JP2009179987A - Reinforced concrete column - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reinforced concrete column which can prevent broken pieces form being scattered together with an explosion sound in crushing and increase a limit distortion angle (toughness), when a hollow outer-shell precast concrete member filled with filling concrete and constituting the reinforced concrete column is formed of ultrahigh-strength concrete. <P>SOLUTION: This reinforced concrete column 1 is formed by arranging a main reinforcement 5 for the column inside the hollow outer-shell precast concrete member 2 in which a shear reinforcement 4 is embedded, and infilling the filling concrete 3. The hollow outer-shell precast concrete member is formed in such a manner that steel fibers with a fiber diameter of 0.1-1 mm and a fiber length of 60 mm or less are mixed into the ultrahigh-strength concrete with a compressive strength of 100 N/mm<SP>2</SP>or more at a mixing ratio which satisfies the following expression (1): R<SB>u</SB>(×10<SP>-3</SP>rad)=2.622×steel-fiber mixing ratio (vol.%)+24.525. In the expression (1), R<SB>u</SB>represents the limit distortion angle, and the steel-fiber mixing ratio (vol.%) is 2% or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, when a hollow outer shell precast concrete member constituting a reinforced concrete column filled with filling concrete is formed of ultra-high-strength concrete, it is possible to prevent debris from being scattered with an explosive sound during crushing, and Relates to a reinforced concrete column capable of increasing the limit deformation angle (toughness).

In the construction of high-rise buildings, reinforced concrete columns (hereinafter referred to as RC columns) using hollow outer shell precast concrete members (hereinafter referred to as outer shell PCa members) are employed in order to streamline construction and shorten the construction period. . The RC pillar is configured by filling the inside of the outer shell PCa member with filled concrete. For example, an RC pillar is known in which the outer shell PCa member is formed by mixing steel fibers in ultrahigh strength concrete having a compressive strength of about 80 N / mm ² (see Patent Document 1).

Further, the ultra-high strength concrete of approximately compressive strength 85N / mm ² to the outer shell PCa member, compressive strength 70N / mm ² approximately RC Columns to use a ultra-high-strength concrete to medium filling concrete are known.
JP 2004-332236 A

The present inventor conducted a force experiment in which a lateral repetitive load was applied in a state where an axial force was applied to the RC column as described above and examined the structural performance. As a result, Fc (compressive strength) was applied to the outer shell PCa member. = In the case of RC columns corresponding to the outer columns of the lower floor receiving high axial force using 100 N / mm ² class concrete, the interlaminar deformation angle is 1/200 (5 × 10 5) when subjected to a huge earthquake. ^-3 ) to 1/100 (10 × 10 ^-3 ) rad, it was found that the RC column end concrete on the compression side collapsed in an explosive manner. This phenomenon is due to the fact that the axial force acting on the outer column of the lower floor increases due to the bending moment generated by the horizontal displacement so that the high-rise part of the building protrudes outward from the low-rise part due to the seismic force. to cause. At the time of this crushing, as shown in an example of the column shear force-interlayer deformation angle curve of FIG. 5, the proof stress decreases temporarily but suddenly, so it is necessary to improve the structural performance. Moreover, since a loud explosive sound is generated at the time of crushing and fragments are scattered, it is necessary to improve it from the viewpoint of comfortability.

  The present invention was devised in view of the above-described conventional problems, and can improve the proof stress performance when the outer shell PCa member constituting the RC pillar is filled with the inside-filled concrete and is formed of ultrahigh-strength concrete. At the same time, it is an object of the present invention to provide an RC pillar capable of preventing debris from being scattered with an explosive sound during crushing.

An RC column according to the present invention is a reinforced concrete column formed by placing a column main reinforcing bar and filling in-filled concrete inside a hollow outer shell precast concrete member in which a shear reinforcing bar is embedded. A shell precast concrete member is mixed with ultra high strength concrete having a compressive strength of 100 N / mm ² or more and steel fibers having a fiber diameter of 0.1 to 1 mm and a fiber length of 60 mm or less at a mixing rate satisfying the following formula (1). Reinforced concrete pillar that is formed.
Formula (1)
Limit deformation angle R _u (× 10 ⁻³ rad) = 2.622 × Steel fiber mixture rate (volume%) + 24.525
However, steel fiber mixing rate (volume%) is 2% or less

  In the RC pillar according to the present invention, when the outer shell PCa member constituting the RC pillar is filled with the filling concrete and formed of the steel fiber mixed ultra high strength concrete, the proof stress performance and the toughness performance can be improved. It is possible to prevent debris from being scattered with an explosive sound during crushing.

  Hereinafter, a preferred embodiment of an RC pillar according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a side sectional view and a plan sectional view of an RC pillar 1 according to the present embodiment. The RC pillar 1 is formed by filling the inside concrete 3 inside the thin outer shell PCa member 2. The outer shell PCa member 2 is formed in the shape of a hollow cylinder having a square cross section. A plurality of annular shear reinforcement bars 4 are embedded in the thick portion of the outer shell PCa member 2 at appropriate intervals in the height direction. A plurality of column main bars 5 are arranged inside the outer shell PCa member 2 at appropriate intervals in the circumferential direction. The column main reinforcement 5 is disposed with a gap with respect to the inner peripheral surface of the outer shell PCa member 2. The filling concrete 3 is filled in the outer shell PCa member 2 so as to embed the column main reinforcement 5. The outer shell PCa member 2 is precast molded by a generally known molding method such as cast molding in which concrete is poured into a mold and molded, or centrifugal molding. A sheer cotter may be formed on the inner surface of the outer shell PCa member 2 in order to improve adhesion to the filling concrete 3.

In particular, the outer shell PCa member 2 is made of ultra high strength concrete having a compressive strength of 100 N / mm ² or more mixed with steel fibers 6. As the steel fiber 6, one having a fiber diameter of 0.1 to 1 mm, preferably about 0.2 to 0.6 mm, and a fiber length of 60 mm or less, preferably 15 to 30 mm is used. When the fiber diameter is less than 0.1 mm, it is difficult to knead the concrete. Moreover, it is inferior to the fluidity | liquidity of concrete. When the fiber diameter exceeds 1 mm, the effect of suppressing cracking is reduced. If the fiber diameter is 0.2 to 0.6 mm, the concrete can be easily kneaded and the fluidity of the concrete can be ensured. Moreover, a moderate crack suppression effect can be expected. When the fiber length exceeds 60 mm, it is difficult to knead the concrete. In addition, it is difficult to physically fill the fiber-containing concrete into a mold for molding the outer shell PCa member having a thickness of about 70 to 80 mm. When the fiber length is 15 to 30 mm, concrete can be kneaded. It is easy to place concrete due to its fluidity. Moreover, a moderate crack suppression effect can be expected.

The steel fibers 6 are mixed into the ultra high strength concrete at a mixing rate that satisfies the following formula (1).
Formula (1)
Limit deformation angle R _u (× 10 ⁻³ rad) = 2.622 × Steel fiber mixture rate (volume%) + 24.525
However, steel fiber mixing rate (volume%) is 2% or less

  In the above formula (1), the “limit deformation angle” means, as will be described later, the first cycle QR in the column shear force (Q) -interlayer deformation angle (R) curve obtained in the demonstration experiment. The interlaminar deformation angle when the proof stress is reduced to 80% from the maximum proof stress on the envelope of the curve. If the mixing ratio of the steel fibers 6 to the ultra-high-strength concrete exceeds 2% by volume%, the concrete cannot be properly mixed, so this is set as the upper limit.

  Below, the verification test about the structural performance of the said RC pillar 1 which resulted in the said Formula (1) is demonstrated.

(A) Outline of Experiment The demonstration test was performed using three RC column specimens “PCN-1”, “PCF-1”, and “PCN-2”. PCF-1 is a fiber reinforced RC column test body corresponding to the RC column 1 according to the present embodiment shown in FIG. 1 and has a steel fiber mixing rate of 1%. PCF-2 is a steel fiber mixing rate of 2% with respect to PCF-1. PCN-1 refers to a steel fiber mixing rate of 0% with respect to PCF-1 and PCF-2, that is, a fiber not reinforced. Table 1 shows the specifications of the three specimens.

  The three specimens are about 1/3 of the actual specimen. All were bend fracture types. In addition to steel fiber 6, 0.2% by volume of organic fiber was mixed in PCF-1 and PCF-2. In this experiment, high strength steel fibers shown in Table 2 were used as the steel fibers 6.

  Moreover, the PVA (polyvinyl alcohol) fiber shown in Table 3 was used as an organic fiber.

No fiber is mixed in the filling concrete 3. The horizontal cross-sectional dimension of the test specimen is 300 × 300 mm, the in-column height is 1080 mm, and the shear span ratio is 1.80. The thickness of the outer shell PCa member 2 is 24 mm, and a sheacotter is provided on the inner surface. The column main muscle 5 is a high strength muscle of D6 and USD 685, and the main muscle ratio pg is 2.65%. As the transverse reinforcement (shear reinforcement 4), the high strength reinforcement of SBPDN1275 is used in RB6.2, and the outer reinforcement and the core reinforcement are arranged at a pitch of 40 mm, and the transverse reinforcement ratio pw is 1.0%. Both outer shell PCa member 2 and filled concrete 3 were kneaded by mixing silica fume with ordinary Portland cement. A crushed stone having a maximum size of 10 mm was used for the concrete of the outer shell PCa member 2, and a crushed stone having a maximum size of 13 mm was used for the filling concrete 3. The target compressive strength was set to 115 N / mm ² for the outer shell PCa member 2 and to 100 N / mm ² for the filling concrete 3.

  Using a Kenken-type force device, a constant axial force was applied with a hydraulic jack, and a positive and negative alternating force was applied repeatedly in the horizontal direction, and an anti-symmetric bending moment was applied to the specimen. As a general rule, the load cycle is repeated twice each with R = ± 1/400, 1/200, 1/100, 1/67, 1/50 rad at the interlayer deformation angle (R). Considering this, R = ± 1/33, 1/25 rad was applied. The introduced axial force is 0.55 in terms of axial force ratio (η).

(B) Experimental results (a) Regarding the fracture condition, Table 4 shows the interlaminar deformation angle R when the concrete at the RC column end (see region X surrounded by a two-dot chain line in FIG. 1) collapses and the proof stress decreases. Show. The interlayer deformation angle R was 1.20 for PCF-1 and 1.06 for PCF-2, with PCN-1 as 1.

Visually, in PCN-1 in which the steel fibers 6 were not mixed, the concrete at the RC column end X collapsed with an explosive sound at about 1/200 (5 × 10 ⁻³ ) rad. Thereafter, peeling of the cover concrete progressed, and at 1/50 rad, the entire RC column end X was damaged. On the other hand, in PCF-1 in which 1% of the steel fiber 6 was mixed, damage to the RC column end portion X was slight even at 1/50 rad. It was found that the fracture situation varies greatly depending on the presence or absence of the steel fibers 6 in the ultra high strength concrete.

  When examining the situation of the RC column end X at 1/200 rad where crushing starts, in PCN-1, the cover concrete of the RC column end X is peeled off by crushing in the second cycle of this interlayer deformation angle R, and the proof stress is It was greatly reduced. In PCF-1, although some signs of crushing were seen in the concrete at the joint, almost no crushing and peeling of the cover concrete was seen in the outer shell PCa member 2.

  Thereafter, crushing occurred at 1/179 to 1/154 rad in the process of reaching the peak of the 1/100 rad cycle, and the yield strength was temporarily reduced, but the degree of the decrease was smaller than that of PCN-1. Since the crushing gradually progressed, the explosion sound generated by PCN-1 and the scattering of the cover concrete accompanying the explosion did not occur.

  In the final fracture situation, in PCN-1, the outer shell PCa member 2 was almost peeled off and the lateral reinforcing bars 4 were exposed. In PCF-1 and PCF-2, the number of cracks was small, and the cover concrete did not peel off. There was no significant difference between PCF-1 and PCF-2 in the destruction situation. It was confirmed that mixing the steel fibers 6 can reduce the degree of concrete collapse at the RC column end X and the degree of peeling of the surrounding concrete cover.

(B) Column shear force-interlayer deformation angle curve The column shear force (Q) -interlayer deformation angle (R) curve is shown in FIG. In PCN-1, the positive direction has a peak of 1/200 (5 × 10 ⁻³ ) rad, and the negative direction has collapsed in the middle of the peak of 1/100 (10 × 10 ⁻³ ) rad. Although PCF-1 and PCF-2 collapsed on the way to the peak of 1/100 rad, the decrease in yield strength accompanying the collapse was small, and an almost stable QR curve was drawn. Thereby, it turned out that the toughness improvement can be expected by mixing the steel fibers 6. The positive envelope of the QR curve is shown in FIG. In PCN-1, the yield strength decreased rapidly due to crushing at 1/200 rad, but in PCF-1 and PCF-2, the yield strength decreased temporarily on the way to 1/100 rad, but recovered immediately. ing. It was found that the tendency to decrease the yield strength due to crushing can be greatly suppressed by the mixing of steel fibers.

(C) Cracks It was confirmed by visual observation that when steel fibers 6 were mixed, the number of cracks was smaller and the crack width was narrower than when not mixed.

(D) Axial Strain Degree In PCN-1, since the peeling of the cover concrete proceeds, it is confirmed that the axial strain increases as compared with PCF-1 and PCF-2 where the cover concrete hardly peels off. In particular, it was found that the mixing of the steel fibers 6 contributes to a decrease in the axial strain when a large deformation is caused.

(E) Lateral reinforcement strain degree The degree of strain of PCF-1 and PCF-2 was somewhat smaller than that of PCN-1 at the RC column end X and the central part. In the process of crushing, it can be said that the outer shell PCa member 2 mixed with the steel fibers 6 has a smaller degree of distortion of the lateral reinforcing bars 4. When cracks expand at the time of large deformation, if the fiber length is short, even if steel fibers 6 are mixed, it is considered that the restraining effect by the fibers cannot be sufficiently obtained.

The experimental values of the relationship limit drift angle R _u and (f) a limit drift angle R _u and steel fiber incorporation ratio, together with the relationship between the average values of both positive and negative directions and mixture ratio of steel fibers limit drift angle R _u (%) As shown in FIG. Limit deformation angle R _u, of the Q-R curve obtained in the experiment, which was obtained as story drift when strength from the maximum strength in the envelope line of the Q-R curve of the first cycle drops 80% It is. From the figure, the limit deformation angle R _u the mixing ratio is increased steel fibers 6 it can be seen that a linearly increasing. A regression equation, the estimated from this equation, the limit deformation angle R _u is compared with the case where the steel fiber incorporation ratio of 0%, it can be said that an increase about 20%, the mixed 2%. Thereby, it can confirm that the reinforcement by the steel fiber 6 is effective for the improvement of toughness. Since the above regression equation is not a wide range such as several tens of percent, but a very narrow range of 0 to 2% at the most, based on three points of data of 0%, 1% and 2%, Can be identified appropriately. In a generally known kneading method and kneading apparatus, kneading becomes difficult if 2% or more of steel fibers 6 are mixed into ultrahigh strength concrete.

(G) Examination of experimental value of maximum yield strength From the experimental values shown in Table 5, as understood from the positive values, PCF-1 and PCF-2 had higher maximum yield strength than PCN-1. . It was confirmed that mixing the steel fiber 6 increases not only the toughness but also the bending strength. It is considered that the increase in the bending strength is that the restraining effect by the outer shell PCa member 2 is further increased by the mixing of the steel fibers 6.

As described above, in the RC pillar 1 according to the present embodiment, the outer shell PCa member 2 is made of ultrahigh strength concrete having a compressive strength of 100 N / mm ² or more, a fiber diameter of 0.1 to 1 mm, and a fiber length. By forming steel fibers 6 of 60 mm or less at a mixing rate that satisfies the following formula (1), the following operational effects can be obtained.
Formula (1)
Limit deformation angle R _u (× 10 ⁻³ rad) = 2.622 × Steel fiber mixture rate (volume%) + 24.525
However, steel fiber mixing rate (volume%) is 2% or less

The degree of concrete crushing at the RC column end X and the degree of peeling of the cover concrete can be reduced. It can suppress that a yield strength falls with crushing by mixing of the steel fiber 6. FIG. When the steel fibers 6 are mixed, the number of cracks is reduced and the crack width can be suppressed narrower than when the steel fibers 6 are not mixed. At the time of large deformation exceeding the interlayer deformation angle R = 1/50 (20 × 10 ⁻³ ) rad, the axial strain of the RC column 1 can be reduced by mixing the steel fibers 6. The limit deformation angle R _u increases linearly with the increase in the mixing rate of the steel fibers 6, and the limit deformation angle R _{u is set} to 20 by mixing 2 (volume%) of the steel fibers 6 as compared with the case of not mixing. % Can be increased. In the RC pillar 1 using the outer shell PCa member 2 mixed with the steel fiber 6, the restraining effect of the outer shell PCa member 2 can be enhanced. By mixing the steel fibers 6, bending strength and toughness can be increased. Thereby, in the RC pillar 1 according to the present embodiment, when the steel fiber mixed outer shell PCa member 2 which is filled with the filling concrete 3 and forms the RC pillar 1 is formed of ultra high strength concrete, the proof stress performance. In addition, the toughness performance can be improved, and the fragments can be prevented from being scattered with an explosive sound during crushing.

  Furthermore, the explosion destruction of the RC column end X can be reduced by mixing the steel fiber 6 only in the cover concrete portion where the crushing occurs, that is, the outer shell PCa member 2, thereby reducing the peeling of the cover concrete and other damages. Therefore, it is not necessary to mix fibers in the filling concrete 3, and reduction of construction cost can be achieved. In addition, mixing organic fibers can further improve the toughness, and can secure fire countermeasures assumed when applied to an actual building.

It is explanatory drawing explaining suitable one Embodiment of RC pillar concerning this invention. It is a figure which shows the graph of the QR curve in the verification test of PCN-1, PCF-1, and PCF-2. It is a figure which shows the graph of the envelope of the positive direction of the QR curve of FIG. The experimental values of the critical deformation angle R _u in demonstration of PCN-1, PCF-1, PCF-2, shown with the relationship between the average value and the mixing ratio of steel fibers in both the positive and negative directions of the limit deformation angle R _u (%) FIG. It is a figure which shows the graph of an example of the QR curve of RC pillar demonstrated by background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 RC pillar 2 Outer shell PCa member 3 Filled concrete 4 Shear reinforcement 5 Column main reinforcement 6 Steel fiber

Claims (1)

Reinforced concrete columns formed by laying column main bars inside and filling filled concrete inside hollow outer shell precast concrete members with embedded shear reinforcement,
The hollow outer shell precast concrete member is mixed with ultra high strength concrete having a compressive strength of 100 N / mm ² or more and a steel fiber having a fiber diameter of 0.1 to 1 mm and a fiber length of 60 mm or less satisfying the following formula (1). Reinforced concrete pillars formed by mixing.
Formula (1)
Limit deformation angle R _u (× 10 ⁻³ rad) = 2.622 × Steel fiber mixture rate (volume%) + 24.525
However, steel fiber mixing rate (volume%) is 2% or less

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