JP7650210B2 - Fire-resistant design method for floor slabs - Google Patents

Description

The present invention relates to a method for fire-resistant design of floor slabs.

The following Patent Document 1 discloses a design method for a fire-resistant structure that includes a floor section partitioned into a polygonal shape in a slab including a tensile force transmission member, a fire-resistant coated beam that supports the periphery of the floor section from below, and an extension beam with a fire-resistant coating that is connected to at least one corner of the floor section. In this design method for a fire-resistant structure, the maximum value of the deflection of the floor section when the fire-resistant structure is heated under specified conditions is calculated, and it is determined whether the maximum value of the deflection is less than a threshold value. The threshold value is determined by the formula (L + l) / 30, where L is the length of the first span and l is the length of the second span that is along the plane of the floor section and intersects the first span.

Patent No. 6741185

For example, in the fire resistance design of floor slabs, floor slabs are sometimes designed taking into account the so-called membrane effect, whereby the floor slab deforms significantly during a fire and the reinforcing bars in the slab are placed in a fully tensile state, exerting a strength greater than the bending strength. When the membrane effect is taken into account, the greater the deformation of the floor slab, the more effectively the tensile force in the reinforcing bars can support vertical loads, and so the greater the deformation, the greater the strength during a fire.

On the other hand, floor slabs are required to not only support the load during a fire (i.e., to be non-damaging), but also to have heat insulation (i.e., the backside temperature must be below an allowable temperature) and fire resistance (i.e., there must be no cracks that would allow flames to escape to the non-heated side). With regard to non-damage, due to the membrane effect mentioned above, the greater the deformation, the greater the resistance during a fire, so it is advantageous to have a larger deformation. However, with regard to heat insulation and fire resistance, large deformation of the floor slab can cause large cracks in the concrete, which can become weak points and result in the loss of heat insulation and fire resistance.

It is difficult to predict cracks in concrete analytically, and in order to ensure heat and fire insulation, performance must be confirmed through fire resistance experiments. Since it is often difficult to conduct fire resistance experiments on a full-scale scale, the experiments are carried out using reduced-scale specimens.

In the design method for fire-resistant structures described in Patent Document 1, it is unclear whether the designed floor slab has fire resistance regardless of the span, and there is a problem in that the fire resistance of the designed floor slab must be confirmed by sequential fire resistance experiments at an actual scale. In other words, the design method for fire-resistant structures described in Patent Document 1 does not reflect the results of experiments in which performance was confirmed using a reduced-scale test specimen (it is unclear how the results of experiments using a reduced-scale test specimen can be applied to an actual-scale floor slab).

The present invention takes into consideration the above facts and aims to provide a method for designing a floor slab's fire resistance, which reflects the experimental results of an experimental concrete floor slab that has been confirmed to have fire resistance through fire resistance tests.

The fire resistance design method for floor slabs described in the first aspect is a fire resistance design method for floor slabs of reinforced concrete construction, the periphery of which is supported by fire-resistant beams, and includes the steps of supporting an experimental concrete floor slab, which is a scaled-down version of the design concrete floor slab to be designed, with experimental beams, loading a specified load on the experimental concrete floor slab and heating the underside, and measuring the experimental deflection of the experimental concrete floor slab that can maintain its fire resistance; calculating a span ratio, which is the ratio of the span of the design beam supporting the design concrete floor slab to the span of the experimental beam supporting the experimental concrete floor slab; specifying a specified deflection amount corresponding to the upper limit of the deflection amount of the design concrete floor slab from the span ratio and the experimental deflection amount; and estimating a preset design deflection amount of the design concrete floor slab in the event of a fire, and designing the floor slab so that the design deflection amount is equal to or less than the specified deflection amount.

According to the fire-resistant design method for floor slabs described in the first aspect, in the event of a fire in the floor slab, the central part of the floor slab will bend downward and become convex due to the load and weight acting on the reinforced concrete floor slab, heat from below, etc. Here, if the periphery of the floor slab is supported by fire-resistant beams, the membrane effect causes the bending of the central part of the floor slab to cause the stretched reinforcing bars to transmit tensile forces in the directions in which they intersect. This improves the load-bearing capacity in the event of a fire.

On the other hand, if the deflection of the floor slab increases, the load-bearing capacity improves, but cracks will appear in the floor slab, causing it to lose its heat and fire insulation properties.

For this reason, the experimental deflection amount that does not cause cracks large enough to cause a loss of heat and fire insulation properties is measured on the experimental concrete slab floor.

Then, a span ratio is calculated, which is the ratio of the span of the design beam supporting the design concrete floor slab to the span of the experimental beam supporting the experimental concrete floor slab. From this span ratio, a specified deflection amount corresponding to the upper limit of the deflection amount of the design concrete floor slab is specified based on the experimental deflection amount. Furthermore, a preset design deflection amount of the design concrete floor slab in the event of a fire is estimated. Next, the floor slab is designed so that the design deflection amount is equal to or less than the specified deflection amount, thereby satisfying the fire resistance performance. Therefore, the floor slab can be designed by reflecting the experimental results of the experimental concrete floor slab that was confirmed to have fire resistance performance by the fire resistance test.

The fire-resistant design method for floor slabs described in the second aspect is the fire-resistant design method for floor slabs described in the first aspect, in which the span ratio is the ratio between the short side span of the design beam and the short side span of the experimental beam.

In an experimental concrete floor slab that is a scaled-down version of the design concrete floor slab to be designed, the ratio of the short side span of the design beam to the short side span of the experimental beam may differ from the ratio of the long side span of the design beam to the long side span of the experimental beam, and the ratio of the short side span of the design beam to the short side span of the experimental beam is often stricter. According to the fire-resistant design method for floor slabs described in the second aspect, by using the ratio of the short side span of the design beam to the short side span of the experimental beam, it is possible to specify a prescribed deflection amount that corresponds to the upper limit of the deflection amount of the design concrete floor slab based on the experimental deflection amount from the stricter span ratio.

The fire-resistant design method for floor slabs described in the third aspect is the fire-resistant design method for floor slabs described in the first or second aspect, in which, if the design deflection exceeds the specified deflection, the reinforcement of the design concrete floor slab is increased, the number of sub-beams connected to the beam that are not fire-resistant coated is reduced, or the thickness of the design concrete floor slab is increased.

According to the fire-resistant design method for floor slabs described in the third aspect, if the design deflection exceeds the specified deflection, the reinforcement of the design concrete floor slab is increased, the number of sub-beams connected to the beam that do not have fire-resistant coating is reduced, or the thickness of the design concrete floor slab is increased. This allows the floor slab to be designed so that the design deflection is equal to or less than the specified deflection.

The fire resistance design method for floor slabs described in the fourth aspect is the fire resistance design method for floor slabs described in any one of the first to third aspects, in which, when a fire compartment wall is arranged below the design concrete floor slab, the design deflection of the design concrete floor slab above the fire compartment wall is predicted, and when the design deflection exceeds the allowable vertical displacement of the fire compartment wall, the small beams arranged in a position close to the fire compartment wall are fire-resistant coated.

According to the fire resistance design method for floor slabs described in the fourth aspect, when a fire compartment wall is placed below the design concrete floor slab, the design deflection of the design concrete floor slab above the fire compartment wall is predicted. If the design deflection exceeds the allowable vertical displacement of the fire compartment wall, the small beams placed near the fire compartment wall are fire-resistant covered. This suppresses the deflection of the small beams placed near the fire compartment wall, and prevents or suppresses the destruction of the fire compartment wall due to deformation of the floor slab.

The method for designing a floor slab for fire resistance according to the present invention allows floor slabs to be designed by reflecting the experimental results of an experimental concrete floor slab that has been confirmed to have fire resistance through fire resistance tests.

FIG. 1A is a plan view showing an example of a building equipped with a floor slab constructed using the fire-resistant design method for floor slabs according to the first embodiment, and FIG. 1B is an elevation view showing an example of a building equipped with a floor slab. FIG. 1 is an example of a test specimen equipped with an experimental concrete floor slab that is a scaled-down version of a design concrete floor slab in the fire resistance design method for floor slabs according to the first embodiment, and is a plan view showing the state in which reinforcing bars have been arranged in the experimental concrete floor slab. FIG. 2 is an elevation view showing an example of a test specimen equipped with an experimental concrete floor slab that is a scaled-down version of a design concrete floor slab in the fire resistance design method for floor slabs according to the first embodiment. FIG. 1 is an explanatory diagram for determining a prescribed deflection amount corresponding to the maximum deflection of a design concrete floor slab using the experimental results of a test specimen. FIG. 2 is a schematic perspective view showing an example of a design model provided with a design concrete floor slab used for thermal stress analysis in the fire resistance design method for floor slabs according to the first embodiment. 1 is a graph showing the relationship between the design deflection amount and time of a designed concrete floor slab in the event of a fire in thermal stress analysis in the fire resistance design method for floor slabs according to the first embodiment. This figure shows the relationship between the maximum deflection, underside temperature, etc. of a designed concrete floor slab during a fire and the design criteria in thermal stress analysis. FIG. 11 is an elevation view showing a building constructed using the fire resistance design method for floor slabs according to the second embodiment, in which a fire compartment wall is provided between the design concrete floor slab of the upper floor and the design concrete floor slab of the lower floor. FIG. 11 is a diagram showing the relationship between the design deflection amount and time of a designed concrete floor slab in the event of a fire at the position of a fire compartment wall in the fire resistance design method for floor slabs according to the second embodiment. FIG. 1A is a plan view showing another example of a building with a floor slab, and FIG. 1B is an elevation view showing another example of a building with a floor slab. FIG. 2A is a plan view showing a building equipped with a floor slab of a comparative example, and FIG. 2B is an elevation view showing the state of deflection and deformation of the floor slab in a building equipped with the floor slab during a fire.

The embodiment of the present invention will be described in detail with reference to the drawings. Note that items that are less relevant to the present invention are omitted from the illustrations. Note that the direction indicated by the arrow UP shown appropriately in each drawing is the upward vertical direction.

First Embodiment
A fire resistance design method for a floor slab according to the first embodiment will be described with reference to Figs. 1 to 7 etc.

<Building structure with floor slab>
First, before describing the fire-resistant design method for a floor slab according to the present embodiment, a building equipped with a floor slab will be described. Figures 1(A) and (B) are plan and elevation views showing an example (standard example) of a building equipped with a floor slab. As shown in Figures 1(A) and (B), the building 10 includes four fire-resistant covered beams 12 arranged in a frame shape, and a plurality of non-fire-resistant covered girders 16 that are hung between two opposing fire-resistant covered beams 12 in a direction substantially perpendicular to the longitudinal direction. Furthermore, the building 10 includes a floor slab 18 supported by the fire-resistant covered beams 12 and the non-fire-resistant covered girders 16.

In the example of the building 10 shown in Figures 1(A) and (B), there are four non-fire-resistant coated girders 16, but the number of non-fire-resistant coated girders 16 can be changed. In Figure 1, to distinguish between the fire-resistant coated girders 12 and the non-fire-resistant coated girders 16, the fire-resistant coated girders 12 are marked with dots (see Figure 1(A)).

As an example, the fire-resistant coated beam 12 is an H-shaped steel with a fire-resistant coating applied to its surface. The fire-resistant coated beam 12 is an example of a beam with a fire-resistant structure. For example, a heat insulating material such as rock wool is used as the fire-resistant coating on the surface of the H-shaped steel. The non-fire-resistant coated sub-beam 16 is an H-shaped steel without a fire-resistant coating applied to its surface, and is thinner than the fire-resistant coated beam 12.

The floor slab 18 is disposed above the fire-resistant covered beams 12 and non-fire-resistant covered joists 16, and is supported from below by the fire-resistant covered beams 12 and non-fire-resistant covered joists 16. The floor slab 18 is a floor slab made of reinforced concrete. The floor slab 18 has a rectangular concrete section 20 formed by pouring and hardening concrete, and reinforcing bars (not shown) are arranged inside the concrete section 20. The four sides of the periphery of the floor slab 18 are supported by four fire-resistant covered beams 12, and the center of the floor slab 18 is supported by multiple non-fire-resistant covered joists 16.

10(A) and (B) are plan and elevation views showing another example (derived pattern) of a building with a floor slab. As shown in FIG. 10(A) and (B), the building 100 has a plurality of fire-resistant coated joists 14 and non-fire-resistant coated joists 16 that are hung between two opposing fire-resistant coated joists 12 in a direction approximately perpendicular to the longitudinal direction, instead of the structure of the building 10 shown in FIG. 1. In the example shown in FIG. 10, there is one fire-resistant coated joist 14 and three non-fire-resistant coated joists 16. In FIG. 10, to distinguish the fire-resistant coated joists 12, the fire-resistant coated joists 14, and the non-fire-resistant coated joists 16, dots are attached to the fire-resistant coated joists 12 and the fire-resistant coated joists 14 (see FIG. 10(A)), and the thicknesses of the fire-resistant coated joists 14 and the non-fire-resistant coated joists 16, which are joists, are different (see FIG. 10(B)).

As an example, the fire-resistant coated beam 14 is an H-shaped steel beam with a fire-resistant coating on its surface, and is thinner than the fire-resistant coated beam 12.

The floor slab 18 is supported from below by fire-resistant covered beams 12, fire-resistant covered joists 14, and non-fire-resistant covered joists 16. The rest of the structure of the building 100 is the same as that of the building 10 shown in FIG. 1.

<Specific examples of fire-resistant design methods for floor slabs>
Next, a method for fire-resistant design of the floor slab according to this embodiment will be described.

The fire resistance design method for floor slabs in this embodiment is a fire resistance design method for floor slabs for designing a reinforced concrete floor slab (see floor slab 18 shown in Figure 1 or Figure 10) supported by a beam with a fire resistance coating around its perimeter (see fire resistance coating beam 12 shown in Figure 1 or Figure 10).

(Heating experiment process)
In the fire resistance design method for floor slabs of this embodiment, in the heating experiment step, a specified load is applied to an experimental concrete floor slab, which is a scaled-down version of a design concrete floor slab, and the experimental deflection of the experimental concrete floor slab that can maintain its fire resistance is measured. More specifically, in the heating experiment step, a loaded heating experiment is performed using an experimental concrete floor slab, which is a scaled-down version of a design concrete floor slab. Figure 2 is a plan view showing a test specimen (i.e., a scaled-down test specimen) 30 used in the loaded heating experiment, and Figure 3 is an elevational view showing the test specimen 30.

Here, "downsizing" means reducing the reinforcement, thickness, cross-sectional shape, etc. of the experimental concrete floor slab in accordance with the design concrete floor slab. In other words, "downsizing" is not limited to an experimental concrete floor slab in which each component of the design concrete floor slab has been reduced in size by an exact ratio, but also includes cases in which the reinforcement, thickness, cross-sectional shape, etc. of the experimental concrete floor slab have been changed compared to the design concrete floor slab, and also includes cases in which the reinforcement, slab thickness, cross-sectional shape, etc. are the same and only the span has been changed.

2 and 3, the test specimen 30 includes an experimental floor slab 32. The experimental floor slab 32 is an example of an experimental concrete floor slab that is a scaled-down version of the design floor slab 62 (see FIG. 5) as a design concrete floor slab to be designed. The test specimen 30 also includes four experimental beams 34 that support the four sides of the experimental floor slab 32, and brackets 35 that fix the four experimental beams 34 to the first furnace wall 36 (see FIG. 3). The test specimen 30 also includes a second furnace wall 38 that is arranged below the first furnace wall 36, supports the first furnace wall 36, and has a width greater than that of the first furnace wall 36 (see FIG. 3). The test specimen 30 also includes a small beam 40 that is arranged in the center of the experimental floor slab 32 in the longitudinal direction and supports the experimental floor slab 32. The small beam 40 is arranged in a direction that intersects (orthogonal in this embodiment) the longitudinal direction of the experimental floor slab 32, and is hung across the experimental beams 34 on both sides. In Figure 2, the experimental beam 34 and the sub-beam 40 are shown in solid lines.

The experimental floor slab 32 comprises a concrete section 42 formed in a substantially rectangular shape, and reinforcing bars 44 arranged inside the concrete section 42 (see FIG. 2). The reinforcing bars 44 comprise a plurality of main bars 46 arranged in a direction perpendicular to the longitudinal direction of the concrete section 42 (short direction), and a plurality of distribution bars 48 arranged in the longitudinal direction of the concrete section 42 (see FIG. 2). The plurality of main bars 46 and the plurality of distribution bars 48 are each arranged at intervals, forming a substantially lattice pattern.

A predetermined loading member (not shown) for loading is placed on the upper part of the experimental floor slab 32, and a specified load is applied. The specified load is, for example, 4900 N/ ^m2 . In the fire resistance design method for floor slabs of this embodiment, a loaded heating experiment is performed in which the experimental floor slab 32 is loaded with a specified load and heated, and the experimental deflection amount of the experimental floor slab 32 that can maintain its fire resistance performance is measured. Although not shown, in the test specimen 30, wires are stretched in the longitudinal direction and in the direction perpendicular to the longitudinal direction (short direction) of the experimental floor slab 32, and the experimental deflection amount is measured by a deformation meter provided on the wire.

In the load heating experiment, as an example, the experimental floor slab 32 is heated by a flame from the underside of the experimental floor slab 32. The heating time of the experimental floor slab 32 is set to be equal to or longer than the preset heating time of the design floor slab 62 (e.g., 108 minutes). As an example, the heating time of the experimental floor slab 32 is 8 hours.

As shown in FIG. 4, for example, in the experimental floor slab 32 of the test specimen 30, the short side span L1 (see L1 in FIG. 2) of the experimental beam 34 in the direction intersecting the longitudinal direction is 3.5 m, and the long side span L2 (see L2 in FIG. 2) of the experimental beam 34 in the longitudinal direction is 6.2 m. In addition, the maximum deflection of the experimental floor slab 32 at the end of heating (after 8 hours, as an example) is 150 mm. This maximum deflection of the experimental floor slab 32 at the end of heating is an example of the experimental deflection amount.

(Span ratio calculation process)
In the fire resistance design method for floor slabs of this embodiment, a span ratio is calculated in the span ratio calculation step, which is the ratio of the span of a design fire-resistant covered beam 64 (see FIG. 5) supporting a design floor slab 62 to the span of an experimental beam 34 supporting an experimental floor slab 32. The design floor slab 62 is an example of a design concrete floor slab to be designed. The design fire-resistant covered beam 64 is an example of a design beam. The span ratio calculation step does not necessarily have to be performed after the heating experiment step.

As shown in Figure 4, for the design floor slab 62 (see Figure 5), the short side span of the design fire-resistant covered beam 64 is 7.2 m, and the long side span of the design fire-resistant covered beam 64 is 10.3 m.

In this embodiment, the span ratio is the ratio between the short side span of the design fire-resistant covered beam 64 and the short side span of the experimental beam 34. In the example shown in FIG. 4, the span ratio is "7.2/3.5", which is the ratio between the short side span of the design fire-resistant covered beam 64 and the short side span L1 of the experimental beam 34.

(Setting the specified deflection amount)
In the fire-resistant design method for floor slabs of this embodiment, in the step of setting the prescribed deflection, the prescribed deflection corresponding to the upper limit of the deflection of the design floor slab 62 is prescribed from the span ratio and the experimental deflection. The prescribed deflection is a criterion (i.e., a design criterion that is a reference value). In the example shown in Fig. 4, the prescribed deflection corresponding to the upper limit of the deflection of the design floor slab 62 is 308 mm [= 105 x (7.2/3.5)] from the span ratio (i.e., 7.2/3.5) and the experimental deflection (i.e., 150 mm).

(Design deflection estimation process)
In the fire resistance design method for floor slabs of this embodiment, the design deflection of the design floor slab 62 in a preset fire event is estimated in the design deflection estimation step. As an example, the design deflection of the design floor slab 62 in a preset fire event is estimated by thermal stress analysis. In addition, as the "preset fire event", for example, the design floor slab 62 is set to a fire from the underside, and the heating time (i.e., the design heating time) is set to 108 minutes.

5 shows an example of a design model 60 with a design floor slab 62 in a perspective view. As shown in FIG. 5, the design model 60 includes a design floor slab 62 and four design fire-resistant covered beams 64 as an example of design beams that support the four sides of the design floor slab 62. The design fire-resistant covered beams 64 are fire-resistant design beams. The design model 60 also includes a fire-resistant covered sub-beam 66 (one in this example) and a plurality of (three in this example) non-fire-resistant covered sub-beams 68 that are arranged in a direction intersecting (orthogonal in this embodiment) the longitudinal direction of the design floor slab 62 and that are hung across the two design fire-resistant covered beams 64. The four corners of the four design fire-resistant covered beams 64 are joined to columns 70. The columns 70 are, for example, fire-resistant covered columns.

The deflection of the design model 60 with the design floor slab 62 shown in Figure 5 is calculated by thermal stress analysis using finite element analysis software or simplified calculations assuming a certain stress state.

Figure 6 shows the relationship between the heating time and the maximum deflection of the design floor slab 62. In the example of Figure 6, the maximum deflection of the design floor slab 62 is the maximum value of the relative deflection between the design floor slab 62 and the two non-fire-resistant coated girders 68 near the center in the foreground in Figure 5. From the graph shown in Figure 6, the deflection amount of the design floor slab 62 at the preset time of heating is estimated. In this embodiment, the design heating time is 108 minutes. At 108 minutes into the design heating time, the maximum deflection of the design floor slab 62 is 300 mm (see Figure 7).

(Design Method)
Next, in the method for fire-resistant design of a floor slab according to the present embodiment, the floor slab is designed so that the design deflection of the designed floor slab 62 is equal to or less than a prescribed deflection. This allows the designed floor slab 62 to satisfy the fire resistance performance.

In terms of the fire resistance of a floor slab in the event of a fire breaking out from the floor below the target floor slab, it is preferable that the maximum deflection of the floor slab satisfies the following formula 1. It is also preferable that the maximum back surface temperature of the floor slab is equal to or lower than the allowable temperature (design criteria, for example, 160°C). Here, the back surface temperature of the floor slab is the temperature on the side opposite the flame side of the floor slab.

In the fire resistance design method for floor slabs of this embodiment, in the example shown in Figure 4, the specified deflection amount (maximum deflection, i.e., design criteria) of the design floor slab 62 is 308 mm (see Figures 4 and 7). As shown in Figure 6, in the deflection deformation of the design floor slab 62 during heating, it can be confirmed that the maximum deflection amount (i.e., 300 mm) of the design floor slab 62 at the 108 minute point of the design heating time does not reach the specified deflection amount (i.e., design criteria) of 308 mm.

As shown in Figure 7, when the backside temperature of the design floor slab 62 during a fire was measured using heat conduction analysis, the backside temperature of the design floor slab 62 at 108 minutes into the design heating time was 70°C. It can be confirmed that this backside temperature of the design floor slab 62 is lower than the specified backside temperature (i.e., the design criteria) of 160°C.

On the other hand, if the design deflection of the design floor slab during a fire exceeds the prescribed deflection, the reinforcement of the design floor slab may be increased, or the number of non-fire-resistant coated sub-beams among the multiple sub-beams connected to the beam (e.g., the design fire-resistant coated beam 64) may be reduced. Alternatively, the thickness of the design floor slab may be increased.

<Action and Effects>
Next, the operation and effects of this embodiment will be described.

Before explaining the fire resistance design method for floor slabs in this embodiment, the state of a floor slab installed in a building during a fire will be described. During a fire in a floor slab, the load and self-weight acting on the reinforced concrete floor slab will cause the center of the floor slab to bend downward and become convex. Here, if the four sides around the periphery of the floor slab are supported by fire-resistant covered beams, the membrane effect will cause the bending of the center of the floor slab to cause the stretched rebars to transmit tensile forces in the directions where they intersect. This improves the load-bearing capacity during a fire.

On the other hand, if the deflection of the floor slab increases, the load-bearing capacity improves, but cracks will appear in the floor slab, causing it to lose its heat and fire insulation properties.

11(A) and (B) show a building 200 equipped with a floor slab 218 of a comparative example. As shown in FIG. 11(A) and (B), the building 200 is equipped with a floor slab 218 and four fire-resistant coated beams 212 that support the four sides of the floor slab 218. The building 200 is also equipped with a fire-resistant coated small beam 214 and a non-fire-resistant coated small beam 216 that are hung across the two fire-resistant coated beams 212 in the short direction and support the floor slab 218. The floor slab 218 is equipped with a concrete section 220, and reinforcing bars (not shown) are arranged inside the concrete section 220.

As shown in FIG. 11B, in the event of a fire in the floor slab 218, the center of the floor slab 218 bends downwardly and convexly at two points between the fire-resistant coated beam 212 and the fire-resistant coated sub-beam 214. When the deflection of the floor slab 218 becomes large and exceeds the upper deformation limit D1, cracks 222 occur in the concrete part 220 of the floor slab 218, causing a loss of fire resistance (i.e., heat insulation and flame insulation).

Therefore, in the fire-resistant design method for floor slabs of this embodiment, the experimental deflection amount that does not cause cracks large enough to cause a loss of heat insulation and fire insulation is measured on the experimental floor slab 32. In other words, with the four peripheral sides of the experimental floor slab 32, which is a scaled-down version of the design floor slab 62, supported by the experimental beams 34, a specified load is applied to the experimental floor slab 32 and the underside is heated, and the experimental deflection amount of the experimental floor slab 32 that can maintain its fire resistance is measured (heating experiment process).

In the fire-resistant design method for floor slabs of this embodiment, a span ratio is calculated, which is the ratio of the span of the design fire-resistant covered beam 64 supporting the design floor slab 62 to the span of the experimental beam 34 supporting the experimental floor slab 32 (span ratio calculation process). From this span ratio, a prescribed deflection amount corresponding to the upper limit of the deflection amount of the design floor slab 62 is determined based on the experimental deflection amount (prescribed deflection setting process).

Furthermore, in the fire resistance design method for floor slabs of this embodiment, a preset design deflection amount of the design floor slab 62 in the event of a fire is estimated (design deflection amount estimation process). Next, the floor slab is designed so that the design deflection amount of the design floor slab 62 is equal to or less than a specified deflection amount, thereby satisfying the fire resistance performance. Therefore, in the fire resistance design method for floor slabs of this embodiment, the design floor slab 62 can be designed by reflecting the experimental results of the experimental floor slab 32, which was confirmed to have fire resistance performance by a fire resistance experiment.

In addition, in the fire-resistant design method for floor slabs in this embodiment, the span ratio is the ratio of the short side span of the design fire-resistant covered beam 64 to the short side span of the experimental beam 34.

In the experimental floor slab 32, which is a reduced version of the design floor slab 62, the ratio of the short side span of the design fire-resistant covered beam 64 to the short side span of the experimental beam 34 (7.2/3.5 in FIG. 4) may differ from the ratio of the long side span of the design fire-resistant covered beam 64 to the long side span of the experimental beam 34 (10.3/6.2 in FIG. 4). In this case, the ratio of the short side span of the design fire-resistant covered beam 64 to the short side span of the experimental beam 34 is often stricter (see FIG. 4). According to the fire-resistant design method for floor slabs of this embodiment, by using the ratio of the short side span of the design fire-resistant covered beam 64 to the short side span of the experimental beam 34 (7.2/3.5 in FIG. 4), it is possible to specify the prescribed deflection amount corresponding to the upper limit of the deflection amount of the design concrete floor slab from the experimental deflection amount based on the stricter span ratio.

In addition, in the method for designing fire-resistant floor slabs of this embodiment, if the design deflection of the design floor slab during a fire exceeds a prescribed deflection, the reinforcement of the design floor slab is increased, the number of non-fire-resistant coated beams among the multiple beams connected to the beam (e.g., the design fire-resistant coated beam 64) is reduced, or the thickness of the design floor slab is increased. This allows the floor slab to be designed so that the design deflection of the design floor slab during a fire is equal to or less than the prescribed deflection.

Second Embodiment
Next, a method for designing a fire-resistant floor slab according to a second embodiment will be described. Note that the same components as those in the first embodiment will be given the same reference numerals and the description thereof will be omitted.

8 is a schematic elevational view showing a part of a design building 80 as an example of a building to be designed. As shown in FIG. 8, the design building 80 includes a design floor slab 82 of a lower floor, a design floor slab 84 of an upper floor, and a fire compartment wall 86 provided between the design floor slab 82 and the design floor slab 84. In other words, in the design building 80, the fire compartment wall 86 is arranged below the design floor slab 84. The design floor slab 84 is an example of a design concrete floor slab. The design floor slab 84 is supported by four design fire-resistant covered beams 64, one fire-resistant covered sub-beam 66, and three non-fire-resistant covered sub-beams 68, similar to the design floor slab 62 of the design model 60 of the first embodiment shown in FIG. 5. In addition, the four corners of the four design fire-resistant covered beams 64 are joined to the columns 70.

The floor slab fire resistance design method of this embodiment includes the same steps as the floor slab fire resistance design method of the first embodiment, but the following step is added to the design deflection estimation step. That is, in addition to the same steps as the floor slab fire resistance design method of the first embodiment, the floor slab fire resistance design method of this embodiment predicts the design deflection of the design floor slab 84 above the fire compartment wall 86.

As shown in Figure 9, it can be confirmed that the deflection of the design floor slab 84 at the position of the fire compartment wall 86 is 200 mm, which is smaller than the maximum allowable deflection of the fire-resistant coated joist 66 near the fire compartment wall 86 (allowable vertical displacement, for example, if the limit deflection in a fire resistance test of a nearby joist is used as the criterion, ^L2 /400d= ⁷²⁰⁰² /400/486=265 mm). Here, L is the short side span of the floor slab to be evaluated in the actual building (7200 mm in this embodiment), and d is the joist depth near the fire compartment wall 86 (486 mm in this embodiment).

On the other hand, in the fire resistance design method for floor slabs of this embodiment, for example, if the design deflection of the design floor slab 84 exceeds the allowable vertical displacement of the fire compartment wall 86 (i.e., ^L2 /400d), the small beams located close to the fire compartment wall 86 are made to have a fire-resistant structure such as a fire-resistant coating.

In addition to the actions and effects of the configuration similar to those of the fire-resistant design method for floor slabs in the first embodiment, the fire-resistant design method for floor slabs in this embodiment provides the following actions and effects.

According to the fire resistance design method for floor slabs of this embodiment, when a fire compartment wall 86 is arranged below the design floor slab 84, the design deflection of the design floor slab 84 above the fire compartment wall 86 is predicted. If the design deflection of the design floor slab 84 exceeds the allowable vertical displacement of the fire compartment wall 86, the small beams arranged near the fire compartment wall 86 are made fireproof, such as with a fireproof coating. This suppresses the deflection of the small beams (i.e., the fireproof coated small beams) arranged near the fire compartment wall 86, and prevents or suppresses the destruction of the fire compartment wall 86 due to the deformation of the building's floor slab.

〔supplementary explanation〕
In the fire-resistant design method for floor slabs of the first and second embodiments, a designed fire-resistant coated beam 64 made of H-shaped steel with a fire-resistant surface coating is used as a fire-resistant beam supporting the four sides of the periphery of the designed floor slab 62, 84, but the present invention is not limited to this configuration. For example, a fire-resistant beam other than H-shaped steel, a steel beam (reinforced concrete beam), or a composite beam may be used as a fire-resistant beam supporting the periphery of the floor slab.

In addition, in the fire-resistant design method for floor slabs of the first and second embodiments, the arrangement and number of fire-resistant coated joists 66 and non-fire-resistant coated joists 68 that are spanned between the design fire-resistant coated beams 64 that support the four peripheral sides of the design floor slabs 62, 84 can be changed.

In the fire-resistant design method for floor slabs in the first and second embodiments, in the design deflection estimation process, the preset design deflection of the design floor slab 62 in the event of a fire is estimated by thermal stress analysis, but the present invention is not limited to this configuration. For example, the preset design deflection of the design floor slab 62 in the event of a fire may be estimated from experimental values obtained from a loaded heating experiment or the like.

In the fire-resistant design method for floor slabs in the first and second embodiments, the "floor slab made of reinforced concrete supported by fire-resistant beams on all sides" is rectangular, but the present invention is not limited to a rectangular shape. For example, the "floor slab made of reinforced concrete supported by fire-resistant beams on all sides" may be a triangular or pentagonal floor slab, a floor slab using curved beams, etc.

Although the present invention has been described in detail with respect to a specific embodiment, it will be apparent to those skilled in the art that the present invention is not limited to such an embodiment, and that various other embodiments are possible within the scope of the present invention.

12 Fireproof coated beam (beam with fireproof structure)
14 Fireproof coated beam (small beam)
16 Non-fireproof coated beam (small beam)
18 Floor slab 32 Experimental floor slab (experimental concrete floor slab)
34 Experimental beam 40 Small beam 62 Design floor slab (design concrete floor slab)
64 Design fireproof coated beam (design beam)
66 Fireproof coated beam (small beam)
68 Non-fireproof coated beam (small beam)
80 Design building 84 Design floor slab (design concrete floor slab)
86 Fire Compartment Wall L1 Short Side Span

Claims (4)

A method for fire-resistant design of reinforced concrete floor slabs supported on fire-resistant beams around the perimeter;
A process of supporting four sides of an experimental concrete floor slab, which is a scaled-down version of a design concrete floor slab, with an experimental beam, loading a specified load on the experimental concrete floor slab and heating it, and measuring an experimental deflection amount of the experimental concrete floor slab that can maintain its fire resistance;
Calculating a span ratio, which is the ratio of the span of a design beam supporting the design concrete floor slab to the span of an experimental beam supporting the experimental concrete floor slab;
A step of determining a prescribed deflection amount corresponding to an upper limit of the deflection amount of the design concrete floor slab based on the experimental deflection amount from the span ratio;
and estimating a preset design deflection amount of the design concrete floor slab in the event of a fire,
A method for fire-resistant design of a floor slab, comprising: designing the floor slab so that the design deflection amount is equal to or less than the specified deflection amount. The method for fire-resistant design of floor slabs according to claim 1, wherein the span ratio is the ratio between the short side span of the design beam and the short side span of the experimental beam. The fire-resistant design method for floor slabs according to claim 1 or claim 2, in which, if the design deflection exceeds the specified deflection, the reinforcement of the design concrete floor slab is increased, the number of sub-beams connected to the beam that are not fire-resistant coated is reduced, or the thickness of the design concrete floor slab is increased. When a fire compartment wall is arranged below the design concrete floor slab, a design deflection amount of the design concrete floor slab above the fire compartment wall is predicted;
A method for fire-resistant design of a floor slab according to any one of claims 1 to 3, wherein, when the designed deflection amount exceeds the allowable vertical displacement of the fire compartment wall, a small beam arranged in a position close to the fire compartment wall is made fire-resistant.