JP7602382B2 - Fire-resistant structural materials and methods for suppressing red heat - Google Patents

Description

The present invention relates to fire-resistant structural materials and methods for suppressing red heat.

Hybrid laminated timber is known as a fire-resistant structural material, and has been certified by the Japan Laminated Timber Industry Association as a one-hour fire-resistant structural column by the Minister of Land, Infrastructure, Transport and Tourism. Hybrid laminated timber has a structure in which a steel frame is covered with a laminated timber made of pure wood without using inorganic materials or chemical impregnation. H-shaped steel is used for the steel frame. The wood species that make up the laminated timber are larch or Douglas fir. Hybrid laminated timber achieves one-hour fire resistance by taking advantage of the thermal conductivity of H-shaped steel and the heat absorption due to the effect of heat capacity, improving the fire-stopping effect of the wood.

Various techniques have also been proposed for obtaining fire-resistant components by providing a burn margin on the surface of wood or a composite material of wood and other materials. For example, Patent Document 1 proposes a structural material that includes a load-supporting layer and a burn margin layer that is placed on the outside of the load-supporting layer and is made of wood with a lower thermal inertia than the load-supporting layer. Patent Document 2 proposes a structural material that includes a load-supporting layer, a fire-retardant layer that is placed on the outside of the load-supporting layer and has a heat insulating material, and a burn margin layer that is placed on the outside of the fire-retardant layer and is made of wood with a predetermined thickness.

JP 2005-36457 A JP 2005-48585 A

In general, it is difficult to stably achieve one-hour fire resistance in pure wood laminated lumber. Specifically, when the laminated lumber is left to cool after heating, red heat may remain on the surface of the pure wood laminated lumber, and the burning may continue. In the hybrid laminated lumber described above, the larch or Douglas fir that constitutes the laminated lumber is a species that is easy to stop burning, and the temperature rise of the wood covering the H-shaped steel is suppressed by the H-shaped steel, so it is believed that the one-hour fire resistance is achieved. The shape of the H-shaped steel is also believed to contribute to the one-hour fire resistance. Specifically, in the hybrid laminated lumber described above, the web part of the H-shaped steel is located in the center of the cross section of the laminated lumber, and the flange part of the H-shaped steel is located on the outer periphery of the cross section, so that heat flows from the flange part to the web part, and heat flows from the outer periphery to the inside where the temperature rise is gradual, which is believed to further improve the fire resistance.

On the other hand, when square steel pipes are used as the steel frame of hybrid laminated timber, the shape of the square steel pipes makes it easy for the temperature to rise across their entire surface, so the thermal capacity effect cannot be utilized as much as with H-shaped steel, and one-hour fire resistance cannot be achieved.
In Patent Documents 1 and 2, there is no consideration whatsoever about achieving one-hour fire resistance when using square steel pipes, and there is room for improvement in fire resistance.

The inventors have thoroughly investigated the reason why red heat remains in the above-mentioned pure wood laminated lumber, and have discovered that after the surface of the pure wood laminated lumber burns and a charred layer is formed, cracks may appear in the charred layer or parts of the charred layer may be chipped, resulting in unevenness on the surface of the charred layer. In such cases, red heat remains inside the charred layer, such as in the cracks that have formed in the charred layer, and burning continues.

The object of the present invention is to provide a fire-resistant structural material and a method for suppressing red heat that can suppress red heat in the fire-resistant structural material.

The present invention provides a fire-resistant structural material comprising a load-bearing part made of wood or steel, a fire-resistant coating layer made of solid wood that covers the load-bearing part, and a burn-resistant coating layer made of solid wood and having a thickness of less than 25 mm that covers the fire-resistant coating layer and burns when exposed to a flame.

The present invention also provides a method for suppressing red heat in which a structural material having a load-bearing part made of wood or steel and a fire-resistant coating layer made of pure wood that covers the load-bearing part is covered with a burnable coating layer made of pure wood that burns and burns when exposed to flames, thereby preventing cracks from occurring on the surface of the fire-resistant coating layer and suppressing the fire-resistant coating layer from red-heating, and the thickness of the burnable coating layer is less than 25 mm.

The present invention provides a fire-resistant structural material and a method for suppressing red heat that can suppress red heat in the fire-resistant structural material.

FIG. 1 is a cross-sectional view showing a fire-resistant structural material according to a preferred embodiment of the present invention. FIG. 2 is a diagram showing positions at which temperature changes were measured when a combustion test was carried out on the fire-resistant structural material of Example 1. FIG. 3 is a diagram showing the positions at which temperature changes were measured when a combustion test was conducted on the fire-resistant structural material of Example 2. FIG. 4 is a diagram showing the positions at which temperature changes were measured when a combustion test was conducted on the fire-resistant structural material of Comparative Example 1. 5(a) to (c) are graphs showing the results of measuring the temperature of the fire-resistant structural material of Example 1 when a combustion test was performed on the fire-resistant structural material. 6(a) to (d) are graphs showing the results of measuring the temperature of the fire-resistant structural material of Example 2 when a combustion test was performed on the fire-resistant structural material. 7(a) to (c) are graphs showing the results of measuring the temperature of the fire-resistant structural material of Comparative Example 1 when a combustion test was performed on the fire-resistant structural material. FIG. 8 is a photograph showing the state of the fire-resistant structural material of Example 1 after the combustion test. FIG. 9 is a photograph showing the state of the fire-resistant structural material of Example 2 after the combustion test. FIG. 10 is a photograph showing the state of the fire-resistant structural material of Comparative Example 1 after the combustion test. FIG. 11 is a graph showing the results of carrying out a combustion test for Example 3 and Comparative Example 2 and measuring the masses of the fire-resistant structural materials.

The present invention will now be described in detail based on preferred embodiments thereof.
A fire-resistant structural material 1A, which is a preferred embodiment of the fire-resistant structural material of the present invention, is shown in Fig. 1. Fig. 1 shows a schematic cross section perpendicular to the axial direction of the fire-resistant structural material 1A. The fire-resistant structural material 1A of this embodiment is a structural square timber used as a beam or pillar of a building. As shown in Fig. 1, the fire-resistant structural material 1A includes a load-bearing portion 11a made of wood or steel, a fire-resistant coating layer 12a, and a burn-off coating layer 13a.

The cross-sectional design of the load support portion 11a is such that the load support portion 11a alone is structurally safe against long-term loads such as fixed loads, live loads, and snow loads. Such cross-sectional design is well known. The cross-sectional shape of the load support portion 11a is rectangular, and the vertical and horizontal lengths of the load support portion 11a in the cross-section of the fire-resistant structural material 1A can be changed as appropriate depending on the shape or size of the beams or columns.

The fire-resistant coating layer 12a covers the load-supporting portion 11a. In this embodiment, the fire-resistant coating layer 12a covers four axial side surfaces of the load-supporting portion 11a. If the fire-resistant structural material 1A is a beam, the fire-resistant coating layer 12a may cover three axial side surfaces of the load-supporting portion 11a. The side of the fire-resistant structural material 1A on which the fire-resistant coating layer 12a is not formed may be covered by placing a floor or the like thereon to cover the upper side of the load-supporting portion 11a.

The burnable coating layer 13a covers the fire-resistant coating layer 12a. The burnable coating layer 13a is designed to burn and be destroyed when exposed to a flame. The thickness of the burnable coating layer 13a is less than 25 mm. Since the thickness of the burnable coating layer 13a is less than 25 mm, the burnable coating layer 13a is reliably destroyed by fire. Because the burnable coating layer 13a has such a configuration, the fire-resistant structural material 1A of this embodiment can prevent the fire-resistant coating layer 12a from becoming red-hot. The reason why the fire-resistant structural material 1A of this embodiment can prevent the fire-resistant coating layer 12a from becoming red-hot is not completely clear, but the inventors speculate as follows.

The combustion of the fire-resistant structural material 1A is considered to proceed in the following order.
When the fire-resistant structural material 1A is exposed to a flame, first, a pyrolysis reaction mainly occurs in the burn-resistant coating layer 13a, and the burn-resistant coating layer 13a is carbonized (first stage). In the first stage, the temperature of the fire-resistant coating layer 12a rises. Then, the pyrolysis reaction of the burn-resistant coating layer 13a ends, and an oxidation reaction of the burn-resistant coating layer 13a mainly occurs, and the burn-resistant coating layer 13a turns to ash and begins to burn (second stage). In the second stage, a pyrolysis reaction mainly occurs in the fire-resistant coating layer 12a, and the fire-resistant coating layer 12a is carbonized. Then, the burn-resistant coating layer 13a is completely burned (third stage). In the fourth stage, an oxidation reaction occurs together with a pyrolysis reaction in the fire-resistant coating layer 12a. Then, the pyrolysis reaction of the fire-resistant coating layer 12a ends, and an oxidation reaction of the fire-resistant coating layer 12a mainly occurs (fourth stage). Thereafter, the oxidation reaction of the fire-resistant coating layer 12a is completed, and the fire-resistant structural material 1A stops burning (fifth stage).
In this way, in the fire-resistant structural material 1A of this embodiment, the pyrolysis reaction of the fire-resistant coating layer 12a occurs some time after the start of combustion. Therefore, the surface of the fire-resistant coating layer 12a can be kept smooth for some time after the start of combustion. In addition, the time during which the fire-resistant structural material 1A is burning during which the pyrolysis reaction or oxidation reaction of the fire-resistant coating layer 12a is occurring can be shortened. Due to these factors, the fire-resistant structural material 1A of this embodiment is less likely to develop cracks in the fire-resistant coating layer 12a, and can be prevented from continuing to glow red.

In addition, even if cracks or the like occur in the burnable coating layer 13a due to a thermal decomposition reaction or an oxidation reaction, and red heat occurs in the cracks, the burnable coating layer 13a is burned away, so the burnable coating layer 13a does not continue to be red-hot. Therefore, the red heat of the burnable coating layer 13a can be prevented from being transmitted to the fire-resistant coating layer 12a. This also contributes to suppressing the red heat of the fire-resistant coating layer 12a.

The thickness of the burnable coating layer 13a is preferably less than 25 mm, more preferably less than 20 mm, from the viewpoint of making the burnable coating layer 13a more likely to burn when the fire-resistant structural material 1A burns. Here, a thickness of 25 mm or more is not preferable because the burning time until burning increases and the member itself continues to burn for a long time. In addition, the thickness of the burnable coating layer 13a is preferably 10 mm or more, more preferably 15 mm or more, from the viewpoint of delaying the start of the thermal decomposition reaction and oxidation reaction of the fire-resistant coating layer 12a.

It is preferable that the fire-resistant structural material 1A of this embodiment satisfies the following criteria (1) and (2) when a combustion test is conducted for 60 minutes using standard heating in accordance with ISO 834-1 on the fire-resistant structural material 1A and a comparative structural material in which the burn-away coating layer 13a of the fire-resistant structural material 1A is replaced with a fire-resistant coating layer 12a.
Criterion (1): Immediately after the end of heating, the fire-resistant structural material 1A has a greater mass reduction rate than the comparative structural material.
Criterion (2): Within 180 minutes after the end of heating, the fire-resistant structural material 1A exhibits a slower rate of mass loss than the comparative structural material.
The fact that the fire-resistant structural material 1A satisfies the criterion (1) is considered to mean that the burnable coating layer 13a is more likely to burn when exposed to a flame. Also, the fact that the fire-resistant structural material 1A satisfies the criterion (2) is considered to mean that the thermal decomposition reaction and oxidation reaction of the fire-resistant coating layer 12a settle at an earlier stage after the burnable coating layer 13a is burned. Therefore, the fire-resistant structural material 1A that satisfies the criteria (1) and (2) can further suppress the red heat of the fire-resistant coating layer 12a.

To describe the comparative structural material in detail, the comparative structural material has the same structure as the fire-resistant structural material 1A, except that the burnable coating layer 13a in the fire-resistant structural material 1A is replaced with a fire-resistant coating layer 12a. The cross-sectional dimensions of the comparative structural material are the same as those of the fire-resistant structural material 1A. The comparative structural material can also be manufactured by using a fire-resistant coating layer 12a having the same thickness as the combined thickness of the burnable coating layer 13a and the fire-resistant coating layer 12a in place of the burnable coating layer 13a and the fire-resistant coating layer 12a in the fire-resistant structural material 1A.

The mass loss rate can be measured, for example, as follows.
<Method for measuring mass loss rate>
First, a 60-minute combustion test is carried out for the fire-resistant structural material 1A and the comparative structural material by standard heating in accordance with ISO 834-1. During the test, the mass change of the fire-resistant structural material is measured.
The mass of the structural material at T minutes after the start of heating is defined as W, and the mass of the structural material at time TΔ, 1 minute after time T _, is defined as _WΔ . The mass reduction rate is calculated using the following formula.
Mass reduction rate (kg/min) = (W - W _Δ ) / (T _Δ - T)
When calculating the mass reduction rate immediately after the end of heating, T may be set to 60 (min).

The thickness of the fire-resistant coating layer 12a is preferably 60 mm or more, more preferably 75 mm or more, from the viewpoint of making the fire-resistant coating layer 12a more likely to remain when the fire-resistant structural material 1A burns and improving the fire resistance of the fire-resistant structural material 1A. In addition, when the load-supporting portion 11a is made of steel, the thickness of the fire-resistant coating layer 12a is preferably 90 mm or less, more preferably 75 mm or less, from the viewpoint of taking advantage of the thermal conductivity and heat absorption due to the influence of the heat capacity and improving the fire-stopping effect of the wood.

Next, the constituent materials of the fire-resistant structural material 1A will be described.
As described above, the load-bearing portion 11a is made of wood or steel. When the load-bearing portion 11a is made of wood, it is possible to use laminated timber, lumber, cross-laminated timber (CLT), laminated veneer lumber (LVL), parallel strand lumber (PSL), etc. When the load-bearing portion 11a is made of wood, it may be a laminate in which a plurality of laminas are laminated and bonded in a direction perpendicular to one direction, and the laminate is arranged in the same direction to have a rectangular cross-sectional shape.
When the load-supporting portion 11a is made of steel, it is possible to use a square steel pipe, an H-shaped steel, a square steel, a flat steel, a channel steel, etc. Also, even if it has a shape other than these, it can be used as the load-supporting portion 11a as long as it can be surrounded by the fire-resistant coating layer 12a.

The fire-resistant coating layer 12a and the burn-off coating layer 13a are made of a wood material made of pure wood. In this specification, pure wood means wood that does not contain fire retardants, non-flammable materials, inorganic materials, etc.

Examples of pure wood that forms the fire-resistant coating layer 12a include laminated timber, lumber, cross-laminated timber (CLT), laminated veneer lumber (LVL), parallel strand lumber (PSL), and plywood. CLT and laminated timber may be made by stacking multiple lamina with rectangular cross sections in the short direction, with the vertices of the rectangles overlapping. Examples of pure wood species that form the fire-resistant coating layer 12a include larch, Douglas fir, red pine, Yezo spruce, white birch, cypress, Japanese cypress, zelkova, Scots pine, and radiata pine, with larch being preferred.

Examples of the pure wood that constitutes the burn-resistant coating layer 13a include laminated timber, lumber, cross-laminated timber (CLT), laminated veneer lumber (LVL), parallel strand lumber (PSL), and plywood. CLT and laminated timber may be made by stacking multiple lamina with rectangular cross sections in the short direction, with the vertices of the rectangles overlapping. Examples of the pure wood that constitutes the burn-resistant coating layer 13a include cedar, fir, SPF, and balsa, with cedar being preferred.

The bonding between the load-bearing portion 11a and the fire-resistant coating layer 12a, the bonding between the fire-resistant coating layer 12a and the burn-off coating layer 13a, and the bonding between the lamina constituting each of the load-bearing portion 11a, the fire-resistant coating layer 12a, and the burn-off coating layer 13a can be performed using various known adhesives that have been conventionally used in the manufacture of fire-resistant structural materials, such as resorcinol resin adhesives, resorcinol-phenol resin adhesives, aqueous polymeric isocyanate resin adhesives, polyurethane adhesives, and vinyl acetate adhesives. Of these, resorcinol-phenol resin adhesives are preferred from the viewpoint of further suppressing red heat.

Next, the glow suppression method of the present invention will be described. A preferred embodiment of the glow suppression method of the present invention is a method of covering a structural material having a load-bearing portion 11a and a fire-resistant coating layer 12a that covers the load-bearing portion 11a with a burnable coating layer 13a. The glow suppression method of this embodiment preferably produces the fire-resistant structural material 1A described above. The glow suppression method of this embodiment can prevent cracks from occurring on the surface of the fire-resistant coating layer 12a and suppress the fire-resistant coating layer 12a from glowing.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
A fire-resistant structural material having the same structure as the fire-resistant structural material 1A shown in Fig. 1 was manufactured. Specifically, a fire-resistant structural material having a wooden load-bearing portion was manufactured. The fire-resistant structural material had a cross-sectional dimension of 360 mm x 360 mm and an axial length of 3500 mm. The cross-sectional dimension of the load-bearing portion was 180 mm x 180 mm, the fire-resistant coating layer had a thickness of 75 mm, and the combustible coating layer had a thickness of 15 mm.
The load-bearing portion and the fire-resistant coating layer were made of larch (density: 0.50 g/ ^cm3 , moisture content: 12.3%) laminated timber. The combustible coating layer was made of cedar (density: 0.40 g/ ^cm3 , moisture content: 11.22%) laminated timber. The adhesive used in the manufacture of the fire-resistant structural material was a resorcinol-phenolic resin adhesive.

Example 2
A fire-resistant structural material having the same configuration as the fire-resistant structural material 1A shown in FIG. 1 was manufactured. Specifically, a fire-resistant structural material having a square steel pipe as a load-supporting part was manufactured. The fire-resistant structural material has a cross-sectional dimension of 385 mm x 385 mm and an axial length of 3300 mm. The square steel pipe as the load-supporting part has a cross-sectional dimension of 200 mm x 200 mm and a thickness of 9 mm. The thickness of the fire-resistant coating layer is 75 mm, and the thickness of the combustible coating layer is 15 mm. In Example 2, a spacer having a thickness of 2.5 mm was disposed between the load-supporting part and the fire-resistant coating layer. The spacer was disposed on each of the four side surfaces along the axial direction of the load-supporting part.
The square steel pipes used were STKR400 as specified in JIS G 3466. The spacers used were plywood made of cedar. The fire-resistant coating layer used was laminated lumber made of larch (density: 0.49 g/cm ³ , moisture content: 12.2%). The combustible coating layer used was laminated lumber made of cedar (density: 0.36 g/cm ³ , moisture content: 10.0%).

(Comparative Example 1)
A fire-resistant structural material was manufactured in the same manner as in Example 1, except for the following points. The thickness of the fire-resistant coating layer was 90 mm, and no burn-off coating layer was provided. The larch had a density of 0.53 g/cm ³ ±10% and a moisture content of 8 to 10%. In addition, a ferroresorcinol co-condensation resin (PRF)-based resin adhesive was used as the adhesive.

(evaluation)
(Combustion test)
The fireproof structural materials of Examples 1 and 2 and Comparative Example 1 were placed in a test furnace in an upright state, and each of the four sides was heated for one hour by standard heating according to ISO834-1, which assumes a normal fire. After the heating was completed, Example 1 and Comparative Example 1 were allowed to cool in the furnace for 8 hours, and Example 2 was allowed to cool for 11 hours. At that time, the temperature change was measured at each position indicated by black dots in Figures 2 to 4, and the temperature change over time at each position was recorded. Hereinafter, each position indicated by black dots in Figures 2 to 4 will be described as position 1, position 2, etc., using the numbers shown in Figures 2 to 4. The results of measuring the temperature change at each position are shown in Figures 5 to 7, respectively. In addition, the state of the heating surface of Examples 1 and 2 and Comparative Example 1 was visually confirmed. The state of the fireproof structural materials of Examples 1 and 2 and Comparative Example 1 after the combustion test is shown in Figures 8 to 10, respectively.

In Example 1, as shown in FIGS. 5(a) to (c), at all positions where the temperature change was measured, after the temperature dropped, the temperature did not rise again until the end of the test.
In addition, in the fire-resistant structural material of Example 1, the cedar boards on the surface continued to burn for a while immediately after the end of heating, but the flaming combustion did not significantly affect the temperature inside the furnace. It was also observed that the temperature inside the furnace also dropped as the flames died down. In addition, the cedar boards that did not burn out during heating continued to burn red hot while attached to the surface layer of the larch, but it was confirmed that they burned out and turned to ash as their volume decreased and they were carbonized, or that they fell off in the form of small charcoal and ash. In addition, since the cedar and the larch were secondary bonded with a resorcinol-based resin adhesive, the cedar did not fall off easily. The red-hot cedar sometimes fell onto the hearth, but the fallen cedar did not burn for a long time. After the cedar burned out, the carbonized layer of the larch gradually became exposed. In Example 1, the surface layer of the carbonized larch was not deeply carbonized to form solid charcoal compared to Comparative Example 1, but was in a relatively shallow carbonized state, and it was observed that the red-hot parts of the surface layer were crumbling away in small pieces.

In Example 2, as shown in FIGS. 6(a) to (d), at all positions where the temperature change was measured, after the temperature dropped, the temperature did not rise again until the end of the test.
In addition, the furnace temperature and the internal temperature of the fire-resistant structural material of Example 2 had both started to decrease sufficiently 12 hours after the start of the combustion test. No large cracks or the like were formed on the surface layer of the fire-resistant structural material of Example 2. Although the surface layer was slightly red-hot when the structural material was removed from the furnace, it was not hot enough to reignite and was burned away after a few hours.

As shown in Figure 7(a) in Comparative Example 1, at position 5, the temperature did not drop from the end of heating to the end of the test, and combustion continued. At positions 3 and 7, the temperature reached a peak, then dropped, before rising again. From this, it is believed that after the flames had gone out at positions 3 and 7, the red heat remaining in other areas was transferred to positions 3 and 7, causing combustion to start again. At positions 12, 13, and 14, the temperature also dropped and then rose, causing the red heat remaining in other areas to be transferred, causing combustion to start again, as shown in Figure 7(b).

In addition, the fireproof structural material of Comparative Example 1 had large cracks on the surface after heating began. Also, many charred layers were observed falling off during heating and in the early stages of cooling. Even after heating ended, strong red-hot combustion continued inside the cracks (uneven parts) that had occurred throughout the component, and significant damage was observed in the fireproof coating layer. In Comparative Example 1, the charred layer of the larch remained relatively solid, and the cracks were deep.
From the results of Examples 1 and 2 and Comparative Example 1, it is apparent that the present invention can suppress the red heat of a fire-resistant structural material.

In addition, in Example 2, as shown in Figure 6(b), the temperature at position 10, which is located at a corner of the fire-resistant structural material, peaks and then starts to decline, and the temperature at position 6, which is located in the portion between the corners of the fire-resistant structural material (hereinafter referred to as the "center"), also peaks and then starts to decline. In contrast, in Example 1, as shown in Figure 5(b), the temperature change at position 6, which is located in the center of the fire-resistant structural material, does not follow the temperature change at position 9, which is located at the corner of the fire-resistant structural material. This difference is thought to be due to the difference in the load-supporting parts of Examples 1 and 2. Specifically, in Example 2, since the fire-resistant structural material has a square steel pipe as a load-supporting part, it is considered that heat in the vicinity of the corner of the structural material, more specifically, at a position where the surface of the corner of the square steel pipe facing the fire-resistant coating layer (hereinafter referred to as the outer surface of the corner of the square steel pipe) and the surface of the fire-resistant coating layer facing the square steel pipe (hereinafter referred to as the inner surface of the fire-resistant coating layer) are approximately parallel, is transferred to the center of the structural material through the square steel pipe, which has a high thermal conductivity. The outer surface of the corner of the square steel pipe and the inner surface of the fire-resistant coating layer being approximately parallel means that the curvature of the outer surface of the corner of the square steel pipe in a direction parallel to the inner surface of the fire-resistant coating layer is approximately 0. According to Example 2, it is possible to suppress the concentration of heat in the vicinity of the corner of the fire-resistant structural material, and it is considered that red heat can be further suppressed.

Example 3
A fire-resistant structural material having the same structure as the fire-resistant structural material 1A shown in Fig. 1 was manufactured. Specifically, a fire-resistant structural material having a wooden load-bearing portion was manufactured. The fire-resistant structural material had a cross-sectional dimension of 330 mm x 330 mm and an axial length of 1600 mm. The cross-sectional dimension of the load-bearing portion was 180 mm x 180 mm, the fire-resistant coating layer had a thickness of 60 mm, and the combustible coating layer had a thickness of 15 mm.
The load-bearing portion and the fire-resistant coating layer were made of larch (density: 0.49 g/cm ³ , moisture content: 9.5%) laminated timber, and the combustible coating layer was made of cedar (density: 0.33 g/cm ³ , moisture content: 10.9%) laminated timber.

(Comparative Example 2)
A fire-resistant structural material was produced in the same manner as in Example 3, except for the following points: The thickness of the fire-resistant coating layer was 75 mm, and no burn-off coating layer was provided. The larch had a density of 0.50 g/cm ³ and a moisture content of 9.7%.

(Evaluation of Mass Loss Rate)
The fireproof structural materials of Example 3 and Comparative Example 2 were hung from the ceiling of a test furnace so that the axial direction of the fireproof structural materials was aligned with the vertical direction, and each of the four sides was heated for one hour by standard heating according to ISO834-1, which assumes a normal fire. After the heating was completed, the materials were left to cool in the furnace for six hours. At that time, the mass change of each fireproof structural material was measured, and the change in mass of each structural material over time was recorded. The results are shown in FIG. 11. Note that, from the start of heating until 30 minutes, the output of the heating burner was increased in order to increase the temperature in the furnace, so the pressure in the furnace was prone to fluctuating, making it difficult to accurately measure the mass. Therefore, FIG. 11 shows the measurement results after 30 minutes when the pressure in the furnace stabilized.

As shown in FIG. 11, immediately after the end of heating, i.e., 60 minutes after the start of heating, Example 3 has a higher mass reduction rate than Comparative Example 2. Furthermore, within 180 minutes after the end of heating, specifically, 30 minutes after the end of heating, Example 3 has a lower mass reduction rate than Comparative Example 2. Immediately after the end of heating, Example 3 has a higher rate of change in mass reduction rate than Comparative Example 2, but thereafter, Example 3 has a lower rate of change in mass reduction rate than Comparative Example 2. Furthermore, when comparing the fire-resistant structural material of Example 3 and the fire-resistant structural material of Comparative Example 2 after the combustion test, the fire-resistant structural material of Example 3 had no large cracks or fissures and no red heat remained, whereas the fire-resistant structural material of Comparative Example 3 had large cracks or fissures and red heat remained. Therefore, it can be seen that the fire-resistant structural material of Example 3 can suppress red heat.

1A Fire-resistant structural material 11a Load-bearing portion 12a Fire-resistant coating layer 13a Burn-away coating layer

Claims (4)

A fire-resistant structural material having a one-hour fire resistance performance,
A load-bearing section made of wood or steel;
A fire-resistant coating layer made of solid wood that covers the load-bearing portion;
a burnable covering layer that covers the fire-resistant covering layer, that burns and burns down when exposed to a flame, and that is made of pure wood and has a thickness of 10 mm or more and less than 20 mm ;
A fire-resistant structural material , in which the pure wood constituting the fire-resistant coating layer and the pure wood constituting the burn-resistant coating layer are joined at the boundary between the fire-resistant coating layer and the burn-resistant coating layer . The wood species constituting the fire-resistant coating layer is larch,
2. The fire-resistant structural material according to claim 1, wherein the wood species constituting the burn-off coating layer is Japanese cedar. The fire-resistant structural material according to claim 1 or 2, wherein the load-bearing portion is a square steel pipe. A structural material having a load-bearing part made of wood or steel and a fire-resistant coating layer made of solid wood that covers the load-bearing part is covered with a burnable coating layer made of solid wood that burns and burns up when exposed to flames,
A method for suppressing red heat by preventing cracks from occurring on the surface of the fire-resistant coating layer and suppressing red heat of the fire-resistant coating layer,
The structural material covered with the burn-resistant coating layer has a one-hour fire resistance, and at the boundary between the fire-resistant coating layer and the burn-resistant coating layer, the pure wood constituting the fire-resistant coating layer and the pure wood constituting the burn-resistant coating layer are joined together,
The heat suppression method according to claim 1, wherein the thickness of the burnable coating layer is 10 mm or more and less than 20 mm.

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