JP7674162B2 - Fire resistance estimation method - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies Shimizu Corporation Research Report No. 98, pages 57 to 66, published on December 21, 2020. Abstracts of the 2021 Japan Association of Fire Sciences Research Presentation, pages 134 to 135, Japan Association of Fire Sciences Research Presentation, published on May 25, 2021.

The present invention relates to a method for estimating the fire resistance of wood-steel hybrid components made of wood and steel.

Previously, the applicant for the present patent has developed composite members that combine steel members and wood members (see, for example, Patent Document 1). In particular, to ensure one-hour fire resistance, the applicant has developed a wood-steel hybrid beam, a structural member in which a steel beam is fire-resistant coated with wood (hereinafter referred to as a wood coating material) (see, for example, Patent Document 2). This wood coating material burns at about 0.7 to 1.0 mm/min during a fire, but stops burning after the fire, thereby suppressing the temperature rise of the steel beam that supports the load and preventing collapse. It is believed that the fire resistance performance of members such as a wood-steel hybrid beam, such as the burning properties of the wood coating material, whether or not the fire stops after the fire, and the temperature transition of the steel, will change depending on the species and coating thickness of the wood coating material, and the shape and cross-sectional dimensions of the steel.

On the other hand, when sprayed rock wool or calcium silicate boards are used as fireproof coating for steel, a method has been proposed in the fireproof performance verification method to calculate the component temperature rise coefficient from the shape and cross-sectional dimensions of the steel and the type and thickness of the fireproof coating, and to estimate the maximum temperature of the steel in the event of a fire (see, for example, Non-Patent Document 1). It is said that the higher the value of the component temperature rise coefficient, the easier it is for the temperature of the steel to rise.

JP 2018-084037 A Patent application No. 2020-148315 (currently unpublished)

The Building Center of Japan, et al., "2001 Edition: Explanation of the Fire Resistance Verification Method and Calculation Examples and Explanations," pp.85-109, pp.173-188, 2001

In developing the above-mentioned wood-steel hybrid beam, the applicant of the present patent created multiple test specimens using the species and thickness of the wood covering material and the cross-sectional dimensions of the steel as parameters, and confirmed the performance of each specification through fire resistance tests. However, when developing components with specifications different from those whose performance was confirmed in the fire resistance tests (specifically, specifications with different species and thickness of the wood covering material, different shapes and cross-sectional dimensions of the steel, etc.), conducting fire resistance tests each time is costly and time-consuming. For this reason, there has been a demand for a method that can easily estimate the fire resistance performance of wood-steel hybrid components without relying on fire resistance tests.

The present invention has been made in consideration of the above, and aims to provide a method for estimating the fire resistance of wood-steel hybrid components that can easily estimate the fire resistance of wood-steel hybrid components.

In order to solve the above problems and achieve the objective, the method for estimating the fire resistance of a wood-steel hybrid member according to the present invention is a method for estimating the fire resistance of a wood-steel hybrid member that comprises a steel material and a wood covering material that provides a fire-resistant covering for the steel material, and is characterized in that it calculates a pseudo-component temperature rise coefficient from the shape and cross-sectional dimensions of the steel material and the species and covering thickness of the wood covering material, and estimates the fire resistance of the wood-steel hybrid member based on the calculated pseudo-component temperature rise coefficient.

The fire resistance performance estimation method for wood-steel hybrid components according to the present invention is characterized in that, in the above-mentioned invention, the pseudo component temperature rise coefficient is calculated as an index showing the ease with which the temperature of steel material covered with an inorganic fire-resistant coating material rises, and is calculated by assuming that the thermal resistance coefficient calculated based on the heat transfer coefficient of the steel material surface and the thermal conductivity of the fire-resistant coating material is 1.

The fire resistance performance estimation method for wood-steel hybrid components according to the present invention is a method for estimating the fire resistance performance of a wood-steel hybrid component comprising a steel material and a wood coating material that provides a fire-resistant coating for the steel material. A pseudo component temperature rise coefficient is calculated from the shape and cross-sectional dimensions of the steel material and the species and coating thickness of the wood coating material, and the fire resistance performance of the wood-steel hybrid component is estimated based on the calculated pseudo component temperature rise coefficient. This has the effect of allowing the fire resistance performance of the wood-steel hybrid component to be easily estimated without fire resistance testing.

FIG. 1 is a schematic diagram of a member to which an embodiment of the method for estimating the fire resistance of a wood-steel hybrid member according to the present invention is applied, where (1) is a cross-sectional view in the case of three-sided heating, (2) is a cross-sectional perspective view thereof, (3) is a cross-sectional view in the case of four-sided heating, and (4) is a cross-sectional perspective view thereof. Figure 2 shows cross-sectional views of the test specimens, with (1) and (2) being test specimen A, (3) and (4) being test specimen B, and (5) and (6) being test specimen C. Additionally, (1), (3) and (5) are general beam sections, and (2), (4) and (6) are cladding attachment sections. FIG. 3 is a diagram showing the transition of steel temperature in a hiba wood-steel hybrid beam. FIG. 4 is a diagram showing the transition of steel temperature in a larch wood-steel hybrid beam. FIG. 5 is a diagram showing the relationship between the pseudo-component temperature rise coefficient and the maximum temperature rise value of the steel material, where (1) is for Hiba and (2) is for Larch.

Below, an embodiment of the method for estimating the fire resistance of a wood-steel hybrid member according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment.

In this embodiment, a pseudo component temperature rise coefficient is calculated from the shape and cross-sectional dimensions of the steel in the wood-steel hybrid component and the species and thickness of the wood covering material, and the maximum temperature of the steel and whether the wood will stop burning are estimated. Then, the fire resistance performance of the wood-steel hybrid component is estimated in a simple manner. In this embodiment, the following (1) to (4) are assumed.

(1) The steel material is assumed to be an H-shaped steel that is heated from three directions (bottom, left, right) (see Figure 1 (1) and (2)), or an H-shaped steel that is heated from four directions (top, bottom, left, right, and right) (see Figure 1 (3) and (4)).

(2) The wood species used for wood covering materials are larch and Japanese cypress.

(3) Calculate the pseudo component temperature rise coefficient (hereinafter referred to as pseudo component temperature rise coefficient) from the shape and cross-sectional dimensions of the steel material of the wood-steel hybrid component and the coating thickness of the wood coating material. The method for calculating the pseudo component temperature rise coefficient is described below.

(4) From the results of multiple fire resistance tests conducted for the purpose of developing a wood-steel hybrid beam that ensures one-hour fire resistance, it has been found that if the pseudo-component temperature rise coefficient is 0.077 or less when larch is used as the wood covering material, and if the pseudo-component temperature rise coefficient is 0.065 or less when Japanese cypress is used as the wood covering material, the maximum temperature of the steel material can be estimated and the wood covering material will stop burning. Therefore, these test results will be used to estimate fire resistance.

The wood-steel hybrid member 10 in Figs. 1(1) and (2) is composed of a steel beam 12 made of H-shaped steel and a wood covering material 14 covering the bottom, left and right three sides. A floor material 16 is provided on the top surface of the steel beam 12. The steel beam 12 and the wood covering material 14 are fastened with a fixing member (not shown), and the surface of the wood covering material 14 that passes through the fixing member is covered with filler wood 18. The fixing member is a rod-shaped body with a head and a threaded portion, and the head is placed on the web of the steel beam 12, and the threaded portion penetrates the web and is screwed into the wood covering material 14. The wood-steel hybrid member 10A in Figs. 1(3) and (4) is composed of a steel beam 12 made of H-shaped steel and a wood covering material 14 covering the top, bottom, left and right four sides.

(Method of calculating pseudo component temperature rise coefficient)
Next, a method for calculating the pseudo component temperature rise coefficient in a wood-steel hybrid component will be described.
In the fire resistance performance verification method, the component temperature rise coefficient h is used as an index showing how easily the temperature of steel material covered with inorganic fire-resistant coating material (sprayed rock wool 25 mm thick or more, or calcium silicate board 20 mm thick or more) rises. The component temperature rise coefficient h is calculated by the following formula (1) based on the cross-sectional shapes of the steel material and the coating material, and the physical properties of the coating material, and it is said that the higher the component temperature rise coefficient h, the easier the steel material temperature rises.

Here, Hs: heated perimeter of the steel [m], As: cross-sectional area of the steel [m ² ], Hi: heated perimeter of the coating material [m], Ai: cross-sectional area of the coating material [m ² ], Hs/As: cross-sectional shape coefficient of the steel [m ^-1 ], φ=Hi/Hs: perimeter ratio of the parts of the coating material and the steel that are subjected to heating [-], K ₀ , R, C: constants determined by the physical properties of the coating material and the type of steel (K ₀ =ht/ρ _scs : basic temperature rise coefficient [m/min] obtained by dividing the heat transfer coefficient of the steel surface by the heat capacity of the steel, R =ht/ki: thermal resistance coefficient [m ^-1 ] obtained by dividing the heat transfer coefficient of the steel surface by the thermal conductivity of the coating material, C =ρ _ici /ρ _scs : heat capacity ratio of the coating material and the steel [-]).

In formula (1), the values of Hs, As, Hi, Ai, and φ can be determined if the cross-sectional dimensions and shapes of the steel and cladding material are known. On the other hand, the constants _K0 , R, and C, which are determined by the physical properties of the cladding material and the type of steel, need to be identified from test results.

According to the following Reference 1, the basic temperature rise coefficient _K0 is uniquely determined by the shape of the steel material and the number of heated surfaces. Therefore, using the values used in the fire resistance performance verification method described in the above Non-Patent Document 1, we will use _K0 = 0.00089 when heated from four sides, and _K0 = 0.00067 when heated from three sides excluding the top surface.

[Reference 1] Junichi Suzuki et al., "Simple prediction formula for temperature rise of uncoated steel during fires," Journal of Structural Engineering, Architectural Institute of Japan, Vol. 553, pp. 143-148, 2002

The heat capacity ratio C is determined by the density and specific heat of the steel and coating material. Therefore, the change in physical properties due to temperature rise is not taken into account, and the heat capacity ratio C is calculated based on the physical properties at room temperature.

The thermal resistance coefficient R is calculated based on the heat transfer coefficient of the steel surface and the thermal conductivity of the covering material, but the value has not been determined when wood is used as the covering material (see Non-Patent Document 1 above). Therefore, for convenience, we will assume that R = 1.

From the above, if we define the component temperature rise coefficient h calculated assuming R = 1 as the pseudo component temperature rise coefficient h', the following equation (2) holds.

(Verification by fire resistance test)
Based on the results of multiple fire resistance tests conducted with the aim of developing a wood-steel hybrid beam that ensures one-hour fire resistance, we verified the possibility of estimating the steel temperature of a wood-steel hybrid beam and whether or not it will stop burning using the pseudo-component temperature rise coefficient h'.

The specifications for which the fire resistance tests were conducted are shown in Table 1, and the specifications of the test specimens are shown in Figure 2. Figure 2 (1) and (2) are test specimen A, (3) and (4) are test specimen B, and (5) and (6) are test specimen C. Figures 3 and 4 show the steel temperature transitions for each specification for which the fire resistance tests were conducted. Table 1 also shows the pseudo-component temperature rise coefficient for each specification for which the fire resistance tests were conducted, the maximum temperature rise from the initial temperature of the steel in the fire resistance tests, and the results of whether or not the wood covering material stopped burning.

[List of results for pseudo-component temperature rise coefficient, maximum temperature rise value of steel, and whether or not burning has stopped]

Using the steel temperature obtained in the test, the average steel temperature was calculated for each time point at the top flange, bottom flange, and web, and the temperature rise from the initial temperature was calculated by subtracting the initial temperature. Table 1 shows the maximum temperature rise ΔT (maximum temperature rise) from the initial temperature. For specimens 2, 3, 9, and 13, the wood covering material did not stop burning even after the test was completed (after a total of 25 hours had passed, including 1 hour of heating and 24 hours of cooling), and the steel temperature was still rising. Therefore, for safety reasons, water was poured onto the specimens after the test was completed to extinguish the fire and cool them down. For specimen 1, the maximum steel temperature reached 450°C or more, and the wood covering material had burned out by the end of the test. In the judgment of burning out, a circle indicates a specimen that stopped burning, and a cross indicates a specimen that did not stop burning or burned out (the maximum steel temperature reached 450°C or more).

Figure 5 shows a graph of the relationship between the pseudo-component temperature rise coefficient h' and the maximum temperature rise value ΔT of the steel material shown in Table 1. Figure 5 (1) shows the case where Japanese cypress was used as the wooden covering material, and (2) shows the case where larch was used as the wooden covering material. In the figure, circles indicate test specimens where the fire stopped, and crosses indicate test specimens where the fire did not stop. The figure also shows the equation for the regression line and correlation coefficient R obtained by regression analysis of the results of test specimens that stopped burning in the fire resistance test, with the pseudo-component temperature rise coefficient h' as x and the maximum temperature rise value ΔT of the steel material as y.

As shown in Figure 5, for both Japanese cypress and larch specimens that stopped burning in the fire resistance test, the greater the pseudo-component temperature rise coefficient, the greater the maximum temperature rise value of the steel. Therefore, if the specifications are such that the fire will stop, it is possible to estimate the maximum temperature rise value of the steel by calculating the pseudo-component temperature rise coefficient from the specifications of the wood covering material and the cross-sectional dimensions of the steel beam.

In addition, considering that the wood-steel hybrid beam using Japanese cypress did not stop burning in test specimen 9 because the length of the filler wood was short, it is estimated that the beam will stop burning if the pseudo-component temperature rise coefficient is 0.065 or less.

On the other hand, in the case of the wood-steel hybrid beam using larch, observation of the specimens after testing suggested that the reason why specimen 13 did not stop burning was possibly due to poor construction of the filler wood. Assuming that there is no poor construction of the filler wood, it is estimated that the wood-steel hybrid beam using larch will stop burning if the pseudo-component temperature rise coefficient is 0.077 or less.

According to this embodiment, by calculating the pseudo component temperature rise coefficient, it is possible to easily estimate the maximum temperature of the steel material of a wood-steel hybrid beam made of Japanese cypress and larch, and whether or not the wood covering material will stop burning. This makes it possible to easily estimate the fire resistance performance of a wood-steel hybrid beam without conducting a fire resistance test. This also reduces the costs and effort involved in fire resistance testing, and improves the efficiency of component development.

In addition, by accumulating fire resistance test data when other tree species are used as wood covering materials, it will be possible to increase the variety of tree species that can be estimated using the pseudo component temperature rise coefficient.

In the above embodiment, the steel material is an H-shaped steel, but the present invention is not limited to this. For example, by accumulating fire resistance test data for other steel shapes, such as square steel, it is possible to expand the variety of steel shapes that can be estimated using the pseudo component temperature rise coefficient.

As described above, the fire resistance performance estimation method for wood-steel hybrid components according to the present invention is a method for estimating the fire resistance performance of a wood-steel hybrid component comprising a steel material and a wood coating material that fire-resistantly covers the steel material. A pseudo component temperature rise coefficient is calculated from the shape and cross-sectional dimensions of the steel material and the species and coating thickness of the wood coating material, and the fire resistance performance of the wood-steel hybrid component is estimated based on the calculated pseudo component temperature rise coefficient, so that the fire resistance performance of the wood-steel hybrid component can be easily estimated without fire resistance testing.

As described above, the fire resistance estimation method according to the present invention is useful for evaluating the fire resistance of wood-steel hybrid components, and is particularly suitable for easily estimating fire resistance.

10, 10A Wood-steel hybrid member 12 Steel beam 14 Wood covering material 16 Floor material 18 Filler wood

Claims (1)

A method for estimating the fire resistance of a wood-steel hybrid member having a steel material and a wood covering material that covers the steel material, comprising:
The method calculates an approximate component temperature rise coefficient from the shape and cross-sectional dimensions of the steel material and the species and thickness of the wood covering material, and estimates the fire resistance of the wood-steel hybrid component based on the calculated approximate component temperature rise coefficient.
This method is characterized in that the pseudo component temperature rise coefficient is calculated as an index showing how easily the temperature of steel material covered with an inorganic fire-resistant coating material rises, and is calculated by assuming that the thermal resistance coefficient calculated based on the heat transfer coefficient of the steel material surface and the thermal conductivity of the fire-resistant coating material is 1 .

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