JPS6121251A - Pc strand bundle and sheath - 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 <Industrial Application Field> The present invention relates to a PC strand bundle and sheath used in PC tanks and the like.

<Problems to be Solved by the Invention> This type of large-capacity PC strand bundle is composed of a plurality of PC steel materials, and is tensioned simultaneously by jacks.

Normally, each strand has a variation in tension, and this tendency increases when the PC strand bundle arrangement includes a curved section, and in this curved section, strands that share the tension exceeding the standard yield load occur.

In order to reduce the variation in the tension of each strand, the strand bundle is twisted in advance before being inserted into the sheath. Measures are needed to prevent this.

Furthermore, it is necessary to suppress the tension of all strands to below the standard yield load.

<Purpose of the Invention> This invention was proposed in view of the above circumstances, and its purpose is to prevent the untwisting of the PC strand bundle and further to suppress the tension of all the strands to below the standard yield load. The purpose of the present invention is to provide a PC strand bundle and a sheath that can be used in various ways.

<Structure of the Invention> The PC strand bundle and sheath according to the present invention have a sheath with a circular cross-sectional shape, and a circular retraction fitting corresponding to the sheath cross-sectional shape is attached to the tip of the pre-twisted PC strand bundle. This is to prevent untwisting.

Furthermore, in another PC strand bundle and sheath according to the present invention, the radius of curvature of the sheath arranged in a curve is R1.
When the central angle is θ and the inner diameter of the sheath is D, one rotation of twist is applied to the PC strand bundle at a pitch γ that satisfies γkuni・R2・θ/D (K: constant), and the tension of all the strands is It is designed to keep the yield load below the standard yield load.

<Example> The present invention will be described below based on an illustrative example. As shown in FIGS. 1 and 2, the sheath 1 has a circular cross-sectional shape, and a retractable cap 3 with a circular shape corresponding to the sheath 1 is attached to the tip of the pre-twisted PC strand bundle 2.
As a result, even if the PC strand bundle tries to untwist during retraction, the retraction cap 3 cannot be rotated, so that it is inserted in a twisted state.

Examples of the sheath 1 include a winding sheath in which a steel band is spirally wound and the ends are overlapped and bonded, a steel pipe with several thicknesses, a vinyl chloride pipe, and the like.

Next, the optimum twist amount of the PC strand bundle '2 is determined.

The Young's modulus of the strand is E1, the cross-sectional area is A1, the average tension is
, the torsion angle given to the entire east strand is ψ(rad),
If the coefficient of variation of the strand tension is CV, then the reliability is 95q6, where R: radius of curvature of the sheath or strand bundle θ: central angle of the sheath or strand bundle D: inner diameter of the sheath, A, 〒 is a constant Furthermore, if we take the envelope of the curve of ■, then the twist pitch γ given to the PC strand bundle is γ−2πRθ/ψ...■, and by substituting ■ into ■, we get 2πR”tj − K・□・γ (K: constant) ・・・■R2θ Here, when we plot the results of measuring the coefficient of variation by giving twist to the PC strand bundle, we get the result shown in Figure 4, which is the result of equation 0. K is the maximum value = '36.67
...■.

Now, if CV is 0.07, the probability that the strand exceeds the standard yield load is about 10-3 or less, so ■,
(2) From the formula, 0.07≧36.67− − γ R2θ is obtained.

When the PC strand bundle 2 is twisted by one rotation (2πrad) at a pitch γ that satisfies Equation 0, the variation in strand tension can be reduced to the level of a straight PC strand bundle.

<Effects of the Invention> As described above, according to the first aspect of the present invention, since the sheath and the retracting fitting are shaped like a circular shape, it is possible to prevent untwisting when retracting, and especially in the curved part, each strand is The variation in tension can be reduced.

Furthermore, according to the second aspect of the present invention, variations in strand tension of a curved PC strand bundle can be reduced by straight line P.
Since the C strand bundle can be reduced by ζ and the strand tension can be prevented from exceeding the standard yield load, safety can be guaranteed.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views and schematic vertical cross-sectional views showing the PC strand bundle and sheath according to the present invention, Figure 3 is a schematic diagram showing the state of the PC strand bundle at a curved portion, and Figure 4 is a twisted view. It is a graph in which the coefficient of variation K was determined by giving 1. Sheath, 2. PC strand bundle, 30. Retractable cap.

Claims (2)

[Claims] (1) A PC strand bundle composed of a plurality of PC steel materials and a sheath through which this strand bundle is inserted, with a sheath cross-sectional shape of a circular shape and a pre-twisted P
A PC characterized in that a circular retraction fitting corresponding to the cross-sectional shape of the sheath is attached to the tip of the C-strand bundle.
Strand bundle and sheath. (2) A PC strand bundle composed of a plurality of PC steel materials and a sheath through which this PC strand bundle is inserted, where the radius of curvature of the curved sheath is R, the center angle is θ, and the inner diameter of the sheath A PC strand bundle characterized in that the PC strand bundle is given one rotation of twist at a pitch γ that satisfies γ≦k・R^2・θ/D (k: constant), where is D. sheath.