JPS5826464B2 - Prestressed concrete method - Google Patents

Description

[Detailed description of the invention] This invention relates to a prestressed concrete construction 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 construction method eliminates grouting work and streamlines the installation work, and is extremely effective in dealing with deflections and cracks in 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 cannot be fully utilized.

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.

In addition, in the tension material of this construction method, the enclosed anti-rust material has a friction-reducing effect, which reduces the frictional loss of tension force caused by the angle change in the semicircular portion of the tension material.

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

The following formula usually used here If we assume that λ−〇 and find μ, we get A measured value of μ=0.04′/rad was obtained.

This is the μ value (
0.1~0.31/rad) or attached P
μ value of C steel stranded wire (0.25~0.30”/rad
) is quite small compared to .

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 against stress concentration in the anchorage concrete. It is requested that reinforcement measures be provided.

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 tension member to the outside, and a compressive region from near the inside of the semicircle to the center of the semicircle. becomes.

The present invention provides reinforcing means under such conditions.

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

In other words, in the case shown in Fig. 3, reinforcing bars are installed between the above-mentioned tension area and compression area to strengthen the integration of the inner area, and both ends are bent along the radius of the semicircular part. The reinforcing bars 5... are arranged radially.

As a result of integrating the tension region and compression region in this way, the cracks that occurred in the case of no reinforcement were able to be eliminated.

[Brief explanation of drawings]

FIG. 1 is a front and side view of a concrete IJ-to flat plate showing a conventional construction method, FIG. 2 is a front view of a concrete flat plate showing another example, and FIG. 3 is a side view and a front view showing the present invention. A simple explanation of the symbols, 1... Concrete flat plate,
2... Unbonded PC steel stranded wire with sheath, 3.
...Fixing tool, 5...Reinforcement bar.

Claims (1)

[Claims] 1. Extend the unbonded PC steel strand in a straight line from the fixing device at one end of the concrete member, and then place it in a semicircular shape in the concrete at the end of the concrete member, and use this part as the fixing part in place of the fixing device. In a construction method characterized by
In the concrete radial direction of the anchorage, a reinforcement with bent ends is constructed between the tensile zone on the outside of the radius and the compression zone on the inside of the radius in a manner that crosses the unbonded PC steel strands, and the surrounding area is A prestressed concrete construction method characterized by integrating and reinforcing the