JP2954523B2 - Pretension type PC member and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prestressed concrete member (hereinafter, referred to as a PC member) into which prestress is introduced by a pretensioning method, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In general, a concrete member has a weak point of being weak against tensile stress, and a PC member is used to reinforce the weak point. This PC member is used for, for example, a bridge girder. In this case, since both ends of the PC member are supported as fulcrums, a load is applied between the fulcrums.

In this case, as shown in FIG. 10 (A), the bending stress due to the load at the center a between the fulcrums of the PC member 1 supported by the fulcrums b, b is the bending tensile stress below the neutral axis and the bending stress below the neutral axis. Since the state becomes a bending compressive stress state, it is necessary to introduce a prestressed so as to cancel this state.

By the way, as shown in FIG. 10, a large amount of eccentricity from the neutral axis of the PC steel group 3 is obtained by keeping the tensile steel material (PC steel) 2 as far as possible below the neutral axis of the PC member 1 and away from the neutral axis. Since the eccentric moment due to the prestressing force increases, the amount of the PC steel used is small, and the method is more economical.

[0005] When the tensile steel material 2 is disposed in this manner, the prestress in the central section a of the PC member 1 is such that a small tensile stress is applied to the upper edge and a large compressive stress is applied to the lower edge, so that the stress caused by the load is canceled. However, in this case, P
Since the bending stress due to the load is 0 in the cross section of the C member, the tensile stress at the upper edge of the cross section due to the prestress of the tensile steel material 2 is P
As shown in FIG.
As shown in Fig. 10A, tensile stress always acts on the concrete at the upper edge of the PC member 1, and it is convenient to arrange the tensile steel material 2 as shown in Fig. 10 (A) for concrete that is weak in tension. bad. For this reason, in the [Road Bridge Instruction Manual for Concrete], the tensile stress during the design load action of the concrete of the PC member on the fulcrums b, b is not allowed.

Therefore, in order to cancel the tensile stress due to the prestress at the upper edge of the cross section of the PC member on the fulcrums b, b in FIG. 10 (A), the cross section of the PC member as shown in FIGS. A tensile steel material (PC steel material) 4 is also arranged on the upper edge of the centroid. In addition, each tensile steel material 2 disposed below the neutral axis
Also, at the end of the girder (that is, in the range near the fulcrums b, b), the adhesion to concrete is cut off, and bond control is performed over a predetermined section to reduce the tensile stress generated at the upper edge by the tensile steel material. However, there is a limit in canceling the tensile stress generated at the upper edge of the PC member 1 by the bond control especially when using ultra-high strength concrete (σ _CK = 600 kg / cm ² or more).

FIG. 11 shows a method of manufacturing the conventional PC member 1. The manufacturing process will be described with reference to the same figure. A horizontal bottom form 5 is placed on a number of sleepers 6 arranged in parallel, and a tensile steel material (PC member) 2
Are arranged so as to extend along the upper part of the bottom
The tension member 2 is stretched between the base pretension abutments 7, 7, and a predetermined tensile force is applied to the tensile steel material 2.

In order to manufacture a plurality of PC members (concrete members) on the upper part of the above-mentioned formwork, force distribution bars, through bars, stirrup bars, etc. corresponding to each member (all not shown).
After assembling, a plurality of sets of side molds 8 are placed on the bottom mold 5.
And an end formwork 10 are arranged, and a tensile steel material (PC steel) 4 is provided through the end formwork 10, and the end of the tensile steel material 4 is related to the pretensioning abutments 7, 7 at the end. Has been stopped.

Next, concrete is cast into a portion surrounded by each mold to form the PC member 1. After the concrete reaches a predetermined strength, the side mold 8 is removed, and then the tensile member is used. Of the tensile steel materials 2 and 4 are released, and prestress is introduced into each concrete member.

[0010]

As described above, in the conventional PC member, the total amount of PC steel used has been increased, and the design has been uneconomical (PC Road Bridge Design and Manufacturing Handbook by J1S Bridge Girder ((Co., Ltd.)). ) Prestressed Concrete Construction Association).

As a result of various studies, the present inventor has found that there is a method capable of canceling the tensile stress at the upper edge of the PC member without disposing the tensile steel material over the entire length of the upper portion of the PC member.

The present invention solves the drawbacks of the prior art in view of the above, and an object of the present invention is to provide a pretension capable of reducing the manufacturing cost of a PC member in which prestress is introduced by a pretension method. It is an object of the present invention to provide a method PC member and a manufacturing method thereof.

[0013]

In order to achieve the above object, the present invention provides a PC member to which a prestress is introduced by a pretensioning method, wherein a required amount of a first tensile steel material is applied over the entire length between supporting points of the PC member. In order to cancel the tensile stress acting on the upper edge of the PC member by the pre-stress force of the first tensile steel material, the support member is moved from the fulcrum to the PC member.
The upper edge bending compressive stress due to the applied load and the first tensile steel material
The sum of the upper edge tensile stress of PC member due to prestress is
The present invention is characterized in that a required amount of the second tensile steel material is provided over a range of a length X or more up to a position at which it becomes zero . Further, the method of manufacturing a PC member by the pretensioning method of the present invention includes:
When manufacturing a PC member in which prestress is introduced by a pretension method, a required amount of a first tensile steel material is disposed between a pair of pretensioning abutments, and the prestressing force of the first tensile steel material is applied to the PC member. to cancel the tensile stress acting on the edge, from the fulcrum, Kuwawa the PC member
Of the upper edge bending compressive stress due to the
The sum of the upper edge tensile stress of PC member due to stress is 0
A required amount of the second tensile steel material, which is preliminarily tensioned at another place, is disposed over a range of the length X or more to a certain position, and concrete is poured around the first and second tensile steel materials. Then, after the concrete hardens, the tension of the second tensile steel material is released, and thereafter, the first tensile steel material tensioned between the pretensioning abutments is released. The present invention can be more easily understood from FIG.
That is, the bending stress at the upper edge and the lower edge of the PC member section due to the load (solid line in FIG. 2) and the P stress due to the pre-stress force
Prestress of upper and lower edges of cross section of C member (dotted line in Fig. 2)
Is as shown in FIG. Here, P
In order to cancel the tensile stress at the upper edge of the C member, a compressive prestress equal to or greater than the tensile prestress due to the prestressing force of the first tensile steel is applied by the second tensile steel, so that the tensile stress is applied to the cross section of all the PC members. Does not occur. Further, since the tensile prestress of the upper edge of the PC member by the first tensile steel material is canceled more toward the inner section than the fulcrum due to the bending and compressive stress of the upper edge of the PC member due to the load, the amount of the second tensile steel material used is increased. The upper edge bending due to the load applied to the PC member from the fulcrum
PC due to compressive stress and pre-stress force of first tensile steel
Length X to the position where the sum of the upper edge tensile stress of the member becomes 0
The second tensile steel material may be arranged over the above range .

According to the present invention, from this viewpoint, by arranging the second tensile steel at least over the range of the length X, the tensile stress is applied to the upper edge of the PC member by using as little PC steel as possible. The concrete can be pre-tensioned so as not to occur.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing a basic mode of the present invention. Both ends of a PC member (for example, a bridge girder) 11 having a predetermined length L are supported by fulcrums b, b. A predetermined number of first tensile steel materials 12 are provided over the entire length. Further, at both ends top of PC member 11, the second tension steel 14 over from the end portion to a predetermined length X ₁ is embedded in the concrete. This length X ₁
Is the length from the end face of the PC member 11 to the tip of the second tensile steel material 14, and the length X is the length from the fulcrum b to the tip of the second tensile steel material 14. This length X is P from the fulcrum b.
The upper edge bending compressive stress due to the load applied to the C member and the first pull
Tensile Stress of PC Member due to Prestress of Upholstered Steel
Is a range not less than the length up to the position where the sum of 0 and 0 becomes zero .

The range of the length X is derived from the description of FIG. 2 as described above. That is, the bending stress at the upper edge and the lower edge of the cross section of the PC member due to the load acting on the PC member 11 (solid line in FIG. 2) and the prestress at the upper and lower edges of the PC member due to the prestressing force (dotted line in FIG. 2). As shown in FIG. 2, in order to cancel the tensile stress on the upper edge of the PC member due to the prestress force, the compression prestress equal to or greater than the tensile prestress due to the prestress force of the first tensile steel material 12 is used.
By applying the tensile steel material 14, the PC member 1
1 No tensile stress is generated in all sections.

Further, the tensile prestress of the upper edge of the PC member by the first tensile steel material 12 is canceled out more toward the cross section inside the fulcrum by the bending and compressive stress of the upper edge of the PC member due to the load. The quantity is fulcrum b, b
The length X can be determined by the above PC member cross section, and the length X is derived from the result. Then, by arranging the second tensile steel material 14 at least over the range of the length X, the pre-tension is applied to the concrete so that tensile stress is not generated on the upper edge of the PC member using as little PC steel material as possible. Can be given.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. FIG. 3 is a partially cutaway side view showing a state in which a plurality of sets of concrete member manufacturing molds and first and second tensile steel materials are provided, and FIG. 4 is a PC manufactured using the mold of FIG. FIGS. 5 to 9 are cross-sectional views of the member 11, and FIGS.

In each of the figures, a horizontal bottom form 5 is placed on a number of crossties 6 arranged in parallel so that the first tensile steel material 12 extends along the bottom form 5. And is stretched between two pretensioning abutments 7, 7, and a predetermined tensile force is applied to the first tensile steel material 12.

In order to manufacture a plurality of PC members (concrete members) on the upper part of the above-mentioned formwork, force distribution bars, through bars, stirrup bars, etc. corresponding to each member (all not shown).
After assembling, a plurality of sets of side molds 8 are placed on the bottom mold 5.
And the end mold 10 are arranged, and the second tensile steel material 14 is held by the end mold 10.

The second tensile steel material 14 does not cover the entire length of the PC member 11 to be manufactured, but has a predetermined length X ₁ from the end.
It is provided over. In addition, the second tensile steel material 14 preliminarily tensions the PC hollow steel bar in another place, and places concrete around the PC hollow steel bar,
After the concrete has hardened, a structure that releases the tension of the PC steel bar is used.

The arrangement of the second tensile steel member 14 and the sectional structure will be described with reference to FIGS. FIG. 5 is a side view of the second tensile steel material 14 to which tension has been applied in another place in advance, and FIG.
FIG. 3 is a cross-sectional view showing a tension applied state. In each figure,
A cap nut 1 is screwed into the tip of a hollow PC steel rod 15 with a screw portion 16.
7, a fixing nut 20 is screwed to the base end of the hollow PC steel rod 15 by a screw portion 18, and the screw is further provided on the base end side of the hollow PC steel rod 15 than the fixing nut 20. One end of the fixing coupler 21 is screwed by the unit 18.

A reaction force PC steel rod 22 is inserted into the hollow PC steel rod 15 from the base end thereof, and the tip is locked inside the cap nut 17. In the fixing coupler 21, a pressing cap 23 is fitted to an end of the reaction force PC steel bar 22, and a pressing holding cylinder 25 is screwed to the other end of the fixing coupler 21 via a screw portion 24. And, this press holding cylinder 2
5, the pressing rod 27 of the jack 26 is inserted into the fixing coupler 21, a reaction force is applied to the supporting point 28 of the fixing nut 20, and the reaction force PC steel rod 22 is pressed through the pressing cap 23 at the tip of the pressing rod 27. By pressing the base end of the
When the hollow PC steel bar 15 is tensioned (extended) between the tip of the steel bar 22 and the support point 28 of the anchoring nut 20, the reaction force PC steel bar 22 and the pressing cap 23 advance, so that this advance is performed. The fixing coupler 21 is screwed in by that amount, and the fixing coupler 21 and the pressing and holding cylinder 25 are advanced to engage with the pressing cap 23.

Thus, after the pressing rod 27 of the jack 26 is retracted and the jack 26 is removed, the hollow PC steel rod 1 is moved by the pressing cap 23 through the reaction force PC steel rod 22.
The tension of 5 is maintained.

As described above, the second tensile steel material 14 to which the hollow PC steel rod 15 has been tensioned is held on one upper side of the end form 8 as shown in FIG. That is, the opening 29 is provided on one side of the upper part of the end form 8, while the insertion hole 3 is provided on the bottom.
The opening edge 32 of the cylindrical holder 31 having the
It is stuck to. By holding the fixing coupler 21 in the cylindrical holder 31 and projecting the hollow PC steel rod 15 into each mold from the insertion hole 30, the end mold 10
The second tensile steel material 14 can be held horizontally or with the tip slightly inclined downward.

Thus, the first tensile steel 12 and the second
A bottom form 5 on which a tensile steel material 14 is disposed, and an end form 10
Then, concrete 33 is poured into the form surrounded by the side form 8 as shown in FIG. At this time, the concrete 33 is removed by the fixing coupler 2 due to the presence of the cylindrical holder 31.
It is filled only around the hollow PC steel bar 15 without going around the outside of 1. After the concrete 33 is poured,
After the concrete has hardened, as shown in FIG.
The fixing coupler 21, the pressing cap 23, and the pressing holding cylinder 25 are detached from the end of the steel rod 15, are detached from the cylindrical holder 31, and the reaction PC steel rod 22 is also the hollow PC steel rod 15.
To be detached from. Further, the end frame 10 is released together with the cylindrical holder 31.

As described above, the fixing coupler 21 and the like
By unscrewing from the base end of the C steel rod 15, the tension applied to the hollow PC steel rod 15 via the reaction force PC steel rod 22 is released, and the hollow PC steel rod 15 contracts. At this time, the surrounding concrete is also contracted integrally with the hollow PC steel bar 15, and prestress is introduced into the concrete at this portion. Thereafter, the prestress is introduced to the entire PC member 11 by releasing the tension of the first tensile steel material 12 disposed between the pretension abutments 7, 7.

Thereafter, as shown in FIG. 8 and FIG.
Screw-in type rust prevention cap 31 at the base end opening of C steel rod 15
3 after removing the cylindrical holding body 31 after screwing
5 is filled with mortar 36, and the manufacture of the PC member 11 is completed.

Incidentally, it is also possible to apply a tensile force by using a steel material having a structure different from that described above as the second tensile steel material.

[0030]

According to the present invention, in a PC member using a first tensile steel material and a second tensile steel material for canceling the tension caused by the first tensile steel material, the second tensile steel material is applied over the entire length between the fulcrums. Since it is not necessary to dispose the PC member, it is possible to minimize the amount of steel used at the center between the fulcrums in the PC member, not only to save the manufacturing cost of the PC member by the pretensioning method, but also to use the first tensile steel material as in the prior art. It is not necessary to perform the bond control, and the manufacturing cost can also be reduced in this regard.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a basic structure of a PC member according to the present invention.

FIG. 2 is an explanatory view showing a relationship between first and second tensile steel members and a load in a PC member supported between fulcrums according to the present invention.

FIG. 3 is an explanatory sectional view showing a method for manufacturing a PC member according to the present invention.

FIG. 4 is a cross-sectional view orthogonal to the longitudinal direction of a PC member manufactured by the method of FIG.

FIG. 5 is a side view of a second tensile steel material used in the present invention.

FIG. 6 is a sectional view of a second tensile steel material used in the present invention.

FIG. 7 is a cross-sectional view of the second tensile steel material of FIG. 5 being set in an end formwork and casting concrete.

FIG. 8 is a cross-sectional view showing a state where the casting of concrete is completed and the form is released.

9 is a sectional view of a second tensile steel material in FIG.

FIG. 10 is an explanatory view showing an arrangement mode of a tensile steel material in a conventional PC member supported between fulcrums.

FIG. 11 is an explanatory sectional view showing a conventional method for manufacturing a PC member.

FIG. 12 is a sectional view orthogonal to the longitudinal direction of the PC member manufactured by the method of FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PC member 2 Tensile steel material 3 PC steel material group 4 Tensile steel material 5 Bottom formwork 6 Sleeper 7 Pretension abut 8 Side formwork 10 End formwork 11 PC member 12 1st tensile steel material 14 2nd tensile steel material 15 hollow PC Steel rod 16 Screw part 17 Cap nut 18 Screw part 20 Fixing nut 21 Fixing coupler 22 Reaction force PC steel rod 23 Press cap 24 Screw part 25 Press holding cylinder 26 Jack 27 Press rod 28 Support point 29 Open hole 30 Insertion hole 31 Cylindrical Holder 32 Opening edge 33 Concrete 34 Rust prevention cap 35 Recess 36 Mortar

Claims (2)

(57) [Claims] In a PC member to which a prestress is introduced by a pretensioning method, a required amount of a first tensile steel material is disposed over the entire length between fulcrums of the PC member,
In order to cancel the tensile stress acting on the upper edge of the PC member due to the pre-stress force of the first tensile steel material, the PC member is moved from the fulcrum to
Upper edge bending compressive stress caused by load applied to steel and first tensile steel
Of PC member upper edge tensile stress due to prestress
A pretensioning type PC member, wherein a required amount of the second tensile steel material is provided over a range of a length X or more up to a position where is zero . 2. A method for manufacturing a PC member in which prestress is introduced by a pretension method, wherein a required amount of a first tensile steel material is disposed between a pair of pretensioning abutments, and a prestress of the first tensile steel material is provided. PC by force
From the fulcrum, to cancel the tensile stress acting on the upper edge of the member ,
The upper edge bending compressive stress due to the load applied to the PC member and the first
Upper edge tensile stress of PC member due to prestress of tensile steel
Over a range of length X or more up to the position where the sum of
After placing a required amount of the second tensile steel material to which tension has been applied in another place in advance, concrete is poured around the first and second tensile steel materials, and after the concrete hardens,
A method of manufacturing a pretension type PC member, comprising releasing the tension of the second tensile steel material, and then releasing the first tensile steel material tensioned between the abutments for pretension.