JP4805879B2 - RC slab - Google Patents

Description

  The present invention relates to an RC slab having fire resistance.

  When the RC slab is subjected to fire heating, the temperature of the lower end reinforcing bar gradually increases, and when the temperature of the lower end reinforcing bar reaches the allowable limit temperature, the strength decreases, and the RC slab cannot hold the load.

  The fireproof performance required for RC slabs should be determined individually according to the structure and application of the building, and is not necessarily high from an economic standpoint. For this purpose, there is a demand for RC slab reinforcement technology that can easily realize the fire resistance obtained at the design stage at the construction site.

  At present, when the fire duration is expected to be long at the design stage and the required fire resistance performance cannot be ensured with the standard designed RC slab structure, the RC slab can be used by the method of Measure 1 or Measure 2 shown below. Reinforces and delays the temperature rise of the lower end rebar.

Measure 1 is a method of increasing the concrete thickness below the lower main reinforcement.
As shown in FIG. 5, in the RC slab 50, the upper main reinforcement 12 and the upper upper reinforcement bar 14, the lower lower reinforcement 16 and the lower lower reinforcement bar 18 are arranged, and when receiving a positive bending moment. The lower main bar bears the tensile force. This is a method of delaying the temperature rise of the lower main reinforcing bar 16 by increasing the concrete thickness (cover thickness) below the lower main reinforcing bar 16 from the standard thickness (thickness L ₂ ) and separating the distance from the flame 22. .

  If measure 1 is adopted, the temperature rise of the lower end reinforcing bar 16 can be delayed. However, by increasing the cover thickness, the position of the neutral shaft moves upward and the structural performance of the RC slab deteriorates. Further, when the cover thickness increases, there is a problem that the construction becomes complicated and management becomes difficult.

Measure 2 is a method of covering the lower surface of the RC slab with a fireproof coating.
That is, as shown in FIG. 6, a fireproof coating 26 is applied to the lower surface of the RC slab 60 to delay the temperature rise of the lower end main reinforcement 16. The cover thickness of the RC slab 60 is a standard thickness (thickness L ₁ ). Other structures are the same as the RC slab 50.

  If measure 2 is adopted, the temperature rise of the lower end reinforcing bar 16 can be delayed. However, the covering area covered with the fireproof coating 26 is wide, and the influence on other works is great. For this reason, there is a problem that the workability is remarkably lowered. Furthermore, the cost is significantly increased.

In addition, as an RC slab reinforcement technique, a method of embedding an upper part of a steel beam in an RC floor slab has been proposed (Patent Document 1).
However, with this method, half of the steel beam is exposed and directly affected by the heat from the fire, so the strength of the beam is expected to decrease. In addition, the upper part of the small beam must be embedded in the RC floor slab, which increases the time required for construction and is not realistic.
JP 7-42293 A

  In view of the above-described facts, an object of the present invention is to improve the fire resistance of an RC slab without increasing the cover thickness or covering it with a fireproof coating.

  The RC slab according to the first aspect of the present invention is an RC slab composed of a lower end main reinforcement and concrete, and is characterized in that a fireproof reinforcing bar is arranged above the lower end main reinforcement.

  According to the first aspect of the present invention, the RC slab is composed of the lower end main reinforcement and the concrete, and the RC slab is provided with the fireproof reinforcing bars above the lower end main reinforcement. Here, the fireproof reinforcing bar means a reinforcing bar that is arranged for the purpose of improving the heat resistance against fire heating.

As a result, first, the temperature of the bottom main reinforcement rises due to the heat of the flame on the lower floor. Since the fireproof reinforcing bars are arranged above the lower main bars, the temperature rise of the fireproof reinforcing bars is delayed from the temperature rise of the lower main bars. For this reason, even if the temperature of the lower main reinforcing bar reaches the allowable limit and the strength of the lower main reinforcing bar decreases, the strength of the fireproof reinforcing bar has not yet reached the allowable limit, and the fireproof reinforcing bar bears the load. The strength of the RC slab is maintained until the temperature of the fireproof reinforcement reaches an allowable limit, and the fireproof time of the RC slab can be increased.
In addition, the fireproof reinforcing bars are simply arranged on the RC slab, and there is little work on construction.

  The invention according to claim 2 is the RC slab according to claim 1, wherein a lower end reinforcing bar is arranged on the lower end main reinforcing bar in a direction orthogonal to the lower end reinforcing bar, and the fireproof reinforcing bar is arranged on the lower end distributing force. It is characterized in that the bars are arranged in the direction orthogonal to the lower end force distribution bars on the lines.

According to invention of Claim 2, RC slab arrange | positions a lower end reinforcement bar on a lower end main reinforcement in a direction orthogonal to a lower end reinforcement, and also distributes a fireproof reinforcement bar on a lower end reinforcement bar. The bars are arranged in a direction perpendicular to the lines.
As a result, the lower end main reinforcement, the lower end reinforcement bar, and the fire reinforcement reinforcement are arranged in order, the position of the fire reinforcement reinforcement in the slab thickness direction is determined, and the cover thickness of the fire reinforcement reinforcement from the bottom surface of the slab is secured. .

The invention according to claim 3 is the RC slab according to claim 2, wherein the fireproof reinforcing bars are staggered between the bottom main bars and the bottom main bars.
According to the invention described in claim 3, the fireproof reinforcing bars are arranged in a staggered manner between the lower main bars and the lower main bars.

  As a result, the reinforcing bars inside the RC slab become dense, but the fireproof reinforcing bars and the bottom main bars do not overlap in the depth direction, and workability at the time of reinforcing bar binding is maintained. Furthermore, generation | occurrence | production of the unfilled part (cavity part) of the concrete around a reinforcing bar is suppressed, and a fireproof reinforcing bar can be arranged without impairing workability.

  According to a fourth aspect of the present invention, in the RC slab according to any one of the first to third aspects, an upper end main reinforcing bar is arranged above the fireproof reinforcing bar.

According to the fourth aspect of the present invention, the upper end main reinforcement is arranged on the upper part of the fireproof reinforcement of the RC slab.
As a result, the strength of the upper main muscle can also be expected.

  The invention according to claim 5 is the RC slab according to any one of claims 1 to 4, wherein the diameter and pitch of the fireproof reinforcing bars are selected according to the required fireproof performance of the RC slab. It is characterized by.

According to the fifth aspect of the present invention, the fire resistance performance of the RC slab can be adjusted by selecting the diameter and pitch of the fireproof reinforcing bars arranged in the RC slab.
As a result, the fire resistance required for the RC slab can be easily realized at the construction site. For example, as a reinforcement for extending the fireproof time of the RC slab, the diameter of the reinforcing bars that serve as the fireproof reinforcing bars may be increased and the pitch of the reinforcing bars may be increased.
When it is desired to slightly increase the fireproof time of the RC slab, the fireproof performance can be improved economically by arranging fireproof reinforcing bars having a diameter smaller than that of the lower main bar at a pitch coarser than that of the lower main bar.

  Since the present invention is configured as described above, the fire resistance of the RC slab can be improved without increasing the cover thickness or covering with a fireproof coating.

As shown in FIG. 1, in the RC slab 10 according to the present invention, the lower end main reinforcement 16 is arranged at the position of the cover thickness L ₁ from the lower surface of the concrete 20 in the lower part of the concrete 20 formed in a flat plate shape. . Lower main reinforcement 16 is a steel rod of an outer diameter D _1, in the same direction at a pitch P _1, a plurality of are Haisuji.

A lower end force distribution bar 18 is arranged on the lower end main bar 16. The lower end reinforcing bar 18 is a steel bar having an outer diameter D _{2, and} a plurality of bars are arranged at a pitch P ₂ (not shown) so as to be orthogonal to the lower end main bar 16 on the lower end main bar 16.

A fireproof reinforcing bar 30 for fireproof reinforcement is arranged on the lower end reinforcing bar 18. Refractory reinforcement 30 is a steel bar having an outer diameter D _3, so as to be perpendicular to the lower distribution force muscle on the lower arrangement forces muscle 18, a plurality at a pitch P ₃ are Haisuji.
Further, an upper end main reinforcing bar 12 is arranged at the upper part of the concrete 20.
Upper main reinforcement 12 is a steel rod of an outer diameter D _4, the position of the upper surface from a depth L ₂ of the concrete 20 (head thickness L _2), a plurality of the same direction at a pitch P ₄ is Haisuji.

An upper end reinforcement bar 14 is arranged below the upper main bar 12. Upper distributing power sources 14, a steel rod having an outer diameter D _5, in a direction perpendicular to the upper main reinforcement 12, a plurality at a pitch P _{5 (not} shown) is Haisuji.

  In the present invention, the fireproof reinforcing bar 30 is arranged on the lower principal bar 16. For this reason, the fireproof reinforcing bar 30 is located inside the concrete 20 from the lower end main reinforcing bar 16.

  As a result, at the time of a fire, first, the temperature of the lower end main reinforcement 16 arranged at the lowest position in the RC slab 10 rises due to the heat of the rising flame 22. The temperature rise of the fireproof reinforcing bar 30 located inside the concrete 20 is delayed from the temperature rise of the lower end main reinforcing bar 16.

  Even if the fire continues, the temperature of the lower reinforcement 16 further rises, reaches the allowable limit, the strength of the lower reinforcement 16 decreases, and the lower reinforcement 16 can no longer bear the load of the slab. The allowable limit is not reached, and the refractory reinforcement 30 bears the load of the slab.

Even if the fire continues further, the fireproof performance of the RC slab 10 is maintained until the temperature of the fireproof reinforcing bar 30 reaches an allowable limit. Thereby, the fireproof time of RC slab 10 can be lengthened.
As a result, the fire resistance of the RC slab can be improved without increasing the cover thickness or covering with a fireproof coating.

Furthermore, in the present invention, it is only necessary to arrange the fireproof reinforcing bar 30 above the lower end main reinforcing bar 16, and there is little trouble in construction.
In the present invention, the lower end reinforcing bar 18 is arranged on the lower end main reinforcing bar 16, and the fireproof reinforcing bar 30 is arranged on the lower end distributing bar 18.

  As a result, the position of the fireproof reinforcing bar 30 in the slab thickness direction is automatically determined, and the cover thickness of the fireproof reinforcing bar from the lower surface of the slab is secured.

  In the RC slab of the present invention, the fireproof reinforcing bar 30 is arranged between the lower principal bars 16. That is, the fireproof reinforcing bar 30 is arranged between the lower main bar 16 and the lower main bar 16, which is staggered when viewed in cross section.

  As a result of adding the fireproof reinforcing bar 30 to the RC slab 10, the reinforcing bar inside the RC slab 10 becomes dense. However, the fireproof reinforcing bar 30 and the bottom main bar 16 are staggered, and the fireproof reinforcing bar 30 and the bottom main bar 16 do not overlap in the depth direction. This maintains the workability during rebar tying.

  Furthermore, by making the refractory reinforcement 30 the bottom main reinforcement 16 and staggered reinforcement, the occurrence of unfilled portions (cavities) of the concrete around the reinforcing bars is suppressed, and the refractory reinforcement 30 is arranged without impairing workability. can do.

In the RC slab 10, the upper main reinforcement 12 is arranged above the concrete 20, and the upper upper reinforcement 14 is arranged below the upper main reinforcement 12 in a direction perpendicular to the upper main reinforcement 12.
As a result, the compressive force is borne by the upper main muscle 12. Combined with the action of the lower main reinforcing bar 16 and the fireproof reinforcing bar 30 that bears the tensile force, the allowable stress of the RC slab 10 can be increased and the fireproof performance can be improved.

Specific effects of refractory reinforcement 30 will be described later, by increasing the outer diameter D ₃ of the refractory reinforcement 30 which is Haisuji the RC slab 10 increases the mechanical strength of the refractory reinforcement 30 itself, RC slab Can improve the fire resistance. Further, the strength of the entire refractory reinforcement 30 increases when the pitch P ₃ of refractory reinforcement 30 tightly, thereby improving the fire resistance of RC slab.

Thus, the fire resistance performance of the RC slab 10 can be adjusted by arbitrarily selecting the outer diameter D ₃ and the pitch P ₃ of the reinforcing bars 30.
As a result, the fire resistance required for the RC slab 10 can be easily realized at the construction site.

Incidentally, the refractory reinforcement 30 is intended to economically realize improvement of fire resistance, the outer diameter D ₃ of the refractory reinforcement 30 may be smaller in diameter than the outer diameter D ₁ of the bottom longitudinal reinforcement 16. Thereby, the amount of reinforcing bars can be reduced.
Next, the effect of the present invention will be described.

  As shown in FIGS. 2A and 2B, the test apparatus 40 for measuring the fire resistance performance of the fireproof reinforcing bar 30 includes a heating furnace 42 having a bottom wall and a side wall formed of a refractory material and having an open top. Yes.

  A test body (RC slab 10) is disposed on the open upper portion of the heating furnace 42. A heating burner (not shown) is provided inside the heating furnace 42, and the lower surface of the RC slab 10 is heated by the burner. To do. The heating temperature of the RC slab 10 can be adjusted by adjusting the combustion intensity of the burner.

  A rod-like support member 46 that horizontally supports both ends of the RC slab 10 is provided outside the upper portion of the side wall of the heating furnace 42. The support method of the RC slab 10 is simple support, and the front end portion in the longitudinal direction is supported by the support member 46 (distance between fulcrums 3390 mm).

  A pressure device (hydraulic jack) 44 that applies a load from the top to the bottom is disposed on the upper surface of the RC slab 10. The pressing portion 45 of the pressurizing device 44 is branched into two, and linearly contacts two points on the upper surface of the RC slab 10. The load position of the pressing portion 45 was set to two equally divided two points (distance between fulcrums 1130 mm).

  The load P applied to the RC slab 10 by the pressing portion 45 is a load at which the bending moment M at the position of the central portion 48 of the RC slab 10 becomes 0.606 which is the value of the ultimate bending moment Mu at normal temperature.

Here, the bending moment M and the final bending moment Mu are obtained by the following equations.
M = 0.606 Mu
Mu = 0.9a _t σ _y D (kN · m)
a _t : cross-sectional area of the lower main reinforcement (m ² )
σ _y : Yield strength of the lower main muscle (kN / m ² )
D: Distance from the center of gravity to the outermost edge on the compression side (m)

  The test method is to apply a load P from the upper surface of the RC slab 10 with the pressing portion 45 and follow the standard heating temperature curve defined by ISO-834 with the load P applied. The bottom surface continued to be heated.

  The deflection amount of the central portion 48 of the RC slab 10 was continuously measured from the start of heating until the RC slab 10 was broken.

  The test body was an RC slab 10 in which the fireproof reinforcing bars 30 are arranged, and an RC slab 11 in which all the other constituent elements are the same as the RC slab 10 without arranging the fireproof reinforcing bars 30. By testing the RC slab 10 and the RC slab 11 under the same heating conditions, the effect of the fireproof reinforcing bar 30 was directly verified.

  As shown in FIG. 3A, the RC slab 11 has an upper end reinforcing bar 12 arranged at the upper part of the concrete 20 and an upper end reinforcing bar 14 arranged below the upper end reinforcing bar 12. In addition, a lower end reinforcing bar 16 is arranged on the lower part of the concrete 20, and a lower end reinforcing bar 18 is arranged on the lower end main reinforcing bar 16. The fireproof reinforcing bar 30 is not arranged.

The width L ₄ of the RC slab 11 was 1000 mm, the depth L ₅ (distance between fulcrums) was 3390, and the thickness T ₁ was 150 mm.

Both the outer diameter _{D 1} of the outer diameter _{D 1} and the lower end main reinforcement 16 of the upper main reinforcement 12 13 mm, both pitch _{P 1} is a 200 mm, the outer diameter of the outer diameter _{D 2} and the lower end distribution force muscle 18 of the upper distribution force muscle 14 D ₂ was 10 mm for all, and pitch P ₂ (not shown) was 200 mm for all.
Further, the head thickness _{L 1} of the lower main reinforcement 16 is 20 mm, cover thickness _{L 3} of the upper main reinforcement 12 was 30 mm.

  As shown in FIG. 3B, the RC slab 10 has an upper main reinforcing bar 12 arranged at the upper part of the concrete 20 and an upper upper distributing bar 14 arranged below the upper main reinforcing bar 12. In addition, a lower principal bar 16 is arranged at the lower part of the concrete 20, a lower reinforcement bar 18 is arranged on the lower principal bar 16, and a fireproof reinforcing bar 30 is arranged on the lower reinforcement bar 18.

Outer diameter _{D 3} of the refractory reinforcement 30 is 10 mm, the pitch _{P 3} was set to 200 mm. Other dimensions are the same as the RC slab 11.

  The test results are shown in FIG. In FIG. 4, the horizontal axis indicates the elapsed time (minutes), and the vertical axis indicates the amount of deflection of the central portion 48 of the RC slab 10. A broken line A indicates the characteristics of the RC slab 11, and a solid line B indicates the characteristics of the RC slab 10.

In ISO-834 “Fireproofing test method for building structural members”, the limit of the load supporting member that receives the bending moment is either of the following values for the bending amount (δa) or the bending speed (δa / dt) of the specimen. It is stipulated when the time is reached.
δa = L ² / (400 × d) (mm) (1)
δa / dt = L ² / (9000 × d) (mm / min) (2)
Where L: Distance between fulcrums (mm)
d: Member composition (mm)

  Therefore, the limit of the amount of bending when the RC slab 10 and the RC slab 11 are displaced by receiving a load is obtained by the equation (1) and indicated by a one-dot chain line C. Further, the bending speed limit when the RC slab 10 and the RC slab 11 are displaced by receiving a load is obtained by the equation (2) and indicated by a two-dot chain line D.

  As shown in FIG. 4, the broken line A and the solid line B both increase in displacement over time. However, the displacement amount of the RC slab 11 indicated by the broken line A is larger than the displacement amount of the RC slab 10 indicated by the solid line B, and reaches the one-dot chain line C that is the bending limit earlier. The time required for the RC slab 11 to reach the deflection limit after the start of the test was 151 minutes (point P).

On the other hand, the RC slab 10 indicated by the solid line B took 188 minutes (Q point) after starting the test until reaching the one-dot chain line C, which is the bending limit.
By arranging the fireproof reinforcing bars 30, a delay effect of 37 minutes was seen in the time to reach the deflection limit, and the effects of the fireproof reinforcing bars 30 were verified.

Note that the broken line A and the solid line B both reach the bending limit before reaching the bending speed limit (inclination angle of the two-dot chain line D), and are not evaluated at the bending speed limit.
In this embodiment, the test was performed with the RC slab 10 in which the upper main bars 12 are arranged. However, a sufficient delay effect can be exhibited without the upper main bars 12.

  Further, the lower end force distribution bar 18 on the lower end main bar 16 is not necessarily required in the design calculation, and if the fireproof reinforcing bar 30 is provided, it is possible to extend the time until the deflection limit is reached.

It is sectional drawing which shows the basic structure of RC slab of this invention. It is sectional drawing which shows the fire resistance test apparatus of RC slab. It is sectional drawing which shows the basic structure of a test body. It is a figure which shows an example of the test result of RC slab of this invention. It is sectional drawing which shows the basic structure of the conventional RC slab. It is sectional drawing which shows the basic structure of the conventional RC slab.

Explanation of symbols

10 RC slabs 12 upper main bars 14 upper end strength bars 16 lower end main bars 18 lower end strength bars 20 concrete 30 fireproof reinforcement bars

Claims (5)

RC slab composed of bottom main reinforcement and concrete,
An RC slab characterized in that a fireproof reinforcing bar is arranged above the lower main bar. A lower end reinforcing bar is arranged on the lower main bar in a direction orthogonal to the lower reinforcing bar, and the fireproof reinforcing bar is arranged on the lower end reinforcing bar in a direction orthogonal to the distributing bar. The RC slab according to claim 1. The RC slab according to claim 2, wherein the fireproof reinforcing bars are staggered between the bottom main bars. The RC slab according to any one of claims 1 to 3, wherein an upper end main reinforcing bar is arranged above the fireproof reinforcing bar. The RC slab according to any one of claims 1 to 4, wherein a diameter and a pitch of the fireproof reinforcing bar are selected according to a required fireproof performance of the RC slab.

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