Design method for fire-resistant coated steel material, manufacturing method for fire-resistant coated steel material

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: Figure 1

Description

[Technical field]

[0001] The present invention relates to a design method for a fire-resistant coated steel material, a manufacturing method for a fire-resistant coated steel material, a fire-resistant coated steel material, and a design program for a fire-resistant coated steel material. [Background technology]

[0002] It is known that the strength of steel materials decreases as the temperature increases. Therefore, when steel materials are used as structural members of a building, it is necessary to ensure fire resistance so that the building does not collapse while residents and users are evacuating in the event of a fire. Therefore, when H-shaped steel beams are used as structural members, 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 Summary of the Invention [Problem to be solved by the invention]

[0004] Although it has been known for some time that the strength of steel material decreases at high temperatures, in order to actually carry out tensile tests on steel material at high temperatures, it is necessary to handle the steel material in a high-temperature state. However, in reality, since it is difficult to handle steel material in a high-temperature state, there are fewer test examples compared to tests at room temperature, and only sporadic test results have been obtained.

[0005] For example, the Japanese Industrial Standards (JIS) recommends that tensile tests of steel materials be performed at a strain rate of 0.3% / min. This is why a strain rate of 0.3% / min is commonly used to evaluate the fire resistance of steel structures. However, recent research has revealed that when a steel structure building is destroyed by fire or other events, the beams and columns are subjected to loads corresponding to strain rates significantly exceeding 0.3% / min. In this way, when the strain rate increases, the high-temperature strength of the steel material may become higher than expected. Therefore, tests are performed based on the conventional test method, and fire-resistant coated steel materials designed based on the test results may have an overestimated fire resistance because the design assumptions are different from the actual situation.

[0006] In addition, when designing the thickness of the fire-resistant coating that covers steel in the case of fire-resistant coated steel, full-scale beams and columns are prepared and heated while a simulated load is applied to these beams and columns to determine their deformation behavior and then the thickness of the fire-resistant coating is determined based on experience, but determining the thickness requires a great deal of time and effort.

[0007] The present invention has been made in consideration of the above circumstances, and makes it possible to easily and appropriately design the thickness of a fire-resistant coating material without impairing the fire resistance performance of a fire-resistant coating steel material. The object of the present invention is to provide a method for designing and manufacturing a fire-resistant coated steel material. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A method for designing a fire-resistant coated steel material for a steel structure having a steel material and a fire-resistant coating material with a thickness of t (mm) covering the surface of the steel material, comprising: Temperature T (℃), strain ε (%), and strain rate ε v A function formula expressing the stress-strain curve of the steel material with (% / min) as a variable The strain rate sensitivity coefficient m in the functional formula (1) below is calculated based on experimental data. , Including the strain rate sensitivity coefficient m obtained From the function formula, the strain rate ε v Stress at 1% strain (N / mm 2) and temperature T, the stress-temperature relationship at 1% strain is Guess The first step, In the first step Guessed The stress-temperature relationship at 1% strain is calculated based on the design load (N / mm 2 ) to obtain a corresponding temperature T', and the temperature T' is set as the allowable temperature (°C) of the steel material at which the steel material is not damaged; A method for designing a fire-resistant coated steel material comprising: a third step of determining a thickness t (mm) of the fire-resistant coating material from the allowable temperature (°C) of the steel material obtained in the second step. σ(T,ε,ε v )=σ 0 (ε v / ε 0 ) m … (1) However, σ in formula (1) 0 is the reference stress value at a strain rate of 0.3% / min, and ε v is the strain rate (% / min) as a variable, and ε 0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient. [ 2 A method for producing 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 a surface of the steel material, the method comprising the steps of: Temperature T (℃), strain ε (%), and strain rate ε v A function formula expressing the stress-strain curve of the steel material with (% / min) as a variable The strain rate sensitivity coefficient m in the functional formula (2) below is calculated based on experimental data. , Including the strain rate sensitivity coefficient m obtained From the function formula, the strain rate ε v Stress at 1% strain (N / mm 2 ) and temperature T, the stress-temperature relationship at 1% strain is Guess The first step, In the first step Guessed The stress-temperature relationship at 1% strain is calculated based on the design load (N / mm 2 ) to obtain a corresponding temperature T', and the temperature T' is set as the allowable temperature (°C) of the steel material at which the steel material is not damaged; A third step of determining a thickness t (mm) of the fire-resistant coating material from the allowable steel temperature (°C) obtained in the second step; and a fourth step of producing the fire-resistant coated steel material by covering the steel material with the fire-resistant coating material having a thickness t obtained in the third step. σ(T,ε,ε v )=σ 0 (ε v / ε 0 ) m … (2) However, σ in Equation (2) 0 is the reference stress value at a strain rate of 0.3% / min, and ε v is the strain rate (% / min) as a variable, and ε 0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient. [3] The steel material has a yield strength of σ y is 235N / mm 2 That's all. [2] The fire-resistant coated steel material described in Manufacturing method . [4] The steel material has a yield strength of σ y is 335N / mm 2 That's all. [2] The fire-resistant coated steel material described in Manufacturing method . [5] The steel material has a yield strength of σ y is 355N / mm 2 That's all. [2] The fire-resistant coated steel material described in Manufacturing method . [6] The steel material has a yield strength of σ y is 385N / mm 2 That's all. [2] The fire-resistant coated steel material described in Manufacturing method . [7] The steel material is either an H-shaped steel, a square steel pipe, or a circular steel pipe. [2] ~ [6] The fire-resistant coated steel material according to any one of claims 1 to 5. Manufacturing method . [8] When the steel material is the H-shaped steel, it is used for either a main beam or a sub-beam in the steel structure. [7] The fire-resistant coated steel material described in Manufacturing method . [9] When the steel material is the square steel pipe or the circular steel pipe, it is used for a column in the steel structure. [7] The fire-resistant coated steel material described in Manufacturing method .

[10] The fire-resistant coating material is any one of a sprayed layer, a painted layer, a molded plate, and a wound body; [2] ~ [9] The fire-resistant coated steel material according to any one of claims 1 to 5. Manufacturing method . Effect of the Invention

[0009] In the design method of fire-resistant coated steel material of the present invention, in the first step, temperature T (℃), strain ε (%) and strain rate ε v The function that expresses the stress-strain curve of the steel material with the variable (% / min) is estimated, and the strain rate ε v Stress at 1% strain (N / mm 2 ) and temperature T, the stress-temperature relationship at 1% strain is calculated. By using this stress-temperature relationship at 1% strain, the relationship between stress and temperature at 1% strain at a strain rate different from the conventionally used strain rate (=0.3% / min) can be obtained. From this relationship, it is possible to evaluate the high temperature strength properties of steel at the strain rate applied to the steel when a building is destroyed by fire. In the second step, the design load (N / mm2) for the steel material to be used in a steel structure is applied to the relationship between the stress at 1% strain and the temperature. 2 ) is introduced to find the temperature T'. This temperature T' is the allowable temperature (℃) at which the steel material will not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature of the steel (℃). The determined thickness t (mm) of the fire-resistant coating material is smaller than the thickness of the fire-resistant coating material designed based on the conventionally used strain rate (=0.3% / min). As described above, according to the design method for fire-resistant coated steel material of the present invention, the thickness of the fire-resistant coating material can be appropriately designed without impairing the fire resistance performance of the fire-resistant coated 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 the conventional method. Therefore, in a building equipped with a fire-resistant coating material designed by 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.

[0010] Furthermore, according to the method for manufacturing fire-resistant coated steel material of the present invention, in addition to the above-mentioned first to third steps, in the fourth step, fire-resistant coated steel material is produced by coating steel material with the fire-resistant coating material of thickness t obtained in the third step, so that fire-resistant coated steel material can be produced 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] In addition, according to the design program for fire-resistant coated steel material of the present invention, in the first step, temperature T (°C), strain ε (%) and strain rate ε v The function that expresses the stress-strain curve of the steel material with the variable (% / min) is estimated, and the strain rate ε v Stress at 1% strain (N / mm 2 ) and temperature T, the stress-temperature relationship at 1% strain is calculated. By using this stress-temperature relationship at 1% strain, the relationship between stress and temperature at 1% strain at a strain rate different from the conventionally used strain rate (=0.3% / min) can be obtained. From this relationship, it is possible to evaluate the high temperature strength properties of steel at the strain rate applied to the steel when a building is destroyed by fire. In the second step, the design load (N / mm2) for the steel material to be used in a steel structure is applied to the relationship between the stress at 1% strain and the temperature. 2 ) is introduced to find the temperature T'. This temperature T' is the allowable temperature (℃) at which the steel material will not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature of the steel (℃). The determined thickness t (mm) of the fire-resistant coating material is 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 material of the present invention makes it possible to appropriately design the thickness of the fire-resistant coating material without impairing the fire resistance performance of the fire-resistant coated 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 the conventional method. Therefore, in a building equipped with a fire-resistant coating material designed by 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. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the relationship between temperature T and strain rate sensitivity coefficient m. [Figure 2A] FIG. 2A is a diagram showing stress-strain curves when a test piece made of steel is subjected to strain at a strain rate of 0.3% / min at 600° C., and shows an actual measured curve and a predicted curve. [Figure 2B] FIG. 2B is a diagram showing stress-strain curves when a test piece made of steel is subjected to strain at a strain rate of 3.0% / min at 600° C., and shows an actual measured curve and a predicted curve. [Figure 2C] FIG. 2C is a diagram showing stress-strain curves when a test piece made of steel is subjected to strain at a strain rate of 7.5% / min at 600° C., and shows an actual measured curve and a predicted curve. [Diagram 3] FIG. 3 is a graph showing the relationship between stress (N / mm2) and temperature T at 1% strain. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a method for designing a fire-resistant coated steel material and a method for manufacturing a fire-resistant coated steel material according to an embodiment of the present invention will be described.

[0015] The design method for fire-resistant coated steel material of this embodiment is a design method 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, and comprises a first step, a second step and a third step.

[0016] The first step is to calculate the temperature T (℃), strain ε (%), and strain rate ε v A function that expresses the stress-strain curve of the steel material with variables ε (% / min) is estimated, and the strain rate ε is calculated from the estimated function. v Stress at 1% strain (N / mm 2 ) and temperature T, and calculate the stress-temperature relationship at 1% strain.

[0017] In the second step, the design load (N / mm2) for the steel structure is applied to the stress-temperature relationship at 1% strain obtained in the first step. 2 ) to find the corresponding temperature T', and the temperature T' is defined as the allowable temperature (℃) of the steel material at which the steel material will not break.

[0018] 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.

[0019] Furthermore, the method for producing a fire-resistant coated steel material of this embodiment includes a fourth step in addition to the above-mentioned first to third steps. In the fourth step, a fire-resistant coated steel material is produced by coating a steel material with the fire-resistant coating material having a thickness t obtained in the third step.

[0020] Each step will be explained below.

[0021] (First Step) The first step is to estimate the functional equation for the stress-strain curve of the steel material.

[0022] The function is temperature T (℃), strain ε (%), and strain rate ε v A function formula expressing the stress-strain curve of steel material with variables ε (% / min) and ε (% / min) can be used. An example of the function formula is shown in the following formula (1). By appropriately setting various parameters in formula (1), it is possible to obtain a stress-strain curve showing the relationship between stress and strain ε using limited experimental data. v It is possible to estimate the stress-strain curve as a function of the variable (% / min). For example, it is possible to estimate the stress-strain curve when a tensile test is performed at 630°C and a strain rate of 0.7% / min.

[0023] Since the high-temperature strength characteristics of steel differ for each type of steel, it is advisable to determine formula (1) for each type of steel.

[0024] σ(T,ε,ε v )=σ0(ε v / ε0) m … (1)

[0025] In equation (1), σ0 is the reference stress value when the strain rate is 0.3% / min, and ε v is the strain rate (% / min) as a variable, ε0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient. Also, σ(T,ε,ε v ) is the estimated value of stress in the stress-strain curve, and is expressed as temperature T (℃), strain ε (%), and strain rate ε v This is an estimate based on (% / min).

[0026] The reference stress σ0 in formula (1) is given by the following formulas (2) to (5). The parameters in each of formulas (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.

[0027] E: Young's modulus σy : Yield stress (0.2% yield strength) σ u : Tensile strength ε y : Yield strain (σ y / E) ε st : Yield shelf end strain ε u : Uniform elongation σ 20 : Stress at 20% strain ε 20 : Strain at 20% k, n: coefficients related to strain hardening α: Coefficient of uniform elongation related to temperature and strain rate

[0028]

number

[0029] Equation (2) is the condition in which the strain ε is 0 or more and the yield strain ε y The reference stress σ0 in the following range is shown. In other words, equation (2) shows the stress in the range of elastic deformation in the stress-strain curve of steel.

[0030] Equation (3) expresses the relationship between the strain ε and the yield strain ε in the stress-strain curve. y Super, Yield plateau end strain ε st The reference stress σ0 in the following range is shown.

[0031] Equation (4) expresses the relationship between the strain ε and the yield plateau strain ε in the stress-strain curve. st Ultra-uniform elongation ε u and the product αε u The reference stress σ0 in the following range is shown. In other words, equation (2) shows the stress between the yield stress and the tensile strength in the stress-strain curve of steel.

[0032] Equation (5) expresses the relationship between strain ε and uniform elongation ε in a stress-strain curve. u and the product αε uIn other words, equation (5) is an equation that shows the decrease in stress after tensile strength in the stress-strain curve of steel.

[0033] Each parameter in formulas (2) to (5), which is a function of temperature T, is experimentally obtained. For example, a tensile test is performed on the target steel in accordance with JIS G 0567:2020 to obtain the relationship between stress and strain. The test specimen is the one specified in Annex A of JIS G 0567:2020. The strain rate is 0.3% / min, and the test temperatures are, 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, and the test temperatures may be set to include the temperatures of the steel material when the fire-resistant coated steel material is exposed to a fire.

[0034] The stress measured value σ for each test temperature was R Based on these measurement data, each parameter σ is calculated so that the above formulas (2) to (5) are most closely matched. y , σ u , ε y , ε st , ε u , σ 20 , ε 20 , k, n, and α are calculated. Each parameter can be optimized 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 , k, n and α are determined as functions of temperature T.

[0035] The coefficient α depends on the strain rate as well as the temperature. u The coefficient α is a function of temperature and strain rate. When the strain rate is 0.3% / min, α is 1 regardless of temperature.

[0036] The strain rate sensitivity coefficient m in the formula (1) is calculated by the following formula (6).

[0037]

number

[0038] In equation (6), for example, m0, m1, m2, and m3 can be set as m0=0.0103, m1=5.5, m2=587, and m3=0.169, respectively.

[0039] The plots in FIG. 1 represent the value of m when the stress-strain curve from an actual tensile test roughly matches equation (1), while the solid lines in FIG. 1 represent equation (6), with m0, m1, m2, and m3 being values ​​adjusted so that the solid lines are close to each plot.

[0040] The range of temperature T at which formula (1) holds can be adjusted by appropriately setting the measurement temperature T of the tensile test of the steel material used to determine each parameter. For example, when the measurement temperature is set to 20 to 800°C as described above, the temperature T can be set to at least the range of 20 to 800°C.

[0041] In addition, the strain rate ε v is not particularly limited, and can be set to any value within the range of, for example, 0.3% / min to 8.0% / min. Preferably, the strain rate ε v may be any value within the range of 5.0% / min to 8.0% / min.

[0042] 2A to 2C are schematic diagrams showing examples of stress-strain curves when a test piece made of steel is strained at 600°C at strain rates of 0.3% / min, 3.0% / min, and 7.5% / min. FIG. 2A shows an example of a strain rate of 0.3% / min, FIG. 2B shows an example of a strain rate of 3.0% / min, and FIG. 2C shows an example of a strain rate of 7.5% / min. In addition, FIG. 2A to FIG. 2C show both an actually measured curve and a curve estimated by the estimation method of the present embodiment. As is clear from the actually measured curves shown in FIG. 2A to FIG. 2C, when the temperature is constant, the stress-strain curve shifts to the high stress side as the strain rate increases. In addition, as is clear from the estimated curves shown in FIG. 2A to FIG. 2C, the estimated curves are in good agreement with the actually measured curves. By estimating equation (1) in the first step, it becomes possible to accurately estimate the stress-strain curve for each temperature or strain rate. In addition, the stress at 1% strain (N / mm 2 ) can also be obtained.

[0043] Next, the stress at 1% strain (N / mm 2 ) and temperature T. For example, by introducing 20 to 800°C as the temperature T and 0.3% / min and 7.5% / min as the strain rates into the estimated formula (1), the stress when the strain ε is 1% is calculated as σ(T=20 to 800°C,ε=1%,ε v =0.3% / min) and σ(T=20~800℃,ε=1%,ε v = 7.5% / min) is calculated. Note that the stress at 1% strain (N / mm 2 The reason for selecting the effective yield strength is that the "Guidelines for Fire-Resistant Design of Steel Structures, Third Edition" (compiled by the Architectural Institute of Japan, published in June 2017) states that "When considering the actual behavior of structures and components during a fire, it is appropriate to use the response stress value shown by the steel material at a strain of about 1%, regardless of the temperature of the components or the type of steel." Based on this description, in this embodiment, the stress at 1% strain (N / mm 2 ) and temperature T.

[0044] Figure 3 shows the stress (N / mm 2 ) and temperature T. FIG. 3 shows an example of the relationship between the tensile strength of 590 N / mm 2 The graph in Fig. 3 shows the stress-strain curve of the steel of the tensile strength 590N / mm 2 For steel of grade 1, the stress at 1% strain (N / mm 2 ) versus temperature T. These curves are derived from equation (1) estimated in the first step.

[0045] As shown in Figure 3, for example, the stress at 1% strain is 300 (N / mm 2 ), the curve for a strain rate of 7.5% / min is at a higher temperature than the curve for a strain rate of 0.3% / min. This shows that the deformation temperature of steel when a certain stress (stress equivalent to the stress at which 1% strain occurs) is applied becomes higher as the strain rate increases. Therefore, at a strain rate at which the steel would be destroyed if a building were to catch fire, the steel does not deform even until it reaches a higher temperature, demonstrating its excellent fire resistance. In other words, this shows that fire resistance can be adequately maintained even if the thickness of the fire-resistant coating material is made thinner.

[0046] (Second step) Next, in the second step, the design load (N / mm2) for the steel structure is applied to the stress-temperature relationship at 1% strain obtained in the first step. 2 ) is introduced to determine the corresponding temperature T', and this temperature T' is set as the allowable temperature (℃) at which the steel material will not break.

[0047] In addition, the "allowable temperature (℃) of steel at which the steel will not break" is desirably a temperature higher than the temperature at which a test specimen is deemed to pass according to the evaluation criteria described in "6. Evaluation" on pages 7 to 8 of the "Fire Resistance Testing and Evaluation Procedure Manual" (created by the General Building Research Corporation of Japan, revised June 15, 2020, 8A-103-01(Rev.4.0)) as a result of testing using the test method described in "4.1 Fire Resistance Test Method" on pages 4 to 8.

[0048] (Third Step) 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. The thickness t (mm) of the fire-resistant coating material may be determined 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 material. That is, in the case of fire-resistant coated steel material, the thickness of the fire-resistant coating material is defined as t (mm), and the temperature of the steel material two hours after the start of heating when the steel material covered with the fire-resistant coating material is heated is defined as T. 2h (℃), then t and T 2h is T 2h =at + b (where a and b are constants determined by the type of fire-resistant coating material), so the thickness t (mm) of the fire-resistant coating material can be determined from the allowable temperature of the steel (℃) based on this relationship.

[0049] (Fourth step) In the fourth step, a fire-resistant coated steel material is manufactured by coating the steel material with the fire-resistant coating material having a thickness t obtained in the third step. The fire-resistant coating material may be applied by any of the following methods: a spraying method in which the fire-resistant coating material is sprayed onto the steel material surface, a coating method in which paint containing the fire-resistant coating material is applied to the steel material surface, a method in which a plate material made of the fire-resistant coating material is attached to the steel material surface, and a method in which a sheet made of the fire-resistant coating material is wrapped around the steel material surface.

[0050] The fire-resistant coated steel material obtained in the above manner has a thickness of the fire-resistant coating material that is the design value determined by going through the first to third steps, and has sufficient fire resistance.

[0051] The steel material used for the fire-resistant coated steel material of this embodiment has a yield strength of σ y is 235N / mm 2 or more, 335N / mm 2 or more, 355N / mm 2 or more, 385N / mm 2 It may be more than that.

[0052] The steel material may be an H-section steel, a square steel pipe, or a circular steel pipe.

[0053] When the steel material is an H-shaped steel, the fire-resistant coated steel material of this embodiment is preferably used for either the main girder or the minor girder of the steel structure. In addition, when the steel material is a square steel pipe or a round steel pipe, the fire-resistant coated steel material of this embodiment is preferably used for columns of a steel structure.

[0054] Furthermore, the fire-resistant coating material is preferably any one of a sprayed layer, a painted layer, a molded plate, and a wound body.

[0055] As described above, in the design method of the fire-resistant coating steel material of this embodiment, in the first step, the temperature T (°C), the strain ε (%) and the strain rate ε v The stress-strain curve of the steel material is expressed as the function (1) with the variable (% / min). Based on the estimated equation (1), the strain rate ε v Stress at 1% strain (N / mm 2 ) and temperature T, the stress-temperature relationship at 1% strain is calculated. By using this stress-temperature relationship at 1% strain, the relationship between stress and temperature at 1% strain at a strain rate different from the conventionally used strain rate (=0.3% / min) can be obtained. From this relationship, it is possible to evaluate the high temperature strength properties of steel at the strain rate applied to the steel when a building is destroyed by fire. In the second step, the design load (N / mm2) for the steel material to be used in a steel structure is applied to the relationship between the stress at 1% strain and the temperature. 2) is introduced to find the temperature T'. This temperature T' is the allowable temperature (℃) at which the steel material will not break. Next, in the third step, the thickness t (mm) of the fire-resistant coating material is determined from the allowable temperature of the steel (℃). The determined thickness t (mm) of the fire-resistant coating material is smaller than the thickness of the fire-resistant coating material designed based on the conventionally used strain rate (=0.3% / min). As described above, according to the design method for a fire-resistant coated steel material 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 coated steel material.

[0056] The design value of the thickness of the fire-resistant covering material obtained by this embodiment is thinner than the thickness of the fire-resistant covering material determined by the conventional method. Therefore, in a building equipped with a fire-resistant covering material designed by the design method according to this embodiment, the space occupied by the fire-resistant covering material is reduced, making it possible to expand the living space and usable space within the building.

[0057] Furthermore, according to the manufacturing method of the fire-resistant coated steel material of this embodiment, in addition to the above-mentioned first to third steps, a fourth step is performed. In the fourth step, a fire-resistant coated steel material is manufactured by covering a steel material with the fire-resistant coating material having a thickness of t obtained in the third step. Therefore, according to the manufacturing method of this embodiment, a fire-resistant coated steel material can be manufactured 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.

[0058] Furthermore, according to the fire-resistant coated steel material of this embodiment, the thickness of the fire-resistant coating material coating the steel material is the thickness t designed by the above-mentioned first to third steps, so that the thickness of the fire-resistant coating material can be made appropriate without compromising the fire resistance performance.

[0059] Next, a design program for a fire-resistant coated steel material for a steel structure according to this embodiment will be described. The design program of this embodiment is a program executed by a computer, and comprises a first step, a second step, and a third step.

[0060] The first step is to calculate the temperature T (℃), strain ε (%), and strain rate ε v A function that expresses the stress-strain curve of the steel material with variables ε (% / min) is estimated, and the strain rate ε is calculated from the estimated function. v Stress at 1% strain (N / mm 2 ) and temperature T, and calculate the stress-temperature relationship at 1% strain.

[0061] In the second step, the design load (N / mm2) for the steel structure is applied to the stress-temperature relationship at 1% strain obtained in the first step. 2 ) to find the corresponding temperature T', and the temperature T' is defined as the allowable temperature (℃) of the steel material at which the steel material will not break.

[0062] 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.

[0063] The functional formula in the first step may be the functional formula expressed by the above formula (1) or the functional formula expressed by the above formula (2).

[0064] The specific contents of the first, second and third steps are as described above for the first, second and third steps of the design method.

[0065] 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 coated steel material. The design value of the thickness of the fire-resistant coating material obtained by this embodiment is thinner than the thickness of the fire-resistant coating material determined by the conventional method. Therefore, in a building equipped with a fire-resistant coating material designed by the design program according to 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.

[0066] The present invention is not limited to the above embodiment, and the function formula used in the first step may be changed. That is, instead of the above formula (1), the following formula (A) may be used as the function formula.

[0067] σ(T,ε,ε v )=σ0(ε v / ε0)m … (A)

[0068] In formula (A), σ0 is the reference stress value at a strain rate of 0.3% / min, and ε v is the strain rate (% / min) as a variable, ε0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient. Also, σ(T,ε,ε v ) is the estimated value of stress in the stress-strain curve, and is expressed as temperature T (℃), strain ε (%), and strain rate ε v This is an estimate based on (% / min).

[0069] The calculation procedure for σ0 and m in formula (A) can be the same as the calculation procedure for σ0 and m in formula (1). EXAMPLES

[0070] Next, examples of the present invention will be described. Note that the present invention is not limited to the examples described below.

[0071] (Example) As a steel material, the tensile strength of the plate is 590N / mm 2 A steel of grade 10 was prepared and cut to an appropriate size to prepare a test piece as specified in Annex A of JIS G 0567:2020. A tensile test was performed on the obtained test piece in accordance with JIS G 0567:2020 at 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 a stress-strain curve. Then, the above formulas (1) to (5) were estimated based on the obtained stress-strain curve.

[0072] Next, based on the estimated formula (1), the stress at 1% strain (N / mm 2 ) and temperature T. Figure 3 shows the relationship between the tensile strength of 590 N / mm 2 For steel of grade 1, the stress at 1% strain (N / mm 2 ) versus temperature T. Figure 3 shows the relationship between the stress (N / mm 2 ) versus temperature T.

[0073] Next, the design load (N / mm2) for the steel structure is added to the stress-temperature relationship at 1% strain shown in Figure 3. 2 ) was introduced to obtain the temperature T' (allowable temperature of steel (℃)). In this example, data for a strain rate of 7.5% / min was used. The design load was 440 / 1.5 = 293 (N / mm 2 In this case, the temperature T' (allowable temperature of steel (℃)) was 650℃.

[0074] Next, the thickness t (mm) of the fire-resistant coating material was determined from the allowable temperature (°C) of the steel (= 650°C). The thickness t (mm) of the fire-resistant coating material was 52 mm.

[0075] Tensile strength of 32mm and 19mm plate thickness: 590N / mm 2 Steel of the same grade was cut to the appropriate size to produce plate material for the upper and lower flanges with a thickness of 32 mm, and plate material for the web with a thickness of 19 mm. The upper flange, lower flange, and web were then welded together to produce an H-shaped steel beam with a height of 1,000 mm and upper and lower web widths of 300 mm.

[0076] Then, the entire H-section steel was covered with a fire-resistant coating material. The thickness of the fire-resistant coating material was 52 mm. In this manner, the fire-resistant coated steel material of the example was manufactured.

[0077] (Reference example) As a reference example, the tensile strength of plate thicknesses of 32 and 19 mm is 590 N / mm 2Steel of the same grade was prepared and cut to the appropriate size to produce plate material for the upper and lower flange portions with a thickness of 32 mm, and plate material for the web portion with a thickness of 19 mm. The upper flange portion, lower flange portion, and web portion were then welded together to produce an H-shaped steel beam with a height of 1,000 mm and upper and lower web portions with widths of 300 mm.

[0078] Then, using this H-beam as a test material, a 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 test and evaluation service method manual" (created by the General Building Research Corporation of Japan, revised version on June 15, 2020, 8A-103-01 (Rev.4.0)), and the temperature at which the test specimen passed the test was measured according to the criteria described in "6. Judgment" on pages 7 to 8. As a result, a temperature of 550°C was obtained.

[0079] Next, the thickness t (mm) of the fire-resistant coating material was determined from the obtained temperature (=550°C), and the thickness t (mm) of the fire-resistant coating material was found to be 65 mm.

[0080] In the same manner as above, the tensile strength of the plate thicknesses of 32 mm and 19 mm was 590 N / mm 2 An H-shaped steel beam was manufactured from grade A steel, having a height of 1000 mm and a width of 300 mm at the upper and lower web portions. Then, the entire H-section steel was covered with a fire-resistant coating material. The thickness of the fire-resistant coating material was 65 mm. In this manner, the fire-resistant coated steel material of the reference example was produced.

[0081] (evaluation) The fire resistance of the fire-resistant coated steel materials of the examples and comparative examples was confirmed. The fire resistance was confirmed in accordance with the above-mentioned "Fire Resistance Testing and Evaluation Procedure Manual." As a result, all of them showed fire resistance of more than 2 hours. Therefore, the fire-resistant coated steel material of the embodiment 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 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 a surface of the steel material, the method comprising the steps of: Temperature T (℃), strain ε (%), and strain rate ε ｖ The strain rate sensitivity coefficient m in the functional equation is calculated based on experimental data, and the strain rate ε is calculated from the functional equation including the strain rate sensitivity coefficient m. ｖ Stress at 1% strain (N / mm ２ A first step of estimating a stress-temperature relationship at 1% strain, which is a relationship between stress (s) and temperature T; The stress-temperature relationship at 1% strain estimated in the first step is applied to the design load (N / mm ２ ) to obtain a corresponding temperature T', and the temperature T' is set as a steel allowable temperature (°C) at which the steel is not damaged; and a third step of determining a thickness t (mm) of the fire-resistant coating material from the allowable steel temperature (°C) determined in the second step. σ(T, ε, ε v )=σ 0 (ε v / ε 0 ) m... (1) In the formula (1), σ 0 is the reference stress value for a strain rate of 0.3% / min, ε v is the strain rate (% / min) as a variable, ε 0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient.

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) covering a surface of the steel material, the method comprising the steps of: Temperature T (℃), strain ε (%), and strain rate ε ｖ The function formula described in the following (2) is used as a function formula expressing the stress-strain curve of the steel material having variables of ε (% / min), and the strain rate sensitivity coefficient m in the function formula is obtained based on experimental data, and the strain rate ε is calculated from the function formula including the obtained strain rate sensitivity coefficient m. ｖ Stress at 1% strain (N / mm ２ A first step of estimating a stress-temperature relationship at 1% strain, which is a relationship between stress (s) and temperature T; The stress-temperature relationship at 1% strain estimated in the first step is applied to the design load (N / mm ２ ) to obtain a corresponding temperature T', and the temperature T' is set as a steel allowable temperature (°C) at which the steel is not damaged; A third step of determining a thickness t (mm) of the fire-resistant coating material from the allowable steel temperature (°C) obtained in the second step; and a fourth step of producing the fire-resistant coated steel material by covering the steel material with the fire-resistant coating material having a thickness t obtained in the third step. σ(T, ε, ε v )=σ 0 (ε v / ε 0 ) m... (2) In the formula (2), σ 0 is the reference stress value for a strain rate of 0.3% / min, ε v is the strain rate (% / min) as a variable, ε 0 is the reference strain rate of 0.3% / min, and m is the strain rate sensitivity coefficient.

3. The steel material has a yield strength σ ｙ is 235N / mm ２ The method for producing a fire-resistant coated steel material according to claim 2 .

4. The steel material has a yield strength σ ｙ is 335N / mm ２ The method for producing a fire-resistant coated steel material according to claim 2 .

5. The steel material has a yield strength σ ｙ is 355N / mm ２ The method for producing a fire-resistant coated steel material according to claim 2 .

6. The steel material has a yield strength σ ｙ is 385N / mm ２ The method for producing a fire-resistant coated steel material according to claim 2 .

7. 7. The method for manufacturing a fire-resistant coated steel material according to claim 2, wherein the steel material is any one of an H-section steel, a square steel pipe, and a circular steel pipe.

8. The method for producing a fire-resistant coated steel material according to claim 7, wherein when the steel material is an H-shaped steel, the steel material is used for either a main girder or a minor girder in the steel structure.

9. The method for producing a fire-resistant coated steel material according to claim 7, wherein when the steel material is made of the square steel pipe or the circular steel pipe, the steel material is used for a column in the steel structure.

10. 10. The method for producing a fire-resistant coated steel product according to claim 2, wherein the fire-resistant coating material is any one of a sprayed layer, a painted layer, a formed plate, and a wound body.

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