Refractory structures

Abstract

To provide a fire-resistant structure that can reduce floor deflection during a fire. [Solution] The fire-resistant structure 1 comprises a plurality of fire-resistant beams 10 having predetermined fire resistance, a plurality of fire-resistant columns 30 having predetermined fire resistance, joined to the plurality of fire-resistant beams, and forming an annular fire-resistant annular body 32 with a part of itself and the plurality of fire-resistant beams as a whole, a fire-resistant beam 35 that is covered with fire-resistant coating 41 but does not have predetermined fire resistance, and both ends are joined to the plurality of fire-resistant beams, and a floor portion 50 in which a tensile force transmission member is provided in the concrete, its outer edge is supported by the fire-resistant annular body and is also supported by the fire-resistant beam, and when the directions that intersect each other within the upper surface 50a of the floor portion are defined as the first intersecting direction X and the second intersecting direction Y, the tensile force transmission member transmits the tensile force between the ends of the floor portion in the first intersecting direction and the tensile force between the ends of the floor portion in the second intersecting direction, respectively.

Description

Technical Field

[0001] The present invention relates to a fire-resistant structure.

Background Art

[0002] Conventionally, in a fire-resistant steel-frame structure that requires fire resistance, a method of reducing heat input during a fire and preventing collapse by applying a fire-resistant coating to columns and beams is common. In Patent Document 1, the slab (floor part) of a fire-resistant structure is supported by a large beam (fire-resistant performance beam) spanned between columns and steel-frame small beams spanned between large beams. The large beam is made of reinforced concrete, and the four sides of the slab are rigidly joined to the large beam.

[0003] On the other hand, in Patent Document 1, the steel-frame small beam consists of an H-shaped steel beam that is not entirely fire-resistant coated. The steel-frame small beam is integrated with the slab by a plurality of studs welded to the upper flange of the steel-frame small beam. The thickness of the slab is designed considering only the long-term stress generated in the slab.

[0004] Here, in Patent Document 1, during a fire in a fire-resistant structure, the load-bearing capacity of the steel-frame small beam may decrease due to heat, or the steel-frame small beam may melt. However, since the slab is designed to have a thickness that can withstand long-term stress even without the steel-frame small beam, the falling off of the slab is suppressed by the strength of the slab itself.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] During a fire, due to reasons such as a decrease in the rigidity of the slab, the central part of the slab in plan view deflects so as to bulge downward. However, in the fire-resistant structure described in Patent Document 1, there is room for improvement regarding the deflection of the floor during a fire.

[0007] This invention has been made in view of the above problems, and aims to provide a fire-resistant structure that can reduce the deflection of the floor during a fire. [Means for solving the problem]

[0008] To solve the aforementioned problems, this invention proposes the following means. (1) Embodiment 1 of the present invention is a fire-resistant structure comprising: a plurality of fire-resistant beams having predetermined fire resistance; a plurality of fire-resistant columns having the predetermined fire resistance and joined to the plurality of fire-resistant beams, forming an annular fire-resistant annular body in part with itself and with the plurality of fire-resistant beams as a whole; fire-resistant beams that are covered with fire-resistant coating but do not have the predetermined fire resistance and whose ends are joined to the plurality of fire-resistant beams, respectively; and a floor portion in which a tensile force transmission member is provided in concrete, and whose outer edge is supported by the fire-resistant annular body and is also supported by the fire-resistant beams, wherein when the directions in which the floor portion intersects each other within the upper surface of the floor portion are defined as the first intersecting direction and the second intersecting direction, the tensile force transmission member transmits the tensile force between the ends of the floor portion in the first intersecting direction and the tensile force between the ends of the floor portion in the second intersecting direction, respectively.

[0009] In this invention, under normal circumstances when no fire is occurring, the floor is supported by multiple fire-resistant columns via multiple fire-resistant beams and fire-reducing beams. On the other hand, during a fire, gravity and other forces acting on the floor cause the central part of the floor to flex downwards in a plan view. However, due to the membrane effect generated by the tensile force transmission members provided in the floor transmitting tensile forces between the ends in a first intersecting direction and tensile forces between the ends in a second intersecting direction acting on the floor, the central part of the floor is supported while the outer edge of the floor is supported by the fire-resistant annular body. Although the fire-resistant beam does not possess the specified fire resistance, it is covered with a fire-resistant coating, so even in the event of a fire, the fire-resistant beam can suppress the deflection of the floor to a certain extent. Therefore, in addition to the membrane effect acted by the tensile force transmission member, the above-mentioned effect of the fire-resistant beam can reduce the deflection of the floor in the event of a fire.

[0010] (2) In aspect 2 of the present invention, the fire-resistant structure described in (1) is also the fire-resistant structure described in (1), wherein the thickness of the fire-resistant coating of the fire-reducing beam is thinner than the thicker of the thickness specified in the "Comparison Table of New and Old Sprayed Rock Wool Covered Fire-Resistant Structures" and the thickness specified in the "Explanation of Fire Resistance Verification Method and Calculation Examples and Explanations Thereof". Here, the thicker of the two thicknesses specified in the "Comparison Table of Old and New Fire-Resistant Structures with Sprayed Rock Wool Coating" and the "Explanation of Fire Resistance Performance Verification Method and Calculation Examples and Explanations," the greater of the two, has a predetermined fire resistance performance. In contrast, in this invention, the thickness of the fire-resistant coating of the fire-reducing beam is thinner than the thickness specified as the greater of the two. Even in this case, the deflection of the floor can be reduced due to the membrane effect.

[0011] (3) Embodiment 3 of the present invention may be a fire-resistant structure as described in (1) or (2), wherein a plurality of fire-reducing beams are provided, and the thickness of the fire-resistant coating of the plurality of fire-reducing beams is substantially equal to each other. In this invention, for example, when the total amount of fire-resistant coating is constant, the deflection of the floor can be reduced when the time elapsed since the fire started is relatively short, compared to when the thickness of the fire-resistant coating varies. [Effects of the Invention]

[0012] The fire-resistant structure of the present invention can reduce the deflection of the floor during a fire. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic perspective view showing a fire-resistant structure according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along the cutting line A1-A1 in Figure 1. [Figure 3] It is a cross-sectional view of the cutting line A2 - A2 in FIG. 1. [Figure 4] It is a perspective view of the analysis model of the refractory structure 1A of the comparative example. [Figure 5] It is a diagram for explaining the analysis result of the deflection of the same refractory structure 1A with respect to time. [Figure 6] It is a perspective view of the analysis model of the refractory structure 1 of the example. [Figure 7] It is a diagram for explaining the analysis result of the deflection of the same refractory structure 1 with respect to time. [Figure 8] It is a perspective view of the analysis model of the refractory structure 1B of the comparative example. [Figure 9] It is a diagram for explaining the analysis result of the deflection of the same refractory structure 1B with respect to time. [Figure 10] It is a perspective view of the analysis model of the refractory structure 1 of the example. [Figure 11] It is a diagram for explaining the analysis result of the deflection of the same refractory structure 1 with respect to time. [Figure 12] It is a perspective view of the analysis model of the refractory structure 2 of the comparative example. [Figure 13] It is a diagram for explaining the analysis result of the deflection of the same refractory structure 2 with respect to time. [Figure 14] It is a perspective view of the analysis model of the refractory structure 2A of the example. <000​​​​​​​​​​​​​​​​​ Hereinafter, one embodiment of the fire-resistant structure according to the present invention will be described with reference to Figures 1 to 18.

[0015] [1. Composition of fire-resistant structures] As shown in Figures 1 to 3, the fire-resistant structure 1 of this embodiment comprises a plurality of fire-resistant beams 10, a plurality of fire-resistant columns 30, a plurality (two in this embodiment) fire-reducing beams 35, and a floor section 50. In Figure 1, the floor section 50 is shown by a dashed line, and the plurality of fire-resistant beams 10 and fire-resistant columns 30 having predetermined fire-resistant properties, which will be described later, are shown with hatching. Figure 2 schematically shows fire-resistant structure 1.

[0016] In the following, in order to define the direction, we will first describe the outline of the floor section 50 using Figure 1. The floor portion 50 is flat. For example, the floor portion 50 has a rectangular shape when viewed in the thickness direction Z. The floor portion 50 is arranged so that the thickness direction Z is aligned with the vertical direction. Here, "A aligns with B (extends along it)" means that the angle between A and B is 30° or less. It is more preferable that this angle is 15° or less.

[0017] Here, the directions that are perpendicular to each other within the upper surface 50a of the floor portion 50 are defined as the first intersecting direction X and the second intersecting direction Y. The first intersecting direction X is, for example, the longitudinal direction of the floor portion 50 when viewed in the thickness direction Z. The second intersecting direction Y is, for example, the short direction of the floor portion 50 when viewed in the thickness direction Z. One side of the first intersecting direction X is called the first side X1 (hereinafter simply referred to as the first side X1). The side of the first intersecting direction X opposite to the first side X1 is called the second side X2 (hereinafter simply referred to as the second side X2). The first intersecting direction X and the second intersecting direction Y are not particularly limited as long as they intersect each other within the upper surface 50a of the floor portion 50.

[0018] The fire-resistant beam 10 is a so-called main beam that spans between multiple fire-resistant columns 30. As shown in Figure 1, the multiple fire-resistant beams 10 consist of two first fire-resistant beams 11 and two second fire-resistant beams 21. The two first fire-resistant beams 11 each extend along the first intersecting direction X. The two first fire-resistant beams 11 are spaced apart from each other in the second intersecting direction Y. The two second fire-resistant beams 21 each extend along the second intersecting direction Y. The two second fire-resistant beams 21 are spaced apart from each other in the first intersecting direction X. A gap S1 is formed between the first fire-resistant beam 11 and the second fire-resistant beam 21, in which a fire-resistant column 30 is positioned.

[0019] As shown in Figure 2, for example, the second fire-resistant beam 21 is formed of an H-shaped steel beam 22 that is coated with a fire-resistant coating 27. The H-shaped steel beam 22 may be rolled H-shaped steel or welded H-shaped steel. The fire-resistant coating 27 uses insulating materials such as rock wool or glass wool. In this case, for example, the fire-resistant coating 27 is formed on the H-shaped steel 22 by a spray painting method.

[0020] The H-shaped steel beam 22 has two flanges 23 and 24, and webs 25 joined to the flanges 23 and 24, respectively. Flange 23 is positioned above flange 24 (closer to the floor 50). In the H-shaped steel beam 22 of the second fire-resistant beam 21, fire-resistant coating 27 is applied along the entire length of the H-shaped steel beam 22, except for the upper surface of the flange 23.

[0021] For example, the thickness of the fire-resistant coating 27, such as rock wool, on the second fire-resistant beam 21 is set as follows, in accordance with the provisions of the "Comparison Table of Old and New Fire-Resistant Structures with Sprayed Rock Wool Coating". The comparison table of old and new sprayed rock wool coated fire-resistant structures is based on individual certifications by member companies of the Rock Wool Industry Association and is available at the following URL. URL: https: / / www.rwa.gr.jp / download / data / taikahikaku.pdf In other words, if the second fire-resistant beam 21 is required to have 1 hour fire resistance (fire resistance duration of 1 hour; 1H), the thickness of the fire-resistant coating 27 shall be 25 mm. Similarly, if the second fire-resistant beam 21 is required to have 2 hours fire resistance, the thickness of the fire-resistant coating 27 shall be 45 mm. If the second fire-resistant beam 21 is required to have 3 hours fire resistance, the thickness of the fire-resistant coating 27 shall be 60 mm.

[0022] Furthermore, for example, the thickness of the fire-resistant coating 27, such as rock wool, in the second fire-resistant beam 21 is set as follows, in accordance with the provisions of "Explanation and Calculation Examples of Fire Resistance Verification Methods and Their Explanations," edited by the Building Guidance Division, Housing Bureau, Ministry of Land, Infrastructure, Transport and Tourism, the Japan Building Officials Conference, and the Japan Building Center Foundation, March 2001, pp. 95-109 (hereinafter referred to as "Explanation and Calculation Examples of Fire Resistance Verification Methods"). For example, if the cross-sectional shape of the second fire-resistant beam 21 is H400x200x8x13 and the limit member temperature is 550 degrees, then the thickness of the fire-resistant coating 27 should be approximately 21 mm if 1 hour fire resistance is required. Similarly, if 2 hours fire resistance is required for the second fire-resistant beam 21, the thickness of the fire-resistant coating 27 should be approximately 40 mm.

[0023] The comparison table of old and new sprayed rock wool coated fire-resistant structures, as well as the explanation of the fire resistance performance verification method and calculation examples, all adhere to the standards required by the Building Standards Act. In the following, the fire resistance performance based on the thicker of the two thicknesses specified in the comparison table of old and new versions of the sprayed rock wool fire-resistant structure in these construction quality control guidelines, and the thickness specified in the explanation and calculation examples of the fire resistance performance verification method, will be referred to as the coating fire resistance performance (specified fire resistance performance). The two second fire-resistant beams 21 each have coating fire resistance performance.

[0024] Furthermore, the specified fire resistance performance may be based on the thinner of the following two thicknesses: the thickness specified in the Comparison Table of Old and New Designs of Sprayed Rock Wool Fire-Resistant Structures in the Construction Quality Management Guidelines, and the thickness specified in the Explanation and Calculation Examples of Fire Resistance Verification Methods. The specified fire resistance performance is not limited to the fire resistance performance of the coating, but can also include, for example, fire resistance performance based on the evaluation of the inherent fire resistance performance by a load heating test, or fire resistance performance based on the evaluation of the inherent fire resistance performance by a fire resistance performance verification method.

[0025] The first fire-resistant beam 11 is constructed in the same way as the second fire-resistant beam 21, except for its length. That is, the first fire-resistant beam 11 is made of H-shaped steel with a fire-resistant coating 17 (see Figure 3). Each of the two first fire-resistant beams 11 has its own fire-resistant coating. Furthermore, the fire-resistant coating may be formed by a molded plate method or a wrapping method. The fire-resistant beam may be made of reinforced concrete (RC), steel-reinforced concrete (SRC), fire-treated wood, or fire-treated wood and steel.

[0026] As shown in Figure 1, for example, the fire-resistant column 30 is formed from an H-shaped steel beam coated with a fire-resistant coating 31. Multiple fire-resistant columns 30 have fire-resistant properties due to their coating. Multiple fire-resistant columns 30 extend along the thickness direction Z. The ends of multiple fire-resistant beams 10 are rigidly joined to the upper ends (partially) of multiple fire-resistant columns 30. The upper ends of the multiple fire-resistant columns 30 and the entirety of the multiple fire-resistant beams 10 form a rectangular (ring-shaped) fire-resistant annular body 32. That is, the region R1 within the fire-resistant annular body 32 is enclosed by the fire-resistant annular body 32.

[0027] Multiple fire-resistant beams 10 may be joined to the intermediate or lower ends of multiple fire-resistant columns 30 in the thickness direction Z. Fire-resistant columns may be formed from any of the following: fire-coated square steel pipes, fire-coated circular steel pipes, concrete-filled steel tubes (CFTs), reinforced concrete, steel-reinforced concrete, fire-treated wood, or fire-treated wood and steel.

[0028] Multiple fire-reducing beams 35 are so-called secondary beams that span between multiple fire-resistant beams 10. As shown in Figures 2 and 3, in this embodiment, the fire-reducing beams 35 are formed from H-shaped steel 36 with a fire-resistant coating 41. However, the fire-reducing beams 35 do not have fire-resistant properties due to the coating. The thickness of the fire-resistant coating 41 on the fire-reducing beam 35 is thinner than the thickness specified in the construction quality control guidelines. The thickness specified in the construction quality control guidelines is 25 mm when a fire-resistant structure 1 (fire-reducing beam) 35 is required to withstand fire for 1 hour, 45 mm when a fire-resistant structure 1 is required to withstand fire for 2 hours, and 60 mm when a fire-resistant structure 1 is required to withstand fire for 3 hours. In other words, the thickness of the fire-resistant coating 41 of the fire-reducing beam 35 is thinner than these thicknesses determined according to the fire resistance time, but thicker than 0 mm.

[0029] Specifically, for example, the thickness of the fire-resistant coating 41 is half the thickness corresponding to the fire resistance time required by the construction quality control guidelines. The thickness of the fire-resistant coating 41 may also be one-third or one-tenth of the thickness corresponding to the fire resistance time required by the construction quality control guidelines.

[0030] The H-shaped steel beam 36 has two flanges 37 and 38, and webs 39 joined to the flanges 37 and 38, respectively. Flange 37 is positioned above flange 38 (closer to the floor portion 50). In the H-shaped steel beam 36 of the fire-reducing performance beam 35, fire-resistant coating 41 is applied along the entire length of the H-shaped steel beam 36, except for the upper surface of the flange 37. As shown in Figure 3, it is preferable that a headed stud (shear force transmission member) 40 is fixed to the flange 37. The headed stud 40 protrudes upward from the flange 37.

[0031] As shown in Figure 1, the multiple fire-reducing beams 35 each extend along the second intersecting direction Y and are arranged at intervals from one another in the first intersecting direction X. The multiple fire-reducing beams 35 are arranged within the fire-resistant annular body 32, i.e., within region R1. The ends of the multiple fire-reducing beams 35 are each joined to the multiple fire-resistant beams 10. Specifically, although not shown in the diagram, for example, the ends of the multiple fire-reducing beams 35 are fixed to gusset plates provided on the web of the first fire-resistant beam 11 by bolts or the like. The ends of the multiple fire-reducing beams 35 are joined to the first fire-resistant beam 11 by so-called pin joints. In other words, the ends of the multiple fire-reducing beams 35 and the first fire-resistant beam 11 are pin-jointed via gusset plates.

[0032] It is preferable that the thickness of the fire-resistant coating 41 of multiple fire-reducing beams 35 be approximately equal to each other. Here, "approximately equal thickness" means, for example, that the ratio of (thickness of one beam / thickness of the other beam) is between 0.7 and 1.3. More preferably, this ratio is between 0.8 and 1.2. The fire-resistant structure 1 is equipped with only a number of fire-reducing beams 35 as secondary beams.

[0033] As shown in Figure 3, in this embodiment, the floor portion 50 is formed from a composite slab. The floor section 50 includes a deck plate 51, concrete 52, and a plurality of reinforcing bars (tensile force transmission members) 53. For example, the deck plate 51, although not shown in detail, is formed by bending a steel plate. The deck plate 51 is positioned above multiple fire-resistant beams 10 and multiple fire-reducing beams 35. The concrete 52 has the same shape as the floor portion 50 when viewed in the thickness direction Z. The concrete 52 is placed on the deck plate 51. Multiple reinforcing bars 53 are provided in the concrete 52. That is, in the floor section 50, multiple reinforcing bars 53 are provided in the concrete 52.

[0034] The configuration of the multiple reinforcing bars 53 is not particularly limited, as long as it includes a first reinforcing bar extending along a first intersecting direction X and a second reinforcing bar extending along a second intersecting direction Y. As shown in Figure 3, in this embodiment, the multiple reinforcing bars 53 include a plurality of first reinforcing bars 53a and a plurality of second reinforcing bars 53b. Note that in Figure 3, only one of the plurality of first reinforcing bars 53a is shown. For example, multiple first reinforcing bars 53a are arranged along the entire length of the concrete 52 in the first intersecting direction X. Multiple first reinforcing bars 53a are arranged spaced apart from each other in the second intersecting direction Y. Multiple second reinforcing bars 53b are arranged along the entire length of the concrete 52 in the second intersecting direction Y. Multiple second reinforcing bars 53b are arranged at intervals from each other in the first intersecting direction X.

[0035] Multiple first reinforcing bars 53a transmit tensile forces between the ends of the floor section 50 in the first intersecting direction X. Multiple second reinforcing bars 53b transmit tensile forces between the ends of the floor section 50 in the second intersecting direction Y. For example, multiple first reinforcing bars 53a transmit the tensile force in the first intersecting direction X generated at the end of the first side X1 of the floor section 50 to the end of the second side X2 of the floor section 50, and transmit the tensile force generated at the end of the second side X2 of the floor section 50 to the end of the first side X1 of the floor section 50, both under normal conditions when no fire is occurring and during a fire. This tensile force is generated by the weight of the floor section 50 and by equipment placed on the floor section 50. The transmission of tensile force between the ends of the floor section 50 in the second intersecting direction Y is the same as the transmission of tensile force between the ends of the floor section 50 in the first intersecting direction.

[0036] As shown in Figure 1, the outer edge of the floor section 50 is supported from below the entire circumference by a fire-resistant annular body 32. The floor section 50 is supported from below by a plurality of fire-resistant beams 35. As shown in Figure 3, the headed studs 40 of the multiple fire-resistant beams 35 are embedded in the concrete 52 of the floor 50.

[0037] Alternatively, the floor section 50 may not have multiple reinforcing bars 53, and the deck plate 51 may function as a tensile force transmission member. The number of fire-reducing beams 35 provided by fire-resistant structure 1 is not limited; it may be one or three or more. The floor may be constructed from a reinforced concrete slab.

[0038] The fire-resistant structure 1 is used, for example, in a building 6 (see Figure 1) having multiple floors (story levels).

[0039] [2. Examination of the fire resistance performance of fire-resistant structures] Next, we will explain the results of evaluating the fire resistance performance of the fire-resistant structures of the examples and comparative examples based on the deflection of the floor section 50. Finite element analysis was used to examine the fire resistance performance of the fire-resistant structure. Furthermore, in the following fire-resistant structures, the configuration of the multiple fire-resistant beams 10 and multiple fire-resistant columns 30 is not limited as long as they have covering fire-resistant properties. The configuration of the floor section 50 is not limited as long as tensile force transmission members are provided in the concrete.

[0040] The following explanation assumes that a fire-resistant structure is required to have a fire resistance time of 2 hours (with a fire-resistant coating thickness of 45 mm) based on the construction quality control guidelines. It is assumed that rock wool (RW) is used for the fire-resistant coating. The comparative example fire-resistant structure 1A shown in Figure 4 has one fire-reducing beam 35 and one first fire-reducing beam 35A in each configuration of fire-resistant structure 1, instead of two fire-reducing beams 35. Below, a schematic analysis model of the fire-resistant structure is shown. The fireproofing thickness of the fire-resistant beam 35 was set to 25 mm (RW25 mm), while the fireproofing thickness of the first fire-resistant beam 35A was set to 0 mm (no fireproofing). Furthermore, the thickness of the fire-resistant coating on multiple fire-resistant beams 10 was set to 45 mm (RW45 mm). For fire-resistant structure 1A, the undersides of multiple fire-resistant beams 10, floor section 50, beams 35, and 35A were heated based on the "standard heating time-temperature curve" specified in ISO 834.

[0041] In fire-resistant structure 1A, the magnitude of downward deflection of the floor section 50 at positions P1 and P2 shown in Figure 4 was calculated. Position P1 is the center of the floor section 50 in plan view. Position P2 is the part of the floor section 50 corresponding to the center of the second intersecting direction Y of the first fire-reducing performance beam 35A.

[0042] The calculated results are shown in Figure 5. In Figure 5, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P1 and P2. The deflection at position P1 is represented by line L1, and the deflection at position P2 is represented by line L2. At both positions P1 and P2, the deflection increases as time increases (time passes). However, up to about 150 minutes, the deflection at position P2 is greater than the deflection at position P1, but beyond about 150 minutes, the deflection at position P1 becomes greater.

[0043] In the fire-resistant structure 1 of the embodiment shown in Figure 6, the thickness of the fire-resistant coating on the two fire-reducing beams 35 was set to 12 mm (RW12 mm). In fire-resistant structure 1, the magnitude of downward deflection of the floor section 50 at positions P3 and P4 shown in Figure 6 was calculated. Position P3 is the center of the floor section 50 in a plan view. Position P4 is the part of the floor section 50 that corresponds to the center of the second intersecting direction Y of the fire-reducing performance beam 35.

[0044] The calculated results are shown in Figure 7. In Figure 7, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P3 and P4. The deflection at position P3 is represented by line L3, and the deflection at position P4 is represented by line L4. At both positions P3 and P4, the deflection increases as time increases. Regardless of time, the deflection at position P3 is greater than the deflection at position P4.

[0045] The comparative example fire-resistant structure 1B shown in Figure 8 has a first fire-reducing beam 35A and a fire-resistant beam 35B in each configuration of fire-resistant structure 1, instead of the two fire-reducing beams 35. The thickness of the fire-resistant coating of the fire-resistant beam 35B is 45 mm (RW45 mm). In fire-resistant structure 1B, the magnitude of downward deflection of the floor section 50 at positions P5 and P6 shown in Figure 8 was calculated. Position P5 is the center of the floor section 50 in plan view. Position P6 is the part of the floor section 50 corresponding to the center of the second intersecting direction Y of the first fire-reducing performance beam 35A.

[0046] The calculated results are shown in Figure 9. In Figure 9, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P5 and P6. The deflection at position P5 is represented by line L5, and the deflection at position P6 is represented by line L6. At both positions P5 and P6, the deflection increases as time increases. Regardless of time, the deflection at position P6 is greater than the deflection at position P5.

[0047] In the fire-resistant structure 1 of the embodiment shown in Figure 10, the thickness of the fire-resistant coating on the two fire-reducing beams 35 was set to 25 mm (RW25 mm). In fire-resistant structure 1, the magnitude of downward deflection of the floor section 50 at positions P7 and P8 shown in Figure 10 was calculated. Position P7 is the center of the floor section 50 in plan view. Position P8 is the part of the floor section 50 corresponding to the center of the second intersecting direction Y of the fire-reducing performance beam 35.

[0048] The calculated results are shown in Figure 11. In Figure 11, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P7 and P8. The deflection at position P7 is represented by line L7, and the deflection at position P8 is represented by line L8. At both positions P7 and P8, the deflection increases as time increases. Regardless of time, the deflection at position P7 is greater than the deflection at position P8.

[0049] The comparative example fire-resistant structure 2 shown in Figure 12 has two first fire-reducing beams 35A and a fire-resistant beam 35B in each configuration of the fire-resistant structure 1, instead of the two fire-reducing beams 35. The first fire-reducing beam 35A, the fire-resistant beam 35B, and the first fire-reducing beam 35A are arranged in this order from the first side X1 to the second side X2. In fire-resistant structure 2, the magnitude of downward deflection of the floor section 50 at positions P11 and P12 shown in Figure 12 was calculated. Position P11 is the center of the floor section 50 in plan view. Position P12 is the part of the floor section 50 corresponding to the center of the second intersecting direction Y of the first fire-reducing performance beam 35A.

[0050] The calculated results are shown in Figure 13. In Figure 13, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P11 and P12. The deflection at position P11 is represented by line L11, and the deflection at position P12 is represented by line L12. At both positions P11 and P12, the deflection increases as time increases. However, up to approximately 115 minutes, the deflection at position P12 is greater than the deflection at position P11, but beyond approximately 115 minutes, the deflection at position P11 becomes greater.

[0051] In the embodiment shown in Figure 14, the fire-resistant structure 2A has three fire-reducing beams 35 in each configuration of the fire-resistant structure 1, instead of two fire-reducing beams 35. In fire-resistant structure 2A, the magnitude of downward deflection of the floor section 50 at positions P13 and P14 shown in Figure 14 was calculated. Position P13 is the center of the floor section 50 in plan view. Position P14 is the part of the floor section 50 that corresponds to the center of the second intersecting direction Y of the fire-reducing performance beam 35 located on the first side X1.

[0052] The calculated results are shown in Figure 15. In Figure 15, the horizontal axis represents the time (minutes) from the start of heating, and the vertical axis represents the deflection (mm) at positions P13 and P14. The deflection at position P13 is represented by line L13, and the deflection at position P14 is represented by line L14. At both positions P13 and P14, the deflection increases as time increases. Regardless of time, the deflection at position P13 is greater than the deflection at position P14.

[0053] Figure 16 shows the results at positions P1, P2, P3, and P4. Up to about 30 minutes, the deflection at position P3 of the fire-resistant structure 1 in the example is smaller than the deflection at position P1 of the fire-resistant structure 1A in the comparative example. Regardless of the time, the deflection at position P4 of the fire-resistant structure 1 in the example is smaller than the deflection at position P2 of the fire-resistant structure 1A in the comparative example. In other words, during the initial heating phase, up to about 30 minutes, at both positions P3 and P4, dividing the fireproof coating thickness into 12mm and 12mm portions reduces deflection more effectively than distributing the fireproof coating thickness between 0mm and 25mm portions.

[0054] Furthermore, in the initial stages of heating, the larger of the deflections at positions P1 and P2 of the fire-resistant structure 1A (maximum deflection) is the deflection at position P2, which is represented by line L2. In the initial stages of heating, the larger of the deflections at positions P3 and P4 of the fire-resistant structure 1 is the deflection at position P3, which is represented by line L3. In the initial stages of heating, the maximum deflection of the fire-resistant structure 1 can be reduced to less than the maximum deflection of the fire-resistant structure 1A.

[0055] Figure 17 shows the results at positions P5, P6, P7, and P8. Up to about 50 minutes, the deflection at position P7 of the fire-resistant structure 1 in the example is smaller than the deflection at position P5 of the fire-resistant structure 1B in the comparative example. Regardless of the time, the deflection at position P8 of the fire-resistant structure 1 in the example is smaller than the deflection at position P6 of the fire-resistant structure 1B in the comparative example. In other words, during the initial heating phase up to about 50 minutes, at both positions P7 and P8, the deflection is reduced more when the thickness of the fire-resistant coating on the joists is divided into 25mm and 25mm than when the thickness of the fire-resistant coating on the joists is unevenly distributed to 0mm and 45mm.

[0056] Furthermore, in the initial stages of heating, the larger of the deflections at positions P5 and P6 of fire-resistant structure 1B is the deflection at position P6, which is represented by line L6. In the initial stages of heating, the larger of the deflections at positions P7 and P8 of fire-resistant structure 1 is the deflection at position P7, which is represented by line L7. In the initial stages of heating, the maximum deflection of fire-resistant structure 1 can be reduced to less than the maximum deflection of fire-resistant structure 1B.

[0057] Figure 18 shows the results at positions P11, P12, P13, and P14. Up to about 20 minutes, the deflection at position P13 of the fire-resistant structure 2A in the example is smaller than the deflection at position P11 of the fire-resistant structure 2 in the comparative example. Up to about 90 minutes, the deflection at position P14 of the fire-resistant structure 2A in the example is smaller than the deflection at position P12 of the fire-resistant structure 2 in the comparative example. In other words, during the initial heating phase up to about 20 minutes, at both positions P13 and P14, the deflection is reduced more when the thickness of the fire-resistant coating on the beams is divided into 12mm, 12mm, and 12mm than when the thickness of the fire-resistant coating on the beams is unevenly distributed to 0mm, 45mm, and 0mm.

[0058] Furthermore, in the initial stages of heating, the larger of the deflections at positions P11 and P12 of the fire-resistant structure 2 is the deflection at position P12, which is represented by line L12. In the initial stages of heating, the larger of the deflections at positions P13 and P14 of the fire-resistant structure 2A is the deflection at position P13, which is represented by line L13. In the initial stages of heating, the maximum deflection of the fire-resistant structure 2 can be reduced to less than the maximum deflection of the fire-resistant structure 2A.

[0059] Furthermore, these results suggest that, in fire-resistant structure 1, when the total amount of fire-resistant coating on the joists is constant, having approximately equal thicknesses of fire-resistant coating on the joists reduces floor deflection when the time elapsed since the start of a fire is shorter, compared to having different thicknesses of fire-resistant coating on the joists.

[0060] [3. Effects of this embodiment] As described above, in the fire-resistant structure 1 of this embodiment, under normal circumstances when no fire is occurring, the floor 50 is supported by multiple fire-resistant columns 30 via multiple fire-resistant beams 10 and fire-reducing beams 35. On the other hand, during a fire, gravity and other forces acting on the floor 50 cause the central part of the floor 50 to flex downwards in a plan view. However, due to the membrane effect generated by the transmission of tensile forces between the ends in the first intersecting direction X and the tensile forces between the ends in the second intersecting direction Y acting on the floor 50 by the multiple reinforcing bars 53 provided in the floor 50, the central part of the floor 50 is supported while the outer edge of the floor 50 is supported by the fire-resistant annular body 32. Although the fire-resistant beam 35 does not possess the specified fire resistance, it is covered with a fire-resistant coating 41, so even in the event of a fire, the deflection of the floor 50 can be suppressed to a certain extent by the fire-resistant beam 35. Therefore, in addition to the membrane effect acted by the multiple reinforcing bars 53, the deflection of the floor 50 in the event of a fire can be reduced by the above-mentioned effect of the fire-resistant beam 35.

[0061] In Japan, a shortage of fireproofing workers is becoming apparent, and by appropriately evaluating the actual behavior of steel structural members subjected to heating by fire, it is hoped that new fireproof structures that reduce the amount of fireproofing required will be put into practical use. As a result of diligent study, the inventors considered using fire-reducing beams 35 in each component of the fire-resistant structure described in Patent Document 1, instead of steel beams that are not entirely fire-resistant coated. Furthermore, according to the "Guidelines for Fire-Resistant Design of Steel Structures" compiled by the Architectural Institute of Japan and published by Maruzen Publishing Co., Ltd., the required fire resistance time (fire duration) for the layer immediately below the floor differs depending on its intended use. For example, if a certain layer is used as a hotel where relatively few flammable materials are considered to be present, the fire resistance time for that layer is 60 minutes. On the other hand, if that layer is used as a commercial facility where relatively many flammable materials are considered to be present, the fire resistance time for that layer is 120 minutes. Thus, the required fire resistance time for the layer directly above the floor varies depending on its intended use.

[0062] The inventors have found that the deflection of the floor section 50 during a fire can be reduced even if the fire-resistant beam 35 does not have fire-resistant coating properties, due to the membrane effect generated by the floor section 50, which is constructed by providing multiple reinforcing bars 53 in concrete 52. For example, even if the use of the layer immediately above the floor section 50 supported by the fire-reducing beam 35 changes, and the required fire resistance time for that layer increases, the deflection of the floor section 50 can be reduced due to the membrane effect.

[0063] Even if the steel beams are made of H-shaped steel beams that have not been treated with fire-resistant coating, as in the fire-resistant structure described in Patent Document 1, it is still necessary to treat the H-shaped steel beams with rust-preventive paint or similar measures. On the other hand, if the fire-reducing beam 35 is treated with fire-resistant coating 41, it is not necessary to treat the H-shaped steel beam 36 with rust-preventive coating. Therefore, the cost of rust prevention treatment for the fire-resistant beam 35 can be eliminated.

[0064] Here, the thickness specified in the construction quality control guidelines has fire-resistant coating performance. In contrast, in this invention, the thickness of the fire-resistant coating 41 of the fire-resistant beam 35 is thinner than the thickness specified in the aforementioned construction quality control guidelines. Even in this case, the deflection of the floor section 50 can be reduced due to the membrane effect. The thickness of the fire-resistant coating 41 of multiple fire-reducing beams 35 may be approximately equal to each other. In this case, for example, when the total amount of fire-resistant coating is constant, the deflection of the floor 50 can be reduced when the time elapsed since the fire started is relatively short, compared to when the thickness of the fire-resistant coating 41 differs from each other.

[0065] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and modifications, combinations, deletions, etc., of the configuration are also included without departing from the spirit of the present invention. [Explanation of Symbols]

[0066] 1 Fireproof structures 10 Fire resistance beam 30 Fire resistance performance pillar 32 Fire-resistant ring body 35 Reduced fire resistance beam 41 Fire-resistant coating 50 Floor 52 Concrete 53 Reinforcing bars (tensile force transmission members) X 1st cross direction Y Second Intersection Direction

Claims

1. Multiple fire-resistant beams having a predetermined fire resistance performance, Multiple fire-resistant columns having the predetermined fire-resistant performance, joined to the multiple fire-resistant beams, and constituting an annular fire-resistant ring body with a part of themselves and the entirety of the multiple fire-resistant beams, A fire-resistant beam is provided with a fire-resistant coating but does not have the predetermined fire resistance performance, and both ends are joined to the plurality of fire-resistant beams, A floor section is provided in concrete, with a tensile force transmission member, whose outer periphery is supported by the fire-resistant annular body, and which is also supported by the fire-reducing beam. Equipped with, When the directions that intersect each other within the upper surface of the floor portion are defined as the first intersecting direction and the second intersecting direction, The tensile force transmission member is a fire-resistant structure that transmits the tensile force between the ends of the floor portion in the first intersecting direction and the tensile force between the ends of the floor portion in the second intersecting direction, respectively.

2. The fire-resistant structure according to claim 1, wherein the thickness of the fire-resistant coating of the fire-reducing beam is thinner than the thicker of the thickness specified in the "Comparison Table of New and Old Sprayed Rock Wool Coated Fire-Resistant Structures" and the thickness specified in the "Explanation of Fire Resistance Verification Methods and Calculation Examples and Explanations Thereof".

3. The facility is equipped with multiple fire-resistant beams, The fire-resistant structure according to claim 1 or 2, wherein the thickness of the fire-resistant coating of the plurality of fire-reducing beams is substantially equal to each other.

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