Fire-resistant coated beam and floor structure

Abstract

To provide a fire-resistant coated beam with reduced fire-resistant coating while suppressing deterioration in strength at the time of fire and improving workability at a construction site.SOLUTION: A fire-resistant coated beam 1 comprises an H-shaped steel 16 having an upper flange 17, a lower flange 18, and a web 19 joined to the upper flange and the lower flange, respectively, and a fire-resistant coating 21 arranged so as to cover the upper flange over the entire length in the longitudinal direction X of the H-shaped steel, the fire-resistant coating does not cover the lower part of the web and the lower flange, respectively, at least in the middle part in the longitudinal direction, and the upper flange is attached to the floor slab 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to fire-resistant coated beam and floor construction. [Background technology]

[0002] Conventionally, the following problems (1) and (2) have been known. (1) Loss of coating on the lower flange In the architectural steel frame market, sprayed rock wool is often used as a fire-resistant coating material. The usage rate of sprayed rock wool accounts for about 70 to 80% of the entire market. However, sprayed rock wool needs to be cured on-site after application. There is a risk that the sprayed rock wool applied to beams (H-shaped steel) made of steel frame components may fall off during application or curing. There is a particular risk of the sprayed rock wool falling off on the underside of the bottom flange of the beam. There is a strong demand in the market to reduce the amount of fire-resistant coating applied to the underside of the bottom flange of the beam.

[0003] (2) Interference between interior materials, equipment piping and fireproof coating The fire-resistant coating on the underside of the bottom flange is likely to interfere with interior materials such as ceilings and partition walls, and with equipment piping. From the perspective of design and equipment design, there is also a high demand for reducing the amount of fire-resistant coating on the underside of the bottom flange.

[0004] In order to solve the problems (1) and (2), if the fire-resistant coating on the underside of the bottom flange is reduced, it is expected that the workability will be further improved. Based on this, Patent Document 1 discloses a beam in which the fire-resistant coating is reduced depending on the stress state. Specifically, fireproofing is applied to the center of the beam in the longitudinal direction where bending stress is large, but not to the bottom flange near the end of the beam where bending stress is small when the beam is simply supported. In addition, at least the lower flange in the center of the beam is provided with a fire-resistant coating in order to make the allowable stress ratio 1.0 or less, so it cannot be said that the problems (1) and (2) are resolved.

[0005] In light of this, Patent Document 2 discloses a beam in which an uncovered area (exposed portion) is provided on the underside of the lower flange along the longitudinal direction of the beam. This makes it possible to avoid interference between the lower flange and other structures such as partition walls at the construction site, thereby resolving the problem in (2). However, in Patent Document 2, it is assumed that the uncovered parts will be covered by partition walls, etc., and it is said that the decrease in fire resistance can be avoided. In addition, by using a plate-like or felt-like material for the fire-resistant covering material, it is possible to prevent the lower flange of the sprayed rock wool from falling off, thereby solving the problem of (1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 08-144393 [Patent Document 2] JP 2005-179904 A Summary of the Invention [Problem to be solved by the invention]

[0007] At first glance, the fire-resistant covered beam in Patent Document 2 appears to improve workability and fire resistance while reducing the amount of fire-resistant covering. However, when covering the uncovered portion with a partition wall or the like, it is necessary to set the dimensions of the uncovered portion according to the shape of the wall, etc., and it cannot be said that the workability at the construction site is improved. In addition, since it is assumed that a structure such as a partition wall with heat insulation properties will be installed under the beam, it cannot be used in cases where a ceiling material without heat insulation properties is attached.

[0008] From the viewpoint of workability, it is desirable to leave the bottom flange and web of the beam unfire-resistant (without fire-resistant coating). However, if there are uncoated parts, the temperature rise of the beam during a fire is unavoidable, and there is a risk that the required fire resistance cannot be secured.

[0009] The present invention has been made in consideration of such problems, and aims to provide a fire-resistant coated beam that reduces the amount of fire-resistant coating while suppressing the decrease in strength during a fire and improving workability at the construction site, and a floor structure equipped with this fire-resistant coated beam. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention proposes the following means. (1) Aspect 1 of the present invention is a fire-resistant coated beam comprising an H-shaped steel beam having an upper flange, a lower flange, and webs joined to the upper flange and the lower flange, respectively, and a fire-resistant coating arranged to cover the upper flange over the entire longitudinal length of the H-shaped steel beam, wherein the fire-resistant coating does not cover the lower portion of the web or the lower flange, at least in the middle portion of the longitudinal direction, and the upper flange is attached to a floor slab.

[0011] In this invention, the fire-resistant coating is arranged to cover the top flange of the H-shaped steel, and the top flange is attached to the floor slab. This allows the top flange and floor slab to withstand a certain amount of stress during a fire, making it possible to suppress a decrease in the strength of the fire-resistant coated beam during a fire. Since the uncoated part of the fire-resistant coated beam does not need to be covered with, for example, a partition wall, a decrease in the strength of the fire-resistant coated beam during a fire can be suppressed, improving workability at the construction site. The fire-resistant coating does not cover the lower part of the web and the lower flange at least in the longitudinal middle part, so that the amount of fire-resistant coating in the fire-resistant coated beam can be reduced.

[0012] (2) A second aspect of the present invention may be a fire-resistant coated beam described in (1), in which the fire-resistant coating is arranged so as not to cover the entire longitudinal length of the lower flange, and is arranged so as to cover the web from the upper end of the web downward to a height capable of transmitting the design shear force of the web. According to the present invention, in the event of a fire, the design shear force transmitted to the web can be reliably transmitted, and the fire-resistant coating can be reduced over a wider area of ​​the lower flange.

[0013] (3) A third aspect of the present invention may be a fire-resistant coated beam as described in (1) or (2), in which a through hole is formed in the web, and the fire-resistant coating is arranged so as not to cover the entire longitudinal length of the lower flange, and is arranged so as to cover the web from the upper end of the web downward to the upper end of the through hole. In this invention, the effective diameter of the through hole is not reduced by the fire-resistant coating, making construction management easier. A relatively wide area from the top of the web downward to the top of the through hole can withstand a certain amount of stress during a fire, and the fire-resistant coating can be reduced over a wider area of ​​the bottom flange.

[0014] (4) A fourth aspect of the present invention may be a fire-resistant coated beam described in any one of (1) to (3), in which a yield bending moment calculated based on a section modulus from the centroid to the upper flange in a cross section perpendicular to the longitudinal direction of the H-shaped steel is greater than a yield bending moment calculated based on a section modulus from the centroid to the lower flange in the cross section. In this invention, even if the portion from the centroid to the lower flange side becomes unable to withstand the bending moment acting on the fire-resistant coated beam in the event of a fire, the portion from the centroid to the upper flange side can withstand the bending moment acting on the fire-resistant coated beam.

[0015] (5) A fifth aspect of the present invention may be a fire-resistant coated beam described in any one of (1) to (4), wherein the cross-sectional area of ​​the upper flange perpendicular to the longitudinal direction is larger than the cross-sectional area of ​​the lower flange perpendicular to the longitudinal direction. In this invention, the heat capacity of the upper flange is greater than that of the lower flange, so the temperature of the upper flange during a fire is lower than when the cross-sectional areas are equal, and this more reliably prevents a decrease in the strength of the upper flange, which mainly withstands a certain amount of stress during a fire.

[0016] (6) A sixth aspect of the present invention may be a fire-resistant coated beam according to any one of (1) to (5), in which the strength of the upper flange is greater than the strength of the lower flange. In this invention, even if the strength of the lower flange decreases during a fire, the strength of the fire-resistant coated beam can be ensured by the upper flange.

[0017] (7) A seventh aspect of the present invention may be a fire-resistant coated beam according to any one of (1) to (6), in which the H-shaped steel has a reinforcing member attached to the underside of the upper flange. According to the present invention, the adhesion of the fire-resistant coating provided on the upper flange can be improved.

[0018] (8) An eighth aspect of the present invention is a floor structure comprising a fire-resistant coated beam according to any one of (1) to (7) and the floor slab. With this invention, a floor structure can be constructed using fire-resistant coated beams that require less fire-resistant coating while minimizing loss of strength during a fire and improving workability at the construction site. Effect of the Invention

[0019] The fire-resistant coated beam and floor structure of the present invention makes it possible to reduce the amount of fire-resistant coating while suppressing a decrease in strength during a fire and improving workability at the construction site. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view showing a floor structure according to one embodiment of the present invention as viewed from the front. [Diagram 2] FIG. [Diagram 3] FIG. 1 is a diagram showing an analytical model of a floor structure 1A having a covering pattern a. [Figure 4] FIG. 2 is a diagram showing an analytical model of a floor structure 1 having a coating pattern b. [Diagram 5] FIG. 13 is a diagram showing an analytical model of a floor structure 1B having a coating pattern c. [Figure 6] FIG. 13 is a diagram illustrating the change in temperature of an H-shaped steel over time in coating pattern a. [Figure 7] FIG. 13 is a diagram illustrating the change over time in each temperature of an H-shaped steel in coating pattern b. [Figure 8] FIG. 13 is a diagram illustrating the change over time in each temperature of an H-shaped steel in coating pattern c. [Figure 9] FIG. 1 is a diagram illustrating the change in temperature of an H-beam steel over time in sample No. 1 and coating pattern a. [Figure 10] FIG. 13 is a diagram illustrating the change over time in each temperature of the H-beam steel in sample No. 2 and coating pattern a. [Figure 11] FIG. 13 is a diagram showing the external force conditions and boundary conditions of a fire-resistant coated beam. [Figure 12] FIG. 1 illustrates bending moments acting on a fire-resistant coated beam. [Figure 13] FIG. 13 is a diagram illustrating the change in temperature of an H-shaped steel sample over time. [Figure 14] FIG. 13 is a diagram illustrating the change in temperature of an H-shaped steel over time depending on the thickness of the fire-resistant coated beam in Sample No. 1. [Figure 15] FIG. 2 is a diagram showing a schematic diagram of temperature distribution and stress distribution corresponding to each position in a cross section of a floor structure at room temperature. [Figure 16] FIG. 1 is a diagram showing a schematic diagram of temperature distribution and stress distribution corresponding to each position in a cross section of a floor structure during a fire. [Figure 17] FIG. 13 is a diagram illustrating the change in deflection of the floor structure over time depending on the thickness of the fire-resistant coated beam in sample No. 2. [Figure 18] FIG. 13 is a diagram illustrating the change in deflection of the floor structure over time due to the sample. [Figure 19]FIG. 13 is a diagram illustrating the change in deflection of the floor structure over time due to the sample. [Figure 20] FIG. 13 is a diagram illustrating the change in deflection of the floor structure over time due to the sample. [Figure 21] FIG. 1 is a graph illustrating the change in disintegration time depending on the coating thickness in sample No. 1 with coating pattern a. [Figure 22] FIG. 13 is a graph illustrating the change in disintegration time depending on the coating thickness in sample No. 2 with coating pattern a. [Figure 23] FIG. 13 is a diagram showing an analytical model of a floor structure of a comparative example. [Figure 24] FIG. 11 is a diagram illustrating the change over time in the temperatures of H-shaped steel in the floor structure of the comparative example. [Diagram 25] FIG. 13 is a diagram illustrating the change in deflection over time in a floor structure of the comparative example. [Figure 26] 1 is a cross-sectional front view of a fire-resistant coated beam according to a first modified example of an embodiment of the present invention. FIG. [Figure 27] 13 is a cross-sectional front view of a fire-resistant coated beam according to a second modified example of an embodiment of the present invention. FIG. [Figure 28] FIG. 30 is a cross-sectional view of a floor structure according to a third modified example of one embodiment of the present invention, taken along the cutting line A1-A1 in FIG. 29. [Figure 29] FIG. [Diagram 30] FIG. 11 is a cross-sectional front view of a fire-resistant coated beam according to a fourth modified example of one embodiment of the present invention. [Diagram 31] 13 is a cross-sectional front view of a fire-resistant coated beam according to a fifth modified example of an embodiment of the present invention. FIG. [Diagram 32] FIG. 13 is a cross-sectional front view of a fire-resistant coated beam according to a sixth modified example of an embodiment of the present invention. [Diagram 33] FIG. 13 is a cross-sectional front view of a fire-resistant coated beam according to a seventh modified example of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, one embodiment of a fire-resistant covered beam and floor structure according to the present invention will be described with reference to Figs.

[0022] [1. Floor structure configuration] As shown in Figs. 1 and 2, the floor structure 1 of this embodiment includes a floor slab 10 and a fire-resistant covered beam 15 of this embodiment. The floor slab 10 is, for example, a concrete slab or a composite slab. The floor slab 10 is formed in a plate shape having a rectangular shape in a plan view. The floor slab 10 is disposed so as to be aligned along a horizontal plane.

[0023] The fire-resistant coated beam 15 has an H-shaped steel 16 and a fire-resistant coating 21. The H-shaped steel 16 is made of steel and is used as a beam. The H-shaped steel 16 has an upper flange 17, a lower flange 18, and a web 19. The upper flange 17, the lower flange 18, and the web 19 are each formed in a flat plate shape. The upper flange 17 and the lower flange 18 are disposed so as to be aligned along a horizontal plane. The upper flange 17 and the lower flange 18 are aligned along an opposing direction Z, which is the up-down direction. The upper flange 17 is disposed above the lower flange 18. The web 19 is disposed between the upper flange 17 and the lower flange 18, and is joined to the center of the upper flange 17 in the width direction and the center of the lower flange 18 in the width direction, respectively.

[0024] The H-shaped steel 16 may be a rolled H-shaped steel or a welded H-shaped steel. The H-shaped steel 16 is disposed so that the longitudinal direction X of the H-shaped steel 16 is along a horizontal plane. Here, a direction perpendicular to the longitudinal direction X and the facing direction Z is defined as an orthogonal direction Y.

[0025] For example, the fireproof coating 21 is made of sprayed rock wool. As shown in FIG. 1, in this embodiment, the fire-resistant coating 21 is disposed over the entire length in the longitudinal direction X so as to cover a part of the upper flange 17 and an upper portion of the web 19. The fire-resistant coating 21 is disposed so as to cover the lower surface of the upper flange 17 and both end surfaces in the orthogonal direction Y. The fire-resistant coating 21 does not cover the upper surface of the upper flange 17. The upper portion of the web 19 here means a portion of the web 19 above the center of the web 19 in the facing direction Z. The fire-resistant coating 21 does not cover a lower portion of the web 19 over the entire length in the longitudinal direction X. The lower portion of the web 19 here means a portion of the web 19 below the center of the web 19 in the facing direction Z. The fire-resistant coating 21 does not cover the bottom flange 18 over its entire length in the longitudinal direction X.

[0026] The upper flange 17 is in contact with the floor slab 10 from below the floor slab 10. For example, the upper flange 17 is attached to the floor slab 10 via a shear force transmitting member such as a headed stud (not shown).

[0027] [2. Numerical analysis of fire resistance of floor structure] The fire resistance of floor structure 1 was verified by numerical analysis. For the numerical analysis, the general-purpose FEM analysis software "SAFIR" was used. In the analysis, first, a heat conduction analysis is performed in a cross section perpendicular to the longitudinal direction X of floor structure 1. Then, a thermal stress analysis of floor structure 1 is performed based on the obtained temperature distribution in the cross section. The details of the analysis model are described below.

[0028] [2.1. Heat conduction analysis] Table 1 shows the materials and dimensions from which each component of the floor structure 1 is made.

[0029] [Table 1]

[0030] Here, the cross section of the H-shaped steel 16 in Table 1 (H-400x200x8x13) is the standard cross section of the H-shaped steel 16. The floor slab 10 is assumed to have no reinforcing bars (unreinforced), and the fillet portion of the H-shaped steel 16 is ignored. The thermal property values ​​of the steel frame forming the H-shaped steel 16 and the concrete forming the floor slab 10 were referenced to Eurocode 2 (see [5.] 1)) and Eurocode 3 (see [5.] 2)). The thermal property values ​​of the sprayed rock wool were referenced to the Fire Resistance Guidebook for Structural Materials (see [5.] 3)). The moisture content of both the concrete and the sprayed rock wool was set to 5.0%. The 25mm-thick sprayed rock wool is rated for one-hour fire resistance as specified by the Building Standards Act.

[0031] The heating history of the floor structure 1 conformed to the standard heating curve of ISO-834 (see [5.] 4)). The conditions were set to heat the underside of the floor slab 10, the fireproof coating 21, and the surface of the H-shaped steel 16. The standard heating curve is defined by the following formula (1). T = 345 × log 10 (8t+1)+20 ··(1) where T is the heating temperature (°C) and t is the heating time (min).

[0032] Analytical models of the floor structures 1A, 1, and 1B are shown in Figures 3 to 5. Note that in Figures 3 to 5 and Figure 23 described later, some of the meshes of the analytical models are omitted. In the following, a specification in which only the upper flange 17 is covered with a fire-resistant coating 21A, as in the floor structure 1A shown in Fig. 3, is referred to as covering pattern a. A specification in which the lower surface of the upper flange 17, both end surfaces in the orthogonal direction Y, and the upper part of the web 19 are covered with a fire-resistant coating 21, as in the floor structure 1 shown in Fig. 4, is referred to as covering pattern b. A specification in which the H-shaped steel 16 is covered with a fire-resistant coating 21B other than the upper surface of the upper flange 17, as in the floor structure 1B shown in Fig. 5, is referred to as covering pattern c. In this analysis, three coating patterns, a, b, and c, were examined.

[0033] Table 2 shows a list of the analyzed cross sections.

[0034] [Table 2]

[0035] In this analysis, H-400x200x8x13 was used as the reference section. The analysis was performed on a section with a constant total cross-sectional area and a difference in the cross-sectional area of ​​the upper flange and the lower flange. Here, section modulus (upper side) Z1 indicates the section modulus of the upper flange side, and section modulus (lower side) Z2 indicates the section modulus of the lower flange side. That is, section modulus Z1 is the section modulus from the centroid to the top flange in a cross section perpendicular to the longitudinal direction of the H-shaped steel. Section modulus Z2 is the section modulus from the centroid to the bottom flange in a cross section perpendicular to the longitudinal direction of the H-shaped steel.

[0036] For example, in sample No. 1, the beam depth H of the H-shaped steel is 400 mm, the width of the upper flange (length in the orthogonal direction Y) b1 is 200 mm, the width of the lower flange b2 is 200 mm, and the thickness of the web tw is 8 mm. The thickness t1 of the upper flange is 13 mm, and the thickness t2 of the lower flange is 13 mm. The section modulus Z1 and the section modulus Z2 are 1148243 mm. 3 It is.

[0037] Therefore, in sample No. 1, which has a vertically symmetrical cross section, section modulus Z1 and section modulus Z2 are equal. On the other hand, in sample No. 2, in which the cross-sectional area of ​​the upper flange is made larger than that of the lower flange, section modulus Z1 (upper side) is larger than section modulus Z2 (lower side). In other words, the yield bending moment calculated based on section modulus Z1 (hereinafter also referred to as upper yield bending moment) is larger than the yield bending moment calculated based on section modulus Z2 (hereinafter also referred to as lower yield bending moment). In sample No. 4, the cross-sectional area of ​​the upper flange perpendicular to the longitudinal direction X is larger than the cross-sectional area of ​​the lower flange perpendicular to the longitudinal direction X. In other words, the strength of the upper flange is larger than the strength of the lower flange. The strength here means the yield strength.

[0038] Figure 3 shows the positions Pft, Pw, and Pfb of the H-shaped steel where the temperatures were extracted in the floor structure 1A (1, 1B). Here, the temperature at the position Pft of the top flange is defined as Tft. Similarly, the temperature at the position Pw of the web is defined as Tw, and the temperature at the position Pfb of the bottom flange is defined as Tfb.

[0039] Figures 6 to 8 show the cross-sectional temperature history obtained from the heat conduction analysis. In this study, the thickness of the web is the same, so the temperature history of the web is roughly the same for each coating pattern. Therefore, in Fig. 6, the web temperature is shown only for sample No. 1 (reference cross section) among samples No. 1 to No. 5. The thick dashed line in Fig. 6 shows the result of the web temperature Tw of sample No. 1. In Fig. 6, the temperature Tft of the top flange in Samples No. 1 to No. 5 is indicated by a circle marked "Tft." The temperature Tfb of the bottom flange in Samples No. 1 to No. 5 is indicated by a circle marked "Tfb." A standard heating curve according to formula (1) is shown in Fig. 6. 7 and 8 are illustrated in the same manner as FIG.

[0040] For example, when focusing on the temperature Tft of the upper flange, the temperature is lower in samples with a larger cross-sectional area of ​​the upper flange. This is because the heat capacity of the upper flange as a plate element is larger. In addition, for coating pattern a, a large difference is observed between samples No. 4 and 5 when the flange width is used as a variable. This is because the position Pft where the temperature of the top flange is extracted is farther from the web as the width of the top flange increases, and the influence of the heat input from the web decreases.

[0041] For coating pattern a of sample No. 1, specifications in which the thickness of the sprayed rock wool was 45 mm, 60 mm, and 75 mm in addition to 25 mm were also analyzed. Here, the coating thickness (thickness of the fireproof coating) of 45 mm and 60 mm corresponds to the 2-hour fireproof specification and the 3-hour fireproof specification, respectively, stipulated in the Building Standards Act Notification. Figure 9 shows the results of a heat conduction analysis of sample No. 1 with the coating thickness as a variable.

[0042] For coating pattern a of sample No. 2, specifications in which the thickness of the sprayed rock wool was increased from 25 mm to 45 mm and 60 mm were also analyzed. Figure 10 shows the results of heat conduction analysis of sample No. 2 with the coating thickness as a variable.

[0043] [2.2. Thermal stress analysis] A thermal stress analysis is performed using the temperatures obtained from the heat conduction analysis described above. In this analysis, an in-plane analysis is performed using two-dimensional beam elements, and the buckling phenomenon is ignored. As shown in Fig. 11, the length (span) L of the floor structure was set to 5400 mm. The floor structure was simply supported by a pin at the first end and a pin roller at the second end. The load condition of the floor structure was a uniformly distributed load ω. At this time, as shown in FIG. 12, at the center of the floor structure in the longitudinal direction, (ωL 2 / 8) bending moment acts on the specimen. Table 3 shows the mechanical properties of the materials forming the floor structure.

[0044] [Table 3]

[0045] For example, the Young's modulus of H-beam is 205,000N / mm 2 It is. In this analysis, the stress load of the fireproof coating was ignored. The strength retention rate and stress-strain relationship of the concrete and steel frame were based on Eurocode 2 and Eurocode 3, respectively. However, for the conventional covering pattern c, the stress load on the floor slab was ignored based on the evaluation method of the general fire-resistant construction certification test. In this analysis, the temperature obtained from the heat conduction analysis was applied to the entire length of the fire-resistant covered beam. Table 4 shows a list of the loads applied to the floor structure.

[0046] [Table 4]

[0047] The load is the maximum bending moment (ωL 2 The yield bending moment was calculated by multiplying the section modulus by the yield value of the steel frame, and the smaller of the yield bending moment on the top flange side and the yield bending moment on the bottom flange side was used. Therefore, the yield bending moment is 270 kN m for load No. 1, 176 kN m for load No. 2 and 3, and 179 kN m for load No. 4 and 5. However, for comparison, the load was the same in all cases, and the load value calculated from the yield bending moment for load No. 2 and 3 (176 kN m) was used.

[0048] The collapse of the floor structure was judged when the deflection displacement at the center of the span of the floor structure (fireproof covered beam) reached the deflection specified value δu. Here, the deflection specified value δu is an index shown in the reference 4) and is expressed by the formula (2). δu=L 2 / (400H) ··(2) Here, H is the beam depth of the H-shaped steel (mm). In addition, the deflection value specified by formula (2) is also applied in domestic fire-resistant construction certification tests. In this study, the length L = 5400, the beam depth H = 400, and the deflection value δu = 182 mm.

[0049] Figures 13 and 14 show the deflection displacement history of coating pattern a obtained from thermal stress analysis. The deflection displacement is the vertical displacement at the center of the span of the floor structure. Samples whose intersection with the line at 60 minutes is equal to or less than the deflection shown in formula (2) meet the 1-hour fire resistance performance. From Figure 13, it can be seen that samples No. 2 and 4, which have a larger cross-sectional area of ​​the upper flange, had a longer collapse time than the other samples. Here, schematic diagrams of temperature distribution and stress distribution corresponding to each position in the cross section of the floor structure at room temperature and during a fire are shown in Figures 15 and 16. In Figures 15 and 16, the neutral axis L1 of the floor structure is shown. After the lower flange 18 and web 19 lose their strength, the neutral axis L1 moves into the floor slab 10, and bending is resisted by the compressive force of the upper part of the floor slab 10 and the tensile force of the upper flange 17. The reason why the collapse time is longer is believed to be that the bending strength of samples Nos. 2 and 4, which have a larger cross-sectional area of ​​the upper flange, is greater than that of the other samples.

[0050] Figure 14 also shows the results when the coating thickness was 45 mm, 60 mm, and 75 mm for sample No. 1. From Figure 14, it can be seen that with a coating thickness of 75 mm, the specified deflection value was not reached at the 60-minute mark, ensuring one-hour fire resistance. Figures 17 and 18 show the results when the coating thickness was set to 45 mm and 60 mm for sample No. 2. Figures 17 and 18 show that with a coating thickness of 45 mm, the specified deflection value was not reached at the 60-minute mark, and one-hour fire resistance was ensured.

[0051] The deflection displacement history of coating pattern b obtained from thermal stress analysis is shown in Fig. 19. From Fig. 19, it can be seen that samples No. 2 and 4, which have a larger cross-sectional area of ​​the upper flange like coating pattern a, had a longer collapse time than the other samples. In addition, in the case of coating pattern b, samples No. 1, 2, and 4 did not reach the specified deflection value at the 60-minute point, which indicates that one-hour fire resistance was ensured.

[0052] The thermal stress analysis results of the coating pattern c obtained from the thermal stress analysis are shown in Figure 20. Here, the analysis shown in Figure 20 ignores the stress burden of the floor slab based on the fire-resistant structure qualification test. As can be seen from Figure 20, sample No. 2 had the shortest collapse time, while sample No. 5 had the longest collapse time. This is believed to be because the cross-sectional area of ​​the bottom flange of sample No. 2 was small, resulting in a significant temperature rise, which resulted in large thermal deflection and caused the bottom flange to yield relatively early. Here, thermal deflection refers to deflection caused by the difference in thermal expansion between the top and bottom flanges, and the greater the temperature difference between the top and bottom flanges, the greater the thermal deflection. From Figure 8, it can be seen that the temperature of the bottom flange of sample No. 2 is significantly higher than that of the other samples. On the other hand, in sample No. 5, the temperature of the top flange is relatively high, which is thought to have reduced the thermal deflection. In addition, all samples secured a one-hour fire resistance.

[0053] Table 5 shows the disintegration times obtained from the analysis.

[0054] [Table 5]

[0055] In Table 5, for example, in sample No. 1, the collapse time was 37 minutes when the stress load of the floor slab was taken into consideration, and the sample did not satisfy the one-hour fire resistance performance. From Table 5, for covering pattern b, samples (No. 1, 2, 4) in which the cross-sectional area of ​​the upper flange was equal to or greater than that of the lower flange secured one-hour fire resistance. Therefore, by considering the stress load on the floor slab, one-hour fire resistance can be secured even if the lower flange and part of the web are left uncovered. On the other hand, none of the samples achieved 1-hour fire resistance in coating pattern A. This shows that if 1-hour fire resistance is to be achieved in coating pattern A, the fire-resistant coating and floor slab must be made thicker.

[0056] Table 6 shows the disintegration time as a function of the coating thickness of sample No. 1.

[0057] [Table 6]

[0058] In Table 6, for example, when the thickness of the fire-resistant coating was 0 mm, the collapse time was 19 minutes, which did not satisfy the 1-hour fire resistance performance. The relationship between coating thickness and collapse time is shown in Figure 21. In this analysis, a coating thickness of 75 mm ensured one-hour fire resistance, but from Figure 21 it is inferred that a coating thickness of 65 mm or more would ensure one-hour fire resistance. Table 7 shows the amount of fire-resistant coating for sample No. 1.

[0059] [Table 7]

[0060] The amount of fireproof coating is the amount of coating per 1m in the longitudinal direction of the fireproof coated beam, and the fillet part of the cross section is ignored. In Table 7, for example, in the case of coating pattern c, when the thickness of the fireproof coating is 25mm, the amount of fireproof coating per 1m of the length of the fireproof coated beam is 29mm. 3 In this case, the coating thickness of coating pattern c is 25 mm. From Table 7, the amount of fire-resistant coating for the coating pattern a with a coating thickness of 65 to 75 mm is equal to or less than that of the coating pattern c with a coating thickness of 25 mm. Therefore, it is possible to ensure 1-hour fire resistance without increasing the amount of fire-resistant coating.

[0061] Table 8 shows the disintegration time as a function of coating thickness for sample No. 2.

[0062] [Table 8]

[0063] In Table 8, for example, when the thickness of the fire-resistant coating was 0 mm, the collapse time was 18 minutes, which did not satisfy the 1-hour fire resistance performance. The relationship between coating thickness and collapse time is shown in Figure 22. In this analysis, a coating thickness of 45 mm ensured one-hour fire resistance, but from Figure 22, it is inferred that a coating thickness of 35 mm or more would ensure one-hour fire resistance. Table 9 shows the amount of fire-resistant coating for sample No. 2.

[0064] [Table 9]

[0065] In Table 9, for example, when the thickness of the fireproof coating is 25 mm in coating pattern c, the amount of fireproof coating per 1 m of the fireproof coating beam is 29 m. 3 In this case, the coating thickness of coating pattern c is 25 mm. From Table 9, the coating thickness of 45 to 60 mm for coating pattern a is less than the coating thickness of 25 mm for coating pattern c. Therefore, it is possible to ensure 1-hour fire resistance while reducing the amount of fire-resistant coating.

[0066] [3. Consideration of shear strength] In this embodiment, the shear force acting on the end of the beam based on the conditions in Figures 11 and 12 can be calculated using equation (3).

[0067]

number

[0068] Here, Q is the shear force acting on the end of the fire-resistant covered beam. The long-term allowable shear strength of a fire-resistant covered beam is calculated by the cross-sectional area A of the web perpendicular to the longitudinal direction. w It can be calculated using equation (4).

[0069]

number

[0070] However, Q d is the long-term allowable shear strength, F is the design strength (=235N / mm2 ). In this case, it is assumed that the shear force is borne only by the web. From equations (3) and (4), the required cross-sectional area of ​​the web, A wd can be calculated using equation (5).

[0071]

number

[0072] We will consider the acting shear force when a long-term allowable bending moment acts on a section of H400x200x8x13. Table 10 shows the long-term bending and shear strength.

[0073] [Table 10]

[0074] Under uniformly distributed load, when the bending moment acting on the center of the fireproof beam is equal to the long-term allowable bending moment, the shear force at the end of the fireproof beam is the largest, and the shear force acting at the end of the fireproof beam is 133kN. Therefore, from formula (4), the required cross-sectional area of ​​the web is 1473mm 2 It becomes. Assuming that the covered area of ​​the web can bear the shear force, the required covering height of the web, h, is calculated from equation (6). wd is (1473 / 8), which is 184mm.

[0075]

number

[0076] However, t w is the thickness of the web. From the above, if the area of ​​184 + 13 = 197 ≒ 200 mm from the top surface of the upper flange is covered, the acting shear force can be transmitted.

[0077] Here, it is assumed that a bending moment equivalent to the long-term allowable bending moment acts on the fire-resistant covered beam. However, in actual design, it is considered that the applied load may be smaller than the long-term bending moment. In this case, it is possible to reduce the covered area of ​​the web according to the applied load. In this study, the necessary covering height was calculated at the end of the fire-resistant covered beam (the position where the acting shear force is the largest), but since the acting shear force becomes smaller as it approaches the center of the span of the fire-resistant covered beam, it is considered that the covered area of ​​the web can be reduced according to the acting shear force. In this case, the covered area of ​​the web changes in the longitudinal direction of the fire-resistant covered beam.

[0078] [4. Numerical analysis of fire resistance of floor structure of comparative example] The cross-sectional samples shown in Table 11 were analyzed under the condition that they were completely unfire-resistant coated.

[0079] [Table 11]

[0080] Figure 23 shows the model cross section for the heat conduction analysis, Figure 24 shows the results of the heat conduction analysis, and Figure 25 shows the results of the thermal stress analysis. Figure 24 shows the temperature history at the temperature sampling points shown in Figure 3. Figure 25 also shows the analysis results when only the upper flange was covered. Note that in both thermal stress analyses, the stress burden of the floor slab was taken into consideration. As can be seen from Fig. 25, the fire resistance performance was improved by covering only the upper flange. In particular, the improvement in fire resistance was most remarkable in sample No. 2, which had a larger cross-sectional area of ​​the upper flange.

[0081] [5. Literature] 1)Eurocode2:”Design of concrete structures Part 1-2: General rules - Structural fire design”,prEN 1992-1-2,2004 2)Eurocode3:”Design of steel structures Part 1-2: General rules - Structural fire design”,prEN 1993-1-2,2005 3) Fire Resistance Guidebook: Architectural Institute of Japan, "Fire Resistance Guidebook for Structural Materials," Maruzen Publishing Co., Ltd., 2017 4)ISO-834:ISO 834-1, ``Fire-resistance tests -Elements of building construction- Part 1: General requirements'', 1999.9

[0082] 6. Effects of this embodiment As described above, in the fire-resistant coated beam 15 of this embodiment, the fire-resistant coating 21 is arranged on the H-shaped steel 16 so as to cover the upper flange 17, and the upper flange 17 is attached to the floor slab 10. This allows the upper flange 17 and the floor slab 10 to withstand a certain amount of stress during a fire, thereby suppressing a decrease in the strength of the fire-resistant coated beam 15 during a fire. Since the uncoated portion of the fire-resistant coated beam 15 is not covered by, for example, a partition wall, a decrease in the strength of the fire-resistant coated beam 15 during a fire can be suppressed, thereby improving workability at the construction site. The fire-resistant coating 21 does not cover the lower portion of the web 19 and the bottom flange 18 over the entire length in the longitudinal direction X. This makes it possible to reduce the amount of fire-resistant coating 21 on the fire-resistant coated beam 15. It is possible to prevent the fire-resistant coating 21 from falling off the bottom flange 18. It is possible to make the ceiling including the fire-resistant coated beam 15 higher by the amount of the fire-resistant coating 21, for example, and it is possible to prevent interference between the fire-resistant coated beam 15 and piping (not shown) or the like arranged below the fire-resistant coated beam 15.

[0083] There are cases where the upper yield bending moment is larger than the lower yield bending moment. In this case, even if the portion from the centroid to the lower flange 18 side cannot withstand the bending moment acting on the fire-resistant covered beam 15 during a fire, the portion from the centroid to the upper flange 17 side can withstand the bending moment acting on the fire-resistant covered beam 15. The cross-sectional area of ​​the upper flange 17 perpendicular to the longitudinal direction X may be larger than the cross-sectional area of ​​the lower flange 18 perpendicular to the longitudinal direction X. In this case, the heat capacity of the upper flange 17 is larger than the heat capacity of the lower flange 18, so that the temperature of the upper flange 17 during a fire is lower than when the cross-sectional areas are equal. This makes it possible to more reliably prevent a decrease in the strength of the upper flange 17, which mainly withstands a certain stress during a fire.

[0084] The strength of the upper flange 17 may be greater than the strength of the lower flange 18. In this case, even if the strength of the lower flange 18 decreases during a fire, the strength of the fire-resistant coated beam 15 can be ensured by the upper flange 17. Furthermore, in the floor structure 1 of this embodiment, the floor structure can be constructed using fire-resistant coated beams 15 that reduce the amount of fire-resistant coating 21 while minimizing the decrease in strength during a fire and improving workability at the construction site.

[0085] 7. Modifications The fire-resistant coated beam 15 and floor structure 1 of this embodiment can have various configurations as described below. In the fire-resistant covered beam 25 of the first modified example shown in Fig. 26, in each configuration of the fire-resistant covered beam 15, a through hole 19a is formed in the web 19. The through hole 19a penetrates the web 19 in the orthogonal direction Y. The through hole 19a is disposed at the center of the web 19 in the opposing direction Z. The fire-resistant coating 21 is disposed over the entire length of the web 19 in the longitudinal direction X so as to cover the web 19 from the upper end of the web 19 downward to the upper end of the through-hole 19a.

[0086] In the fire-resistant coated beam 25 of the first modified example configured in this manner, the effective diameter of the through hole 19a is not reduced by the fire-resistant coating 21, and the application range of the fire-resistant coating 21 is clear, making application management easy. A relatively wide range, from the upper end of the web 19 downward to the upper end of the through hole 19a, can withstand a certain amount of stress during a fire, and the fire-resistant coating 21 can be reduced over a wider range at the lower flange 18. In addition, when passing a pipe (not shown) through the through hole 19a after the fireproof coating 21 is applied, the lower flange 18 can be used as a handrail, improving workability compared to JP 2016-37718 A (hereinafter referred to as the prior patent). In addition, in the prior patent, there is a possibility that the fireproof coating of the lower flange may come into contact with the fireproof coating during work and be damaged. However, with the fireproof coated beam 25 of the first modification, there is a low possibility of coming into contact with the fireproof coating 21, and the risk of damaging the fireproof coating 21 can be reduced.

[0087] A fire-resistant coated beam 25A of a second modified example shown in Fig. 27 has an H-shaped steel 16A instead of the H-shaped steel 16 in each configuration of the fire-resistant coated beam 15. The H-shaped steel 16A has a stiffener 26 in addition to each configuration of the H-shaped steel 16. The stiffener 26 is fixed above the center of the facing direction Z in the web 19 and extends along the horizontal plane. Even by configuring the fire-resistant coated beam 25A of the second modified example having the stiffener 26, the upper yield bending moment becomes larger than the lower yield bending moment, as compared to the fire-resistant coated beam 25.

[0088] The floor structure 2 of the third modified example shown in Figures 1, 28, and 29 includes a fire-resistant covered beam 30 instead of the fire-resistant covered beam 15 in each configuration of the floor structure 1. In Figure 29, the portion provided with the fire-resistant covering 31 described later is shown by hatching. Figure 1 is a cross-sectional view of the cutting line A2-A2 in Figure 29. The fire-resistant coated beam 30 has an H-shaped steel 16 and a fire-resistant coating 31. The intermediate part of the floor structure 2 in the longitudinal direction X has the cross-sectional shape shown in Fig. 1. The intermediate part of the floor structure 2 in the longitudinal direction X here means, for example, a range of 25% of the length of the floor structure 2 in the longitudinal direction X on both sides of the longitudinal direction X from the center of the floor structure 2 in the longitudinal direction X. Both ends of the floor structure 2 in the longitudinal direction X have a cross-sectional shape shown in Fig. 28. Both ends of the floor structure 2 in the longitudinal direction X refer to parts of the floor structure 2 other than the middle part in the longitudinal direction X. The fire-resistant coating 31 is arranged so as to cover the H-shaped steel 16 other than the upper surface of the upper flange 17.

[0089] For example, when both ends of the floor structure 2 in the longitudinal direction X are fixed, it is desirable to cover the negative bending region of the fire-resistant covered beam 30 (the region in which the bottom flange 18 is compressed, including both ends of the floor structure 2 in the longitudinal direction X) with a fire-resistant covering 31 as shown in Fig. 28. It is desirable to cover the other regions of the floor structure 2 with a fire-resistant covering 31 as shown in Fig. 1.

[0090] A fire-resistant coated beam 35 of a fourth modified example shown in FIG. 30 has a fire-resistant coating 36 that is thicker than the fire-resistant coating 21A in each configuration of the fire-resistant coated beam 15A. In this way, it is desirable to adjust the thickness of the fire-resistant coating 36, the coverage area, and the thickness of the floor slab 10 according to the required fire resistance performance and live load. For example, when the required fire resistance is one hour, only the upper flange 17 is covered with sprayed rock wool, and the thickness of the covering is 75 mm.

[0091] A fire-resistant coated beam 25B of a fifth modified example shown in FIG. 31 is configured such that in the fire-resistant coated beam 25 of the first modified example, the through hole 19a is disposed below the center of the web 19 in the opposing direction Z. By configuring the fire-resistant coated beam 25B of the fifth modified example, the area in which the web 19 is covered by the fire-resistant coating 21 can be secured to be wide.

[0092] A fire-resistant coated beam 40 of a sixth modified example shown in Fig. 32 has an H-shaped steel 16B instead of the H-shaped steel 16 in each configuration of the fire-resistant coated beam 15. The H-shaped steel 16B has a reinforcing member 41 in addition to each configuration of the H-shaped steel 16. A plurality of recesses 41a are formed on the underside of the reinforcing member 41. The recesses 41a are arranged at intervals from one another in the orthogonal direction Y. The reinforcing member 41 is attached to the underside of the upper flange 17 from below the upper flange 17 by welding or the like. The H-shaped steel 16B has two reinforcing members 41. The two reinforcing members 41 are arranged to sandwich the web 19. Each reinforcing member 41 is attached to at least a portion of the upper flange 17 in the longitudinal direction X.

[0093] The fire-resistant coating 21 is disposed so as to cover the two reinforcing members 41 . By configuring the fire-resistant coated beam 40 of the sixth modified example, the cross-sectional area of ​​the H-shaped steel 16B can be increased relatively easily. Furthermore, the adhesion of the fire-resistant coating 21 provided on the upper flange 17 can be improved. The number of recesses 41a formed in the reinforcing material 41 may be one. The number of reinforcing materials 41 included in the H-shaped steel 16B may be one.

[0094] A fire-resistant covered beam 40A of a seventh modified example shown in Fig. 33 has an H-shaped steel 16C instead of the H-shaped steel 16B in each configuration of the fire-resistant covered beam 40 of the sixth modified example. The H-shaped steel 16C has a reinforcing member 46 instead of the reinforcing member 41 in each configuration of the H-shaped steel 16B. The reinforcing member 46 is formed in a C-shape that is open to the outside in the orthogonal direction Y. The reinforcing member 46 is fixed to the lower surface of the upper flange 17 from below the upper flange 17. The fire-resistant covered beam 40A of the seventh modified example can also achieve the same effects as those of the fire-resistant covered beam 40 of the sixth modified example.

[0095] In the fire-resistant coated beam of the eighth modified example, in each configuration of the fire-resistant coated beam 15, the fire-resistant coating is arranged so as to cover the web 19 over the entire length in the longitudinal direction X, from the upper end of the web 19 downward to a height at which the design shear force of the web 19 can be transmitted. The height at which the design shear force of the web 19 can be transmitted downward from the upper end of the web 19 here means, for example, 0.5 times the length of the web 19 in the facing direction Z. By configuring the fire-resistant covered beam as in the eighth modified example, the design shear force transmitted to the web 19 during a fire can be reliably transmitted, and the fire-resistant covering can be reduced over a wider range in the lower flange 18. Furthermore, since the fire-resistant covering 21 covers the upper ends of the upper flange 17 and the web 19, and heat transfer from the upper flange 17 to the floor slab 10 can be expected, the temperatures of the upper ends of the upper flange 17 and the web 19 become relatively low during a fire. Therefore, the shear strength of the fire-resistant covered beam can be increased compared to, for example, the shear strength of a fire-resistant covered beam in which the upper flange is not covered with a fire-resistant covering as disclosed in the prior patent.

[0096] Although one embodiment of the present invention and a modified example thereof have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and the present invention also includes modifications, combinations, deletions, etc. of the configurations within the scope of the gist of the present invention. Furthermore, it goes without saying that the configurations shown in the embodiment and modified examples can be used in appropriate combinations. For example, in the above-described embodiment and modified examples, the fire-resistant coating is not limited to sprayed rock wool, and may be formed of a plate-like or felt-like material. [Explanation of symbols]

[0097] 1,2 floor structure 10 Floor slab 15,25,25A,25B,30,35,40 Fireproof coated beam 16,16A,16B,16C H-beam steel 17 Upper flange 18 Lower flange 19 Web 19a Through hole 21, 31, 36 Fireproof coating 41,46 Reinforcement X Longitudinal direction

Claims

1. an H-shaped steel having an upper flange, a lower flange, and a web joined to the upper flange and the lower flange, respectively; A fireproof coating arranged to cover the upper flange over the entire length of the H-shaped steel in the longitudinal direction; Equipped with The fire-resistant coating does not cover a lower portion of the web and the lower flange at least in the longitudinal intermediate portion, A fire-resistant coated beam, the top flange of which is attached to a floor slab.

2. 2. A fire-resistant coated beam as described in claim 1, wherein the fire-resistant coating is arranged so as not to cover the entire longitudinal length of the lower flange, and is arranged so as to cover the web from the upper end of the web downward to a height capable of transmitting the design shear force of the web.

3. The web is formed with a through hole, 2. A fire-resistant coated beam as described in claim 1, wherein the fire-resistant coating is arranged so as not to cover the entire longitudinal length of the lower flange, and is arranged so as to cover the web from the upper end of the web downward to the upper end of the through hole.

4. A fire-resistant coated beam as described in any one of claims 1 to 3, wherein the yield bending moment calculated based on the section modulus from the centroid to the upper flange in a cross section perpendicular to the longitudinal direction of the H-shaped steel is greater than the yield bending moment calculated based on the section modulus from the centroid to the lower flange in the cross section.

5. A fire-resistant coated beam as described in any one of claims 1 to 3, wherein a cross-sectional area of ​​the upper flange perpendicular to the longitudinal direction is larger than a cross-sectional area of ​​the lower flange perpendicular to the longitudinal direction.

6. The fire-resistant coated beam according to claim 1 , wherein the strength of the upper flange is greater than the strength of the lower flange.

7. The fire-resistant coated beam according to claim 1 , wherein the H-shaped steel has a reinforcement attached to the underside of the upper flange.

8. A fire-resistant coated beam according to any one of claims 1 to 3; The floor slab; A floor structure comprising:

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