JP2007063840A - Simple prestress introducing construction method by torque - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple prestress introducing construction method by torque, capable of reducing construction cost, and capable of expanding a use range, by adopting a further simple construction method by the torque. <P>SOLUTION: A screw part 11 is arranged in an end part of a tendon 1, and a fastening nut 2 is installed in this screw part 11. Tensional force P is imparted to the tendon 1 by screwing the fastening nut 2 in the screw part 11 exposed from an end surface of a structure C, and the tensional force P is imparted in the axial direction without imparting the torque T of the rupture size to the tendon 1 by interposing a lubricant between a thread of the tension material 1, a thread of the fastening nut 2 and a contact surface of a nut, a washer and an anchoring plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a prestress introduction method in which a tension force in the axial direction is applied to a tension material arranged in a structure made of concrete or the like.

Japanese Patent Laid-Open No. 11-62237 Japanese Patent Laid-Open No. 11-343657

  A pre-stress introduction method for improving the strength of a structure by applying a tension force, which is a force in the axial direction, to a tension material such as a PC steel rod arranged in a structure made of concrete or the like is well known. This is because the compressive force is applied to the concrete structure in advance by the above tension, and the characteristics of the concrete structure, which is weaker to the tensile load than the compressive load, are improved. Widely used for members and building materials.

  Conventionally, when prestress is introduced into a tension member, a device for applying tension force such as a jack and a hydraulic pump is used for the end of the tension member in order to perform highly accurate tension management based on the tension load and the elongation amount of the steel material. A construction method that applied tension to give tension. However, this method has a drawback that it requires a large amount of space, such as a back space and power supply equipment for installing the above-mentioned apparatus. In addition, there is a problem that the construction cost increases due to the necessity of monitoring an engineer having specialized knowledge for tension management.

  Therefore, as a simplified method, a method using the tool described in Patent Document 1 or Patent Document 2 has been proposed. The tool used in this construction method is provided with a pull rod attached to the end of the tendon and a pulling nut for applying a pulling direction force to the pull rod. By applying a torque to the pulling nut, it is possible to apply only a tension force in the axial direction via the pull rod without applying a twisting force to the tension material. However, this method uses a dedicated tool as described above, and still leaves room for reduction in construction costs.

  In addition, the use of the pre-stress introduction method is not limited to large structures that require great tension, and it should be considered to expand the application to small structures that have not been used in the past. Furthermore, it should be considered that even a large structure is limited to a locally necessary part. It should also be considered to use a prestressing method for the purpose of controlling cracks and deflection of structures.

  In view of the above, the present invention adopts a simple prestress introduction method using torque, which can reduce the construction cost by adopting a simpler method using torque, and can expand the range of use. The issue is to provide.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present application provides the strength of the structure C by applying a tension force P in the axial direction to the tension material 1 disposed in the structure C. The end of the tendon 1 is provided with a thread portion 11 having a thread on the outer peripheral surface, and the thread portion 11 has a thread on the inner periphery. A screw nut in the other end 1y of the tension member 1 exposed from the end surface of the structure C in a state where the one end 1x of the tension member 1 is fixed. 11, the tightening nut 2 is screwed in, and the tightening nut 2 is screwed in while pressing the end surface of the structure C, whereby the tension material 1 is imparted with the tension force P described above. A lubricant 5 is interposed between the thread of the tendon 1 and the thread of the tightening nut 2. Thus, during the above screwing, the tension material 1 is given the tension force P in the axial direction without giving the tension material 1 the twisting force T in the rotational direction, which is large enough to cause the tension material 1 to break. A simple pre-stress introduction method using torque is provided.

  The invention according to claim 2 of the present application provides a simple prestress introduction method using torque according to claim 1, wherein the tendon 1 is a PC steel rod.

  The invention according to claim 3 of the present application provides a simple prestress introduction method using torque according to claim 1 or 2, wherein the lubricant 5 contains molybdenum disulfide. .

  In the invention according to claim 4 of the present application, a grease containing molybdenum disulfide is used as the lubricant 5, and the grease 5 is contained in an amount of 40% by mass or more and 70% by mass. The simple prestress introduction method by torque according to claim 3, characterized by containing the following molybdenum disulfide.

In the present invention, the lubricant 5 is interposed between the thread of the tension member 1 and the screw thread of the tightening nut 2 and the contact surface of the nut, washer and fixing plate. A tension force P in the axial direction is applied to the tendon material without giving a twisting force T in the rotational direction that is broken. Therefore, since it is only necessary to use a general tool such as a torque wrench and screw the tightening nut 2 into the tension material 1, a very simple construction is possible. Further, since a device for applying tension, such as a jack and a hydraulic pump, is unnecessary, back space and power supply equipment for this device are not required on site. Moreover, a dedicated tool is not necessary. Therefore, the construction cost can be reduced similarly to the simplification of the construction.
In addition, since no large-scale equipment is required, it has become easier to apply to small structures where the conventional prestress introduction method has not been adopted, and at the same time, local tightening force is introduced to large structures. Is also possible. In addition, it is easy to use the prestress introduction method for the purpose of controlling cracks and deflection of the structure, and the use of the prestress introduction method can be expanded.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of the end of the PC steel bar of this example, FIG. 2 shows the arrangement of the PC steel bar relative to the structure, and FIG. 3 shows the screw thread of the PC steel bar and the screw thread of the clamping nut. Show the relationship.

The simple prestress introduction method of this example uses an unbonded PC steel bar 1, a tightening nut 2, a washer 3, and an anchor plate 4 as tension members, and is manually tightened with a torque wrench or the like. By applying torque to 2, tension P is applied and prestress is introduced into the concrete structure C.
As the tension material, in addition to the unbonded PC steel bar 1 of this example, a pre-grout PC steel bar, an unbonded PC strand formed by bringing steel wires close together, and various other types conventionally used in prestress introduction methods. It is possible to use any tension material.

  The simple prestress introduction method of this example is applied to a post-tension method in which prestress is introduced into the unbonded PC steel rod 1 after the concrete has already been poured and the structure C is formed. Note that the present invention can also be applied to a post-tension method using a conventional sheath. Moreover, you may apply to the pretension system which is a system into which concrete is poured after prestress is introduced into the unbonded PC steel rod 1.

The unbonded PC steel bar 1 is a steel bar 1a whose surface is coated with a rust preventive material such as grease and is housed in a tube (sheath) 1b made of synthetic resin. Both ends 1x and 1y of the unbonded PC steel bar 1 are in a state in which the steel bar 1a is exposed, and a threaded part 11 in which a thread is formed on the outer peripheral surface of the exposed steel bar 1a by rolling. Is provided. The threaded portion 11 has a length that allows the tightening nut 2 to be sufficiently screwed in order to introduce necessary prestress.
In addition, about the tension | tensile_strength material which cannot provide the thread part 11 directly, such as an unbonded PC strand, after connecting the steel bar etc. to the edge part integrally, the thread part 11 is provided in this steel bar.

  As an example of the unbonded PC steel bar 1 used in the present invention, the PC steel bar has a nominal diameter of 11 mm, the screw nominal is M12, the screw pitch is 1.5 mm, and the PC steel bar has a nominal of 13 mm and a nominal thread. Is M14 and the screw pitch is 1.5 mm, but other sizes may be adopted. Moreover, although the thread formed on the threaded portion 11 is a metric thread defined in JIS B0205, a special thread may be formed.

  As shown in FIG. 1, the unbonded PC steel rod 1 is disposed on the front side from the bottom surface of the box opening hole C1 formed on the end surface of the concrete structure C on which concrete is cast, specifically, on the end surface of the concrete structure C. It arrange | positions so that the edge parts 1x and 1y may be exposed. As a result, the screw portion 11 is exposed to the box opening hole C1.

  Here, the box opening hole C1, which was required in the conventional prestress introduction method, required a considerable depth in order to secure the jacking allowance. Since the introduction method can be constructed with a general tool, a smaller box opening hole C1 may be used. Therefore, the construction effort for filling the box opening hole after construction and the influence on the structure are reduced.

  As shown in FIG. 1, an anchor plate 4 is provided on the bottom surface of the box opening hole C1. The anchor plate 4 has a pressing surface 41 for pressing the concrete structure C by the tightening nut 2 tightened on the unbonded PC steel rod 1. Since the concrete structure C can be pressed by the entire pressing surface 41, the tension force P generated in the unbonded PC steel rod 1 can be reliably transmitted to the concrete structure C.

As the tightening nut 2, a hexagonal nut dedicated to the PC steel bar whose name coincides with the threaded part 11 of the unbonded PC steel bar 1 is used, but the two-face width and diagonal distance of the hexagonal nut are the same as those of a general nut. Dimensions. Therefore, since the tool generally used widely can be used, versatility is high. Further, it is more preferable to use the tightening nut 2 itself that has been subjected to a friction reducing process (deflick coating process).
Note that a general flat washer is also used for the washer 3.

Here, simply screwing the tightening nut 2 into the threaded portion 11 of the unbonded PC steel bar 1 causes the tightening due to the friction generated between the thread of the unbonded PC steel bar 1 and the thread of the tightening nut 2. As the nut 2 rotates, a twisting force T is also generated in the PC steel bar. In this way, when the twisting force T is generated indefinitely, the PC steel rod may be broken by being twisted. For this reason, in the conventional invention described in Patent Document 1, a dedicated tool for interrupting the torsional force T is used so that the torsional force T is not generated in the unbonded PC steel rod 1.
Here, in the present invention, as shown in FIG. 3, the lubricant 5 is interposed between the thread of the unbonded PC steel bar 1 and the thread of the tightening nut, thereby reducing friction and tightening. When the nut 2 is screwed, a tension force P in the axial direction can be applied to the unbonded PC steel bar 1 without giving a twisting force T that is large enough to cause the unbonded PC steel bar 1 to break. It is said that. Therefore, it is possible to introduce prestress without using any special tool. Specifically, in this example, the equivalent stress, which is an axial stress taking into account the generated torsional force T, does not exceed the 0.2% proof stress of the unbonded PC steel rod 1.
In the simple prestress introduction method of this example, the prestress introduced into the unbonded PC steel rod 1 is about 50 to 100 kN.

  As the lubricant 5, various substances can be used as long as they have the ability to reduce friction. In particular, it is desirable to use a lubricant containing molybdenum disulfide having excellent ability. In this example, grease containing molybdenum disulfide is used. In the case of grease, the component preferably contains 40% by mass or more and 70% by mass or less of molybdenum disulfide, and particularly contains 45% by mass or more and 55% by mass or less of molybdenum disulfide. desirable.

  The grease 5 is applied to the threaded portion 11 of the unbonded PC steel bar 1 to reduce friction between the tightening nut 2 and the grease 5 to be applied between the tightening nut 2 and the washer 3. However, it is desirable because the rotational resistance of the tightening nut 2 can be further reduced.

Here, when the inventor of the present application uses the following greases (1) to (6), the torque applied to the tightening nut 2 and the tension P applied to the unbonded PC steel rod 1 An experiment was conducted to measure the relationship.
(1) Molybdenum grease (containing 50% by mass of molybdenum disulfide)
(2) Molybdenum grease (containing 25% by mass of molybdenum disulfide)
(3) Molybdenum grease (containing 2% by mass of molybdenum disulfide)
(4) Lithium soap base grease (5) Silicone grease (with fluorine resin)
(6) Silicone grease (with metal soap)

As a result, the tension P at the same torque was highest in (1). This indicates that the torsional force T generated by the torque applied to the tightening nut 2 is the smallest and the tension force P is most effectively applied.
Further, even among the molybdenum-based greases (1) to (3), (1) has the best results, and it is proved that the grease containing more molybdenum disulfide is more effective for the present invention. Results were obtained.

  In this example, grease containing molybdenum disulfide is used as the lubricant 5. However, the type of the lubricant 5 in the present invention is not limited to grease. For example, it can be implemented in various forms such as liquid, paste, and powder. Further, as in this example, the lubricant 5 is not separately applied to the unbonded PC steel rod 1, but the thread portion 11 of the unbonded PC steel rod 1 is impregnated with the lubricant 5 from the beginning. good.

In addition, after prestress is introduced into the unbonded PC steel rod 1, the box opening hole C1 is filled with concrete, so that the tightening nut 2 is fixed with concrete. Therefore, even if the friction between the screw portion 11 and the tightening nut is reduced as in this example, the tightening nut 2 once tightened does not loosen with respect to the unbonded PC steel rod 1. .
When the simple prestress introduction method of this example is used for the purpose of controlling the deflection and cracking of the structure C, the tightening nut is not filled in the box opening hole C1 as described above. 2 may be appropriately tightened according to the situation.

As described above, the simple prestress introduction method of the present example only needs to screw the tightening nut 2 into the unbonded PC steel rod 1, and a very simple construction is possible and the construction cost can be reduced. .
In addition, since there is no cost merit in the past, it is easy to apply to a small structure where the prestress introduction method has not been adopted. In addition, even a large structure can be easily tightened locally, and a prestress introduction method for the purpose of controlling cracks and deflection of the structure can be easily used.
In this example, the application of the prestress introduction method to a concrete structure has been described. However, the structure to which the present invention is applied is not limited to a concrete structure, and can be applied to various structures including wood. It is.

It is explanatory drawing of the principal part cross section which shows the structure of the edge part of the PC steel rod of this example. It is explanatory drawing which shows arrangement | positioning of the PC steel bar with respect to a structure. It is explanatory drawing of the principal part cross section which shows the relationship between the thread of a PC steel bar, and the thread of a clamping nut.

Explanation of symbols

1 Tensile Material, PC Steel Bar 1x, 1y End of Tensile Material 11 Threaded Part 2 Tightening Nut 5 Lubricant, Grease C Structure P Axial Tension Force T Torsional Force

Claims (4)

A pre-stress introduction method that can improve the strength of the structure (C) by applying axial tension (P) to the tension material (1) disposed in the structure (C). There,
At the end of the tendon (1), a threaded portion (11) having a thread on the outer peripheral surface is provided,
A fastening nut (2) having a thread on the inner periphery is attached to the thread portion (11).
In the state where one end (1x) of the tendon (1) is fixed, the thread (11) at the other end (1y) of the tendon (1) exposed from the end surface of the structure (C) The above-mentioned clamping nut (2) is screwed,
The tightening nut (2) is screwed while pressing the end surface of the structure (C), whereby the tension (P) is applied to the tension material (1).
By interposing the lubricant (5) between the thread of the tendon (1) and the thread of the clamping nut (2),
The tension (P) in the axial direction is not applied to the tension material (1) at the time of the screwing, without giving a twisting force (T) in the rotational direction that would cause the tension material (1) to break. A simple prestress introduction method using torque, characterized by being applied.   The simple prestress introduction method using torque according to claim 1, wherein the tendon (1) is a PC steel rod.   The simple prestress introduction method by torque according to claim 1 or 2, wherein the lubricant (5) contains molybdenum disulfide.   A grease containing molybdenum disulfide is used as the lubricant (5). The grease (5) contains 40% by mass or more and 70% by mass or less of molybdenum disulfide in its components. The simple prestress introduction method using torque according to claim 3, wherein:

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