JPH1136224A - Prestress introducing method and introducing device for prestress concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prestress introducing method and its device for prestress concrete capable of introducing prestress to concrete in response to the distribution state of the required prestress and reducing the introducing devices such as reaction members and jacks and the reinforcement of a steel product to the minimum required. SOLUTION: This prestress introducing device is provided with reaction members 25 provided at both ends in the longitudinal direction of a steel product 20, an outer cable 26 suspended between them, stretching means 28 stretching the outer cable 26, and struts 27 provided between the outer cable 26 and the steel product 20. When the outer cable 26 is stretched, bending stress with uniform distribution is applied to the steel product 20 from the reaction members 25. Bending stress with biased distribution made maximum at the center section is applied to the steel product 20 via the struts 27, concrete 29 is placed at the tensile stress side portion of the steel product 20, the stretching of the outer cable 26 is released after hardening, and prestress is introduced to the concrete 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prestressed concrete in which a prestress is applied to concrete by the restoring force of a steel material. Prestressing in prestressed concrete that can be easily introduced as much as possible in accordance with the prestress distribution form required by concrete by simultaneously applying the bending stress of The present invention relates to a method and an apparatus for introducing the same.

[0002]

2. Description of the Related Art In general, in order to construct a large span structure such as a bridge girder or a large span beam, a composite beam composed of a steel frame and concrete, commonly called a pre-beam, is used. This pre-beam is to insert high-strength concrete around the lower flange of a steel beam that has been pre-deflected in advance and surround it, and to introduce pre-stress into the lower flange concrete by using the restoring force of the steel frame itself. Published by Japan Concrete Institute, Concrete Engineering, VOL.25, etc.)

[0003] That is, as shown in FIG.
Is manufactured with a back calculation (camber) so that the pre-beam itself becomes horizontal at the time of design load (FIG. 7).
). A pre-flexion (pre-reflection) load P1 that includes the bending stress distribution at the time of the design load is applied to the beam 1,
Flex the steel beam (Figure 7). Concrete 2 is poured into the lower flange while maintaining the state where the pre-reflection stress is applied (FIG. 7). When the pre-reflection stress is released when the concrete has given strength, the tensile force of the lower flange compresses the surrounding concrete, and the pre-stress is introduced (FIG. 7). The process up to this point is carried out at the factory. The beam in a state in which only the lower flange is hit with concrete is carried into the site, and is installed at a predetermined position. Then, concrete of a floor slab is cast on the upper portion (FIG. 7), and the pre-beam 3 is completed.

[0004] As described above, there are two conventional pre-beam methods for introducing pre-stress into concrete by utilizing the bending stiffness of steel.

In the first method, as shown in FIG. 8 (a), both ends of a steel girder 4 made of I-shaped steel are supported at a fulcrum 5, and a front bending load P1 is applied from above the middle part, and the steel girder 4 (Hereinafter referred to as “loading method”). As a specific example of this loading method, for example, as shown in FIG. 9, two steel girders 4 made of H-shaped steel are tied together so that their upper flanges face each other, and these steel girders 4 , 4 are interposed with bearings 6 orthogonal to the respective steel girders, then press frames 7 are fitted into both ends of the steel girders 4, and a load P 1 is applied to both ends of the steel girders 4 by jacks 8. Thereby, the bearing body 6 is caused to act as the fulcrum 5,
A pre-bending load P1 is applied to the steel girder 4, and while maintaining this state, concrete is poured into the lower flange portion on the tensile stress side of the steel girder 4, 4 and, after the concrete has hardened, the pre-bending occurs. Method of releasing the load P1 (Japanese Patent Publication No. 50-31)
No. 563).

The second method is a method called “out cable method” in which a prestress is introduced into the steel girder 4 using the out cable 11 as shown in FIG. As a specific example of this out-cable system, as shown in FIG. 11, for example, both ends of a steel girder 4 having upper and lower flanges are supported, and fixing members 12, 13 serving as reaction materials are provided on both ends of the upper flange of the steel girder 4. By applying a predetermined tensile force to the out cable 11 stretched between the fixing devices, a pre-bending load P1 is applied to the plurality of steel girders 4, and in this state, the steel girders 4 There is a method of placing concrete 14 on the lower flange portion on the tensile stress side and releasing the pre-bending load after the concrete has hardened (Japanese Patent Publication No. 4-26025).

[0007]

By the way, the tensile stress generated in the concrete after the introduction of the prestress varies depending on the factor of the tensile stress, such as a uniform distribution or an uneven distribution.

[0008] For example, tensile stress caused by steel material constraining the drying shrinkage of concrete, and thermal tensile stress caused by the difference in thermal conductivity between steel material and concrete occur uniformly in the length direction of the member. On the other hand, the bending tensile stress generated in the concrete due to the vertical load perpendicular to the steel girder becomes larger toward the center of the member.

Therefore, the prestress added to the prestressed concrete is adjusted to the required distribution of the required prestress so as to be able to counter the tensile stress expected to occur under the use condition of the prebeam. It is desirable to introduce it.

[0010] However, when the prestress is introduced by the above-mentioned conventional loading method, both ends of the steel girder are supported by the fulcrum, so that as shown in FIG. Bending stress is applied, and pre-stress with an uneven distribution that increases toward the center can be introduced into the concrete.However, the bending stress applied to the steel girder at the fulcrum position is zero, so the concrete part at the end of the member of the steel girder Cannot introduce prestress. In other words, in the case of the loading method, the tensile stress uniformly generated in the length direction of the member (the tensile stress generated by the steel material restraining the drying shrinkage of the concrete, the temperature tensile stress generated by the difference in thermal conductivity between the steel material and the concrete, etc.) ) Cannot be countered near the end of the member.

On the other hand, when prestress is introduced by the above-mentioned conventional out-cable system, bending stress is uniformly applied in the length direction of the steel girder as shown in FIG. Prestress can be introduced into the concrete portions at both ends, but only uniform prestress can be introduced over the entire length of the steel girder. In other words, in order to counter the bending tensile stress at the center of the member caused by the vertical load applied to the steel girder,
A prestress capable of canceling out the bending and tensile stress at the center must be uniformly applied over the entire length of the member. Therefore, excessive prestress is applied more than necessary near both ends of the member, and an excessive moment must be applied to both ends of the steel girder with an out cable. In addition, there is a problem that reinforcement of the steel girder becomes large and uneconomical.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a prestressed concrete in which prestress is applied to concrete by utilizing the restoring force of a steel material. It is possible to easily introduce a prestress that matches the required prestress distribution form as much as possible, and it is possible to reduce the size of the introduction device such as reaction materials and jacks and to minimize the reinforcement of steel materials. It is an object of the present invention to provide a method and an apparatus for introducing prestress in prestressed concrete which requires only a limited amount of time.

[0013]

In order to achieve the above object, a method for introducing prestress in prestressed concrete according to the present invention is to stretch out cables between reaction force members provided at both longitudinal ends of a steel material. A tension is applied to the out cable to apply a uniform distribution of bending stress to the steel material, and a bundle is provided between the steel and the steel at an arbitrary position in the middle of the out cable. A concentrated load is applied to the steel material from the cable to apply a biased bending stress to the steel material with an uneven distribution in which the central portion of the member is maximized. In this state, concrete is poured into the tensile stress side portion of the steel material, and after the concrete is hardened. The pre-stress is introduced into the concrete by releasing the tension of the out cable.

Further, the prestress introduction device of the present invention
A reaction material provided at both ends in the longitudinal direction of the steel material, an out cable stretched between the reaction materials, tensioning means for tensioning the out cable, and the steel material at an arbitrary position in the middle of the out cable. And a bundle material interposed therebetween.

[0015] The bending stress applied to the steel material is given through a bundle material in the middle of the out-cable and the uniformly distributed bending stress applied from both reaction force members at both ends in the longitudinal direction of the steel by tensioning the out-cable. And the partial distribution bending stress caused by the concentrated load. For this reason, the prestress is also introduced into the concrete portions at both ends of the steel material by the uniform distribution of bending stress, and at the same time, a larger prestress is introduced toward the center of the steel material by the uneven distribution of bending stress. The distribution form and size of the prestress to be introduced can be arbitrarily set by appropriately selecting the height of the reaction force material or the bundle material, the tension of the out cable, and the arrangement position of the bundle material. it can.

Accordingly, the tensile stress uniformly generated in the longitudinal direction of the steel material (such as the tensile stress generated by the steel material restraining the drying shrinkage of the concrete and the temperature tensile stress generated by the difference in thermal conductivity between the steel material and the concrete). ) And the bending stress at which the central part of the member is maximized are required and sufficient in accordance with the distribution form of the required prestress required for the concrete.
Moreover, it can be easily applied to concrete without applying an excessive pre-deflection load, and large-scale reinforcement of reaction materials and steel materials is not required.

Further, the present invention is not limited to the form of the steel material, and the above-mentioned steel material is, for example, a steel plate obtained by welding a steel plate having a lower end of a T-type steel and having a stud bolt on the outer surface wider than the T-type steel. Or H with upper and lower flanges
The present invention can be applied even in the form of a shape steel such as a shape steel. Therefore, the present invention includes the following specific embodiments.

(1) A steel sheet wider than the T-type steel and having stud bolts on the outer surface is welded to the lower end of the T-type steel, and reaction force members are provided at both ends in the long side direction of the obtained steel material. By applying a uniform distribution bending stress to the steel by tensioning the out cable stretched between the force members, a bundle is provided between the steel and the steel in the middle of the out cable, and the bundle is provided through the bundle. By applying a concentrated load to the steel material by applying a concentrated load to the steel material from the out cable, concrete is placed on the outer surface of the steel plate on the tensile stress side in this state, and after the concrete has hardened, the concrete is hardened. A prestressing method for steel plate driven prestressed concrete slabs that releases tension in the cable and introduces prestress into concrete.

This is suitable for producing a steel plate-dried prestressed concrete slab such as the case of forming an exposed concrete wall of a large-hole outer shell steel plate shell.

(2) A reaction material is provided at both ends of the long side of the steel material having the upper and lower flanges, and a bending stress having a uniform distribution is applied to the steel material by tensioning an out cable stretched between the reaction force materials. On the other hand, a bundle is provided between the out cable and the steel material in the middle of the out cable, and a concentrated load is applied to the steel material from the out cable via the bundle material to impart a biased bending stress to the steel material. Concrete is poured into the lower flange of the steel material, which is on the tensile stress side in the state, and after the concrete is hardened, the tension of the out cable is released to introduce a prestress into the concrete, and the prestress of the prestressed composite beam is introduced. How to introduce stress.

This is suitable for manufacturing steel girders or composite beams (pre-beams) for building large span structures such as bridge girders and large span beams.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

First, a case where prestress is introduced into a steel plate driven prestressed concrete slab which constitutes a concrete wall which is exposed to the inside of a large-sized outer shell steel plate shell will be described.

As shown in FIGS. 4 and 5, the steel shell of the large-sized hole shell is made of a steel plate 22 welded to the lower end of a T-shaped steel 21. A steel material 20 having a cross section is formed. Steel plate 22
Is about 10 m, and the width W of the steel plate 22 is about 3 m, which is wider than the T-shaped steel 21. This wide steel plate 2
2, a stud bolt 23 is provided upright on the outer surface (lower surface in FIG. 4) for strengthening the connection with concrete. 24 is a reinforcing plate.

In this way, the relatively long steel material 20 which is formed as a whole with a working cross section is actually not a straight line when viewed in the longitudinal direction, but as shown in FIG. As a curved shape. However, in the following description of FIGS. 1 and 2, in order to facilitate understanding here, it is assumed that the steel material 20 does not have a curvature as a large hole outer shell.

In FIG. 1 (a), first, as described above, a steel plate 22 having a cross section formed by welding a steel plate 22 which is wider than the T-shaped steel and has a stud bolt 23 on the outer surface is welded to the lower end of the T-shaped steel 21 as described above.
The reaction material 25 is attached to both ends of the upper flange 21 of the T-section steel 21.
Attach it by protruding to the a side. And this reaction material 2
The out cable 26 is stretched between 5, 5 and 25. At this time, the bundle 27 holding the height of the out cable 26 at a position higher than the protruding length from the upper flange of the reaction material 25 is placed on the steel 20. Attached. Here, one or more (two in this example) bundles 27 are previously configured as a unit, and a roller on which the out cable 26 can slide is provided at the top of each bundle. Is preferred.

The position at which the plurality of bundles 27 are provided depends on the distribution of the stress to be introduced, but near the center of the out cable. In this example, the steel 2
Of the seven boundaries that divide the length L of 0 into eight, one bundle 27 is provided at a position corresponding to the boundary on both sides of the center boundary (fourth boundary from the end). The upper portion (upper flange 21a) and the out cable 26 are supported. The out cable 26 is provided with a jack 28 operated by a hydraulic pump (not shown) as tensioning means at a position outside the reaction member 25. In this example, out cable 2
Although one jack 28 is provided at each of both ends of 6, the jack 28 may be provided only on one side, and the other side may be fixed by a coupling tool. The tensioning means is not limited to a hydraulic jack, and a screw jack or the like can be used.

Next, as shown in FIG. 1B, a tension is applied to the out cable 26 with a jack 28. As a result, a uniform and uniform bending stress is applied to the steel material 20 by the end reaction members 25, 25, and a concentrated load from the bundles 27, 27 in the middle of the out-cable 26 causes the central portion of the member to move. A central bending stress having a partial distribution with a maximum portion is applied.

In this state, concrete 29 is placed on the lower side of steel material 20 which is on the tensile stress side, here, on the outer surface of lower steel plate 22.
Is installed.

Further, after the concrete is hardened, as shown in FIG. 1 (c), the tension of the out cable 26 by the jack 28 is released and prestress is introduced into the concrete 29.

Then, as shown in FIG. 1D, the reaction force member 25, the out cable 26, the bundle member 27 and the jack 28
To obtain a desired steel plate driving prestressed concrete plate.

This steel plate driving prestressed concrete slab is connected as a plurality of sheets in the direction of the width W of the steel plate shell to constitute an upper panel of a larger face block, and a hinge is attached to a lower panel similarly constituted as a large face block. Then, it is erected as an upper panel following the lower panel, and is used as a part of an exposed concrete wall (upper panel) of a large-hole outer steel plate shell.

FIG. 2 shows the state of bending immediately before the introduction of the prestress (FIG. 2A) and the distribution of bending stress applied to the steel material under the state (FIG. 2B). FIG.
As shown in FIG. 10, the bending stress applied to the steel material 20 is a uniform distribution bending stress (see FIG. 10) given from the reaction materials 25 at both ends in the longitudinal direction of the steel material by tensioning the out cable 26. This is a composite of the uneven distribution center bending stress (see FIG. 8) due to the concentrated load applied through the bundle material in the middle of the out cable 26.

The prestress is also introduced into the concrete portions at both ends of the steel material 20 due to the uniform distribution of bending stress, so that the tensile stress (drying shrinkage of concrete caused by the concrete The effect of introducing the prestress is exerted even at the end of the steel material against the tensile stress caused by the restraint of the steel and the temperature tensile stress caused by the difference in thermal conductivity between the steel material and the concrete.

Further, the prestress is introduced in the center of the steel material 20 due to the above-mentioned uneven distribution of the central bending stress, so that the prestress introduced into the concrete 29 is distributed by the vertical load perpendicular to the steel material 20. The distribution is such that the bending tensile stress (increased toward the center of the member) generated at the center is canceled out. For this reason,
It is no longer necessary to introduce excessive stress required for the out-cable method and to reinforce the reaction material and the steel material.

The bending stress distribution of the steel material 20 depends on the bundle 2 interposed between the out cable 26 and the steel material 20.
7 and its position, the height of the end reaction material 25, and the setting of the tension of the out cable 26 can be appropriately combined to introduce necessary prestress in accordance with the required distribution. It can be easily adjusted as needed. This is also one of the advantages of the prestress introduction method of the present invention.

Since the exposed concrete wall of the steel shell of the large-hole outer shell actually has a curve as the outer shell of the large-hole in advance, when this is taken into consideration, the prestressing of the pre-stressed concrete plate is performed. The later shape is not a straight line as in FIG. 1 (d), but a curved shape as shown in FIG. FIG. 6 shows how the steel material 20 is actually deformed when a stress is applied thereto. The steel material 20 which is normally in an upwardly convex state (the position indicated by the dotted line) has a bending stress due to the tension of the out cable 26. Is deformed to a state close to a straight line (solid line position), and in that state, the concrete is cast on the tension side.

In the above embodiment, a method of introducing a prestress into a steel plate driven prestressed concrete slab constituting an exposed concrete wall of a large hole outer shell steel plate shell has been described as an example. The present invention can also be applied when manufacturing a steel girder or a composite beam (pre-beam) for making a spanned structure.

In this case, a steel girder made of a section steel such as an H-section steel having upper and lower flanges is used as the steel material. That is, a steel girder (steel material 2) made of a mold steel having upper and lower flanges.
0), the reaction members 25 are provided at both ends in the girder direction.
The steel cable is given a uniform distribution of bending stress by tensioning an out cable 26 stretched between 25 with a jack 28, and a bundle material 27 is provided between the out cable 26 and the steel girder in the middle of the out cable 26. By applying a concentrated load to the steel girder from the out cable 26 via the bundle material, the steel girder is given a biased central bending stress in which a member central portion is maximized, and in this state, the steel girder is on the tensile stress side. Concrete 29 is cast on the lower flange of the steel girder, and after the concrete 29 has hardened, the out cable 26
Is released and prestress is introduced into the concrete 29. As a result, the prestressed composite beam is
A prestress corresponding to the bending stress distribution shown in (b) can be introduced.

[0040]

As described above, according to the present invention, the bending stress given to the steel material in advance is the same as the bending stress having a uniform distribution given from the reaction materials at both ends in the longitudinal direction of the steel material by tensioning the out cable. And the central bending stress of the partial distribution, which is applied to the center of the member via the bundle material in the middle of the out cable, and has the maximum distribution. Therefore, since the prestress is also introduced into the concrete portions at both ends of the steel material where the prestress cannot be introduced by the conventional loading method, the tensile stress uniformly generated in the longitudinal direction of the steel material also at the end of the member. Against.

Further, the pre-stress is more introduced toward the center of the steel material, and the distribution becomes such that the bending and tensile stress generated in the concrete is canceled by the vertical load perpendicular to the steel material. The prestress required at each part can be effectively applied to the concrete over the entire length of the member without the need for introducing an excessive stress or a large reinforcement of the reaction material and the steel material.

Further, the height of the bundle material interposed between the out cable and the steel material, the arrangement position thereof, the height of the end reaction material,
By appropriately adjusting the tension of the out-cable, it is possible to easily introduce pre-stress into the concrete that matches the pre-stress distribution required in use, and it is not necessary to introduce excessive stress. Therefore, it is possible to reduce the size of the introduction device for the reaction material, the bundle material, the jack, and the like, and it is possible to minimize the reinforcement of the steel material.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for introducing prestress into prestressed concrete according to the present invention.

FIG. 2 is a diagram showing a bending state given to a steel material by a method of the present invention and a bending stress distribution thereof.

FIG. 3 is a view showing a state in which a prestress is introduced into an actual steel plate driving prestressed concrete slab having a curved surface as a large hole shell in advance in the embodiment of the present invention.

FIG. 4 is a diagram showing a cross section of a steel material used in FIGS. 1 and 3 in the embodiment of the present invention.

FIG. 5 is a perspective view showing the shape of an actual steel plate shell having a curve as a large-hole shell in advance in the embodiment of the present invention.

FIG. 6 is a view showing how the actual steel plate shell of FIG. 5 is deformed.

FIG. 7 is an explanatory view of a conventional pre-beam method.

FIG. 8 is a diagram showing a pre-beam method by a conventional loading method and a bending stress distribution in that case.

FIG. 9 is a diagram showing an example of a conventional pre-beam method using a loading method.

FIG. 10 is a diagram showing a conventional pre-beam method using an out-cable method and a bending stress distribution in that case.

FIG. 11 is a view showing an example of a conventional pre-beam method using an out-cable method.

[Explanation of symbols]

 Reference Signs List 20 steel material 21 T-shaped steel 21a upper flange 22 steel plate 23 stud bolt 24 reinforcing plate 25 reaction material 26 out cable 27 bundle material 28 jack 29 concrete P1 pre-flexion (pre-reflection) load P1 L steel plate length W steel plate width

Claims (2)

[Claims] An out cable is stretched between reaction force members provided at both ends in the longitudinal direction of a steel material, and the out cable is tensioned to apply a uniform distribution of bending stress to the steel material. A bundle material is provided between the steel material at an arbitrary position on the way and a concentrated load is applied to the steel material from the out-cable through the bundle material, and a bias stress having an uneven distribution in which the central portion of the member becomes maximum in the steel material. In this state, concrete is poured into the tensile stress side portion of the steel material, and after the concrete is hardened, the tension of the out cable is released to introduce prestress into the concrete. Prestress introduction method. 2. A reaction member provided at both longitudinal ends of a steel material,
An out cable stretched between the reaction force members, a tensioning means for tensioning the out cable, and a bundle material interposed between the steel material at an arbitrary position in the middle of the out cable. An apparatus for introducing prestress in prestressed concrete, characterized in that: