JP7524121B2 - Method for preventing the protrusion of existing PC steel rods and a device for preventing the protrusion of existing PC steel rods - Google Patents

Description

The present invention relates to a method for preventing the protrusion of existing PC steel bars, and a device for preventing the protrusion of existing PC steel bars used therein, which can prevent the PC steel bars from protruding outside the concrete member by appropriately absorbing the large impact force that occurs instantly (because the bars are steel bars) when existing PC steel bars (not including PC steel wires and PC steel strands) that apply compressive force to prestressed concrete members that are preferably used in concrete beams, girders, and other building members in the civil engineering and construction field break due to corrosion caused by the passage of time or insufficient grout filling amount (the cause of breakage is not limited in the present invention). ...

In this invention, the terms wedge, shim, wedge, and wedge may be used, but they all have the same structure. In addition, since this invention is directed to existing PC steel bars, even if the term is simply used as PC steel bar, it indicates that the bar is an existing PC steel bar.

PC steel bars are used in large numbers as tension members in PC box girder bridges built before 2000 (Heisei 12), and as bridges age, corrosion may also progress in the PC steel bars. In particular, if air bubbles remain in the sheath when the grout is injected, or if there is a problem with the grout material itself, sufficient rust prevention may not be achieved, and corrosion of the PC steel bars may progress and lead to breakage. Furthermore, when used as anchors, ground movement may increase the tension in the PC steel bars, which may exceed the designed tension and cause the PC steel bars to break.

At that time, because the PC steel rods were tensioned (tensioning the PC steel rods applies a compressive force to the PC structure), there was a risk that the broken PC steel rods would fly out from the surface of the structure and cause concrete fragments to fall into the surrounding area. In other words, the PC steel rods are subjected to a large tension, and when they break, the entire cross section breaks instantly (unlike, for example, PC steel strands), so the impact force caused by the breakage is large, and in particular, when a PC steel rod that is placed perpendicular to the road surface breaks, the impact force can cause the roadbed to rise, hindering vehicle travel and causing concrete fragments to fall into the surrounding area.

If the impact force of the PC steel rods popping out causes the roadbed to swell or concrete pieces to fall, it could lead to unexpected incidents for people or passing vehicles. For this reason, measures have been taken to prevent concrete pieces from falling due to the breakage of the PC steel rods by placing steel plates on the surface of the PC structure at the points where the ends of the PC steel rods are located and attaching aramid fiber sheets or the like to the top of the steel plates with an adhesive such as epoxy resin.

Conventional measures like these, which involve attaching steel plates or aramid fiber sheets to the surface of PC structures, are extremely tedious to install when placed on the road surface, and when attached to the exterior of a structure, there is a possibility that the structure's appearance will be undesirable (depending on the finish of the exterior). Also, if the steel plates are too thin or corroded, or if the ejection energy of the PC steel rods is too high, it is not possible to prevent the PC steel rods from ejecting, and concrete fragments from falling on the surrounding area.

In view of these conventional circumstances, for example, JP 2007-314970 A (Patent Document 1) discloses an anchoring structure with a mechanism for preventing PC steel bars from jumping out, which can reliably prevent broken PC steel bars from jumping out and prevent concrete fragments from falling, without adding components such as steel plates or aramid fiber sheets that would mar the appearance of the surface of the PC structure.
The fixing structure with a mechanism for preventing the PC steel rod from jumping out disclosed in Patent Document 1 is a fixing structure that fixes the end of the PC steel rod with an anchor member having a penetration portion through which the PC steel rod is inserted and a fixing nut that screws into the PC steel rod and abuts against the anchor member, and

(1) A band-shaped protrusion is provided on the outer periphery of each anchor member on the fixed end side and the tension end side of the PC steel bar so as to protrude radially outward,
(2) At the tension end side of the PC steel rod, a jump-out prevention plate is fixed to an anchor bolt fixed to an anchor member so as to face the end face of the PC steel rod;
(3) The present invention is characterized in that, at the fixed end side of the PC steel rod, in addition to the fixing nut abutting against the fixed end side of the anchor member, a pop-out prevention nut is provided which screws into the PC steel rod and abuts against the tension end side of the anchor member.

With these configurations (1) to (3), even if the PC steel rod is found to be broken after it has been put into service, the anti-jump plate prevents the PC steel rod from jumping out from the tension end, and the double nut consisting of a fixed nut and an anti-jump nut prevents the PC steel rod from jumping out from the fixed end. In this case, the energy of the broken PC steel rod is transmitted to the anchor members on the tension end and fixed end sides, but because the outer periphery of these anchor members has a band-shaped protrusion that protrudes radially outward, the energy of the jump is released from the band-shaped protrusion to the concrete structure, effectively preventing the PC steel rod from jumping out and concrete pieces from falling.

JP 2007-314970 A

However, the anchoring structure with a mechanism to prevent the PC steel bars from jumping out, disclosed in the above-mentioned Patent Document 1, is merely suitable for use when constructing prestressed concrete members for the first time. PC box girder bridges constructed before 2000 (Heisei 12) use a large number of PC steel bars as tendons, and as bridges age, corrosion of the PC steel bars is also progressing. In light of this background, applying the technology disclosed in Patent Document 1 to existing prestressed concrete members poses major construction problems and is practically impossible to implement.

In particular, for box girder bridges, which are an example of such existing PC structures, in the event that the PC steel bars that have been applying compressive force to the PC structure for many years corrode and break, there is a need to develop a construction method that can withstand the impact force of the PC steel bars breaking and prevent deformation of the road surface and concrete fragments from falling, and there is a strong demand for a construction method that can be implemented without traffic restrictions on box girder bridges in service. In response to such a strong demand, there is a problem in that the fixing structure with a mechanism to prevent the PC steel bars from jumping out, as disclosed in Patent Document 1, cannot be suitably applied. In addition, if intermediate fixing devices are installed to prevent protrusion and the impact force when the PC steel bars break is completely absorbed, the compressive force remaining between the intermediate fixing devices and the concrete surface (section) remains unchanged or is large, so if the PC steel bars in that section break again, the PC steel bars may protrude.

The present invention was developed in consideration of the above-mentioned problems of the prior art, and its purpose is to provide an existing PC steel bar protrusion prevention method and an existing PC steel bar protrusion prevention device used therefor, which can prevent the PC steel bar from protruding out of the concrete member due to the large impact force generated when the existing PC steel bar that applies compressive force to the prestressed concrete member in service breaks, while the work is in service. Furthermore, the present invention provides an existing PC steel bar protrusion prevention method and an existing PC steel bar protrusion prevention device used therefor, which can receive the large impact force generated when the PC steel bar breaks and cushion the impact force, thereby reducing the compressive force remaining in the section between the existing PC steel bar protrusion prevention device and the concrete surface, thereby reducing the possibility of the PC steel bar protruding if the PC steel bar in that section breaks again.

In order to achieve the above-mentioned object, the method for preventing protrusion of existing PC steel bars and the device for preventing protrusion of existing PC steel bars used therein according to the present invention employ the following technical measures.
That is, the method for preventing protrusion of an existing PC steel bar according to one aspect of the present invention is a method for receiving an impact force when an existing PC steel bar that applies a compressive force to an existing prestressed concrete member breaks by using a protrusion prevention device including a wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and a sleeve having a taper that can be combined with the wedge and a structure that can be attached to the existing PC steel bar, thereby preventing the existing PC steel bar from protruding outside the concrete member, the method including an exposure step of chipping off concrete at a position 0.25 m to 2.0 m along the existing PC steel bar from the surface of the concrete member where the existing PC steel bar is expected to protrude, to expose the existing PC steel bar; The method includes a wedge mounting step of mounting two or more split wedge pieces to the exposed existing PC steel bar so that the taper of the wedge narrows in the direction toward the surface, a sleeve mounting step of mounting a sleeve having a structure that can be mounted on the existing PC steel bar to the exposed existing PC steel bar so that the taper of the sleeve narrows in the direction toward the surface, a sleeve functioning step of making the sleeve function as a sleeve that can be combined with the wedge, and an insertion step of inserting the two or more wedge pieces mounted to the exposed existing PC steel bar in the split state into the sleeve that has been made to function as a sleeve, by aligning the taper direction of the wedge with the taper direction of the sleeve.

Preferably, when the length L along the existing PC steel bar from the surface of the concrete member from which the existing PC steel bar is predicted to protrude to the other surface of the concrete member from which the existing PC steel bar is predicted to protrude exceeds 2.5 m to 3.5 m, the exposing step includes a step of chipping off two portions of the concrete at a first position 0.25 m to 2.0 m from the surface and at a second position 0.25 m to 2.0 m from the other surface to expose the existing PC steel bar at the two positions, and the first position and the second position are the surface, the first position, the second position, the position, and the other surface in that order, and the wedge attachment step includes a step of attaching two or more divided wedge pieces to the exposed existing PC steel bar using one wedge for each chipping location so that the taper of the wedge narrows in the direction toward the closer surface, and the sleeve attachment step can be configured to include a step of attaching a sleeve having a structure that can be attached to the existing PC steel bar to the exposed existing PC steel bar using one sleeve for each chipping location so that the taper of the sleeve narrows in the direction toward the closer surface.

More preferably, when the length L along the existing PC steel bar from the surface of the concrete member from which the existing PC steel bar is expected to protrude to the other surface of the concrete member from which the existing PC steel bar is expected to protrude does not exceed 2.5 m to 3.5 m, the exposing step includes a step of chipping the concrete at a location 0.25 m to 2.0 m from either the surface or the other surface to expose the existing PC steel bar at the one location, the wedge attachment step includes a step of attaching two or more divided wedge pieces to the exposed existing PC steel bar using two wedges for one chipping location so that the tapers of the two wedges narrow in the direction facing each other, and the sleeve attachment step includes a step of attaching a sleeve having a structure that can be attached to the existing PC steel bar to the exposed existing PC steel bar using two sleeves for one chipping location so that the tapers of the two sleeves narrow in the direction facing each other.

More preferably, the inserting step may be configured to include a step of manually inserting the wedge into the sleeve by an operator without using a jack.
In addition, a protrusion prevention device for existing PC steel bars according to another aspect of the present invention is a protrusion prevention device used in the protrusion prevention construction method for existing PC steel bars described in any of the above, and includes a wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and a sleeve divided into an inner tube side sleeve piece with a taper that can be combined with the wedge and an outer tube side sleeve piece that is provided on the outside of the inner tube side sleeve piece, and is characterized in that for the inner tube side sleeve piece and the outer tube side sleeve piece, at least the inner tube side sleeve piece has a notch portion through which the existing PC steel bar can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and the inner tube side sleeve piece and the outer tube side sleeve piece are joined together to form a sleeve that is integrated and functions as a sleeve that can be combined with the wedge. The sleeve piece on the outer tube side may be, for example, a sheet made of FRP (Fiber Reinforced Plastics), and the sleeve piece on the inner tube side and the sleeve piece on the outer tube side may be integrated as the sleeve by wrapping the sheet-like sleeve piece on the outer tube side around the outer periphery of the sleeve piece on the inner tube side. In this case, the notch portion of the sheet-like sleeve piece on the outer tube side is not an essential component.

Preferably, a key can be provided spanning a key groove provided on the outer peripheral surface of the sleeve piece on the inner tube side and a key groove provided on the inner peripheral surface of the sleeve piece on the outer tube side, and the sleeve piece on the inner tube side and the sleeve piece on the outer tube side can be joined together to form an integrated sleeve.
More preferably, the sleeve piece on the inner tube side and the sleeve piece on the outer tube side can be configured so that they are integrated as a sleeve by screwing together a male thread provided on the outer peripheral surface of the sleeve piece on the inner tube side and a female thread provided on the inner peripheral surface of the sleeve piece on the outer tube side.

In addition, according to yet another aspect of the present invention, the protrusion prevention device for existing PC steel bars is a protrusion prevention device used in any of the above-mentioned methods for preventing protrusion of existing PC steel bars, and includes a wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and a sleeve having a taper that can be combined with the wedge and a slit portion into which the existing PC steel bar can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and is characterized in that the opposing wall surfaces in the slit portion are connected using a connecting member to regulate the spacing of the slit portion when viewed from the perpendicular plane, thereby functioning as a sleeve that can be combined with the wedge.

Preferably, the connecting member includes a female threaded hole provided in at least one of the opposing wall surfaces and a male screw passed through a hole provided in the other wall surface, and the male screw is screwed into the female threaded hole to connect the wall surfaces, thereby regulating the spacing of the slit portions as viewed from the vertical plane.
More preferably, the connecting member includes a female threaded hole provided in at least one of the opposing wall surfaces and a male screw passed through a hole provided in the other wall surface, and the male screw is screwed into the female threaded hole to connect the wall surfaces, thereby regulating the spacing of the slit portions as viewed from the vertical surface, and by changing the diameter of the male screw, the rigidity of the connecting member can be changed when the spacing of the slit portions as viewed from the vertical surface is regulated, thereby enabling the cushioning capacity to be adjusted when the PC steel rod breaks.

More preferably, the sleeve further includes a flat plate joined to the sleeve at the end face in the direction in which the taper of the sleeve widens and perpendicular to the longitudinal direction of the existing PC steel bar, the plate being configured so that the existing PC steel bar can be inserted as viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar, and the plate has a notch through which a wedge protrusion provided at the end of the wedge in the direction in which the taper widens can protrude, and the plate is joined to the end face of the sleeve, so that the wedge is positioned at a predetermined position on the sleeve and the wedge protrusion protrudes from the notch of the plate.

More preferably, the wire clip further includes a three-dimensional wire clip, the wire clip having at least a straight portion in the sleeve corresponding to the longitudinal length of the existing PC steel bar, an arc portion that is fitted into a wedge groove provided on the outer periphery of the end of the wedge in the direction in which the taper widens on the side where the taper of the sleeve widens from the straight portion, and an insertion piece that is fitted into a sleeve hole provided on the end face of the sleeve in the direction in which the taper narrows, perpendicular to the longitudinal direction of the existing PC steel bar, on the side where the taper of the sleeve narrows from the straight portion, and the arc portion of the wire clip is fitted into the wedge groove and the insertion piece of the wire clip is fitted into the sleeve hole, so that the wedge is positioned at a predetermined position in the sleeve and the straight portion of the wire clip is arranged along the outer periphery of the sleeve.

The existing PC steel bar protrusion prevention method and existing PC steel bar protrusion prevention device used therein according to the present invention can prevent the PC steel bar from protruding out of the concrete member due to the large impact force generated when the existing PC steel bar that applies compressive force to the prestressed concrete member in service breaks, while the work is in service. Furthermore, the existing PC steel bar protrusion prevention method and existing PC steel bar protrusion prevention device used therein according to the present invention can receive the large impact force generated when the PC steel bar breaks and buffer the impact force, thereby reducing the compressive force remaining in the section between the existing PC steel bar protrusion prevention device and the concrete surface, and can reduce the possibility of the PC steel bar protruding if the PC steel bar in that section breaks again.

1 is a diagram for explaining a PC box girder bridge 10, which is an example of a PC structure (prestressed concrete member) in which the use of an extrusion prevention device 30 according to an embodiment of the present invention is envisaged. This figure is for explaining the use of the protrusion prevention device 30 when the length L from the upper deck to the lower deck in Figure 1 (the length along the existing PC steel bar, that is, the length L from the surface of the concrete member where the existing PC steel bar is predicted to protrude to another surface of the concrete member where the existing PC steel bar is predicted to protrude) is long. 3 is a diagram for explaining a usage mode of the protrusion prevention device 30 (a protrusion prevention device 32 formed by combining two protrusion prevention devices 30) when the length L in FIG. 2 is short. FIG. 1A is a plan view of a sleeve 100 (corresponding to sleeve S) and (B) a wedge 140 (corresponding to wedge W) that constitute the protrusion prevention device 30. FIG. 5A is a plan view showing a state in which the sleeve 100 (corresponding to sleeve S) in FIG. 4 functions as a sleeve that can be combined with a wedge 140 (corresponding to wedge W), and FIG. 5B is a diagram for explaining the function of a shear key. This figure explains the procedure for attaching the protrusion prevention device 30 using the sleeve 100 (corresponding to sleeve S) and wedge 140 (corresponding to wedge W) in Figure 4 to an existing PC steel rod exposed from a PC structure. 13 is a plan view of (A) a sleeve 200 (corresponding to sleeve S) (different from sleeve 100) and (B) a wedge 240 (corresponding to wedge W) (different from wedge 140) that constitute the protrusion prevention device 30. FIG. This figure explains the procedure for attaching a protrusion prevention device 30 using the sleeve 200 (corresponding to sleeve S) and wedge 240 (corresponding to wedge W) in Figure 7 to an existing PC steel rod exposed from a PC structure. This is a plan view showing the state in which sleeve S10, sleeve S11 or sleeve S20 (corresponding to sleeve S) that constitutes the protrusion prevention device 30 (separate from sleeve 100 and sleeve 200) functions as a sleeve that can be combined with wedge W (same as wedge 140). FIG. 1 is a diagram (part 1) showing test results in which a protrusion prevention device 30 according to an embodiment of the present invention was evaluated using a test specimen. 11A and 11B are diagrams for explaining a protrusion prevention device according to a first modified example of an embodiment of the present invention. 13A and 13B are diagrams for explaining a protrusion prevention device according to a second modified example of an embodiment of the present invention. FIG. 2 is a diagram (part 2) showing the test results of evaluating a protrusion prevention device 30 according to an embodiment of the present invention using a test specimen. FIG. 1 is a schematic diagram of the entire test equipment used in fracture and etrusion experiments using specimens simulating decks and webs. This is an outline diagram of the test specimen at the upper deck level. This is an outline diagram of the test specimen at the lower deck level. FIG. 1 is a schematic diagram of a test specimen for the buffer fixing device level. This figure shows the residual displacement at the -1m level with pavement in section A. This shows the residual displacement at the -2m level with pavement in section A. This is a diagram showing the condition of the concrete top surface at unpaved level in section B. This figure shows the residual displacement at the -8m level with pavement in section C. FIG. 13 is a diagram showing the fracture energy in fracture and etrusion experiments using specimens simulating a deck and a web.

The following describes in detail an embodiment of the present invention, which is a protrusion prevention device that prevents the existing PC steel rod from protruding outside the concrete member by receiving the impact force when the existing PC steel rod that applies compressive force to the existing prestressed concrete member breaks, and a construction method for preventing the existing PC steel rod from protruding outside the concrete member, which can be implemented while using the existing prestressed concrete member using the protrusion prevention device. Note that the structure of this protrusion prevention device itself may include parts similar to a fixing device, and since it is a buffer material in the sense that it cushions the impact force, this protrusion prevention device can also be called a buffer fixing device, and therefore in this specification there may be no distinction between the protrusion prevention device and the buffer fixing device. However, this protrusion prevention device differs from a fixing device in that it is not fixed at the time the construction method for preventing the existing PC steel rod from protruding, which will be described later, is completed (until the existing PC steel rod breaks).

In the drawings referenced in the following description, in order to facilitate understanding of the present invention, parts that should be shown in their external form rather than their internal form may be shown as if looking through the interior, parts that should be shown in cross-section rather than in their external form may be shown in their external form, parts that should be shown in their external form rather than in their cross-section may be shown in cross-section, cross-sections may not be hatched, non-cross-sections may be hatched, detailed structures may be omitted, and drawings of the same components may not match due to the omission of detailed structures.

<Structures and areas where protrusion prevention devices are expected to be used>
First, with reference to FIG. 1, a PC box girder bridge 10 will be described as an example of a PC structure (prestressed concrete member) in which the use of a protrusion prevention device (buffer fixing device) 30 according to an embodiment of the present invention is envisaged.
The PC box girder bridge 10 shown in Figure 1 is, as the name suggests, a bridge in the shape of a box (box shape 40), where cars pass over the bridge (paved road surface 12), and the cavity SP inside the box is designed for workers to enter during bridge inspections, etc. Also, the part of the pillar 20 that covers the top surface of the box (sometimes written as web 20 or concrete 20) can be made of concrete or steel, but in this case it is made of prestressed concrete.

More specifically, the PC box girder bridge 10 is composed of an upper deck 14, a lower deck 16, and two or more webs 20, and is therefore used in many long bridges and curved bridges, such as continuous girder bridges and rigid frame bridges, taking advantage of its cross-sectional properties, such as its ability to resist large compressive forces due to bending moments, its ability to effectively arrange PC steel materials (PC steel bars in this case), and its high torsional rigidity.

The protrusion prevention device 30 in this embodiment absorbs the impact force when the PC steel rod arranged vertically between the upper deck 14 and the lower deck 16 of the PC box girder bridge 10 breaks, thereby preventing the existing PC steel rod from protruding outside the concrete member.
First, regarding a method for preventing the protrusion of existing PC steel bars that can be performed on such a PC box girder bridge 10 while it is in service, we will explain the use of the protrusion prevention device 30 when the length L from the upper deck 14 to the lower deck 16 (the length along the existing PC steel bar B, which is approximately equal to the length L from the surface of the concrete member where the existing PC steel bar B is predicted to protrude to the other surface of the concrete member where the existing PC steel bar is predicted to protrude) is long and when the length L is short.

FIG. 2 shows a usage state of the protrusion prevention device 30 when the length L exceeds 2.5 m to 3.5 m, and FIG.
1 and 2 are schematic diagrams showing the use of the protrusion prevention device 32 when the length L does not exceed 2.5 m to 3.5 m. Although described in detail later, the protrusion prevention device 30 is used by combining a wedge W that sandwiches the existing PC steel bar B on its inner surface and has a tapered outer surface, and a sleeve S that has an inner surface that conforms to the tapered surface of the wedge W. Furthermore, the protrusion prevention device 32 is used by combining two protrusion prevention devices 30. The materials used for the sleeve S and the wedge W include metal, resin, chemical fiber, etc., and are not particularly limited, but the following description will be given assuming that they are metals of a type normally used as fixing devices for PC steel materials.

With reference to FIG. 2, the use of the protrusion prevention tool 30 when the length L exceeds 2.5 m to 3.5 m will be described. As shown in FIG. 2, the protrusion prevention tool 30 chips the concrete 20 at two locations: the concrete 20 at the first position P(1) where the first length L(1) is 0.25 m to 2.0 m from the surface (here, near the upper deck 14), and the concrete 20 at the second position P(2) where the first length L(1) is 0.25 m to 2.0 m from the other surface (here, near the lower deck 16), exposing the existing PC steel bar at two locations, and is applied to the exposed existing PC steel bar B. As shown in FIG. 2, the length L and the first length L(1) are in the above-mentioned range, and the positional relationship between the first position P(1) and the second position P(2) is the surface (here, near the upper deck 14), the first position P(1), the second position P(2), and the other surface (here, near the lower deck 16).

Then, for each chip, one wedge W and one sleeve S are attached to the exposed PC steel bar so that the taper of the wedge W and sleeve S narrows toward the closer surface (toward the upper deck 14 at the first position P(1), and toward the lower deck 16 at the second position P(2)). More specifically, one wedge W and one sleeve S are used for the first position P(1), and one wedge W and one sleeve S are used for the second position P(2).

With reference to FIG. 3, the use of the protrusion prevention device 32 when the length L does not exceed 2.5 m to 3.5 m will be described. As shown in FIG. 3, the protrusion prevention device 32 is installed on the exposed existing PC steel bar B by chipping the concrete 20 at the third position P(3) where the second length L(2) is 0.25 m to 2.0 m from the surface (here, near the upper deck 14) or the third length L(3) is 0.25 m to 2.0 m from another surface (here, near the lower deck 16). Note that, as shown in FIG. 1, the length L, the second length L(2), and the third length L(3) are in the above-mentioned range, and the positional relationship of the third position P(3) is the surface (here, near the upper deck 14), the third position P(3), and the other surface (here, near the lower deck 16).

Then, for one chip, two wedges W and two sleeves S are attached to the exposed PC steel bar so that the tapers of the two wedges W narrow in a direction facing each other, and so that the tapers of the two sleeves S narrow in a direction facing each other. More specifically, for the third position P(3), two wedges W and two sleeves S are used so that the tapers narrow in a direction facing each other.

The construction method shown in FIG. 3 is preferable to the construction method shown in FIG. 2 in that it can reduce the labor (including chipping work) and construction costs.
In addition, in Figure 2, since only the first position P(1) can prevent the roadbed (paved road surface 12) from rising due to the impact force of the PC steel bar jumping out, in the present invention, only the first position P(1) in Figure 2 or only the second position P(2) in Figure 2 may be used.

Here, it will be explained that the first length L(1), the second length L(2), and the third length L(3) are 0.25 m to 2.0 m in Fig. 2 and Fig. 3. As shown in Fig. 2, it is not known at what position of the PC steel bar embedded in the concrete 20 the existing PC steel bar B will break. As shown in Fig. 2, the assumed breakage position is a position on the lower deck 16 side that is 0.25 m to 2.0 m from the surface (near the upper deck 14 here) and on the upper deck 14 side that is 0.25 m to 2.0 m from the other surface (near the lower deck 16 here). Naturally, the PC steel rod may break at a position other than the assumed breakage position, closer to the upper deck 14 or closer to the lower deck 16. However, for example, even if the PC steel rod breaks between the upper deck 14 and the protrusion prevention device 30 installed at the first position P(1), the breaking energy of the PC steel rod toward the upper deck is small, and the breaking energy can be absorbed by the cover concrete, so such a range of 0.25 m to 2.0 m is set (the same applies when the PC steel rod breaks between the lower deck 16 and the protrusion prevention device 30 installed at the second position P(2). Here, if there is a concern about insufficient concrete cover in the cover concrete portion, or if insufficient grout filling in this portion is found, it is preferable to reinject grout only in this section in order to increase the resistance of the PC steel rod to breakage.

The protrusion prevention tool 30 used in the construction method shown in FIG. 2 and the protrusion prevention tool 32 used in the construction method shown in FIG. 3 are both configured as a wedge W that sandwiches the existing PC steel bar B on its inner surface and has a taper on its outer surface, and a sleeve S that has an inner surface that follows the tapered surface of the wedge W. Here, the sleeve S of the protrusion prevention tool 32 may be a single composite sleeve that is integrated in the axial direction and has two tapers in one member, rather than using two sleeves 100 or 200 described later side by side in the longitudinal direction of the existing PC steel bar B. In the following, the sleeve S of the protrusion prevention tool 32 will be described as using two sleeves 100 or 200 described later side by side in the longitudinal direction of the existing PC steel bar B. For this reason, the construction procedure (existing PC steel bar protrusion prevention construction method) described later will be described only for the first position P (1) in FIG. 2.

In the protrusion prevention device according to the present embodiment, the sleeve S is roughly classified into two types (the inner cylinder-outer cylinder type shown in Figs. 4 to 8 and the slit wall surface connecting type shown in Fig. 9) and the wedge W is two types (the wedge W differs only in the number of divisions, while the sleeve S has a significantly different structure).
4 to 6, a sleeve 100 (inner cylinder, outer cylinder type, shear key joint type) is described as the sleeve S, and a wedge 140 (split into three parts) is described as the wedge W.
7 and 8, a sleeve 200 (an inner-cylinder, outer-cylinder type screw-in type) will be described as the sleeve S, and a wedge 240 (split into two parts) will be described as the wedge W.
9A and 9B, sleeves S10 and S20 (slit wall surface connection type) will be described as the sleeve S (wedge W in FIG. 9 is the same as wedge 240 (divided into three)).

Furthermore, two modified examples that can be commonly used will be described with reference to FIGS.
An intermediate fixing device that can be used as the protrusion prevention device according to the present invention is known. Although it is a known technology and will not be described in detail, it is attached to the intermediate part of a tension member (PC steel material including PC steel bar) in which tension has already been introduced and both ends are fixed to a structure, and fixes the tension member to a surrounding structure while maintaining the state in which tension is introduced to the tension member. For example, as described in JP 2018-017029 A, a fixing block is formed by connecting a pair of separable half blocks, a tension member in a tensioned state is inserted into a hollow hole formed between the pair of half blocks, and then the pair of half blocks are connected to each other by multiple rows of bolts arranged in the axial direction of the tension member. In the following explanation, an intermediate fixing device in which a sleeve is formed in this hollow hole and combined with a wedge corresponding to this sleeve (the configuration in which a wedge is combined with a sleeve in the intermediate fixing device described in JP 2018-017029 A is a configuration in which the half sleeve is bolted together using a half sleeve and a half wedge, and this configuration is approximately equivalent to the intermediate fixing device described in JP 57-084220 A filed by one of the applicants of the present application) may be described as prior art or comparative example.

<1: Inner cylinder/outer cylinder type: shear key joint type>
First, the sleeve 100 and the wedge 140 will be described.
FIG. 4(A) shows a plan view of sleeve 100 constituting protrusion prevention device 30 (or protrusion prevention device 30, two of which are used in protrusion prevention device 32, but will hereinafter be simply referred to as protrusion prevention device 30), FIG. 4(B) shows a plan view of wedge 140, FIG. 5(A) shows a plan view showing the state in which sleeve 100 (corresponding to sleeve S) shown in FIG. 4 functions as a sleeve that can be combined with wedge 140 (corresponding to wedge W), FIG. 5(B) shows a diagram for explaining the function of the shear key in the state in which it functions as a sleeve, and FIG. 6 shows a diagram for explaining the procedure in which protrusion prevention device 30 is attached to existing PC steel rod B exposed from the PC structure using sleeve 100 and wedge 140 so that sleeve 100 (corresponding to sleeve S) functions as a sleeve that can be combined with wedge 140 (corresponding to wedge W).

This protrusion prevention device 30 is composed of a sleeve 100 shown in Fig. 4(A) and a wedge 140 shown in Fig. 4(B) which is combined with the sleeve 100. Note that the side view (partial cross-sectional view) on the left side of Fig. 4(A) is a view seen from the direction of the arrow X shown in the front view on the right side, and the side view on the left side and the front view on the right side of Fig. 4(B) are views of the three divided wedge pieces combined to form the wedge 140. Here, the front view is a view seen from a plane perpendicular to the longitudinal direction of the existing PC steel bar B, and the side view is a view seen from a plane parallel to the longitudinal direction of the existing PC steel bar B (the same applies below).

As shown in FIG. 4(B), the wedge 140 is divided into two or more wedge pieces (here, it is divided into three pieces, that is, wedge piece 142, wedge piece 144, and wedge piece 146) when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B. Because it is divided in this way, it can be attached to the existing PC steel bar B. In addition, the wedge 140 has a taper 140T by combining the three wedge pieces.

As shown in FIG. 4A, the sleeve 100 is divided into a hollow cylindrical inner sleeve piece 110 having a taper 100T that can be combined with the taper 140T of the wedge 140, and a hollow cylindrical outer sleeve piece 120 that is joined to the inner sleeve piece 110 by a shear key K. The outer surface 116 of the inner sleeve piece 110 has a key groove 118 that contains the shear key K, and the inner surface 126 of the outer sleeve piece 120 has a key groove 128 that contains the shear key K. In addition, in order to prevent the shear key K from moving in the longitudinal direction of the PC steel bar B from the key groove, it is also preferable, for example, to provide a hole in the bottom surface of the key groove 118 of the sleeve piece 110 on the inner tube side to engage a protrusion provided on the shear key (further, a female threaded hole is cut in the bottom surface of the groove and a female threaded hole that passes through the shear key K is cut, and the female threaded hole of the shear key K and the female threaded hole at the bottom surface of the groove are screwed together with a fully threaded bolt (a bolt with a male thread cut along its entire length and a hexagonal hole at its end surface, sometimes called a set screw)) (shown by a dotted line on the shear key K). The sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side have cutouts (cutout 114 in which part of the body 112 in the sleeve piece 110 on the inner tube side is cut out, and cutout 124 in which part of the body 122 in the sleeve piece 120 on the outer tube side is cut out) into which the existing PC steel bar B can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B.

Furthermore, the sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side each have a shear key K embedded in their respective key grooves 118 (sleeve piece 110 on the inner tube side) and 128 (sleeve piece 120 on the outer tube side), and the sleeve pieces 110 and 120 are joined together to form the integrated sleeve 100, which functions as a sleeve that can be combined with the wedge 140.

More specifically, the sleeve piece 110 has a body 112 with a taper 100T (corresponding to the existing PC steel rod B) through the center, through which the existing PC steel rod B is inserted, and since a portion of the body 112 is made into a notch 114, the taper 100T does not exist along the entire circumference, and only the portion of the notch 114 does not have the taper 100T, but this does not affect the function of this protrusion prevention device 30.

Here, the function of the shear key K will be described with reference to Fig. 5. Fig. 5(A) shows a side view (left side) and a front view (right side) of the extrusion prevention device 30 composed of the sleeve 100 and the wedge 140 (more specifically, the shear key K) in a state in which the sleeve piece 110 and the sleeve piece 120 are joined together to form the sleeve 100 and function as a sleeve to be combined with the wedge 140. In the protrusion prevention device 30 shown in Figure 5 (A) which is composed of a sleeve 100 (more specifically, the sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side) and a wedge 140 (more specifically, the shear key K), when the wedge 140 clamps the existing PC steel rod B and tension is applied to the existing PC steel rod B (more specifically, when the existing PC steel rod B breaks), the wedge 140 bites into the sleeve piece 110 on the inner tube side due to a wedge effect (indicated by the black arrow in Figure 5 (B)), causing the cutout portion 114 to expand (the notch width of the cutout portion 114 to widen) (indicated by the curved arrow in Figure 5 (B)). At this time, since the sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side are joined via the shear key K (contained in each other's key grooves 118 and 128), the deformation of the sleeve piece 110 on the inner tube side (expansion of the notch portion 114) caused by the shear key K catching is transmitted to the sleeve piece 120 on the outer tube side via the shear key K, so that the deformation of the sleeve piece 110 on the inner tube side (expansion of the notch portion 114) is borne by the sleeve piece 120 on the outer tube side. Therefore, the deformation of the sleeve piece 110 on the inner tube side is suppressed, the desired wedge effect is produced, and the desired tension can be applied to the (broken) existing PC steel bar B.

The protrusion prevention device 30 having such a structure is attached to the existing PC steel rod B at the first position P(1), second position P(2) or third position P(3) shown in FIG. 2 as follows. Here, the procedure for attaching the protrusion prevention device 30 to the existing PC steel rod B at the first position P(1) in FIG. 2 will be described (since only the taper direction is different). Note that if the existing PC steel rod B to which the protrusion prevention device 30 is attached is buried in concrete, an exposure step is required before the wedge attachment step described below, in which the concrete is chipped to expose the existing PC steel rod B in a tensioned state; however, the details of the exposed location, etc. have been described above, so they will not be described again here (same below).

As shown in Figure 6 (A), two or more divided wedge pieces (here, it is divided into three, so there are three wedge pieces 142, 144, and 146) are attached to the exposed existing PC steel bar B as a wedge attachment step so that the narrowing direction of the taper 140T of the wedge 140 is toward the surface (here, the upper deck 14) (see the black arrow on the wedge side).

In the sleeve installation step, the split sleeve pieces (here, split into two, two inner sleeve pieces 110 and two outer sleeve pieces 120) are installed on the exposed existing PC steel bar B so that the narrowing direction of the taper 100T of the sleeve 100 is toward the surface (here, the upper deck 14) (see the black arrow on the sleeve side). More specifically, the two inner sleeve pieces 110 and the outer sleeve piece 120 are installed close to the existing PC steel bar B from the left and right directions in Figure 6 (A).

Next, as shown in FIG. 6B, in order to integrate the divided sleeve pieces (here, because they are divided into two, the two inner sleeve pieces 110 and the outer sleeve piece 120) into the sleeve 100 and function as a sleeve that can be combined with the wedge 140 (for the sleeve functioning step), the shear key K contained in the key groove 118 provided on the outer peripheral surface 116 of the inner sleeve piece 110 is contained in the key groove 128 provided on the inner peripheral surface 126 of the outer sleeve piece 120. (Conversely, the shear key K contained in the key groove 128 provided on the inner peripheral surface 126 of the sleeve piece 120 on the outer tube side may be contained in the key groove 118 provided on the outer peripheral surface 116 of the sleeve piece 110 on the inner tube side), and the sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side are brought close to each other in the longitudinal direction of the existing PC steel bar B (by sliding one or both in the longitudinal direction of the existing PC steel bar B), and the sleeve piece 110 on the inner tube side and the sleeve piece 120 on the outer tube side are joined. As a result, the divided sleeve pieces (here, the two sleeve pieces 110 on the inner tube side and the sleeve piece 120 on the outer tube side because they are divided into two) are integrated as a sleeve and can function as a sleeve 100 that can be combined with the wedge 140.

Finally, in an insertion step, two or more divided wedge pieces (in this case, three wedge pieces 142, 144 and 146, as the wedge is divided into three) attached to the exposed existing PC steel bar B are inserted into the sleeve 100, which has been integrated and can function as a sleeve to be combined with the wedge 140, by aligning the direction of the taper 140T of the wedge 140 with the direction of the taper 100T of the sleeve 100.
In this way, the protrusion prevention device 30 is attached to the existing PC steel rod B at the first position P(1) in Fig. 2. The work of attaching such a protrusion prevention device 30 to the existing PC steel rod B can be performed while the prestressed concrete member (the PC box girder bridge 10, as an example) is in use (without closing the bridge).

<2: Inner and outer cylinder type: Screw-on type>
Next, the sleeve 200 and the wedge 240 will be described.
Figure 7(A) shows a plan view of sleeve 200 that constitutes protrusion prevention device 30, Figure 7(B) shows a plan view of wedge 240, and Figure 8 is a diagram for explaining the procedure for attaching protrusion prevention device 30 to existing PC steel rod B exposed from the PC structure by using sleeve 200 and wedge 240 so that sleeve 200 (corresponding to sleeve S) functions as a sleeve that can be combined with wedge 240 (corresponding to wedge W).

This protrusion prevention device 30 is composed of a sleeve 200 shown in Fig. 7(A) and a wedge 240 shown in Fig. 7(B) that is combined with the sleeve 200. Note that the side view (partial cross-sectional view) on the left side of Fig. 7(A) is a view seen from the direction of the arrow X shown in the front view on the right side, and the side view on the left side and the front view on the right side of Fig. 7(B) are views of the wedge 240 formed by combining two divided wedge pieces.

As shown in FIG. 7(B), the wedge 240 is divided into two or more wedge pieces (here, two wedge pieces 242 and 244, as it is divided into two) when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B. Because it is divided in this way, it can be attached to the existing PC steel bar B. In addition, the wedge 240 has a taper 240T by combining the two wedge pieces.

As shown in Fig. 7(A), the sleeve 200 is divided into an inner tube sleeve piece 210 having an outer thread (male thread) 216 with a taper 200T that is combined with the taper 240T of the wedge 240, and an outer tube sleeve piece 220 having an inner thread (female thread) 226 that is screwed into the outer thread (male thread) 216 of the inner tube sleeve piece 210. The inner tube sleeve piece 210 and the outer tube sleeve piece 220 have cutouts (cutouts 214 in which a part of the main body 212 in the inner tube sleeve piece 210 is cut out and cutouts 224 in which a part of the main body 222 in the outer tube sleeve piece 220 is cut out) into which the existing PC steel bar B can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B. It should be noted that the sleeve piece 210 on the inner tube side is required to have at least the notch portion into which the existing PC steel bar B can be inserted, and as long as the sleeve piece 220 on the outer tube side and the sleeve piece 110 on the inner tube side can be joined, the sleeve piece 220 on the outer tube side does not necessarily have to have the notch portion 224 into which the existing PC steel bar B can be inserted. For example, the sleeve piece 220 on the outer tube side may be, for example, a sheet made of FRP, and the sleeve piece 210 on the inner tube side and the sleeve piece 220 on the outer tube side may be integrated as a sleeve by wrapping the sheet-like sleeve piece 220 on the outer tube side around the outer periphery of the sleeve piece 210 on the inner tube side, and function as a sleeve that can be combined with the wedge 240. In this case, the notch portion 224 of the sheet-like sleeve piece 220 on the outer tube side is not an essential component. Furthermore, the sleeve piece 210 on the inner tube side and the sleeve piece 220 on the outer tube side are integrated as the sleeve 200 by engaging the outer thread (male thread) 216 and the inner thread (female thread) 226, and function as a sleeve that can be combined with the wedge 240.

More specifically, the sleeve piece 210 has a body 212 with a taper 200T (corresponding to the existing PC steel rod B) through the center, through which the existing PC steel rod B is inserted, and since a portion of the body 212 is made into a notch 214, the taper 200T does not exist along the entire circumference, and only the portion of the notch 214 does not have the taper 200T, but this does not affect the function of this protrusion prevention device 30.

The protrusion prevention device 30 having such a structure is attached to the existing PC steel rod B at the first position P(1), second position P(2) or third position P(3) shown in Figure 2 as follows. Here, the procedure for attaching the protrusion prevention device 30 to the existing PC steel rod B at the first position P(1) in Figure 2 (because only the taper direction is different) will be described.
As shown in Figure 8 (A), two or more divided wedge pieces (here, two wedge pieces 242 and wedge piece 244 because it is divided into two) are attached to the exposed existing PC steel bar B as a wedge attachment step so that the narrowing direction of the taper 240T of the wedge 240 is toward the surface (here, the upper deck 14) (see the black arrow on the wedge side).

In the sleeve installation step, the split sleeve pieces (here, two inner sleeve pieces 210 and an outer sleeve piece 220, as it is split into two) are installed on the exposed existing PC steel bar B so that the narrowing direction of the taper 200T of the sleeve 200 is toward the surface (here, the upper deck 14) (see the black arrow on the sleeve side). More specifically, the two inner sleeve pieces 210 and the outer sleeve piece 220 are installed close to the existing PC steel bar B from the left and right directions in Figure 8 (A).

Next, as shown in FIG. 8(B), in order to integrate the divided sleeve pieces (here, because it is divided into two, the two inner tube side sleeve pieces 210 and the outer tube side sleeve piece 220) as a sleeve 200 and function as a sleeve that can be combined with the wedge 240 (for the sleeve functioning step), the outer thread (male thread) 216 of the inner tube side sleeve piece 210 and the inner thread (female thread) 226 of the outer tube side sleeve piece 220 are screwed together. This allows the divided sleeve pieces (here, because it is divided into two, the two inner tube side sleeve pieces 210 and the outer tube side sleeve piece 220) to be integrated as a sleeve and function as the sleeve 200 that can be combined with the wedge 240.

Finally, in an insertion step, two or more divided wedge pieces (in this case, two wedge pieces 242 and 244 because the wedge is divided into two) attached to the exposed existing PC steel bar B are inserted into the sleeve 200 so that the orientation of the taper 240T of the wedge 240 matches the orientation of the taper 200T of the sleeve 200 and the integrated sleeve can function as a sleeve that can be combined with the wedge 240.
In this way, the protrusion prevention device 30 is attached to the existing PC steel rod B at the first position P(1) in Fig. 2. The work of attaching such a protrusion prevention device 30 to the existing PC steel rod B can be performed while the prestressed concrete member (the PC box girder bridge 10, as an example) is in use (without closing the bridge).

<3: Slit wall connection type>
The protrusion prevention device 30 composed of the sleeve 100 and the wedge 140 and the protrusion prevention device 30 composed of the sleeve 200 and the wedge 240 described above are both of the inner cylinder/outer cylinder type, but next, the protrusion prevention device 30 including the sleeve S10, the sleeve S11, and the sleeve S20 of the slit wall surface connection type will be described in detail below with reference to Fig. 9. Note that the wedge W shown in Fig. 9, which is combined with the sleeve S10, the sleeve S11, and the sleeve S20, is the same as the wedge 140 composed of the above-mentioned three divided wedge pieces, so a repeated description will not be given here.

Figure 9(A) shows a plan view of sleeve S10 that uses a headed hexagon socket bolt (hereinafter referred to as a cap bolt) T10 as the connecting member constituting protrusion prevention device 30, Figure 9(B) shows a plan view of sleeve S11 that uses a headless hexagon socket bolt (fully threaded bolt, so-called set screw, hereinafter referred to as a fully threaded bolt) T20 as the connecting member, and Figure 9(C) shows a plan view of sleeve S20 that is different from sleeve S10 and sleeve S11. Note that while sleeve S20 shown in Figure 9(C) uses cap bolt T10 as the connecting member, fully threaded bolt T20 may also be used as the connecting member.

These slit wall connection types shown in Figure 9 are different from the inner tube outer tube type (split type) described above in that they have a taper that can be combined with a wedge W, and a slit portion into which the existing PC steel rod B can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel rod B, and the opposing wall surfaces at this slit portion are connected using a connecting member, thereby regulating the spacing of the slit portion when viewed from the perpendicular plane, and they function as a sleeve that can be combined with the wedge W.

Although the sleeve S10 shown in FIG. 9(A) and the sleeve S11 shown in FIG. 9(B) have different connecting members (the cap bolt T10 in FIG. 9(A) and the fully threaded bolt T20 in FIG. 9(B)), the structure of the sleeve is the same except that the hole provided in the portion B10 is hole H10 (sleeve S10) and the female threaded hole H11 (sleeve S11). The sleeves S10 and S11 have a hollow cylindrical shape with an eccentric hollow portion (in which the wedge 140 and the existing PC steel rod B are contained). Due to the eccentricity, the thicker side (the side where the portion B10 and the portion B12 are located) has a slit portion into which the existing PC steel rod B can be inserted, and the opposing wall surfaces in the slit portion are connected using a connecting member.

When the connecting member is a cap bolt T10, as in the sleeve S10 shown in FIG. 9(A), it has a female threaded hole H12 on at least one of the opposing wall surfaces (here, one of the wall surfaces) in the slit portion (here, the wall surface on the part B12 side) and a hole H10 on the other wall surface (here, the wall surface on the part B10 side). The male thread of the cap bolt T10 passed through the hole H10 (not a threaded hole but a through hole) is screwed into the female threaded hole H12, connecting the opposing wall surfaces, thereby regulating the spacing of the slit portion as viewed from a vertical plane and functioning as a sleeve that can be combined with the wedge W.

In contrast, when the connecting member is a fully threaded bolt T20, as in the sleeve S11 shown in FIG. 9(B), a female threaded hole H12 is provided in at least one (here, both) of the opposing wall surfaces in the slit portion (here, the wall surface on the part B12 side) and a female threaded hole H11 is provided in the other wall surface (here, the wall surface on the part B10 side). The male thread of the fully threaded bolt T20 threadedly inserted into the female threaded hole H11 is threaded into the female threaded hole H12, connecting the opposing wall surfaces, thereby regulating the spacing of the slit portion as viewed from a vertical plane and functioning as a sleeve that can be combined with the wedge W. In the sleeve S11 shown in Figure 9 (B), not only is a female threaded hole H12 provided on the part B12 side, but a female threaded hole H11 is also provided on the part B10 side, and a fully threaded bolt T20 is used as the connecting member. Therefore, compared to the sleeve S10 shown in Figure 9 (A), in which a hole H10 rather than a female threaded hole is provided on the part B10 side, and a cap bolt T10 is used as the connecting member, excessive tightening by the connecting member can be prevented.

Next, compared to the sleeve S10 shown in FIG. 9(A) and the sleeve S11 shown in FIG. 9(B), the sleeve S20 shown in FIG. 9(C) has a hollow prism shape with an eccentric hollow portion (in which the wedge 140 and the existing PC steel bar B are contained). That is, the sleeve S10 shown in FIG. 9(A) and the sleeve S11 shown in FIG. 9(B) have a hollow cylindrical shape, while the sleeve S20 shown in FIG. 9(C) has a hollow prism shape. And, the sleeve S20 is the same as the sleeve S10 and the sleeve S11 in that the sleeve S20 has a slit portion into which the existing PC steel bar B can be inserted on the thicker side (the side where the parts B10 and B12 are located) due to the eccentricity, and the opposing wall surfaces of the slit portion are connected by a connecting member, so that the spacing of the slit portion as viewed from a vertical plane is regulated and the sleeve S20 functions as a sleeve that can be combined with the wedge W.

More specifically, in the sleeve S20, as in the sleeve S10 shown in Fig. 9(A), the male thread of the cap bolt T10 passed through the hole H10 (not a screw hole but a through hole) is screwed into the female threaded hole H12, and the opposing wall surfaces are connected to each other, so that the spacing of the slits as viewed from a vertical plane is regulated and the sleeve functions as a sleeve to be combined with the wedge W. As described above, the sleeve S20 shown in Fig. 9(C) uses the cap bolt T10 as the connecting member, but the fully threaded bolt T20 may be used as the connecting member. In this case, as in the sleeve S11 shown in Fig. 9(B), in the sleeve S20, the male thread of the fully threaded bolt T20 passed through the female threaded hole H11 is screwed into the female threaded hole H12, and the opposing wall surfaces are connected to each other, so that the spacing of the slits as viewed from a vertical plane is regulated and the sleeve functions as a sleeve to be combined with the wedge W.

As shown in FIG. 9, the connecting member includes a female threaded hole provided in at least one of the opposing wall surfaces and a male screw threaded through a hole provided in the other wall surface, and functions as a sleeve by restricting the spacing of the slits as viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B when the male screw is screwed into the female threaded hole to connect the wall surfaces. In this case, the rigidity of the connecting member is changed by changing the diameter of the male screw threaded into the female threaded hole when the spacing of the slits as viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B is restricted, and therefore the characteristic is that the cushioning capacity can be adjusted when the PC steel bar B breaks.

The protrusion prevention device 30 having such a structure is attached to the existing PC steel rod B at the first position P(1), second position P(2) or third position P(3) shown in Figure 2 as follows. Here, the procedure for attaching the protrusion prevention device 30 to the existing PC steel rod B at the first position P(1) in Figure 2 (because only the taper direction is different) will be described. Below, the case of using the protrusion prevention device 30 shown in Figure 9 (A) will be described.

Although not shown, two or more divided wedge pieces (here, it is divided into three, so that there are three wedge pieces 142, 144 and 146) are attached to the exposed existing PC steel bar B as a wedge attachment step so that the narrowing direction of the taper 140T of the wedge 140 is toward the surface (here, the upper deck 14).
In the sleeve mounting step, a sleeve S10 having a slit portion is mounted on the exposed existing PC steel bar B so that the narrowing direction of the taper 100T of the sleeve 100 is the direction toward the surface (here, the upper deck 14). More specifically, the existing PC steel bar B is inserted through the slit portion of the sleeve S10 to mount it.

Next, the male thread of the cap bolt T10 is passed through a hole H10 (not a threaded hole but a through hole) provided in a portion constituting one of the opposing wall surfaces of the slit portion of the sleeve S10, and is screwed into the female threaded hole H12, connecting the opposing wall surfaces, thereby regulating the spacing of the slit portion as viewed from a vertical plane, and allowing the sleeve to function as a sleeve that can be combined with the wedge W (sleeve functioning step). In this way, in the sleeve S10 with a slit portion, by connecting the opposing wall surfaces of the slit portion, the spacing of the slit portion as viewed from a vertical plane is regulated, and the sleeve can function as a sleeve (here, sleeve 100) that can be combined with the wedge W.

Finally, in an insertion step, two or more divided wedge pieces (in this case, three wedge pieces 142, 144 and 146, as the wedge is divided into three) attached to the exposed existing PC steel bar B are inserted into the sleeve 100, which has been integrated and can function as a sleeve to be combined with the wedge 140, by aligning the direction of the taper 140T of the wedge 140 with the direction of the taper 100T of the sleeve 100.
In this way, the protrusion prevention device 30 is attached to the existing PC steel rod B at the first position P(1) in Fig. 2. The work of attaching such a protrusion prevention device 30 to the existing PC steel rod B can be performed while the prestressed concrete member (the PC box girder bridge 10, as an example) is in use (without closing the bridge).

<First evaluation>
The results of testing such a protrusion prevention device 30 (device to prevent protrusion of existing PC steel bars) and a construction method using this protrusion prevention device 30 (construction method to prevent protrusion of existing PC steel bars) (whether or not it is possible to prevent the PC steel bars from protruding outside the concrete member, etc.) using a test specimen (total length 13.7 m, with a maximum breaking position of 12 m) are described with reference to Figure 10.
As shown in Figure 10, in a test specimen simulating a web 20 (prestressed concrete to which a compressive force is applied by tensioned PC steel bars), a protrusion prevention device 30 was attached to the existing PC steel bar B at a position of length L(1) from the surface of the test specimen (the right end in Figure 10 corresponding to the vicinity of the upper deck 14 described above) using the procedure described above.

Here, in FIG. 10 , "casting PC without a box" refers to the case where the protrusion prevention device 30 is attached to the existing PC steel rod B and then backfilled with concrete, and "pushing in by hand without using a jack" refers to the case where the wedge W is inserted into the sleeve S by the worker manually without using a jack in the wedge attachment step described above. Except for "pushing in by hand without using a jack," the wedge W was inserted into the sleeve S using a jack (with the press-in force on the horizontal axis of the graph) in the wedge attachment step described above.

Fracture of the existing PC steel bar B was simulated by intentionally cutting it at positions 2 m, 4 m, 8 m, and 12 m from the protrusion prevention device 30. The parameters are the pressure-insertion force (horizontal axis of the graph in Figure 10) for inserting the wedge (by jack or by hand) into the sleeve in the insertion step, and the tension force (vertical axis of the graph in Figure 10) between the protrusion prevention device 30 and the upper deck (within the range of length L(1)) after the existing PC steel bar B was cut.

(Evaluation 1)
In either case, it was confirmed that the existing PC steel rod B did not protrude outside the test specimen (concrete member) simulating the web 20, and that protrusion of the existing PC steel rod when it breaks could be appropriately prevented.
(Evaluation 2)
It was found that, as shown in FIG. 10, tension remains except for a part between the protrusion prevention tool 30 and the upper deck (within the range of length L(1)), and the tension is not zero, so that the existing PC steel bar in this part can be prevented from shifting or moving. In other words, no large tension remains. However, the location where this re-breakage occurs is not a big problem because even if the PC steel bar first breaks between the upper deck 14 and the protrusion prevention tool 30 installed at the first position P(1), the breaking energy of the PC steel bar toward the upper deck is small, and the breaking energy can be absorbed by the cover concrete, so the first length L(1), second length L(2), and third length L(3) are set to 0.25 m to 2.0 m.

(Evaluation 3)
Although some parts of Evaluation 2 include cases where almost no tension remains (for example, when the wedge W is manually inserted into the sleeve S by an operator), it was confirmed that even when the wedge W is manually inserted into the sleeve S in such a way, it is possible to appropriately prevent the existing PC steel bar from protruding when it breaks, as in Evaluation 1.
Thus, it has become clear that in the above-mentioned wedge installation step, the wedge W may be inserted into the sleeve S using a jack, or may be inserted manually by an operator without using a jack.

(Evaluation 4)
It was confirmed that protrusion of the existing PC steel bar when it breaks can be appropriately prevented regardless of whether or not the cut-out portion is repaired (backfilled). Therefore, it became clear that it is not necessary to backfill the chipped concrete after attaching this protrusion prevention device 30 to the existing PC steel bar (after the wedge attachment step).
In this way, we have provided a method for preventing the protrusion of existing PC steel bars, which can prevent the PC steel bars from protruding outside the concrete member due to the large impact force that occurs when an existing PC steel bar that is applying compressive force to a prestressed concrete member in service breaks, by performing work while the member is in service, and a device for preventing the protrusion of existing PC steel bars used therein.

<Modification>
The following describes a protrusion prevention device according to a modified embodiment of the present invention (which receives the impact force when an existing PC steel bar that applies a compressive force to an existing prestressed concrete member breaks, thereby preventing the existing PC steel bar from protruding outside the concrete member). The protrusion prevention device according to the first modified embodiment and the protrusion prevention device according to the second modified embodiment described below are intended to make it easy to check and determine the construction situation in order to set a wedge in a narrow and dark space, and more specifically, are provided with a structure for easily checking the presence of the wedge itself and checking that the wedge is held in the set position (preventing it from falling off).
In addition, the method for preventing the protrusion of existing PC steel bars other than the confirmation of the presence of the wedge itself and the confirmation of the maintenance of the set position of the wedge (prevention of falling off) is the same as the above-mentioned explanation, so it will not be repeated here. Also, in the following, the same reference numerals are used for members (e.g. wedges, etc.) having the same structure as the above-mentioned structure, and since the structure and the effect are the same, they will not be explained again here.

Furthermore, the protrusion prevention device according to the two modified examples shown below has the basic structure of the protrusion prevention device shown in FIG. 7, but as shown in FIG. 7, the sleeve is divided into an inner tube side sleeve piece with an outer thread and an outer tube side sleeve piece with an inner thread that is screwed into the outer thread of the inner tube side sleeve piece, and the sleeve piece on the inner tube side and the sleeve piece on the outer tube side are not limited to being integrated as a sleeve by screwing the inner thread and the outer thread. For example, the sleeve piece on the inner tube side and the sleeve piece on the outer tube side may be integrated as a sleeve by screwing a set screw passed through a set screw mounting hole into a set screw tap. In addition, in FIG. 11 and FIG. 12, in order to easily understand these modified examples, there are cases where some cross sections are not hatched and the existing PC steel bar B is only shown in some of the figures. Also, FIG. 11(G) shows the A-A cross section of FIG. 11(F), and FIG. 12(G) shows the A-A cross section of FIG. 12(F).

<<First Modification>>
As shown in Figure 11, the protrusion prevention device of this modified example is a pressure plate type, and the presence of the wedge itself can be confirmed by providing a protrusion at the rear end of the wedge that protrudes from the rear end of the sleeve to make it visible, and the wedge is maintained in its set position (to prevent it from falling off) by providing a pressure plate that can be connected to the sleeve with bolts, and pressing this pressure plate to a specified position with bolts.

More specifically, as shown in FIG. 11(E) and FIG. 11(A) showing the A-A cross section of FIG. 11(E), the pressure plate 300 is a flat plate, for example made of metal, with a notch 324 into which the existing PC steel bar B can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar B, and has a bolt hole 302 for connecting the pressure plate 300 to the sleeve 2100 described below with a bolt 310 (more specifically, connecting the bolt 310 by screwing together the female threaded hole 2222 provided in the sleeve piece 2220 on the outer tube side).

As shown in FIG. 11B, the wedge 340 is the three-piece wedge 140 described above, and is provided with a protrusion 342 at the rear end of the wedge 340 that protrudes from the rear end of the sleeve 2100 .
As shown in Fig. 11(C), the sleeve piece 2220 on the outer cylinder side is provided with a female threaded hole 2222 having a female thread for screwing with the bolt 310 in the sleeve piece 220 on the outer cylinder side described above. As shown in Fig. 11(D), the sleeve piece 210 on the inner cylinder side is the same as the sleeve piece 210 on the inner cylinder side described above, and is therefore given the same reference numeral. The sleeve piece 2220 on the outer cylinder side shown in Fig. 11(C) and the sleeve piece 210 on the inner cylinder side shown in Fig. 11(D) constitute the sleeve 2100 in the protrusion prevention device according to this modified example.

In the protrusion prevention device of this modified example having such a structure, the method of confirming the presence of the wedge itself and the method of confirming that the wedge is maintained in its set position (preventing it from falling off) will be described below with reference to Figures 11 (E) to 11 (G).
When everything other than the pressure plate 300 and the bolt 310 shown in Figure 11 (A) is assembled to the existing PC steel bar B as shown in Figure 11 (F), the pressure plate 300 is set in the direction of the black arrow shown in Figure 11 (E) so that the positions of the bolt hole 302 and the female thread hole 2222 match up with the positions of the protrusion prevention device to which everything other than the pressure plate 300 and the bolt 310 has been assembled to the existing PC steel bar B.

The bolt 310 is passed through the bolt hole 302 of the pressing plate 300, and the bolt 310 is screwed into the female threaded hole 2222 (here, fully at two places, top and bottom). During this work process, the presence of the wedge 340 itself can be easily confirmed by visually checking the protrusion 342 protruding from the rear end of the sleeve 2100 at the rear end of the wedge 340. In addition, since the pressing plate 300 can be securely connected by screwing with the sleeve 2100 and the bolt 310, the pressing plate 300 can be pressed down to a specified position (a position where the bolt 310 is fully screwed into the female threaded hole 2222) by the bolt 310, and the set position can be easily secured and the bolt 310 can be prevented from falling off.

<<Second Modification>>
As shown in Figure 12, the protrusion prevention device of this modified example is a wire clip type, and the presence of the wedge itself is confirmed by visually checking that the wire clip is in a predetermined position because the position of the wire clip would not be determined without the wedge being present, and the set position of the wedge is maintained (prevented from falling off) by restraining the end of the wedge with the wire clip and fixing the end of the wire clip to the sleeve to determine the positional relationship between the wedge and the sleeve.

12(A), the wire clip 400 is a metal wire with a predetermined shape that is symmetrical in the vertical direction of the paper of FIG. 12(A). The wire clip 400 is made up of an insertion piece 402 that is inserted into an insertion hole 2212 provided on the end face of the sleeve 2200 (more specifically, the sleeve piece 2210 on the inner tube side) described later in the direction in which the taper of the sleeve narrows, an end face piece 404 that is bent at a substantially right angle from the insertion piece 402 (in the plan view shown in FIG. 12(A)) and positioned on the end face of the sleeve 2200 in the direction in which the taper narrows, and an end face piece 404 that is bent at a substantially right angle from the end face piece 404 (in the plan view shown in FIG. 12(A)) and positioned on the outer peripheral surface of the sleeve 2200. (More specifically, the outer circumferential surface of the sleeve piece 220 on the outer tube side), a restraining end surface piece 408 that is bent at a right angle from the outer circumferential surface piece 406 (in the plan view shown in FIG. 12(A)) and is positioned on the end surface of the sleeve 2200 in the direction in which the taper widens, and an arc-shaped restraining arc piece 410 (as viewed from the direction shown in FIG. 12(F)) that is continuous from the restraining end surface piece 408 and is fitted into a restraining groove 148 provided on the end surface of the wedge 140 in the direction in which the taper widens.

The characteristic structure of this wire clip 400 is that it includes an insertion piece 402 that is inserted into an insertion hole 2212 provided on the end face of the sleeve 2200 in the direction in which the taper narrows, and an arc-shaped restraining arc piece 410 that is inserted into the restraining groove 148 of the wedge 140. Note that the dimension L in Fig. 12(A) corresponds to the length of the existing PC steel bar B in the sleeve 2200 in the longitudinal direction.
As shown in Fig. 12B, the wedge 140 is the same as the three-piece wedge 140 described above, and is therefore denoted by the same reference numeral. Note that in Fig. 4B, the reference numeral for the restraining groove 148 is not attached to the wedge 140.

As shown in Fig. 12(C), the sleeve piece 2210 on the inner tube side is provided with a fitting hole 2212 into which the fitting piece 402 of the wire clip 400 is fitted in the sleeve piece 210 on the inner tube side described above. As shown in Fig. 12(C), the sleeve piece 220 on the outer tube side is the same as the sleeve piece 220 on the outer tube side described above, and is therefore given the same reference numeral. The sleeve piece 220 on the outer tube side shown in Fig. 12(C) and the sleeve piece 2210 on the inner tube side shown in Fig. 12(D) constitute the sleeve 2200 in the protrusion prevention device according to this modification.
In the protrusion prevention device of this modified example having such a structure, the method of confirming the presence of the wedge itself and the method of confirming that the wedge is maintained in its set position (preventing it from falling off) will be described below with reference to Figures 12 (F) to 12 (G).

When the wire clip 400 shown in FIG. 12(A) is assembled to the existing PC steel bar B, as shown in FIG. 12(E) and FIG. 12(G), the wire clip 400 is set by fitting the insertion piece 402 of the wire clip 400 into the fitting hole 2212 provided on the end face of the sleeve 2200 in the direction in which the taper narrows, and fitting the restraining arc piece 410 of the wire clip 400 into the restraining groove 148 of the wedge 140. In this work process, the presence of the wedge 140 itself can be easily confirmed by visually confirming that the wire clip 400 is present in a predetermined position. In addition, the wire clip 400 restrains the restraining groove 148 at the end of the wedge 140 and fixes the end of the wire clip 400 (insertion piece 402) to the sleeve (fitting hole 2212), thereby determining the positional relationship between the wedge and the sleeve, and thus ensuring the set position and preventing it from falling off can be easily achieved.

<Second evaluation>
The evaluation of such a protrusion prevention device 30 (device to prevent protrusion of existing PC steel bars) and a construction method using this protrusion prevention device 30 (construction method to prevent protrusion of existing PC steel bars) will be described with reference to Figure 13, along with the results of testing using test specimens along with reference weights (including wedges).
Note that the prior art is an intermediate fixing device described in JP 2018-017029 A that combines a sleeve with a wedge and is fastened with four bolts, and is used as the protrusion prevention device 30. Example 2 is the protrusion prevention device 30 shown in Figure 9(A), Example 3 is the protrusion prevention device 30 shown in Figure 9(B), Example 4 is the protrusion prevention device 30 shown in Figure 9(C), and Example 5 is the protrusion prevention device 30 shown in Figures 4 to 6.

As shown in Figure 13 (A), compared to the prior art (two-piece sleeve, four fastening bolts, reference weight 8.8 kg), Example 2 (no split sleeve, two fastening bolts, reference weight 6.2 kg), Example 3 (no split sleeve, two fastening bolts, reference weight 6.1 kg), Example 4 (no split sleeve, two fastening bolts, reference weight 6.8 kg), and Example 5 (two-piece sleeve, two fastening bolts, reference weight 8.0 kg) showed a reduction in the number of parts, weight, and man-hours required for fastening, improving workability.

Next, the results of the performance verification test (static tensile test) are shown in FIG.
The test outline is as follows: a 32 mm PC steel bar (B type No. 2) (as an example of PC steel material) is placed in a horizontal tensile testing machine, and a tensile test is performed with one end fixed with a fixing nut commonly used for PC steel bars and the other end fixed with the protrusion prevention device of the present invention. The maximum load during the test is recorded, and the fixing efficiency, which indicates the ratio of the maximum load to the standard maximum tensile load (949 kN) of the PC steel bar, is calculated.

The results of such tests are shown in Figure 13 (B). In Examples 2 to 4, the anchoring efficiency was 100% or more, and the breakage position was the fixing nut and not the position of the protrusion prevention device of the present invention, so sufficient performance as a protrusion prevention device (anchoring device when an existing PC steel bar breaks) was confirmed. For Example 3, similar performance can be expected by using the same shape and bolt diameter as Example 2. Also, for Example 5, the anchoring efficiency (which leads to protrusion prevention efficiency when an existing PC steel bar breaks) is smaller than the other examples, but this is because the maximum load is determined by the destruction of the shear key K, and it is expected that the anchoring efficiency can be increased by reviewing the cross-sectional shape of the shear key K, etc.

Next, the performance verification test results (impact test) were carried out using the test piece shown in FIG. 13(C), and the results are shown in FIG. 13(D).
As an outline of the test, as shown in Fig. 13(C), a 26 mm PC steel bar (B type No. 1) and a 32 mm PC steel bar (B type No. 2) are connected and placed in a horizontal tensile testing machine, and an existing PC steel bar protrusion prevention device (protrusion prevention device 30) is placed on the 32 mm PC steel bar via a dedicated stand. The tensile test is started in this state, and when the load is 500 kN, a wedge is pushed in with a force of 60 kN using a mini jack, and then the tensile test is resumed to break the 26 mm PC steel bar (standard maximum tensile load of 574 kN or more).

The test results are shown in FIG.
As shown in Fig. 13(D), in comparison with the prior art, in all of the examples 2 to 5 which are the protrusion prevention devices 30 according to the embodiment of the present invention, the residual tension is kept low, and it can be seen that the protrusion of the existing PC steel bar when it breaks can be effectively prevented. More specifically, when the protrusion energy of the PC steel bar is 1.57 kNm or less, the residual tension/breaking load is: Example 2 = 20.9%, Example 3 = 24.3%, Example 4 = 24.2%, Example 5 = 2.02%, and the residual tension/breaking load is not only less than 100%, but is preferably kept low to less than half (50%), and more preferably to less than 25%, so that the protrusion of the existing PC steel bar when it breaks can be effectively and reliably prevented.

<Fracture and protrusion experiments using test specimens simulating decks and webs>
The following describes the results of fracture and protrusion experiments conducted on test specimens simulating a deck and web to demonstrate the prevention of PC steel bar protrusion by the protrusion prevention device 30 according to an embodiment of the present invention, and to demonstrate the prevention of protrusion on the upper deck side or the lower deck side, which are sections where the protrusion prevention device 30 cannot be inserted. Note that in the following, the protrusion prevention device may be referred to as a buffer fixing device.

<< Overview of Breaking and Ejection Experiments >>
In past studies, when the PC steel rod is broken in the section from the buffer anchor to the lower deck, if tension remains between the upper deck and the buffer anchor, it is considered to pass the test. However, since the test did not assume the case where the PC steel rod is broken in the section from the buffer anchor to the upper deck or the section from the buffer anchor to the lower deck, it was decided to examine how the upper deck or the lower deck would resist the protrusion of the PC steel rod in such a case. Specifically, the properties of the upper deck or the lower deck when the A section or the B section shown in Figure 2 breaks are understood. Furthermore, in order to confirm how the situation that was judged to be pass when the PC steel rod is broken in the past, the destruction state of the upper deck when the C section shown in Figure 2 breaks is evaluated.

Figure 14 shows an overview of the entire test equipment. The test specimen consisted of an upper or lower deck slab and a web. PC steel bars were placed within the web, and a cutting hole was provided so that the PC steel bars could be cut at the expected locations by introducing a specified tension. Furthermore, as a situation in which the grout was insufficiently filled was assumed, it was decided not to fill the grout. The upper or lower deck slab and the web were manufactured separately, and a structure was adopted in which they were connected by PC steel bars.

The detailed outline of the test specimen is shown below. First, the outline of the test specimen at the upper deck level is shown in Figure 15. Since the upper deck had pavement laid, the upper deck with pavement was prepared. The upper deck was 500 mm thick, and pavement was constructed on top of it with FB13 35 mm thick as the base layer and high-performance I-type 40 mm thick as the surface layer. Fixing devices for PC steel bars were installed in the upper deck, and the post-cast concrete was reproduced by filling it in. The post-cast concrete used was ordinary concrete with a strength of about 46 N/ ^mm2 at the time of cutting. Regarding the cover of the PC steel bars, the PC steel bars were positioned up to the top of the upper deck to be evaluated on the safe side, and the cover was set to 0 mm. The tension introduced into the PC steel bars differs depending on the environmental conditions. Therefore, in this test, the PC steel bar fracture time was assumed to be 10 years after construction, the outside air temperature was 6°C (Hokkaido), the web thickness was 500mm, and the steel bar spacing was 1000mm. The reduction in prestress was calculated from the specifications for road bridges, and the tension introduced to the PC steel bar was set to 583kN (upper deck side). The fixing device is generally used as a fixing system for shear reinforcement steel bars, and the anchor glock is generally used as the fixing device, so it was adopted. Regarding the cutting position of the PC steel bar, in the experiment assuming the upper deck, the cutting was performed at a position where the distance from the bearing plate to the cutting position was 1000mm or 2000mm. The cutting method was cutting with a disk sander. The fracture energy was 1.05kN・m at 1000mm and 2.10kN・m at 2000mm.

Next, the outline of the test specimen at the lower deck level is shown in Figure 16. In the case of the lower deck, the anchoring part of the PC steel bar is a dead anchor type, so the anchoring body was embedded in this test as well. The thickness of the lower deck was 500 mm. The concrete strength of the lower deck was 46 N/ ^mm2 , and the cover of the PC steel bar was 50 mm, referring to the actual construction. The tension introduced to the PC steel bar was 583 kN, the same as the upper deck level. The anchoring tool was also the same as the upper deck level. Regarding the cutting position of the PC steel bar, in the experiment assuming the lower deck, the cutting was performed at a position where the distance from the bearing plate to the cutting position was 1000 mm. In addition, regarding the installation direction of the lower deck, since it is originally the lower deck, it should be downward compared to the cutting position, but this time, it was installed and cut so that it was upward relative to the cutting position for the convenience of the experiment. The breaking energy is 1.05 kN・m.

Next, an outline of the test specimen conducted to confirm the fracture mode of the upper deck through the buffer anchor in case of fracture in section C is shown in Figure 17 (buffer anchor level). The thickness of the upper deck, pavement conditions, installation conditions of the PC steel bar, tension, post-cast concrete conditions, etc. were the same as those of the upper deck level. In this level, the PC steel bar was cut on the lower deck side of the buffer anchor installed on the upper deck side. Specifically, the buffer anchor was installed at a position 1000 mm from the anchor, and post-filling of the box cutout part was not performed. The cutting position was set at a position 8000 mm from the anchor. The buffer anchor tried this time was a prototype anchor made in a past study. In addition, the gap generated by installing the buffer anchor in the box cutout was filled with steel plates to prevent the sleeve and wedge from falling off. The fracture energy was 8.38 kN・m.

<<Protrusion confirmation experiment: results>>
・Results for paved road - 1m level (Section A)
The condition after the test for this level is explained for the pavement-1m section. The mesh is shown at 200mm intervals, but even when the PC steel bar was cut at the 1m position, no protrusion of the PC steel bar was observed in the specimen with pavement. In addition, the maximum residual displacement of the pavement was 3mm, and the range was about 10cm (Figure 18). After the test, the pavement was pulled out and the condition of the post-cast section was checked, and it was found that the post-cast section had protruded slightly.
・Results for paved road - 2m level (Section A)
The condition after the test for this level is explained for the pavement-2m section. The mesh is shown at 200mm intervals, but even when the PC steel bar was cut at the 2m position, no protrusion of the PC steel bar was observed in the specimen with pavement. In addition, the maximum residual displacement of the pavement was 6mm, and the range was about 15cm (Figure 19). After the test, the pavement was pulled out and the condition of the post-cast section was checked, and it was found that the post-cast section had protruded slightly.

・Results for unpaved road (section B)
Figure 20 shows the condition after the test for the unpaved level. The mesh is shown at 100 mm intervals, but even when the PC steel bar was cut 1 m from the lower deck, the PC steel bar of this specimen with a cover of 50 mm did not protrude. When the deformation was confirmed, cracks were confirmed at the top of the concrete deck, which were radially generated from the PC steel position. The crack width was 0.05 mm or less, and it was a fine crack. In addition, no residual displacement of the concrete deck or lifting or peeling of the concrete was confirmed.
・Buffer anchorage - 8m level results (Section C)
The following explains the condition after the test for this level of shock-absorbing anchorage -8m. The mesh is shown at 200mm intervals, but even when the PC steel bar was cut 8m from the upper deck, the PC steel bar did not protrude in this test specimen that had shock-absorbing anchorage and pavement. In addition, the residual displacement of the pavement was a maximum of 7mm, and the range was about 15cm (Figure 21). After the test, the pavement was pulled out and the condition of the post-cast portion was checked, and it was found that the post-cast portion had come out slightly.

・Observation of the box removal point In order to understand the behavior of the shock absorber when the PC steel bar is cut, the box removal point was observed. Before the PC steel bar breaks, the sleeve and wedge of the shock absorber are in contact. Next, after the cut, a gap appears between the wedge and the support plate that was installed to fill the gap. When this was confirmed using a video, it was found that the wedge was pushed into the sleeve when the PC steel bar broke, and then the wedge moved in the same way as the PC steel bar stretched due to its reaction, and was pushed into the sleeve again several times, and finally the wedge was pushed into the sleeve. Past studies have suggested that the above phenomenon is less likely to occur when the inside of the box is post-struck because the residual tension is large, but it is presumed that the shock absorber absorbs the energy when the PC steel bar breaks by the wedge and sleeve.

Summary of the cutting test: In a fracture test of a specimen simulating the case where the PC steel bar broke in section A (between the buffer anchor and the upper deck), the PC steel bar did not protrude whether the distance from the upper deck was 1m or 2m. In addition, the deformation of the pavement laid on top of the upper deck was only about 6mm of residual displacement, and the degree of damage was judged to be minor. Therefore, if the buffer anchor is installed within 2m from the top of the upper deck, it can be judged that even if the PC steel bar breaks in that section, the PC steel bar will not protrude if the pavement conditions are the same.

A fracture test of a specimen simulating the case where the PC steel rod broke in section B (between the buffer anchor and the lower deck) showed that the PC steel rod did not protrude when the distance from the lower deck was 1m or less. In addition, the lower deck only showed radial cracks, and no floating or spalling of concrete was observed, so the damage was judged to be minor. Therefore, if the buffer anchor is installed within 1m from the bottom edge of the lower deck, it can be judged that even if the PC steel rod breaks in that section, the PC steel rod will not protrude if the cover conditions and reinforcement conditions are the same.

A fracture experiment on a specimen simulating the case where a PC steel bar breaks in section C showed that if the distance from the upper deck to the break point was 8m and a buffer anchor was provided between them, the PC steel bar would not protrude. The deformation of the pavement laid on top of the upper deck had a residual displacement of about 7mm, and the damage level was judged to be minor. Furthermore, in this experiment, the box-out section where the buffer anchor was installed was not post-cast. Therefore, it is presumed that the buffer function would be further improved if post-casting was performed. Furthermore, if two buffer anchors are installed on the upper deck and lower deck, it can be determined that the PC steel bar will not protrude if the distance between the buffer anchors is within 7m.

For reference, the breaking energy during each test is shown in FIG.
It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

For example, the following changes are included:
- The device to prevent the existing PC steel rod from protruding (protruding prevention device 30) is composed of a wedge that grips the existing PC steel rod B and a sleeve that stores the wedge, and it is preferable that the wedge and sleeve are made of metal or resin.
- The wedge and sleeve may have any structure as long as they can be attached to the existing PC steel bar, and the structure described above is merely one example.
The wedge may be divided into two or more parts, and the sleeve may be a half-part that can be fastened with a bolt, or may have a slit (cutout) through which the PC steel rod can pass, and its shape may be cylindrical, hollow cylindrical, solid cylindrical, rectangular prism, or polygonal prism.

The sleeve may have a taper in one direction (protrusion prevention device 30) or in two opposing directions (protrusion prevention device 32) relative to the longitudinal direction (material axis) of the PC steel bar.
The taper angle of the sleeve and wedge is arbitrary, but is preferably about 5 to 15 degrees.
- The longitudinal length of the PC steel rods of the sleeve and wedge is arbitrary, but a length of approximately 20 mm to 200 mm is preferable.
The material used for the sleeve and wedge may be metal, resin, or synthetic fiber.

The present invention is preferable as a measure to prevent the protrusion of PC steel bars when existing PC steel bars that apply compressive force to prestressed concrete members break, and is particularly preferable in that it can prevent the PC steel bars from protruding outside the concrete member due to the large impact force that occurs when existing PC steel bars break.

10 PC box girder bridge 100 Sleeve 110, 120 Sleeve piece 140 Wedge 142, 144, 146 Wedge piece 200 Sleeve 210, 220 Sleeve piece 240 Wedge 242, 244 Wedge piece S Sleeve W Wedge B Existing PC steel bar

Claims (10)

A construction method for preventing the existing PC steel rod from protruding outside the concrete member by receiving an impact force when the existing PC steel rod, which applies a compressive force to the existing prestressed concrete member, breaks, using an anti-protrusion device including a wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel rod, and a sleeve having a taper that can be combined with the wedge and a structure that can be attached to the existing PC steel rod, the method comprising:
An exposure step of exposing the existing PC steel rod by chipping off the concrete at a position of 0.25 m to 2.0 m along the existing PC steel rod from the surface of the concrete member where the existing PC steel rod is expected to protrude,
A wedge mounting step of mounting two or more divided wedge pieces to the exposed existing PC steel bar so that the taper of the wedge narrows in the direction toward the surface;
A sleeve mounting step of mounting a sleeve having a structure that can be mounted on the existing PC steel bar to the exposed existing PC steel bar so that the taper of the sleeve narrows in a direction toward the surface;
a sleeve functionalization step of making the sleeve function as a sleeve that can be combined with the wedge;
and an insertion step of inserting two or more wedge pieces attached to the exposed existing PC steel bar in the divided state into the sleeve functioning as a sleeve by aligning the taper direction of the wedge with the taper direction of the sleeve. When the length L along the existing PC steel rod, from the surface of the concrete member from which the existing PC steel rod is predicted to protrude to another surface of the concrete member from which the existing PC steel rod is predicted to protrude, exceeds 2.5 m to 3.5 m,
The exposing step includes a step of chipping off two portions of concrete at a first position 0.25 m to 2.0 m from the surface and a second position 0.25 m to 2.0 m from the other surface to expose the existing PC steel rod at the two positions;
The first position and the second position are in the order of the surface, the first position, the second position, and the other surface,
The wedge mounting step includes a step of mounting two or more divided wedge pieces to the exposed existing PC steel bar using one wedge for each chipping location such that the taper of the wedge narrows in a direction toward the closer surface,
The sleeve attachment step includes a step of attaching a sleeve having a structure that can be attached to the existing PC steel bar to the exposed existing PC steel bar, using one sleeve for each chipping location, so that the taper of the sleeve narrows in the direction toward the closer surface. A method for preventing protrusion of an existing PC steel bar as described in claim 1. The length along the existing PC steel rod, from the surface of the concrete member from which the existing PC steel rod is predicted to protrude to the other surface of the concrete member from which the existing PC steel rod is predicted to protrude, is not more than 2.5 m to 3.5 m.
The exposing step includes a step of chipping off one portion of concrete at a position 0.25 m to 2.0 m from either the surface or the other surface to expose the existing PC steel bar at the one portion,
The wedge mounting step includes a step of mounting two or more divided wedge pieces to the exposed existing PC steel bar using two wedges for one chipping location such that the tapers of the two wedges narrow in a direction facing each other,
The sleeve attachment step includes a step of attaching a sleeve having a structure that can be attached to the existing PC steel rod to the exposed existing PC steel rod using two sleeves for one chipping location so that the taper directions of the two sleeves narrowing are facing each other, the method for preventing protrusion of existing PC steel rods as described in claim 1. The method for preventing protrusion of existing PC steel bars according to any one of claims 1 to 3, wherein the insertion step includes a step of manually inserting the wedge into the sleeve by a worker without using a jack. A protrusion prevention device used in the existing PC steel bar protrusion prevention method according to any one of claims 1 to 4,
A wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar;
a sleeve divided into an inner sleeve piece having a taper that is combined with the wedge and an outer sleeve piece provided on the outside of the inner sleeve piece;
With respect to the sleeve piece on the inner tube side and the sleeve piece on the outer tube side, at least the inner tube side sleeve piece is provided with a notch portion into which the existing PC steel rod can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel rod,
The sleeve piece on the inner cylinder side and the sleeve piece on the outer cylinder side are joined together to form an integrated sleeve that functions as a sleeve to be combined with the wedge ,
This device prevents the protrusion of existing PC steel bars, characterized in that a key is provided across a key groove provided on the outer peripheral surface of the sleeve piece on the inner tube side and a key groove provided on the inner peripheral surface of the sleeve piece on the outer tube side, and the sleeve piece on the inner tube side and the sleeve piece on the outer tube side are joined to form an integrated sleeve . A protrusion prevention device used in the existing PC steel bar protrusion prevention method according to any one of claims 1 to 4,
A wedge divided into two or more wedge pieces when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel bar;
A sleeve having a taper that can be combined with the wedge and a slit portion into which the existing PC steel rod can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel rod,
This device prevents the protrusion of existing PC steel bars, characterized in that opposing wall surfaces in the slit section are connected in an open state without blocking the slit section using a connecting member, and when the slit section is viewed from the vertical plane , the wall surfaces within the slit section are connected by the connecting member and the connecting member is present within the slit section where the wall surfaces face each other, regulating the spacing of the slit section with respect to the existing PC steel bar, and the two opposing wall surfaces and the connecting member are integrated to function as a sleeve that can be combined with the wedge. The connecting member includes a female screw hole provided in at least one of the opposing wall surfaces and a male screw passing through a hole provided in the other wall surface,
The device for preventing protrusion of an existing PC steel bar as described in claim 6 , characterized in that the spacing of the slit portion as viewed from the vertical plane is regulated by screwing the male screw into the female threaded hole to connect the wall surfaces. The connecting member includes a female screw hole provided in at least one of the opposing wall surfaces and a male screw passing through a hole provided in the other wall surface,
The male screw is screwed into the female screw hole to connect the wall surfaces, thereby restricting the spacing of the slit portions as viewed from the vertical plane,
The device for preventing protrusion of an existing PC steel rod as described in claim 6, characterized in that by changing the diameter of the male screw, the rigidity of the connecting member is changed when the spacing of the slit portion as viewed from the vertical plane is regulated, thereby adjusting the cushioning capacity when the PC steel rod breaks. The sleeve further includes a flat plate joined to the sleeve at an end surface in the direction in which the taper widens and perpendicular to the longitudinal direction of the existing PC steel rod,
The plate has a notch portion into which the existing PC steel rod can be inserted when viewed from a plane perpendicular to the longitudinal direction of the existing PC steel rod, and into which a wedge protrusion provided at an end of the wedge in a direction in which the taper widens can protrude,
An existing PC steel bar protrusion prevention device as described in any of claims 5 to 8, characterized in that the plate is joined to the end face of the sleeve, thereby positioning the wedge at a predetermined position on the sleeve and the wedge protrusion portion protruding from the cutout portion of the plate. Further comprising a three-dimensional shaped wire clip;
The wire clip is
A straight portion in the sleeve corresponding to the longitudinal length of the existing PC steel rod;
a wedge groove provided on an outer periphery of an end of the wedge in a direction in which the taper of the wedge widens, the wedge being fitted into the wedge groove on a side of the sleeve where the taper of the wedge widens from the straight portion;
The sleeve has a hole provided on an end surface perpendicular to the longitudinal direction of the existing PC steel bar, the end surface being in the direction in which the taper of the sleeve narrows, and the sleeve hole provided on the end surface being perpendicular to the longitudinal direction of the existing PC steel bar, the end surface being in the direction in which the taper of the sleeve narrows, the end surface being perpendicular to the longitudinal direction of the existing PC steel bar, and the sleeve has a hole provided on the end surface being perpendicular to the longitudinal direction of the existing PC steel bar.
An existing PC steel bar protrusion prevention device as described in any of claims 5 to 8, characterized in that the arc portion of the wire clip is fitted into the wedge groove portion and the fitting piece of the wire clip is fitted into the sleeve hole portion, thereby positioning the wedge at a predetermined position in the sleeve and positioning the straight portion of the wire clip along the outer periphery of the sleeve.

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