JPH0543134Y2 - - Google Patents

Description

[Detailed explanation of the invention] (Field of industrial application) This invention is an unbonded method that introduces compressive stress into concrete structures using the post-tension method.
Regarding PC steel bars.

(Conventional technology) Conventional unbonded PC steel materials include sheathed PC
Strands, coated unbonded PC steel bars, etc. are known. The above sheath PC strand is the third
As shown in the cross-sectional structure in Figure a, the surface of the strand S, which is made by twisting 7 or 19 thin PC steel wires, except for the anchoring part at the end, is covered with a plastic or polyethylene sheath P, The gap between the sheath P and the strand S is filled with grease G. The above-mentioned coated unbonded PC steel bar uses a large diameter PC steel bar with a threaded part formed at the end, and as shown in the cross-sectional structure in Figure 3b, the threaded part which is the anchoring part of the steel bar 1 is excluded. An asphalt-based rust preventive agent 2' is applied to the surface of the parallel portion, and a protective tape 3 is wrapped around the outer periphery of the asphalt-based rust preventive agent 2'.

In the post-tension method, no matter which type of unbonded PC steel material is used, the unbonded PC steel material is placed in concrete in advance and unbonded when the concrete hardens and reaches the specified strength. Compressive stress is introduced into the concrete by anchoring the prestressing steel under tension. The state of the anchored portion after stress is introduced is as shown in Fig. 3c, taking for example the sheathed PC strand as an example.

In Figure 3c, C is concrete, and S is sheath covered with sheath P except for the vicinity of the ends.
A is a PC strand, A is an anchor plate, W is a wedge, CO is a cone, and after stress is introduced, the box hole H is filled with mortar M.

(Problems with the prior art) Unbonded PC steel materials are originally coated with grease G and sheath P or asphalt-based rust preventive agent 2' and buried in concrete C with a pH of 12 to 13. Since the parts are also covered with mortar M, they should be completely protected from corrosion, but there have been reports of fractures at or near the anchoring parts of unbonded PC steel over time.

Examining the above fracture example, rainwater or corrosive liquid is caused by shrinkage of concrete C, shrinkage of mortar M, and incomplete filling that occur after introducing prestress, causing the wall surface of box hole H shown as the arrow route to connect with mortar M. A path that follows the gap...the gap between the anchor plate A and the cone CO...and a path that follows the gap between the wall of the box hole H and the mortar M shown as the arrow route...the gap between the anchor plate A and the concrete C... or directly through the arrow and route that penetrates into the concrete C or mortar M to reach the surface of the PC steel material in the non-rust-proofed part = anchoring part or near the anchoring part, corroding that part,
It is confirmed that this causes breakage accidents.

The same applies to the coated unbonded PC steel bar that uses screws and nuts instead of the cone CO and wedge W described above.

In order to avoid breakage accidents, for example, as disclosed in Japanese Patent Publication No. 57-501737, a plastic cover filled with grease or the like is used to protect the cone exposed inside the box hole H after anchoring. A method has been attempted in which the box hole H is filled with mortar M after covering C and the wedge W, but this method is not practical because the material cost is high and the construction is extremely complicated.

(Purpose of the invention) This invention was made to solve the above-mentioned problems existing in conventional unbonded PC steel materials.
The purpose is to propose an unbonded PC steel bar that does not require any effort in construction and has no risk of breaking at or near the anchorage.

(Structure of the invention) The structure of the invention is as follows: (a) In a prestressed and concrete steel bar with a threaded portion formed at the end, a rust preventive agent that coats the outer periphery of the steel bar is (b) viscous. An asphalt-based rust preventive agent, (c) applied to a predetermined length of the parallel part and the threaded part connected to the parallel part, and (d) the coating of the threaded part screwed onto the threaded part. It is located on the unbonded PC steel bar, which moves in an extruded manner in the spiral direction by a nut that acts as a gap filler.

(Function of the device) The device of the present invention, when introducing compressive stress into concrete,
The nut that is screwed onto the threaded part extrudes the asphalt-based coating that is applied to the threaded part and maintains its viscosity. It penetrates into the steel rod insertion through-holes of the anchor plate and the gaps between the steel rods, and functions as a gap filler that fills these gaps.

(Example) The present invention will be described in detail below according to an example shown in FIG.

In FIG. 1, 10 is an example unbonded PC
1 is a steel rod for prestressed concrete having a parallel portion 11 and a threaded portion 12 of a predetermined length formed at its end (hereinafter simply referred to as a steel rod);
2 is an asphalt-based rust preventive agent, and 3 is a protective tape.

The asphalt-based rust preventive agent 2 has a predetermined viscosity...
The penetration rate, softening point, etc. are in accordance with the quality test method and judgment criteria (draft) for rust preventive agents set by the Architectural Institute of Japan, and when the steel bar 1 is under tension, the steel bar 1 is in a good state for extension. It has the property of being trackable, and is applied over a predetermined length range of the parallel portion 11 of the steel bar 1 and the threaded portion 12 connected to the parallel portion 11. To be more specific about the application range on the threaded part 12, at least the parallel area including the thickness of the nut, which is screwed onto the threaded part 12 and screwed until it comes into contact with the anchor plate when introducing compressive stress into concrete, is located. It must be applied to the threaded part 12 extending from part 11.

The above protective tape 3 is an asphalt-based rust preventive agent 2
has a predetermined viscosity, the unbonded PC
It is wound around the surface of the asphalt-based rust preventive agent 2 to prevent the steel rod 10 from coming into contact with other objects and being peeled off or adhering to other objects until it is used after manufacture. The material may be of any kind, such as thin and flexible polymeric or kraft paper. When stress is introduced, at least a portion near the threaded portion 12 is peeled off and cut off from the asphalt-based rust preventive agent 2;
The asphalt-based rust preventive agent 2 is exposed.

FIG. 2 shows the state of the end of concrete after compressive stress is introduced into the concrete using the embodiment of the present invention having the above configuration.

The asphalt-based rust preventive agent 2 applied to the predetermined length range of the threaded portion 12 maintains a predetermined viscosity as described above and is soft, so that it can be used as a nut that can be screwed into the threaded portion when compressive stress is introduced into the concrete. As the nut 4 advances, it is sequentially pushed and moves toward the parallel part 11 while rising on the end face in the advancing direction of the nut 4, and at the time the nut 4 comes into contact with the anchor plate A, the gap between the contact surfaces of the nut 4 and the anchor plate A, It penetrates into the gap between the steel rod insertion hole of anchor plate A and the steel rod 1 passing through it, and the gap between the anchor plate and concrete contact surface as shown in black as 21, and closes these gaps. That will happen.

Therefore, due to shrinkage of concrete C, shrinkage of mortar M, and incomplete filling that occur after compressive stress is introduced, rainwater or corrosive liquid may reach the vicinity of the anchorage via the route shown by the arrow in Figure 3c. Even so, not only the parallel part 11 but also all the gaps that directly enter the anchoring part are filled with asphalt-based rust preventive agent 2.
In addition, the surface of the steel rod 1 itself at the anchorage is completely covered with the asphalt-based rust preventive agent 2, so rainwater or corrosive liquids can leak into the anchorage or the steel rod near the anchorage. 1 is prevented from directly touching the steel rod 1, thus rainwater or corrosive liquids are prevented from touching the steel rod 1.
There is no risk of corrosion.

It should be noted that even if a PC steel material with a threaded section is covered with a hard plastic or polyethylene sheath P up to the threaded section, the sheath P will not follow the steel material during tension and will not expand sufficiently, resulting in breakage or cracking. It goes without saying that it cannot be expected to enter the gap as in the present invention, but there is a risk that rainwater or corrosive liquid may come into contact with the steel rod from the fractured or cracked part of the sheath P, and in addition, with the above structure, it is difficult to actually tighten the nut. (If it were possible, it would be done while destroying the coating layer), and such a structure is a measure to prevent breakage due to corrosion at or near the anchoring part. It is inappropriate as such.

(Effects of the invention) This invention extends the asphalt-based rust preventive agent that was previously applied to the parallel parts of coated unbonded PC steel bars, excluding the threaded parts, to a predetermined length range of the threaded parts connected to the parallel parts. To provide an unbonded prestressed steel bar which has the same structure as before, does not require any special effort by simply following the same construction as conventional methods, and has no risk of breakage at the anchoring part or in the vicinity of the anchoring part. The award was given as a significant contribution to the improvement of construction technology.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional front view of the unbonded PC steel bar according to the present invention near the anchorage, and Fig. 2 is a partially cross-sectional front view of the vicinity of the concrete end after compressive stress is introduced using the unbonded PC steel bar of the present invention. , Figure 3 a and b
3 is a cross-sectional view of a conventional unbonded PC steel material, and FIG. 3c is a partial cross-sectional front view of the vicinity of the edge of concrete after compressive stress is introduced, illustrating the problems existing in the conventional unbonded PC steel material. 10...Unbonded PC steel bar, 1...(PC) steel bar, 11...Parallel part, 12...Threaded part, 2...Asphalt-based rust preventive agent.

Claims (1)

[Scope of Claim for Utility Model Registration] In a prestressed and concrete steel bar with a threaded end formed, the rust preventive agent coating the outer periphery of the steel bar is a viscous asphalt-based rust preventive agent. , the coating is applied to a predetermined length range of the parallel part and the threaded part connected to the parallel part, and the coating of the threaded part is pushed out in the spiral direction by the nut screwed onto this threaded part and fills the gap. Unbonded PC steel bar characterized by acting as a filler.