JPH0571746B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of constructing a reinforced concrete structure in which prestress is introduced for temporary construction.

<Prior Art> Prestressed concrete is a type of concrete in which a compressive force corresponding to the stress is applied in advance so as to cancel out the stress generated in concrete members due to the application of a load.

In reinforced concrete structures, there is a construction method that introduces prestressing for the purpose of early dismantling of formwork.

However, in the case of prestressed concrete, prestressing should be introduced only after the compressive strength of the concrete reaches approximately 85% of the design strength, and this was also the case when introducing prestressing for temporary construction.

The reason for this was thought to be that if prestress is introduced all at once before reaching about 85%, the following defects will occur.

(1) Creep occurs excessively.

(2) The concrete in the introduction section will be destroyed.

(3) The short-term and long-term properties of prestressing before it reaches about 85% are unknown.

<Problems to be solved by the present invention> After the compressive strength reaches approximately 85% of the design strength,
The conventional method of introducing prestress has the following problems.

<B> Although the purpose is to quickly dismantle the formwork, etc., it ends up taking a longer time to install the formwork and shoring that supports the concrete.

Therefore, for example, in construction work, formwork and shoring for at least two layers are required.

<B> There is a high possibility that cracks will occur in concrete members due to the long period of curing before introducing prestress.

<Object of the present invention> The present invention has been made to improve the above-mentioned drawbacks, and provides a reinforced concrete structure whose formwork and shoring can be dismantled within a short period of time after concrete is poured. The purpose is to provide a construction method.

<Structure of the Present Invention><A> Characteristics of Reinforced Concrete at a Young Age Innumerable experiments have been conducted on concrete test pieces, including changes in strength at different ages, and other experiments.

However, the relationship between the material age and properties of reinforced concrete as a product has hardly been studied.

The inventor of the present invention focused on this point and repeated experiments to determine the relationship between material age and vibration frequency (rigidity), and obtained the results shown in FIG. 1.

As a result, we found for the first time that even when concrete is loaded at a young age, its properties do not deteriorate due to loading too early, and that stiffness steadily increases with age thereafter. .

<B> Introduction of early tension force Therefore, in reinforced concrete structure 1 as shown in Figure 2,
Regarding the timing and method of introducing prestress to the PC steel wire 2, the following conclusions were reached.

(1) Prestressing may be introduced at any time after concrete is poured.

(2) The earliest period of introduction is the moment when concrete itself becomes able to maintain its shape without the support of formwork.

(3) The amount of force to be introduced is determined according to the compressive strength of the concrete at that time.

Therefore, it was found that when the material is young, it is sufficient to introduce a small prestress value depending on the strength at that time.

That is, in the present invention, prestress is introduced as soon as the concrete structure has developed enough strength to maintain its shape, and the introduced prestress is used to dismantle the formwork. When the concrete itself can maintain its shape without the need for formwork, prestress is introduced depending on the strength at that time, but at this time, prestress is applied to the anchor side of the PC steel wire and A concentrated external force may be applied to the tension side.

Therefore, local cracking or crushing may occur.

In order to avoid such a phenomenon, the external force can be received and dispersed by a steel support plate with a large area.

<Effects of the present invention> As described above, the present invention introduces prestress at an early stage according to the strength at that time, once the concrete itself can maintain its shape without being maintained by formwork. It's a method.

Therefore, the following effects can be expected.

<B> By introducing tension at an early stage, concrete members can maintain their shape, and the load during construction (concrete on upper floors, formwork, etc.) can be maintained.
(e.g. the weight of shoring).

In other words, the formwork can be dismantled immediately after concrete is poured and used for construction of the upper floors.

Therefore, a small number of temporary members can be quickly repurposed, and the construction period can be shortened.

<B> Strong pressure can be applied to concrete at a stage when it can maintain its shape, that is, when hydration is actively progressing.

The mechanism is similar to pressed concrete and centrifugal concrete, and high strength concrete can be obtained.

[Brief explanation of the drawing]

Figure 1: An explanatory diagram of the relationship between the material age and rigidity of a reinforced concrete member. Figure 2: An explanatory diagram when using prestress as a temporary structure.

Claims (1)

[Scope of Claims] 1. A method for constructing a reinforced concrete structure in which reinforcing bars are arranged inside and concrete is poured into a hierarchically assembled formwork, in which an unbonded type PC steel wire is arranged. The first step is to pour concrete into the frame, and immediately after the concrete is poured, once the concrete structure has developed enough strength to maintain its shape, prestressing for temporary construction is carried out according to the developed strength of the concrete. A method for constructing a reinforced concrete structure, comprising: a second step of introducing a mold; and a third step of removing the formwork.