the diaphragm 12 increases the width of the column 10. Therefore, by joining the flange 24 to the diaphragm 12, it is possible to make it more eccentric than when joining the flange 24 to the main body of the column 10.

Further, the flange 24 has a widened portion 24a and a widened portion 24b in a predetermined range along the longitudinal direction of the beam from the beam end joint (range indicated by _Lh in FIG. 1A). In addition, within the range where the widened portions 24a and 24b are provided on the flange 24 (range of length _Lh : equivalent to a predetermined range), the position corresponding to the end opposite to the haunch base end (widening start position) This is also called the tip of the corbel.

As shown in FIG. 1A, the width of the flange 24 is constant outside the predetermined range (L−L _h ), and the width of the flange 24 (corresponding to the flange width) is defined as B. Further, the thickness of the flange 24 is assumed to be _tf .

The widened portion 24a (corresponding to the first widened portion) is provided on one side of the flange 24 in the beam width direction in the predetermined range, and widens the flange width on the one side of the flange 24. As shown in FIG. 1A, the width (maximum width) of the widened portion 24a is B _h1 . Specifically, the width of the widened portion 24a increases from the tip of the corbel toward the pillar 10, and becomes the width B _h1 .

The widened portion 24b (corresponding to the second widened portion) is provided on the other side of the flange 24 in the beam width direction in the predetermined range, and widens the flange width on the other side of the flange 24. As shown in FIG. 1A, the width (maximum width) of the widened portion 24b is B _h2 . Specifically, the width of the widened portion 24b increases from the tip of the corbel toward the pillar 10, and becomes the width B _h2 .

As shown in FIG. 1A, in the beam 20 (flange 24) of this embodiment, the width B _h2 of the widened portion 24b is different from the width B _h1 of the widened portion 24a, and the width B _h1 of the widened portion 24a is It is smaller than the width B _h2 of the widened portion 24b (B _h1 <B _h2 ). Further, if the total width of the widened part (hereinafter also referred to as widened part width) is B _h (=B _h1 + B _h2 ), then the width BH of the haunch base end of the flange 24 is calculated using the flange width B and the widened part width B _h. Therefore, BH=B+B _h .

Note that the ratio of the width B _h1 of the width of the widened portion 24a to the widened portion width B _h (corresponding to the added value) is also referred to as haunch sharing ratio x (%), and in this embodiment, the following conditions are set. has been established.

When the shear span ratio L/D is 3 or more and less than 4.5,
{-10×(L/D)+45}≦x<50
When the shear span ratio L/D is 4.5 or more,
0<x<50
Thereby, as will be described later, it is possible to improve the design and suppress a decrease in yield strength.

=== Regarding the design and evaluation of the beam 20 ===
Next, the design and evaluation of the beam 20 of this embodiment will be explained.

<<About the shape of the widened part (haunch share ratio)>>
FIG. 2 is an explanatory diagram of the shape of the widened portion (corresponding proportion of haunches).

In the beam shown on the left side of FIG. 2, the widened portions on both sides of the flange have the same width (50% on one side). Hereinafter, such a beam (a beam in which the widened portions on both sides of the flange have the same width) will be referred to as a same-width haunch beam, or simply as a same-width haunch. Further, in the beam shown on the right side of FIG. 2, the widened portion is provided only on one side of the flange (0% on one side). Hereinafter, such a beam will be referred to as a one-sided haunch beam, or simply a one-sided haunch.

In this embodiment, as shown in the center of FIG. 2, the widened portions (widened portions 24a, 24b) on both sides of the flange 24 have different widths. In the following description, such a beam will be referred to as a different-width haunch beam, or simply as a different-width haunch.

In addition, in the same-width haunch, the different-width haunch, and the one-sided haunch shown in FIG. 2, the joining position of the column 10 and the web 22 is all the same (eccentric with respect to the center of the column 10). However, the joints between the flanges 24 (specifically, the widened portions 24a and 24b) and the diaphragm 12 are different from each other. Specifically, since the widened parts 24a and 24b have different widths in the same-width corbel, different-width corbel, and single-sided corbel, by changing the width of the diaphragm 12 (length in the beam width direction), it is possible to connect it to the entire flange. I have to. For example, in the same-width haunch, the width of the diaphragm 12 in the beam width direction (the amount of protrusion from the pillar 10) is the largest, and in the one-sided haunch, the width of the diaphragm 12 (the amount of protrusion from the pillar 10) is the smallest.

As shown in Figure 2, if the beam is eccentric to the column and placed near the outer wall, for example, the same-width haunch has widened parts on both sides, so for example, the beam and the outer wall are This requires a lot of space between them, which is not desirable in terms of design. On the other hand, a one-sided haunch can achieve a compact fit, but it is easily twisted, so there is a risk that the yield strength will decrease.

Therefore, in this embodiment, by using haunches of different widths, the design is improved and the reduction in yield strength is suppressed.

As shown in FIG. 2, if the width B _h1 of the widened portion 24a is x%, the width B _h2 of the widened portion 24b is (100−x)%. For example, when the width B _h1 is 20%, the width B _h2 of the widened portion 24b is 80%, and the ratio of the width B _h1 to the sum of the width B h1 and the width B _h2 (widened portion width B _{h )} is 20%. /(20+80)=1/5.

Hereinafter, an analysis (FEM analysis) using the ratio of the width B _h1 to the widened portion width B _h (haunch share ratio x%) as a parameter was conducted (FEM analysis) to confirm the influence of the haunch share ratio on the yield strength.

<<About analysis conditions>>
The conditions for analysis are shown below. Note that the unit of length (including width, thickness, etc.) is mm.
・Beam shape: Horizontal haunch beam (see Figure 2)
・Column cross section: □-600×600×32
・Beam cross section (beam depth D, flange width B, web thickness _tw , flange thickness _tf )
Cross section a: H-600 x 200 x 19 x 25 (SN490B)
Cross section b: H-600 x 200 x 12 x 25 (SN490B)
Cross section c: H-600 x 200 x 7.5 x 25 (SN490B)
・Beam eccentricity: Yes (eccentricity 0.33Dc (Dc: column diameter))
・Haunch sharing ratio (x%): 0 (one side), 5, 10, 15, 20, 30, 40, 50 (same width)
・Length of widened part L _h : 300 (=0.5D)
- Width of widened part B _h : With the tip of the corbel as the critical cross section (the part that yields first), the total plastic bending strength of the corbel base, taking into account the moment gradient, is 1.2 times the total plastic bending strength of the corbel tip. The widened portion width B _h was designed as follows. The reason why the total plastic bending strength at the end of the corbel is 1.2 times that of the tip of the corbel is because it is generally 490N/mm, and steel beams made of ^second grade steel (SN490B, etc.) are expected to have a strength increase of 1.2 times. (Refer to “Ministry of Land, Infrastructure, Transport and Tourism, National Institute for Land and Infrastructure Management, et al.: 2020 Edition Explanation of Structural Technical Standards for Buildings”). Note that it is desirable to design such that the load when the total plastic bending strength at the corbel base end is reached is 1.2 times or more the load when the total plastic bending strength at the corbel tip is reached. Thereby, after the tip of the corbel has yielded, it is possible to prevent the base end of the corbel from yielding under a load that is 1.2 times or more greater than the load applied at that time. Therefore, the corbel base end can be prevented from being destroyed (the corbel base end can be protected).

Hereinafter, a specific procedure for designing the widened portion width B _h will be shown.

The total plastic bending strength _Mf of only the flange at the base end of the haunch is expressed by the following formula (1).
M _f = BH x t _f x (D - t _f ) x σy (1)
Here, BH: Haunch base end width
t _f :Flange thickness
σy: Yield point or yield strength

Further, the required bending strength M _fd of the haunch base end is expressed by the following equation (2).
M _fd = α x M _p x L/(LL _h ) x σy (2)
Here, α: Yield strength increase rate (=1.2)
M _p : Total plastic bending strength at the tip of the haunch Z _p ×σy
Z _p : plasticity coefficient of corbel tip

From equations (1) and (2), the ratio M _f /M _fd of the total plastic bending strength M _f of only the flange at the corbel base end to the required bending strength M _fd at the corbel base end should be around 1.0. Then, the widened portion width B _h was determined.

<<About the analysis model>>
FIG. 3 is a schematic diagram of the analytical model. Although the figure shows a haunch beam of different widths (this embodiment), a similar model was used for a haunch beam of the same width and a haunch beam on one side.

<Analysis model>
・T-shaped frame (column length: 3000mm, beam length: span L)

<Cross-sectional quantities>
・Beam depth D (mm): 600
・Shear span L (mm): 1800, 2400, 2700, 3000, 3600
・Shear span ratio L/D: 3, 4, 4.5, 5, 6
・Diaphragm: Plate thickness 32mm (outer dimension 25mm)

<Analysis elements>
・A first-order quadrilateral shell element is used, and the beam flange within a range of 1200 mm from the beam end joint is divided into mesh at a 10 mm pitch, and the rest is divided at a 50 mm pitch.

<Boundary conditions>
・Column: The upper and lower ends restrict displacement and rotation around the z-axis.
- Beam: The y-direction end (beam end) restricts rotation around the y- and z-axes and applies forced displacement in the z-direction. In order to prevent the beam from buckling laterally, the displacement of the beam in the x direction was restrained at a position 1200 mm from the beam end joint.

Note that the x direction corresponds to the beam width direction in FIG. 1, the y direction corresponds to the beam longitudinal direction in FIG. 1, and the z direction corresponds to the vertical direction in FIG.

<<About analysis results>>
FIGS. 4A to 4C are diagrams showing examples of stress distributions obtained by analysis. Each figure shows the Mises stress distribution at the analytical value aQy of the yield strength of cross section b (H-600×200×12×25). FIG. 4A shows the results when x=50%, FIG. 4B shows the results when x=20%, and FIG. 4C shows the results when x=0%.

The following can be confirmed from FIGS. 4A to 4C.
- When x = 50% (same width haunch beam), stress is generated equally on the left and right sides of the beam.
- When x = 0% (one-sided haunch beam), stress is concentrated on either the left or right side of the beam.
- When 0<x<50 (different width haunch beam), the tendency is intermediate between the same width haunch beam and the single width haunch beam.

5A to 5E are diagrams showing the relationship between load Q and deformation δ. 5A to 5E show cases where the shear span ratio L/D is 3, 4, 4.5, 5, and 6, respectively. Again, the analysis results for cross section b (H-600×200×12×25) are shown, and illustration of the results for cross sections a and c is omitted.

The analytical value aQy of the yield strength is the load when the tangential stiffness in the load Q - deformation δ relationship decreases to 1/3 of the initial stiffness ("Building Research Institute, Japan Iron and Steel Federation: Structures of Steel Structured Buildings"). (Report of the Research Committee on Performance Evaluation Test Methods, April 2002). With this method, if the load-deformation relationship is obtained, the yield strength can be determined, so a unified evaluation can be performed. However, the method for determining yield strength is not limited to the above method.

Furthermore, the broken line in the figure represents the calculated yield strength cQy (equivalent to the design value) when the corbel tip is the critical cross section, and was calculated using the following equation (3).
cQy=cMy/(L- _Lh )...(3)
here,
cMy: Calculated yield bending moment of the uniform cross-section of the beam L: Shear span of the beam L _h : Length of the widening section Note that the uniform cross-section of the beam refers to the portion where the cross-sectional shape perpendicular to the longitudinal direction of the beam is the same (the main In the embodiment, this is a portion in which the widened portion is not formed on the flange).

The following can be confirmed from FIGS. 5A to 5E.
- The smaller the haunch share x is, the smaller the yield strength of the load Q-deformation δ relationship becomes.
- The smaller the shear span ratio L/D, the larger the difference in the load Q-deformation δ relationship due to the difference in haunch sharing ratio x.

For each shear span ratio L/D, from the load Q - deformation δ relationship, the haunches share ratio x and the yield strength of the beam (analytical value aQy: load when the tangential stiffness decreases to 1/3 of the initial stiffness) I sought a relationship with.

6A to 6E are diagrams showing the relationship between the ratio of the analytical value aQy of the yield strength to the calculated value cQy (aQy/cQy) and the haunches share x. Note that the horizontal axis of each figure is the haunch share x%, and the vertical axis is the ratio (aQy/cQy) between the analytical value aQy and the calculated value cQy.

6A to 6E show the results for shear span ratios L/D of 3, 4, 4.5, 5, and 6, respectively. Further, each figure shows the results for cross sections a, b, and c, respectively. If the vertical axis (aQy/cQy) is larger than 1 (that is, if the analytical value aQy of the yield strength exceeds the calculated value cQy), it can be said that there is no need to reduce the calculated yield strength.

The following can be confirmed from FIGS. 6A to 6E.
- The smaller the haunch share x is, the smaller the ratio between the analytical value aQy and the calculated value cQy (aQy/cQy) is, and the yield strength is lower.
- When the shear span ratio L/D=3, the analytical value aQy of the yield strength is lower than the calculated value cQy at x=10%. On the other hand, when x=15% or more, the analytical value aQy of the yield strength exceeds the calculated value cQy.
- In the case of shear span ratio L/D=4, the analytical value aQy of yield strength is lower than the calculated value cQy at x=0%. On the other hand, when x=5% or more, the analytical value aQy of the yield strength exceeds the calculated value cQy.
- In the case of shear span ratio L/D = 4.5, 5, 6, the analytical value aQy of yield strength exceeds the calculated value cQy even if x = 0%.

Note that when the shear span ratio L/D is between the conditions of this embodiment, the haunch sharing ratio ) can be obtained. For example, when the shear span ratio L/D is 3.5, the lower limit of the haunch share x when the shear span ratio L/D is 3, and the haunch share x when the shear span ratio L/D is 4. It can be determined by linear interpolation with the lower limit of .

FIG. 7 is an explanatory diagram of the range in which the analytical value aQy of the yield strength exceeds the calculated value cQy. The horizontal axis of the figure is the shear span ratio L/D, and the vertical axis is the corbel share ratio x (%). Areas where it has been confirmed that no reduction in calculated yield strength is required are hatched. The non-hatched areas are areas where it has been confirmed that a reduction in calculated yield strength is required (L/D≧3) or areas that have not been examined (L/D<3).

From Figure 7, the conditions under which it is not necessary to reduce the calculated yield strength are as follows:
・If the shear span ratio L/D is 3 or more and less than 4.5 (3≦L/D<4.5),
{-10×(L/D)+45}≦x<50
・If the shear span ratio L/D is 4.5 or more (L/D≧4.5),
0<x<50
It became.

That is, by determining the shear span ratio L/D and the corbel share ratio x so as to satisfy the above relationship, it is possible to improve the design and suppress a decrease in yield strength.

===About other embodiments===
The embodiments described above are intended to facilitate understanding of the present invention, and are not intended to be interpreted as limiting the present invention. It goes without saying that the present invention may be modified and improved without departing from its spirit, and that the present invention includes equivalents thereof. In particular, even the embodiments described below are included in the present invention.

In the above-described embodiment, the pillar 10 is a square steel pipe, but it is not limited to this; for example, it may be a round steel pipe or an H-shaped steel.

Further, in the embodiment described above, the diaphragm 12 is a through diaphragm, but the present invention is not limited to this. For example, it may be an inner diaphragm provided inside (inside) the column, or an outer diaphragm provided outside the column. In addition, in the case of an inner diaphragm, the flange 24 of the beam 20 will be joined not to the diaphragm but to the column body.

10 Column 12 Diaphragm 20 Beam 22 Web 24 Flange 24a Widened part (first widened part)
24b Widened part (second widened part)

Claims (6)

A method for designing a beam having a flange connected to a column, the method comprising:
The flange has a first widened part in which the flange width is widened on one side in the width direction intersecting the longitudinal direction in a predetermined range along the longitudinal direction of the beam from the joint with the pillar, and It has a second widened part in which the flange width on the other side is widened,
When the shear span ratio, which is the ratio of the shear span to the beam width, is a certain value, the ratio of the width of the first widened part to the sum of the width of the first widened part and the width of the second widened part and the yield strength of the beam is determined by analysis,
Determining the ratio in which the analytical value of the yield strength of the beam exceeds the design value of the yield strength with the end of the predetermined range opposite to the joint as a critical cross section;
A beam design method characterized by: The beam design method according to claim 1, comprising:
When the shear span ratio is a different value from the certain value, the relationship between the ratio and the yield strength of the beam is determined by analysis,
determining the percentage by which the analytical value of the yield strength of the beam exceeds the design value;
A beam design method characterized by: The beam design method according to claim 2,
The ratio when the shear span ratio is between the certain value and the another value is determined by interpolation between the ratio when the shear span ratio is the certain value and the ratio when the ratio is the other value.
A beam design method characterized by: A beam design method according to any one of claims 1 to 3, comprising:
The yield strength of the beam is the load when the tangential stiffness of the load-deformation relationship decreases to 1/3 of the initial stiffness.
A beam design method characterized by: A beam design method according to any one of claims 1 to 3, comprising:
designing the joint to yield after the end yields;
A beam design method characterized by: The beam design method according to claim 5,
Designed so that the load when the total plastic bending strength of the joint part is reached is 1.2 times or more the load when the total plastic bending strength of the end part is reached.
A beam design method characterized by:

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