JP2022165122A - Expansion method for prestressed concrete floor slab - Google Patents

Abstract

To provide an expansion method for a prestressed concrete floor slab capable of extending a concrete floor slab into which prestress is introduced by extending a tendon without abruptly releasing the tension force of an existing tendon.SOLUTION: An expansion method for a prestressed concrete floor slab is an expansion method for a concrete floor slab into which prestress is introduced and includes: a step of exposing a tendon by chipping the concrete of a floor slab near the end on the expanding side; a step of attaching an intermediate anchorage to the exposed tendon; a step of heating the exposed tendon; a step of cutting the heated tendon; a step of attaching a connector to the end of the cut tendon and dismantling the floor slab on the expanding side; a step of connecting the tendon of an expansion part to the connector; a step of placing concrete in the expansion part of the concrete floor slab; and a step of tensioning the tendon of the expansion part to introduce prestress into the concrete in a widening part after the placed concrete is hardened.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for expanding prestressed concrete floor slabs (PC floor slabs) of existing bridges and the like.

When widening an existing bridge, the method described in Patent Document 1 is known as a widening method when the bridge is a PC floor slab.
The method consists of the following steps.
(a) Peel the concrete of the floor slab to expose the tendon (b) Attach the intermediate anchorage to the exposed tendon (c) Backfill the hanging part (d) Cover the existing anchorage Remove the existing anchorage and expose the end of the tendon (e) Attach a connector to the exposed end of the tendon and connect the extension tendon (f) Widening (g) After the cast concrete has hardened, tension is introduced into the extension tendons and prestress is introduced into the concrete of the widening part. It is possible to expand the width of the bridge while keeping it in service.
Patent Literature 2 describes an intermediate fixing tool that can be used in this construction method.

JP 2017-193899 A JP 2017-186814 A

In step (d) above, when the concrete covering the existing fixture is removed by chipping, the chipping reduces the cross-section of the concrete behind the bearing plate of the fixture, reducing its bearing stress. When the compressive strength is exceeded, there is a risk that the concrete will collapse or the bearing plate will slip and lose its anchoring function, resulting in a sudden release of the tension.
Since the sudden release of the tension is accompanied by an impact, when it is transmitted to the intermediate fixing device, the tendon slips and the tension on the service side is reduced.
And when slippage occurs, in the wedge-type intermediate fixture, cross-sectional defects due to shaving and abrasion of the tendon, and deterioration of the fixing performance due to wedge edge chipping, and in the expansive material-type intermediate fixture, it causes the expansive material to break. .
Furthermore, even if we try to recover the once-reduced tension on the service side by tensioning the tendons connected for the extension of the widened section, it is almost impossible to know the extent of the reduction in the tension of the tendons due to sliding with impact. Not only is it impossible to find the necessary moving tension, but the introduction of excessive tension affects not only the tendon itself, but also the safety of the concrete that is prestressed by the tension. influence.
In addition, such reduction and recovery of tension, that is, variation of tension, cause the tendon to expand and contract, causing the tendon to lose its adhesion to the grout surrounding it, and the integrity of the PC tendon and concrete in that part. is lost.

INDUSTRIAL APPLICABILITY The present invention is a prestressed concrete floor slab expansion method capable of extending a prestressed concrete floor slab by extending a prestressed tendon without abruptly releasing the tension of the existing tendons. intended to provide

A first invention of the present application, which has been made to achieve the above object, is a method for expanding a concrete floor slab into which prestress is introduced, wherein the concrete of the floor slab is scraped off near the end on the side to be expanded. a step of exposing a tendon, a step of attaching an intermediate fixing device to the exposed tendon, a step of heating the exposed tendon, a step of cutting the heated tendon, and a step of cutting the cut tendon. dismantling the floor slab on the side to be expanded; connecting tendons of the expanded portion to the connecting device; and pouring concrete into the expanded portion of the concrete floor slab. and a step of introducing prestress to the concrete of the widened portion by tensioning the tendon of the widened portion after the concrete of the widened portion has hardened. provide an expansion method for
The second invention of the present application is a method for expanding a concrete floor slab to which prestress has been introduced, comprising a step of exposing tendons by stripping the concrete of existing floor slabs remaining after expansion, and a step of attaching an intermediate fixing device to the prestressed tendon; a step of backfilling the concreted portion of the floor slab; A step of exposing the tendon, a step of heating the exposed tendon, a step of cutting the heated tendon, attaching a connector to the end of the cut tendon, and expanding the floor slab a step of connecting the tendon of the expanded portion to the connector; a step of placing concrete in the expanded portion of the concrete floor slab; and a step of introducing prestress to the concrete of the widening part by tensioning the tendon of the part.

The present invention can obtain at least one of the following effects by the means for solving the above problems.
(1) By heating the tendon, the tension is gradually reduced, and there is no shock caused by sudden release of the tension when the tendon is cut.
(2) Since there is no shock associated with the sudden release of the tension, the tendon does not slip on the intermediate fixture and the tension on the service side does not decrease.

Explanatory diagram (1) of the process of the expansion method of the PC floor slab of the first embodiment Explanatory diagram (2) of the process of the expansion method of the PC floor slab of the first embodiment Explanatory diagram (3) of the process of the expansion method of the PC floor slab of the first embodiment Explanatory diagram (1) of the process of the PC floor slab expansion method of the second embodiment Explanatory diagram (2) of the process of the PC floor slab expansion method of the second embodiment Explanatory diagram (3) of the process of the PC floor slab expansion method of the second embodiment

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
<1> Bridges to which the present invention can be applied A bridge to which the PC floor slab expansion method of the present invention can be applied has a concrete floor slab, and tension is introduced into tendons placed in the floor slab. , prestress is introduced into the concrete slab.
In the embodiments of the present application, the expansion of the PC floor slab in the width direction of the bridge will be described, but the present invention is not limited to this, and can be applied to the expansion of the existing PC floor slab in the direction in which prestress is introduced. can be applied.

<2> Exposure of the existing tendon 2a is exposed by scraping the concrete of the floor slab 1a near the side end of the existing floor slab 1a on the side where the width is to be widened (Fig. 1 (a) ). If the hinge position is too close to the existing anchorage 3a, the tension introduced into the tendon 2a will cause the concrete near the anchorage 3a to collapse and the tension to be released, possibly reducing the prestress of the floor slab 1a. Therefore, the chipped portion 4 is positioned away from the fixture 3a to a position where the concrete is not crushed by the tension force.
The range of the chipped portion 4 in the bridge axis direction is basically the interval between tendons 2a, but a plurality of strands may be hung together at places where the interval is narrow such as at the end of a girder.
The exposed tendon 2a is cleaned and removed of adhering grout and the like.

<3> Mounting of Intermediate Fixing Tool The intermediate fixing tool 5 is attached to the exposed tendon 2a (Fig. 1(b)).
The intermediate fixing member 5 grips the tendon 2a and transmits its tension to the floor slab 1a, and is preferably the intermediate fixing member (i-fix (registered trademark)) described in Patent Document 2 mentioned above. be.

The intermediate fixing member 5 used in the present invention comprises a fixing force generating part 5a and an adjusting bearing plate 5b. In this process, the following two operations are performed to mount the intermediate fixing member.

<3.1> Attachment of Fixing Force Generating Part The fixing force generating part 5a grips the tendon 2a with a built-in wedge to generate a fixing force. The wedge is press-fitted with a force greater than the existing tension of the tendon 2a, and generates a sufficient fixing force so that slippage does not occur even if tension is applied by cutting the tendon 2a.

<3.2> Insertion of Adjusting Bearing Pressure Plate The adjusting bearing pressure plate 5b is inserted between the fixing force generating component 5a and the service side of the floor slab 1a, and brought into close contact with both. An adjustment bolt is built in between the two adjustment bearing pressure plates 5b, and by rotating this, the gap between the two adjustment bearing pressure plates 5b is widened and brought into close contact, thereby reducing the fixing force generated in the fixing force generating component 5a. , to the service side of the floor slab 1a. When a predetermined torque is applied to the adjustment bolt when rotating the adjustment bolt, the two adjustment bearing pressure plates 5b are forcibly spread apart, increasing the tension of the portion. By doing so, the tension loss due to the running-in of the intermediate anchor 5 that occurs when the tendon 2a is cut is corrected, and the tension on the service side from the intermediate anchor 5 remains at the existing value even after the tendon 2a is cut. can be maintained.

<4> Heating and cutting tendon The tendon 2a is heated and cut using the gas cutter 6 (Fig. 2(c)).
Heating and cutting are performed by the following two processes.

<4.1> Heating step First, the tendon 2a in the vicinity of the cutting position is heated by the gas cutter 6 .
The gas cutter 6 can switch between preheating and cutting functions by changing the amount of acetylene and oxygen supplied.
In this step, the tendon 2a is heated with a preheating flame to cause thermal expansion and a decrease in extensional rigidity, thereby gradually reducing the tension.
The heating range is widened in the longitudinal direction of the tendon 2a to about twice the diameter of the tendon (the diameter of the bundle when there are a plurality of tendons). The reason for this is that the temperature of the acetylene flame is as high as about 3000°C, and when the flame is concentrated in one place as in general gas cutting, the temperature rises rapidly locally, and the tensile strength of the heated part decreases and breaks. because of fear.
In addition, since the reduction in tension due to heating becomes remarkable in the temperature range of about 450°C to 550°C, as a guideline for the heating work, the surface of the tendon 2a is colored dark red (about 600°C) from the start of heating. ), widen the heating range and slow down the heating rate until ), the tension becomes almost 0 kN.

<4.2> Cutting step The tendon 2a is fused and cut by increasing the supply of oxygen (Fig. 2(d)). The tendon 2a, which has been sufficiently heated in the heating process and whose tension has been reduced, can be easily cut without impact.
Since there is no impact due to sudden release of the tension, the tendon 2a does not slip on the intermediate fixture 5, and the tension on the service side does not decrease.
In addition, both the heating process and the cutting process are performed simply by heating and cutting with the gas cutter 6, which can be easily performed without danger.

<5> Attachment of connecting device After cutting the tendon 2a, cut off the tendon 2a leaving the extra length necessary for attaching the connecting device (Fig. 3 (e)), and attach the connecting device 7 ( FIG. 3(f)). At the same time, in order to construct the floor slab for the expanded portion, the existing floor slab 1a on the side to be expanded is dismantled and the ends are shaped.

<6>Construction of Extended Portion Finally, in order to construct the extended portion 1b of the floor slab, formwork is assembled and reinforcing bars are arranged. Since the intermediate fixing member 5 and the connecting member 7 are accommodated in the expanded portion 1b of the floor slab, the sheath 8 covers not only the tendon 2b of the expanded portion but also the intermediate fixing member 5 and the connecting member 7. - 特許庁When constructing the expansion part with precast members, the intermediate fixture 5 and the connector 7 are embedded in the interstitial part between the existing part 1a and the expansion part 1b. Placement of muscle and sheath 8 is performed.
Next, the tendon 2b of the expanded portion is inserted into the sheath and connected to the connector 7, and the concrete of the expanded portion is placed.
Then, when the placed concrete hardens and reaches a tensionable strength, a jack is used to tension the tendon 2b of the expanded portion and fix it with the fixture 3b of the expanded portion, thereby forming the expanded portion of the floor slab. A prestress is introduced to 1b, and it is integrated with the existing portion 1a (FIG. 3(g)). After tensioning is completed, the grout is injected to complete the construction of the extension. When pre-grouting steel material is used for the pre-grouted tendon 2b of the expanded portion, grouting of that portion after completion of tensioning can be omitted.

[Second embodiment]
In the above-described first embodiment, the intermediate fixation of the tendon 2a and the connection of the tendon 2b were performed within the range of one beam portion 4. It may not be possible to provide a stripping area to just anchor and connect.
In such a case, the chipping range shall be two and the following shall be carried out.

<1> Exposing Existing Tenants The existing tendons 2a are exposed by piling the concrete of the existing floor slab 1a (Fig. 4(a)). The position of the chipped portion 4 is set at a position away from the existing fixing device 3a and remaining after construction of the expanded portion. The range of the chipping portion 4 is based on the spacing of the tendons 2a, but a plurality of tendons may be hung together at places where the spacing is narrow, such as at the end of a girder.
The exposed tendon 2a is cleaned and removed of adhering grout and the like.

<2> Mounting of Intermediate Fixing Tool The intermediate fixing tool 5 is attached to the exposed tendon 2a (Fig. 4(b)).
The intermediate fixing tool 5 transmits the tension force of the tendon 2a to the floor slab 1a, and the intermediate fixing tool described in the above-mentioned Patent Document 2 is suitable.
An intermediate fixture 5 is fixed to the service side of the chipping portion 4 to compensate for the increased tension.

<3> Backfilling of the chipped part and exposure of the cut part The chipped part 4 is backfilled, and the chipped part 9 for cutting is placed with concrete of the existing floor slab 1a at a position close to the anchorage group where the existing anchoring tool 3a is located. to expose the existing tendon 2a (Fig. 5(c)).
Since the chipping range of the chipping part 9 for cutting is near the fixing end, its size and position are set so as not to affect the concrete stress as much as possible.

<4> Cutting tendon The tendon 2a is cut at the cutting edge 9 (Fig. 5(d)).
This process is performed in the same manner as the tendon cutting process of the first embodiment.
After that, the tendon 2a is removed, the existing floor slab 1a is dismantled, the ends are shaped (Fig. 6(e)), the connector is attached, and the extension part is constructed (Fig. 6(f)). Do the same.

1a: existing floor slab, 1b: floor slab expansion part 2a: existing tendon, 2b: expansion part tendon 3a: existing anchorage, 3b: expansion part anchorage 4: chipping part 5: intermediate anchorage Tool 6: Gas cutter 7: Connector 8: Sheath 9: Cutting hook

A first invention of the present application, which has been made to achieve the above object, is a method for expanding a concrete floor slab into which prestress is introduced, wherein the concrete of the floor slab is scraped off near the end on the side to be expanded. a step of exposing a tendon, a step of attaching an intermediate fixing device to the exposed tendon, a step of heating the exposed tendon, a step of cutting the heated tendon, and a step of cutting the cut tendon. dismantling the floor slab on the side to be expanded; connecting tendon of the expansion portion to the connecting device; A step of covering the tendon of the above with a sheath and placing concrete in the expanded portion of the concrete floor slab; and a step of introducing prestress into the prestressed concrete floor slab.
The second invention of the present application is a method for expanding a concrete floor slab to which prestress has been introduced, comprising a step of exposing tendons by stripping the concrete of existing floor slabs remaining after expansion, and a step of attaching an intermediate fixing device to the tendon thus formed; a step of covering the intermediate fixing device and the exposed tendon with a sheath ; The steps of exposing the tendon by tapping the concrete of the floor slab near the end, heating the exposed tendon, cutting the heated tendon, and cutting the cut tendon. A step of dismantling the floor slab on the side to be expanded while attaching the connector to the end portion, a step of connecting the tendon of the expanded portion to the connector, and connecting the connector and the tendon of the expanded portion with a sheath. A step of covering and placing concrete in the expanded portion of the concrete floor slab, and after the cast concrete in the expanded portion has hardened, tensioning tendons in the expanded portion to introduce prestress to the concrete in the widened portion. To provide a prestressed concrete floor slab expansion method comprising the steps of:

Claims (2)

A concrete floor slab expansion method in which prestress is introduced,
a step of exposing the tendon by tapping the concrete of the floor slab near the end on the expanding side;
attaching an intermediate anchor to the exposed tendon;
heating the exposed tendon;
cutting the heated tendon;
a step of attaching connectors to the ends of the cut tendons and dismantling the floor slab on the expanding side;
connecting an extension tendon to the connector;
A step of placing concrete in the expanded portion of the concrete floor slab;
after the concrete in the expanded portion has hardened, tensioning the prestressing tendons in the expanded portion to introduce prestress into the concrete in the widened portion;
Expansion method for prestressed concrete floor slabs. A concrete floor slab expansion method in which prestress is introduced,
a step of exposing tendons by stripping the concrete of existing floor slabs remaining after expansion;
attaching an intermediate anchor to the exposed tendon;
a step of backfilling the concreted portion of the floor slab;
a step of exposing the tendon by tapping the concrete of the floor slab near the end on the expanding side;
heating the exposed tendon;
cutting the heated tendon;
a step of attaching connectors to the ends of the cut tendons and dismantling the floor slab on the expanding side;
connecting an extension tendon to the connector;
A step of placing concrete in the expanded portion of the concrete floor slab;
after the concrete in the expanded portion has hardened, tensioning the prestressing tendons in the expanded portion to introduce prestress into the concrete in the widened portion;
Expansion method for prestressed concrete floor slabs.

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