JPS5826465B2 - 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 method eliminates grouting work and streamlines the installation work, making it extremely effective in controlling deflection and cracking of structures.

However, its actual usage is still at a low level.The reason for this is that the cost of the fixing device when using PC steel stranded wire or PC steel wire as the tension material for introduction is extremely expensive compared to the cost of the tension material itself. However, due to the cost/performance ratio, its characteristics 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 when using it without using expensive products. The idea was to achieve the same performance as the conventional fixing device, and the idea was to place unbonded PC steel strands in a semicircular shape in the concrete at the end of the member as a substitute for the conventional fixing device. There is.

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 sheathed unbonded PCm stranded wire 2, which has been buried in advance and has a rust preventive material sealed inside, is fixed by the fixing tool 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 semicircular 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−〇, 04”/
A measurement value of 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, the one shown in Fig. 3 has a spiral reinforcing bar T wrapped around the semicircular part, and the concrete inside the spiral reinforcing bar 7 acts as a deformation restraint area, resulting in an increase in the diameter of the tendon. It is assumed that the force acting on the compression area is dispersed.

The failure mode of the construction method of the present invention as described above is shown in FIG.

In addition, the compressive strength test results of the concrete cylindrical specimens used in this case were 144 to 19.
9 kg/i, and the experiment was conducted by keeping the concrete 4 strength low, and as a reinforcing reinforcing bar, S]) 30
．． Using D6, tension strength is 4840 kg/cut
Met.

The thickness of the test specimen is 100y+m, and the tension material is placed in the center, and the tension material is φ12.7 PC steel stranded wire (7 pieces).
The material was coated with asphalt-based anti-rust grease and covered with a polyethylene sheath.

The test specimen was displayed by arranging the semicircular radius (rD60
J indicates the present invention with a semicircular portion radius of 60 crfL).

Moreover, rOJ indicates that without reinforcement. From this result, the fracture mode is dominated by splitting fracture within the longitudinal section of the member, and the fracture occurs rapidly regardless of the presence or absence of reinforcement, and there is no visible change during the tension process.

For unreinforced test specimens, the fracture strength is semicircular diameter D = 80C1
In the case of rL, the improvement is 45% over that in the case of D=60 cm.

The failure mode of the specimen of the present invention was similar to that of the unreinforced specimen.

In the case of the present invention, the concrete inside the spiral iron remained as it was even after the loop portion was destroyed, and it seems that it worked effectively as the expected deformation restraint area.

The fracture strength of the reinforced specimens is 44% and 33% higher than the unreinforced specimens, respectively.

[Brief explanation of drawings]

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, Figure 3 is a front view of a concrete slab attached with an enlarged view of the main parts of the present invention, FIG. 4 is a front view of a concrete flat plate attached with a fracture strength table and a partial side view showing fracture modes in the present invention. A simple explanation of the symbols, 1... Concrete flat plate,
2... Unbonded PC steel stranded wire with sheath, fixing device, 7... Spiral reinforcing bar. 3...

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 an anchoring part in place of the fixing device. In a construction method characterized by
When spiral reinforcing bars are wrapped around the unbonded PC steel strands of the anchorage part, the concrete inside the spiral reinforcing bars acts as a deformation restraint area, which increases the diameter of the tendon and disperses the force acting on the compression area. This is a prestressed concrete construction method that is characterized by the use of toss.