JP2005146601A - Reinforced column structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reinforced column (RC column) structure which can prevent crushing/separation of cover concrete, and contributes to reduction of material costs. <P>SOLUTION: According to the RC column structure, cover concrete 3a arranged at a lower end of the RC column 10 is formed of a PCa cylinder body 30 made of super-high-strength high-tenacity concrete, and cover concrete 3b arranged over an area other than the lower end is made of super-high-strength concrete and formed in one body with core concrete 4. Thus only the cover concrete 3a at the lower end of the RC column 10, at which the cover concrete 3 is susceptible to crushing/separation at the time of an earthquake or the like, is made of the super-high-strength high-tenacity concrete. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reinforced concrete column structure, and more particularly to a reinforced concrete column structure that receives a very large axial compressive force.

In recent years, reinforced concrete structures (hereinafter referred to as “RC structures”) have been actively promoted to increase the height and span. Since a very large axial compressive force acts on the lower floor pillar of such an RC structure, high strength concrete (hereinafter referred to as “ultra high strength concrete”) having a design standard strength of 100 N / mm ² or more. There is a lot to use.

FIG. 7 is a graph schematically showing the relationship between compressive stress and strain of concrete.
As shown in FIG. 7, the unconstrained ultra-high-strength concrete has a tendency that the stress decrease after reaching the maximum compressive stress becomes sharper as the maximum compressive strength becomes larger, and it tends to break with a small strain (a in FIG. 7). B, c). On the other hand, the ultra-high strength concrete in a restrained state has a gentle stress drop after reaching the maximum compressive stress and a large strain at the time of failure (see d in FIG. 7). For this reason, an extremely large compressive axial force is acting on an RC column made entirely of ultra high strength concrete (hereinafter abbreviated as “ultra high strength RC column” where appropriate), and further due to an earthquake or the like. When horizontal force is applied, the core concrete constrained by the reinforcing bars is healthy, but the cover concrete not constrained by the reinforcing bars collapses and peels with a strain (deformation) smaller than the design value. There is a phenomenon peculiar to ultra high strength RC pillars. The crushing and peeling of the cover concrete is not preferable from the viewpoint of the durability and fire resistance of the reinforcing bars, and repair is difficult because of the use of ultra high strength concrete. Further, when the cover concrete is crushed and peeled off, there is a problem that the effective cause of the RC column is reduced and the bending strength is lowered.

On the other hand, as a conventional RC column structure, an inclined structure concrete member has been devised in which the surface layer concrete has higher strength and higher durability than the inner concrete (see, for example, Patent Document 1). The surface layer portion of such an inclined structure concrete member has a maximum compressive strength exceeding 100 N / mm ² and a strain at the same time as that of normal high-strength concrete (the maximum compressive strength does not exceed 80 N / mm ² ). Since it is made of concrete (hereinafter referred to as “ultra-high-strength high-toughness concrete” (see d ′ in FIG. 7)), it has a structure in which cracks, chips, etc. are unlikely to occur on the surface due to local impact. .

Patent Document 2 discloses a cylindrical column precast embedded form (hereinafter referred to as “PCa cylinder”) formed of a fiber-reinforced hardener. According to this PCa cylinder, the PCa cylinder itself has a predetermined tensile strength and shear strength by the action of the fibers in the hardened material. Therefore, when concrete is placed inside the PCa cylinder, the concrete is restrained from protruding to the side by the tensile strength of the PCa cylinder and the compressive strength is increased, and the shear strength of the PCa cylinder is increased. This reinforces the shear strength of the internal concrete. As a result, it is possible to reduce the amount of reinforcing bars of the strip or spiral muscle, or to omit it depending on circumstances.
JP 2001-233656 A ([0008]-[0012], [0036]) Japanese Patent Laid-Open No. 11-293964 ([0007]-[0011], FIGS. 1 and 4)

  By the way, the crushing and peeling of the cover concrete during the earthquake of the ultra high strength RC column is a phenomenon that appears prominently near the lower end of the column. Therefore, for the cover concrete other than the lower end of the column, ultra high strength high toughness concrete is used. There is no need to use it for construction. However, the RC column structure described in Patent Document 1 described above is one in which the cover concrete from the lower end to the upper end of the column is formed by one continuous PCa member. For this reason, there is a problem that the concrete other than the lower end portion also becomes ultra-high strength and high toughness concrete and the material cost increases.

  In addition, the RC column structure described in Patent Document 2 is a structure in which the concrete of the lower structure is placed and then the PCa cylinder is stacked to replace the formwork, and the concrete is placed in the hollow portion of the PCa cylinder. is there. At this time, since the PCa cylinder is simply installed on the concrete of the lower structure, there is a problem that the integrity of the concrete of the lower structure and the PCa cylinder cannot be ensured.

The present invention has been made in view of these problems, and an object of the present invention is to provide an RC column structure that can prevent crushing and peeling of cover concrete during an earthquake and reduce material costs. .
A second object of the present invention is to provide an RC column structure that is strong against earthquakes by ensuring the integrity of the lower structure and the PCa cylinder.

  The reinforced concrete column structure according to claim 1 is a reinforced concrete column structure formed of concrete having a different composition from the concrete covered at the lower end of the column and the concrete at the other portion, It is formed of a precast cylinder made of ultra high strength and high toughness concrete (hereinafter referred to as “PCa cylinder”), and the other parts of the concrete are formed of ultra high strength concrete. .

Here, “ultra-high-strength concrete” refers to concrete whose maximum compressive strength exceeds 100 N / mm ² . Table 1 shows an example of blending ultra high strength concrete. “Ultra high strength and high toughness concrete” means that the maximum compressive strength exceeds 100 N / mm ² and at the same time as normal high strength concrete (the maximum compressive strength does not exceed 80 N / mm ² ). It refers to concrete with strain.

The ultra high strength and high toughness concrete, for example, powder of cement and silica, silica fume, silica sand, 180 kg of about a water unit water to superplasticizers (finished concrete volume 1 m ³ per) (water / ratio of cement 22% Compressive strength 200-220 N / mm ² , bending strength 40-45 N / mm ² , bond strength 10-90 N / Mm ² , air permeability 2.5 × 10 ⁻¹⁸ m ² , water absorption 0.05 kg / m ³ , salt diffusion coefficient 0.02 × 10 ⁻¹² m ² / sec, elastic coefficient 55 KN / mm ² Fiber-reinforced ultra-high strength and high toughness concrete can be used.

According to such a reinforced concrete column structure, the cover concrete at the lower end portion of the column is formed of ultra high strength and high toughness concrete. The same level of durability can be demonstrated. Moreover, since the cover concrete of the said lower end part is formed with the PCa cylinder, only the cover concrete part of the lower end part of a pillar can be formed with ultra high strength high toughness concrete.
In addition, it is empirically known that crushing and peeling of the cover concrete at the lower end of the column occurs from the lower end of the column in a range of a height dimension substantially the same as the width of the column. It is preferable to use high-strength and tough concrete.

  A reinforced concrete column structure according to claim 2 is the reinforced concrete column structure according to claim 1, wherein the lower end portion of the precast cylinder is embedded in the concrete of the lower structure.

  According to such a structure, since the lower end portion of the PCa cylinder arranged at the lower end portion of the column is embedded in the concrete of the lower structure, it is possible to ensure the integrity of the lower structure and the PCa cylinder. . That is, in the event of an earthquake, the concrete of the lower structure and the PCa cylinder show an integral behavior, so that it is possible to provide a column structure that is more durable than conventional in terms of peeling off the covering concrete.

In addition, since the compressive force equivalent to the axial compressive force received by the RC column acts on the substructure directly under the RC column, it is constructed using ultra-high strength concrete like the core concrete of the RC column. There is a need. On the other hand, the beam portion of the substructure does not need to resist such a large axial compressive force, so it is economical to use concrete with a lower compressive strength than the RC column core concrete. . Therefore, it is necessary to conclude the mixing of concrete at the beam-column joint.
At this time, if the PCa cylinder for the lower end of the RC column is installed on the reinforcing bar assembled at the beam column joint before placing the concrete of the lower structure, the range for installing the concrete stopper is reduced. be able to.

  According to the RC column structure according to claim 1, since the cover concrete at the lower end of the column is constructed using ultra-high-strength and high-toughness concrete, it is as durable as the core concrete portion restrained by the strip. Can demonstrate its sexuality. That is, it is possible to prevent the cover concrete portion from being crushed and separated even though the core concrete portion constrained by the band reinforcing bar is healthy. Further, according to the RC column structure according to the present invention, the super high strength and toughness concrete can be selectively used at the location where the bending stress is concentrated by the PCa cylinder, so that the cover concrete is prevented from being crushed and peeled off. On the other hand, it is possible to reduce the material cost by reducing the amount of ultra-high-strength and high-toughness concrete that has higher material costs than ultra-high-strength concrete.

  According to the RC column structure according to claim 2, since the lower end portion of the PCa cylinder installed at the lower end portion of the RC column is embedded in the concrete of the lower structure, the concrete of the lower structure and the PCa cylinder Unity with the body can be ensured. Moreover, since the range which installs a concrete stopper is reduced, workability | operativity can be improved.

<First Embodiment>
First, a first embodiment of a reinforced concrete column structure according to the present invention will be described in detail with reference to the drawings. In the drawings to be referred to, FIG. 1 is a perspective view showing an RC pillar according to the first embodiment. FIG. 2 is a horizontal cross-sectional view of the RC pillar taken along the line AA shown in FIG.

(Structure of RC pillar 10)
As shown in FIGS. 1 and 2, the RC column 10 is composed of a column reinforcement 2 composed of a main reinforcement 2 a and a strip reinforcement 2 b, a cover concrete 3 (3 a, 3 b) covering the outer periphery of the column reinforcement 2, and a cover concrete 3. It is comprised from the core concrete 4 cast and filled inside.

  The column rebar 2 has a hoop-shaped strip 2b vertically spaced around the main bars 2a, 2a,... It is configured to be installed in a space (see FIG. 4).

  As shown in FIG. 2, the cover concrete 3 is concrete that surrounds the outer periphery of the column reinforcement 2. In the present embodiment, the cover concrete 3a at the lower end is composed of a PCa cylinder 30 made of ultra high strength and high toughness concrete, and the cover concrete 3b other than the lower end is described later using ultra high strength concrete. It is formed integrally with the core concrete 4. That is, only the lower end portion where the cover concrete 3 is likely to be crushed and peeled off by an earthquake is formed of ultra high strength and high toughness concrete.

  The core concrete 4 is concrete on the inner side of the cover concrete 3 and is formed by being cast with ultra high strength concrete in this embodiment. The super high strength concrete cast as the cover concrete 3b other than the core concrete 4 and the lower end portion is cured, so that the RC column 10 is formed integrally with the column rebar 2 and the PCa cylinder 30. Since the core concrete 4 is constrained by the reinforcing bars 2b of the column reinforcing bars 2, the core concrete 4 does not cause brittle fracture with respect to deformation at the time of an earthquake and can resist tenaciously.

FIG. 3 is a perspective view showing the PCa cylinder 30.
As shown in FIG. 3, the PCa cylinder 30 is a precast concrete member formed in a square cylinder shape and has a hollow portion 31. The hollow portion 31 is open at the upper and lower ends, and the PCa cylinder 30 is installed at the lower end portion 3 a of the RC column 10 so that the column rebar 2 is inserted into the hollow portion 31.

  The PCa cylinder 30 is manufactured using ultra high strength and high toughness concrete in order to prevent the cover concrete 3 from being crushed and peeled off. Since ultra high strength and high toughness concrete has high toughness, it is not necessary to arrange reinforcing bars in the PCa cylinder 30 and the thickness of the PCa cylinder 30 can be reduced. Therefore, the wall thickness of the PCa cylinder 30 can be made equal to or slightly smaller than the design cover thickness of the RC pillar 10.

  In addition, since the crushing and peeling of the cover concrete 3 are likely to occur in the range of the same height as the width of the RC column 10, the height of the PCa cylinder 30 is about the same as the width of the RC column 10. It is preferable to form in a height dimension.

  Thus, the RC pillar 10 has the cover concrete 3a at the lower end formed of the PCa cylinder 30 made of ultra-high strength and high toughness concrete. Therefore, the cover concrete at the lower end at the time of an earthquake with a relatively small strain (deformation). It can prevent crushing and peeling of 3a.

(Construction of RC pillar 10)
FIG. 4 is a perspective view schematically showing the construction status of the RC pillar 10.
First, in a precast member manufacturing factory or a precast member manufacturing yard, for example, by placing ultra-high strength and high toughness concrete on a formwork (not shown) formed to a required size and removing the frame after curing, the PCa cylinder 30 is produced.

  Next, at the construction position of the RC pillar 10, the main bars 2a, 2a,... Are erected in correspondence with the four corners of the pillar, and hoop-like band bars 2b are provided at predetermined intervals in the vertical direction. Assemble and assemble the column rebar 2.

  Then, as shown in FIG. 4, the PCa cylinder 30 is lifted by a lifting machine such as a crane C and the column rebar 2 is inserted into the hollow portion 31, and the PCa cylinder 30 is attached to the lower end of the RC column 10. Install.

  The PCa cylinder 30 is preferably lifted using a lifting tool that does not cause bending stress on the member so that the concrete is not cracked. As an example of such a hanger, as shown in FIG. 4, a hanger made of two wires W attached to the horizontal member HT at a distance substantially equal to the width of the PCa cylinder 30 is suitable. is there. Moreover, when such a hanging tool is used, the PCa cylinder 30 can be suspended to the lower end of the column reinforcing bar without the wire W and the reinforcing bar 2b contacting each other.

  Next, although illustration is omitted, a formwork (wooden formwork or the like) is formed in a rectangular cylinder shape upward from the upper end of the PCa cylinder 30 (the cover concrete 3a at the lower end) installed at the construction position of the RC pillar 10. Install. At this time, it is preferable to install so that the lower end part of a square cylindrical formwork may fit the upper end part of the PCa cylinder 30 inside. Then, ultra high strength concrete is cast and filled in the casting space formed in this way. Thereby, the cover concrete 3b other than the core concrete 4 and the lower end portion is integrally placed (see FIG. 1). As a result, the cover concrete 3b other than the lower end portion can be manufactured with ultra high strength concrete, and the use range of the PCa cylinder 30 made of ultra high strength high toughness concrete can be reduced. Material costs can be reduced.

<Second Embodiment>
Next, an embodiment of a reinforced concrete column structure according to claim 2 will be described in detail with reference to the drawings. In the drawings to be referred to, FIG. 5 is a cross-sectional view of the RC pillar and the lower structure according to the second embodiment. Moreover, FIG. 6 is sectional drawing which shows the formwork assembly condition of the lower structure of RC pillar which concerns on 2nd Embodiment. In addition, the same number is attached | subjected about the same member as above-mentioned 1st Embodiment, and the overlapping description is abbreviate | omitted.

(Structure of RC pillar 20)
As shown in FIG. 5, the RC column 20 includes a cover concrete 3, a core concrete 4 covered with the cover concrete 3, and a column reinforcing bar 2 (see FIG. 6). The RC column 20 is erected on a beam column joint J described later.

As shown in FIG. 5, the lower end portion of the cover concrete 3 is composed of a PCa cylinder 30 made of high strength and high toughness concrete. Further, the cover concrete 3 other than the lower end portion is formed by being cast integrally with the core concrete 4 using ultra high strength concrete.
And the lower end part 30a of the said PCa cylinder 30 is embed | buried in the concrete of the lower structure D only by the depth t equivalent to the cover thickness of the lower structure D. FIG. Thereby, the integrity of the PCa cylinder 30 and the concrete of the lower structure D is ensured. In addition, the range h in which the PCa cylinder 30 covers the lower end portion of the RC column 20 is preferably in the same range as the horizontal width of the RC column 20. The process of embedding the PCa cylinder 30 in the lower structure D will be described in detail later.

  The lower structure D is a structure (a part of the structure) constructed at the lower part of the RC pillar 20. In the present embodiment, the lower structure D is composed of an RC column Q constructed on the lower floor of the floor on which the RC column 20 is constructed, RC beams BL and BR, and a beam column joint J.

  The RC column Q of the lower structure D is located just below the RC column 20 and is made of ultra high strength concrete like the core concrete of the RC column 20 so that the axial compressive force acting on the RC column 20 can be supported. Is built.

On the other hand, the RC beams BL and BR are constructed of concrete having a compressive strength smaller than that of the ultra high strength concrete because a large axial compressive force does not act like the RC pillar 20.
In addition, in order to prevent low-strength concrete from entering the area that must be constructed with high-strength concrete, a concrete stopper is provided at the boundary between the RC beams BL and BR and the beam-column joint J as necessary. (See FIG. 6).

The beam-column joint portion J is a portion where the RC beams BL, BR and the RC column Q are joined in the lower structure D, and is made of ultra-high-strength concrete so that the axial compressive force acting on the RC column 20 can be supported. It is built using.
The RC column 20 is constructed immediately above the beam column joint J, and the lower end portion 30a of the PCa cylinder 30 constituting the lower end portion of the RC column 20 is formed between the RC column 20 and the beam column junction J. In order to improve the unity, it is embedded in the concrete of the beam-column joint J.

(Construction of RC pillar 20)
The construction of the RC pillar 20, particularly the process of embedding the PCa cylinder 30 in the lower structure D will be described in detail. As shown in FIG. 6, the PCa cylinder 30 is installed just before placing the concrete of the lower structure D, that is, when the beam reinforcement BS, the formwork K, and part of the column reinforcement 2 are assembled. The

  First, in the state where the concrete is cast up to the upper end portion of the RC column Q and hardened, the beam reinforcing bars BS of the RC beams BL ′ and BR ′ (beam main bars BSa and band bars BSb) are assembled. Also, the column reinforcing bars 2 (the main reinforcing bars 2a and the band reinforcing bars 2b) are also assembled to the required height. The beam reinforcement BS and the column reinforcement 2 intersect at the beam-column joint J ′.

  Next, the PCa cylinder 30 is installed on the upper part of the beam-column joint portion J ′. Specifically, the PCa cylinder 30 is placed on the beam reinforcing bar BS arranged in the horizontal direction so that the main reinforcing bar 2a arranged in the vertical direction is inserted into the hollow portion 31. The PCa cylinder 30 is fixed by an appropriate method so as not to move due to the pressure of the concrete when the concrete is placed.

  Then, the formwork K is assembled according to the construction dimensions of the RC beams BL ′ and BR ′. Specifically, the plywood G is installed at positions corresponding to the lower and side surfaces of the RC beams BL ′ and BR ′, and the periphery thereof is reinforced with a single pipe P. The plywood G and the single pipe P installed on the opposite side surfaces are connected and fixed by a separator (not shown). Further, for example, a pipe support PS or a frame scaffold is installed below the RC beams BL ′ and BR ′ to support the weight of the concrete to be placed.

  Next, a concrete stopper E is installed at the boundary position between the beam-column joint portion J ′ and the RC beams BL ′ and BR ′. The concrete stopper E is formed by processing expanded metal, for example, and plays a role of preventing low-strength concrete cast on the RC beams BL ′ and BR ′ from flowing into the beam-column joint J ′. Fulfill. The upper end of the concrete stopper E is in contact with the lower end of the PCa cylinder 30. That is, the PCa cylinder 30 plays the role of the concrete stopper E in the range corresponding to the cover concrete of the lower structure D (see t in FIG. 5). Therefore, the concrete stopper E can be reduced.

Then, ultra high strength concrete is placed in the beam-column joint J ′, and concrete having a predetermined strength is placed in the RC beams BL ′ and BR ′. At this time, since the boundary between the two is partitioned by the concrete stopper E and the lower end 30a of the PCa cylinder 30, the blending does not mix and can be driven from either side.
The concrete at the beam-column joint J ′ is driven to the same height as the RC beams BL ′ and BR ′. In other words, ultra high strength concrete is also poured into the PCa cylinder 30 to a predetermined height. As a result, the lower end 30a of the PCa cylinder 30 is embedded in the lower structure D.

  The preferred embodiments of the present invention have been described above with some examples. However, the present invention is not limited to these, and can be appropriately changed within the scope of the same technical idea of the present invention. .

  For example, in the present embodiment, the planar cross-sectional shape of the column is a quadrangular shape, but it may be a circular shape or an elliptical shape, or may be another polygonal shape such as a triangle, pentagon, or hexagon. Further, the cross-sectional shape of the PCa cylinder may be any shape as long as it has a hollow portion.

  The blending of ultra-high strength and high-toughness concrete and ultra-high-strength concrete is not limited to those shown in Table 1 and the like. Also good.

  In the second embodiment, the RC column Q of the lower structure D is constructed, and then the RC beams BL and BR are assembled, the PCa cylinder 30 is installed, and the formwork is assembled. These operations may be performed after assembling the reinforcing bar and formwork of the RC column Q, and the RC column Q, the RC beams BL and BR, and the beam column joint J may be simultaneously placed.

It is a perspective view showing RC pillar concerning a 1st embodiment. It is a horizontal sectional view of the RC pillar in the arrow AA shown in FIG. It is the perspective view which showed the structure of the PCa cylinder. It is the perspective view which showed the construction condition of RC pillar 1 typically. It is sectional drawing which showed the lower end part and lower structure of RC pillar which concern on 2nd Embodiment. It is sectional drawing which showed the formwork assembly condition of the lower structure of RC pillar which concerns on 2nd Embodiment. 3 is a graph schematically showing the relationship between compressive stress and strain of concrete.

Explanation of symbols

10 RC pillar 2 Column reinforcement 3 Cover concrete 3a Cover concrete at lower end 3b Cover concrete other than lower end 4 Core concrete 30 PCa cylinder

Claims (2)

It is a reinforced concrete column structure that is formed of concrete with different mix between the cover concrete at the lower end of the column and the other part concrete,
The lower end cover concrete is formed of a precast cylinder made of ultra high strength and high toughness concrete,
Reinforced concrete column structure, wherein the other portion of concrete is made of ultra high strength concrete.   The reinforced concrete column structure according to claim 1, wherein a lower end portion of the precast cylinder is embedded in concrete of a lower structure.

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