Design method for fire-resistant coated steel, manufacturing method for fire-resistant coated steel, fire-resistant coated steel, and design program for fire-resistant coated steel.

Abstract

To provide a method for designing a fire-resistant coated steel material by which the thickness of a fire-resistant coating material can be simply and appropriately designed without impairing the fire-resistant performance of the fire-resistant coated steel material.SOLUTION: A method for designing a fire-resistant coated steel material for a steel structure including a steel material and a fire-resistant coating material having a thickness t (mm), the method comprising: a first step of estimating a function expression representing a stress-strain curve of a steel material using a temperature T, a strain ε, and a strain rate εv as variables, and obtaining a stress-temperature relationship at 1% strain, which is a relationship between a stress at 1% strain at the strain rate ε v and the temperature T, from the estimated function expression; a second step of obtaining a corresponding temperature T' by introducing a design load in the case of being used as a steel structure into the stress-temperature relationship at 1% strain obtained in the first step, and setting the temperature T' as a steel material allowable temperature at which the steel material is not broken; and a third step of determining the thickness of the fire-resistant covering material from the allowable temperature (°C) of the steel material obtained in the second step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for designing fire-resistant coated steel materials, a method for manufacturing fire-resistant coated steel materials, fire-resistant coated steel materials, and a design program for fire-resistant coated steel materials. [Background technology]

[0002] It is known that the strength of steel decreases as the temperature rises. Therefore, when using steel as a structural member of a building, it is necessary to ensure fire resistance so that the building does not collapse while residents and users evacuate in the event of a fire. For this reason, when using H-shaped steel or similar materials as beams in a structural member, the outer surface of the H-shaped steel is covered with a fire-resistant coating material (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6409396 [Patent Document 2] Patent No. 4198292 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, while it has long been known that the strength of steel decreases at high temperatures, actually conducting tensile tests on steel at high temperatures requires handling the steel in a high-temperature state. However, in reality, handling high-temperature steel is difficult, so there are fewer test examples compared to tests at room temperature, and currently only sporadic test results have been obtained.

[0005] Furthermore, for example, the Japanese Industrial Standards (JIS) recommend conducting tensile tests on steel materials at a strain rate of 0.3% / min. Therefore, a strain rate of 0.3% / min is conventionally used when evaluating the fire resistance of steel structures. However, recent research is revealing that when steel structures are destroyed by fire or other disasters, the beams and columns are subjected to loads corresponding to strain rates significantly exceeding 0.3% / min. Thus, higher strain rates can lead to unexpectedly high-temperature strength in steel materials. Consequently, fire-resistant coated steel materials designed based on conventionally used test methods may have overestimated fire resistance because the design assumptions differ from reality.

[0006] Furthermore, conventionally, the deformation behavior of steel materials in tensile tests at strain rates of less than 0.3% / min or less than 0.1% / min has been largely ignored when evaluating the fire resistance performance of steel materials.

[0007] Furthermore, when designing the thickness of the fire-resistant coating material covering fire-resistant steel materials, full-scale beams and columns are prepared, and their deformation behavior is observed by heating them while a simulated load is applied. Based on this observation, the thickness of the fire-resistant coating material is determined based on empirical rules. However, determining this thickness requires considerable effort and time.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for designing fire-resistant coated steel materials, a method for manufacturing fire-resistant coated steel materials, and a design program for fire-resistant coated steel materials, which enable the simple and appropriate design of the thickness of the fire-resistant coating material without impairing the fire resistance performance of the fire-resistant coated steel material. Furthermore, the present invention aims to provide a fire-resistant coated steel material equipped with a fire-resistant coating material of a thickness that does not impair fire resistance. [Means for solving the problem]

[0009] To solve the above problems, the present invention adopts the following configuration. [1] A design method for a fire-resistant coated steel material for a steel structure, comprising a steel material and a fire-resistant coating material with a thickness t (mm) covering the surface of the steel material, wherein: A function formula representing the stress-strain curve of the steel material with temperature T (°C), strain ε (%), and strain rate ε v (% / min) as variables is inferred, and from the inferred function formula, the stress (N / mm v ) at 1% strain at the strain rate ε 2 The first step of obtaining the stress-temperature relationship at 1% strain, which is the relationship between the stress at 1% strain and temperature T; The design load (N / mm 2 ) when used as the steel structure is introduced into the stress-temperature relationship at 1% strain obtained in the first step to obtain the corresponding temperature T', and the second step of setting the temperature T' as the allowable temperature (°C) of the steel material at which the steel material does not break; [[ID=

[14] ] The third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step. A design method for a fire-resistant coated steel material comprising the above steps. [2] A design method for a fire-resistant coated steel material for a steel structure, comprising a steel material and a fire-resistant coating material with a thickness t (mm) covering the surface of the steel material, wherein: A function formula representing the stress-strain curve of the steel material with temperature T (°C), strain ε (%), and strain rate ε v (% / min) as variables is inferred, and from the inferred function formula, the stress (N / mm v ) at 1% strain at the strain rate ε 2 The first step of obtaining the stress-temperature relationship at 1% strain, which is the relationship between the stress at 1% strain and temperature T; The design load (N / mm 2 ) when used as the steel structure is introduced into the stress-temperature relationship at 1% strain obtained in the first step to obtain the corresponding temperature T', and the second step of setting the temperature T' as the allowable temperature (°C) of the steel material at which the steel material does not break; The third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step. The design method for a fire-resistant coated steel material comprises the above steps, where the function formula is the following formula (1). A design method for a fire-resistant coated steel material. σ(T, ε, ε v)=σ0(ε v / ε0) m(T) … (1) However, in equation (1), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v ε is the strain rate (% / min) as a variable, in the range of 0.01% / min or greater, ε0 is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain obtained by high-temperature tensile tests of the steel material under the conditions of temperature: T(°C) and strain rates: 0.3% / min and 7.5% / min. [3] A method for manufacturing a fire-resistant coated steel material for a steel structure, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε v A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε v Stress at 1% strain (N / mm 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2 The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step involves determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step, A fourth step is to manufacture the fire-resistant coated steel material by covering the steel material with the fire-resistant coating material of thickness t obtained in the third step, A method for manufacturing fire-resistant coated steel materials. [4] A method for manufacturing a fire-resistant coated steel material for a steel structure, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε vA function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε v Stress at 1% strain (N / mm 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2 The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step involves determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step, A fourth step is to manufacture the fire-resistant coated steel material by covering the steel material with the fire-resistant coating material of thickness t obtained in the third step, Equipped with, A method for manufacturing fire-resistant coated steel, wherein the aforementioned function is equation (2) below. σ(T,ε,ε v )=σ0(ε v / ε0) m(T) … (2) However, in equation (2), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v ε0 is the strain rate (% / min) as a variable, in the range of 0.01% / min or greater, ε0 is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T(°C) and strain rates of 0.3% / min and 7.5% / min. [5] A fire-resistant coated steel material for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε v A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate εv Stress at 1% strain (N / mm 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2 The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step in which the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature (°C) of the steel material obtained in the second step, and a fire-resistant coated steel material having a fire-resistant coating material of the thickness t determined by the third step. [6] A fire-resistant coated steel material for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε v A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε v Stress at 1% strain (N / mm 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2 The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step involves determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material determined in the second step, and having a fire-resistant coating material of the thickness t determined by the third step. A fire-resistant coated steel material in which the above function equation is equation (3) below. σ(T,ε,ε v )=σ0(ε v / ε0) m(T) … (3) However, in equation (3), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and εv ε0 is the strain rate (% / min) as a variable, where ε0 is the reference strain rate of 0.3% / min and is in the range of 0.01% / min or higher, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T(°C) and strain rates of 0.3% / min and 7.5% / min. [7] The fire-resistant coated steel material according to [5] or [6], wherein the fire-resistant coating material is one of a sprayed layer, a painted layer, a molded plate, or a wrapped body. [8] The steel material has a yield strength σ at 20°C y 235 N / mm 2 The above applies to the fire-resistant coated steel materials described in [5] or [6]. [9] The steel material has a yield strength σ at 20°C y 335 N / mm 2 The above applies to the fire-resistant coated steel materials described in [5] or [6].

[10] The steel material has a yield strength σ at 20°C y 355 N / mm 2 The fire-resistant coated steel materials described above [5] or [6].

[11] The steel material has a yield strength σ at 20°C y 385 N / mm 2 The above applies to the fire-resistant coated steel materials described in [5] or [6].

[12] A design program for fire-resistant coated steel materials for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε v A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε v Stress at 1% strain (N / mm 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A design program for fire-resistant coated steel, comprising: a third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step.

[13] A design program for fire-resistant coated steel materials for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, A function equation representing the stress-strain curve of the steel material is estimated, with temperature T (°C), strain ε (%), and strain rate εv (% / min) as variables. From the estimated function equation, the stress at 1% strain at strain rate εv (N / mm²) is calculated. 2 The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T. The design load (N / mm²) when used as the steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. 2 The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. The process comprises a third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material determined in the second step, A design program for fire-resistant coated steel, where the above function is given by equation (4) below. σ(T,ε,ε v )=σ0(ε v / ε0) m(T) … (4) However, in equation (4), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v ε0 is the strain rate (% / min) as a variable, in the range of 0.01% / min or greater, ε0 is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T(°C) and strain rates of 0.3% / min and 7.5% / min. [Effects of the Invention]

[0010] In the fire-resistant coated steel material design method of the present invention, in the first step, temperature T (°C), strain ε (%) and strain rate ε v We estimate a function equation representing the stress-strain curve of steel, with (% / min) as the variable, and based on the estimated function equation, we determine the strain rate ε v Stress at 1% strain (N / mm 2 The stress-temperature relationship at 1% strain is determined, which is the relationship between stress and temperature T. By using this stress-temperature relationship at 1% strain, the relationship between stress at 1% strain and temperature can be obtained at strain rates different from the conventionally used strain rate (=0.3% / min). From this relationship, it becomes possible to evaluate the high-temperature strength characteristics of steel at the strain rate applied to steel when a building is destroyed by fire. Furthermore, in the first step, the above equation (1) is used as the functional equation representing the stress-strain curve of the steel material, and the coefficient m obtained from the results of high-temperature tensile tests conducted under strain rate conditions of 0.3°C / min and 7.5°C / min is used as the strain rate sensitivity coefficient in the above equation (1), and the strain rate ε, which is the variable in equation (1), is used. v The range (% / min) is extended to 0.01% / min or greater. Next, in the second step, the relationship between stress at 1% strain and temperature is defined as the design load (N / mm²) when the steel material is used in a steel structure. 2 The temperature T' is determined by introducing the formula. This temperature T' represents the allowable temperature (°C) at which the steel material does not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature (°C) of the steel material. The determined thickness t (mm) of the fire-resistant coating material will be smaller than the thickness of the fire-resistant coating material designed based on the conventionally used strain rate (=0.3% / min). As described above, the fire-resistant coating steel design method of the present invention allows for the appropriate design of the thickness of the fire-resistant coating material without impairing the fire resistance performance of the fire-resistant coating steel material. The design value of the thickness of the fire-resistant coating material obtained by the present invention is thinner than the thickness of the fire-resistant coating material determined by conventional methods. Therefore, in buildings equipped with fire-resistant coating materials designed using the design method of the present invention, the space occupied by the fire-resistant coating material is reduced, making it possible to expand the living space and usable space within the building. Furthermore, the strain rate ε is a variable in equation (1). v By extending the range of (% / min) to 0.01% / min or higher, the deformation behavior of steel materials at strain rates lower than the conventionally used strain rate (=0.3% / min) can be reflected in the stress-temperature relationship at 1% strain, enabling the design of fire-resistant coatings with higher precision.

[0011] Furthermore, according to the method for manufacturing fire-resistant coated steel materials of the present invention, in addition to the first to third steps described above, in the fourth step, the steel material is covered with a fire-resistant coating material of thickness t obtained in the third step, thereby manufacturing fire-resistant coated steel materials in which the thickness of the fire-resistant coating material is appropriately designed without impairing the fire resistance performance of the fire-resistant coated steel material.

[0012] Furthermore, with respect to the fire-resistant coated steel material of the present invention, since the thickness of the fire-resistant coating material covering the steel material is the thickness t designed by the first to third steps described above, the thickness of the fire-resistant coating material can be set to an appropriate thickness without impairing the fire resistance performance.

[0013] Furthermore, according to the design program for fire-resistant coated steel materials of the present invention, in the first step, temperature T (°C), strain ε (%) and strain rate ε v We estimate a function equation representing the stress-strain curve of steel, with (% / min) as the variable, and based on the estimated function equation, we determine the strain rate ε v Stress at 1% strain (N / mm 2The stress-temperature relationship at 1% strain is determined, which is the relationship between stress and temperature T. By using this stress-temperature relationship at 1% strain, the relationship between stress at 1% strain and temperature can be obtained at strain rates different from the conventionally used strain rate (=0.3% / min). From this relationship, it becomes possible to evaluate the high-temperature strength characteristics of steel at the strain rate applied to steel when a building is destroyed by fire. Furthermore, in the first step, equation (2) above is used as the functional equation representing the stress-strain curve of the steel material, and the coefficient m obtained from the results of high-temperature tensile tests conducted under strain rate conditions of 0.3°C / min and 7.5°C / min is used as the strain rate sensitivity coefficient in equation (2), and the strain rate ε in equation (4) is used. v Extend the range of (% / minute) to include 0.01% / minute or greater. Next, in the second step, the relationship between stress at 1% strain and temperature is given to the design load (N / mm²) when the steel material is used in a steel structure. 2 The temperature T' is determined by introducing the formula. This temperature T' represents the allowable temperature (°C) at which the steel material does not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature (°C) of the steel material. The determined thickness t (mm) of the fire-resistant coating material will be smaller than the thickness of the fire-resistant coating material designed based on the conventionally used strain rate (=0.3% / min). As described above, the design program for fire-resistant coated steel materials of the present invention allows for the appropriate design of the thickness of the fire-resistant coating material without impairing its fire resistance performance. The design value for the thickness of the fire-resistant coating material obtained by the present invention is thinner than the thickness of the fire-resistant coating material determined by conventional methods. Therefore, in buildings equipped with fire-resistant coating materials designed using the design method of the present invention, the space occupied by the fire-resistant coating material is reduced, making it possible to expand the living space and usable space within the building. Furthermore, the strain rate ε is a variable in equation (4). vBy extending the range of (% / min) to 0.01% / min or higher, the deformation behavior of steel materials at strain rates lower than the conventionally used strain rate (=0.3% / min) can be reflected in the stress-temperature relationship at 1% strain, enabling the design of fire-resistant coatings with higher precision. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a graph showing the relationship between temperature T and the strain rate sensitivity coefficient m. [Figure 2A] Figure 2A is a reference example, showing a graph of the relationship between the stress at 1% strain obtained from a high-temperature tensile test of steel at 700°C and the strain rate, which is a condition for the high-temperature tensile test. [Figure 2B] Figure 2B is a graph showing the relationship between the stress at 1% strain obtained from a high-temperature tensile test of steel at 700°C and the strain rate, which is a condition for the high-temperature tensile test. [Figure 3] Figure 3 shows the results of a high-temperature deformation test conducted by applying a load at 700°C to an H-shaped steel beam with a support span of 5400 mm, a web width of 200 mm, and a height of 400 mm, as well as the results of a simulation of the said high-temperature deformation test. [Figure 4] Figure 4 compares the load at the point when the displacement reaches 1 / 300 of the support span (5400 / 300 = 18 mm) with the results shown in Figure 3. [Figure 5A] Figure 5A shows the stress-strain curve when a steel specimen is subjected to strain at a strain rate of 0.03% / min at 700°C, and includes both the measured curve and the estimated curve. [Figure 5B] Figure 5B shows the stress-strain curve when a steel specimen is subjected to strain at a strain rate of 0.1% / min at 700°C, and includes both the measured curve and the estimated curve. [Figure 5C] Figure 5C shows the stress-strain curve when a steel specimen is subjected to strain at a strain rate of 0.3% / min at 700°C, and includes both the measured curve and the estimated curve. [Figure 5D]Figure 5D shows the stress-strain curve when a steel specimen is subjected to strain at a strain rate of 3.0% / min at 700°C, and includes both the measured curve and the estimated curve. [Figure 5E] Figure 5E shows the stress-strain curve when a steel specimen is subjected to strain at a strain rate of 7.5% / min at 700°C, and includes both the measured curve and the estimated curve. [Figure 6] Figure 6 is a graph showing the relationship between stress (N / mm2) and temperature T at 1% strain. [Modes for carrying out the invention]

[0015] The following describes the design method and manufacturing method of fire-resistant coated steel materials, which are embodiments of the present invention.

[0016] The fire-resistant coated steel material design method of this embodiment is a method for designing fire-resistant coated steel material for a steel structure comprising a steel material and a fire-resistant coating material with a thickness t (mm) covering the surface of the steel material, and comprises a first step, a second step, and a third step.

[0017] The first step involves determining the temperature T (°C), strain ε (%), and strain rate ε. v We infer a functional equation representing the stress-strain curve of steel material with (% / min) as the variable, and from the inferred functional equation, we determine the strain rate ε v Stress at 1% strain (N / mm 2 We will determine the stress-temperature relationship at 1% strain, which is the relationship between ( ) and temperature T.

[0018] In the second step, the design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step. 2 The formula is used to determine the corresponding temperature T', and temperature T' is defined as the allowable temperature (°C) at which the steel material does not break.

[0019] In the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature (°C) of the steel material obtained in the second step.

[0020] Furthermore, the method for manufacturing fire-resistant coated steel according to this embodiment includes a fourth step in addition to the first to third steps described above. In the fourth step, fire-resistant coated steel is manufactured by covering the steel with a fire-resistant coating material of thickness t obtained in the third step.

[0021] The following explains each step.

[0022] (Step 1) In the first step, we first estimate the functional equation of the stress-strain curve of the steel material.

[0023] The function is given by temperature T (°C), strain ε (%), and strain rate ε v A functional equation can be used to represent the stress-strain curve of steel material with (% / min) as the variable. An example of such a functional equation is shown in equation (1) below. By appropriately setting the various parameters in equation (1), a stress-strain curve consisting of the relationship between stress and strain ε can be obtained from limited experimental data, with temperature T and strain rate ε v It becomes possible to estimate the stress-strain curve as a function with (% / min) as the variable. For example, it becomes possible to estimate the stress-strain curve when a tensile test is performed at 630°C and a strain rate of 0.7% / min.

[0024] Since the high-temperature strength properties of steel differ depending on the type of steel, equation (1) should be calculated for each type of steel.

[0025] σ(T,ε,ε v )=σ0(ε v / ε0) m(T) … (1)

[0026] In equation (1), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v σ(T,ε,ε) is the strain rate (% / min) as a variable, where ε0 is the reference strain rate of 0.3% / min and m(T) is the strain rate sensitivity coefficient. Also, the left side of equation (1) is σ(T,ε,εv ) is an estimated value of stress in the stress-strain curve, which is estimated by temperature T (°C), strain ε (%), and strain rate ε v (% / min).

[0027] The reference stress σ0 in Equation (1) is given by the following Equations (2) to (5). The parameters in each of Equations (2) to (5) are as follows. These parameters σ y , σ u , ε y , ε st , ε u , σ 20 , ε 20 , k, n, and α are all functions of temperature T.

[0028] E: Young's modulus σ y : Yield stress (0.2% proof stress) σ u : Tensile strength ε y : Yield strain (σ y / E) ε st : End strain of yield plateau ε u : Uniform elongation σ 20 : Stress at 20% strain ε 20 : Strain at 20% k, n: Coefficients related to strain hardening α: Coefficient related to temperature and strain rate of uniform elongation

[0029] <​​​​​​​​​​​​​Equation (6) shows that in the stress-strain curve, strain ε is equal to yield strain ε y Extreme surrender shelf end strain ε st The reference stress σ0 is shown within the following range.

[0032] Equation (7) shows that in the stress-strain curve, strain ε is equal to yield rack end strain ε st Super, uniform elongation ε u The product of αε and the coefficient α u The reference stress σ0 in the following range is shown. That is, equation (7) represents the stress in the stress-strain curve of steel between the yield stress and the appearance of tensile strength.

[0033] Equation (8) shows that in the stress-strain curve, the strain ε is equal to the uniform elongation ε. u The product of αε and the coefficient α u This shows the reference stress σ0 in the range above. In other words, equation (8) is an equation that shows the decrease in stress after tensile strength in the stress-strain curve of steel.

[0034] Each parameter in equations (5) to (8), which is a function of temperature T, can be determined experimentally. For example, a tensile test is performed on the steel in question in accordance with JIS G 0567:2020 to obtain the relationship between stress and strain. The test specimens shall be those specified in Annex A of JIS G 0567:2020. The strain rate shall be 0.3% / min, and the test temperatures shall be, for example, 20°C, 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, and 800°C. Note that the test temperatures are not limited to those exemplified; the test temperatures should be set to include the temperature of the steel when the fire-resistant coated steel is exposed to fire.

[0035] The tensile test determined the measured stress value σ for each test temperature. R Combined data of and strain ε are obtained. Based on these measurement data, each parameter σ is adjusted so that equations (5) to (8) above fit best. y , σ u , ε y , ε st , ε u , σ 20 , ε 20Determine k, n, and α. Optimization of each parameter can be done using, for example, differential evolution (DE). By optimizing each parameter, each parameter σ y , σ u , ε y , ε st , ε u , σ 20 , ε 20 Determine k, n, and α as functions of temperature T.

[0036] Note that the coefficient α depends on the strain rate in addition to temperature, which is ε u This coefficient takes into account the change in temperature, and the coefficient α is a function of temperature and strain rate. When the strain rate is 0.3% / min, α = 1 regardless of temperature.

[0037] The strain rate sensitivity coefficient m(T) in equation (1) is a function of temperature T and is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with temperature T (°C) and strain rates of 0.3% / min and 7.5% / min. The method for deriving the strain rate sensitivity coefficient m(T) is described below.

[0038] For example, the measurement temperature T' is set to 400°C, 500°C, 600°C, 700°C, and 800°C. At each measurement temperature T', a high-temperature tensile test is performed on the target steel material under conditions of 0.3% / min and 7.5% / min, in accordance with JIS G 0567:2020. This allows the stress at 1% strain to be obtained for each strain rate of 0.3% / min and 7.5% / min.

[0039] By introducing the 1% strain stress at 0.3% / min and 7.5% / min strain rates, and the measurement temperature T' obtained from high-temperature tensile tests of steel materials, into equation (1), the strain rate sensitivity coefficient m(T') for each temperature T' is determined. Then, a plot is obtained with temperature T on the horizontal axis and the strain rate sensitivity coefficient m(T) on the vertical axis. Then, for the strain rate sensitivity coefficient m(T') determined for each temperature T', m(T) at an arbitrary temperature T is determined.

[0040] To find m(T) at an arbitrary temperature T, we use the function in equation (9) below.

[0041]

number

[0042] In equation (9), for example, m0, m1, m2, and m3 can be set to m0=0.0103, m1=5.5, m2=587, and m3=0.169, respectively.

[0043] The plots in Figure 1 represent the values ​​of m(T') when the stress-strain curve from an actual tensile test approximately matches equation (1), while the solid line in Figure 1 represents equation (9), with m0, m1, m2, and m3 being values ​​adjusted so that the solid line is close to each plot.

[0044] The temperature range T for which equation (1) holds can be adjusted by appropriately setting the measurement temperature T of the tensile test of the steel material used when determining each parameter. For example, if the measurement temperature is set to 20 to 800°C as described above, then the temperature T can be set to at least the range of 20 to 800°C.

[0045] The strain rate sensitivity coefficient m(T) is determined based on the stress at 1% strain of steel at strain rates of 0.3% / min and 7.5% / min, while the strain rate ε is a variable in equation (1). v The strain rate ε in equation (1) is not limited to the range of 0.3 to 7.5% / min, but may be in the range of 0.01 to less than 0.3% / min, or in the range of 7.5% / min or more. v This can be set to a range of 0.01% / minute or more. The reason for this is explained below.

[0046] Figure 2A plots the relationship between the stress at 1% strain obtained from high-temperature tensile tests of steel at 700°C and the strain rate, which is a condition for the high-temperature tensile test. The strain rates used are 0.03, 0.1, 0.3, 3.0, and 7.5% / min. The vertical axis is the logarithm of the stress at 1% strain, and the horizontal axis is the logarithm of the strain rate. In the range of strain rates above 0.3% / min, the straight line is the line connecting the two plot points at strain rates of 0.3% / min and 7.5% / min, and in the range of strain rates below 0.3% / min, it is the logarithm of the stress at 1% strain at a strain rate of 0.3% / min.

[0047] Figure 2B plots the relationship between the stress at 1% strain obtained from high-temperature tensile tests of steel at 700°C and the strain rate, which is a condition for the high-temperature tensile test. The strain rates are 0.03, 0.1, 0.3, 3.0, and 7.5% / min. When the vertical axis is the logarithm of the stress at 1% strain and the horizontal axis is the logarithm of the strain rate, there is an almost linear relationship between the stress at 1% strain and the strain rate. The straight line in the figure connects the plots of two points at strain rates of 0.3% / min and 7.5% / min. As shown in Figure 2B, this line is close to the plots in the range of 0.03 to 0.3% / min, and it can be seen that extrapolation is possible using the straight line connecting the plots at 0.3% / min and 7.5% / min.

[0048] Figure 3 shows the results of a high-temperature deformation test on an H-beam with a support span of 5400 mm, a web width of 200 mm, and a height of 400 mm, after being heated to 700°C and then loaded. The load was applied by pushing down with jacks at a speed of 0.05 kN / second at two locations 900 mm apart on both sides of the longitudinal direction from the longitudinal center of the H-beam. The vertical dashed line in Figure 3 indicates a displacement equivalent to 1 / 300 of the support span. The "Design Criteria for Allowable Stress of Steel Structures" (Architectural Institute of Japan, revised October 15, 2019) sets a limit on the amount of deflection of beam members supporting live loads at room temperature, and recommends that the design ensure that this deflection is less than or equal to 1 / 300 of the support span. The line labeled A in Figure 3 shows the relationship between the load and the displacement of the longitudinal center of the H-shaped steel beam. The line labeled B in Figure 3 is a straight line connecting two plots of strain rates, 0.3% / min and 7.5% / min, as shown in Figure 2A. The range above 7.5% / min is extrapolated, and the range below 0.3% / min is kept constant at the logarithmic value of the stress at 1% strain at a strain rate of 0.3% / min. Based on this relationship, the simulation was performed according to the first step of this embodiment. Note that this result is for reference only. Furthermore, the line labeled C in Figure 3 is a straight line connecting two plotted points representing strain rates of 0.3% / min and 7.5% / min, as shown in Figure 2B. The ranges of 0.01 to 0.3% / min and 7.5% / min and above are the results of a simulation performed according to the first step of this embodiment, based on the relationship obtained by extrapolating this straight line.

[0049] Figure 4 shows the load at displacement δ = L / 300 (the load in the vertical dashed line in Figure 3) for each curve A to C in Figure 3. Here, L is the support span, and L = 5400 mm. As shown in Figures 3 and 4, when the simulation was performed based on the relationship shown in Figure 2B, the relationship between the measured and simulated behavior up to reaching the deflection limit at room temperature design was better in agreement with the measured behavior compared to when the simulation was performed based on the relationship shown in Figure 2A. From this, the strain rate sensitivity coefficient m(T) obtained based on the stress at 1% strain at strain rates of 0.3% / min and 7.5% / min is given by equation (1) with respect to the strain rate ε v It can be said that this is applicable to strain rates of 0.01% / min or more, preferably in the range of 0.01 to 10% / min. Therefore, strain rate ε v This should be in the range of 0.01% / min or more. Preferably, it may be in the range of 0.01 to 10% / min.

[0050] Figures 5A to 5E schematically show examples of stress-strain curves when a steel specimen is subjected to strain at strain rates of 0.03% / min, 0.1% / min, 0.3% / min, 3.0% / min, and 7.5% / min at 700°C. Figure 5A shows the example for a strain rate of 0.03% / min, Figure 5B shows the example for a strain rate of 0.1% / min, Figure 5C shows the example for a strain rate of 0.3% / min, Figure 5D shows the example for a strain rate of 3.0% / min, and Figure 5E shows the example for a strain rate of 7.5% / min. Figures 5A to 5E also show both the measured curves and the curves estimated using the estimation method of this embodiment. As is clear from the measured curves shown in Figures 5A to 5E, when the temperature is constant, it can be seen that the stress-strain curve shifts to the higher stress side as the strain rate increases. Furthermore, as is clear from the inferred curves shown in Figures 5A to 5E, the inferred curves are in good agreement with the measured curves. By inferring equation (1) in the first step, it becomes possible to accurately predict the stress-strain curve for each temperature or strain rate. In addition, from the predicted stress-strain curve, the stress at 1% strain (N / mm²) can be calculated. 2 It also becomes possible to calculate ).

[0051] Next, based on equation (1), which is the functional equation of the predicted stress-strain curve, the stress at 1% strain (N / mm²) is calculated. 2 The relationship between ) and temperature T is determined. For example, by introducing 20 to 800°C as the temperature T into the estimated equation (1), and introducing 0.3% / min and 7.5% / min as strain rates, the stress when the strain ε is 1% is σ(T=20~800°C, ε=1%, ε v =0.3% / min) and σ(T=20~800℃, ε=1%, ε v Calculate the stress (N / mm²) at 1% strain. 2 The reason for selecting (N / mm²) is that the "Guidelines for Fire-Resistant Design of Steel Structures, 3rd Edition" (edited by the Architectural Institute of Japan, published June 2017) states that "when examining the actual behavior of frames and members during a fire, it is appropriate to use the response stress value exhibited by the steel material at a strain of approximately 1% as the effective yield strength, regardless of the member temperature or steel type." Based on this description, in this embodiment, the stress at 1% strain (N / mm²) is used.2 We are trying to find the relationship between ) and temperature T.

[0052] Figure 6 shows the stress (N / mm²) at 1% strain. 2 An example of the relationship between ) and temperature T is shown in the graph. Figure 6 shows a tensile strength of 590 N / mm 2 This graph was obtained based on the stress-strain curve calculated from equation (1) for the steel of the specified grade. Figure 6 shows the tensile strength of 590 N / mm². 2 For grade steel, the stress at 1% strain (N / mm²) is calculated for strain rates of 0.3% / min and 7.5% / min. 2 The curves between ) and temperature T are shown. These curves are derived from equation (1) which was inferred in the first step.

[0053] As shown in Figure 6, for example, the stress at 1% strain is 300 (N / mm²). 2 In this case, the curve for a strain rate of 7.5% / min is higher at higher temperatures than the curve for a strain rate of 0.3% / min. This indicates that the deformation temperature of steel under a constant stress (stress equivalent to the stress that causes 1% strain) increases with increasing strain rate. Therefore, at strain rates that would cause steel to break in a building fire, the steel does not deform until it reaches a higher temperature, demonstrating superior fire resistance. In other words, it shows that sufficient fire resistance can be maintained even with a thinner fire-resistant coating.

[0054] (Step 2) Next, in the second step, the design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step. 2 By introducing ), the corresponding temperature T' is determined, and this temperature T' is taken as the allowable temperature (°C) at which the steel material does not break.

[0055] Furthermore, the "allowable temperature (°C) at which steel does not break" should preferably be higher than the temperature at which the test specimen is deemed acceptable according to the criteria described in "6. Judgment" on pages 7-8 of the "Fire Resistance Performance Testing and Evaluation Procedure Manual" (created by the Japan Building Research Institute, revised June 15, 2020, 8A-103-01 (Rev. 4.0)), based on the test method described in "4.1 Fire Resistance Performance Test Method" on pages 4-8.

[0056] (Step 3) In the third step, the thickness t (mm) of the fire-resistant coating is determined from the allowable temperature (°C) of the steel material obtained in the second step. The method for determining the thickness t (mm) of the fire-resistant coating can be based on the conventionally known relationship between the allowable temperature (°C) of the steel material and the thickness t (mm) of the fire-resistant coating. That is, in the case of fire-resistant coated steel material, let the thickness of the fire-resistant coating be t (mm), and when the steel material coated with the fire-resistant coating is heated, the temperature of the steel material after 2 hours from the start of heating is T. 2h If we let (°C), then t and T 2h is, T 2h The relationship is =at + b (where a and b are constants determined by the type of fire-resistant coating material), so based on this relationship, the thickness t (mm) of the fire-resistant coating material can be determined from the allowable temperature (°C) of the steel material.

[0057] (Step 4) In the fourth step, fire-resistant coated steel is manufactured by coating the steel with a fire-resistant coating material of thickness t obtained in the third step. The fire-resistant coating material may be applied by any of the following methods: spraying the fire-resistant coating material onto the surface of the steel; painting a paint containing the fire-resistant coating material onto the surface of the steel; attaching a plate made of the fire-resistant coating material to the surface of the steel; or wrapping a sheet made of the fire-resistant coating material around the surface of the steel.

[0058] The fire-resistant coated steel material obtained in this manner has a thickness of fire-resistant coating material that matches the design value determined through the first to third steps described above, and thus possesses sufficient fire resistance.

[0059] The steel material used in the fire-resistant coated steel material of this embodiment has a yield strength σ at 20°C. y 235 N / mm 2 It may be greater than or equal to 335 N / mm 2 It may be greater than or equal to 355 N / mm 2 It may be greater than or equal to 385 N / mm 2 That's fine too.

[0060] Furthermore, the steel material may be any of H-shaped steel, square steel pipe, or circular steel pipe.

[0061] In this embodiment, when the steel material consists of H-shaped steel, it is preferable to use the fire-resistant coated steel material for either the main beam or the secondary beam of the steel structure. Furthermore, when the steel material consists of rectangular or circular steel pipes, the fire-resistant coated steel material of this embodiment is preferably used for columns of steel structures.

[0062] Furthermore, it is preferable that the fire-resistant coating material is one of the following: a sprayed layer, a painted layer, a molded board, or a wrapped body.

[0063] As explained above, in the fire-resistant coated steel material design method of this embodiment, in the first step, temperature T (°C), strain ε (%) and strain rate ε v We deduce equation (1), which is a functional equation representing the stress-strain curve of steel, with (% / min) as the variable, and based on the deduction of equation (1), we determine the strain rate ε v Stress at 1% strain (N / mm 2 The stress-temperature relationship at 1% strain is determined, which is the relationship between stress and temperature T. By using this stress-temperature relationship at 1% strain, the relationship between stress at 1% strain and temperature can be obtained at strain rates different from the conventionally used strain rate (=0.3% / min). From this relationship, it becomes possible to evaluate the high-temperature strength characteristics of steel at the strain rate applied to steel when a building is destroyed by fire. Next, in the second step, the relationship between stress at 1% strain and temperature is given to the design load (N / mm²) when the steel material is used in a steel structure. 2The temperature T' is determined by introducing the formula. This temperature T' represents the allowable temperature (°C) at which the steel material does not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature (°C) of the steel material. The determined thickness t (mm) of the fire-resistant coating material will be smaller than the thickness of the fire-resistant coating material designed based on the conventionally used strain rate (=0.3% / min). Furthermore, in the first step, equation (1) is used, and as the strain rate sensitivity coefficient in equation (1), the coefficient m(T) obtained from the results of high-temperature tensile tests conducted under strain rate conditions of 0.3% / min and 7.5% / min is used, and the strain rate ε, which is the variable in equation (1), is used. v The range of (% / min) is extended to include values ​​of 0.01% / min or higher. This allows the deformation behavior of steel materials at strain rates lower than the conventionally used strain rate (=0.3% / min) to be reflected in the stress-temperature relationship at 1% strain, enabling the design of fire-resistant coatings with higher precision. As described above, the design method for fire-resistant coated steel materials of this embodiment allows for the appropriate design of the thickness of the fire-resistant coating material without impairing its fire resistance performance.

[0064] The design thickness of the fire-resistant coating obtained by this embodiment is thinner than the thickness of the fire-resistant coating determined by conventional methods. Therefore, in buildings equipped with fire-resistant coatings designed using the design method of this embodiment, the space occupied by the fire-resistant coating is reduced, making it possible to expand the living space and usable space within the building.

[0065] Furthermore, according to the manufacturing method of fire-resistant coated steel of this embodiment, in addition to the first to third steps described above, a fourth step is performed. In the fourth step, the steel material is coated with a fire-resistant coating material of thickness t obtained in the third step, thereby manufacturing the fire-resistant coated steel. Therefore, according to the manufacturing method of this embodiment, it is possible to manufacture fire-resistant coated steel with an appropriately designed thickness of fire-resistant coating material without impairing the fire resistance performance of the fire-resistant coated steel.

[0066] Furthermore, with the fire-resistant coated steel material of this embodiment, since the thickness of the fire-resistant coating material covering the steel material is the thickness t designed by the first to third steps described above, the thickness of the fire-resistant coating material can be set to an appropriate thickness without impairing the fire resistance performance.

[0067] Next, the design program for fire-resistant coated steel materials for steel structures according to this embodiment will be described. The design program of this embodiment is a program to be executed by a computer, and consists of a first step, a second step, and a third step.

[0068] The first step involves determining the temperature T (°C), strain ε (%), and strain rate ε. v We infer a functional equation representing the stress-strain curve of steel material with (% / min) as the variable, and from the inferred functional equation, we determine the strain rate ε v Stress at 1% strain (N / mm 2 We will determine the stress-temperature relationship at 1% strain, which is the relationship between ( ) and temperature T.

[0069] The second step involves applying the design load (N / mm²) when used as a steel structure to the 1% strain stress-temperature relationship obtained in the first step. 2 The formula is used to determine the corresponding temperature T', and temperature T' is defined as the allowable temperature (°C) at which the steel material does not break.

[0070] The third step involves determining the thickness t (mm) of the fire-resistant coating material based on the allowable temperature (°C) of the steel material obtained in the second step.

[0071] The function expression in the first step may be the function expression represented by equation (1) above, or the function expression represented by equation (2) above.

[0072] The specific details of Step 1, Step 2, and Step 3 are as described in Step 1, Step 2, and Step 3 of the design method mentioned earlier.

[0073] According to the design program of this embodiment, the thickness of the fire-resistant coating material can be appropriately designed without impairing the fire resistance performance of the fire-resistant steel coating material. The design value of the fire-resistant coating material thickness obtained by this embodiment is thinner than the thickness of the fire-resistant coating material determined by conventional methods. Therefore, in buildings equipped with fire-resistant coating materials designed using the design program of this embodiment, the space occupied by the fire-resistant coating material is reduced, making it possible to expand the living space and usable space within the building. Also, strain rate ε v By extending the range of (% / min) to include 0.01% / min and above, the deformation behavior of steel materials at strain rates lower than the conventionally used strain rate (=0.3% / min) can be reflected in the stress-temperature relationship at 1% strain, enabling the design of fire-resistant coatings with higher precision.

[0074] The present invention is not limited to the above embodiments, and the function formula used in the first step may be changed. That is, instead of formula (1) above, formula (A) below may be used as the function formula.

[0075] σ(T,ε,ε v )=σ0(ε v / ε0) m(T) … (A)

[0076] In equation (A), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε v This is the stress value at (% / min), where σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v σ(T,ε,ε) is the strain rate (% / min) as a variable, where ε0 is the reference strain rate of 0.3% / min and m(T) is the strain rate sensitivity coefficient. Also, the left side of equation (A) is σ(T,ε,ε v ) is an estimated value of stress in the stress-strain curve, where temperature T (°C), strain ε (%), and strain rate ε v This is an estimated value based on (% / minute).

[0077] The procedure for calculating σ0 and m(T) in equation (A) can be the same as the procedure for calculating σ0 and m(T) in equation (1). [Examples]

[0078] Next, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0079] (Examples) As a steel material, the plate thickness is 48 mm and the tensile strength is 590 N / mm². 2 Grade steel was prepared and cut to appropriate sizes to form test specimens as specified in Annex A of JIS G 0567:2020. Tensile tests were performed on the obtained test specimens in accordance with JIS G 0567:2020, with a strain rate of 0.3% / min and test temperatures of 20°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C, to obtain stress-strain curves. Based on the obtained stress-strain curves, equations (1) to (5) above were estimated.

[0080] Furthermore, the strain rate sensitivity coefficient m(T) in equation (1) was determined, as mentioned above, based on the stress at 1% strain for steel materials at temperature T(°C) and strain rates of 0.3% / min and 7.5% / min.

[0081] Next, based on the estimated equation (1), the stress at 1% strain (N / mm 2 The relationship between ) and temperature T was determined. Figure 6 shows the tensile strength of 590 N / mm². 2 For grade steel, stress at 1% strain (N / mm²) 2 The relationship between () and temperature T is shown in the graph. Figure 6 shows the stress (N / mm²) at 1% strain for strain rates of 0.3% / min and 7.5% / min. 2 The curve between ) and temperature T is shown.

[0082] Next, in the stress-temperature relationship at 1% strain shown in Figure 6, the design load (N / mm²) when used as a steel structure is calculated. 2The temperature T' (allowable temperature of steel (°C)) was determined by introducing the formula. In this example, data of a strain rate of 7.5% / min was used. The design load was 440 / 1.5 = 293 (N / mm²). 2 The temperature T' (allowable temperature of the steel (°C)) in this case was 650°C.

[0083] Next, the thickness t (mm) of the fire-resistant coating material was determined from the obtained allowable temperature (°C) (=650°C). The thickness t (mm) of the fire-resistant coating material was 52 mm.

[0084] Tensile strength of 590 N / mm for plates with thicknesses of 32 mm and 19 mm. 2 By cutting grade steel to an appropriate size, plate material with a thickness of 32 mm was cut to form the upper and lower flange sections, and plate material with a thickness of 19 mm was cut to form the web section. By welding the upper flange section, lower flange section, and web section together, an H-beam with a height of 1000 mm and a width of 300 mm for the upper and lower web sections was manufactured.

[0085] Then, the entire H-shaped steel beam was covered with a fire-resistant coating. The thickness of the fire-resistant coating was 52 mm. In this way, the fire-resistant coated steel material of the embodiment was manufactured.

[0086] (Reference example) For reference, the tensile strength of plates with thicknesses of 32mm and 19mm is 590N / mm². 2 Grade steel was prepared and cut to an appropriate size to produce plates with a thickness of 32 mm for the upper and lower flange sections and plates with a thickness of 19 mm for the web section. By welding the upper flange section, lower flange section and web section together, an H-beam was manufactured with a height of 1000 mm and a width of 300 mm for the upper and lower web sections.

[0087] Then, using this H-shaped steel as the test material, the test was conducted according to the test method described in "4.1 Fire Resistance Test Method" on pages 4 to 8 of the "Fire Resistance Performance Testing and Evaluation Procedure Manual" (created by the Japan Building Research Institute, revised June 15, 2020, 8A-103-01 (Rev. 4.0)), and the temperature at which the test specimen was deemed acceptable according to the judgment criteria described in "6. Judgment" on pages 7 to 8 was measured. As a result, a temperature of 550°C was obtained.

[0088] Next, the thickness t (mm) of the fire-resistant coating material was determined from the obtained temperature (=550℃), and the thickness t (mm) of the fire-resistant coating material was found to be 65mm.

[0089] Similarly to the above, the tensile strength of 590 N / mm for plates with thicknesses of 32 mm and 19 mm was determined. 2 We manufactured an H-shaped steel beam made of graded steel, with a height of 1000 mm and a width of 300 mm between the upper and lower web sections. Then, the entire H-shaped steel beam was covered with a fire-resistant coating. The thickness of the fire-resistant coating was 65 mm. In this way, the fire-resistant coated steel material for the reference example was manufactured.

[0090] (evaluation) The fire resistance performance of the fire-resistant coated steel materials in the examples and comparative examples was confirmed. The fire resistance performance was confirmed in accordance with the "Methods for Testing and Evaluating Fire Resistance Performance" described above. As a result, all materials showed fire resistance for 2 hours or more. Therefore, the fire-resistant coated steel material of the embodiment, which is an example of the present invention, exhibited fire resistance performance equivalent to that of the reference example, even though the thickness of the fire-resistant coating material was thinner than that of the reference example.

Claims

1. A method for designing fire-resistant coated steel material for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε ｖ A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε is determined. ｖ Stress at 1% strain (N / mm ２ The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T, The design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. ２ The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. The process comprises a third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material determined in the second step, A design method for fire-resistant coated steel, wherein the aforementioned function is equation (1) below. σ (T, e, e) ｖ )=s ０ (e) ｖ / e ０ ) ｍ（Ｔ） … (1) However, in equation (1), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε ｖ This is the stress value in (% / min), σ ０ This is the standard stress value at a strain rate of 0.3% / min, and ε ｖ This is the strain rate (% / min) as a variable, and is in the range of 0.01% / min or more, ε ０ is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain obtained by high-temperature tensile tests of the steel material under the conditions of temperature: T (°C) and strain rates: 0.3% / min and 7.5% / min.

2. A method for manufacturing a fire-resistant coated steel material for a steel structure, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε ｖ A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε is determined. ｖ Stress at 1% strain (N / mm ２ The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T, The design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. ２ The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step involves determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step, A fourth step is to manufacture the fire-resistant coated steel material by covering the steel material with the fire-resistant coating material of thickness t obtained in the third step, Equipped with, A method for manufacturing fire-resistant coated steel, wherein the aforementioned function is the following equation (2). σ (T, e, e) ｖ )=s ０ (e) ｖ / e ０ ) ｍ（Ｔ） … (2) However, in equation (2), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε ｖ This is the stress value in (% / min), σ ０ This is the standard stress value at a strain rate of 0.3% / min, and ε ｖ This is the strain rate (% / min) as a variable, and is in the range of 0.01% / min or more, ε ０ is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T (°C) and strain rates of 0.3% / min and 7.5% / min.

3. A fire-resistant coated steel material for steel structures, comprising a steel material and a fire-resistant coating material having a thickness t (mm) that covers the surface of the steel material, Temperature T (°C), strain ε (%), and strain rate ε ｖ A function equation representing the stress-strain curve of the steel material, with (% / min) as a variable, is estimated, and from the estimated function equation, the strain rate ε is determined. ｖ Stress at 1% strain (N / mm ２ The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T, The design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. ２ The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. A third step is to determine the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material determined in the second step, and the fire-resistant coating material having the thickness t determined by the third step, A fire-resistant coated steel material in which the above function equation is equation (3) below. σ (T, e, e) ｖ )=s ０ (e) ｖ / e ０ ) ｍ（Ｔ） … (3) However, in equation (3), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε ｖ This is the stress value in (% / min), σ ０ This is the standard stress value at a strain rate of 0.3% / min, and ε ｖ ε is the strain rate (% / min) as a variable, ０ is a reference strain rate of 0.3% / min and is in the range of 0.01% / min or higher, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T (°C) and strain rates of 0.3% / min and 7.5% / min.

4. The fire-resistant coated steel material according to claim 3, wherein the fire-resistant coating material is any of a sprayed layer, a painted layer, a molded plate, or a wrapped body.

5. The aforementioned steel material has a yield strength σ at 20°C. ｙ 235 N / mm ２ The above is the fire-resistant coated steel material according to claim 3.

6. The aforementioned steel material has a yield strength σ at 20°C. ｙ 335 N / mm ２ The above is the fire-resistant coated steel material according to claim 3.

7. The aforementioned steel material has a yield strength σ at 20°C. ｙ 355 N / mm ２ The above is the fire-resistant coated steel material according to claim 3.

8. The aforementioned steel material has a yield strength σ at 20°C. ｙ 385 N / mm ２ The above is the fire-resistant coated steel material according to claim 3.

9. A design program for fire-resistant coated steel material for steel structures, comprising a steel material and a fire-resistant coating material with a thickness t (mm) covering the surface of the steel material, A function equation representing the stress-strain curve of the steel material is estimated, with temperature T (°C), strain ε (%), and strain rate εv (% / min) as variables. From the estimated function equation, the stress (N / mm²) at 1% strain at strain rate εv is calculated. ２ The first step is to determine the stress-temperature relationship at 1% strain, which is the relationship between ) and temperature T, The design load (N / mm²) when used as a steel structure is applied to the 1% strain stress-temperature relationship obtained in the first step described above. ２ The second step involves introducing a formula to determine the corresponding temperature T', and setting the temperature T' as the allowable temperature (°C) at which the steel material does not break. The process comprises a third step of determining the thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material determined in the second step, A design program for fire-resistant coated steel, wherein the function expression is equation (4) below. σ (T, e, e) ｖ )=s ０ (e) ｖ / e ０ ) ｍ（Ｔ） … (4) However, in equation (4), σ represents temperature: T (°C), strain: ε (%), and strain rate: ε ｖ This is the stress value in (% / min), σ ０ This is the standard stress value at a strain rate of 0.3% / min, and ε ｖ This is the strain rate (% / min) as a variable, and is in the range of 0.01% / min or more, ε ０ is the reference strain rate of 0.3% / min, and m(T) is the strain rate sensitivity coefficient, which is a coefficient determined based on the stress at 1% strain of the steel material measured by a high-temperature tensile test according to JIS G 0567:2020, with a temperature of T (°C) and strain rates of 0.3% / min and 7.5% / min.

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