JP6993067B2 - Structure to prevent peeling of structures - Google Patents

Description

The present invention relates to an exfoliation prevention structure of a structure that prevents a deteriorated surface layer portion of a concrete skeleton from exfoliating from a structure such as a tunnel or a bridge.

Conventionally, as a structure to prevent the deteriorated surface layer part of the concrete frame from peeling off from the structure such as tunnels and bridges, a mesh-like peeling prevention net is placed on the surface of the structure, and the peeling prevention net is used as a structure. A structure is known in which a strip-shaped holding plate is placed on the opposite side, an anchor bolt is inserted through the holding plate and the peeling prevention net, driven into the structure, and pressed by the holding plate to fix the peeling prevention net to the surface of the structure. There is. This structure has an advantage that the surface of the structure can be visually observed even after installation, and the state of the surface of the structure can be confirmed and inspected (Patent Document 1 (paragraph [0001], [0004]). , [0020], [0027], FIG. 3), Patent Document 2 (see paragraphs [0002], [0015], FIGS. 1 to 4)).

Japanese Unexamined Patent Publication No. 2004-293150 JP-A-2007-120231

However, in the structure in which the peeling prevention net is fixed to the surface of the structure by pressing with the strip-shaped pressing plate described above, the peeling prevention net is only pressed by the strip-shaped pressing plate, so that a load is applied to the peeling prevention net. Then, the load is concentrated on the thread of the peeling prevention net that is engaged with the anchor bolt and the stud, and there is a risk that the thread at that part will be cut. In addition, the holding plate and the peeling prevention net may be displaced at the time of installation, or may be displaced later from the installed position, and the peeling prevention net may be loosened or hung down. Such slackening or hanging of the peeling prevention net causes the peeling prevention net to be separated from the surface of the skeleton to allow peeling. It also interferes with the visual inspection of the surface of the structure.

The present invention has been proposed in view of the above problems, and prevents the thread from being locally cut due to the concentration of the local load of the peeling prevention net, further prevents the position from shifting from the installation position, and prevents the peeling prevention net. It is possible to eliminate the slack and sagging of the structure, to stably and substantially close the peeling prevention net to the surface of the structure, to prevent the peeling of a large load with high stability, and to perform a good visual inspection. It is an object of the present invention to provide an exfoliation prevention structure of a structure to be used.

The exfoliation prevention structure of the structure of the present invention is provided with a mesh-like exfoliation prevention net arranged substantially closely along the surface of the structure and the exfoliation prevention net on the opposite side of the structure. A strip for imposing the strip prevention net and an anchor member for fixing the strip to the structure are provided, and a plurality of protrusions are formed on the strip prevention net side of the strip at intervals, and the plurality of protrusions are formed. Each of the protrusions is inserted corresponding to the mesh of the peeling prevention net , and the peeling prevention net is a PVC-coated PET mesh .
According to this, the protrusion of the strip enters the mesh of the strip prevention net, so that the load applied to the strip prevention net is evenly distributed along the strip, so that the threads constituting the net can be locally cut. It can withstand a large load of peeling. Further, the positional relationship between the strip and the peeling prevention net can be fixed, and the positional deviation from the installation position of the peeling prevention net can be prevented. Therefore, it is possible to eliminate the slackening and sagging of the peeling prevention net, to make the peeling prevention net substantially close to the surface of the structure, and to stably install the net, so that it is possible to prevent the peeling of a large load with high stability. can. In addition, since the peeling prevention net can be prevented from being displaced, slackened, or hung down, and the peeling prevention net can be stably brought into close contact with the surface of the structure, it is possible to perform a good visual inspection on the surface of the structure. Will be.

Further, by using a PVC-coated PET mesh for the peeling prevention net, the rigidity of the peeling prevention net can be increased, and loosening and sagging of the peeling prevention net can be prevented more reliably. Further, the PVC coated PET mesh has a predetermined rigidity and a predetermined flexibility, and can follow along the surface of a curved structure such as the inner peripheral surface of a tunnel. Therefore, it can be used as a peeling prevention net having excellent versatility. Further, by using a PVC-coated PET mesh for the peeling prevention net, the weather resistance, water resistance, and durability of the peeling prevention net can be improved, and the durability of the peeling prevention structure can be improved. Further, the PVC-coated PET mesh can be cut to a required size in the field and used, and can be used even when the shape of the surface of the structure is complicated, and has high adaptability to the construction site.

In the exfoliation prevention structure of the structure of the present invention, an insertion hole for the anchor member is formed in the central portion in the width direction of the strip, and the regions on both sides of the central portion are spaced apart in the longitudinal direction of the strip. It is characterized in that a plurality of the protrusions are arranged in a row.
According to this, a plurality of protrusions arranged in the longitudinal direction in both side regions in the width direction of the strip are allowed to enter the mesh of the peeling prevention net, so that the load is distributed and supported on both sides of the fixed portion by the anchor member. At the same time, the positional relationship of the peeling prevention net can be fixed on both sides, and the load distribution effect and the misalignment prevention effect of the peeling prevention net can be exhibited with higher stability. In addition, a plurality of protrusions arranged in rows on both sides in the width direction of the strip are substantially brought into contact with the surface of the structure by pressing the surface of the structure, and the strip is brought into contact with the surface of the structure in the width direction. It can be installed and fixed in a state of being substantially parallel to the surface of the strip, and the stability of the installation state of the strip can be improved.

In the exfoliation prevention structure of the structure of the present invention, the anchor member is a resin injection type expansion anchor, the expansion portion of the expansion anchor is expanded, and the gap between the expansion anchors is filled with a cured resin. In this state, the expansion anchor is fixed to the structure, and the strip is urged to be pressed toward the structure by a flange portion provided near the rear end of the expansion anchor. It is characterized by being.
According to this, the resin injection type expansion anchor makes the anchor member and the strip stable at the back of the structure with high strength, that is, the sound skeleton deep part instead of the fragile surface layer part where there is a concern of peeling off. It can be fixed to, and the stability of the installation state of the peeling prevention net can be further improved. Further, even when there is a sign of deterioration on the surface layer portion of the concrete skeleton and the mechanical fixing force of the anchor is uneven, the anchor fixing force can be stably secured by resin injection. Further, by urging the strip at the flange portion near the rear end of the expansion anchor, it is not necessary to provide a nut at the rear end portion of the expansion anchor, and the risk of the nut falling can be eliminated.

According to the exfoliation prevention structure of the structure of the present invention, the exfoliation prevention net prevents the thread from being locally cut due to the concentration of the local load, and further prevents the thread from being displaced from the installation position. By eliminating slack and sagging, the peeling prevention net can be stably and substantially in close contact with the surface of the structure, and it is possible to prevent the peeling of a large load with high stability, and also perform a good visual inspection of the surface of the structure. be able to.

An explanatory perspective view showing a state in which the exfoliation prevention structure of the structure of the embodiment according to the present invention is installed on the inner wall of the tunnel. Partial front view of the exfoliation prevention structure of the structure of the embodiment. Partial cross-sectional view of the exfoliation prevention structure of the structure of embodiment. The partial vertical sectional view of the exfoliation prevention structure of the structure of an embodiment. The schematic perspective view of the state in which the exfoliation prevention net in the exfoliation prevention structure of the structure of an embodiment is arranged along the surface of a structure. A schematic perspective view of a state in which a strip is applied to a peeling prevention net in the peeling prevention structure of the structure of the embodiment and viewed from the structure side. (A) is a partial perspective view of the peeling prevention net in the peeling prevention structure of the structure of the embodiment, and (b) is a partial perspective view of the strip in the peeling prevention structure of the structure of the embodiment. (A) is a partial perspective view of the peeling prevention net of FIG. 7 (a) in a curved state, and (b) is a partial perspective view of a strip of FIG. 7 (b) in a curved state. Explanatory drawing which shows the deformation example of the attachment state of the peeling prevention net and a strip in this invention.

[Structure to prevent exfoliation of the structure of the embodiment]
The exfoliation prevention structure of the structure according to the present invention is provided for, for example, a structure such as a tunnel or a bridge, and is preferably provided for a concrete structure formed of concrete. In the example of FIG. 1, the concrete skeleton 100 of the tunnel is used as a structure, and the structure for preventing peeling of the structure of the present embodiment is installed.

In the structure for preventing exfoliation of the structure of the present embodiment, as shown in FIGS. 1 to 5, a mesh-like structure is formed along and substantially closely or closely to the surface of the inner peripheral surface of the concrete skeleton 100 of the tunnel. The peeling prevention net 1 is arranged. The peeling prevention net 1 is stretched along the surface of the concrete skeleton 100, and a plurality of peeling prevention nets 1 are arranged adjacently or close to each other, or the ends of the adjacent peeling prevention nets 1 and 1 are overlapped with each other. Depending on the arrangement, they are arranged side by side in the direction of the tunnel axis. When the exfoliation prevention net 1 is provided on the inner peripheral surface of the concrete skeleton 100 of the tunnel, it is preferable to provide it at least from the top end of the upper half of the tunnel to the side wall.

The peeling prevention net 1 can be used as long as it is formed in a mesh shape or a lattice shape and the mesh 11 is provided between the threads at regular intervals so as to prevent the surface layer portion of the concrete skeleton 100 from peeling off. For example, a net having a length of 5 to 20 mm and a width of 5 to 20 mm, preferably a net having a length of 10 to 15 mm and a width of 10 to 15 mm. The weaving method of the peeling prevention net 1 is appropriate, but for example, a leno weave or a plain weave is preferable.

Further, the peeling prevention net 1 is excellent in water resistance, durability and weather resistance, has the required tensile strength and rigidity, and has the required flexibility, and has a curved structure such as the inner peripheral surface of a tunnel. It is preferable to have a structure that can follow the surface of an object, and in this embodiment, a PET (polyethylene terephthalate) mesh is coated with PVC (polyvinyl chloride) as a peeling prevention net 1 having such a structure. I am using the one that I did.

On the opposite side of the concrete skeleton 100, an elongated plate-shaped strip 2 for imposing the peeling prevention net 1 is provided with respect to the peeling prevention net 1 arranged along the surface of the concrete skeleton 100, and the strip 2 is also a structure. It is installed so as to follow the shape of the surface of the concrete skeleton 100 which is an object (see FIGS. 1 to 8). The strip 2 in the present embodiment is excellent in water resistance, durability, and weather resistance, is thicker than the peeling prevention net 1, has higher rigidity and strength than the peeling prevention net 1, and is lower than the peeling prevention net 1 to some extent. It is made of a flexible material and shape, and has a structure that can follow the surface of curved structures such as the inner peripheral surface of a tunnel, and is GFRP (glass fiber reinforced plastic). It is highly versatile and can be applied to the surface of various structures formed of, for example, and has excellent water resistance, durability, and weather resistance, and has a curvature that follows the curved shape of the inner peripheral surface of a tunnel. It is also possible to have a configuration in which the shape is curved in the thickness direction.

A plurality of strips 2 on which the peeling prevention net 1 is placed are provided at intervals in the tunnel axial direction. The installation interval of the strips 2 is appropriate, but it is preferably 800 mm at the maximum from the viewpoint of ensuring the prevention of slackening of the peeling prevention net 1. When the exfoliation prevention net 1 is provided from the top half of the tunnel to the side wall, it is preferable that the strip 2 is also provided from the top half of the tunnel to the side wall correspondingly. The strip 2 provided from the top end of the upper half to the side wall may be composed of a plurality of strips 2 in addition to a series of strips 2 in the circumferential direction from the top half of the tunnel to the side wall. Further, the strip 2 installed around the top end and the strip 2 installed on the side wall located below the top edge are installed so as to be displaced in the tunnel axial direction. Is also possible.

The strip 2 is formed with an insertion hole 21 for an anchor member penetrating the central portion in the width direction, and a plurality of insertion holes 21 are provided at intervals in the longitudinal direction of the strip 2. A plurality of protrusions 22 are formed on both sides of the central portion of the strip 2 at intervals on the peeling prevention net 1 side, and a plurality of protrusions 22 are spaced apart in the longitudinal direction of the strip 21 in the regions on both sides. The protrusions 22 of the above are arranged in rows. In the present embodiment, protrusions 22 are formed in vertical and horizontal arrangement in each of the regions on both sides of the central portion of the strip 2, and two protrusions 22 are arranged at regular intervals in the width direction of the strip 2. The protrusions 22 are arranged in a row at regular intervals in the longitudinal direction of the strip 2.

The installation interval of the plurality of protrusions 22 is set so that each protrusion 22 corresponds to the mesh 11 of the peeling prevention net 1, and in the present embodiment, the plurality of protrusions 22 arranged vertically and horizontally are arranged in the peeling prevention net 1. In the vertical and horizontal arrangement of the above, the adjacent meshes 11 are respectively inserted correspondingly. Further, the shape and size of each protrusion 22 is such that the protrusion 22 can be smoothly inserted into the mesh 11 of the peeling prevention net 1, and the shape of the protrusion 22 in the illustrated example is substantially cylindrical. The protrusion 22 that has entered the mesh 11 of the peeling prevention net 1 is arranged so that the tip thereof substantially abuts on the inner peripheral surface of the concrete skeleton 100 that is the surface of the structure.

The strip 2 is fixed to the concrete skeleton 100 by an expansion anchor 3, which is an anchor member for fixing the strip 2 to the structure. The expansion anchor 3 in the present embodiment is a so-called anchor pin with a resin injection port, has a substantially cylindrical main body 31 having a hollow inside, and an arcuate groove 32 is formed along the outer periphery of the main body 31 near the tip. In addition, the slit 33 is cut in the longitudinal direction from the tip of the main body 31 beyond the arcuate groove 32, and the tip end side of the arcuate groove 32 is an expanded portion 34 divided by the slit 33.

In the hollow portion of the main body 31, an expanded body 35 having a substantially conical shape in which the front portion expands in diameter toward the rear and a substantially cylindrical shape in the rear portion is incorporated. The tip end side portion of the hollow portion of the main body 31 is formed with an inner diameter smaller than the maximum outer diameter of the expanding body 35 via the step portion protruding inward, and this hollow portion reaches a position where it does not reach the tip end of the main body 31. It is formed. Further, a circumferential flange portion 36 protruding outward is provided near the rear end of the main body 11, and an opening communicating with the hollow portion of the main body 31 is formed in the center of the flange portion 36. An annular sealing material 37 such as a butyl seal is externally fitted to the main body 31 on the tip end side of the flange portion 36 so as to be adjacent to the tip surface of the flange portion 36.

When installing the expansion anchor 3, a perforation 101 is formed in the concrete skeleton 100, a peeling prevention net 1 is arranged along the surface of the concrete skeleton 100, and a protrusion 22 corresponds to the mesh 11 of the peeling prevention net 1. The strip 2 is arranged so as to allow the concrete to enter. Then, the washer 4 is arranged so as to push the strip 2, the expansion anchor 3 in the non-expanded state is inserted into the insertion hole 21 of the washer 4 and the strip 2, and the washer 4 is expanded in the non-expanded state. The anchor 3 is driven in to partially break the peeling prevention net 1 to penetrate it, and the unexpanded anchor 3 in the non-expanded state is inserted into the perforation 101. As a result, the strip 2 is pressed from the opposite side of the concrete skeleton 100 by the flange portion 36 of the expansion anchor 3 via the annular sealing material 37 and the washer 4.

After that, as shown in FIGS. 3 and 4, the expanded body 35 of the expanded anchor 3 inserted into the perforation 101 is driven by inserting a driving rod through an opening communicating with the hollow portion of the main body 31, and the expanded body is inserted. The expansion portion 34 is expanded by passing the step portion of the hollow portion through the 35, the expansion portion 34 is made to bite into the hole wall, and the expansion anchor 3 is mechanically fixed to the concrete skeleton 100. By mechanical fixing of the expansion anchor 3, the strip 2 urged toward the concrete skeleton 100 side by the flange portion 36 via the annular sealing material 37 and the washer 4 is fixed so as to follow the surface of the concrete skeleton 100, and the protrusions are formed. The exfoliation prevention net 1 positioned by entering the mesh 11 of 22 is supported by a fixed strip 2 so as to be along the surface of the concrete skeleton 100 and not to be separated from the surface of the concrete skeleton 100. ..

Further, the expansion anchor 3 of the present embodiment is fixed to the concrete skeleton 100 by a resin injection type. That is, a resin such as a two-component mixed curing epoxy resin is injected into the hollow portion of the expanded anchor 3 in which the expanded portion 34 is expanded by using an injection device (not shown), and the resin is injected inside the hollow portion. By filling the perforation 101 with resin by flowing from the slit 33 into the gap between the perforation 101 and the expansion anchor 3, the gap between the hollow portion of the expansion anchor 3 and the gap between the expansion anchors 101 are predetermined. It is filled with the cured resin 5 that has been cured over time. Further, if a highly permeable resin is injected, the anchor placement site in the deteriorated concrete skeleton 100 is also modified at the same time.

According to the present embodiment, the load applied to the exfoliation prevention net 1 is distributed evenly along the strip 2 due to the entry of the exfoliation prevention net 1 of the protrusion 22 of the strip 2 into the mesh 11. There is no local cutting of the threads that make up the material, and it can withstand heavy load peeling. Further, the positional relationship between the strip 2 and the peeling prevention net 1 can be fixed, and the positional deviation of the peeling prevention net 1 from the installation position can be prevented. Therefore, it is possible to eliminate the slackening and sagging of the peeling prevention net 1 and to bring the peeling prevention net 1 substantially in close contact with the surface of the structure such as the concrete skeleton 100 so that the peeling prevention net 1 can be stably installed along the surface. Can be prevented from peeling off. In addition, since the peeling prevention net can be prevented from being displaced, slackened, or hung down, and the peeling prevention net can be stably brought into close contact with the surface of the structure, it is possible to perform a good visual inspection on the surface of the structure. Will be.

Further, by allowing a plurality of protrusions 22 arranged in the longitudinal direction in both side regions in the strip width direction to enter the mesh 11 of the peeling prevention net 1, the load is distributed and supported on both sides of the fixed portion by the expansion anchor 3. In addition, the positional relationship of the peeling prevention net 1 can be fixed on both sides, and the load distribution effect and the misalignment prevention effect of the peeling prevention net 1 can be exhibited with higher stability. Further, a plurality of protrusions 22 arranged in rows on both sides in the width direction of the strip are substantially brought into contact with the surface of the structure by pressing the surface of the structure, and the strip 2 is widened as shown in FIG. It can be installed and fixed in a state of being substantially parallel to the surface of the peeling prevention net 1 or the structure in the direction, and the stability of the installed state of the strip 2 can be improved.

Further, by using the PVC-coated PET mesh for the peeling prevention net 1, the rigidity of the peeling prevention net 1 can be increased, and loosening and sagging of the peeling prevention net 1 can be prevented more reliably. Further, the PVC coated PET mesh has a predetermined rigidity and a predetermined flexibility, and can follow along the surface of a curved structure such as the inner peripheral surface of a tunnel. Therefore, the peeling prevention net 1 having excellent versatility can be obtained. Further, the weather resistance, water resistance, and durability of the peeling prevention net 1 can be improved, and the durability of the peeling prevention structure can be improved. Further, the PVC-coated PET mesh can be cut to a required size in the field and used, and can be used even when the shape of the surface of the structure is complicated, and has high adaptability to the construction site.

In addition, the resin injection type expansion anchor 3 makes the expansion anchor 3 and the strip 2 stable with high strength and stable at the back of the structure, that is, a sound skeleton rather than a fragile surface layer where there is a risk of peeling. It can be fixed in a deep part, and the stability of the installation state of the peeling prevention net 1 can be further improved. Further, even when there is a sign of deterioration in the surface layer portion of the concrete skeleton 100 and the mechanical fixing force of the anchor is uneven, the anchor fixing force can be stably secured by resin injection. Further, by urging the strip 2 at the flange portion 36 near the rear end of the expansion anchor 3, it is not necessary to provide a nut at the rear end of the expansion anchor, and the risk of the nut falling can be eliminated. can.

[Scope of inclusion of the invention disclosed herein]
The invention disclosed in the present specification is specified by changing the partial contents thereof to other contents disclosed in the present specification to the extent applicable, in addition to the inventions and embodiments listed as inventions. Alternatively, those specified by adding other contents disclosed in the present specification to these contents, or those specified by deleting these partial contents to the extent that a partial action and effect can be obtained and making them into a higher concept. Include. The invention disclosed in the present specification also includes the following modifications and additional contents.

For example, in the exfoliation prevention structure of the structure of the present invention, a plurality of protrusions are formed at intervals on the exfoliation prevention net side of the strip, and the plurality of projections each enter corresponding to the mesh of the exfoliation prevention net. An appropriate structure is included, for example, a configuration in which protrusions are arranged in a row at regular intervals in the longitudinal direction of the strip in each of the regions on both sides of the central portion in the width direction of the strip, or a strip. It is possible to form an insertion hole for the anchor member on one side in the width direction, provide a plurality of protrusions on the other side, and attach the strip to the surface of the structure in a state of being tilted in the width direction. be. Further, the present invention is not limited to a configuration in which a plurality of adjacent protrusions on the strips enter corresponding to the adjacent mesh of the strip prevention net, for example, a plurality of adjacent protrusions on the strips are placed on one of the strip prevention nets. It is also possible to configure the structure so that it can be inserted in correspondence with multiple meshes such as.

Further, the anchor member in the present invention is not limited to the resin injection type expansion anchor 3 of the above embodiment, and includes an appropriate anchor member for fixing the strip to the structure. For example, if a sleeve driving type anchor is used to insert the bolt into the insertion hole 21 of the strip 2 and tighten the nut, the peeling prevention net 1 or the strip 2 needs to be replaced. The net 1 and the strip 2 can be replaced by simply removing the nut, and the anchor body can be reused as it is. Further, the interval between the anchor members is appropriately set between the insertion holes of the anchor members of the strip corresponding to the anchor members, and is preferably about 400 to 500 mm, for example.

Further, when the peeling prevention net in the present invention is, for example, a PET mesh formed of a leno weave coated with PVC, the frictional force at the intersection of the weft and the warp is high, so that the load is applied as a whole when a load is applied. However, the configuration of the peeling prevention net is not limited to this, and an appropriate peeling prevention net can be used within the scope of the gist of the present invention. Further, the mesh of the peeling prevention net in the present invention is not limited to the mesh of vertical and horizontal arrangement, and is appropriate, for example, a mesh of a staggered arrangement, and the protrusion of the strip is formed at a position corresponding to this mesh. It can be configured.

Further, the length and width of the peeling prevention net and the length and width of the strip in the present invention can be appropriately set within the scope of the purpose of the present invention. Further, it is preferable that the strip can be cut to a required size in the field and used like the above-mentioned GFRP, whereby even if the shape of the surface of the structure is complicated, it can be dealt with. High adaptability to the construction site can be obtained, but the material is not limited to GFRP as long as it can achieve this purpose. Further, in places where slack is likely to occur in the peeling prevention net due to a large curvature of the curved shape on the surface of the structure, the installation interval of the strip 2 in the tunnel axis direction may be adjusted, or the strip 2 may be shorter than the strip 2. It is also possible to additionally install the strips 2a, 2b, etc. of the above as auxiliary strips between the strips 2 and 2 (see FIG. 9).

The present invention can be used, for example, to prevent the peeled pieces from falling on the inner wall of a tunnel, the lower part of a bridge, or the like.

1 ... Peeling prevention net 11 ... Mesh 2, 2a, 2b ... Band plate 21 ... Insertion hole 22 ... Protrusion 3 ... Expansion anchor 31 ... Main body 32 ... Arc-shaped groove 33 ... Slit 34 ... Expansion part 35 ... Expansion body 36 ... Collar 37 ... Circular sealing material 4 ... Washer 5 ... Hardened resin 100 ... Concrete skeleton 101 ... Drilling

Claims (3)

A mesh-like anti-stripping net that is placed almost closely along the surface of the structure,
A strip provided on the opposite side of the structure with respect to the peeling prevention net, and a strip for imposing the peeling prevention net.
An anchor member for fixing the strip to the structure is provided.
A plurality of protrusions are formed at intervals on the peeling prevention net side of the strip, and the plurality of protrusions each enter the mesh of the peeling prevention net corresponding to the mesh .
A peeling prevention structure for a structure , wherein the peeling prevention net is a PVC-coated PET mesh . An insertion hole for the anchor member is formed in the central portion of the strip in the width direction.
The peeling prevention structure for a structure according to claim 1, wherein a plurality of the protrusions are arranged in a row in the regions on both sides of the central portion at intervals in the longitudinal direction of the strip. The anchor member is a resin injection type expansion anchor.
The expansion anchor is fixed to the structure in a state where the expansion portion of the expansion anchor is expanded and the gap between the expansion anchors is filled with the cured resin.
The peeling of the structure according to claim 1 or 2 , wherein the strip is urged so as to be pressed toward the structure by a flange portion provided near the rear end of the expansion anchor. Prevention structure.

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