JP4519088B2 - Reinforced concrete member lap joint reinforcement method - Google Patents

Description

  The present invention relates to a method for reinforcing a lap joint portion of a plurality of reinforced concrete members.

  In reinforced concrete (RC) ramen viaducts, it is necessary to ensure the required seismic performance at joints between piles and columns or joints such as columns. However, in order to construct such a joint, temporary earth retaining work is required, and low-strength concrete (pile head slime) containing slime during pile construction is removed in a narrow work space. It is necessary to assemble and disassemble the rebar and formwork.

  As a method of solving this, conventionally, the method of using the steel pipe to reinforce the joint between the pile and the column (root-wrapped steel pipe) has been used for the joint between the pile and the column at the time of construction. The applicant has already proposed (Patent Document 1). This method does not require the pile head slime removal of the pile, and does not require the connection between the pile and the column reinforcement, but there is a problem that the steel pipe is expensive.

Therefore, the present applicant has also proposed a construction method in which the periphery of the lap joint between the pile and the column reinforcing bar is surrounded by a spiral steel material without using an expensive root-wound steel pipe and concrete is placed (Patent Document 2).
JP 9-328759 A JP 2004-76362 A

  The proposed method of surrounding the lap joints of piles and pillars with spiral steel is cheaper than the method of rooted steel pipe, but it is more sufficient to ensure sufficient strength and toughness rate. It is necessary to take appropriate measures.

The present invention is intended to solve the above-mentioned problem, and in a method for reinforcing a reinforced concrete member in which a lap joint portion of a plurality of axial rebars is surrounded by a reinforcing rebar, economical reinforcement and sufficient strength and toughness ratio are achieved. The purpose is to secure.
The present invention is a method for reinforcing a reinforced concrete member including a reinforced joint of a plurality of axially reinforced joints, wherein the reinforcing reinforcing bars are separated from the axial reinforcing bars and the reinforcing reinforcing bars are in contact with each other, or the reinforcing reinforcing bars When the yield ratio of the lap joint part is 5 or more, the lap joint length is 25 times or more of the diameter of the axial rebar to ensure a toughness ratio of 10 or more. To do.
Further, the present invention is a method for reinforcing a reinforced concrete member including a reinforced joint of a plurality of axially reinforced joints, wherein the reinforcing reinforcing bars are separated from the axial reinforcing bars and the reinforcing reinforcing bars are in contact with each other, or When the strength ratio of the lap joint is 2 or more, the lap joint length is 30 times or more of the diameter of the axial rebar, and a toughness ratio of 10 or more is ensured. Features.
Moreover, this invention is arrange | positioned in the state which the axial direction reinforcement of the lap joint part mutually_contact | adhered or spaced apart.

  The present invention can economically reinforce the lap joint portion of the axial rebar with a reinforcing steel material. When the yield ratio of the lap joint portion is 5 or more, the lap joint length is 25 times the diameter of the axial rebar. As described above, when the proof joint ratio of the lap joint is 2 or more, it is possible to ensure a toughness ratio of 10 or more by setting the lap joint length to 30 times or more of the diameter of the axial reinforcing bar.

Embodiments of the present invention will be described below.
The present invention proposes, for example, a reinforcing method in a joint portion (lap joint portion) 4 between a pile 2 and a column 3 that supports a railway viaduct 1 as shown in FIG. An example using this will be described below. In the present invention, not only spiral reinforcing bars but also hoop bars may be used as the reinforcing steel material.

2A and 2B are conceptual diagrams for explaining the lap joint portion. FIG. 2A is a longitudinal sectional view, and FIG. 2B is a transverse sectional view.
In the illustrated example, the axial reinforcing bars 11 overlap each other over the joint length L with the axial reinforcing bar 11 of the reinforced concrete member 10 inside and the axial reinforcing bar 21 of the reinforced concrete member 20 facing outside. Spiral rebar 30 as a reinforcing steel material is wound at a predetermined pitch over a range longer than the joint length L, and the reinforced concrete members 10 and 20 are joined by placing a formwork around them and placing concrete. Here, illustration of the reinforcing bars and the like of the lap joint portion is omitted. In the lap joint portion, the nearest axial rebars 11 and 21 are paired to transmit force to each other, but the paired axial rebars may be in close contact with each other or separated from each other. That is, since a force applied to the reinforcing bars is transmitted to each other through the concrete around the joint, when a tensile force or a compressive force acts on the lap joint, the concrete around the lap joint transmits this force. At this time, the periphery of the concrete in the lap joint is surrounded by a spiral reinforcing bar and closed to restrain the deformation of the concrete. As a result, it is possible to ensure adhesion between the reinforcing bar and the concrete necessary for transmission of the tensile force and compressive force of the reinforcing bar. The spiral reinforcing bars may be wound with the reinforcing bars in close contact with each other, or may be wound with an interval between them. Further, when the interval is opened, the interval may not be constant.

Next, an experiment performed to determine specific specifications in the present embodiment will be described.
First, the specimen shape will be described.
FIG. 3 shows a specimen shape A (with slime) in which a low-strength slime portion is provided in the column portion immediately above the footing 40, and a pile and column lap joint is provided on the slime portion. FIG. FIG. 3B is a cross-sectional view of the front view. In the test body shape A, the column reinforcing bars are arranged outside and the pile reinforcing bars are arranged inside, and in addition to the outer winding spiral surrounding the lap joint portion, part of the pile reinforcing bars are surrounded to provide the inner winding spiral (FIG. 3 ( b)).
FIG. 4 shows a specimen shape B (no slime) provided with a pile and column lap joint immediately above the footing 40, FIG. 4 (a) is a longitudinal sectional view, and FIG. 4 (b) is a transverse sectional view. In the test body shape B, the column reinforcing bars are arranged on the inner side and the pile reinforcing bars are arranged on the outer side.

  For both test specimen shapes A and B, the spiral height (spiral rebar height) is equal to the diameter (D) of the column, a predetermined axial force (load) is applied to the column, and it is horizontally horizontal at a predetermined shear span position. The power is applied alternately.

  Table 1 shows a list of specimen parameters, and Table 2 shows a list of test results.

  In Table 1, Specimen No. 1-4 are specimen shape A (FIG. 3), specimen no. 5-18 performed the test by the test body shape B (FIG. 4). The column diameter (see FIGS. 3 and 4) is 700 mm for specimen No. 18 and 500 mm for the other specimens. The shear span is the distance from the top of the footing to the position where the horizontal force is applied, the SP diameter is the diameter of the spiral reinforcing bar, the SP cross section is the thickness of the spiral reinforcing bar, the SP pitch is the winding pitch of the spiral reinforcing bar, and the parenthesis is the inner winding spiral Is the pitch. In addition, No. 1, no. No. 3 does not have an inner spiral.

The SP reinforcing bar ratio indicates the degree of shear reinforcement by spiral reinforcing bars, which will be described with reference to FIG.
In FIG. 5, when the cross-sectional area (thickness) of the spiral reinforcing bar is Asp, the helical diameter is b, and the helical pitch is s, the SP reinforcing bar ratio is the cross-sectional area of the reinforcing bar with respect to the area (b · s) of the shaded portion in the figure. The ratio Asp / b · s.

  The diameter of the reinforcing bar used was D13 (mm), D16 (mm), or D19 (mm). The number of rebars is the same for each column and pile, and the axial rebar ratio is the ratio of the area occupied by the rebar to the column cross-sectional area.

As for the vacancy of the joint, the length (LS) where the axial rebars overlap each other is the joint, and the net separation obtained by subtracting the diameter of the axial rebar from the core interval of the axial rebar is vacant. The lap joint length is defined as a net joint length Ls in consideration of the joint clearance, which will be described with reference to FIG.
In FIG. 6, when the distance between the axial reinforcing bars (the distance between the center lines of the reinforcing bars) is 5φ (5 times the diameter of the reinforcing bar), the clearance is 4φ. Then, considering that force is transmitted along the 45-degree line between the axial rebars, the upper and lower portions are subtracted to obtain the lap joint length Ls = LS−2 × 4φ. In Table 1, Specimen No. 1 to 4 are corrected in this way, and the values in parentheses are values before correction. Specimen No. In 5-18, since the vacancy of the joint is 1φ, LS is used as the value of the joint length Ls as it is.

  Next, the test method will be described with reference to Table 3.

The test was conducted by a horizontal alternating loading test. The axial compressive force shown in Table 2 was applied to the column head with a vertical jack, and a horizontal alternating loading test was performed statically at a loading point of 1.15 m in height (No. 18 is 1.70 m) from the top of the footing. . The yield displacement δy at the time of the horizontal alternating loading test was set to 1δ when the strain of the axial rebar at the outermost edge reached the yield strain obtained from the material test result (see the yield strain in Table 2). Thereafter, horizontal loading was repeated for an integral multiple of the yield displacement (δy). Table 3 shows the loaded horizontal displacement in each specimen.

In determining the parameters of the test body, the strength ratio at the base of the column and the axial rebar joint length of the column and pile were considered. The yield strength ratio is defined as follows.
Vy / Vmu: Strength ratio Vy: Design shear strength Vy = Vc + Vs
Vc: Design shear strength of a bar member that does not use shear-reinforced steel (mainly the shear strength that concrete handles, taking into account the effects of effective height, axial rebar, and axial force)
Vs: Design shear strength of the bar member supported by the shear reinforcement steel material (shear strength of the spiral rebar)
Vmu: Shear force when the member reaches the bending strength Vmu = Mu / a
Mu: Bending stress a: Shear span In Table 2, the axial force is the load actually applied to the column, and the push / pull is pushed when the horizontal actuator is pushed in the horizontal alternating load test, and pulled when pulled. Each load is as follows.

Yield load (push side): Load when the outermost reinforcing bar of the column cross-section when it is pressed Yield load (pull-side): Load when the outermost reinforcing bar of the column cross-section when it is pulled Maximum load ( Push side): The value when the load is the largest when pushed The maximum load (pull side): The value when the load is the largest when pulled The Vc, Vs, and Vmu are as follows.

Vc: Shear strength of concrete, axial rebar, etc. as calculated, Vs: Shear strength of shear reinforcement (here, spiral rebar) as calculated Vmu: Shear strength ratio when bending moment is maximized Thus, (Vc + Vs) / Vmu.

The toughness rate is a value obtained by dividing the yield displacement when the yield load is lower than the yield load after yield yield is divided by the yield displacement in the load displacement curve obtained in the positive / negative alternating load test. Will be described.
FIG. 7 is a diagram showing an example of the relationship between load and displacement. The test method is that each load is positive and negative once until the axial rebar at the base of the specimen yields. After that, a displacement that is an integral multiple of the yield displacement is positive and negative once per displacement control, and the maximum load The test ends when the value falls below the yield load. In the figure, the displacement at the load Py at which the axial reinforcing bar yields is δy, and after that, the yield displacement is δy and the integral multiple of displacement is discharged one by one positive and negative, and the test ends when the maximum load falls below the yield load Py. The displacement at this time is δu, and the toughness rate is δu / δy. When the toughness rate is large, the tenacity after the member yields is large.

  No. The test specimens 10, 7, and 17 have a yield ratio of approximately the same as 4.2 to 5.1, and lap joint lengths of 20φ, 25φ, and 30φ, respectively. The toughness rates at this time are 5.9, 13.5, and 21.1. It can be seen that the longer the lap joint length, the greater the energy absorption capacity after yield load application.

  FIG. The transition of the strain of the axial rebar height of 500 mm of the column in the test bodies of 10, 7, and 17 is shown. From the figure, it is considered that although the displacement is increased, the strain is decreased and the adhesion failure is caused. When attention is paid to the peak of strain at this time, no. 10 is 4δ, no. 7 is 7δ, no. 17 is 16δ. From this, it can be seen that the longer the lap joint length, the less likely the adhesion failure occurs, and the longer the lap joint length, the axial rebar is attached to healthy concrete.

FIG. 7, no. 9 shows the relationship between the displacement 9 and the load.
No. 7 and no. The test body of No. 9 is a test body in which the lap joint length is 25φ and the concrete strength is substantially equal to about 29 N / mm ² , but the strength ratio is changed by changing the diameter and pitch of the spiral reinforcing bar. In this case, the yield strength ratios are 5.1 and 13.1, respectively. No. 9 has a larger energy absorption capacity after yield load, and the toughness is 22.9 (Table 2). And No. After the test of No. 7, a lateral crack occurred at a height of 300 mm from the footing. Further, as shown in FIG. 8, the strain peaked at 7δ after the maximum load, and thereafter decreased. For this reason, it is considered that adhesion failure occurs at a height of 300 mm or less.

  On the other hand, no. The axial rebar after 9 tests was cut and the experiment was completed. This is thought to be due to the breakage of the rebar due to low cycle fatigue before the joint failure occurred. From this, it is considered that the core concrete with spiral rebar is healthy and the binding force is small (the yield strength ratio is small), and adhesion failure is likely to occur. .

FIG. 10 shows the relationship between the joint length and the yield ratio, and FIG. 11 shows the relationship between the lap joint length, the yield ratio, and the toughness ratio of all the specimens.
As shown above, if the toughness ratio is large, the toughness after the yielding of the member will be large, and if the toughness ratio is 10 it will not be abruptly reduced in yield strength and will retain sufficient deformation performance. It is possible. Therefore, in the present invention, a condition for ensuring a toughness rate of 10 or more is considered.

  As shown in FIG. 11, a linear relationship was observed between the yield strength ratio and the toughness ratio for each lap joint length. Of these, specimen No. As shown in Table 2, for 3, 4, 8, and 18, it was impossible to confirm the toughness rate at the end of the test due to the capability of the testing machine. From this result, it can be seen that reinforcing the spiral rebar so that the yield strength ratio is 5 or more and the lap joint length is 25φ or more ensures a toughness ratio of 10 or more. This is based on the results of FIGS. Can also conclude.

  In addition, the specimen No. Focusing on the linear relationship between FIGS. 8 and 17 (FIG. 11) and further testing, it was found that when the proof stress ratio is 2 or more, a toughness ratio of 10 or more can be secured if the lap joint length is 30φ or more.

  In addition, No. 1-No. No. 4 has a slime part. 2 and No. 4 has an inner spiral. No. 1, no. No. 2 specimens had a toughness ratio of 9.6 and 14.8, respectively, and the specimens with the inner winding spiral were larger. 3, no. The toughness rates of the specimens No. 4 are almost the same when the toughness rate is 20 or more. From this, it was found that if the yield ratio is 20 or more and the lap joint length is 12φ or more, the toughness ratio is 20 or more regardless of the presence or absence of the inner spiral.

  According to the present invention, economical reinforcement is possible, and a toughness ratio of 10 or more can be ensured, so the industrial utility value is great.

It is a figure explaining application of the present invention to a joint part of a railway viaduct pile and a pillar. It is a conceptual diagram explaining a lap joint part. It is a figure explaining a test body shape. It is a figure explaining a test body shape. It is a figure explaining SP muscle ratio. It is a figure explaining the lap joint length. It is a figure which shows the example of the relationship between a load and a displacement. It is the figure which showed transition of distortion. It is the figure which showed the relationship between a displacement and a load. It is the figure which showed the relationship between joint length and yield strength ratio. It is the figure which showed the relationship of the lap joint length of all the test bodies, a yield strength ratio, and a toughness rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 ... Reinforced concrete member, 11, 21 ... Axial rebar, 30 ... Spiral rebar.

Claims (3)

A method for reinforcing a reinforced concrete member including a reinforced joint of a lap joint portion of a plurality of axial rebars,
The reinforcing reinforcing bars are spaced apart from the axial reinforcing bars, and the reinforcing reinforcing bars are in contact with each other or arranged at intervals equal to or less than the diameter of the reinforcing reinforcing bars,
When strength ratio of the lap joint portion is 5 or more, lap joint portion of the reinforced concrete member, characterized in that the lap joint length so as a more than 25 times the diameter of the longitudinal bars to secure more toughness index 10 Reinforcement method. A method for reinforcing a reinforced concrete member including a reinforced joint of a lap joint portion of a plurality of axial rebars,
The reinforcing reinforcing bars are spaced apart from the axial reinforcing bars, and the reinforcing reinforcing bars are in contact with each other or arranged at intervals equal to or less than the diameter of the reinforcing reinforcing bars,
When strength ratio of the lap joint portion is 2 or more, lap joint portion of the reinforced concrete member, characterized in that the lap joint length so as a more than 30 times the diameter of the longitudinal bars to secure more toughness index 10 Reinforcement method. The method according to claim 1 or 2, wherein the axial reinforcing bars of the lap joint portion are arranged in a state of being in close contact with or spaced apart from each other.

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