JPS61221458A - Prestress introducing apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a prestress introduction device for preventing cracks in reinforced concrete buildings due to load application or drying shrinkage of concrete.

(2) Conventional technology As a conventional prestress introducing device of this type, a bearing plate is slidably fitted into each end of a PC steel bar with threads formed on the circumferential surface of both ends, and the pressure plate is slidably inserted into the outside of the prestress introduction device. It is known that nuts are screwed together. Then, the conventional device is attached, for example, to reinforcement near the corner of the opening of the window frame, a formwork is set, and concrete is poured into the formwork. In order to prevent the nuts and bearing plates of the device from being buried in the concrete during this driving R, a concrete inflow prevention plate is attached to the formwork, and after the concrete has hardened, the formwork is removed and both nuts are removed. After tightening, the concrete between the inner skin pressure plates is prestressed by the inner skin pressure plates, and then concrete is embedded in the places between these nuts and the bearing pressure plates, and the concrete wall is completed.

Ru.

(3) Problems to be Solved by the Invention According to this conventional device, a flow prevention plate is attached to the formwork during construction to prevent concrete from flowing into the nuts and bearing plates during concrete pouring. There are disadvantages in that it takes time and effort to embed concrete in the location after prestressing, and that prestressing cannot be applied unless the concrete hardens and the formwork is removed, and the concrete has not reached a predetermined strength.

An object of the present invention is to provide a prestress introduction device that can apply prestress in advance before construction and that can be easily installed.

(4) Means for Solving the Problems In order to achieve this object, the present invention includes a method in which a bearing plate is slidably fitted into each end of a PC steel bar having threads formed on the circumferential surface of at least both ends. At the same time, a nut is screwed to the outside of the support plate, and a holder made of a material that becomes brittle in an alkaline atmosphere is interposed between these support plates.

(5) Effect If the nuts at both ends of the PC steel bar are tightened in advance to apply compressive force to the holding body, and the prestress introduction device is attached to the reinforcement before concrete is poured, the prestress introduction device can be attached to the reinforcement before concrete is poured. When the device is buried in concrete, the holding body is weakened by the alkaline atmosphere of the concrete and cannot hold the compressive force, and the compressive force acts on the concrete and introduces prestress, thus causing cracks in the concrete. It will no longer occur.

(6) Embodiment One embodiment of the present invention will be described with reference to FIGS. 1 to 4.

(1) shows the prestress introducing device, (2) shows the PC steel bar, and the PC steel bar (2) has threads (2a) on both ends.
(2a) are formed, and the threads (
2a) Into (2a), the bearing plates (3) (3), which are made of steel and have a disc shape and have a through hole in the center, are slidably inserted, respectively, and the nuts (3) (3) are inserted from the outside of these bearing plates (3) (3). 4) (4
) were screwed together. The holder (5) interposed between these bearing plates (3) (3) is made of polyester resin, vinyl acetate resin, acrylic resin, etc., which becomes brittle by hydrolysis in an alkaline atmosphere, and is formed into a cylindrical shape. ing.

Next, the use of the prestress introducing device (1) of the above embodiment will be explained.

First, as shown in the second figure, a prestress introduction device t (
Tighten the nuts (4) (4) of (1) to apply compressive force to the holder (5).The prestress introduction device (1) with the compressive force applied in this way is inserted into the window frame as shown in Figure 3. After attaching diagonally to the outer reinforcing bars at the corners of the opening (6) by tying wire or the like, a formwork is set and concrete is poured into the formwork. Thus, the prestress introduction device (1
) is embedded in the concrete (7) as shown in Figure 4, and due to the alkalinity of the concrete (7), the holder (5) in contact with it starts to weaken and is unable to maintain the compressive force. The compressive force by the bearing plates (3) (3) is applied to the concrete (3) between these bearing plates (3) (3).
7), and prestress is introduced into the concrete (7). After the concrete (7) to which prestress has been introduced in this way is cured, the formwork is removed to obtain a reinforced concrete wall. Here, due to drying shrinkage of the concrete wall, cracks (
Even if A) is about to occur, the prestress introduction device (1)
Since there is prestress in the concrete (7), no cracks will occur. The fifth @ shows another example, and in this example, the disk is placed in contact with the inside of the bearing plate (3) (3). It is constructed by intervening holding bodies (5) (5) in the form of a shape, and further interposing concrete c8") between these holding bodies (5) (5), and FIG. 6 shows still another embodiment. ,
In this example, the concrete (
FIG. 7 shows yet another embodiment, in which a plurality of columnar holders (5) (5) are further inserted in Holding body (5)・
...(5) is constructed by intervening between bearing plates (3) (3) along the circumferential surface of a PC steel rod (2). Furthermore, the fifth
In the figures and FIG. 6, (9) indicates a lubricating material such as asphalt, rubber, or polyethylene.

Next, another example of the use of the prestress introduction device (1) will be explained as shown in Fig. 8! ! Cracks (B) occur in wall-like structures due to temperature changes, but the cracks (A) can be prevented by embedding a prestress introduction device (1) in the concrete of the structure as shown in Figure 9. Moreover, as shown in FIGS. 10 and 11, precast members (10
) (10) When placing post-cast concrete (11) at the joint of
By installing the concrete in advance, post-cast concrete) (
11) Cracks can be prevented.

(7) Effects of the Invention As described above, according to the prestress introducing device of the present invention, the bearing plates are slidably fitted into the threads at both ends of the PC steel bar, and nuts are screwed to the outside of the bearing plates. Since a holding body made of a material that becomes brittle in an alkaline atmosphere was used, the nuts at both ends of the PC steel bar were tightened in advance to apply compressive force to the holding body, and the prestress introducing device was installed before concrete was poured. If the device is installed in the reinforcement, the device will be buried in the concrete and the holding body will be weakened by the alkaline atmosphere of the concrete and will not be able to hold the compressive force, and the compressive force will act on the concrete. Prestressing is introduced, thus preventing cracks from occurring in the concrete, and furthermore, construction is made easier as there is no need to attach inflow prevention plates to the formwork or embed concrete after prestressing, which was required in the past. Become,
It also has the advantage of being simple in structure and inexpensive.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of one embodiment of the device of the present invention, Fig. 2 is a front view showing the device in a state where the nut is tightened and compressive force is applied to the holder, and Fig. 3 is a cross-sectional view of the device in the corner of the opening. FIG. 4 is a front view showing the device buried in a reinforced concrete wall around the area, FIG. 4 is a front view showing the device buried in concrete, and FIGS. 5 to 7 are sectional views of other embodiments, Figure 8 is a perspective view of the wall-like structure before the pre-stress introduction device is buried, Figure 9 is a perspective view of the wall-like structure after the device is buried, and Figure 10 is the precast structure after the pre-stress introduction device is buried. FIG. 11 is a perspective view of a joint portion of one member, and a front view thereof. (1)...Prestress introducing device (2)...PC steel rod (2a)...Thread (3)
... Bearing plate (4) ... Nut (5) ...
holding body

Claims (1)

[Claims] Threads are formed on the circumferential surface of at least both ends, and a bearing plate is slidably inserted into each end of the PC steel bar, and a nut is screwed on the outside of the bearing plate, which is weakened in an alkaline atmosphere between these supporting plates. A prestress introducing device characterized by intervening a holder made of a material that