JPH0754441A - Tension steel member - Google Patents

Abstract

PURPOSE:To obtain a steel member which has a high yield point and requires consumption of large energy by combining a tension steel part of high strength and a tension steel part of low strength in the same section of a steel bar in its longitndinal direction. CONSTITUTION:A heating temperature of heat treatment of a prestressing bar is set at a temperature lower than an ordinary one, and quenching and tempering is performed in a state where residual ferrite exists, and a composite steel bar 10 of two-phase heat treatment material which has a mixed construction of ferrite and martensite inside is formed. The composite steel bar 10 is used in a concrete beam 9, joined to a precast concrete column 8 and prestressed below the yield point of a high strength part, and prestressing is introduced into the concrete. Therefore, collapse by earthquake etc., is prevented from happening and safety is enhance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tensile steel material used for prestressing concrete beams, columns and walls of buildings.

[0002]

2. Description of the Related Art PC steel wire, PC stranded wire, PC steel bar, steel bar for reinforced concrete, etc. are known as this kind of steel material. Each of these conventional steel materials is manufactured so that the strength in the longitudinal cross section is substantially uniform, and the tensile steel material having the uniform strength is used by introducing prestress into the concrete structure. .

[0003]

In the conventional steel materials as described above, the stress of PC steel bar and steel bar for reinforced concrete-
A schematic drawing of the strain curve is shown in Fig. 2. Although the yield point of the steel bar 1 for reinforced concrete is low, stress is applied up to the displacement U point, and when the stress is removed thereafter, it returns to the V point,
The energy of the portion surrounded by OSV is consumed.

On the other hand, although the PC steel bar 2 has a high yield point, stress is applied until it reaches the T point where the strain is the same as that of the steel bar 1 for reinforced concrete, and even if the stress is removed thereafter, it returns to the O point and energy is not consumed. The inventors confirmed that when the concrete structure receives external energy such as an earthquake, when the energy is consumed as the energy of the steel material, collapse of the structure by the consumed energy is prevented.
We focused on preventing the collapse of concrete structures by using steel materials with high yield points and high energy consumption.

[0005]

[Means for Solving the Problems] Therefore, focusing on how to obtain a steel material having a high yield point and a large energy consumption, as a result of a test study, a high-strength portion and a low-strength portion coexist in one cross section. We were able to solve this problem by using a composite steel material.

[0006] As a concrete structure for coexistence,
The following three are representative, but of course the present invention is not limited to this. (1) A steel rod in which a high-strength structure and a low-strength structure are mixed in the cross-section of the steel rod by a two-phase heat treatment. (2) A steel rod obtained by subjecting a low-strength steel rod to surface heat treatment to increase the strength around the cross section of the steel rod and reduce the internal strength. (3) A steel rod obtained by tempering only the surface of a quenched steel rod to increase the internal strength of the cross section of the steel rod and reduce the strength of the periphery.

[0007]

FUNCTION The composite steel material constructed as in the preceding paragraph schematically shows a stress-strain curve in which the high-strength portion and the low-strength portion are superposed, as shown in FIG. That is, the composite steel material 10 changes the elastic coefficient at the same S point as the strain at which the low strength portion 11 reaches the yield point, and yields at the same X point as the strain at which the high strength portion 12 reaches the yield point. Therefore, after loading the composite steel material up to point W,
When unloading, it returns to point Y parallel to OS, so OSW
Energy in the area surrounded by the -Y point will be consumed. Therefore, as compared with the conventional low-strength steel material, it has a high yield point strength and possesses a large amount of energy consumption that cannot be achieved by the conventional high-strength steel material. It is also possible to apply prestress to the conventional high-strength steel by applying tension that exceeds the yield point to increase energy consumption, but this reduces safety and increases relaxation, making it unusable for practical use. .

[0008]

EXAMPLE As one example of the present invention, by lowering the heating temperature of the heat treatment of a normal PC steel bar and quenching and tempering in the presence of residual ferrite (undissolved ferrite), ferrite was formed inside, Φ2, which is a two-phase heat treatment material having a mixed structure with martensite by quenching and tempering
3mm composite steel bar, yield point 420kN, tensile load 47
The one with 9 kN was used. The load-elongation curve is shown in FIG. Similar to the load at the time of introducing prestress in a general PC steel rod, this composite steel rod 10 was loaded to the point W where the elongation reached 0.4%, and then unloading left 0.04% elongation. That is, in FIG. 3, it can be seen that the energy of the area surrounded by the range from the position of elongation O to the position of elongation 0.04% through W on the curve was consumed.

In the concrete structure, as shown in FIG. 4, the steel rod 10 is tensioned by applying a load up to a point B up to the same strain (elongation) as in the case of tensioning a conventional PC steel rod. To do. This elongation is 0.4%, and since this steel bar is considered to be a composite of the high-strength part and the low-strength part, point B is H of the high-strength part.
Point, which corresponds to point L of the low strength portion.

After the steel rod 10 which has been strained to the point B is strained by the earthquake and the load increases and reaches the point D, when the increased load is removed, it passes through the point F to the point G. Return to.
This is because the high-strength part goes from the H point to the I point and then returns to the R point, and the low-strength part goes from the L point to the N point and then passes through the P point and returns to the Q point. It is a superposition.

After this, if there is a similar increase in load, the steel rod
10 goes from the G point to the C point to the D point. This is because the high strength part goes from the R point to the I point and the low strength part goes from the Q point to the M point.
It is a superposition of the ones that pass through the points and reach the N point.
Area of a part surrounded by D-F-G-C (N-P-Q-M
The same as the area surrounded by) is the energy consumption per earthquake of the steel rod 10 during an earthquake.

FIG. 5 shows a test body in which the composite steel rod 10 of the present invention is used for a concrete beam 9 and joined to a precast concrete column 8. In the figure, 7 is a sheath, 6 is a fixing tool,
Reference numeral 5 denotes a dry pack mortar. The composite steel rod 10 inserted into the sheath 7 is tensioned and stopped by the fixing tool 6, prestress is introduced into the concrete beam 9, and it is rigidly joined to the precast concrete column 8. .

A positive and negative repetitive load was applied to the beam end of the test body, and the load and the displacement of the beam end were measured. FIG. 6 shows the outermost edge envelope of the shear force-displacement relationship curve, and the solid line is the one using the composite steel bar of the present invention. For comparison, the dotted line is the result of a similar test piece using a conventional ordinary PC steel material.

As is clear from the figure, the one using the composite steel rod of the present invention has a larger area surrounded by the outermost edge envelope than the one using the conventional ordinary PC steel material and has a large energy consumption. Is shown. This means that when a building such as a test piece made of steel is subjected to an earthquake, the amount of seismic energy consumed as energy for the steel is large, and the consumption of this steel energy prevents the building from collapsing. It indicates that there is peeling.

[0015]

As described above, the tensile steel material of the present invention is composed of the high-strength tensile steel material portion and the low-strength steel material portion coexisting, so that the yield point is high and the energy consumption is large. Steel can be easily manufactured and used.
In addition, in using it, since tension is applied below the yield point of the high-strength part to introduce prestress to the concrete, the ratio of the tensile force of the steel material to the yield point can be the same as before, and relaxation is also possible. High strength steel material can be applied. The use of the tensile steel material of the present invention prevents the concrete structure from collapsing due to an earthquake or the like and enhances safety.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a stress-strain curve of a composite steel material.

FIG. 2 is a schematic diagram of stress-strain curves of a conventional steel bar for reinforced concrete and a PC steel bar.

FIG. 3 is a load-elongation curve diagram of the example composite steel bar.

FIG. 4 is a schematic diagram of a stress-load curve of a composite steel rod in a concrete structure using an example.

FIG. 5 is a structural diagram for explaining the structure of a test body.

FIG. 6 is an outermost edge envelope diagram of a shear force-displacement relationship curve for explaining a test result of a test body.

[Explanation of symbols]

 1 Steel bar for reinforced concrete 2 PC steel bar 5 Dry pack mortar 6 Fixing device 7 Sheath 8 Precast concrete column 9 Concrete beam 10 Composite steel bar 11 Low strength part 12 High strength part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Eiji Yamashita Eiji Yamashita No. 5893 Tamura, Hiratsuka-shi, Kanagawa High frequency heat-melting company (72) Inventor Fumio Watanabe 5-3, Donomae, Uemachi-cho, Muko City, Kyoto Prefecture

Claims (4)

[Claims] 1. A tensile steel material comprising a high-strength portion and a low-strength portion coexisting in one cross section. 2. The tensile steel material according to claim 1, wherein the coexistence is such that a high-strength structure and a low-strength structure are mixed in the cross section of the steel rod by subjecting the steel rod to a two-phase heat treatment. 3. The coexistence is characterized in that the strength around the cross section of the steel rod is increased and the strength inside is reduced by subjecting the low strength steel rod to surface heat treatment. Tensile steel material. 4. The tensile steel material according to claim 1, wherein the coexistence is such that only the surface of the heat treated steel bar is tempered to increase the internal strength of the cross section of the steel bar and reduce the peripheral strength.