JP4326518B2 - Pre-tension member - Google Patents

Description

  The present invention relates to a pretension member in which the tensile strength of a concrete member is increased by applying a compressive stress in advance via a tendon.

  A prestressed concrete member increases the strength of the concrete member by introducing a compressive stress in advance through a tendon material, so that the compressive stress counteracts with the tensile stress applied to the concrete member after use. The cross-sectional shape of this is to be reduced in size and weight.

  A prestressed concrete member is a so-called post-tension method in which a concrete material is placed after placing a tension material such as a PC cable and prestress is introduced into the tension material after the concrete is cured, or a tension material to which a tensile force is applied. After placing the concrete, the concrete is placed, and after the concrete is hardened, the prestress is introduced by releasing the tension material.

  However, the former post-tensioning method has a problem that it takes time and labor for installation because it requires the placement of PC cables and fixing tools, pre-stress introduction work, and grouting work during construction on site. In addition, it is necessary to secure a work space for facilities for introducing prestress, and there is a problem that a sufficient space may not be secured, for example, when it is used for a beam of a building.

  Moreover, since the latter pre-tensioning method expects the introduction of a pre-stress force to the adhesion between the tendon and the concrete, it requires an initial concrete strength expression and uses high-strength concrete. Therefore, there has been a problem that the cost becomes high.

Therefore, for example, as shown in Patent Document 1, a pretensioned prestressed concrete member (hereinafter simply referred to as “pretensioning member”) using a deformed reinforcing bar excellent in adhesion to concrete as a tension material is disclosed. Have been implemented.
Japanese Unexamined Patent Publication No. 3-93929 (page 3, FIGS. 1-5)

  However, as shown in FIGS. 5 (a) to 5 (c), the pretension member 101 using the deformed reinforcing bar 110 as the tension material has a too high adhesion force between the deformed reinforcing bar 110 and the concrete 111, and therefore, due to the tension force. Bond split fracture (crack 120) may occur at the end of the concrete member. In this case, there is a problem that the covered concrete may not be used as a structural member due to exfoliation of the covering concrete or an extremely long tension material fixing length (fixing area) for transmitting tension. It was. In addition, the pretension member also has a problem in that splitting may occur due to the external pressure when the tension force is introduced (when the tension material is released).

Here, the adhesion split fracture is caused by the force P1 that the concrete 11 around the reinforcing bar 10 deforms radially around the reinforcing bar 10 when the excessive tensile force P of the reinforcing bar is transmitted to the concrete. This refers to the occurrence of cracks along the reinforcing bars, which occurs mainly when the reinforcing bars 10 are densely packed or when the concrete covering thickness is thin (see FIGS. 3A and 3B).
The bare pressure is a force acting on the concrete due to the expansion of the tension material when the tension force is introduced (when the tension material is released). In other words, the tension material of the pretension member is reduced in diameter by introducing a tensile force, but the tensile force at both ends of the tension material becomes 0 by releasing the tensile force (releasing the tension material). The diameter first returns to the diameter. The introduction of prestress is constant at the center side of the fixing area of the pretension member, and the diameter of the tendon is thinner than both ends. In other words, the tension material expands in the fixing area of the pretension member, and the diameter gradually increases from the center toward the tip. Therefore, the expansion force (bare pressure) of the tension material is applied to the concrete in the fixing area. It is working.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to propose a pre-tension member that is unlikely to cause split fracture even when a high-strength tension material such as a deformed reinforcing bar is used. .

In order to solve the above-mentioned problems, the present invention is a pretensioning member that tensions deformed reinforcing bars and introduces prestress into concrete, and is provided with an adhesion split prevention portion by unbonding the deformed reinforcing bars at both ends. Is .

  Such a pretensioning member forms an adhesion split prevention part that is a section where the deformed reinforcing bar is unbonded at both ends where adhesive splitting is likely to occur, and reduces the load on the concrete due to the pulling force of the deforming reinforcing bar. Prevents damage to members. And since the prestress which acts via a deformed reinforcing bar acts in the center part from the position which entered the predetermined length inner side with respect to the longitudinal direction of the pretension member, it is hard to produce an adhesion split fracture. Further, the pre-tension member is prevented from being split due to the external pressure when the tension force is introduced (when the tension member is released) by the adhesion split prevention portion which is a non-stressed concrete portion provided at the end portion. In other words, the pretensioning member restrains the fixing area (section where the prestress is not completely introduced) adjacent to the center side (opposite the end of the member) of the adhesion split prevention part by the adhesion split prevention part. Prevent the occurrence of destruction.

In the present invention, at least in a portion adjacent to the center side of the adhesion split prevention portion, a force that radially spreads the concrete centering on the deformed reinforcing bar acts to cause adhesion split fracture. A spiral reinforcing bar is arranged around the deformed reinforcing bar.

  Such a pretensioning member forms an adhesion split prevention portion at both ends where adhesion split fracture is likely to occur, and restrains splitting due to the external pressure at the time of adhesive split fracture and tension force introduction (when tension material is released) from both ends. The force that spreads radially around the deformed reinforcing bar is constrained by disposing the spiral reinforcing bar around the deformed reinforcing bar at the site adjacent to the center side of the adhesion split preventing part. As a result, the prestress acting via the deformed reinforcing bar acts on the part other than the adhesion split prevention part at both ends of the pretensioning member, and this part is restrained from both ends by the adhesion splitting prevention part and is also tensioned by the spiral reinforcing bar. This makes it possible to prevent the separation of the deformed reinforcing bar, which is a material, and the concrete, thereby preventing the bond splitting failure.

Further, in the second invention, there is a possibility that adhesion splitting fracture is caused by a force that radially spreads the concrete centering on the deformed reinforcing bar at least at a portion adjacent to the center side of the adhesion splitting prevention portion. is characterized in that member thickness portion is increased.

  Such a pretensioning member forms an adhesion split prevention portion at both ends where adhesion split fracture is likely to occur, and restrains splitting due to the external pressure at the time of adhesive split fracture and tension force introduction (when tension material is released) from both ends. The splitting strength of the concrete can be increased by increasing the member thickness of the pretension member in the part adjacent to the center side of the adhesion splitting prevention part than in other parts. As a result, the deformed reinforcing bar has a sufficiently long split line length in the cross section of the pretension member, and prevents the deformed reinforcing bar, which is a tension material, from separating from the concrete. Yes. Further, the pretension member restrains the fixing area adjacent to the center side of the adhesion split prevention portion by the adhesion split prevention portion which is a non-stressed concrete portion provided at the end portion, and the occurrence of split fracture occurs. Is prevented.

  Here, as shown in FIG. 4, the split line length in the cross section of the pretension member is the length of the crack in the cross section direction of the member that occurs due to the adhesion split fracture, The total of the crack lengths t1 and t3 and the crack length t2 generated between the reinforcing bars (deformed reinforcing bars) 10.

  In addition, unbonded deformed reinforcing bars at both ends where adhesive split fracture is likely to occur, placement of spiral reinforcing bars in the concrete surrounding the deformed reinforcing bars, and increase of the thickness of the parts will increase the load on the concrete in this part. Can be reduced and the splitting strength of concrete can be increased. This ensures that the deformed reinforcing bar has a sufficiently long split line length in the cross section of the pretension member, and prevents the deformed reinforcing bar, which is a tension material, from separating from the concrete, thereby preventing adhesion splitting fracture. In addition, the adhesion split prevention part, which is a non-stressed concrete part provided at the end, restrains the fixing area adjacent to the center side of this adhesion split prevention part, and when the tension force is introduced (when the tension material is released) Splitting by adhesion pressure and bond splitting are prevented.

  Here, the area where the deformed reinforcing bar is unbonded, the section where the spiral reinforcing bar is arranged, and the section where the member thickness is increased are appropriately set according to the prestressing force, concrete covering thickness, concrete strength, reinforcing bar diameter, etc. .

  According to the present invention, it has become possible to construct a pre-tension member that does not easily cause bond splitting fracture even when a tension material having a high adhesion force such as a deformed reinforcing bar is used.

Preferred embodiments of the present invention will be described below with reference to the drawings. In the description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.
Here, FIG. 1 is a view showing a prestressed beam (pretension member) according to a preferred embodiment of the present invention, where (a) is an overall view, and (b) is an A portion of (a). It is a fragmentary perspective view shown. FIG. 2 is a diagram showing a portion A of FIG. 1A according to each embodiment, where FIG. 2A is a transverse sectional view according to the first embodiment, and FIG. FIG. 4C is a transverse sectional view according to the second embodiment, FIG. 4D is a longitudinal sectional view thereof, FIG. 5E is a transverse sectional view according to the third embodiment, and FIG. FIG.

<First Embodiment>
As shown in FIG. 1A, the prestress beam 1 according to the first embodiment is a member that is horizontally provided between left and right pillars 2 and 2 that are erected with a predetermined interval. And it is comprised by the deformed reinforcing bar 10 and the concrete hardening body 11 to which tension | tensile_strength was provided. Here, the code | symbol 3 in drawing is a floor slab.

  And the adhesion split prevention part U is formed in the both ends of the prestress beam 1 by making the deformed reinforcing bar 10 unbonded as shown in FIG.1 (b).

  As shown in FIGS. 2 (a) and 2 (b), the adhesion splitting prevention portion U has a pipe material 12 disposed around the deformed reinforcing bar 10 in a fixed region at both ends of the prestressed beam 1, and this deformed shape. An unbond material 13 is filled in the gap between the reinforcing bar 10 and the pipe material 12. That is, the adhesion split prevention part U is an unstressed concrete part in which the deformed reinforcing bar 10 is unbonded at both ends of the prestressed beam 1 and no prestressed force is introduced by this configuration.

  In the prestressed beam 1 according to the first embodiment, concrete is placed in a formwork in which deformed reinforcing bars 10 are loaded with tensile forces from both ends, and after the concrete is hardened, deformed reinforcing bars 10 is a prestressed concrete member by a so-called pre-tension system, which is constituted by releasing the tensile force of 10 and removing the formwork.

  The deformed reinforcing bar 10 is a known high-strength deformed reinforcing bar, and the diameter of the reinforcing bar is appropriately determined according to an assumed external force or a prestressing force applied in advance. Moreover, what is necessary is just to set suitably also about the number and the bar arrangement pitch of the deformed reinforcement 10.

  In the first embodiment, as shown in FIGS. 2 (a) and 2 (b), the prestress is applied as a purpose of expressing a sufficient proof stress with respect to a bending moment due to an overload acting on the prestress beam 1. Prestress is introduced into the deformed reinforcing bar 10 arranged below the beam 1. In addition, since the bending moment acts on the central portion with respect to the longitudinal direction of the prestressed beam 1, it is sufficient that prestress is applied to this portion. 10 and the hardened concrete body 11 can be reduced in adhesion force.

  As the concrete constituting the hardened concrete body 11, concrete having a composition designed according to the external force or prestressing force acting on the prestressed beam 1 is used. High strength concrete may be used. And the concrete hardening body 11 is formed in the rectangular parallelepiped shape, as shown in FIG.1 (b).

  As the pipe member 12, as shown in FIGS. 2 (a) and 2 (b), a pipe member into which the deformed reinforcing bar 10 can be inserted is used. That is, the inner diameter of the pipe material 12 is formed larger than the outer diameter including the bar of the deformed reinforcing bar 10. The material of the pipe material 12 is not limited, and is appropriately selected from known pipe materials.

  Here, the length (predetermined region) Lu of the pipe material 12 is appropriately set according to the prestressing force, the concrete covering thickness, the concrete strength, the reinforcing bar diameter, etc. to be introduced. Then, it is set to about 5 times the nominal diameter D of the deformed reinforcing bar 10.

  The unbond material 13 seals the gap between the deformed reinforcing bar 10 and the pipe material 12 and prevents the deterioration of the prestressed beam 1, and uses a material having a high viscosity such as grease or asphalt, for example. And

  In the first embodiment, the pipe material 12 filled with the unbond material 13 is disposed around each deformed reinforcing bar 10 at both ends of the prestressed beam 1. However, the deformed reinforcing bar 10 is unbonded. If possible, the pipe material 12 is not necessarily arranged. For example, the pipe material is obtained by a method in which the unbond material 13 is applied around the deformed reinforcing bar 10 in a predetermined range in advance, or a method of separating the adhesion between the deformed reinforcing bar 10 and the concrete in the predetermined range by arranging the formwork. 12 may be omitted. Moreover, when there is no fear of deterioration of the deformed reinforcing bar 10 or the hardened concrete body 11, the pipe material 12 may be disposed only without filling the unbond material 13.

  Because the prestressed beam 1 according to the first embodiment causes the deformed reinforcing bars 10 to be unbonded in certain regions at both ends of the prestressed beam 1 where adhesive split fracture is likely to occur, the hardened concrete body 11 in this part. Reduce the load on the to prevent damage (adhesion split fracture). And since the prestress which acts via a deformed reinforcing bar acts in the center rather than the adhesion split prevention part U of the both ends of the prestress beam 1, it is hard to produce an adhesion split fracture. That is, the adhesion splitting prevention part U, which is a non-stressed concrete part provided at the end, restrains the fixing area adjacent to the center side of the adhesion splitting prevention part U, and when tension is introduced (when tension material is released) ) Is prevented from cracking and adhesion splitting due to bare pressure.

  In addition, the shape (length Lu etc.) will not be limited if the adhesion split prevention part U is formed so that adhesion split fracture and the cracking by the external pressure at the time of tension | tensile_strength introduction | transduction can be prevented. Although, for example, the expression (1) is satisfied so that the binding force (tensile strength ft × length Lu × width b) by the adhesion split prevention unit U is larger than the bare pressure (tensile force, adhesion stress, etc.) You may form so that it may do.

<Second Embodiment>
As in the first embodiment, the prestressed beam 1 according to the second embodiment has left and right pillars 2 and 2 erected with a predetermined interval, as shown in FIG. It is a member laid laterally, and is composed of a deformed reinforcing bar 10 to which tension is applied and a hardened concrete body 11.

  As shown in FIGS. 2 (c) and 2 (d), the prestressed beam 1 is provided with a pipe material 12 around the deformed reinforcing bar 10 in the first regions at both ends thereof, and the deformed reinforcing bar 10 and the pipe An unbonded material 13 is filled in the gap with the material 12, and spiral reinforcing bars 14 are arranged around the deformed reinforcing bars 10 in the second regions at both ends thereof. That is, the prestressed beam 1 is provided with an adhesion split prevention part U with the deformed reinforcing bar unbonded at both ends (see FIG. 1B), and the adhesion split prevention part including the adhesion split prevention part U is provided. A spiral reinforcing bar 14 is disposed around the deformed reinforcing bar 10 at a portion adjacent to the center side of U.

Here, since the deformed reinforcing bar 10 according to the second embodiment is the same as that shown in the first embodiment, detailed description thereof is omitted.
Moreover, since the pipe material 12 and the unbond material 13 which concern on 2nd Embodiment are the same as that of what was shown in 1st Embodiment, detailed description is abbreviate | omitted.
Furthermore, since the structure of the concrete hardening body 11 is the same as that of what was shown in 1st Embodiment, detailed description is abbreviate | omitted.

The spiral reinforcing bar 14 is a reinforcing bar processed into a coil (spiral) shape, and the diameter of the arc formed in a spiral shape can be inserted into the deformed reinforcing bar 10 with a predetermined interval. Is formed. Further, the range (second region) where the spiral reinforcing bar 14 is arranged is prestressed force, concrete covering thickness, concrete strength, reinforcing bar introduced in the center direction from the adhesion split preventing part at both ends of the prestress beam 1. The length may be set as appropriate according to the diameter or the like, but it is necessary to include a concrete part material axial direction section Ld to which an adhesive force is applied from the deformed reinforcing bar 10 as shown in FIG. . The Ld is about 10 to 15 times the nominal diameter of the deformed reinforcing bar 10. The method for verifying that the bond splitting is avoided according to the present embodiment is obtained by dividing the bond splitting strength τ _bu incorporating the effect of the spiral rebar 14 by the safety factor n by satisfying the formula (2). value is that is above the bond stress of tau _f.

  As shown in FIG. 2 (d), in the second embodiment, the second region where the spiral reinforcing bar 14 is arranged is defined as a range including the concrete part material axial direction section Ld to which the adhesive force is applied, and the prestressed beam 1 is the section from the center of the length of the concrete part material axial direction section Ld to which an adhesion force is applied from the tip of the pipe material 12 (adhesion split prevention part U). In other words, the reinforcement is arranged in the section (second section = Lu + Ld) obtained by adding the concrete part material axial direction section Ld to which the adhesive force is applied to the length (first area) Lu of the pipe member 12 with respect to the longitudinal direction of the prestressed beam 1. To do.

  According to the prestressed beam 1 according to the second embodiment, the deformed reinforcing bar 10 is unbonded at the end where adhesion split fracture is likely to occur, thereby reducing the load on the hardened concrete body 11 in this part. Then, by arranging the spiral reinforcing bars 14 around the hardened concrete body 11, the force P1 (see FIG. 3) that spreads radially around the deformed reinforcing bars 10 caused by the prestress P is constrained to split the hardened concrete body 11 Strength is increased. Thereby, in the deformed reinforcing bar 10, the portion attached to the hardened concrete body 11 becomes a portion other than where the pipe material 12 is disposed (a central portion other than the first region at both ends of the prestressed beam 1). The prestress acting via the deformed reinforcing bar acts at the central portion from the position inside the predetermined length (Lu) with respect to the longitudinal direction of the prestressed beam 1. The prestressed beam 1 is fixed to the fixing area adjacent to the center side of the adhesion split prevention portion U (prestress force is completely introduced) by the adhesion split prevention portion U which is a non-stressed concrete portion provided at the end. The section which is not) is restrained, and the splitting and adhesion splitting breakage due to the external pressure when the tension force is introduced (when the tension material is released) are prevented. Further, since the spiral reinforcing bars 14 are arranged farther from the center than the pipe member 12, the end portion where the prestress acts, that is, the concrete hardened body 11 at the tip end portion of the pipe member 12 is reinforced, and this portion is provided. To prevent damage.

<Third Embodiment>
As in the first embodiment, the prestressed beam 1 according to the third embodiment has left and right columns 2 and 2 erected with a predetermined interval, as shown in FIG. It is a member laid laterally, and is composed of a deformed reinforcing bar 10 to which tension is applied and a hardened concrete body 11.

  As shown in FIGS. 2 (e) and 2 (f), the prestressed beam 1 is provided with pipe material 12 around the deformed reinforcing bar 10 in the first region at both ends thereof, and both ends thereof. In the second region, spiral reinforcing bars 14 are arranged around the deformed reinforcing bars 10, and the member thickness of the concrete hardened body 11 is increased in the second regions at both ends thereof. Further, an unbond material 13 is filled in the gap between the deformed reinforcing bar 10 and the pipe material 12. With this configuration, the prestressed beam 1 is formed with an adhesion split prevention portion U in which the deformed reinforcing bars are unbonded at both ends (see FIG. 1B), and the adhesion split split prevention portion U and the center side of the adhesion split prevention portion U In the part adjacent to the reinforcing bar, the arrangement of the reinforcing bar 14 and the thickness of the spiral reinforcing bar 14 are increased around the deformed bar.

Here, since the deformed reinforcing bar 10 according to the third embodiment is the same as that shown in the first embodiment, detailed description thereof is omitted.
Moreover, since the pipe material 12 and the unbond material 13 are the same as those shown in the first embodiment, detailed description thereof is omitted.
Further, since the configuration of the spiral reinforcing bar 14 is the same as that shown in the second embodiment, the detailed description is omitted.

  As shown in FIG. 2 (e), the hardened concrete body 11 has a trapezoidal cross section at the both ends of the prestressed beam 1 before and after the general portion 11a formed in a rectangular cross section (left and right in FIG. 2 (e)). The member thickness is increased by the thickened portions 11b and 11b. That is, as shown in FIGS. 2E and 2F, the thickness is increased at both ends of the rectangular parallelepiped. Here, in the third embodiment, the thickened portion 11b is formed in a trapezoidal cross section for the purpose of increasing the concrete covering thickness of the deformed reinforcing bar 10 disposed below the prestressed beam 1. The shape of the thickened portion 11b is not limited, and may be set as appropriate according to the shape of the prestressed beam 1 and the arrangement of the deformed reinforcing bars 10. The range of the thickened portion 11b may be set as appropriate according to the prestressing force introduced into the prestressing beam 1, the concrete covering thickness, the concrete strength, the reinforcing bar diameter, etc. In the third embodiment, It shall be performed about the range equivalent to the range of the 2nd area | region which arranges the spiral reinforcement shown in 2nd Embodiment.

According to the prestressed beam 1 according to the third embodiment, the deformed reinforcing bar 10 is unbonded at the end portion (first region) where adhesion split fracture is likely to occur, thereby reducing the load on the concrete in this portion. At the same time, an adhesion split prevention part U, which is a non-stressed concrete part, is formed, and the fixing area adjacent to the center side of the adhesion split prevention part U is restrained, and when tension force is introduced (when the tension material is released) Prevents splitting due to bare pressure and fracture of bond splitting.
Further, at the end portion (second region) of the prestressed beam 1, the splitting strength of the concrete is enhanced by arranging the spiral reinforcing bars 14 and increasing the member thickness on the surrounding concrete. Thereby, since the spiral reinforcing bar 14 is arranged to the center side from the pipe material 12, it adjoins the edge part which the prestress acts, ie, the front-end | tip part (the center side of the adhesion split prevention part U). The hardened concrete body 11 of the part) is reinforced, and the force P1 (see FIG. 3) that spreads radially around the deformed reinforcing bar 10 due to the prestress P is constrained to prevent breakage in this part. Moreover, the member thickness is increased in the second region at the end of the prestressed beam 1, and the splitting fracture length (see FIG. 4) in the concrete cross section is ensured to prevent the adhesion split fracture.

The preferred embodiments according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention.
For example, the prestressed beam according to the present invention is preferably used as a precast member that is produced in advance in a factory or the like. However, the prestress beam in the field is suitable for application to a large-scale member that is difficult to transport as a precast member. As long as it is possible to secure the necessary space for installation and installation of equipment necessary for power introduction, construction may be performed by on-site construction.

  Moreover, although each said embodiment demonstrated the case where the pretension member of this invention was used as a beam member, it cannot be overemphasized that the use application of the pretension member of this invention is not limited.

  Further, in addition to the configuration shown in each of the above embodiments, an excellent pretension member may be constructed by appropriately combining the configuration shown in each of the above embodiments. For example, in the predetermined region (first region) at both ends of the pretension member, the deformed reinforcing bars are unbonded and the member thickness is increased in the predetermined region (second region) at both ends, thereby increasing the both ends of the pretension member. While reducing the load to the concrete in the 1st area | region of a part, you may raise the splitting strength of the concrete in the 2nd area | region of both ends. Thereby, it becomes possible to prevent separation of the deformed reinforcing bar, which is a tendon material, and concrete, and to prevent the adhesion split fracture.

  Also, in addition to unbonding deformed reinforcing bars, high strength concrete is used for the predetermined areas at both ends of the pretension member to prevent separation between deformed reinforcing bars, which are tendons, and concrete. It may be configured to prevent the occurrence. In this case, for example, fiber reinforced concrete may be employed as the high-strength concrete.

  Further, in the second embodiment and the third embodiment, the arrangement of spiral reinforcing bars in the section obtained by adding the axial direction section of the concrete part material in which the adhesion force is added to the length of the pipe material (adhesion split prevention part). However, with respect to the adhesion split prevention part, it is not necessary to arrange spiral reinforcing bars or increase the member thickness. ) Only for spiral reinforcing bars or increase in member thickness.

It is a figure which shows the prestress beam concerning suitable embodiment of this invention, Comprising: (a) is a general view, (b) is a fragmentary perspective view which shows A part of (a). It is a figure which shows A part of Fig.1 (a) concerning each embodiment, (a) is a cross-sectional view concerning 1st Embodiment, (b) is the longitudinal cross-sectional view, (c) is the same. FIG. 4 is a transverse sectional view according to a second embodiment, FIG. 4D is a longitudinal sectional view thereof, FIG. 5E is a transverse sectional view according to a third embodiment, and FIG. (A), (b) is explanatory drawing of adhesion split fracture. It is explanatory drawing of the split line length in a concrete member cross section. It is a figure which shows the conventional pretension member, (a) is a front view, (b) is a cross-sectional view which shows the B part of (a), (c) is a longitudinal cross-sectional view which shows the B part of (a) It is.

Explanation of symbols

1 Prestressed beam (pretension member)
DESCRIPTION OF SYMBOLS 10 Deformation reinforcement 11 Concrete hardening body 12 Pipe material 13 Unbond material 14 Spiral reinforcement U Adhesion split prevention part

Claims (2)

A pretensioning member that introduces prestress into concrete by tensioning deformed reinforcing bars,
At both ends, the deformed reinforcing bar is unbonded to provide an adhesion split prevention part,
At least in the part adjacent to the center side of the adhesion split prevention part, the part having the possibility of causing bond splitting fracture due to the action of a force that radially pushes the concrete around the deformed reinforcement, the deformed reinforcement A pretensioning member characterized in that a spiral reinforcing bar is arranged around the periphery. A pretensioning member that introduces prestress into concrete by tensioning deformed reinforcing bars,
At both ends, the deformed reinforcing bar is unbonded to provide an adhesion split prevention part,
At least a part adjacent to the center side of the adhesion split prevention part, and a part thickness may be caused by a force that radially spreads the concrete around the deformed reinforcing bar to cause adhesion split fracture. A pretensioning member characterized in that it is increased.

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