Steel materials, fire-resistant coated steel materials, structures, methods for evaluating steel materials, and methods for designing structures.

Abstract

To enable the use of steel materials in high-temperature environments. [Solution] The standard strength is F(N / mm 2 A steel material 20 used as ) having a tensile strength of σ u (N / mm 2 ) and the yield strength is σ y (N / mm 2 ) when 0.7σ u ≥F, and σ y ≥F.

Description

Technical Field

[0001] The present invention relates to steel materials, fire-resistant coated steel materials, structures, evaluation methods for steel materials, and evaluation methods for design methods of structures.

Background Art

[0002] Conventionally, for example, a steel material described in Patent Document 1 below is known. This steel material improves heat resistance by adjusting its components and the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For steel materials used in structures, like this type of steel material, it is desired to be usable in a high-temperature environment.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to make a steel material usable in a high-temperature environment.

Means for Solving the Problems

[0006] <1> The steel material according to one aspect of the present invention is a steel material used with a reference strength of F (N / mm 2 ), having a tensile strength of σ u (N / mm 2 ), and when the yield strength is σ y (N / mm 2 ), 0.7σ u ≧ F and σ y ≧ F. <2> In the steel material according to <1> above, a configuration where 0.7σ u > F and σ y > F may be adopted. <3> the above <2> For steel materials related to this, 0.65σ u >F, and σ y You may adopt a configuration that is F. <4> the above <1> from <3> For steel materials relating to any one of the following items, F≧0.10σ u Furthermore, F≧0.10σ y You may adopt the following configuration. <5> the above <1> from <4> For steel materials relating to any one of the items, the tensile strength at t(°C) is σ u、t Furthermore, the tensile strength at room temperature is σ u、RT And the yield strength at t(°C) is σ y、t Furthermore, the yield strength at room temperature is σ y、RT When that is the case, σ y、RT >235N / mm 2 , and, σ y、600℃ >(235 / 1.5)N / mm 2 , and, σ y、RT / σ u、RT A configuration where ≤ 0.98 may be adopted. <6> the above <5> In steel materials related to σ y、RT >325N / mm 2 You may adopt the following configuration. <7> the above <6> In steel materials related to σ y、RT >355N / mm 2 You may adopt the following configuration. <8> the above <1> from <7> In the case of steel materials relating to any one of the items, a configuration of H-shaped steel, square steel pipe, or circular steel pipe may be adopted. <9> the above <8> The steel material in question may be H-shaped steel, and a configuration used for main beams or secondary beams may be adopted. <10> the above <8> or <9> The steel material used may be an H-shaped steel beam with a welded web and flange. <11> the above <7> The steel materials used may be square or circular steel pipes, and a configuration that is used for columns may be adopted. <12> A fire-resistant coated steel material according to one aspect of the present invention is the above <1> from <11> The material comprises a steel material relating to any one of the items in the paragraph, and a fire-resistant coating provided on the steel material. <13> A structure according to one aspect of the present invention is the above <1> from <11> Steel materials relating to any one of the above items, or the above <12> It is equipped with fire-resistant coated steel as a structural member. <14> A structure according to one aspect of the present invention has a tensile strength of σ u (N / mm 2 ) and the yield strength is σ y (N / mm 2 A structure comprising steel material as a structural member, wherein the tensile stress acting on the steel material is 0.7σ u It is less than σ y It is less than. <15> A method for evaluating steel materials according to one aspect of the present invention, wherein the tensile strength is σ u (N / mm 2 ) and the yield strength is σ y (N / mm 2 Regarding steel materials, the standard strength F(N / mm²) 2 ) to 0.7σ u Set the value to satisfy both ≥F and σy ≥ F. <16> A method for designing a structure according to one aspect of the present invention is as described above. <15> The structure is designed using the steel material, whose standard strength F is determined according to the steel material evaluation method described above, as a structural member. <17> A method for designing a structure according to one aspect of the present invention is as described above. <1> from <11> Steel materials relating to any one of the above items, or the above <12> The structure is designed using fire-resistant coated steel materials as structural members.

[0007] The inventors of this application have identified the following factors as causes of steel materials becoming unusable in high-temperature environments. These factors are due to the fact that as the temperature of the steel material rises, the tensile strength and yield strength of the steel material decrease, and the tensile stress acting on the steel material becomes larger than the tensile strength and yield strength of the steel material, causing the steel material to be unable to withstand the load. Therefore, the inventors of the present invention realized that if the tensile strength and yield strength of the steel material are sufficiently higher than the tensile stress acting on the steel material at room temperature (in other words, if the tensile strength and yield strength of the steel material are set with a margin of safety relative to the tensile stress actually acting on the steel material), then the steel material can be used in high-temperature environments. Here, the standard strength is cited as a value related to the tensile stress that actually acts on the steel material. The standard strength is set for each type of steel. The standard strength is specified, for example, in Ministry of Construction Notification No. 2464 (Regarding the standard strength of allowable stress and material strength for steel materials and welded joints). The higher the standard strength of the steel, the greater the allowable tensile stress. Therefore, the inventor of the present invention conceived of making steel usable in high-temperature environments by defining the relationship between the tensile strength and yield strength of steel and the standard strength of steel.

[0008] In the steel material according to the present invention, 0.7σ u ≥F, and σ y ≥F. Therefore, the tensile strength σ u or surrender strength σ y This is sufficiently high compared to the standard strength F. In other words, the standard strength of the steel is set lower (with a margin) than the actual tensile strength and yield strength. Therefore, for example, even if the upper limit of the allowable tensile stress at room temperature is applied to this steel, the tensile strength and yield strength of the steel will be sufficiently high compared to that tensile stress. As a result, even if the tensile strength and yield strength of the steel decrease in a high-temperature environment, the tensile strength and yield strength of the steel will remain higher than the actual tensile stress applied, allowing the steel to be used in high-temperature environments.

[0009] Generally, steel materials are given a heat resistance temperature. Based on the Building Standards Act, the following conditions are imposed on the heat resistance temperature: Let the heat resistance temperature of the steel material be t (°C), and the yield strength of the steel material at t (°C) be σ. y、t The standard strength of the steel material is set to F(N / mm²). 2 When this is the case, the following equation (1) must be satisfied.

[0010] σ y、t ≥F / 1.5 … (1)

[0011] In view that the heat resistance temperature of the steel material is set considering the above equation (1), if the standard strength of the steel material is set lower (with a margin) than the actual tensile strength or yield strength, as in the steel material according to the present invention, the heat resistance temperature of the steel material can be set higher.

[0012] Furthermore, when the steel material is, for example, so-called high-tensile steel or ultra-high-tensile steel (hereinafter referred to as high-tensile steel, etc.), the high tensile strength is maintained even at high temperatures, so the aforementioned effects are particularly effective. Here, for example, when the steel material is manufactured by welding multiple steel plates, it becomes easy to make the steel material high-tensile steel, etc. Therefore, when the steel material is structural steel and is manufactured by welding multiple steel plates, the effects of the present invention are particularly effective. Furthermore, when high-tensile steel is used, the amount of steel required to achieve the same level of strength is reduced compared to when non-high-tensile steel is used, thus enabling weight reduction. On the other hand, a reduction in the amount of steel can decrease the heat capacity of the steel, raising concerns about reduced fire resistance. Therefore, as mentioned above, by setting the standard strength of the steel lower than its actual strength and setting the heat resistance temperature of the steel higher, concerns about reduced fire resistance can be mitigated. [Effects of the Invention]

[0013] According to the present invention, steel materials can be used in high-temperature environments. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view showing a fire-resistant coated steel material according to one embodiment of the present invention. [Figure 2] This graph shows the relationship between the temperature of steel and the stress at 1% strain. [Modes for carrying out the invention]

[0015] (Fire-resistant coated steel) The fire-resistant coated steel material 10 according to one embodiment of the present invention will be described below with reference to the drawings. As shown in Figure 1, the fire-resistant coated steel material 10 comprises a steel material 20 and a fire-resistant coating 30 provided on the steel material 20. The steel material 20 is an H-shaped steel, a square steel pipe, or a circular steel pipe. In this embodiment, the steel material 20 is an H-shaped steel, and the fire-resistant coated steel material 10 is used for a main beam or secondary beam. However, the steel material 20 may be a square steel pipe or a circular steel pipe, and the fire-resistant coated steel material 10 may be used for a column.

[0016] In the illustrated example, the fire-resistant coated steel member 10 is used as a secondary beam. The fire-resistant coated steel member 10 supports the slab S. Generally, a fire-resistant coated steel member 10 used as a secondary beam is designed as a structural member that supports the load of the slab S. In other words, in the design of a building (structure 1), secondary beams are not designed as members that bear horizontal loads (such as seismic forces) acting on the building.

[0017] The steel member 20 comprises a web 21, an upper flange 22 (first flange), and a lower flange 23 (second flange). The thicknesses of the upper flange 22 and the lower flange 23 are equivalent. The thicknesses of the upper flange 22 and the lower flange 23 are, for example, 2.3 mm to 40 mm, preferably 6 mm to 32 mm, and more preferably about 13 mm. The web 21 is thinner than the upper flange 22 and the lower flange 23. The thickness of the web 21 is, for example, 2.3 mm to 25 mm, preferably 6 mm to 22 mm, and more preferably about 8 mm. The upper flange 22 is fixed to the slab S. The upper surface of the upper flange 22 is in contact with the lower surface of the slab S. Note that the upper and lower limits and numerical values ​​of the various numerical ranges described in this embodiment can be combined with the upper and lower limits and numerical values ​​of other numerical ranges exemplified to set other suitable numerical ranges.

[0018] The web 21 and flanges 22 and 23 of the steel material 20 are welded together. In other words, the steel material 20 is not a steel material formed integrally by rolling. The web 21 and flanges 22 and 23 are each steel plates made of so-called high-tensile steel or ultra-high-tensile steel (hereinafter referred to as high-tensile steel, etc.). The web 21 and flanges 22 and 23 are, for example, steel plates of 600 MPa class or higher (i.e., 600 MPa class or above 600 MPa class).

[0019] The ratio of the width of the steel member 20 (width of the upper flange 22, width of the lower flange 23) to the depth of the steel member 20 (distance between the upper surface of the upper flange 22 and the lower surface of the lower flange 23) is, for example, 3.0 or more and 5.0 or less, preferably 4.0. The ratio of the thickness of the web 21 to the depth of the steel member 20 is, for example, 100 or more and 160 or less, preferably 111 or more and 155 or less. The steel member 20 can be said to be a beam (main beam or secondary beam) with high cross-sectional efficiency.

[0020] The fireproof coating 30 covers the steel material 20. The fireproof coating 30 covers the steel material 20 along its entire length in the direction of the material axis. The fireproof coating 30 covers the portion of the steel material 20 excluding the upper surface of the upper flange 22. The thickness of the fireproof coating 30 is uniform throughout, regardless of its location. The thickness t1 of the portion of the fireproof coating 30 covering the web 21, the thickness t2 of the portion covering the upper flange 22, and the thickness t3 of the portion covering the lower flange 23 are all the same. These thicknesses t1, t2, and t3 are, for example, about 65 mm.

[0021] The fire-resistant coating 30 is formed by methods such as spraying, painting, forming a molded plate, or wrapping. For example, wrapped rock wool is a type of dry fire-resistant coating material. Wrapped rock wool is a component with a two-layer structure, formed by laminating a nonwoven fabric onto rock wool. The nonwoven fabric is provided to prevent dust from scattering from the rock wool. Rock wool is formed by melting inorganic materials at high temperatures and then blowing them into fibers using centrifugal force. Examples of inorganic materials include steel slag and basalt. Furthermore, inorganic board materials such as gypsum board, calcium silicate board, ALC, and cement board can be used as fireproofing for the molded board.

[0022] Here, the steel material 20 has a standard strength of F(N / mm²). 2 It is used as ). The standard strength is specified in Ministry of Construction Notification No. 2464 (Regarding the standard strength of allowable stress and material strength of steel materials and welded parts). And the tensile strength of steel material 20 is σ u (N / mm 2 ) and the yield strength of the steel material 20 is σ y (N / mm 2 ) Let's assume that in this embodiment, the steel material 20 satisfies the following equations (11) and (12).

[0023] 0.7σ u ≥F … (11) σ y ≥F … (12)

[0024] Furthermore, it is preferable that the steel material 20 satisfies equations (13) and (14) below, and more preferably satisfies equations (15) and (16) below.

[0025] 0.7σ u >F … (13) σ y >F … (14)

[0026] 0.65σ u >F … (15) σ y >F … (16)

[0027] Here, equations (11) to (16) above are equations relating to the upper limit of the standard intensity. In equations (11), (13), and (15), the upper limit of the standard strength is the tensile strength σ u It is set based on the following. Specifically, the reference strength is the tensile strength σ u It is 0.7 times or less (Equation (11)), preferably the tensile strength σ u It is less than 0.7 times (Equation (13)), and more preferably the tensile strength σu It is less than 0.65 times (Equation (15)). Thus, the standard strength is the tensile strength σ u It is set with ample margin. In equations (12), (14), and (16), the upper limit of the reference strength is the yield strength σ y It is set based on the yield strength σ. Specifically, the reference strength is the yield strength σ y The following is true (Equation (12)), preferably yield strength σ y It is less than ((Equations 14 and 16)). Therefore, the reference strength is the yield strength σ y It is set with ample margin.

[0028] Furthermore, it is preferable that the steel material 20 satisfies equations (17) and (18) relating to the lower limit of the standard strength.

[0029] F≧0.10σ u … (17) F≧0.10σ y … (18)

[0030] In equation (17), the lower limit of the reference strength is the tensile strength σ u It is set based on the following. Specifically, the reference strength is the tensile strength σ u It is more than 0.10 times. As a result, the standard strength is the tensile strength σ u It is set without being underestimated. In equation (18), the lower limit of the reference strength is the yield strength σ y It is set based on the yield strength σ. Specifically, the reference strength is the yield strength σ y It is more than 0.10 times. As a result, the standard strength is the yield strength σ y It is set without being underestimated.

[0031] The tensile strength σ mentioned above u For example, this is the tensile strength specified in JIS G 3101:2015. Yield strength σ y This is, for example, the yield point or proof strength specified in JIS G 3101:2015. These tensile strengths σ u and yield strength σ yThese are all the tensile strength and yield strength of steel material 20 at normal temperature. Normal temperature is, for example, the normal temperature defined in JIS Z 2241:2011. Normal temperature is, for example, 20°C ± 15°C (5°C to 35°C).

[0032] Here, when the steel material 20 is at t (°C), the tensile strength of the steel material 20 is σ u、t and when the steel material 20 is at normal temperature, the tensile strength of the steel material 20 is σ u、RT Let's assume so. When the steel material 20 is at t (°C), the yield strength of the steel material 20 is σ y、t and when the steel material 20 is at normal temperature, the yield strength of the steel material 20 is σ y、RT Let's assume so. At this time, it is preferable that the steel material 20 satisfies all of the following formulas (21) to (23). Further, it is more preferable that the steel material 20 satisfies the following formula (24) in addition to the following formulas (21) to (23), and it is even more preferable that the steel material 20 satisfies the following formula (25) in addition to the following formulas (21) to (24).

[0033] σ y、RT > 235 N / mm 2 … (21) σ y、600℃ >(235 / 1.5) N / mm 2 … (22) σ y、RT / σ u、RT ≦ 0.98 … (23)

[0034] σ y、RT > 325 N / mm 2 … (24)

[0035] σ y、RT > 355 N / mm 2 … (25)

[0036] By the steel material 20 satisfying the above formulas (21) and (22), for example, even if the reference strength is 235 N / mm 2 the reference strength is set with a margin with respect to the actual tensile strength and yield strength. The reference strength is 235 N / mm 2When this is the case, and further when the steel material 20 satisfies the above formula (24), the reference strength is set with more margin with respect to the actual tensile strength and yield strength. In this case, and further when the steel material 20 satisfies the above formula (25), the reference strength is set with even more margin with respect to the actual tensile strength and yield strength.

[0037] In addition, when the steel material 20 satisfies the above formula (23), in other words, when the yield ratio (YR) of the steel material 20 is 98% or less, the following effects are achieved. In this case, for example, even if an earthquake occurs and a tensile stress caused by the earthquake acts on the steel material 20, in the process of the tensile stress increasing, until the tensile stress reaches the yield strength σ y of the steel material 20 and the steel material 20 yields, and until the tensile stress reaches the tensile strength σ u of the steel material 20, the steel material 20 can undergo plastic deformation. Therefore, the input energy of the earthquake can be absorbed by the steel material 20. The yield ratio can be changed, for example, according to the energy absorption capacity required for the steel material 20. When a high absorption capacity is required for the steel material 20, it is preferable that the yield ratio of the steel material 20 is smaller.

[0038] (Structure) In the structure 1 according to the present embodiment, the above steel material 20 is provided as a member that bears the entire load. At this time, the tensile stress acting on the steel material 20 is less than 0.7σ u and less than σ y . It is preferable that the tensile stress is less than 0.65σ u .

[0039] (Evaluation method of steel material) The evaluation method of the steel material according to the present embodiment is for a steel material 20 having a tensile strength of σ u (N / mm 2 ) and a yield strength of σ y (N / mm 2 ), and the reference strength F (N / mm 2The standard strength F is preferably set to a value that satisfies equations (11) and (12) above. It is preferable that the standard strength F is set to a value that satisfies equations (13) and (14) above, and more preferably that it is set to a value that satisfies equations (15) and (16) above. It is also preferable that the steel material 20 satisfies all of equations (21) to (23) above. Furthermore, it is more preferable that the steel material 20 satisfies equation (24) in addition to equations (21) to (23) above, and even more preferable that it satisfies equation (25) in addition to equations (21) to (24) above. As a conventional method for evaluating steel materials, for example, see the National Institute for Land and Infrastructure Management Report 2012 (edited and published by...). One example is the method described in "Quality Control of Steel Materials and Specification of Standard Strength" published by the National Institute for Land and Infrastructure Management.

[0040] (Structural design methods) The building design method according to this embodiment involves designing a structure 1 using the steel material 20 described above, or steel material 20 whose standard strength F is set according to the evaluation method for the steel material described above, as structural members. The structure 1 is completed by constructing the structure 1 designed based on this design method.

[0041] (Effects and Benefits) The inventors of this application have identified the following factors as causes for the steel material 20 becoming unusable in high-temperature environments. These factors are that, as the temperature of the steel material 20 rises, the tensile strength and yield strength of the steel material 20 decrease, and the tensile stress acting on the steel material 20 becomes larger than the tensile strength and yield strength of the steel material 20, causing the steel material 20 to become unable to withstand the load. Therefore, the inventors of the present invention realized that if the tensile strength and yield strength of the steel material 20 are sufficiently higher than the tensile stress acting on the steel material 20 at room temperature (in other words, if the tensile strength and yield strength of the steel material 20 are set with a margin of safety relative to the tensile stress actually acting on the steel material 20), then the steel material 20 can be used in a high-temperature environment. Here, the standard strength is a value related to the tensile stress actually acting on the steel material 20. The standard strength is set for each steel material 20. The higher the standard strength of the steel material 20, the greater the tensile stress that can be allowed on the steel material 20. Therefore, the inventor of the present invention conceived of making the steel material 20 usable in high-temperature environments by defining the relationship between the tensile strength and yield strength of the steel material 20 and the standard strength of the steel material 20.

[0042] In the steel material 20 according to this embodiment, 0.7σ u ≥F, and σ y ≥F. Therefore, the tensile strength σ u or surrender strength σ y This is sufficiently high compared to the standard strength F. In other words, the standard strength of steel material 20 is set lower (with a margin) than the actual tensile strength and yield strength. Therefore, for example, even if the upper limit of the tensile stress that can be allowed on steel material 20 at room temperature is applied to this steel material 20, the tensile strength and yield strength of steel material 20 will be sufficiently high compared to that tensile stress. As a result, even if the tensile strength and yield strength of steel material 20 decrease in a high-temperature environment, the tensile strength and yield strength of steel material 20 will remain higher than the actual tensile stress applied, and steel material 20 will be usable in a high-temperature environment.

[0043] Generally, a heat resistance temperature is set for the steel material 20. Based on the Building Standards Act, the following conditions are imposed on the heat resistance temperature: Let the heat resistance temperature of the steel material 20 be t (°C), and the yield strength of the steel material 20 at t (°C) be σ. y、t The standard strength of the steel material 20 is set to F(N / mm²). 2 When this is the case, the following equation (1) must be satisfied.

[0044] σ y、t ≥F / 1.5 … (1)

[0045] In view that the heat resistance temperature of the steel material 20 is set considering the above equation (1), if the standard strength of the steel material 20 is set lower (with a margin) than the actual tensile strength and yield strength, as in the steel material 20 according to the present invention, the heat resistance temperature of the steel material 20 can be set higher.

[0046] Furthermore, if the steel material 20 is, for example, a so-called high-tensile steel, the high tensile strength is maintained even at high temperatures, and the aforementioned effects are significantly more pronounced. The graph shown in Figure 2 illustrates the relationship between the temperature of the steel material and the 1% strain stress of the steel material at each temperature. The horizontal axis of this graph represents the temperature of the steel material, and the vertical axis represents the 1% strain stress of the steel material. Of the two graph lines L1 and L2, the solid line L1 (legend: ○) represents 600 MPa class steel material, and the dashed line L2 (legend: △) represents 400 MPa class steel material. As is clear from comparing graph lines L1 and L2 in this figure, graph line L1, which represents relatively high-tensile steel, can maintain higher tensile strength even in higher temperature ranges than graph line L2, which represents relatively low-tensile steel.

[0047] For example, if the steel material 20 is manufactured by welding multiple steel plates together, it becomes easy to make the steel material 20 high-tensile steel or the like. Therefore, the effects of this embodiment are particularly pronounced when the steel material 20 is a structural steel and is manufactured by welding multiple steel plates together.

[0048] Moreover, when the steel material 20 is high-tensile steel, the amount of steel material 20 required to maintain the same level of strength is reduced compared to when the steel material 20 is not high-tensile steel, thus enabling weight reduction. On the other hand, a reduction in the amount of steel material can lead to a decrease in the heat capacity of the steel material 20, raising concerns about reduced fire resistance. Therefore, as mentioned above, by setting the standard strength of the steel material 20 lower than its actual strength and setting the heat resistance temperature of the steel material 20 higher, concerns about reduced fire resistance can be mitigated.

[0049] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0050] For example, the fire-resistant coating 30 is not necessary.

[0051] Furthermore, without departing from the spirit of the present invention, the components in the above embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate. [Explanation of Symbols]

[0052] 1 structure 10 Fire-resistant coated steel 20 Steel 21 Web 22 Flange 23 Flange 30 Fire-resistant coating F Reference strength

Claims

1. The standard strength is F (N / mm²). ２ Steel material used as, Tensile strength is σ ｕ (N / mm ２ ) and the yield strength is σ ｙ (N / mm ２ ) when 0.7σ ｕ ≥ F, and σ ｙ Steel material such that F is greater than or equal to F.

2. 0.7σ ｕ > F and σ ｙ The steel material according to claim 1, which is > F and σ

3. 0.65σ ｕ > F, and σ ｙ > The steel material according to claim 2, which is F.

4. F ≥ 0.10σ ｕ , and F ≥ 0.10σ ｙ The steel material according to any one of claims 1 to 3.

5. The tensile strength at t (°C) is σ ｕ、ｔ Furthermore, the tensile strength at room temperature is σ ｕ、ＲＴ And the yield strength at t (°C) is σ ｙ、ｔ Furthermore, the yield strength at room temperature is σ ｙ、ＲＴ At that time, σ ｙ、ＲＴ >235 N / mm ２ , and, σ ｙ、６００℃ >(235 / 1.5)N / mm ２ , and, σ ｙ、ＲＴ / σ ｕ、ＲＴ A steel material according to any one of claims 1 to 4, wherein the coefficient is ≤ 0.

98.

6. σ ｙ、ＲＴ >325 N / mm ２ The steel material according to claim 5.

7. σ ｙ、ＲＴ >355 N / mm ２ The steel material according to claim 6.

8. The steel material according to any one of claims 1 to 7, which is an H-shaped steel, a square steel pipe, or a circular steel pipe.

9. The steel material according to claim 8, which is an H-shaped steel and is used as a main beam or secondary beam.

10. The steel material according to claim 8 or 9, wherein it is an H-shaped steel, and the web and flange are welded together.

11. The steel material according to claim 7, which is a square steel pipe or a circular steel pipe used for a column.

12. A steel material according to any one of claims 1 to 11, A fire-resistant coated steel material comprising a fire-resistant coating provided on the aforementioned steel material.

13. A structure comprising a steel material according to any one of claims 1 to 11, or a fire-resistant coated steel material according to claim 12, as a structural member.

14. Tensile strength is σ ｕ (N / mm ２ ) and the yield strength is σ ｙ (N / mm ２ A structure that includes steel material as a structural member, The tensile stress acting on the aforementioned steel material is 0.7σ ｕ It is less than σ ｙ A structure that is less than [a certain value].

15. Tensile strength is σ ｕ (N / mm ２ ) and the yield strength is σ ｙ (N / mm ２ Regarding steel materials, the standard strength F (N / mm²) ２ ) to 0.7σ ｕ ≥ F, and σ ｙ A method for evaluating steel materials, where the value is set to satisfy ≥ F.

16. A method for designing a structure, wherein the steel material whose standard strength F is set according to the steel material evaluation method described in claim 15 is used as a structural member to design the structure.

17. A method for designing a structure using a steel material according to any one of claims 1 to 11, or a fire-resistant coated steel material according to claim 12, as a structural member.

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