KR100483915B1 - Concrete structure with fiber reinforced plastic bar as reinforcement thereof - Google Patents

Abstract

The present invention relates to a concrete structure for improving ductile behavior by improving the attachment structure of a fiber-reinforced plastic bar functioning as a reinforcement in a concrete bending member such as a slab or a beam. The concrete structure includes a concrete body having a slab or beam shape, and concrete A fiber reinforced plastic bar is inserted and attached to one surface of the concrete body along the longitudinal direction of the main body and functions as a reinforcement material. The fiber reinforced plastic bar includes an attachment part attached to the concrete body through an attachment material, and an unattached non-attached material to the concrete body. Consists of parts. Therefore, the concrete body exhibits ductile behavior until the fiber-reinforced plastic bar is destroyed after cracking due to bending load or bending moment, and suppresses brittle fracture, thereby improving safety and structural reliability of the concrete structure. The non-bonding method of the fiber-reinforced plastic bar can be applied to both the portion receiving the constant moment and the parent portion in the bending member.

Description

Concrete structures using fiber-reinforced plastic bars as stiffeners {CONCRETE STRUCTURE WITH FIBER REINFORCED PLASTIC BAR AS REINFORCEMENT THEREOF}

The present invention relates to a concrete structure using a fiber-reinforced plastic bar as a reinforcement, and more particularly, to a concrete structure to improve the attachment structure of the fiber-reinforced plastic bar to the concrete structure to ensure ductile behavior.

In general, concrete is strong in compression but weak in tension, and most concrete structures reinforce tensile load by using reinforcing bars. However, since rebar is corroded over time, the structural performance and durability deterioration due to the corrosion of reinforcing bars, especially in social indirect facilities such as marine structures and reinforced concrete structures of civil engineering and reinforced concrete buildings of construction, are a big problem. Is emerging.

Therefore, as a reinforcement of concrete structures to replace the reinforcing bar, it has excellent strength, has little concern about corrosion, and is lighter than rebar, which can reduce the weight of concrete structure. Abbreviated as FRP Bar ').

The FRP bar is installed on bending members such as slabs and beams using a conventional Near Surface Mounted (NSM) method, and the FRP bar is a surface embedded method according to the prior art in FIGS. 13 and 14, respectively. The flexural member to which the bar was attached and the side cross section around the FRP bar were enlarged.

The prior art bending member 50 forms the groove 51 in the surface of the bending member 50 along the longitudinal direction of the bending member 50, and inserts the FRP bar 52 into the groove 51 inside. Next, the FRP bar 52 is fixed therein by filling the groove 51 with an adhesive 53 such as epoxy. At this time, the FRP bar 52 is attached to the bending member 50 over the entire surface of the FRP bar 52 through the attachment member 53.

However, despite the above-mentioned advantages, the FRP bar 52 used as a substitute for rebar has a brittle property that breaks at a moment when a tensile load, a bending load, or a bending moment is applied to the FRP bar 52. It has a very weak disadvantage.

FIG. 15 is a stress (σ) -strain (ε) plot for tensile load of a typical FRP bar, where the FRP bar is linearly elastic until tensile load is applied to reach maximum stress Shows brittle tendency to break. This property is because the reinforcing fibers of the FRP bar are arranged side by side along the length direction of the FRP bar, and therefore the FRP bar is temporarily destroyed at the maximum elongation of the reinforcing fiber itself.

Therefore, due to the brittle characteristics of the FRP bar 52 described above, the bending member 50 using the FRP bar 52 as a reinforcing material exhibits an aspect that is temporarily destroyed after reaching the maximum strength. FIG. 16 is a load (P) -deflection (δ) diagram for explaining the bending behavior of the bending member shown in FIG. 13, wherein the bending member is deflected due to bending load and then immediately after reaching the maximum strength. Loss of strength results in brittle fracture.

However, the flexural members such as slabs and beams used in the building must secure the ductile behavior, that is, to maintain the strength for a certain period after reaching the maximum strength for the safety of the structure. Therefore, the conventional concrete bending member has a disadvantage of causing material loss because it uses more FRP bars than necessary by applying a large safety factor to prevent brittle fracture.

Therefore, the present invention is to solve the above problems, an object of the present invention is to improve the structural reliability by reducing the brittle fracture by improving the attachment structure of the fiber-reinforced plastic bar to the concrete structure, ensuring the ductile behavior To provide a concrete structure that can be made.

In order to achieve the above object, the present invention,

A concrete body formed of a slab or beam shape, and a fiber reinforced plastic bar embedded in one surface of the concrete body along the longitudinal direction of the concrete body and functioning as a reinforcement material, wherein the fiber reinforced plastic bar is attached to the concrete body through the attachment material; The present invention provides a concrete structure that is composed of an unattached portion that is not attached to a concrete body, and exhibits a ductile behavior until the concrete body breaks after the fibrous reinforced plastic bar after the cracking due to a bending load or a bending moment.

Preferably, the attachment portion is located at both ends of the fiber reinforced plastic bar, and the non-attachment portion is located at the center except for the attachment portion of the fiber reinforced plastic bar.

Preferably, the fiber-reinforced plastic bar is composed of a rod-like resin layer and a group of fibers in which two or more kinds of fibers having different elongation are mixed in the resin layer, and the low elongation of the fiber group is first broken. It is then made of a fiber-reinforced plastic bar of multi-fiber structure that plastically deforms until the high elongation of the fiber group is destroyed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view of a concrete structure according to an embodiment of the present invention, Figures 2 and 3 are cross-sectional views of the line AA and BB of Figure 1, respectively, showing a beam (beam) as an example of the concrete structure to function as a bending member. .

The bending member 1 according to the present embodiment is inserted into one surface of the concrete body 2 along the longitudinal direction of the concrete body 2, the fiber-reinforced plastic bar (3) (functioning as a reinforcing material) Hereinafter, the FRP bar 3 is abbreviated as 'FRP bar', and only a part of the FRP bar 3 is attached to the concrete body 2 through the attaching material 4 to allow ductile behavior of the bending member 1. .

More specifically, the concrete body 2 forms a groove 2a for inserting the FRP bar 3 in one end thereof, and the groove 2a is filled with an adhesive 4 such as epoxy and filled with the FRP bar ( 3) is attached to the concrete body (2). At this time, the FRP bar (3) is attached to the concrete body (2) attached to the concrete body (2) through the attachment member 4, and is separated from the attachment material (4) by a certain distance is not attached to the concrete body (2) It consists of an unattached part (D).

The FRP bar 3 attaches, for example, a tube 5 having a diameter larger than the diameter of the FRP bar 2 on the outer circumference corresponding to the non-attachment portion D, and with the tube 5 mounted. It may be inserted into the groove 2a of the concrete body and attached to the concrete body 2 through the attachment material 4. The FRP bar 3 thus forms an unattached portion D by the spacing between the FRP bar 3 and the tube 5.

Preferably, the non-attachment part D is formed at a portion where cracking is likely to occur when a bending load or a bending moment is applied to the bending member 1, and, for example, when a bending load is applied to the center portion of the bending member 1. The attachment part D is located in the center part of the bending member 1 in which a crack easily occurs. And the attachment portion (C) is located at both ends of the FRP bar (3) to firmly fix the entire FRP bar (3) inside the concrete body (2).

Thus, when the non-attachment part D is formed around the dangerous end surface of the bending member 1, when a crack generate | occur | produces in the bending member 1 by a bending load or a bending moment, the FRP bar ( The strain of 3) is determined according to the curvature of the bending member 1 irrespective of the increase in the crack width occurring in the bending member 1. Therefore, the bending member 1 can prevent a brittle fracture by securing a predetermined soft section.

Here, the FRP bar 3 to be applied to the bending member 1, as shown in Figure 4, a plurality of reinforcing fibers 11, for example carbon fiber or glass fiber inside the rod-shaped resin layer 10 These may be made of a fiber-reinforced plastic bar of a single fiber structure arranged along the longitudinal direction of the resin layer (10).

In addition, as shown in FIG. 5, the FRP bar is a mixture of two or more different fiber groups having different elongation in the resin layer, so that the low elongation of the fiber group is destroyed first and then the high elongation of the fiber group is obtained. It may be made of a multi-fiber structured FRP bar that plastically deforms until fracture.

The FRP bar 20 of the multi-fiber structure is, for example, a plurality of first fibers 21 having a small elongation is arranged in the longitudinal direction of the first resin layer 22 inside the first resin layer 22 The first mother body 23 and the plurality of second fibers 25 having a higher elongation than the first fibers 21 in the second resin layer 24 surrounding the outer circumferential surface of the first mother body 23 are the first mother body. It consists of a 2nd matrix 26 organized in grid shape surrounding (23).

The FRP bar 20 of the multi-fiber structure is a tensile load by structurally arranging the first fibers 21 side by side along the longitudinal direction of the first matrix 23, in addition to the material of the fibers with different elongation. The elastic modulus of the FRP bar 20 is increased by causing the first matrix 23 to break at the ultimate elongation of the first fiber 21 itself under the conditions.

In addition, the FRP bar 20 having a multi-fiber structure is a second fiber 25 having a high elongation, and surrounding the first fiber 21 having a low elongation to form the second fiber 25 in a lattice shape to form a second fiber 25. ) To increase its strain as much as possible. As a result, the FRP bar 20 secures a plastic deformation section under tensile conditions and improves shear strength.

FIG. 6 is a stress (σ) -strain (ε) plot for tensile load of a FRP bar having a multi-fiber structure, in which the FRP bar 20 is subjected to initial failure at which the first fiber 21 is broken (point A in the drawing). Afterwards, it shows a high plastic deformation zone of 3% or more in elongation strain while repeating the increase and decrease of stress until the final breakdown of the second fiber 25 occurs.

7 is a stress (σ) -strain (ε) diagram for shear load of a FRP bar having a multi-fiber structure, wherein the FRP bar 20 surrounds the first fiber 21 with a first resin layer 22. After the initial fracture (indicated by the point B in the graph), the second fiber 25 having a high elongation supports the shear load, and then the local failure of the second matrix 26 without destroying the second resin layer 24. By the final tendency to break.

As described above, the flexural member 1 according to the present embodiment may use both the aforementioned single fiber structure FRP bar and multiple fiber structure FRP bar, but the FRP bar having excellent tensile and shear properties as reinforcement material may be used as the reinforcement material. More preferred.

Hereinafter, the failure mechanism of the flexural member to which the FRP bar of the multi-fiber structure is applied as the reinforcement in the configuration of FIG. 1 will be described with reference to FIGS. 8 and 9.

First, when the bending load P acts on the center of the bending member 1 having a length L as shown in FIG. 8 (a), FIG. 8 (b) is a bending moment diagram of the bending member, in which the bending load P is applied. The maximum bending moment M _max of PL / 4 occurs at the center of the flexure member 1. 8 (c) is a strain diagram of the FRP bar at a stage before cracking occurs in the flexural member, and the FRP bar 20 is deformed according to the strain property thereof so that the flexural member 1 to which the bending load P is applied. Represents the maximum strain (ε _max ) at the center of.

FIG. 9 (a) is an enlarged view of a portion of a flexure member in which cracking occurs due to a bending load. When bending cracking occurs in a portion that receives a maximum bending load, the portion of the portion where the FRP bar 20 is located as the load increases. The crack width w increases. At this time, since a part of the FRP bar 20 is not attached to the dangerous cross section of the bending member 1, the FRP bar 20 is shown in Fig. 9 (regardless of the increase in the crack width in the bending member 1). It exhibits a constant average strain ε _average as shown in b).

Therefore, the flexural member 1 according to the present embodiment exhibits a constant average strain as shown in FIG. 9 (b) without causing brittle fracture of the FRP bar 20 even when a crack occurs due to the bending load P. FIG. In addition, even after the bending member 1 reaches the maximum strength, ductile behavior is secured.

FIG. 10 is a schematic diagram of a simple supported reinforced concrete flexural member subjected to a bending load. The minimum unattached length for securing ductile behavior under extreme conditions in the illustrated flexural member 1 is shown in the following equation. At this time, the FRP bar used for the bending member 1 shown here consists of the FRP bar 20 of the multi-fiber structure mentioned above.

Where L _ub is the unattached length of the FRP bar 20, ε _p is the strain at yield of the FRP bar 20, ε _cu is 0.003, f _ck is the compressive strength of the concrete, β ₁ is the equivalent stress block of the compression stage Depth factor, b is the width of the flexural member 1, d _F is the distance from the compression end to the center of the FRP bar 20, A _s is the cross-sectional area of the tension bar 28, f _y is the yield of the tension bar 28 Strength, A _f is the cross-sectional area of the FRP bar 20, sigma _p is the yield strength of the FRP bar 20, L is the distance between the flexure members 1, f is 10 for a three-point load, equal distribution load or 4 3, d _s for the point load represents the distance from the compression end to the center of the tensile reinforcement 28, and ω _max represents the maximum width of the section to yield upon failure of the FRP bar 20 (see FIG. 11).

Next, in each of the reinforced concrete beam according to the present embodiment in which a part of the FRP bar is not attached to the concrete body, and the reinforced concrete beam according to the prior art in which the entire FRP bar is attached to the concrete body, the reinforced concrete beam by bending load Explain the results of the behavior test. At this time, the FRP bars used in the experiments of the Examples and Comparative Examples are all FRP bar of the multi-fiber structure described above, the conditions of the reinforced concrete beams applied in the Examples and Comparative Examples experiment are shown in Table 1 below. The length of the FRP bar used in the experiment was a total of 2.0m, of which the non-adhesive length was 1.2m in Example 1, 0.8m in Example 2.

Reinforced concrete beam rebar FRP Bar Force type Width (mm) Depth (mm) Length (mm) Seal compression At surrender Cross section (mm ² ) Depth (mm) At surrender At break Cross section (mm ² ) Depth (mm) Cross section (mm ² ) Depth (mm) Strength (kg _f / cm ² ) % Strain Strength (kg _f / cm ² ) % Strain Strength (kg _f / cm ² ) % Strain 150 250 2500 254 220 142 30 3000 0.0015 63.6 20 6700 1.344 6700 3.507 3 points

Under the experimental conditions of the above table, the behavior test of the reinforced concrete beam according to the present embodiment was carried out twice, and the behavior test of the reinforced concrete beam according to the prior art was performed twice, compared with Examples 1 and 2 in FIG. The load-deflection diagrams of reinforced concrete beams measured by Examples 1 and 2 are shown.

As shown, the reinforced concrete beams of Examples 1 and 2 exhibited ductile behavior after reaching the maximum strength to maintain maximum strength, but the strength dropped sharply after reaching the maximum strength of Comparative Examples 1 and 2, respectively. And brittle destruction. Therefore, it can be confirmed that the bending member according to the present embodiment, in which a part of the FRP bar is not attached, has high ductility without causing brittle fracture as compared with the bending member according to the prior art.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the range of.

As described above, the concrete structure according to the present invention exhibits a ductile behavior that maintains the strength for a certain period of time after reaching the maximum strength, thereby suppressing brittle fracture and greatly improving the safety and structural reliability of the concrete structure. In addition, the concrete structure according to the present invention can apply an appropriate safety factor in using the reinforcement, it is possible to prevent material waste due to the use of excessive reinforcement.

1 is a schematic view of a concrete structure according to an embodiment of the present invention.

2 and 3 are cross-sectional views taken along line A-A and line B-B of Fig. 1, respectively.

4 and 5 is a schematic view of the FRP bar applicable to the concrete structure of the present invention.

6 and 7 are stress-strain diagrams for tensile loads and stress-strain diagrams for shear loads, respectively, of a multi-fiber structure FRP bar.

8 and 9 are schematic views for explaining the failure mechanism of the bending member to which the FRP bar made of a multi-fiber structure.

10 is a schematic view of a simple supported bending member subjected to a bending load.

11 is a partially enlarged view of a bending member for explaining the maximum deformation width of the FRP bar.

12 is a load-deflection diagram of reinforced concrete beams according to an embodiment of the present invention and reinforced concrete beams according to the prior art.

Figure 13 is a schematic view of a concrete structure with a FRP bar attached to the surface embedding method according to the prior art.

14 is an enlarged cross-sectional view of the periphery of the FRP bar shown in FIG.

15 is a stress-strain plot of tensile load of a typical FRP bar.

16 is a load-deflection diagram of the concrete structure shown in FIG.

Claims (5)

A concrete body formed of a slab or beam shape, and a fiber-reinforced plastic bar embedded in one surface of the concrete body along the longitudinal direction of the concrete body and functioning as a reinforcing material, The fiber reinforced plastic bar includes an attachment part attached to the concrete body through an attachment material and an unattached part not attached to the concrete body so that the fiber reinforced plastic bar is destroyed after the concrete body is cracked due to a bending load or a bending moment. Concrete structures characterized by exhibiting ductile behavior until. The method of claim 1, The attachment portion is located at both ends of the fiber-reinforced plastic bar, the non-attachment portion is located in the center of the fiber-reinforced plastic bar except the attachment portion. The method of claim 1, The fiber-reinforced plastic bar is a concrete structure consisting of a rod-shaped resin layer and a plurality of reinforcing fibers arranged along the longitudinal direction of the resin layer inside the resin layer. The method of claim 1, The fiber-reinforced plastic bar is composed of a rod-shaped resin layer and a group of fibers in which two or more kinds of fibers having different elongation are mixed in the resin layer, and a high elongation after the low elongation of the fiber groups is first broken out of the fiber groups. The concrete structure which plastically deforms until the fiber group of the fiber is destroyed. The method of claim 1, A concrete structure in which the unattached length of the fiber reinforced plastic bar for the concrete body satisfies the following conditions. Where L _ub is the unattached length of the FRP bar, ε _p is the strain at yield of the FRP bar, ε _cu is 0.003, f _ck is the compressive strength of the concrete, β ₁ is the equivalent stress block depth coefficient of the compression end, b is the bending The width of the member, d _F is the distance from the compression end to the center of the FRP bar, A _s is the cross-sectional area of the tensile bar, f _y is the yield strength of the tensile bar, A _f is the cross-sectional area of the FRP bar, σ _p is the yield strength of the FRP bar , L is the distance between the flexural members, f is 10 for three-point loads, 3 for equally distributed or four-point loads, d _s is the distance from the compression end to the center of the tension bar, and ω _max is the fracture of the FRP bar. It represents the maximum width of the section to yield time.