JP3759995B2 - Concrete structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention improves the steel fiber reinforced concrete, dramatically improves the bending strength and toughness of the structure, eliminates the rebar, eliminates the complexity of the bar arrangement work, speeds up the construction and reduces the construction cost Further, the present invention relates to a concrete structure capable of obtaining a dense and smooth concrete surface and a method for constructing the same.
[0002]
[Prior art]
Conventionally, when constructing a concrete structure, the main reinforcing bars are assembled, band reinforcing bars are arranged at a predetermined pitch for the purpose of reinforcing the shearing force, and after the formwork is assembled outside this, the concrete is placed in the formwork Was.
In this case, the amount and arrangement of the strip reinforcing bars are generally constructed so that the shear strength is larger than the bending strength. Therefore, the concrete structure becomes a failure mode of the bending failure preceding type, and the main reinforcing bars that reinforce the tensile force are used. The tensile toughness keeps the load bearing capacity after reaching the yield load.
[0003]
However, this conventional method for constructing a concrete structure requires a band rebar and its arrangement, and requires the production of the band rebar and the tightening with a steel wire or clip, which is cumbersome and laborious, and is thus constructed. Depending on the location conditions, the amount of rebar, and the construction of the concrete structure, there is a risk that the rebar will shear and the structure may be sheared and destroyed, which was demonstrated in the Great Hanshin-Awaji Earthquake. ing.
[0004]
Therefore, as a means for enhancing the shearing force of the concrete structure, a method of increasing the amount of the reinforcing bars and welding all the intersections with the main reinforcing bars can be considered.
However, in this case, the work of bar rebar placement is extremely complicated and time-consuming, resulting in an increase in construction costs and a prolonged construction period, as well as a decrease in fluidity because the movement of the concrete is blocked by the band rebar when placing concrete. The problem that it is easy to produce a jumper is expected.
[0005]
By the way, conventionally, in order to improve the tensile strength, bending strength, crack strength, toughness or impact resistance of concrete in roads, runways, tunnels, etc., short steel fibers such as carbon steel and stainless steel are evenly distributed. Distributed steel fiber reinforced concrete is used.
[0006]
However, this conventional steel fiber reinforced concrete is mainly for the purpose of improving cracks, and its strength is low depending on the strength of the steel fiber. It cannot be used immediately for beams and walls.
[0007]
[Problems to be solved by the invention]
The present invention solves such problems, improves the steel fiber reinforced concrete, dramatically improves the bending strength and toughness of the structure, eliminates the rebar, and eliminates the complexity of the bar arrangement work. and, Hakare reduction of faster and construction costs of construction, yet dense and smooth concrete - concrete obtained the up surface - and to provide the door structure.
[0008]
[Means for Solving the Problems]
Therefore, the invention of claim 1 is a concrete structure in which a plurality of main reinforcing bars are unconstrained and arranged in a plurality of rows inside a concrete, and steel fibers are dispersedly arranged . The steel fibers with an aspect ratio of about 50 are distributed and arranged at about 1.0 percent of the total cast concrete volume over the entire area, eliminating the steel bars and reducing the size and weight of the steel fibers. In addition to reducing the weight of the concrete structure and reducing the weight of the concrete structure, providing a dense and smooth concrete surface, increasing the mixing rate of steel fibers and improving the bending strength and toughness ratio of the structure. A practical seismic structure that receives both shear forces is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to a pillar of a building such as a building or a condominium that is a concrete structure will be described below. In FIGS. The main reinforcing bar 2 is erected in a non-restrained state at a predetermined position, that is, without restricting the reinforcing bar 2 with a conventional band reinforcing bar.
In this case, the material, dimensions, arrangement, quantity, and the like of the main reinforcing bars 2 are determined based on the building design standard in consideration of the maximum load acting on the column and the safety factor.
In addition, as shown in FIG. 2, the band reinforcement 3 may be arrange | positioned to the main reinforcement 2 at a rough pitch, and this may be restrained suitably.
[0010]
On the base 1, a mold 4 is assembled outside the main rebar 2, and concrete 6 mixed with a predetermined amount of steel fibers 5 is placed inside the frame 4.
The steel fiber 5 is formed by cutting carbon steel or stainless steel having a diameter of 0.6 mm into a length of 30 mm (aspect ratio: 50) and forming the surface in a sawtooth shape or a wave shape, and the mixing rate is the total beat. It is set to about 1.0% of the installed concrete volume.
[0011]
The condition after the concrete 6 is hardened is as shown in FIG. 4, and the steel fibers 5 are arranged in a uniform and random direction over the entire cross section of the column 7 which is a concrete structure.
The pillar 7 constructed in this way is constructed when a building such as a building or a condominium is constructed. First, concrete is placed on the constructed land to create a base 1, and at the same time a plurality of main reinforcing bars 2 are mounted on the base 1. Are assembled at predetermined intervals.
When constructing beams and walls other than columns, the main reinforcing bars 2 are assembled at predetermined intervals in the length direction thereof.
[0013]
In this case, if necessary, a small amount of rebar 3 may be used to constrain the predetermined position of the main rebar 2, so that the main rebar 2 can be prevented from shaking and the space occupied. In addition, the shear strength acting on the column 7 can be borne by the band reinforcing bar 3 and the shear strength can be enhanced.
As described above, the present invention eliminates the conventionally used band rebar 3 and eliminates the production of the band rebar 3 and its complicated bar arrangement work, thereby speeding up the construction and reducing the construction cost.
[0014]
After the main reinforcing bars 2 are assembled in this way, the mold frames 4 are assembled at positions outside them, and the concrete 6 is placed inside the mold frames 4.
A predetermined amount of steel fiber 5 is mixed in the concrete 6, and the mixing rate is set to about 1.0% of the total cast concrete volume, which is thrown together with the concrete 6 and moves in the mold 4. To fill.
[0015]
In this case, since only the plurality of main reinforcing bars 2 are arranged in the mold 4, the wraparound and fluidity of the concrete 6 are better than those in which a large number of strip reinforcing bars 3 are attached to the main reinforcing bars 2. Fill the inside of the frame 4 precisely and reliably.
Therefore, generation | occurrence | production of a jumper is prevented and a concrete surface is formed smoothly, and the effort of those repairs can be eliminated.
[0016]
If the formwork 4 is removed after the concrete 6 is hardened and the surface thereof is appropriately finished, a series of construction work of the pillars 7 is completed.
The cross section of the pillar 7 thus constructed is as shown in FIG. 4, and the steel fibers 5 are uniformly distributed over the entire area of the pillar 7, and the directions thereof are randomly arranged.
[0017]
In order to examine the shear strength of the column 7 thus constructed, the applicant made an experiment with a similar specimen.
In this shear strength test, the specimen is held vertically, a certain axial compressive stress is applied to the upper end portion thereof, and a horizontal load, that is, a shear load is applied alternately to the upper portion thereof. The yield load is set to 180 kN or more, and this is gradually increased to an integral multiple of the yield load to obtain the relationship between the displacement of the column 7 and the horizontal load. On the other hand, is the horizontal load less than 80% of the yield load? Alternatively, the experiment was terminated when the compressive load could not be maintained.
[0018]
Therefore, in this experiment, when a horizontal load corresponding to the yield load is first applied to the specimen, cracks of about 0.1 mm are generated at several locations on the specimen surface in a direction substantially perpendicular to the axial direction. The specimens are distributed obliquely at the upper and lower positions of the specimen, and these grow gradually in the shear direction, that is, approximately 45 ° with the axial direction of the specimen as the horizontal load increases. Progress gradually inside.
[0019]
In this case, even if the cracks communicate with each other, while the main rebar 2 and the steel fiber 5 are soundly interposed, they retain the load, and then the main rebar 2 resists its bending strength. When the specimen breaks, the specimen is bent and fractured along the cut surface perpendicular to the axial direction.
The horizontal load at this time was about 200 kN.
Therefore, the fracture form in this case is a bending fracture leading type, and the main rebar 2 and the steel fiber 5 absorb and hold the shear energy before the fracture, and the fracture speed is suppressed.
[0020]
FIG. 5 shows the result of the above experiment. After the yield of the main reinforcing bar 2, the displacement increases despite the fact that the load does not increase so much, and therefore the energy absorption capacity is large, and its toughness and toughness ratio (load-displacement curve). The size of the area surrounded by the horizontal axis is suggested to be large.
From the experimental results, it was found that 10 times the yield displacement of the main rebar 2 is less than 80% of the yield horizontal load, and the toughness rate can be expected to about 10.
[0021]
Next, a specimen having no main reinforcing bar 2 was prepared, and the same experiment was conducted on the specimen. As a result, the toughness ratio was zero and the horizontal load at the time of failure was about 100 kN. Therefore, the concrete structure in which only the steel fibers 5 are arranged is equivalent to a substantially brittle member because the toughness cannot be expected compared to the structure in which the main reinforcing bars 2 are arranged, and the bending strength is about 1/6 of the latter. Met.
This is considered to be due to the fact that the bond between the steel fibers 5 and the concrete 6 lacks continuity and directionality, resulting in the formation of a mosaic-like bonded body.
[0022]
Further, when a similar experiment was performed on plain concrete, the result shown in FIG. 6 was obtained.
In this experiment, after the main rebar 2 reached the yield displacement, oblique cracks presumed to be caused by shearing force occurred in the specimen at an early stage, which grew and the horizontal load was rapidly lost.
[0023]
Thus, the structure of the present invention in which the main reinforcing bar 2 is disposed on the steel fiber 5 has a toughness ratio dramatically improved as compared with a concrete structure in which only the steel fiber 5 is disposed, and its fracture mode is bending fracture. Since it is a leading type, the seismic strength is greatly improved, and it is suitable for pillars, walls, floors, piers, etc. of buildings subjected to shear loads.
[0024]
Therefore, for example, when a large earthquake occurs after the column 7 is constructed and the column 7 receives a shearing force in the horizontal direction, the main reinforcing bar 2 and the steel fiber 5 resist the shearing force and bending, and the column 7 is cracked. While preventing, the dispersion | distribution of a crack is promoted and the deformation | transformation and destruction of the pillar 7 are suppressed.
[0025]
Moreover, the toughness of the column 7 is improved by mixing the steel fibers 5 and the shock or shear load due to the earthquake is absorbed, so that the deformation and the breaking speed of the column 7 are suppressed.
As the impact and amplitude of the earthquake gradually increase, cracks begin to disperse, which grows and increases the opening width. Finally, the main rebar 2 yields and bends and breaks. In this case, cracks grow. Until the column 7 is bent and broken, the steel fiber 5 and the main rebar 2 withstand the impact and vibration of the earthquake, and when the main rebar 2 yields and breaks, the column 7 is bent and broken.
In addition, since the tensile stress is transmitted by the steel fiber 5 on the cracked surface, the shear strength of the concrete 6 itself is improved, and the failure mode of the bending failure preceding type is promoted to increase the seismic strength.
[0026]
As described above, the present invention eliminates the conventionally used band reinforcing bars in the concrete structure subjected to the shearing force. Therefore, the material cost of the reinforcing bars can be reduced and the construction cost can be reduced. This eliminates the complexity and labor of muscular work, and can be applied quickly, shortening the construction period and reducing construction costs, and placing concrete precisely and reliably.
[0027]
Further, according to the present invention, the steel fibers 5 are dispersed and arranged in the concrete 6 instead of the band reinforcing bars, and the fibers 5 and the main reinforcing bars 2 resist the shearing force and bending acting on the structure. The toughness rate and bending strength of the object are dramatically improved, and a concrete structure having sufficient seismic strength can be obtained.
In addition, by arranging the steel fibers 5 and the main rebar 2, the strength, particularly the toughness rate, of the conventional steel fiber reinforced concrete is dramatically improved, and a practical seismic concrete structure can be provided.
[0028]
【The invention's effect】
As described above, according to the first aspect of the present invention, the steel fibers having an aspect ratio of about 50 are dispersed and arranged at about 1.0 percent of the total cast concrete volume over the entire area of the concrete. Eliminate reinforcing bars, reduce the size and weight of steel fibers, achieve uniform dispersion and light weight of the concrete structure, obtain a dense and smooth concrete surface, and increase the mixing rate of steel fibers It is possible to provide a practical seismic structure that improves both the bending strength and toughness rate of the object and receives both bending and shearing forces .
[Brief description of the drawings]
FIG. 1 is a perspective view sequentially illustrating a construction method according to the present invention.
FIG. 2 is a perspective view showing another embodiment of the construction method according to the present invention, and shows a state in which the main reinforcing bars are constrained by a small number of reinforcing bars.
FIG. 3 is a perspective view showing a state of a constructed structure according to the present invention.
4 is a cross-sectional view taken along line AA in FIG.
FIG. 5 is an experimental diagram showing the relationship between load and displacement in a column shear strength experiment to which the present invention is applied.
FIG. 6 is an experimental diagram showing a relationship between load and displacement in a shear strength test of plain concrete.
[Explanation of symbols]
2 Main reinforcement 5 Steel fiber 6 Concrete 7 Concrete structure (column)

Claims (1)

In a concrete structure in which a plurality of main reinforcing bars are arranged in a plurality of rows in an unconstrained manner in a concrete and steel fibers are dispersedly arranged , an aspect ratio of about 50 is provided over the entire area of the concrete. A concrete structure characterized in that the steel fibers are distributed at about 1.0 percent of the total cast concrete volume .

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