JPH0513770B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a multi-component circular section made of steel for anchoring tensile members such as steel wires to concrete structures, for example for anchoring prestressing members for prestressed concrete. Concerning a method for manufacturing a wedge.

[Conventional technology]

Conventionally, as this type of circular cross-section wedge, a multi-component circular cross-section wedge made of steel for fixing a prestress member serving as a tensile member used in prestressed concrete is known. This circular cross-section wedge has a truncated conical shape as a whole, and uses a wedge action based on tensile force to tighten the prestressed member and fix it to the prestressed concrete. It thus consisted of two or more wedge sectors separated from each other, and the inner surface of the wedge sector in contact with the prestressing member had tooth profiles.

In addition, this type of circular cross-section wedge is used not only for anchoring prestressed members for prestressed concrete, but also for anchoring cable-stayed cables of cable-stayed bridges to concrete structures such as towers and bridge girders. .

In this way, to anchor tension members made of steel rods, steel wires, or steel strands to concrete structures, circular cross-section wedges are used based on the wedge anchoring principle; It consists of at least two, and most often three wedge sectors, which surround the tension member to be secured.

When fixing tensile members, such as prestressing members for prestressed concrete, which are loaded with this kind of tensile load, the wedge sector is moved by the tensile force applied to the tension member into a conical shape in the anchoring body in the direction of the axis of the tension member. It is drawn into the hole of the shape. In this way, a clamping force is created in the wedge sector that is directed at right angles to the tension member axis, which force prevents the tension member from moving. The prerequisite is that the coefficient of friction between the tension member and the wedge is greater than that between the wedge and the conical hole. To achieve this, the inner surface of the wedge sector is provided with a tooth profile so that the wedge wedges firmly into the surface of the tension member. This profile consists of a single thread for simplicity. This thread is cut into an axial hole in the frustoconical wedge blank before it is divided into individual wedge sectors (GB 869923).

[Problem that the invention seeks to solve]

The above-described known wedge fixing devices for use with smooth and stranded steel wires of high hardness have weaknesses in terms of fatigue rate, ie, strength against permanently fluctuating tensile loads. What is known in practice is that steel wires and steel strands always break in the front region of the fastening device, ie at the narrow end of the wedge. The cause of this failure is essentially the strong lateral compression in the area of force introduction and the tooth profile of the initial part of the fixation device, i.e. the narrow tip of the wedge.
These tooth profiles are created by the sharp corners of the threads. The inner diameter of each wedge sector is somewhat smaller than the outer diameter of the tension member, so that the sharp corners of the threads terminating at the longitudinal edges of the wedge sectors cut into the surface of the tension member.

In addition, in order to eliminate this defect, the inside of the thin tip of the wedge is ground so that the sharp corner of the thread becomes gradually flattened toward the tip of the wedge, so that there is no thread at all at the tip. This is also being done. However, if you do it like this,
At the tip of the wedge, where extremely strong clamping pressure is applied, there are no longer any sharp teeth cut into the surface of the tension member, but at this point the tension member is clamped and fixed only by friction. . However, when such a wedge is used when it is subjected to a permanent vibration load, that is, repeated stress, such as when anchoring the cable-stayed cables of a cable-stayed bridge, the tooth Friction occurs in the area where the corners of the thread forming the shape are ground and flattened, and as a result of this friction, frictional corrosion occurs between the wedge and the tension member, causing early failure of the tension member at this location. I've come to understand that.

[Means for solving problems]

The basic problem of the invention is to develop an economical method for improving the fatigue limit of a wedge fixing device of the type described at the outset, ie its performance against permanently fluctuating loads.

This problem is solved by the present invention having the following features. That is, the circular cross-section wedge is composed of a plurality of wedge sectors separated from each other by radial divisions, and a tensile member such as a steel wire, which has teeth on the inner surface that abuts the tensile member, is attached to a concrete structure. A method of manufacturing a steel multi-component circular cross-section wedge for anchoring, the tooth profile is first formed by providing an axial screw hole in a truncated conical wedge material, and then the wedge material is individually cut into wedge sectors in the longitudinal direction, further subjecting each wedge sector to a quenching treatment, and finally forming a convex curved portion on at least a portion of the surface of each wedge sector with a radius smaller than the radius of the screw hole. Carrying out a barrel polishing process using a free grinding wheel, the free grinding wheel uniformly polishes the tip of the rib over the entire length of the screw forming a tooth pattern, and the corners are rounded. This is a characteristic feature.

The invention starts from a known method for removing contamination or remaining burrs from metal parts, for example cast parts, in the following manner. That is, the metal part is processed by placing it in a polishing drum or the like together with a free grinding wheel made of ceramic material. These metal members are moved together with the free wheel as the polishing drum rotates.
In this case, the movement is relative, and the surface of the casting etc. is smoothed by the grinding action of the grinder. This kind of surface treatment is called barrel polishing.

[Effect]

The basis of this invention is the following recognition. In other words, when the wedge sector obtained by dividing the wedge material after carving a single thread to form a tooth pattern on the inner surface is processed together with a grinding wheel through an abrasive drum, the thread of the wedge sector is is not destroyed, only the tips of the ribs of the twisted helix are polished and rounded. This barrel polishing
It is carried out after the quenching process of the wedge sector in order to avoid excessive grinding of the tooth profile.

In this way, when barrel polishing is performed after quenching, the decarburized layer that is generally formed on the surface of the tooth profile of the wedge sector due to quenching is thinner on the side surface of the screw thread due to the shape of the tooth profile that comes into contact with the atmosphere during quenching. The thickness becomes thicker at the tip of the thread, and the quenched hardened layer that forms under the decarburized layer is usually formed at the tip of the thread to have an approximately arcuate cross section. Therefore, when barrel polishing is performed, the decarburized layer with low hardness at the tip of the screw thread is easily polished off, and the hardened layer with high hardness, which has an arc-shaped cross section with an appropriate arc radius, is exposed on the surface. It is also easy to get results.

In order to carry out such barrel polishing, it is extremely effective to use a free wheel that has a convex curved portion on at least a portion of its surface with a radius smaller than the radius of the screw hole formed in the wedge material. be.

Furthermore, the free grinder is preferably made of a ceramic material, such as glass powder, alumina or the like, or to which is further added corundum, metal oxides or the like. .

According to this invention, only the tip of the thread of the wedge sector is surface-treated and rounded over its entire length, so that when the wedge is used, the tip of the thread does not cut into the tension member, but touches the surface of the tension member. This has the advantage of being press-fitted only. The surface layer of the tension member is thereby not fractured, but undergoes plastic deformation due to the press-fit, resulting in local cold work hardening and thereby increasing the stiffness of the tension member. The wedge treated according to the invention provides an improved fatigue limit without further treatment and a static increase in the fixation device which corresponds to up to 100 percent of the stiffness in the free length or normal portion of the tensile member. Tensile strength can be achieved.

〔Example〕

Embodiments of the present invention will be described in more detail based on the drawings.

In the wedge fixing device shown in longitudinal section in FIG. 1, by way of example a prestressed steel wire strand 1 is fixed in a conical hole 3 of an anchoring body 4 by means of a multi-component circular cross-section wedge 2. The fixing body 4 is supported in a manner known per se by means of a contact surface 5 on a support plate (not shown) for the transmission of clamping forces.

FIG. 2 shows a circular cross-section wedge 2 in a perspective view. Circular cross section wedge has three wedge sectors 2
It is composed of a, 2b, and 2c. These wedge sectors are each approximately 120 degrees wide and, including the narrow longitudinal slit 6, form a complete ring cross-section (FIG. 3). The sector has an annular groove 8 on the outer surface of the thicker wedge end 7. A spring ring 9 is inserted into this annular groove to facilitate assembly of the wedge sectors.

In particular, as shown in Figure 4, each wedge sector 2
a, 2b, and 2c each have a tooth pattern 11 on the inner surface 10. This tooth profile 11 consists of a screw with a thread 12 which is inserted into an axial bore of the truncated conical wedge body and which is inserted into the individual wedge sectors 2.
It was engraved before it was divided into a, 2b, and 2c.

According to the invention, wedge sectors 2a, 2b,
2c, especially after surface hardening, is placed in an abrasive drum together with a free wheel of ceramic material, such as glass powder, alumina or the like, and circulated therein continuously.
The grinding wheel can have essentially any shape, but at least in partial areas of its surface there is a convex curvature. The radius of curvature of this convex curved portion is shorter than the radius of the screw hole, so that the wheel can effectively act on the tip of the screw thread 12.

The barrel polishing process of the wedge sector is the thread 1
Wire strand 1 where 2 is a prestressing member
Screw thread 1 to avoid cutting into the surface of the
It is sufficient to carry out step 2 until the sharp edges of the rib tips that occur during threading are removed and the corners are rounded (Fig. 5). Usually, as shown in FIG. 6, the cross section of the thread 12 of the wedge sector that has been hardened has a decarburized layer 14 with low hardness on the surface, a hardened hardened layer 15 with high hardness on the inside thereof, and the thread 1
The decarburized layer 14, which forms a thin layer on the side surface of the thread 12, becomes thicker at the tip of the thread 12 due to the influence of the surrounding atmosphere during quenching, and the hardened layer 15 curves in an arcuate cross-section at the tip, as shown in the figure. often formed. Therefore, when such a wedge sector is subjected to barrel polishing as described above, the lower hardness portion 16 at the tip of the thread 12 shown by the dashed line in FIG.
is easily removed by polishing, and the quenched and hardened layer 15 having high hardness and an arcuate cross section is exposed on the surface, making it easy to obtain a rounded tip with high hardness.

〔Effect of the invention〕

Since the present invention has the above-described structure and operation, according to this manufacturing method, the sharp tip of the rib of the tooth-shaped screw is attached to the free grinder over the entire length of the wedge. It is polished uniformly and the corners are rounded, and since the polishing and removal is done by barrel polishing using a specific free grinder, it can be carried out efficiently and reliably.
The manufactured circular cross-section wedge has a uniform and strong tightening force over the entire length against tensile members such as steel wires such as prestressed members for prestressed concrete, while the tip of the tooth-shaped thread has high hardness. And because it is rounded, there is no possibility of cutting into the surface of the tension member and damaging the tension member with the thin end of the wedge. The plastic deformation caused by press-fitting the tooth shape into the surface gives the effect of cold work hardening, increasing its strength.The tooth shape itself is made of steel and has elasticity as a whole, so it can be used as a tensile member. The present invention provides a method for manufacturing a wedge for anchoring a prestressed member for prestressed concrete, which has a high fatigue limit even when subjected to repeated stress over a long period of time, and does not cause frictional corrosion as described above. The present invention can be very effective not only as a method for manufacturing anchoring wedges for tension members such as cable-stayed cables of cable-stayed bridges that are constantly subjected to vibration loads.

[Brief explanation of the drawing]

1 is a longitudinal sectional view of a strand wedge fixing device with a multi-component circular cross-section wedge, FIG. 2 is a perspective view of the circular cross-section wedge, FIG. 3 is a plan view of the circular cross-section wedge of FIG. 2, and FIG. is a longitudinal sectional view of the circular cross-sectional wedge taken along the - line in FIG. 3, FIG. FIG. 7 is a partially enlarged cross-sectional explanatory view of the tooth pattern after barrel polishing. Symbols in the figure, 1... Steel wire strand, 2...
Circular cross-section wedge, 2a, 2b, 2c...wedge sector, 3...conical hole, 4...fixer, 5...
Contact surface, 6...Slit, 7...Wedge end, 8
... Annular groove, 9 ... Spring ring, 10 ... Inner surface,
11...Tooth pattern, 12...Screw thread.

Claims (1)

[Claims] 1. A tensioning device such as a steel wire, in which the circular cross-section wedge is composed of a plurality of wedge sectors separated from each other by a radial division, and has a tooth profile on the inner surface that abuts the tension member. A method for manufacturing a steel multi-component circular cross-section wedge for anchoring a member to a concrete structure, the method comprises first forming a tooth pattern by providing an axial screw hole in a truncated conical wedge material; longitudinally cutting the wedge material into individual wedge sectors, subjecting each wedge sector to a hardening treatment, and finally, for each wedge sector, at least a portion of the surface has a radius smaller than the radius of the screw hole. A barrel polishing process is performed using a free grinding wheel having a convex curved part, and the free grinding wheel uniformly grinds the tip of the tooth-shaped rib of the screw over the entire length, and the corners are polished. A method for manufacturing a steel multi-component circular cross-section wedge characterized by being rounded. 2. The free grinding wheel is a ceramic material such as glass powder, alumina or the like;
or made of a ceramic material to which corundum, metal oxides or the like are added.
The method described in.