JP2022111782A - Hot-rolled steel strip, H-shaped steel, floor structure, floor structure design method, and floor structure construction method - Google Patents

Abstract

To provide an H-shaped steel that can be preferably used as a structural element even when a width-thickness ratio of a web is equal to or larger than a certain value.SOLUTION: Provided is an H-shaped steel 25. A maximum strength that the H-shaped steel 25 can bear is equal to or larger than an elastic local buckling bearing force of the H-shaped steel 25. In a case where a load is applied to the H-shaped steel 25, rigidity of the H-shaped steel 25 decreases when the load becomes equal to or larger than the elastic local buckling bearing force. the H-shaped steel 25 has a function to be restored to an initial position in a case where the load is removed before the load applied to the H-shaped steel 25 reaches the maximum bearing force of the H-shaped steel 25.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a hot-rolled steel strip, an H-section steel, a floor structure, a floor structure design method, and a floor structure construction method.

H-section steel, which has high bending rigidity and bending strength per steel mass, is widely used for small beams that support floors of buildings from the viewpoint of suppressing deflection and vibration of the floor. H-beam steel has a cross-sectional specification that is excellent in geometrical moment of inertia and section modulus, and the thinner the web and the thicker the flange, the higher the cross-sectional efficiency. However, H-beams with thin webs and flanges are poor in plastic deformation performance after reaching the maximum yield strength, and are subject to local external forces unexpected by the designer (for example, overloaded trucks running). When a heavy concentrated load acts on the H-section steel, there is a risk that the H-section steel will fracture early. For this reason, in general steel-framed buildings, an upper limit is set for the width-thickness ratio of the plate elements that make up the H-section steel cross section, and even if an unexpected local load acts, the redundancy of the H-section steel is maintained. It is common to secure the web, and there is a limit to the thinning of the web.
For example, in Patent Document 1, when the width-to-thickness ratio of the web is greater than a certain value (for example, 75), the web may undergo local buckling at an early stage and the plastic deformation capability may be insufficient. It states that it is necessary to take measures such as stiffening.

Japanese Unexamined Patent Application Publication No. 2011-001792

However, the H-section steel having a large width-to-thickness ratio of the web can reduce the mass per unit length of the H-section steel while maintaining the magnitude of the moment of inertia of area, for example. For this reason, even if the yield strength of H-section steel is sacrificed, it is conceivable that H-section steel with a web width-to-thickness ratio greater than a certain value may be used as a structural element of a building by utilizing its high rigidity.

The present invention has been made in view of such problems, and includes an H-section steel that can be preferably used as a structural element even if the width-to-thickness ratio of the web is greater than a certain value, and this H-section steel An object of the present invention is to provide a floor structure, a hot-rolled steel strip used for this H-section steel, a design method for this floor structure, and a construction method for this floor structure.

In order to solve the above problems, the present invention proposes the following means.
In the H-section steel of the present invention, when the Young's modulus of the material used in the H-section steel is E and the yield strength of the material is _σy , the load acting on the H-section steel is If it is equal to or greater than the elastic local buckling strength of the H-section steel, elastic local buckling occurs in the H-section steel and the rigidity of the H-section steel decreases, and the load is less than the maximum strength that the member can withstand. In the case, the H-beam is characterized by elastic recovery when the load is removed.

According to this invention, when the width-to-thickness ratio of the web is relatively large, when an external force acts on the building due to a natural disaster such as an earthquake or wind or a disturbance such as the passage of vehicles inside the building, the H-section steel is When the applied load exceeds the elastic local buckling strength, elastic local buckling occurs in the H-section steel, reducing the rigidity of the H-section steel. redistribution is caused, and the load concentration on the H-beam is relieved, thereby transferring force to other beams adjacent to the H-beam, for example. As a result, it is possible to alleviate the concentration of the load on a specific H-section steel. It is possible to prevent the H-section steel from being damaged by a large load unexpected by the designer acting on the section steel.
And if the applied load is less than the maximum yield strength of the H-section steel, the H-section steel will elastically restore to its initial state when the load is removed. For this reason, it is possible to maintain the same function against repeated natural disasters such as earthquakes without causing serious structural damage to the H-section steel, making it possible to use the H-section steel preferably as a structural element for a long period of time. can.

Further, the floor structure design method of the present invention designs a floor structure comprising H-section steel used as a beam, a support beam, and a floor slab joined to the H-section steel and the support beam, respectively. In the floor structure design method, when the load acting on the H-section steel is equal to or greater than the elastic local buckling capacity of the H-section steel, local buckling occurs in the H-section steel. designed to reduce the stiffness of the H-beam so that at least a portion of the load is transferred to the support beam through the floor slab, until the load is less than the elastic local buckling capacity The H-section steel is characterized by being designed to restore to the initial position when reduced.
In addition, a floor structure construction method of the present invention constructs a floor structure comprising H-shaped steel used as a beam, supporting beams, and floor slabs joined to the H-shaped steel and the supporting beam, respectively. In the floor structure construction method, when the load acting on the H-section steel is equal to or greater than the elastic local buckling strength of the H-section steel, local buckling occurs in the H-section steel. By reducing the rigidity of the H-section steel, construction is performed so that at least part of the load is transmitted to the support beams through the floor slab, and the load is reduced to less than the elastic local buckling capacity. The H-section steel is constructed so as to restore to the initial position when it is reduced.

According to these inventions, when the width-to-thickness ratio of the web is relatively large, local buckling occurs in the H-section steel when the load acting on the H-section steel is equal to or greater than the elastic local buckling capacity. It is designed (constructed) so that at least part of this load acts on the support beams through the floor slab by reducing the rigidity of the H-beam. Therefore, for example, load redistribution within a building in which H-beams are used can be promoted to prevent relatively large loads from acting on the H-beams.
Then, when the applied load is reduced to less than the elastic local buckling strength, the H-section steel is elastically restored. For this reason, it is possible to maintain the same function against repeated natural disasters such as earthquakes without causing serious structural damage to the H-section steel, making it possible to use the H-section steel preferably as a structural element for a long period of time. can.

Further, in the H-section steel, the H-section steel includes the web and a pair of flanges arranged to sandwich the web, and by satisfying formula (1), the H When the magnitude of the load acting on the shaped steel is equal to or greater than the elastic local buckling strength, and when the magnitude of the load acting on the H-shaped steel among the loads is smaller than the elastic local buckling strength. In comparison, the proportion of the load acting on the H-section steel is reduced, and the load is reduced before the magnitude of the load acting on the H-section steel reaches the maximum yield strength of the H-section steel. When removed, the H-beam may be designed to recover to its original state without serious structural damage.
where E: Young's modulus of the H-section steel, _σy : yield strength of the H-section steel, _bw : width of the web, _tw : thickness of the web, _bf : width of the pair of flanges, t _f : the thickness of the pair of flanges.

According to this invention, the inventors found out the following as a result of earnest studies. That is, since the H-section steel satisfies the inequality on the left side in formula (1), when the load is greater than the elastic local buckling strength, the maximum strength of the H-section steel always exceeds the elastic local buckling strength. Therefore, when a load is applied to the H-section steel, the H-section steel undergoes elastic local buckling and exhibits the effect of lowering its rigidity. can be restored to the initial state (position) without By satisfying the inequality on the right side of formula (1), the H-section steel can reduce the deflection occurring in the center of the web to 3 mm or less, which is equal to or less than that of the current H-section steel for building structures. Therefore, it is possible to eliminate the risk that local deformation of the web due to thinning will impair workability.

Further, in the H-section steel, the H-section steel includes the web and a pair of flanges arranged to sandwich the web, and by satisfying formula (2), the load is applied to the elastic local When the load is equal to or greater than the buckling strength, the proportion of the load acting on the H-section steel is reduced, and when the load is less than the elastic local buckling strength, the load is elastic when the load is removed. can be restored to
However, E: Young's modulus of the H-section steel, _σy : yield strength of the H-section steel, _tw : thickness of the web, _bf : width of the pair of flanges, _tf : width of the pair of flanges thickness.

According to this invention, the inventors found out the following as a result of earnest studies. That is, since the H-section steel satisfies the inequality on the left side of formula (2), when the load is greater than the elastic local buckling strength, the maximum strength of the H-section steel always exceeds the elastic local buckling strength. Therefore, when a load is applied to the H-section steel, the H-section steel undergoes elastic local buckling and exhibits the effect of lowering its rigidity. can be restored to its original state. Then, when the H-section steel satisfies the inequality on the right side of the formula (2), the thickness of the flange can be made equal to or greater than the thickness of the web, and the sectional performance of the H-section steel, such as the moment of inertia of area, can be enhanced. For example, if the H-beam is a welded assembled H-beam, the flange can be completely melted through its thickness when the web is welded to the flange, preventing holes in the flange.

Moreover, in the H-section steel, the H-section steel may be a small beam.
According to the present invention, it is possible to provide a small beam that can be preferably used as a structural element even if the width-to-thickness ratio of the web is greater than a certain value.

In the H-section steel, the H-section steel may be a weld assembled H-section steel in which the web and a pair of flanges are welded to each other.
ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide a welded assembly H-section steel that can be preferably used as a structural element even if the width-to-thickness ratio of the web is greater than a certain value.

Moreover, in the H-section steel, the yield strength _σy of the H-section steel may be 235 MPa or more and 1000 MPa or less.
According to the present invention, the yield strength σ _y of general H-section steel can be handled.

Further, the hot-rolled steel strip of the present invention is characterized by being used for the web or the pair of flanges of the H-section steel, which is the welded assembled H-section steel described above.
According to the present invention, even if the width-to-thickness ratio of the web is greater than a certain value, it can be preferably used as a structural element. Obi can be provided.

Further, a floor structure of the present invention includes any one of the above-described H-section steel, and a floor slab supported from below by an upper flange of the H-section steel and joined to the upper flange, The movement of the upper flange along the horizontal plane is constrained by the floor slab.
According to this invention, in the floor structure, the movement of the upper flange along the horizontal plane is restrained by the floor slab. Therefore, for example, it is possible to suppress elastic local buckling of the H-section steel.

Further, another floor structure of the present invention includes the H-section steel according to any one of the above and a pair of flanges of the H-section steel at at least one end in the axial direction of the H-section steel. and a support member joined or in contact with at least one end of the H-section steel, wherein compressive force or tensile force of the H-section steel is transmitted between the at least one end of the H-section steel and the support member. is characterized by
According to this invention, in a floor structure, a compressive or tensile force from a support member is transmitted to at least one of a pair of flanges at at least one end of the H-beam. Therefore, H-section steel can be used as a structural element that withstands compressive or tensile forces.

According to the hot-rolled steel strip, H-section steel, floor structure, floor structure design method, and floor structure construction method of the present invention, even if the width-thickness ratio of the web is greater than a certain value, the H-section steel is It can be preferably used as.

1 is a perspective view of a building provided with a floor structure according to one embodiment of the invention; FIG. 2 is a cross-sectional view taken along a cutting line A1-A1 in FIG. 1; FIG. It is sectional drawing orthogonal to the material axial direction of H-shaped steel in the said floor structure. It is a perspective view which shows the outline|summary of the analysis model of the same H-section steel. It is a figure which shows the analysis result using the same analysis model. FIG. 5 is a diagram showing the relationship between the web yield strength ratio and the flange yield strength ratio in an analysis case in which the maximum yield strength exceeds the elastic local buckling yield strength; FIG. 5 is a diagram showing the relationship between the web yield strength ratio and the flange yield strength ratio in an analysis case where the maximum yield strength is lower than the elastic local buckling strength; FIG. 4 is a diagram showing an outline of a model considering web deflection. FIG. 5 is a diagram showing the relationship between the width-thickness ratio and the area ratio of the web;

An embodiment of a hot-rolled steel strip, an H-section steel, a floor structure, a method for designing a floor structure, and a method for constructing a floor structure according to the present invention will be described below with reference to FIGS.
In the following description, the floor structure design method is simply referred to as the design method, and the floor structure construction method is simply referred to as the construction method.

[1. Configuration of hot-rolled steel strip, H-shaped steel, and floor structure]
A floor structure 2 is used in a building 1, as shown in FIG. In FIG. 1, a floor slab 35, which will be described later, is indicated by a chain double-dashed line.
As shown in FIGS. 1 and 2, the floor structure 2 includes a plurality of column members 10, a plurality of large beams (supporting members) 15, a plurality of small H-shaped steel beams 25, and a floor slab 35. Prepare.
Note that the floor structure 2 does not have to include the plurality of column members 10 . The floor structure 2 may also be free of multiple girders 15 or H-beams 25 .

The plurality of column members 10 are made of steel, RC (Reinforced Concrete), SRC (Steel Reinforced Concrete), CFT (Concrete Filled Steel Tube), or the like. For example, the multiple column members 10 extend along the vertical direction. The plurality of columnar members 10 are arranged at the intersections of a plurality of straight lines forming a lattice in plan view (lattice pattern).
For example, the girders 15 are made of H-beam steel. The girders 15 extend in a direction along the horizontal plane. The girders 15 have a first web 16 , a first upper flange 17 and a first lower flange 18 . A plurality of girders 15 are constructed across the plurality of column members 10 . A plurality of girders 15 are arranged in a frame shape in a plan view and surround a predetermined area.
A gusset plate 19 is joined to the first web 16 and the like of the girders 15 by welding or the like (see FIG. 2).

The H-section steel 25 is a welded assembled H-section steel. The H-section steel 25 extends in the axial direction of the H-section steel 25 along the horizontal plane. The H-section steel 25 has a second web (web) 26 , a second upper flange (flange, upper flange) 27 and a second lower flange (flange) 28 .
As shown in FIG. 2 , the second web 26 is formed in a rectangular plate shape when viewed in the thickness direction of the second web 26 . The second web 26 is arranged such that the thickness direction of the second web 26 is along the horizontal plane.
The flanges 27 and 28 are formed in a flat plate shape, and arranged such that the thickness direction of the flanges 27 and 28 extends along the vertical direction. The second lower flange 28 is arranged below the second upper flange 27 . The flanges 27 and 28 are arranged so as to vertically sandwich the second web 26 . The second web 26 connects the widthwise center of the lower surface of the second upper flange 27 and the widthwise center of the upper surface of the second lower flange 28 .

For the second web 26 and/or the flanges 27 and 28 configured as described above, a hot-rolled steel strip (not shown) (a strip of hot-rolled steel plate) is used.

A plurality of H-shaped steels 25 are used in the building 1 . The H-section steel 25 is manufactured by welding and joining together a second web 26 and flanges 27, 28 that are separately manufactured in advance.
As shown in FIGS. 1 and 2, the plurality of H-section steels 25 are provided inside the area surrounded by the plurality of large girders 15 (within the area surrounded by the plurality of large girders 15). A plurality of H-shaped steels 25 are arranged side by side with a space therebetween.
Both ends of the plurality of H-section steels 25 are constructed on the plurality of large beams 15 . A plurality of H-beams 25 are pinned to a plurality of girders 15 . Specifically, as shown in FIG. 2, the second web 26 of the H-section steel 25 and the gusset plate 19 are joined together by fastening members 29 including high-strength bolts and the like. The second upper flange 27 abuts and contacts the first upper flange 17 of the girders 15 from the side of the first upper flange 17 . The second lower flange 28 is arranged above the first lower flange 18 of the girders 15 .
That is, the second upper flanges 27 are in contact with the first upper flanges 17 of the girders 15 at both axial ends of the H-shaped steel 25 .

The second upper flange 27 may be in contact with the first upper flange 17 of the girder 15 at one axial end of the H-section steel 25 . Not only the second upper flange 27 but also the second lower flange 28 may contact the first lower flange 18 of the girder 15 .
The second upper flange 27 may be joined to the first upper flange 17 of the girders 15 by welding or the like.

Here, as shown in FIG. 3, the dimensions and the like of the H-section steel 25 in a cross section orthogonal to the material axis direction are defined. It should be noted that SI units such as "m" are preferably used for the units of length and the like to be described below.
The thickness of the second web 26 is defined as _tw . The width of the second web 26 (the length in the direction along the thickness of the second web 26 and in the direction orthogonal to the material axis direction) is defined as _bw . The thickness of the flanges 27, 28 is defined as _tf . The width of the flanges 27 and 28 (the length in the direction along the thickness of the flanges 27 and 28 and the length in the direction orthogonal to the material axial direction) is defined as _bf . A Young's modulus of the H-shaped steel 25 (the second web 26 and the flanges 27, 28) is defined as E. The yield strength of the H-section steel 25 is defined as _σy .
The width-to-thickness ratio (b _w /t _w ) of the second web 26 is 4.4√(E/σ _y ) or more. More preferably, the width-thickness ratio of the second web 26 is 5.3√(E/σ _y ) or more. For example, the width-to-thickness ratio of the second web 26 is 200 or less.
The yield strength _σy of the H-section steel 25 is 235 MPa (megapascal) or more and 1000 MPa or less.

Below, among the plurality of H-section steels 25, the H-section steel 25 closest to which a load (concentrated load) acts may be referred to as the H-section steel 25A. Of the plurality of H-section steels 25, those other than the H-section steel 25A may be called H-section steel (support beam) 25B.

As shown in FIG. 2 , the floor slab 35 is provided above the plurality of girders 15 and the plurality of H-beams 25 . The floor slab 35 is supported from below by the first upper flanges 17 of the plurality of girders 15 and the second upper flanges 27 of the plurality of H-section steels 25 . In this embodiment, floor slab 35 is a composite deck slab. The floor slab 35 comprises a deck plate 36 , concrete 37 , reinforcing bars 38 and shear connectors 39 .
The deck plate 36 is formed by bending a steel plate or the like. The deck plate 36 is placed on the first upper flange 17 of the girders 15 and the second upper flange 27 of the H-beam 25 respectively.
The concrete 37 is formed in a flat plate shape whose thickness direction is along the vertical direction. Concrete 37 is placed on deck plate 36 .

The floor slab 35 has a plurality of reinforcing bars 38 . A first reinforcing bar 38 a that is part of the plurality of reinforcing bars 38 extends along a certain H-section steel 25 among the plurality of H-section steels 25 . A second reinforcing bar 38b, which is the remainder of the plurality of reinforcing bars 38, extends in a direction orthogonal to the first reinforcing bar 38a. The first reinforcing bars 38 a and the second reinforcing bars 38 b are embedded in the concrete 37 .
For example, shear connector 39 is a headed stud. The floor slab 35 has a plurality of shear connectors 39 . The lower ends of the shear connectors 39 are fixed to the upper surfaces of the first upper flange 17 of the girders 15 and the second upper flange 27 of the H-section steel 25 with a space therebetween. Shear connector 39 is embedded in concrete 37 through deck plate 36 .
The floor slab 35 is joined to the first upper flange 17 and the second upper flange 27 as described above. The movement of the first upper flange 17 and the second upper flange 27 along the horizontal plane is restrained by the floor slab 35 .

In the floor structure 2 configured as described above, compressive force or tensile force of the H-section steel 25 is transmitted between both axial ends of the H-section steel 25 and the girders 15 .

[2. Examination of the relationship between the cross-sectional shape of the H-shaped steel and the yield strength of the H-shaped steel]
In the following, the results of examining the relationship between the cross-sectional shape such as the width-thickness ratio of the H-section steel 25A and the elastic local buckling strength (load threshold) and the maximum strength of the H-section steel 25A will be described.
Note that the second web 26 may be simply referred to as the web 26 below. Similarly, the second upper flange 27 may be simply referred to as the upper flange 27, the second lower flange 28 may be simply referred to as the lower flange 28, and the H-section steel 25A may be simply referred to as the H-section steel 25.

[2.1. Effect of rigidity reduction due to elastic local buckling]
FIG. 4 shows an overview of the analysis model of the H-section steel 25. As shown in FIG. An axis along the material axial direction of the H-section steel 25 is defined as a Y-axis. The axis along the thickness of web 26 is defined as the X-axis. The axis along the thickness of flanges 27, 28 is defined as the Z-axis.
Analysis conditions were set as follows.
・The cross-sectional shape perpendicular to the Y-axis of the H-shaped steel 25 was H-700×175×3.2×4.5.
・Assuming the case where four-point bending acts on the H-shaped steel 25, considering its symmetry, the boundary conditions are given as shown in Fig. 4, and the web (A in the figure) is forcibly deformed in the Z-axis direction. An elasto-plastic analysis was performed to give
- It is assumed that the movement of the upper flange 27 along the horizontal plane (the direction along the X-axis in FIG. 4) is constrained by the floor slab 35 .

Using the analysis model, a large deformation elastic-plastic analysis was performed by the finite element method (FEM).
FIG. 5 shows the analysis results. In FIG. 5 , the horizontal axis represents the displacement (mm) of the end of the H-section steel 25 in the vertical direction, and the vertical axis represents the load (kN) acting on the H-section steel 25 . In FIG. 5, the analysis result is indicated by a solid line L1. A line extending the initial stiffness of the analysis result is indicated by a dotted line L2. The vertical axis shows the bending moment _Fcr when the compressive stress generated in the H-section steel 25 by the bending moment F1 reaches the elastic local buckling strength _σcr . The elastic local buckling strength σ _cr is an eigenvalue obtained by buckling eigenvalue analysis, and the bending moment F _cr is a value obtained by multiplying the elastic local buckling strength σ _cr by the section modulus of the H-section steel.

Based on FIG. 5, the relationship between the load (bending moment F1) and the displacement of the H-section steel 25 was confirmed. When the bending moment F1 acts on the H-section steel 25, when the bending moment F1 reaches the elastic local buckling strength _Fcr (when the bending moment F1 becomes equal to or greater than the elastic local buckling strength _Fcr ), the rigidity of the H-section steel 25 decreases (see region R1 in FIG. 5), but as the load increases thereafter, the yield strength (bending moment F1) of the H-section steel 25 increases, and it is confirmed that the bending moment F1 reaches the maximum yield strength _Fmax . can. The maximum yield strength F _max means the maximum value of yield strength that the H-section steel 25 can withstand.
In this way, the H-section steel having a specification in which the elastic local buckling strength _Fcr is lower than the maximum strength _Fmax that the H-section steel 25 can bear (the maximum strength _Fmax is equal to or greater than the elastic local buckling strength _Fcr ) 25 is used. Then, when the bending moment F1 acts on the H-section steel 25, it is possible to reliably lower the bending rigidity of the H-section steel 25 before reaching the maximum yield strength _Fmax .

[2.2. Restriction on the lower limit of the width-thickness ratio of H-shaped steel at which the elastic local buckling strength is smaller than the maximum strength]
The lower limit of the width-to-thickness ratio of the web 26 and the flanges 27 and 28, at which the effect of [2.1] is exhibited, will be analyzed.
Analysis was performed under the following conditions.
・The height of the H-shaped steel 25 was set to 700 mm.
・The width of the H-shaped steel 25 was set to four types of 175 mm, 350 mm, 525 mm, and 700 mm.
- The thickness _tf of the flanges 27 and 28 was set to six types of 3.2 mm, 4.5 mm, 6 mm, 9 mm, 12 mm, and 16 mm.
- The thickness _tw of the web 26 was 3.2 mm, 4.5 mm, 6 mm, and 9 mm.
The thickness _tf of the flanges 27 and 28 is set to be greater than the thickness _tw of the web 26. FIG.
- The yield strength _σy of the H-shaped steel 25 was set to 235 MPa, 295 MPa, 325 MPa, 385 MPa, 440 MPa, and 500 MPa.
・It is assumed that an equal bending moment acts on the H-beam 25.

FIG. 6 shows an analysis case in which the maximum strength F _max exceeded the elastic local buckling strength σ _cr among the obtained analysis results. In FIG. 6, the horizontal axis is the square root of the value obtained by dividing the material strength (yield strength) σ _y of the web 26 by the elastic local buckling strength σ _{cr_web} of the web 26 (√(σ _y /σ _{cr_web} )) (hereinafter referred to as web (referred to as the generalized width-thickness ratio of ). The material strength _σy means a 0.2% offset (0.2% proof stress according to JIS Z 2241) obtained from a tensile test of the material. The vertical axis represents the square root of the value obtained by dividing the material strength σ _y of the flanges 27 and 28 by the elastic local buckling strength σ _{cr_flange} of the flanges 27 and 28 (√(σ _y /σ _{cr_flange} )) (hereinafter referred to as the generalized width of the flange thickness ratio). Note that the elastic local buckling strength σ _{cr_web} and the elastic local buckling strength σ _{cr_flange} are values obtained by the formulas (3) and (4).
However, ν is the Poisson's ratio of the H-section steel 25 .

FIG. 7 shows an analysis case in which the maximum yield strength F _max is lower than the elastic local buckling strength F _cr among the obtained analysis results. The horizontal and vertical axes in FIG. 7 are the same as the horizontal and vertical axes in FIG. 6, respectively.

From FIG. 6, the analysis results where the maximum strength F _max exceeds the elastic local buckling strength F _cr are areas where the generalized width-thickness ratio of the web is 0.94 or more, or the generalized width-thickness ratio of the flange is 1.46 or more. is found to exist in In addition, when combined with FIG. 7, the generalized width-thickness ratio of the web is 1.15 or more, or the generalized width-thickness ratio of the flange is 1.46 or more, so that the maximum strength F _max It was found that the analysis result exceeded the buckling strength _Fcr .

Considering that the Young's modulus E of the steel material is 205000 N/mm ² and the Poisson's ratio ν is 0.3, the calculation is performed by substituting the generalized width-thickness ratio of the web with the formula (4) and the physical properties of the steel material. Then, the lower limit of the generalized width-thickness ratio of the web for the maximum strength F _max to be greater than the elastic local buckling strength F _cr is given by the width-thickness ratio of the web 26 (b _w /t _w ).

Considering that the Young's modulus E of the steel material is 205000 N/mm ² and the Poisson's ratio ν is 0.3, the generalized width-thickness ratio of the flange is obtained by formula (3) and the physical properties of the steel material. When calculating by substituting the values, the lower limit of the generalized width-thickness ratio of the flanges for the maximum strength _Fmax to be larger than the elastic local buckling strength _Fcr is obtained from the flanges 27 and 28 as shown in the equation (6). width-thickness ratio (b _f /t _f ).

By satisfying the formula (5) or (6), when the load acting on the H-section steel 25A is equal to or greater than the elastic local buckling strength _Fcr , the proportion of the load acting on the H-section steel 25A is reduced. In addition, when the load is removed, the H-section steel 25A can be restored to its initial state (initial position) without significant structural damage. That is, the H-section steel _25A has a restoring function ( functions).

In this case, when the load acting on the H-section steel 25A is equal to or greater than the elastic local buckling resistance _σcr , the plate elements forming the cross section of the member deform out of the plane due to the elastic local buckling of the H-section steel 25A. As a result, the stress distribution in the cross section becomes uneven, stress redistribution occurs in the cross section, and the flexural rigidity of the member as a whole decreases. Then, load redistribution within the building 1 is promoted to prevent damage to the H-section steel 25A.
These stiffness reductions are caused by elastic local buckling of the H-section steel 25 and not by member yielding of the H-section steel 25 . Therefore, when the load acting on the H-section steel 25A is removed, the H-section steel 25A restores to its initial state causing significant structural damage.

[2.3. Upper Limit of Width-thickness Ratio of Web]
Subsequently, the upper limit of the width-to-thickness ratio of the web was analyzed.
The web 26 has a pre-deflection due to the welded assembly. According to the existing document 1 (JIS G 3353: 2011 Welded lightweight H-section steel for general structure), in the welded and assembled lightweight H-section steel, the maximum out-of-plane deflection occurring in the web is controlled at 2 mm or less. .
Therefore, it is considered that even in the weld assembled H-section steel, a maximum deflection of about 2 mm occurs due to the weld assembly.
Considering that the weight of the upper flange 27 or the lower flange 28 acts on the web 26, which is initially flexed by this welding assembly, the original flexure (deflection) of the web 26 is further increased.

Therefore, for example, if the web 26 is intended to be extremely thin, the web 26 cannot support the weight of the upper flange 27 or the lower flange 28, making it difficult to maintain the shape of the H-shaped steel 25. be.
Therefore, the dimensions of the web 26 and the flanges 27 and 28 were changed as follows.
- The width _bf of the flanges 27 and 28 was varied between 100 mm and 1000 mm at intervals of 100 mm.
- The width _bw of the web 26 was varied between 100 mm and 1000 mm at intervals of 100 mm.
- The thickness t _w of the web 26 and the thickness t _f of the flanges 27 and 28 are set to 0.4 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.6 mm, 2.3 mm, 3.2 mm, 4 .5 mm, 6 mm, 9 mm, 12 mm, 16 mm, 19 mm, 22 mm, 25 mm, and 28 mm.
The cross-sectional specifications of the H-shaped steel 25 in which the deflection of the web 26 exceeds 3 mm were investigated when the dimensions were changed as described above.

In the past document 2 (JIS G 3192:2014 Shapes, dimensions, masses and their tolerances of hot-rolled shaped steel), shape irregularities in the out-of-plane direction of the web of members having an H-shaped steel cross section are allowed up to 3 mm. ing. Considering this, when the weight of the upper flange 27 or the lower flange 28 acts on the H-shaped steel 25 (web 26) that has an initial deflection (= 2 mm) due to welding assembly, the out-of-plane deformation of the web 26 is 3 mm We investigated the following member specifications.

Figure 8 shows an overview of the model considered. In this study, the following conditions were set.
- The web 26 is regarded as an infinite length plate element simply supported at both ends in the vertical direction.
• _The initial deflection of the web 26 was taken as δ1.
Assuming a load condition in which the self-weight F3 of the flanges 27 and 28 acts on the ends of the web 26, the cross-sectional shape of the H-section steel 25 where the deflection δ2 generated in the central portion of the web 26 is greater than ₃ mm was investigated. .

FIG. 9 shows the survey results. In FIG. 9, the horizontal axis represents the width-to-thickness ratio of the web 26, and the vertical axis represents the value of ( _{bftf /} ( _{bwtw )} ). The value of (b _f t _f /(b _w t _w )) represents the ratio of the area of flanges 27 and 28 to the area of web 26 (hereinafter referred to as area ratio).
The results indicated by ◯ marks in FIG. 9 are cases in which the deflection δ2 of the web 26 in the out-of-plane direction is greater than ₃ mm. * The result indicated by the mark is the case where the deflection δ2 of the web 26 in the out-of-plane direction is ₃ mm or less.
As a result of investigation, it was found that the threshold value can be evaluated by using the relationship of the area ratio for the condition that the bending of the web 26 becomes larger than 3 mm. A curve L4 in FIG. 9 satisfies the formula (7-1). The H-section steel 25 corresponding to the region where the width-thickness ratio of the web 26 is smaller than that of the curve L4, that is, the H-section steel corresponding to the region where the value of ( _bftf /( _bwtw )) is _smaller than that of the curve _L4 25, the deflection .delta.2 occurring in the central portion of the web 26 is found to be ₃ mm or less.
By applying the above conditions to the formula (7-1) and modifying the formula, the formula (7-2) is obtained.

[2.4. Upper limit of flange width-thickness ratio]
In general, the thickness _tf of the flanges 27 and 28 is equal to or greater than the thickness _tw of the web 26 for reasons such as enhancing the cross-sectional performance of the H-section steel 25 . Equation (8) is obtained from this condition.

Equation (9) for the width-to-thickness ratio of the web 26 is obtained from equations (5) and (7-2). Equation (10) for the width-thickness ratio of the flanges 27 and 28 is obtained from equations (6) and (8).
When the H-section steel 25 satisfies the formula (9) or (10) and the load acting on the H-section steel 25A is removed before reaching the maximum yield strength _Fmax of the H-section steel 25A, the H-section The steel 25 has the restoring function.

In the design method (construction method) of the present embodiment, when the load acting on the H-section steel 25A is equal to or greater than the elastic local buckling strength _Fcr , the H-section steel 25A undergoes elastic local buckling, It is designed (constructed) so that at least part of the load is transmitted to the H-section steel 25B through the floor slab 35 by reducing the rigidity of the H-section steel 25A. The H-section steel 25A is designed (constructed) so that when the load acting on the H-section steel 25A is removed, the H-section steel 25A is restored to its initial state without significant structural damage.

As described above, in the H-section steel 25 of the present embodiment, when the width-to-thickness ratio of the second web 26 is 5.3√(E/σ _y ) or more, which is relatively large, the H-section steel 25A has an elastic localized area. At least a portion of this load acts on the H-section steel 25B because buckling occurs and the rigidity of the H-section steel 25A is reduced. Therefore, it is possible to promote load redistribution within the building 1 in which the H-section steel 25A is used, and prevent the load from being extremely concentrated on the H-section steel 25 .
If the load acting on the H-section steel 25A does not exceed the maximum yield strength of the H-section steel 25A, the H-section steel 25A restores to its initial state without significant structural damage when the load is removed.
In this way, even if a load that reduces the rigidity of the H-beam 25A acts on the H-section steel 25A, after the load is removed, the member will be restored to its initial state, so it will withstand repeated seismic forces. The effects of the present invention can be continuously maintained, and the H-section steel 25A can be preferably used as a structural element.

The H-section steel 25A satisfies the formula (9). The inventors found out the following as a result of earnest studies. That is, the H-section steel 25A satisfies the inequality on the left side in the formula (9), so that when the load acting on the H-section steel 25 is equal to or greater than the elastic local buckling strength _Fcr , the H-section steel 25A has the maximum strength Before reaching _Fmax , elastic local buckling occurs in the H-section steel 25A, the rigidity of the H-section steel 25A is reduced, and the load acting on the H-section steel 25A reaches the maximum yield strength of the H-section steel 25A. The H-section steel 25A can be restored to its initial state without significant structural damage when removed before reaching. Then, the H-section steel 25A satisfies the inequality on the right side in the formula (9), so that the deflection occurring in the central part of the second web 26 is 3 mm or less, which is equal to or less than that of the current H-section steel for building construction. be able to. Therefore, it is possible to eliminate the risk that local deformation of the second web 26 due to thinning impairs workability.

The H-section steel 25 satisfies the formula (10). The inventors found out the following as a result of earnest studies. That is, when the H-section steel 25A satisfies the inequality on the left side in the formula (10), and the load acting on the H-section steel 25A is equal to or greater than the elastic local buckling strength _Fcr , the H-section steel 25 has the maximum strength Before reaching _Fmax , elastic local buckling occurs in the H-section steel 25A, the rigidity of the H-section steel 25A is reduced, and the load acting on the H-section steel 25A reaches the maximum yield strength of the H-section steel 25A. If removed before reaching it, it can be restored to its initial state without significant structural damage. Then, the H-section steel 25A satisfies the inequality on the right side of the formula (10), so that the thickness of the flanges 27 and 28 is made equal to or greater than the thickness of the second web 26, and the moment of inertia of area of the H-section steel 25A, etc. Section performance can be improved. If the H-section steel 25A is a welded assembly H-section steel, when the second web 26 is welded to the flanges 27, 28, the flanges 27, 28 are completely melted in the thickness direction, and the flanges 27, 28 are 28 can be prevented from being perforated.

The H-section steel 25A is a small beam. Therefore, even if the width-to-thickness ratio of the second web 26 is larger than a certain value, it is possible to provide a small beam that can be preferably used as a structural element.
The H-section steel 25A is a welded assembly H-section steel. Therefore, even if the width-to-thickness ratio of the second web 26 is greater than a certain value, it is possible to provide a welded assembly H-section steel that can be preferably used as a structural element.

The yield strength _σy of the H-section steel 25A is 235 MPa or more and 1000 MPa or less. This makes it possible to correspond to the yield strength σ _y of general H-section steel 25A.
Further, the hot-rolled steel strip of the present embodiment is used for the second web 26 or the flanges 27, 28 of the H-section steel 25, which is a weld assembled H-section steel. Therefore, even if the width-to-thickness ratio of the second web 26 is larger than a certain value, it can be preferably used as a structural element. A hot-rolled steel strip can be provided.

The floor structure 2 includes H-section steel 25A and a floor slab 35 . In the floor structure 2 , the movement of the second upper flange 27 along the horizontal plane is restrained by the floor slab 35 . Therefore, it is possible to suppress lateral buckling of the H-section steel 25A, for example.
The floor structure 2 includes H-beams 25A and girders 15 . In the floor structure 2, compressive or tensile forces from the girders 15 are transmitted to the second upper flanges 27 at both ends of the H-section steel 25A. Therefore, the H-beam 25A can be used as a structural element that withstands compressive or tensile forces.

In addition, in the design method and design method of the present embodiment, when the width-thickness ratio of the second web 26 is relatively large at 5.3√(E/σ _y ) or more, the load acting on the H-section steel 25A is elastic. If the local buckling strength _Fcr or more, elastic local buckling occurs in the H-section steel 25A, and the rigidity of the H-section steel 25A is reduced, so that at least part of this load is transferred to the floor. It is designed (constructed) to act on the H-section steel 25B through the slab 35. Therefore, it is possible to promote load redistribution within the building 1 in which the H-section steel 25A is used, for example, and prevent a large load from acting intensively on the H-section steel 25A due to a local concentrated load.
Then, when the load borne by the H-section steel 25A among the acting loads is removed before the load reaches the maximum yield strength of the H-section steel 25A, the H-section steel 25A does not cause significant structural damage in the initial stage. Restore to state.
For this reason, the load redistribution effect due to the reduction in rigidity of the H-section steel 25A according to the present invention can be continuously exhibited against natural disasters such as repeated earthquakes, and the H-section steel 25A is preferable as a structural element. can be used.

As described above, one embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and the configuration can be changed, combined, or deleted without departing from the scope of the present invention. etc. are also included.
For example, in the above embodiment, the H-section steel 25 does not have to satisfy the formulas (9) and (10).
The H-section steel 25 may be a rolled H-section steel instead of a weld assembled H-section steel.
The H-section steel 25 may be a large beam instead of a small beam. In this case, the support member is the column member 10 .
The yield strength σ _y of the H-section steel 25 may be less than 235 MPa or may exceed 1000 MPa.

2 floor structure 15 girders (supporting members)
25, 25A H-shaped steel (small beam)
25B H-shaped steel (supporting beam)
26 Second Web (Web)
27 second upper flange (flange, upper flange)
28 Second lower flange (flange)

Claims (11)

H-shaped steel,
The maximum strength that the H-section steel can bear is equal to or greater than the elastic local buckling strength of the H-section steel,
When a load acts on the H-section steel, if the load exceeds the elastic local buckling strength, the rigidity of the H-section steel decreases,
An H-section steel having a function of restoring the H-section steel to its initial position when the load acting on the H-section steel is removed before reaching the maximum yield strength of the H-section steel. H-shaped steel,
The H-shaped steel is
web and
a pair of flanges arranged to sandwich the web;
with
(1) By satisfying the formula, the maximum strength that the H-section steel can bear is equal to or greater than the elastic local buckling strength of the H-section steel,
When a load acts on the H-section steel, if the load exceeds the elastic local buckling strength, the rigidity of the H-section steel decreases,
An H-section steel having a function of restoring the H-section steel to its initial position when the load acting on the H-section steel is removed before reaching the maximum yield strength of the H-section steel.
where E: Young's modulus of the H-section steel, _σy : yield strength of the H-section steel, _bw : width of the web, _tw : thickness of the web, _bf : width of the pair of flanges, t _f : the thickness of the pair of flanges.

H-shaped steel,
The H-shaped steel is
web and
a pair of flanges arranged to sandwich the web;
with
By satisfying the formula (2), when a load acts on the H-section steel, the rigidity of the H-section steel decreases when the load exceeds the elastic local buckling strength of the H-section steel, and
An H-section steel having a function of restoring the H-section steel to its initial position when the load acting on the H-section steel is removed before reaching the maximum yield strength of the H-section steel.
However, E: Young's modulus of the H-section steel, _σy : yield strength of the H-section steel, _tw : thickness of the web, _bf : width of the pair of flanges, _tf : width of the pair of flanges thickness.

The H-section steel according to any one of claims 1 to 3, wherein the H-section steel is a joist. The H-section steel according to any one of claims 1 to 4, wherein the H-section steel is a weld assembled H-section steel in which a web and a pair of flanges are welded together. The H-section steel according to any one of claims 1 to 5, wherein the H-section steel has a yield strength _σy of 235 MPa or more and 1000 MPa or less. A hot-rolled steel strip for use in a web or a pair of flanges of H-section steel, which is a weld assembled H-section steel, according to any one of claims 1 to 6. H-section steel according to any one of claims 1 to 6;
a floor slab supported from below by an upper flange of the H-section steel and joined to the upper flange;
with
The floor structure, wherein the movement of the upper flange along the horizontal plane is restrained by the floor slab. H-section steel according to any one of claims 1 to 6;
a supporting member joined or in contact with at least one of a pair of flanges of the H-section steel at at least one end in the axial direction of the H-section steel;
with
A floor structure, wherein compressive force or tensile force of the H-section steel is transmitted between the at least one end of the H-section steel and the support member. H-shaped steel;
a support beam;
a floor slab joined to the H-beam and the support beam, respectively;
A floor structure design method for designing a floor structure comprising
When the load acting on the H-section steel is equal to or greater than the elastic local buckling capacity of the H-section steel, the H-section steel buckles to reduce the rate at which the load acts on the H-section steel. so that at least part of the load acts on the support beam through the floor slab, and
A method of designing a floor structure, wherein, if the load is less than the elastic local buckling capacity, the H-section steel is designed to restore to the initial position when the load is removed. H-shaped steel;
a support beam;
a floor slab joined to the H-beam and the support beam, respectively;
A floor structure construction method for constructing a floor structure comprising
When the load acting on the H-section steel is equal to or greater than the elastic local buckling capacity of the H-section steel, the H-section steel buckles to reduce the rate at which the load acts on the H-section steel. so that at least part of the load acts on the support beam through the floor slab,
A method of constructing a floor structure, wherein, if the load is less than the elastic local buckling capacity, the H-section steel is constructed so as to restore to the initial position when the load is removed.

Images