JPS5826463B2 - Prestressed concrete method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a prestressed concrete concrete method.

In general, in the boss tension prestressed concrete method, tensile force is applied to tendons placed in the member to prestress the concrete, and anchors are installed at both ends of the member to transmit the reaction force of this tensile force to the concrete as prestress. is used.

In particular, the unbonded prestressed concrete method eliminates grouting work and streamlines the installation work, making it extremely effective in controlling deflection and cracking of structures.

However, its usage record is still at a low level.

The reason for this is that the cost of the fixing device when using PC steel strands or PC steel wire as the tension material for introduction is extremely expensive compared to the cost of the tension material itself, and its characteristics are not sufficient in terms of cost-performance ratio. It is in a place where it is not possible to make full use of it.

In view of the above circumstances, we have attempted to drastically reduce the cost of anchoring equipment, thereby making the prestressed concrete method superior to conventional methods in terms of cost and performance, and making it possible to use it without using expensive products. In an attempt to achieve the same performance, it has been proposed that unbonded PC steel strands be placed in a semicircular shape in the concrete at the end of the member in place of the conventional fixing device. .

In other words, its basic form is as shown in Figure 1, with a concrete flat plate 1 as a member (this method is applicable to precast concrete slabs, precast plates that also serve as lower molding frames of synthetic slabs, cast-in-place slabs, and large precast walls). etc. are possible.

) The unbonded PC steel stranded wire 2 with a sheath, which has been buried in advance and has a rust preventive material sealed inside, is fixed by the fixing device 3 at one end A of the flat plate 1, but at the other end B.
are arranged in a semicircular shape, and the tension force is introduced from A, and on the B side, prestress is directly introduced into the concrete from the semicircular PC steel wire 2.

Therefore, no fixing device is required on the B side.

In this way, the conventional boss tension construction method requires four fixing devices as shown in the figure, but only two fixing devices are required, which reduces costs.

Moreover, in the tendons of this method, the enclosed anti-rust material has a friction-reducing effect, which reduces the frictional loss of tension force caused by angle changes in the loops of the tendons.

When the friction loss of the tension force was actually measured, the reduction rate due to loop fixation of the tension force (angle change α=π) was about 12%.

Here, if we calculate μ by assuming λ = 0 in the following equation that is commonly used, μ = 0.04'/
A measurement value of rad was obtained.

This is the μ value (
0.1~0.314a, degree) or PC with adhesion
This value is considerably smaller than the μ value of steel stranded wire (0.25 to 0.30'4d).

FIG. 2 shows another case in which the present method is applied to the flat plate 1.

That is, the sheathed unbonded PC steel stranded wire 2a is first arranged in a semicircle on the B side, then arranged in a semicircle on the A side, and then arranged in a semicircle on the B side, and then placed on the A side. The wire 2b was brought in and is fixed on the A side by the fixing tool 3a, while the other sheathed unbonded PC steel wire 2b is brought in the reverse arrangement and fixed on the B side by the fixing tool 3b.

In this case, the conventional method of construction using the boss tension method would require 12 anchors, but the present method requires only four, making it possible to take full advantage of its advantages.

However, in this construction method, it is particularly necessary to ensure the stability of the semicircular anchorage part and to provide effective reinforcement for the concentration of concrete in the anchorage part, and this method is suitable. It is desired to provide a reinforcing means.

In other words, in this construction method, the distribution of radial strain in the concrete at the semicircular anchorage caused by the introduction of prestress is a tensile region from near the inside of the semicircular tendon to the outside, and a compressive region from near the inside of the semicircle to the center of the semicircle. area.

The present invention provides reinforcing means under such conditions.

Details of this will be explained below based on the drawings.

In other words, the one shown in Fig. 3 is characterized by dispersing the force acting on the compression area and by erecting a connecting member between the compression area and the tension area to integrate and reinforce the western area. 6 in the figure is a curved flat steel or semicircular steel placed along the compression area, that is, inside the semicircle (in this case:
The inside of the semicircle is directed toward wire 2 from the unbonded PC steel with sheath), and the force acting on the compression area is dispersed through this.

In addition, 4 in the figure is a mesh in which a compression region and a tension region are arranged on the upper and lower sides of a semicircular portion, thereby integrating the west region.

Therefore, in order to reinforce the present invention as described above, the force acting on the compression region is dispersed, and at the same time, the compression region is integrated with the tension region by the connecting member mesh 4, so that the strength is increased. It's increasing.

[Brief explanation of the drawing]

Figure 1 is a front and side view of a concrete slab showing a conventional construction method, Figure 2 is a front view of a concrete slab showing another example, and Figure 3 is an enlarged view of the main parts of a concrete slab showing an embodiment of the present invention. FIG. A simple explanation of the symbols, 1... Concrete flat plate,
2... Unbonded PC steel stranded wire with sheath, 3.
...Fixing tool, 4...Mitshu, 6...
...Flat steel or semicircular steel.

Claims (1)

[Claims] 1 In the prestressed concrete construction method, which is characterized by placing unbonded PC steel strands in a semicircular shape in concrete at the end of the member, and using this part as an anchoring part in place of an anchor, A prestressed concrete construction method characterized in that flat steel or semicircular steel is placed on the top and bottom of the semicircular part, and meshes are placed on the upper and lower sides of the semicircle to extend the inside and outside of the semicircle for reinforcement.