JP2008007898A - High-strength pc steel stranded wire and concrete structure using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PC (prestressed concrete) steel stranded wire having higher strength than conventional strength and affording sufficient fixing efficiency and to provide a concrete structure using the steel stranded wire. <P>SOLUTION: The high-strength PC steel stranded wire having the higher strength than the conventional strength and affording the fixing efficiency sufficient for practical use can be obtained as follows. The steel stranded wire is 7 stranded constitution prepared by stranding one central wire with 6 side wires. The steel stranded wire is regulated so that the outside diameter is 15.0-15.6 mm, the total cross-sectional area is 135-148 mm<SP>2</SP>, the tensile load of the whole stranded wire is ≥310 kN and the tensile load of the side wires is ≥80% of the tensile load of the central wire. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-strength PC steel stranded wire produced by twisting a plurality of wires drawn by cold drawing, and a concrete structure using the same.

  PC steel stranded wire is usually manufactured by a method in which a wire specified in JIS G 3502 is cold-drawn and then twisted together, and then subjected to a blueing treatment for removing residual strain in the final process. Those that meet the JIS G 3536 standard are used.

On the other hand, in Patent Document 1, the standard diameter of the 19 stranded wires in JIS G 3536 is 19.3 mm, the stranded wire configuration and the outer diameter are the same, and the total cross-sectional area is also the nominal cross-sectional area. PC steel strands (PC strands) have been proposed that have the same degree and a tensile load that greatly exceeds the lower limit of the standard value. If PC steel strands with increased tensile load are used in this way, the strength of concrete structures will be improved and workability will be improved, that is, PC steel strands with a smaller diameter than conventional ones will be used, or PC steel strands will be inserted. It becomes possible to increase the pitch.
Japanese Patent No. 3684186

  However, even if the tensile load is increased as compared with the conventional PC steel stranded wire described in Patent Document 1, if the fixing efficiency is low, it may be difficult to be put to practical use. Here, the fixing efficiency means a ratio of a tensile load to a standard tensile load when a fixing tool is set on a PC steel stranded wire and a tensile test is performed through the fixing tool.

  An object of the present invention is to provide a PC steel stranded wire having a higher strength than the conventional one and obtaining a sufficient fixing efficiency, and a concrete structure using the same.

In order to solve the above-mentioned problems, the high-strength PC steel stranded wire of the present invention has a seven-stranded structure in which one center line and six side wires are twisted together, and has an outer diameter of 15.0 to 15.5. It was 6 mm, the total cross-sectional area was 135 to 148 mm ² , the tensile load of the entire stranded wire was 310 kN or more, and the tensile load of the side wire was 80% or more of the tensile load of the center line.

  That is, the standard diameter of the seven stranded wires in JIS G 3536 with a standard diameter of 15.2 mm is the same, and the total cross-sectional area is the same as the nominal cross-sectional area with the same stranded wire configuration and outer diameter. By adjusting the tensile load so that the tensile load is significantly higher than the lower limit of the standard value (261 kN) and the ratio of the tensile load between the side line and the center line is 80% or more, it is stronger and more practical than before. Fixing efficiency can be obtained.

Here, the total cross-sectional area is limited to the above range because if the total cross-sectional area is less than 135 mm ² , it becomes difficult to ensure the tensile strength required for the center line and the side line alone, and the total cross-sectional area exceeds 148 mm ² . This is because it becomes difficult to keep the outer diameter within the allowable range (15.0 to 15.6 mm) of the standard diameter of 15.2 mm. Moreover, if the tensile load of the whole strand wire is less than 310 kN, the strength improvement allowance with respect to the conventional thing is small, and the merit of the high intensity | strength of a concrete structure using it and workability improvement is small. When the tensile load on the side line is less than 80% of the center line, the burden on the side line becomes large, fixing efficiency is lowered, and it becomes difficult to put it to practical use.

  Further, by using the high-strength PC steel stranded wire having the above-described configuration for the concrete structure, it is possible to increase the strength or improve the workability while ensuring the fixing stability of the structure.

  As described above, the PC steel stranded wire of the present invention has a tensile load that greatly exceeds the lower limit of the JIS standard value and sufficient fixing efficiency can be obtained. Can be used practically.

  Further, the concrete structure of the present invention uses a high-strength PC steel stranded wire having the above-mentioned characteristics, so that it has sufficient fixing stability and has higher strength than conventional ones or is excellent in workability. It will be.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The high-strength PC steel stranded wire of this embodiment has a seven-strand structure in which one center line (wire diameter: 5.20 mm) and six side wires (wire diameter: 5.00 mm) are twisted together. The outer diameter is 15.20 mm and the total cross-sectional area is 139 mm ² . This stranded wire configuration, outer diameter, and total cross-sectional area conform to those of the standard diameter of seven stranded wires in JIS G 3536 of 15.2 mm. Further, as the strands of the center line and the side line, SWRS82A and SWRS82B specified in JIS G 3502, C: 0.90 to 1.3 wt%, Si: 0.5 to 1.2 wt%, Mn: 0 Adjusted so that the tensile load of the entire stranded wire is 310 kN or more by using a suitable combination of steel wire of hypereutectoid steel containing 0.1 to 1.0 wt% and Cr: 0.05 to 1.5 wt% Has been.

  In the method for producing the PC steel stranded wire, first, the above-described strand (wire diameter: 13.0 mm) is subjected to a patenting treatment, the strength thereof is adjusted to 1490 to 1550 MPa, and then continuous stretching having nine dies. Cold drawing is performed to the diameters of the center line and the side line by a wire machine. And after twisting a center line and a side line and performing a stretching process, a blueing process is performed at 380 degreeC. This stretching process is performed by applying an appropriate tensile load to the stranded wire between two capstans installed in the middle of the stranded wire process. In the bluing treatment, high-frequency heating is performed for 2 to 3 seconds in a heating furnace, and then water cooling is performed through a water-cooled tank. In addition, it is air-cooled for several seconds between a heating furnace and a water cooling tank.

  Next, an experiment for examining the influence of the ratio of the tensile load between the side line and the center line on the PC steel stranded wire on the fixing efficiency will be described. In the experiment, first, five types of test pieces having different tensile load ratios by changing the combinations of the side wire and the center wire were produced. Then, a wedge-type fixing tool for SM method was set on each test piece, and a fixing test was performed through this fixing tool to determine fixing efficiency. Regarding the fixing efficiency, 95% or more is required by the Japan Society of Civil Engineers standards (edited by the Japan Society of Civil Engineers Concrete Committee PC Method Design and Construction Guidelines Revision Subcommittee, “Concrete Library 66-Prestressed Concrete Method Design and Construction Guidelines” ~ ", 1991, p.15).

  FIG. 1 shows the results of the above experiment. As is apparent from this figure, the fixing efficiency increases as the ratio of the tensile load between the side line of the PC steel stranded wire and the center line increases. This is considered to be due to the fact that teeth for gripping the stranded wire of the fixing tool bite into the side line and lower the fixing efficiency, and that the load on the side line decreases as the tensile load on the side line increases. It was confirmed that if the tensile load on the side line is 80% or more of the center line, the fixing efficiency exceeds 95%, which is the standard value by the Japan Society of Civil Engineers.

  In addition, when a concrete structure was manufactured using the PC steel stranded wire shown in FIG. 1 having a tensile load ratio of 80% or more between the side line and the center line, the fixing stability was equal to or higher than the conventional one. It was possible to increase the strength or improve the workability while securing the properties.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

The graph which shows the relationship between the ratio of the tensile load of the side line of the PC steel strand of embodiment, and the center line, and fixing efficiency

Claims (2)

A seven-strand structure in which one center line and six side lines are twisted together, the outer diameter is 15.0 to 15.6 mm, the total cross-sectional area is 135 to 148 mm ² , and the tensile of the entire stranded wire A high-strength PC steel stranded wire having a load of 310 kN or more and a side line tensile load of 80% or more of the center line tensile load.   A concrete structure using the high-strength PC steel stranded wire according to claim 1.

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