KR102534869B1 - Precast concrete reinforced with steel fiber of hooked type - Google Patents

Abstract

Provided is a precast concrete segment with a reinforced hooked-type steel fiber, which may improve resistance power for a weight. The hooked-type steel fiber provided by one embodiment of the present invention comprises: a central unit which extends in a straight-line form; a first refraction unit which is bent to have a first inclination angle with the central unit at one end of the central unit and extends in the straight-line form; a second refraction unit which is bent to have a second inclination angle with the central unit at the other end of the central unit and extends in the straight-line form; a third refraction unit which is bent at the first refraction unit and extends in the straight-line form; and a fourth refraction unit which is bent at the second refraction unit and extends in the straight-line form. The third refraction unit and the fourth refraction unit may extend to be parallel to the central unit. The first refraction unit and the second refraction unit may extend in different side directions based on the extension direction of the central unit.

Description

Precast concrete segments reinforced with hooked steel fibers {PRECAST CONCRETE REINFORCED WITH STEEL FIBER OF HOOKED TYPE}

The present invention relates to precast concrete segments reinforced with hooked steel fibers.

Concrete is a brittle material with low tensile strength and low elongation ability. Accordingly, it is known that when steel fibers are mixed into concrete materials that are advantageous in compression but show vulnerability to bending and tension, the fatigue resistance, bending tension, shear force, and flexibility are improved to a certain level according to the increase in the mixing amount.

However, when the steel fibers are mixed, a problem has been raised that the manufacturing cost of concrete increases, and attempts have been made to improve the physical properties of concrete while reducing the amount of steel fibers mixed.

For example, a hook-shaped steel fiber in which both ends are bent to a straight steel fiber, an arch-shaped steel fiber to which both ends are bent to an arcuate steel fiber, and a steel fiber having a ring shape with both ends spaced apart have been developed.

However, in the case of conventional hook-type steel fibers, resistance to load (i.e., anchoring effect) is low, so cracking load and breaking load are low, making it difficult to achieve effective stiffness increase.

In the case of arch-shaped steel fiber, it has the advantage of improving the overall adhesion performance with concrete, but in order to be applied to shotcrete, which is a secondary support material, floor slab, etc. during tunnel excavation, the cross section has to be reduced, and in the end, only the manufacturing cost for producing arch-shaped steel fiber is incurred. There were cases in which it rose and did not have a significant effect on improving the physical properties of concrete, and there was a problem that brittle fracture occurred at the boundary with the distal end bent in the arcuate steel fiber.

In addition, steel fibers having various shapes, for example, having a waveform, forming concave grooves on the surface to improve adhesion to concrete, or having a shape that bends the distal end multiple times have been suggested as alternatives, but the bent portion and the concave surface have been proposed as alternatives. There was a problem that brittle fracture frequently occurred in the center.

In addition, conventional hook-shaped steel fibers have a problem in that the improvement in physical properties of concrete is not large compared to the amount of mixing, since only those with bent ends are arbitrarily manufactured in factories.

Therefore, in a hook-type steel fiber having a predetermined thickness, the shape, length, and bent angle of both ends of the hook-type steel fiber bent in detail are specifically controlled to improve the physical properties of the steel fiber itself as well as the physical properties of concrete reinforced with the steel fiber. It is necessary to develop a precast concrete segment including the same.

The problem to be solved by the present invention is to specifically control the shape, length, and bent angle of both bent ends of a hook-type steel fiber having a predetermined thickness, so that not only the physical properties of the steel fiber itself but also the physical properties of the steel fiber-reinforced concrete are improved. , to provide a precast concrete segment reinforced with hooked steel fibers.

In order to solve the above problems, the present invention provides a precast concrete segment reinforced with hook-type steel fibers, wherein the hook-type steel fibers include: a central portion extending in a straight line; a first bending part bent at one end of the central part to have a first inclination angle with the central part and extending in a straight line; a second bending part bent at the other end of the central part to have a second inclination angle with the central part and extending in a straight line; a third bending part bent from the first bending part and extending in a straight line; And a fourth bend bent from the second bend and extending in a straight line shape; the third bend and the fourth bend extend parallel to the central portion, and the first bend and the The second bent part provides precast concrete segments reinforced with hook-shaped steel fibers extending in different lateral directions based on the extension direction of the central part.

According to one embodiment of the present invention, the precast concrete segment incorporating the hook-type steel fiber of the present invention has improved resistance to load compared to the conventional hook-type steel fiber, thereby improving the bending strength, residual bending tensile strength, initial cracking load, and breaking load. this can be improved.

1 shows a conventional hook-type steel fiber.
2 shows a hook-type steel fiber according to an embodiment of the present invention.
3 to 6 show hook-type steel fibers according to each embodiment of the present invention.
7 to 11 show numerical analysis test methods and results for hook-type steel fibers according to various embodiments of the present invention.
12 shows a conventional hook-type steel fiber.
13 to 15 show a mock-up test method and test results for a precast concrete segment according to an embodiment of the present invention in which hook-type steel fibers are incorporated according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention are described in detail. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms, but only the present embodiments make the disclosure of the present invention complete and provide the content of the present invention to those skilled in the art. It is provided to inform you more completely.

In this specification, when an element is referred to as being positioned 'above' or 'below' another element, this means that the element is positioned directly 'above' or 'below' another element, or an additional element is present between them. It includes all meanings that can be intervened. In this specification, the term 'upper' or 'lower' is a relative concept established from the observer's point of view, and if the observer's point of view changes, 'upper' may mean 'lower', and 'lower' may mean 'upper' could mean

In a plurality of drawings, like reference numerals denote substantially the same elements. In addition, terms such as 'comprise' or 'have' are intended to designate that the described feature, number, step, operation, component, part, or combination thereof exists, but one or more other features, numbers, or steps However, it should be understood that it does not preclude the possibility of existence or addition of operations, components, parts, or combinations thereof.

On the other hand, the form in which the first and second bends extend in different lateral directions based on the extension direction of the central portion referred to in this specification refers to the form shown in FIG. 2 as a REVERSE END HOOKED TYPE, The form in which the first bend and the second bend extend in the same lateral direction based on the extension direction of the central portion refers to the form shown in FIG. 1 as an end hooked type.

Hereinafter, it will be described in detail with reference to drawings.

1 shows a conventional hook-type steel fiber. Referring to FIG. 1, conventional hook-type steel fibers are manufactured so that both ends are bent in the same lateral direction in order to lower the manufacturing cost (END HOOKED TYPE). However, the inventors of the present invention found that when manufacturing segments by mixing such conventional hook-type steel fibers into concrete, resistance to load may be improved compared to the case where they are not mixed, but resistance to load relative to the amount of steel fiber used (i.e., Anchoring effect) was low, and it was confirmed through the test that the effect of the steel fiber incorporation was not large. That is, the inventors of the present invention set various variables that can maximize the resistance to load (ie, anchoring effect) when mixing the same amount of steel fiber, and performed various trial and error tests while performing related numerical analysis tests and field mock-up tests. After going through, I came to complete the present invention.

2 shows a hook-type steel fiber according to an embodiment of the present invention.

Referring to FIG. 2, the hook-type steel fiber 1 is incorporated into concrete and applied to improve the physical properties of the segment, and includes a central portion 10, a first bending portion 11, a second bending portion 12, and a second bending portion 12. It is composed of three bends (13) and a fourth bend (14).

The central portion 10 occupies more than half of the total length and has a shape extending in a straight line.

The first bending part 11 is bent at one end of the central part 10 to have a first inclination angle (a) with the central part 10 and extends in a straight line shape.

The second bending part 12 is bent at the other end of the central part 10 to have a second inclination angle b with the central part 10 and extends in a straight line shape.

The third bending part 13 is bent at the first bending part 11 and extends in a straight line shape. At this time, the third bending part 13 is bent to have a third inclination angle c with the first bending part 11 and extends in a straight line shape.

The fourth bent part 14 is bent at the second bent part 12 and extends in a straight line shape. At this time, the fourth bent part 14 is bent to have a fourth inclination angle d with the second bent part 12 and extends in a straight line shape.

At this time, the third bent part 13 and the fourth bent part 14 extend parallel to the central part 10, and the residual flexural tensile strength of the concrete segment in which the hook-shaped steel fiber 1 of the present invention is mixed, the initial Uniform physical properties can be achieved by easily controlling the expression of crack load, fracture load, and resistance to load (i.e., anchoring effect).

In addition, as shown in FIG. 2, the present invention is REH (Reverse End Hooked) in which the first bendable part 11 and the second bent part 12 extend in different lateral directions based on the extension direction of the central part 10. The residual flexural tensile strength, initial crack load, fracture load, and resistance to load (i.e., anchoring effect) of the concrete segment incorporating the hook-type steel fiber (1) of the present invention ) can be improved.

The angle of inclination, length, thickness, and horizontal distance of the hook-type steel fiber 1 of the present invention can be controlled, and these configurations are organically combined to form a concrete segment incorporating the hook-type steel fiber 1 of the present invention. Residual flexural tensile strength, initial crack load, breaking load, and load resistance can be improved. Hereinafter, this is explained.

The first inclination angle (a) to the fourth inclination angle (d) may be 90° to 160°, for example, 120° to 140°, and in one embodiment, 130°. When the first inclination angle (a) to the fourth inclination angle (d) have the above numerical range, the shear force of the first bending part 11 and the second bending part 12 is greatly generated, thereby improving the resistance to the load. The residual flexural tensile strength, initial crack load, and breaking load of the concrete segment incorporated with the hook-type steel fiber 1 of the present invention can be improved.

The overall length of the hook-shaped steel fiber 1 of the present invention is not particularly limited, and the length ratio can have an effect. For example, the length l 3 of the third bent part ₁₃ and the fourth bent part based on when the length l ₁₀ between both ends measured in the direction in which the central part 10 extends is 61 mm. The length (l ₄ ) of (14) is 2 to 4 mm, and the distance (h 1 ) and the distance (h ₁ ) of the third bend (13) from the central portion (10) and the distance (h) of the fourth bend (14) are spaced apart. ₂ ) is 1.5 mm to 2.3 mm, and the length (l ₁ ) of the first bent part 11 and the length (l ₂ ) of the second bent part 12 are within 0.5 to 5 mm, the first inclination angle (a) to the fourth inclination angle (d) and the distance (h ₁ ) of the third bend (13) from the central portion (10) and the distance (h ₂ ) of the fourth bend (14) may be defined. . When the hook-type steel fiber 1 of the present invention has the above length ratio, the shear force of the first bending part 11 and the second bending part 12 is generated greatly within the range in which the workability of the distal end is guaranteed, so that By improving the resistance, the residual flexural tensile strength, initial crack load, and breaking load of the concrete segment in which the hook-type steel fiber 1 of the present invention is incorporated can be improved.

The hook-shaped steel fiber 1 of the present invention may have a thickness and/or a diameter of 0.5 to 1.5 mm, for example, 0.75 mm. The aforementioned effect can be achieved by organically combining with the angle of inclination, the length, and the horizontally spaced distance within the above numerical range.

As an example, the hook-type steel fiber 1 of the present invention may have a point-symmetrical shape with respect to the center of the central portion 10.

As an embodiment, the hook-type steel fiber 1 of the present invention is the length of the first bent part 11 measured along the direction in which the first bent part 11 extends and the length of the third bent part 13 extended. The length of the third bent part 13 measured along the direction may be the same, and the length of the second bent part 12 measured along the direction in which the second bent part 12 extends and the length of the fourth bent part ( 14) may have the same length as the fourth bent part 14 measured along the extending direction.

As an example, it may have a point-symmetrical shape with respect to the center of the central portion 10 .

On the other hand, the hook-type steel fiber 1 has a straight shape and may cause poor adhesion between the central portion 10 occupying most of the total length and concrete.

As shown in FIG. 3, in one embodiment, the hook-shaped steel fiber of the present invention may have protrusions 20 formed on the surface, for example, protrusions 20 may be formed on the surface of the central portion 10a. . A plurality of projections 20 are formed, and when the area in contact with the surface of the central portion 10a is referred to as the area of the projection 20, the adjacent projections 20 are spaced at a distance greater than or equal to the area of the projection 20. It can be formed spaced apart. Accordingly, adhesion between the central portion 10a and concrete can be improved.

As shown in FIG. 4, in one embodiment, the protrusion may include a first protrusion 21 in contact with the surface of the central portion 10b and one or more second protrusions 22 formed on the first protrusion 21. there is. Accordingly, adhesion between the central portion 10b and concrete can be improved.

As shown in FIG. 5, in one embodiment, the protrusion includes a first protrusion 21 in contact with the surface of the central portion 10c, one or more second protrusions 22 formed on the first protrusion 21, and a second protrusion. It may include one or more third projections 23 formed on (22). Accordingly, adhesion between the central portion 10c and concrete can be improved.

As shown in FIG. 6, in one embodiment, the hook-type steel fiber may have steel fiber cilia 24 protruding in the form of cilia from the protrusions described above. The thickness of the steel fiber cilia 24 may be formed to be 0.001 to 0.1 times the thickness of the hook-type steel fiber. Accordingly, adhesion between the central portion 10d and concrete can be improved. At this time, the steel fiber cilia 24 include first steel fiber cilia (not shown) protruding from the above projections in the form of cilia, second steel fiber cilia (not shown) extending in the form of cilia from the side surface of the first steel fiber cilia, and the first steel fiber cilia (not shown). It may include third filament cilia (not shown) extending in the form of cilia on the side of the filamentous filament. Accordingly, a network structure is formed by the first, second, and third steel fiber cilia in the space between the above-mentioned protrusions, so that the adhesion performance between the central portion 10c and the concrete can be greatly improved.

In one embodiment, the protrusions 20, 21, 22, and 23 described with reference to FIGS. 3 to 6 may be continuously formed in a spiral shape along the surfaces of the central portions 10a, 10b, 10c, and 10d (not shown). ). Accordingly, improved uniformity of quality of the hook-type steel fibers due to the inclusion of the protrusions 20, 21, 22, and 23 can be ensured.

Hereinafter, the inventors of the present invention hook-type steel fibers of the present invention to improve the residual flexural tensile strength, initial crack load, breaking load, and resistance to load of the concrete segment in which the hook-type steel fibers (1) of the present invention are incorporated. The results of numerical analysis tests and on-site mock-up tests on the inclination angle, length, thickness, and distance in the horizontal direction of (1) are explained.

Test Example 1: Numerical analysis test

In this test example, MIDAS GTS NX was used as a numerical analysis program, and as shown in FIG. The analysis conditions are as follows.

-Concrete: Physical properties were entered as concrete stiffness, and boundary conditions were set as fixed.

-Steel fiber: a circular shape with a diameter of 1mm, the length of the first bent part 11 measured in the direction in which the first bent part 11 extends and the third bent part 13 measured in the direction in which the third bent part 13 extends. The length of the bent part 13 is the same

-Pulling force: Pulling out from the surface of the third bend (13), which is the end of the steel fiber, at 100kg

-Shear force analysis: Since the shear force is large, it means that the member force generated in the steel fiber increases due to the anchoring effect, so it is measured by the amount of shear force generated at the first bend (11). If the shear force is 2.00E-06 or more, it is interpreted as having a higher effect than the conventional hook-type steel fiber

Test Example 1-1: Numerical analysis results according to the change of the third inclination angle

In the hook-type steel fiber of the present invention, 90 °, 100 °, 110 °, 120 °, 130 °, 140 °, 150 °, and 160 ° were input as variables of the third inclination angle (c).

The shear force analysis results according to the change of the third inclination angle (c) are shown in FIGS. 8 and 9.

8 and 9, it was found that the shear force was 2.00E-06 or more when the third inclination angle (c) was 120° to 140°, and in particular, the shear force was the highest when the third inclination angle (c) was 130°. appeared to be large.

Test Example 1-2: Numerical analysis results according to the length of the third bend

In the hook-type steel fiber of the present invention, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, and 5.0 mm were input as the length variable of the third bent part 13.

The shear force analysis results according to the change of the third bend 13 are shown in FIGS. 10 and 11 .

Referring to FIGS. 10 and 11 , when the length of the third bent part 13 is 1.0 mm to 4.0 mm, it is found that the shear force is 2.00E-06 or more. However, since it is extremely inefficient to bend the third bendable part 13 and the fourth bendable part 14 twice with a length of 1mm in the industrial field, it is recommended that the length of the third bent part 13 is 2.0mm to 4.0mm. appeared to be desirable. However, as the lengths of the third and fourth bends 13 and 14 increase, the shear force decreases, and considering the ease of manufacture in industrial settings, the length of the third bend 13 is 2.0 mm to 3.0 mm. mm was found to be preferred.

Test Example 2: mock-up test

In this test example, it was confirmed through actually manufactured concrete segments that the load resistance of the concrete segment incorporating the hook-type steel fiber 1 according to an embodiment of the present invention is improved compared to the conventional concrete segment incorporating the hook-type steel fiber. did

Test Example 2-1: Flexural toughness test

In this test example, a 3-point bending test was performed according to EN 14651:2005 on a concrete segment (30 in FIG. 13) manufactured by incorporating the hook-type steel fiber 1 according to an embodiment of the present invention. The hook-shaped steel fiber 1 according to the embodiment of the present invention used in this test example has a length of 61 mm between both ends measured in the direction in which the central portion extends, and the third bent portion 13 and the fourth The length of the bend 14 is 2 to 3 mm, and the distance between the third bend 13 and the fourth bend 14 from the central portion 10 (h ₁ , h ₂ ) is 1.5 mm to 2.3 mm. mm, the first inclination angle (a) and the second inclination angle (b) are 120 ° to 140 °, for example, 130 °, and the overall shape is point symmetrical with respect to the center of the central portion 10 It was applied.

The test was conducted at the age of 28 days by manufacturing a 150 × 150 × 550 mm prismatic specimen according to ASTM test standards. After curing in water until the required age, a notch with a depth of 25 mm was given to the lower part of the specimen 24 hours before the bending test, and a clip gauge fixing jig was attached to the center around the notch.

The test piece was prepared as follows.

Example 1: REH (1100) (30 kg/m ³ )

Fabrication of seven concrete segments (#1 to #7, see Table 1) with a strength of 45 MPa incorporating 30 kg/m ³ of hook-type steel fiber according to an embodiment of the present invention with a tensile strength of 1100 MPa

Example 2: REH (1200) (30 kg/m ³ )

Fabrication of seven concrete segments (#1 to #7, see Table 1) with a strength of 45 MPa incorporating 30 kg/m ³ hook-type steel fiber according to an embodiment of the present invention with a tensile strength of 1200 MPa

Comparative Example 1: EH (1100) (30 kg / m ³ )

Three concrete segments (#1 to #3, see Table 1) with a strength of 45 MPa incorporating 30 kg/m ³ of hook-type steel fibers with a tensile strength of 1100 MPa, the hook-type steel fibers have the shape shown in FIG.

Specimens that satisfy the age and have been pretreated are subjected to CMOD (Crack Mouth Opening Displacement) 0.05 mm/min up to 0.1 mm at the speed suggested in EN 14651:2005 using a displacement control UTM (Shimadzu, Japan) with a capacity of 250 kN. The bending performance test was conducted based on the loading speed of 0.2 mm/min up to CMOD 4 mm.

After conducting the flexural performance test, the flexural strength, residual flexural tensile strength, and load-crack opening displacement (CMOD) curves of the specimen were obtained. The flexural strength was calculated by the formula below.

The residual flexural tensile strength was calculated by the following formula using the resistance load value according to the crack opening displacement (CMOD) of 0.5 mm, 1.5 mm, 2.5 mm, and 3.5 mm.

The flexural toughness test process performed according to this test example is shown in FIG. 13, Example 1 (REH (1100) (30kg/m ³ )), Example 2 (REH (1200) (30kg/m ³ )) , The test results according to Comparative Example 1 (EH (1100) (30kg/m ³ )) are shown in Table 1 below.

Here, F _LOP is the flexural strength, and f _R1 to F _R4 represent the residual flexural tensile strength when the crack opening displacement (CMOD) is 0.5 mm, 1.5 mm, 2.5 mm, and 3.5 mm, respectively.

Referring to Table 1, in the case of the concrete segment 30 incorporating the hook-type steel fiber 1 manufactured according to an embodiment of the present invention, the first bending part 11 and the second bending part 12 are at the central part. It was found that the flexural strength was significantly higher than that of the concrete segment incorporating the conventional hook-type steel fiber (Comparative Example 1, see FIG. 12) extending in the same plane centered on.

In addition, in the case of the concrete segment 30 incorporating the hook-type steel fiber 1 manufactured according to an embodiment of the present invention, the first bending part 11 and the second bending part 12 are centered around the central part 10 Residual deflection in all sections of Crack Opening Displacement (CMOD) of 0.5 mm, 1.5 mm, 2.5 mm, and 3.5 mm compared to concrete segments incorporating conventional hook-type steel fibers (Comparative Example 1, see FIG. 12) extending in the same plane. It was found that the tensile strength was greatly improved.

In addition, in the case of the concrete segment 30 in which the hook-type steel fiber 1 is mixed according to an embodiment of the present invention, the first bending part 11 and the second bending part 12 have the same tensile strength, but the central part ( 10), the flexural strength was increased by 18.3%, and the residual flexural tensile strength was increased by 18.3% compared to the concrete segment incorporating the conventional hook-type steel fiber (Comparative Example 1, see FIG. 11.9% when the crack opening displacement was 1.5 mm, 16.6% when the crack opening displacement was 2.5 mm, 24.2% when the crack opening displacement was 2.5 mm, and 24.4% when the crack opening displacement was 3.5 mm.

Test Example 2-2: Test in real life

In this test, a bending test of the TBM segment (40 in FIG. 14) was performed.

The test piece was prepared as follows.

Example 3

A hook-type steel fiber (1) according to an embodiment of the present invention having a tensile strength of 1100 MPa is mixed with 30 kg/m ³ and a reinforcing bar amount of 199 kg/m ³ TBM segment (40)

Comparative Example 2

A TBM segment in which 30 kg/m ³ of hook-type steel fiber having a tensile strength of 1100 MPa is mixed and the amount of reinforcement is 199 kg/m ³ , and the hook-type steel fiber has the shape shown in FIG. 12

Comparative Example 3

TBM segment with 324 kg/m ³ reinforcing bars without mixing of hook-type steel fibers

As shown in the conceptual diagram shown in FIG. 14 (a), 2 points were loaded on the arch part as both ends movable points for 1 piece (standard type, A-Type) of the TBM segment 40, and the initial crack load while gradually increasing the load and breaking load were measured. In this live loading test shown in FIG. 14(b), a hydraulic actuator (maximum loading capacity of 400 tons) installed in the center of the loading system was used to load the top of the specimen. As a result of the test in real life, the state of the TBM segment 40 is shown in FIG. 15, and the test results are shown in Table 2.

Average value of initial crack load test (3 times) (MPa) Average value of breaking load test (3 times) (MPa) Example 3 (REH) 24.3 58.9 Comparative Example 2 (EH) 22.3 58.3 Comparative Example 3 (rebar) 11.09 50.7

Referring to Table 2, the TBM segment (standard type, A-Type) 40 mixed with the hook-type steel fiber 1 according to an embodiment of the present invention has a significantly higher initial value than that of Comparative Example 3 in which only reinforcing bars are mixed. It was found to have crack load values and fracture load values.

In addition, the TBM segment (standard type, A-Type) incorporating the hook-type steel fiber according to an embodiment of the present invention has the same tensile strength, but the first and second bends have the same side surface based on the extension direction of the central part. Compared to the conventional hook-type steel fiber extending in the direction (Comparative Example 2, see FIG. 13), the initial cracking load value was improved by about 20%, and the breaking load value was also higher.

As described above, the detailed description of the present invention has been made by the embodiments with reference to the accompanying drawings, but since the above-described embodiments have only been described as preferred examples of the present invention, it is believed that the present invention is limited only to the above embodiments. Should not be understood, the scope of the present invention should be understood as the following claims and equivalent concepts.

For example, the drawings are schematically shown with each component as the main body to aid understanding, and the thickness, length, number, etc. of each component shown may differ from the actual one in the progress of drawing. In addition, the material, shape, dimensions, etc. of each component shown in the above embodiment are only examples and are not particularly limited, and various changes are possible within a range that does not substantially deviate from the effects of the present invention.

1: hooked steel fiber
10, 10a, 10b, 10c, 10d: central portion
11: first bend
12: second bend
13: third bend
14: 4th bend
20: projection
21: first protrusion
22: second protrusion
23: 3rd protrusion
24: steel fiber cilia
30: concrete segment
40: TBM segment

Claims (5)

In the precast concrete segment reinforced with reverse hooked steel fiber (REVERSE END HOOKED TYPE),
The reverse hook-type steel fiber,
a central portion extending in a straight line;
a first bending part bent at one end of the central part to have a first inclination angle with the central part and extending in a straight line;
a second bending part bent at the other end of the central part to have a second inclination angle with the central part and extending in a straight line;
a third bending part bent from the first bending part and extending in a straight line; and
a fourth bend bent from the second bend and extended in a straight line;
composed of,
The third and fourth bends extend parallel to the central portion,
The first bending part and the second bending part extend in different lateral directions based on the extension direction of the central part,
Based on a length of 61 mm between both end portions measured in the direction in which the central portion extends, the length of the third and fourth bends is 2 mm to 4 mm, and the third bend from the central portion And the distance at which the fourth bend is spaced apart from each other is 1.5 mm to 2.3 mm,
The thickness is 0.5 mm to 1.5 mm,
The first tilt angle and the second tilt angle are 130 °,
It has a shape that is point symmetrical with respect to the center of the central portion,
The precast concrete segment reinforced with the reverse hook-type steel fiber (REVERSE END HOOKED TYPE) has the same tensile strength as the hook-type steel fiber, but the first bending part and the second bending part are based on the extension direction of the central part Compared to concrete segments incorporating end hooked steel fibers extending in the same lateral direction, the flexural strength is increased by more than 10%, and the residual flexural tensile strength in the range of crack opening displacement 0.5mm to 3.5mm is increased by more than 10% Characterized in that, a precast concrete segment reinforced with reverse hook-type steel fibers.
delete delete delete The method of claim 1,
The precast concrete segment reinforced with the reverse hooked steel fiber (REVERSE END HOOKED TYPE) is a TBM segment,
The initial cracking load value measured as a two-point load on the arch portion as the movable point at both ends of the TBM segment is that the TBM segment mixed with the reverse hook-type steel fiber has the same tensile strength as the reverse hook-type steel fiber However, the first bend and the second bend are increased by 15% or more compared to TBM segments incorporating hook-type steel fibers (END HOOKED TYPE) extending in the same lateral direction based on the extension direction of the central portion. A precast concrete segment reinforced with reverse hooked steel fibers.

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