JPH0643752B2 - Construction method of concrete structure - Google Patents

Description

The present invention relates to a method for constructing a concrete structure, and particularly to a method suitable for constructing a concrete structure having a large member thickness.

Conventionally, various construction methods have been provided as a construction method of a concrete structure having a large member thickness, and a representative construction method is as shown in FIG.

The construction method shown in FIG. 4A is a so-called integral casting method, in which a form is built in a portion corresponding to the member thickness (W) and concrete is cast at one time to form the structure 18. Is.

In addition, the construction method of FIG.
Is divided into a plurality of layers (W ₁ to W _n ) and formed sequentially from the bottom layer, which is a so-called layering method.

Further, in the construction method of FIG. 6C, the member thickness (W) of the structure 18 is divided into a plurality of layers (W ₁ to W _n ), and a plurality of directions (l ₁ ) are orthogonal to the member thickness (W). It is a so-called block striking method in which the structure is divided into 1 to 1 _n ).

However, the conventional construction methods as described above have the following drawbacks.

That is, in the one-shot construction method, since the member thickness of the concrete is large, the temperature difference caused by the reaction heat when the concrete hardens becomes large, and there is a high possibility that the surface will crack.

In addition, in the piling method, the concrete formed in the second layer (W ₂ ) and later is cracked in the vertical direction in the concrete in the second layer and later by being restrained by the existing concrete layer formed before that. Is likely to occur.

Further, in the block driving method, although cracks do not occur relatively, there are problems that the number of joints is large, the weak points of the structure are increased, and the construction takes time.

The present invention has been made in view of the above-mentioned conventional problems, and the purpose thereof is without extending the construction period, and without increasing the number of joints that are weak points of the structure, It is an object to provide a method for constructing a concrete structure that can prevent cracking.

In order to achieve the above object, the present invention is a method for constructing a concrete structure having a large member thickness, in which concrete is placed in the peripheral portion of the transverse cross section of the constructed concrete structure leaving a central region. And a subsequent step of placing concrete in the central region after the peripheral concrete has hardened, and the width of the peripheral portion is 0.5 to 2.0 m over the entire cross section. Moreover, it is characterized in that it is set to a value of 10% to 2% with respect to the diameter of the concrete structure.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 shows an embodiment of a method for constructing a concrete structure according to the present invention.

The construction method shown in the figure is applied when constructing a concrete structure having a relatively large member thickness (W), and the concrete structure to be constructed has a central part region (space part) in its cross section. ) 10 and a peripheral edge region, and a preceding step of forming relatively thin peripheral edge portions 12 and 12 that face each other so as to define the central space 10 while leaving the central space 10 (FIG. 2A). (Refer to FIG. 4), after the cast concrete in the peripheral portions 12, 12 is hardened and the strength is sufficiently developed, the concrete is cast in the central space portion 10 and the peripheral portions 12, 1
2 and a subsequent step (shown in FIG. 2B) of integrally forming the central space portion 10.

The width dimension H of the peripheral portions 12 and 12 is set to 0.5 to 2.0 m over the entire cross section and set to a value of 10% to 2% with respect to the diameter of the concrete structure. It is preferable in that it prevents

Now, when constructing a concrete structure in the above-mentioned process, when concrete is placed in the central space portion 10 as shown in FIG. 2 (b), the temperature of this portion rises due to the hydration reaction of cement, The peripheral portion 1 located outside this
Since 2 and 12 are cold, the central space portion 10 is subjected to compressive stress so as to be prestressed as a whole.

Therefore, in general, when a structure as shown in FIG. 1 or 2 is constructed, in the member cross section due to the temperature difference between the inside and the outside,
Although tension and compressive stress are applied to the center from the surface, according to the construction method of the present invention, the degree of tensile stress on the surface is relaxed by the action of the prestress described above, and the occurrence of cracks is suppressed.

Next, when concrete is poured into the central space 10 and heat is transferred to the surroundings after a certain amount of time has passed,
Since the peripheral portions 12, 12 also increase in temperature and extend, the entire structure is in a tensile stress state.

However, since a prestress (compressive stress) is applied when the temperature rises as described above, a large tensile stress does not suddenly occur.

Further, at this point, the central space portion is hardened to some extent and the tensile strength is increased, so that the allowable tensile stress is large, and thus cracks are also prevented.

Furthermore, when the temperature of the cast concrete as a whole drops, the peripheral edges 12, 12 are considerably thinner than the central space 10, so the temperature drops early and the concrete is poured into the central space 10. It acts like a broom that tightens the concrete from the periphery and keeps the entire concrete structure on the compressive stress side.

Therefore, even when the temperature has dropped, the structure as a whole is in a compressive stress state and cracks are less likely to occur.

FIG. 3 is a graph of the result of measuring the relationship between the above-mentioned time lapse and stress state, which is a comparison of the surface portion (C) and the central portion (D) of the concrete structure formed by the construction method of the present invention. For this reason, the behavior of the surface portion (A) and the central portion (B) formed by the one-piece construction method shown in FIG.
Is represented as.

As is clear from this figure, the tensile strength of the structure increases with time and reaches an equilibrium state after a certain period of time. In the strip, the tensile stress exceeds the strength and cracks occur.

On the other hand, in the construction method of the present invention, the generation of cracks is prevented by the action of prestress (compressive stress) as described above, and this effect can be obtained without increasing the joint size as in the conventional block striking. The construction period will not be extended.

In addition, the joint surface between the central space portion 10 and the peripheral edge portions 12, 12 is equivalent to the member thickness (W) of the concrete structure and is smaller than the conventional layering method, and the action of the prestress force This also prevents cracks occurring on the joint surface.

4 (a), (b), and (c) show another embodiment of the present invention, and only the characteristic points will be described below.

In the second embodiment shown in FIG. 4 (a), the peripheral portion 12,
A hollow flat plate-shaped water stop plate 14 is interposed in the joint surface between the central space 10 and the space 12 so as to be orthogonal to this surface, which is convenient when water leakage becomes a problem.

Further, in the third embodiment of FIG. 4 (b), the peripheral portions 12, 1
The joint surface between 2 and the central space portion 10 is an inclined surface, and this figure (c) is a step surface, which is suitable for use in a concrete structure in which shear stress due to an external force poses a problem. .

The embodiment of the present invention is not limited to the above-mentioned one, and the peripheral edge portion 12 may be formed in a frame shape so as to surround the periphery of the central space portion 10.

As described above in detail in the examples, according to the method of constructing a concrete structure according to the present invention, after the temperature of the concrete in the peripheral portion that has been cast and hardened in the preceding step has cooled, the center of the subsequent step Since concrete is cast in the partial region, the concrete in the central region receives compressive stress even if the temperature rises, and as a result, the tensile stress on the surface is relieved and cracking can be prevented. Moreover, it does not involve the extension of the construction period and does not increase the number of joints.

[Brief description of drawings]

1 (a), (b), and (c) are cross-sectional views showing the conventional construction method, and FIG. 2 is a cross-sectional view showing the construction order of the construction method of the present invention. The process is performed in the order shown in FIG. FIG. 3 is a graph showing the stress level of a structure formed by the construction method shown in FIG. 1 (a) and the construction method of the present invention. FIGS. 4 (a), (b) and (c) are sectional views showing the second to fourth embodiments of the present invention. 10 ... central space 12 ... peripheral part 14 ... water stop plate

Claims (1)

[Claims] 1. A method of constructing a concrete structure having a large member thickness, which comprises a preceding step of placing concrete in a peripheral portion of a concrete structure to be constructed, which has a central region in a cross section thereof, and the peripheral portion. The subsequent step of placing concrete in the central region after the concrete has hardened, and the width dimension of the peripheral portion is 0.
A method for constructing a concrete structure, which is set to a value of 5 to 2.0 m and a value of 10% to 2% with respect to the diameter of the concrete structure.