JP3294091B2 - Apparatus and method for generating cracks in reinforced concrete walls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crack in a reinforced concrete wall which generates cracks at the above-mentioned specific joints in order to prevent the occurrence of random cracks in places other than specific joint grooves of the reinforced concrete wall. The present invention relates to a generator and a crack generation method.

[0002]

2. Description of the Related Art In a reinforced concrete wall, when concrete is poured into a formwork, when the concrete expands due to hydration heat or when the concrete dries and shrinks, thermal cracks are generated due to thermal stress generated inside the concrete. May occur. When the thermal crack enters an unexpected location in an arbitrary direction, a structural defect occurs in the reinforced concrete wall, or the aesthetic appearance of the reinforced concrete wall surface is impaired. So, conventionally,
By providing a joint groove called an induced joint in the vertical direction so as to face each other on both surfaces of the reinforced concrete wall, a part of the cross section of the reinforced concrete wall is deleted, and a thin portion is formed on the reinforced concrete wall, thereby reducing the thickness of the reinforced concrete wall. Cracks are induced in the part, and the cracks are concentrated on the thin part.

However, in the joint grooves provided in the reinforced concrete wall, it is not possible to guarantee the occurrence of cracks. Therefore, a flat pipe or bag having elasticity is erected between the joint grooves, and concrete is poured. A crack generating apparatus has been proposed which forcibly generates cracks by injecting water under pressure into the pipe or bag after dismantling the mold or by injecting an inflating agent (Japanese Patent Application Laid-Open No. Sho 61).
-126250).

[0004] In addition, between joint grooves provided vertically on the both sides of the reinforced concrete wall so as to face each other,
There has been proposed a crack generation device in which a steel plate or a large-diameter pipe is buried, a thin portion having a cross-sectional defect of 50% or more with respect to the thickness of a reinforced concrete wall is provided, and a crack is induced in the thin portion (JP-A-Hei. 7-48880).

[0005]

By the way, in the crack generating apparatus for a reinforced concrete wall which injects water into the flat pipe or the bag under pressure or injects an expanding agent,
For flat pipes or bags in reinforced concrete walls,
Insufficient strength of reinforced concrete wall. Therefore, it is necessary to replace the water in the flat pipe or bag with mortar or concrete, and there is a problem that it takes time, and when filling the flat pipe or bag with an inflating agent, the filling operation is troublesome, There is a problem that management of the expansion time of the expanding agent is troublesome.

Further, in the above-described crack generating apparatus for a reinforced concrete wall using an iron plate or a large-diameter pipe between joint grooves, since the iron plate or the large-diameter pipe is buried widely so as to close a narrow joint groove, the apparatus is installed in a formwork. When placing concrete, there is a problem that the iron plate or the large diameter pipe hinders the movement of the concrete, and the workability at the time of placing the concrete deteriorates.

Accordingly, an object of the present invention is to provide a crack generating device for a reinforced concrete wall which can easily and surely generate cracks at specific locations and prevent cracks from occurring in unexpected directions at unexpected locations. And a method for generating cracks.

[0008]

In order to achieve the above object, a crack generating apparatus for a reinforced concrete wall according to claim 1 is provided with a thin portion sandwiched between joint grooves provided on both surfaces of the reinforced concrete wall so as to face each other. A plurality of thermal expansion rods each having no nodes embedded at predetermined intervals, and a power supply device for heating the thermal expansion rods by supplying a current to each of the thermal expansion rods. .

According to the crack generating device for a reinforced concrete wall according to the first aspect of the present invention, the power supply unit supplies a current to each of the thermal expansion rods, and heats and thermally expands each of the thermal expansion rods. Due to the thermal expansion in the direction, the tensile stress acts in a direction perpendicular to the plane including the respective thermal expansion bars between the joint grooves, so that cracks can be forcibly generated in the thin portion of the reinforced concrete wall. Since the plurality of thermal expansion rods have no nodes and their cross-sectional shapes do not change in the longitudinal direction, the tensile stress due to thermal expansion in the longitudinal direction of each thermal expansion rod hardly acts on concrete. Also, when the concrete is cast, the concrete slips between the thermal expansion rods,
Since it can be easily moved, workability at the time of placing concrete can be improved. After the cracks are formed in the reinforced concrete wall, the thermal expansion rod can be used as it is as a part of the structure.

[0010] In the crack generating device for a reinforced concrete wall according to the second aspect of the present invention, in the crack generating device for a reinforced concrete wall according to the first aspect, the plurality of thermal expansion rods are:
It is characterized by being substantially parallel to the joint groove.

According to the crack generating device for a reinforced concrete wall according to the second aspect, the plurality of thermal expansion rods are buried in the thin portion between the joint grooves of the reinforced concrete wall substantially in parallel with the joint grooves. Since the tensile stress acts over a wide range with a small number of thermal expansion rods, cracks can be effectively induced in the thin portion of the reinforced concrete wall.

Further, the crack generating device for a reinforced concrete wall according to claim 3 is characterized in that, in the crack generating device for a reinforced concrete wall according to claim 2, a peeling member is provided on the outer periphery of the plurality of thermal expansion rods.

According to the third aspect of the present invention, since the concrete does not adhere to the outer periphery of the thermal expansion rod due to the peeling member, even if the thermal expansion rod thermally expands in the longitudinal direction, the thermal expansion does not occur. Because the concrete is not affected by the stress and only the thermal expansion in the radial direction of the thermal expansion rod causes stress in the concrete, the thin part sandwiched between the joint grooves reliably generates cracks,
Cracks can be prevented from being generated at unnecessary portions.

According to a fourth aspect of the present invention, there is provided the crack generating apparatus for a reinforced concrete wall according to any one of the first to third aspects, wherein the crack is buried in the reinforced concrete wall to detect the temperature of the concrete. It is characterized by having a sensor.

According to the apparatus for generating cracks in a reinforced concrete wall according to the fourth aspect, by monitoring the temperature of the concrete detected by the temperature sensor, before the concrete is solidified and the strength is sufficiently developed, and During the period until the concrete temperature becomes maximum due to the hydration exothermic reaction and the temperature crack occurs, the above-mentioned thermal expansion rods are energized to thermally expand each of the expansion rods, and are sandwiched between joint grooves of the reinforced concrete wall. Cracks can be reliably generated in the thin portion.

According to a fifth aspect of the present invention, there is provided the crack generating apparatus for a reinforced concrete wall according to the fourth aspect, wherein the signal indicating the temperature of the concrete is received from the temperature sensor to display the temperature of the concrete. The display device is provided with a display device.

According to the crack generating apparatus for a reinforced concrete wall according to the fifth aspect, an operator can easily confirm the temperature of the concrete detected by the temperature sensor, and based on the temperature of the concrete, a plurality of thermal expansion rods are provided. It is possible to accurately determine when to energize.

In the crack generating device for a reinforced concrete wall according to claim 6, in the crack generating device for a reinforced concrete wall according to claim 2, an interval between the thermal expansion rods adjacent to each other is reduced by the heat generated by the power supply device. Due to the thermal expansion of the expansion rod and the expansion and contraction of the concrete due to the hydration exothermic reaction, the interval of the minimum value of the tensile stress generated between the adjacent thermal expansion rods is narrower than the interval when the tensile strength of the concrete exceeds the tensile strength. The distance between the bottom of the joint groove and the thermal expansion rod is set by the thermal expansion of each of the thermal expansion rods heated by the power supply device and the expansion and contraction of the concrete due to the hydration heat generation reaction. The interval when the minimum value of the tensile stress generated between the bottom of the joint groove and the thermal expansion rod becomes equal to or greater than the tensile strength of concrete. It is characterized by is set to be narrower Ri.

According to the crack generating apparatus for a reinforced concrete wall according to the sixth aspect of the present invention, the space between the thermal expansion rods adjacent to each other and the space between the bottom of the joint groove and the thermal expansion rod are calculated in advance by a thermal stress analysis or the like. By setting the distance within the maximum distance at which cracks occur, cracks can be reliably generated in the thin portion sandwiched between joint grooves of the reinforced concrete wall, and the distance between adjacent thermal expansion rods and the thermal expansion rod The gap with the bottom of the rift is not so wide that cracks do not occur.

Further, according to a seventh aspect of the present invention, there is provided a method for generating cracks in a reinforced concrete wall, wherein a thin portion sandwiched between joint grooves provided on both sides of the reinforced concrete wall in a formwork forming the reinforced concrete wall, Arranging a plurality of thermal expansion bars having no nodes at predetermined intervals substantially in parallel with the joint groove; placing concrete in the mold in which the plurality of thermal expansion bars are arranged; After the internal temperature of the reinforced concrete wall rises and reaches a maximum due to the hydration heat reaction of the concrete poured into the concrete, the tensile stress generated in the reinforced concrete wall by the hydration heat reaction exceeds the tensile strength of the concrete. And heating the respective thermal expansion rods by passing a current through the respective thermal expansion rods before the temperature crack occurs. It is.

According to the method for generating cracks in a reinforced concrete wall according to the seventh aspect, the concrete is solidified in the above period, but the tensile strength is not sufficiently developed and the strength is low. Even if the temperature rise is low (for example, around 150 ° C.) and the thermal expansion of the thermal expansion rod is small, cracks can be generated in the thin portions sandwiched between the joint grooves before thermal cracks occur. After casting the concrete, the concrete is not sufficiently solidified until the internal temperature of the concrete reaches the maximum, so if the thermal expansion rods are thermally expanded at this time, cracks are unlikely to occur. . If the concrete is sufficiently solidified and cracks are to be generated in the thin portions sandwiched between the joint grooves, each of the thermal expansion rods must be heated to a high temperature and thermally expanded. Deteriorates,
Structural defects occur in reinforced concrete walls. On the other hand, according to claim 7, since the thermal expansion rod is thermally expanded at a low temperature to generate cracks, the thermal expansion rod is increased in cross-sectional area or supplied power is increased. It is not necessary to greatly expand the thermal expansion, so that the plurality of thermal expansion rods may hinder concrete placing work, or the equipment for supplying power to the thermal expansion rods may become excessively uneconomical. There is no. In the above period, the expansion and contraction due to the hydration exothermic reaction generates a tensile stress in the concrete, and the tensile stress acts in a direction to promote the crack of the concrete. Since the proportion of the stress caused by the thermal expansion of the expansion rod can be reduced, the temperature rise of the thermal expansion rod is further reduced, and the deterioration of the concrete around the thermal expansion rod is prevented.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus and method for cracking a reinforced concrete wall according to the present invention will be described below in detail with reference to the embodiments shown in the drawings.

(First Embodiment) FIG. 1 is a side view of a reinforced concrete wall in which cracks are generated by using a device and a method for generating cracks in a reinforced concrete wall according to a first embodiment of the present invention. Is a group of reinforcing bars (only two are shown in FIG. 1) as a plurality of thermal expansion rods buried at predetermined intervals in the reinforced concrete wall 11; 2 is an AC power supply device for supplying power to the reinforcing bar group 1; A first temperature sensor, which is buried approximately in the center between the reinforcing bar groups 1 in the reinforced concrete wall 11 and detects the concrete temperature,
The second is embedded in the vicinity of the reinforcing bar group 1 in the reinforced concrete wall 11 and detects the concrete temperature in the vicinity of the reinforcing bar group 1.
The temperature sensors 5 are display devices that receive signals indicating the concrete temperature from the first and second temperature sensors 3 and 4 and respectively display the concrete temperatures. The reinforced concrete wall 11 is formed by casting concrete in a form described later on a base 12 cast on a base concrete 13.

FIG. 2 is a vertical sectional view taken along line II-II of FIG. FIG. 1 shows a state in which the mold is removed, but FIG. 2 shows a state before the molds 10 and 10 are removed. The reinforcing bar group 1 is composed of three nodeless reinforcing bars 1A, 1B, 1C buried at predetermined intervals substantially parallel to the joint grooves 21, 21, and the lower end of the reinforcing bar 1A and the lower end of the reinforcing bar 1B are connected. The rebars 1A, 1B, and 1C are connected in series by connecting the upper end of the reinforcing bar 1B and the upper end of the rebar 1C with the energizing connecting member 6 while connecting with the energizing communication member 6. The connecting member 7 is connected to the upper end of the reinforcing bar 1A, the connecting member 8 is connected to the lower end of the reinforcing bar 1C, and the output terminals of the AC power supply 2 are connected to the connecting members 7, 8, respectively. The current from the device 2 is made to flow through the rebars 1A, 1B, and 1C connected in series. The above reinforced concrete wall 1
A plurality of vertical reinforcing bars 22 and a plurality of horizontal reinforcing bars 23 are embedded in the inside 1 and the base portion 12.

FIG. 3 is an enlarged horizontal sectional view taken along line III-III of FIG. 2, and FIG. 4 is a vertical sectional view taken along line IV-IV of FIG. In FIG. 3, induction joint bars 20, 20 are arranged so as to face each other over the entire length in the vertical direction on the opposing side surfaces of two substantially parallel molds 10, 10 at a predetermined interval. And the above-mentioned joint bar 20,
The reinforcing bars 1A, 1B, and 1C are arranged between
A peeling member 30 is provided on the outer periphery of each of A, 1B, and 1C (FIG. 4).
reference). In addition, the peeling member 30 provided on the outer periphery of the reinforcing bars 1A, 1B, 1C is an elastic material such as vinyl tape, grease, and paraffin which does not hinder the thermal expansion of the reinforcing bars, and concrete does not adhere to the reinforcing bars. What is necessary is just such.

In the crack generating apparatus having the above structure, the AC power supply device 2 applies 800A to 1000A to the reinforcing bar group 1.
(AC voltage of about 3V), and supply each reinforcing bar 1A, 1B, 1C
When the reinforced concrete wall 11 is heated and thermally expanded,
Adjacent rebar 1A, 1B, between the reinforcing bar 1A and 1C, between the bottom of 1C and eye Rift 21, rebar 1A, 1B, tensile stress intensity generated in a direction perpendicular to the plane containing 1C sigma _A Figure 5 (a)
(Only a part is shown in FIG. 5A). In addition, in the process in which the concrete temperature falls past the peak value due to the hydration exothermic reaction, thermal stress generated by the action of the internal restraint action or the external restraint action causes the reinforced concrete wall 11 to move between the adjacent reinforcing bars 1A, 1B, 1C. Between the reinforcing bars 1A, 1C and the bottom of the joint groove 21, the reinforcing bars 1A, 1B, 1C
The tensile stress level σ _B generated in a direction perpendicular to the plane including is distributed almost uniformly as shown in FIG. 5 (b).
(Only a part is shown in FIG. 5 (b)). The degree of tensile stress σ _B generated in concrete due to this thermal stress is, for example, FE
It can be calculated by a thermal stress analysis method using an M (finite element method) analysis model. Then, the tensile stresses σ _A , σ _B
Together with the reinforcing bar 1 adjacent to the reinforced concrete wall 11
The tensile stress σ _C generated between A, 1B, 1C and between the reinforcing bars 1A, 1C and the bottom of the joint groove 21 in a direction perpendicular to the plane including the reinforcing bars 1A, 1B, 1C is shown in FIG. The distribution is as shown in FIG. 5C (only a part is shown in FIG. 5C). In addition, FIG.
Although not shown in (c), the distribution of the tensile stress generated between the reinforcing bars 1A and 1B and between the reinforcing bar 1A and the bottom of the joint groove 21 is the same as the tensile stresses σ _A , σ _B and σ _C. .

A description will now be given of the tensile stress generated in the concrete due to the thermal expansion of the reinforcing steel in the concrete.

FIG. 6 shows the tensile stress σ generated in concrete at a distance L in the horizontal direction from the center point O of the cross section when the reinforcing bar 40 (diameter R) having a circular cross section thermally expands. In FIG. 6, the reinforcing bar 40 having a diameter R before thermal expansion is indicated by a dotted line, and the reinforcing bar 40 after thermal expansion is indicated by a solid line. The outward stress in the radial direction when the reinforcing bar 40 thermally expands is p
Then, the tensile stress degree σ is represented by [Equation 1] σ = pi (r / L) ² (radius r = R / 2). Further, assuming that the radial outward displacement amount of the reinforcing bar 40 is Δr and the shear elastic modulus of the reinforcing bar is G, the ratio Δr / r between the displacement amount Δr and the radius r is represented by [Equation 2] Δr / r = −pi / (2G) · r / L, and when the stress pi is obtained from the above equation 2, the following equation is obtained: [formula 3] pi = − △ r / r ² · 2GL Then, when Equation 3 is substituted into Equation 1, [Equation 4] σ = Δr / L · 2G. Here, assuming that the strain in the radial direction of the reinforcing bar 40 is ε, the displacement amount Δr = ε · R / 2, and therefore, Equation 4 is expressed by [Equation 5] σ = ε · R / L · 2G. .

Then, into Equation 5, [Equation 6] strain ε = α · Δt [Equation 7] Shear modulus G = E / (2 (1 + ν)) is substituted. Here, α is the coefficient of thermal expansion of the reinforcing bar, Δt is the amount of change in temperature, E is the elastic coefficient of concrete, and ν is the Poisson's ratio. Thus, at a horizontal distance L from the center point O of the cross section of the reinforcing bar 40, the tensile stress a generated in the concrete is expressed by the following equation.

[Equation 8] σ = (α △ tREＲ) / (2L (1 + ν)) For example, when the above equation 8 is applied under the following conditions, the horizontal direction from the center point O of the reinforcing bar 40 is obtained. The degree of tensile stress a generated in concrete with respect to the distance L is distributed as shown in FIG.

R = 30 [mm] Δt = 100 [° C.] α = 10 × 10 ⁻⁶ [/ ° C.] E = 20 × 10 ⁴ [kgf / cm ² ] ν = 0.166666 After determining the diameter R, the amount of temperature change △
By controlling t, that is, by supplying a necessary amount of power to the reinforcing bar and setting the temperature change amount Δt of the reinforcing bar to a desired value, a tensile stress degree σ required to generate a crack is obtained. be able to.

When the concrete temperature exceeds 200.degree. C., the compressive strength of the concrete decreases greatly as the temperature rises. Therefore, the temperature change .DELTA.t of the reinforcing bar 40 is set so that the concrete temperature around the reinforcing bar becomes 200.degree. It is desirable to set.

In FIG. 5A, the center and joint grooves 21 between the reinforcing bars 1B, 1C are expanded due to the thermal expansion of the reinforcing bars 1A, 1B, 1C.
Let σ _A1 and σ _A2 be the tensile stresses generated at the bottom of
In FIG. 5B, the tensile stresses generated at the center between the reinforcing bars 1B and 1C and at the bottom of the joint groove 21 due to thermal stress are σ _B1 and σ _{B2, respectively} (when the reinforcing bar is energized). And FIG.
As shown in (c), the center between the reinforcing bars 1B and 1C and the joint groove 2
At the bottom of 1, the tensile stresses σ _C1 , σ _C2 that combine the tensile stresses σ _A1 , σ _A2 due to thermal expansion of the reinforcing bars 1A, 1B, 1C and the tensile stresses σ _B due to thermal stress work. The tensile stress σ _C1 is the minimum value of the tensile stress generated between the reinforcing bars 1B and 1C, and the tensile stress σ _C2 is the minimum value of the tensile stress generated between the reinforcing bar 1C and the bottom of the joint groove 21. It is.

Further, when the tensile stresses σ _C1 , σ _C2 exceed the tensile strength f of the concrete (when the reinforcing bar is energized), the maximum distance between the reinforcing bars 1B, 1C is L _1max , and the bottom of the _joint groove 21 and the reinforcing _bar 1C _{Is defined} as L _2max . When the maximum distance L ₁ and the distance L ₂ exceed the distances L _1max and L _2max , respectively, the tensile stresses σ _C1 and σ _{C2 at} the center between the reinforcing bars 1B and 1C and at the bottom of the _joint groove 21 become the tensile strength f of the concrete. There is a possibility that cracks cannot be introduced to the entire thin portion sandwiched between the joint grooves 21, 21. Therefore, the degree of tensile stress σ _A acting on concrete due to the thermal expansion of each of the reinforcing bars 1A, 1B, and 1C is calculated in advance, and the degree of tensile stress σ _B generated in concrete due to thermal stress is calculated by thermal stress analysis. The maximum intervals L _1max and L _2max are obtained, and the above intervals L ₁ and L _2
Are set to be _smaller than the maximum distances L _1max and L _2max , _respectively , so that cracks are always generated over the thin portions sandwiched between the _joint grooves 21, 21.

Next, the time when the concrete is poured into the above-mentioned molds 10, 10 and which is suitable for energizing the above-mentioned reinforcing bars 1A, 1B, 1C will be described with reference to FIGS.

FIG. 8 shows the change in the concrete temperature with respect to the age of the concrete placed. The concrete temperature increased by the exothermic hydration reaction after the concrete was placed falls after the peak temperature T _P. At first, the temperature finally approaches the outside air temperature T _Q. In the process, due to thermal stress by the internal restraint action or external restraint action, tensile stresses occurring in the concrete at the concrete temperature T ₀ is exceeds the tensile strength of the concrete, crack will occur in the concrete.

[0037] Therefore, in order to prevent the generation of unnecessary cracks, concrete temperature detected by the first temperature sensor 3 rises from the time D _P that peaked temperature T _P, the internal constraining action or external in the period D to the point D ₀ becomes the temperature T ₀ at which the tensile stress level occurring in the concrete by thermal stress due to restraint action exceeds the tensile strength of the concrete, the rebar 1A, 1B, by energizing the 1C, reinforced concrete Cracks must be generated between the joint grooves 21 of the wall 11.

FIG. 9 shows the tensile strength of the concrete put into place with respect to the material age. The concrete strength gradually increased with the passage of the material age after the concrete was placed. The final tensile strength S _Q at the time point D _Q becomes about 30 kg / cm ² . However, the tensile strength of the concrete at the time D ₀ to be point D _P and a temperature T ₀ to be the peak temperature T _P S _P, S ₀ is smaller than the final tensile strength S _Q, in the period D Even the highest tensile strength S ₀ is about half the final tensile strength S _Q.

Accordingly, in the above period D, although the concrete is solidified, the tensile strength is not sufficiently developed, the strength is low, and the tensile stress is generated in the concrete due to the expansion due to the hydration exothermic reaction. Since this tensile stress acts in the direction of promoting cracking of concrete, cracking can be generated even if the temperature increase of the reinforcing bar is suppressed to a low temperature and the thermal expansion of the reinforcing bar is reduced. Therefore, the concrete around the reinforcing bar (in FIG. 1 and FIG. 2, around the thin portion sandwiched between joint grooves that induce cracks) does not become hot and deteriorates.

When the form is dismantled at an early stage due to construction reasons, the concrete kept warm by the form is exposed to the outside air by removing the form, and the concrete temperature fluctuates rapidly. Temperature cracking may occur. In this case, while monitoring the change in the concrete temperature detected by the first temperature sensor 3 buried in the concrete, it is determined whether or not the time to energize the reinforcing bars 1A, 1B, 1C is before the mold dismantling. . In addition,
When a temperature sensor or a display device is not used, or when it is difficult to judge the timing and there is a possibility that the concrete temperature may suddenly drop due to exposure to the outside air, a crack is generated before the form is dismantled.

Thus, the reinforced concrete wall 11
Joint grooves 21 provided on both sides of the
In the thin part sandwiched between 21, three knotless reinforcing bars 1A, 1
B and 1C are respectively buried at predetermined intervals, and an electric current is applied to each of the reinforcing bars 1A, 1B and 1C by the AC power supply device 2 to heat them.
By thermally expanding the reinforced concrete walls 1B and 1C, a tensile stress acts between the joint grooves 21 and 21 of the reinforced concrete wall 11 in a direction perpendicular to the plane including the reinforcing bars 1A, 1B and 1C, and the joints of the reinforced concrete wall 11 are removed. Cracks occur in the thin portions sandwiched between the trenches 21, 21. Therefore, a crack can be forcibly generated at a predetermined portion of the reinforced concrete wall 11. In addition, the concrete can pass through the space between the reinforcing bars 1A, 1B, and 1C at the time of concrete placement and can be easily moved, so that the workability at the time of concrete placement can be improved. The reinforced concrete wall 11
After the cracks are formed in the thin portions sandwiched between the joint grooves 21, 21, the reinforcing bars 1A, 1B, 1C can be used as a part of the structure as it is. In addition, the above reinforcing bars 1A, 1B,
By arranging the reinforcing bars 1C substantially in parallel at predetermined intervals, the distribution of the tensile stress σ _A due to the thermal expansion of the reinforcing bars 1A, 1B, 1C in the vertical direction becomes substantially the same, so that the reinforcing bars 1A, 1B, 1C
Cracks can be generated more reliably by preventing the degree of tensile stress from varying due to the thermal expansion of the steel.

Further, the reinforcing bars 1A, 1B, and 1C are buried in the thin portions sandwiched between the joint grooves 21, 21 of the reinforced concrete wall 11 so as to be substantially parallel to the joint grooves 21, 21. Since the tensile stress acts over a wide range, the thin portion of the reinforced concrete wall 11 can effectively induce cracks.

Further, since the peeling member 30 is provided on the outer periphery of each of the reinforcing bars 1A, 1B, 1C, concrete does not adhere to the outer periphery of each of the reinforcing bars 1A, 1B, 1C by the peeling member 30, and the reinforcing bars 1A, 1B , 1C is not affected by the thermal expansion in the longitudinal direction, so that cracks are not generated at unnecessary portions around the reinforcing bars 1A, 1B, 1C.

The concrete temperature is detected by the first temperature sensor 3 embedded in the reinforced concrete wall 11, and the change in the concrete temperature due to the hydration exothermic reaction is monitored. ,
Electricity is supplied to each reinforcing bar 1A, 1B, 1C, and each reinforcing bar 1A, 1B, 1C is heated and thermally expanded, and the joint groove 2 of the reinforced concrete wall 11 is formed.
Cracks can be surely generated in the thin portion sandwiched between the first and second portions. In addition, the concrete temperature at which the temperature crack occurs is calculated in advance by thermal stress analysis or the like, and before the temperature at which the temperature crack occurs, electricity is supplied to the reinforcing bars 1A, 1B, and 1C to thereby increase the strength of the reinforced concrete wall 11. Cracks can be reliably generated in the thin portions sandwiched between the joint grooves 21.

The display device 5 displays the concrete temperature from the first temperature sensor 3 in response to the signal indicating the concrete temperature from the first temperature sensor 3, so that the worker can easily check the concrete temperature, and based on the concrete temperature. Thus, it is possible to accurately determine when to supply power to the reinforcing bars 1A, 1B, and 1C. Further, the second temperature sensor 4 is connected to the reinforcing bars 1A, 1B,
Reinforcing bar 1 heated by being buried near 1C
A, 1B, 1C raises the temperature of the surrounding concrete and increases the temperature (for example, 200
(° C. or more).

The distance L ₁ between the reinforcing bars 1A, 1B, 1C adjacent to each other and the distance L ₂ between the bottom of the joint groove 21 and the reinforcing bars 1A, 1C are determined by the maximum distance L calculated in advance by the thermal stress analysis.
_1max, by within L _2max, the distance L _1, is too wide pitch L _2, is not that cracks will not occur. Therefore, cracks can be reliably generated in the thin portions sandwiched between the joint grooves 21 of the reinforced concrete wall 11. Further, even if the temperature increase of the reinforcing bars 1A, 1B, 1C is suppressed to a low level and thermal expansion is performed, the cracks can be surely generated.
The reinforced concrete wall 11 can be used as a structure even after cracks are generated without being deteriorated under the influence of the temperatures 1B and 1C.

Further, the concrete temperature rises due to the exothermic reaction of hydration of the poured concrete, and the peak temperature T
From the time D _P composed by _P, within the period D to the point D ₀ of the resulting tensile stress level in the concrete is higher tensile strength of the concrete in the expansion and contraction caused by pre-calculated heat of hydration reaction, each rebar An electric current is applied to 1A, 1B, 1C to heat the reinforcing bars 1A, 1B, 1C. Accordingly, before the time D ₀ to cracking due to thermal stress is generated, eye cracks thin portion sandwiched between Graben 21, 21 forcibly generated, expected arbitrary direction cracks at locations not occurred Can be reliably prevented. In the period D,
Although concrete is solidified, it has low tensile strength and low strength.In addition, expansion due to hydration exothermic reaction generates tensile stress in concrete, which promotes cracking of concrete. Since it works in the direction, even if the thermal expansion of the reinforcing bars 1A, 1B, 1C is reduced, that is, even if the temperature rise of the reinforcing bars 1A, 1B, 1C is suppressed, cracks can be generated, and the reinforcing bars 1A, 1B, Heating 1C to high temperature does not degrade concrete. Further, the rebars 1A, 1B, 1C are cooled to a low temperature (for example, 1
For example, when a welding machine is used as a power supply device, the energization time required for heating to (50 ° C.) may be as short as about 10 minutes, and the execution time can be shortened. Further, since the reinforcing bars 1A, 1B, and 1C are thermally expanded at a low temperature to generate cracks, the cross-sectional area of the reinforcing bars 1A, 1B, and 1C is increased, and the power supply is increased to increase the reinforcing bars 1A, 1B, and 1C. There is no need to greatly expand 1C, so that the reinforcing bars 1A, 1B,
1C does not hinder the concrete placing work, and the AC power supply 2 does not become uneconomical. Further, in the period D, a tensile stress is generated in the concrete due to the thermal stress due to the hydration exothermic reaction, and this works in a direction to promote the cracking of the concrete. Therefore, the reinforcing bars 1A, 1B, It is possible to reduce the share of stress due to thermal expansion of 1C. Therefore, since the temperature rise of the reinforcing bars 1A, 1B, 1C can be further reduced, the reinforcing bars 1A, 1B, 1C are heated to a high temperature, and the concrete around the thin portion sandwiched between the joint grooves 21, 21 deteriorates. No structural defects occur.

(Second Embodiment) FIG. 10 shows a second embodiment of the present invention.
It is a vertical sectional view of a reinforced concrete wall which generates a crack using a crack generation device and a crack generation method of a reinforced concrete wall of an embodiment, and 101 is a plurality of thermal expansion bars embedded at a predetermined interval in a reinforced concrete wall 111. 102, an AC power supply for supplying power to the reinforcing bar group 101; 103, a first temperature sensor 10 embedded in substantially the center between the reinforcing bar groups 101 in the reinforced concrete wall 111 to detect concrete temperature;
Reference numeral 5 denotes a display device that receives a signal indicating the concrete temperature from the first temperature sensor 3 and displays the concrete temperature. The reinforced concrete wall 111 is formed by casting concrete in a mold 110 on a base 112 cast on a base concrete 113. Although not shown, a second temperature sensor for detecting the concrete temperature near the reinforcing bar group 101 is embedded near the reinforcing bar group 101 in the reinforced concrete wall 111.

The reinforcing bar group 101 includes joint grooves 121, 12
In the thin portion sandwiched between the two, there are six jointless reinforcing bars 101A to 101E which are buried approximately vertically and horizontally in the joint grooves 121 at a predetermined interval from each other. The above-mentioned reinforcing bars 101A to 101E connect the connecting member 107 to one end of the reinforcing bar 101A, and connect the other end of the reinforcing bar 101B to the other end via the conductive connecting member 106, and connect the other end of the reinforcing bar 101B to one end of the reinforcing bar 101C. Connected by member 106,
Hereinafter, similarly, the rebars 101A to 101E are connected in series. Then, the connecting member 108 is connected to the other end of the reinforcing bar 101E, and the connecting members 107 and 108 are connected.
Are connected to the output terminals of the AC power supply device 102, respectively, so that the current from the AC power supply device 102 is connected in series.
A to 101E. The form 1
10, a hole (not shown) penetrating the reinforcing bars 101A to 101E is provided in advance, and a peeling member (not shown) is provided on the outer periphery of the reinforcing bars 101A to 101E, similarly to the first embodiment. . A plurality of vertical reinforcing bars 122 and a plurality of horizontal reinforcing bars 123 are embedded in the reinforced concrete wall 111 and the base 112.

Thus, the reinforced concrete wall 11
Joint grooves 12 provided on both sides of the joint 1 so as to face each other
In the thin portion sandwiched between 1,121, six rebars 101A to 101E having no nodes are buried at predetermined intervals, and an electric current is applied to the rebars 101A to 101E by the AC power supply device 102 to heat the rebars. By thermally expanding 101A to 101E, joint grooves 121, 1 of reinforced concrete wall 111 are formed.
The tensile stress acts in the direction perpendicular to the plane including the reinforcing bars 101A to 101E between the joints 21 and cracks occur in the thin portions sandwiched between the joint grooves 121 of the reinforced concrete wall 111. Therefore, a crack can be forcibly generated at a predetermined portion of the reinforced concrete wall 111. In addition, since concrete can easily move through the reinforcing bars 101A to 101E during concrete placement, the workability at the time of concrete placement can be improved. After the cracks are formed in the thin portions sandwiched between the joint grooves 121 of the reinforced concrete wall 111, the reinforcing bars 101A to 101E can be directly used as a part of the structure. In addition, the above reinforcing bar 1
By arranging the reinforcing bars 101A to 101E substantially in parallel at predetermined intervals, the state of the horizontal distribution of the tensile stress due to the thermal expansion of the reinforcing bars 101A to 101E becomes substantially the same. Cracks can be more reliably generated by preventing the degree of variation.

Since a peeling member (not shown) is provided on the outer periphery of each of the reinforcing bars 101A to 101E, concrete does not adhere to the outer periphery of each of the reinforcing bars 101A to 101E due to the above-mentioned peeling member. The concrete is affected by the thermal expansion in the longitudinal direction and
Cracks do not occur in unnecessary portions around 1E.

The concrete temperature is detected by the first temperature sensor 103 embedded in the reinforced concrete wall 111, and a change in the concrete temperature due to the hydration exothermic reaction is monitored, and when the concrete temperature reaches a predetermined temperature. Power is supplied to each of the rebars 101A to 101E,
A to 101E are heated and thermally expanded, so that cracks can be surely generated in the thin portions sandwiched between the joint grooves 121 of the reinforced concrete wall 111. Further, the concrete temperature at which the temperature crack occurs is calculated in advance by thermal stress analysis or the like, and the steel bars 101A to 101E are energized before reaching the temperature at which the temperature crack occurs, whereby the joint groove of the reinforced concrete wall 111 is formed. 121,1
Cracks can be reliably generated in the thin portion sandwiched between the two.

Further, the display device 105 for displaying the concrete temperature allows the worker to easily confirm the concrete temperature, and based on the concrete temperature, the rebar 1
It is possible to accurately judge when to energize 01A to 101E. Further, the heated rebars 101 are heated by a second temperature sensor embedded near the rebars 101A to 101E.
A-101E raises the temperature of the surrounding concrete and causes a high temperature (for example, 200
(° C. or more).

The reinforcing bars 101A to 101A to 10
By setting the interval of 1E within the maximum interval calculated in advance by the thermal stress analysis,
There is no case where the intervals of 01A to 101E are too wide and cracks do not occur. Therefore, cracks can be reliably generated in the thin portions sandwiched between the joint grooves 121 of the reinforced concrete wall 111. Further, even if the temperature increase of the rebars 101A to 101E is suppressed to a low value and thermal expansion is performed, cracks can be reliably generated, so that the concrete is not deteriorated under the influence of the temperature of the rebars 101A to 101E. Even after the cracks are generated, the reinforced concrete wall 111 can be used as a structure.

[0055] Also, as in the first embodiment, as shown in FIG. 8, from the time D _P as the peak temperature T _P concrete temperature is raised by heat of hydration reaction of pouring the concrete, pre period D of between expansion due calculated hydration exothermic shrinkage to the point D ₀ resulting tensile stress level in the concrete is higher tensile strength of the concrete
An electric current is supplied to each of the reinforcing bars 101A to 101E to heat the reinforcing bars 101A to 101E. Accordingly, before the time D ₀ to cracking due to thermal stress is generated, eyes Graben 21,2
Cracks are forcibly generated in the thin portion sandwiched between the two, so that it is possible to reliably prevent the occurrence of cracks in arbitrary directions at unexpected locations. In addition, the above period D
The concrete is solidified, but the tensile strength is not so much developed, it is low strength, and the expansion due to the hydration exothermic reaction causes tensile stress in the concrete, which causes cracks in the concrete. Since it works in the direction of accelerating, even if the thermal expansion of the rebars 101A to 101E is reduced, that is, even if the temperature rise of the rebars 101A to 101E is kept low, cracks can be generated, and
Heating 1A to 101E to a high temperature does not deteriorate concrete. Further, the rebars 101A to 101E
For example, when a welding machine is used as a power supply,
A short time of about 0 minutes may be sufficient, and the execution time can be reduced. Further, since the reinforcing bars 101A to 101E are thermally expanded at a low temperature to generate cracks,
It is not necessary to increase the cross-sectional area of A to 101E or to increase the supplied power, so that the rebars 101A to 101E do not need to be greatly thermally expanded. The device 102 does not become bulky and uneconomical. Further, in the period D, a tensile stress is generated in the concrete due to the thermal stress due to the hydration exothermic reaction, and this acts in a direction to promote cracking of the concrete, so that the reinforcing bars 101A to 101E at the time of generating the cracking. It is possible to reduce the share of stress due to thermal expansion. Therefore, since the temperature rise of the reinforcing bars 101A to 101E can be further reduced, the reinforcing bars 101A to 101E are heated to a high temperature, and the concrete around the thin portion sandwiched between the joint grooves 121, 121 is not deteriorated. No structural defects occur.

In the first and second embodiments, the reinforcing bars 1A, 1B, 1C and the reinforcing bars 101A to 101E are used as the thermal expansion rods. Any metal or a current-carrying substance other than metal having a high coefficient of expansion may be used, and its cross-sectional shape may be circular, elliptical, rhombic, or the like.

In the first and second embodiments, the AC power supplies 2 and 102 are used as the power supply. However, the power supply is not limited to this and may be a DC power supply.

In the first and second embodiments, the joint grooves 21, 21 and the joint grooves 121, 121 are provided over the entire length of the reinforced concrete walls 11, 111 in the vertical direction, but the joint grooves are not limited to the vertical direction. It may be provided diagonally on both sides of the reinforced concrete wall so as to face each other.

Further, in the first and second embodiments, the reinforced concrete walls 11 and 111 are provided with three thermal expansion rods.
1A, 1B, 1C and 6 rebars 101A-101
E was buried respectively, but the number of thermal expansion rods may be an appropriate number according to the thickness of the reinforced concrete wall and the like.

In the first and second embodiments, the plurality of thermal expansion rods embedded in the reinforced concrete wall are thermally expanded to induce cracks in the thin portions between joint grooves provided in the reinforced concrete wall. However, it goes without saying that the present invention may be applied to not only reinforced concrete walls but also reinforced concrete structures such as beams and floors.

In the first embodiment, the reinforcing bars 1A, 1B, and 1C as the thermal expansion rods do not have to be arranged over the entire length of the reinforced concrete wall 11 in the vertical direction. The arrangement over the entire length in the direction is more preferable in order to induce cracks.

[0062]

As is apparent from the above description, the crack generating apparatus for a reinforced concrete wall according to the first aspect of the present invention has a thin portion sandwiched between joint grooves provided on both sides of the reinforced concrete wall so as to face each other. It comprises a plurality of no-node thermal expansion rods buried at predetermined intervals, respectively, and a power supply for heating each of the thermal expansion rods by applying a current to each of the thermal expansion rods.

Therefore, according to the crack generating apparatus for a reinforced concrete wall according to the first aspect of the present invention, the thermal expansion rod is energized by the power supply device, and the thermal expansion rod is heated and thermally expanded. Due to the thermal expansion in the direction, a tensile stress acts in a direction perpendicular to the plane including the respective thermal expansion bars between the joint grooves, so that a crack can be forcibly generated at a predetermined portion of the reinforced concrete wall. In addition, since concrete can easily move through the thermal expansion bars during concrete placement, workability during concrete placement can be improved. After the formation of the crack, the thermal expansion rod can be used as a part of the structure as it is.

According to a second aspect of the present invention, in the crack generating apparatus for a reinforced concrete wall according to the first aspect, the plurality of thermal expansion rods are substantially parallel to the joint groove. It was made.

Therefore, according to the crack generating apparatus for a reinforced concrete wall according to the second aspect of the present invention, the plurality of thermal expansion rods are buried in the thin portion between the joint grooves of the reinforced concrete wall substantially in parallel with the joint grooves. By doing so, the tensile stress acts over a wide range with a small number of thermal expansion rods, so that cracks can be effectively induced in the thin portion of the reinforced concrete wall.

In the crack generating apparatus for a reinforced concrete wall according to the third aspect of the present invention, the peeling member is provided on the outer periphery of the plurality of thermal expansion rods in the crack generating apparatus for the reinforced concrete wall according to the second aspect. As a result, concrete does not adhere to the outer periphery of the thermal expansion rod, and the concrete is not affected by the thermal expansion in the longitudinal direction of the thermal expansion rod, and cracks that deteriorate the periphery of the thermal expansion rod do not occur.
Therefore, only the radial thermal expansion of the plurality of thermal expansion rods causes tensile stress in the concrete,
Cracks can be reliably generated in the thin portions sandwiched between the joint grooves.

Further, the crack generating apparatus for a reinforced concrete wall according to the invention of claim 4 is provided by any one of claims 1 to 3.
Crack generator on two reinforced concrete walls
Since it is embedded in the reinforced concrete wall and has a temperature sensor that detects the temperature of the concrete, it detects the temperature of the concrete with the temperature sensor and monitors the temperature change of the concrete due to the hydration exothermic reaction. Before the strength is fully developed, and
During the period suitable for generating cracks until the concrete temperature becomes maximum and temperature cracks occur due to the hydration exothermic reaction, the above-mentioned thermal expansion rods are energized to thermally expand each of the expansion rods, and the reinforced concrete wall. Cracks can be surely generated in the thin portion sandwiched between the joint grooves.

According to a fifth aspect of the present invention, there is provided the crack generating apparatus for a reinforced concrete wall according to the fourth aspect, wherein the signal indicating the concrete temperature is received from the temperature sensor to display the concrete temperature. Since the display device is provided, the operator can easily confirm the concrete temperature, and can accurately judge when to energize the plurality of thermal expansion rods based on the concrete temperature.

In the crack generating apparatus for a reinforced concrete wall according to the present invention, the space between the adjacent thermal expansion rods is heated by the power supply device. The interval when the minimum value of the tensile stress generated between the adjacent thermal expansion rods due to the thermal expansion of each thermal expansion rod and the expansion and contraction of the concrete due to the hydration exothermic reaction exceeds the tensile strength of concrete The distance between the bottom of the joint groove and the thermal expansion rod is set to be narrower, and the expansion and contraction of the concrete due to the thermal expansion and hydration heat reaction of the thermal expansion rods heated by the power supply device. When the minimum value of the tensile stress generated between the bottom of the joint groove and the thermal expansion bar becomes equal to or more than the tensile strength of concrete, Since the interval is set to be smaller than the interval, the interval between the adjacent thermal expansion rods and the interval between the bottom of the joint groove and the thermal expansion rod should be within the maximum interval where cracks occur in concrete calculated in advance by thermal stress analysis etc. By doing so, it is possible to surely generate a crack in the thin portion sandwiched between the joint grooves of the reinforced concrete wall. In addition, since the plurality of thermal expansion rods are thermally expanded at a low temperature, concrete does not deteriorate due to the effect of the temperature of the thermal expansion rods, and even after cracks are generated, the reinforced concrete wall is used as a structure. it can.

A method for generating cracks in a reinforced concrete wall according to a seventh aspect of the present invention is a thin portion sandwiched between joint grooves provided on both sides of the reinforced concrete wall in a formwork forming the reinforced concrete wall. Disposing a plurality of thermal expansion rods having no nodes at predetermined intervals substantially in parallel with the joint groove; placing concrete in a mold in which the plurality of thermal expansion rods are disposed; and After the internal temperature of the reinforced concrete wall rises and reaches a maximum due to the hydration exothermic reaction of the concrete poured into the frame, the tensile stress generated on the reinforced concrete wall by the hydration exothermic reaction exceeds the tensile strength of the concrete. And heating the thermal expansion rods by applying a current to each of the thermal expansion rods until the temperature cracks occur.

Therefore, according to the method for generating cracks in a reinforced concrete wall according to the present invention, cracks are forcibly generated in a thin portion sandwiched between joint grooves before temperature cracks due to thermal stress occur. In addition, it is possible to reliably prevent the occurrence of cracks in unexpected directions at unexpected locations. In the above period, the concrete was solidified, but the tensile strength was not sufficiently developed, the strength was low, and the degree of tensile stress generated in the concrete due to the thermal stress due to the hydration exothermic reaction caused the concrete to crack. It works in the direction that promotes the thermal expansion of the thermal expansion rod, so that the temperature rise of the thermal expansion rod is kept low and even if the thermal expansion of the thermal expansion rod is reduced, cracks can be generated. Does not deteriorate. Furthermore, the energization time required to heat the plurality of thermal expansion rods to a relatively low temperature may be as short as about 10 minutes when a welding machine is used as a power supply, for example, and the execution time can be reduced. it can. In addition, since the plurality of thermal expansion rods are thermally expanded at a low temperature to generate cracks, it is necessary to increase the cross-sectional area of the thermal expansion rods or to increase the supplied power to greatly expand the thermal expansion rods. Therefore, the thermal expansion rod does not hinder the concrete placing operation, and the facility for supplying electric power to the thermal expansion rod is not excessively uneconomical. In the above-mentioned period, the expansion and contraction due to the hydration exothermic reaction causes a tensile stress in the concrete, which acts in a direction to promote cracking of the concrete. The share of stress due to expansion can be reduced. Therefore, the temperature rise of the plurality of thermal expansion rods can be further reduced, so that the heating of the thermal expansion rods deteriorates the concrete around the thin portion sandwiched between the joint grooves and causes structural defects in the reinforced concrete wall. There is no such thing.

[Brief description of the drawings]

FIG. 1 is a side view of a reinforced concrete wall that generates cracks by using a device and a method for generating cracks in a reinforced concrete wall according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is an enlarged horizontal sectional view of a reinforced concrete wall in which a reinforcing bar of the crack generating device is embedded.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a schematic diagram for explaining stress acting on concrete in which the reinforcing bar of the crack generation device is buried.

FIG. 6 is a diagram showing a degree of tensile stress generated in concrete with respect to a horizontal distance from a center point of the reinforcing bar.

7 is a diagram showing a change in the degree of tensile stress generated in concrete with respect to a distance in the horizontal direction from a center point of a reinforcing bar in FIG.

FIG. 8 is a diagram showing a change in concrete temperature with respect to the age of concrete.

FIG. 9 is a diagram showing a change in tensile strength with respect to the age of concrete.

FIG. 10 is a vertical sectional view of a reinforced concrete wall in which cracks are generated by using the device and the method for generating cracks in the reinforced concrete wall according to the second embodiment of the present invention.

[Explanation of symbols]

1 ... rebar group, 1A, 1B, 1C ... rebar, 2 ... AC power supply,
DESCRIPTION OF SYMBOLS 3 ... 1st temperature sensor, 4 ... 2nd temperature sensor, 5 ... Display device, 6 ... Electric connection member, 7, 8 ... Connection member, 10 ... Formwork, 11 ... Reinforced concrete wall, 12 ... Base, 13 ... Base concrete , 20 ... induced joint bar, 21 ... joint groove,
22: vertical reinforcing bar, 23: horizontal reinforcing bar, 30: peeling member.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuya Hironaka 2-2-2 Matsuzaki-cho, Abeno-ku, Osaka-shi, Osaka Prefecture Okumura Gumi Co., Ltd. (56) References JP-A-7-48880 (JP, A) JP-A-61-126250 (JP, A) JP-A-62-117929 (JP, A) JP-A-4-28973 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) E04B 1 / 62

Claims (7)

(57) [Claims] 1. A plurality of jointless thermal expansion rods buried at predetermined intervals in thin portions sandwiched between joint grooves provided on both sides of a reinforced concrete wall so as to face each other, An apparatus for generating cracks in a reinforced concrete wall, comprising: a power supply device for supplying an electric current to the rods to heat the respective thermal expansion rods. 2. The crack generating apparatus for a reinforced concrete wall according to claim 1, wherein the plurality of thermal expansion rods are substantially parallel to the joint groove. 3. The crack generating apparatus for a reinforced concrete wall according to claim 1, wherein a peeling member is provided on an outer periphery of the plurality of thermal expansion rods. 4. The crack generating apparatus for a reinforced concrete wall according to claim 1, further comprising a temperature sensor buried in the reinforced concrete wall and detecting a temperature of the concrete. Crack generator for reinforced concrete walls. 5. The crack generating device for a reinforced concrete wall according to claim 4, further comprising a display device for receiving a signal indicating the temperature of the concrete from the temperature sensor and displaying the temperature of the concrete. Cracking equipment for reinforced concrete walls. 6. The crack generating apparatus for a reinforced concrete wall according to claim 2, wherein a distance between the adjacent thermal expansion rods is adjusted by a thermal expansion and a hydration heat generation reaction of each of the thermal expansion rods heated by the power supply device. The expansion and contraction of the concrete by the above, the minimum value of the tensile stress generated between the thermal expansion bars adjacent to each other is set to be smaller than the interval when the tensile strength of the concrete or more, and the joint groove The distance between the bottom of the joint groove and the thermal expansion rod is increased by the thermal expansion of each of the thermal expansion rods heated by the power supply device and the expansion and contraction of concrete caused by the hydration heat generation reaction. The reinforcing bar is characterized in that the minimum value of the tensile stress generated between the bar and the bar is set so as to be smaller than the interval when the tensile strength of concrete exceeds the tensile strength. Cracking unit of the cleat wall. 7. A thin portion sandwiched between joint grooves provided on both sides of the reinforced concrete wall in a formwork forming a reinforced concrete wall at a predetermined interval substantially parallel to the joint groove. Disposing a plurality of thermal expansion rods, casting concrete in the form where the plurality of thermal expansion rods are disposed, and exothermic hydration reaction of the concrete placed in the form After the internal temperature of the reinforced concrete wall rises and reaches a maximum by the hydration exothermic reaction, the above-mentioned temperature is increased until the tensile stress generated in the reinforced concrete wall becomes higher than the tensile strength of concrete and the temperature crack occurs. Applying a current to the thermal expansion rods to heat each of the thermal expansion rods.