Prestress structure and precast concrete member using the same

Abstract

To provide a prestressed structure capable of preventing bending cracks at ends, and a precast concrete member using the same.SOLUTION: A precast concrete member 1 according to the present invention is a floor slab employing a pre-tension type prestress structure, including two end sections 3a and 3b including the areas near each end of a PC steel stranded wire 2, and an intermediate section 3c sandwiched between them. In the end section 3a, an annular reaction force body 4 is arranged, the shaft of which is positioned along the shaft of the PC steel stranded wire 2. When the tension force introduced into the PC steel stranded wire 2 is transmitted to the concrete in the end section 3a, the annular reaction force body 4 tensilely supports the expansion force generated from the circumferential surface of the PC steel stranded wire 2 in a direction perpendicular to the shaft, so that the reaction force of the expansion force is generated from the PC steel stranded wire 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a prestress structure applied to a pretensioning method using PC steel materials, particularly PC steel wires, and a precast concrete member using the same.

Background Art

[0002] Prestressed concrete (PC) is roughly classified into a pretensioning method and a post-tensioning method according to the timing of introducing prestress. In the post-tensioning method, since the tendons can be freely arranged in the concrete, it is possible to easily introduce a large prestress to in-situ concrete of various shapes.

[0003] On the other hand, in the pretensioning method, a tensile force is introduced into the tendon by taking reaction force from a reaction bed to which the tendon is attached, and after placing concrete in this state, the tendon is removed from the reaction bed after waiting for the strength of the concrete to develop. Therefore, basically, it is adopted when manufacturing precast concrete (PCa) members in a factory.

[0004] Here, different from the post-tensioning method, the pretensioning method does not require time for arranging the sheaths while being complicated with the steel bar work, nor does it require space or scaffolding for installing the hydraulic jack. Therefore, it is widely adopted for the renewal of road bridge decks where there is a great demand for shortening the construction period.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the pretension method, since the tensile force cannot be sufficiently transmitted at the ends of precast concrete members, in this section, the design often does not consider the tensile force. However, when joining and integrating multiple precast concrete members, it is necessary to have a structure that can resist bending at the joint. In that case, there has been a problem that a tensile force must be separately introduced to prevent bending cracks.

Means for Solving the Problems

[0007] The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a prestress structure capable of preventing bending cracks at the ends and a precast concrete member using the same.

[0008] To achieve the above object, as described in claim 1, the prestress structure according to the present invention is such that PC steel bars such as PC steel wires are embedded in concrete that extends into two end sections including the vicinity of each end of the PC steel bars and an intermediate section sandwiched therebetween, and the tensile force introduced into the PC steel bars is transmitted to the concrete through adhesion to the concrete. In the prestress structure, a spiral reaction body whose axis is positioned along the axis of the PC steel bar is arranged in at least one of the two end sections. When the tension is transmitted to the concrete, the spiral reaction body supports the expansion force acting in a direction perpendicular to the material axis from the peripheral surface of the PC steel material towards the material axis by the tensile force and the adhesive force with the concrete or by the elastic restoring force, and generates a reaction force of the expansion force towards the PC steel material, so that the fixing length at the time of tension introduction is shortened. and the spiral reaction body is constituted by a coil spring It is such a thing.

[0012] In addition, the precast concrete member according to the present invention Claim 1 employs the prestress structure described above.

[0013] Conventionally, in a prestress structure of the pretension method, since the tension of the PC steel material is not sufficiently transmitted in the end section, when a plurality of precast concrete members are joined and integrated, in order to prevent bending cracks at the joint, it may be necessary to separately introduce tension at the joint.

[0014] The applicant of the present application conducted research and development focusing on the fact that the decrease in the transmission force of the tension in the end section is caused by the decrease in the adhesive force due to the expansion of the concrete, and thus arrived at the present invention.

[0015] That is, in the prestress structure according to the present invention, an annular reaction body or a spiral reaction body positioned such that the material axis is along the material axis of the PC steel material is arranged in at least one of the two end sections. (The annular reaction body is a reference invention) .

[0016] Here, in the prestress structure of the pretension method, the tension of the PC steel material is transmitted to the concrete through the adhesion between the PC steel material and the concrete. The tension is transmitted to the concrete as a compression force by the component force in the direction parallel to the material axis of the PC steel material, while the component force in the direction perpendicular to the material axis goes in the radial direction centered on the material axis from the peripheral surface of the PC steel material and is transmitted to the concrete as an expansion force.

[0017] This expansive force not only causes cracks in the concrete, but also reduces the adhesion between the PC steel material and the concrete, and thus causes a decrease in the transmission of the tensile force in the end section.

[0018] However, in the present invention, in the case of an annular reaction body, the expansive force is supported in tension by its tensile strength performance, and the reaction force is generated toward the PC steel material. In the case of a spiral reaction body, it is supported by the tensile force and the adhesion to the concrete or by the elastic restoring force, and the reaction force of the expansive force is generated toward the PC steel material. (The annular reaction body is a reference invention) 。

[0019] Therefore, the concrete surrounding the PC steel material is restrained from deforming to bulge in the direction orthogonal to the material axis and is pressed against the PC steel material, increasing the adhesion. Thus, the range of introduction of the tensile force in the end section expands, and as a result, the decrease in the transmission of the tensile force in the end section is suppressed. Also, in the case of joining and integrating a plurality of precast concrete members, it is possible to prevent bending cracks at the joining location without separately introducing the tensile force.

[0020] In the post-tensioning prestressed structure, reinforcing bars may be provided in the vicinity of the bearing plate. However, these reinforcing bars are for reinforcing against the load acting from the bearing plate and are not for the load acting in the radial direction from the peripheral surface of the PC steel material, and the technical idea is essentially different from that of the present invention.

[0021] The annular reaction body or the spiral reaction body only needs to be provided in at least one of the two end sections, and it is optional whether to provide it only in one of the end sections or in each of the two end sections. (The annular reaction body is a reference invention) 。

[0022] Annular reaction body (Reference invention)As long as it is configured to support the expansion force directed from the peripheral surface of the PC steel material in a direction perpendicular to its material axis and to generate a reaction force of the expansion force toward the PC steel material, the configuration is arbitrary, and includes endless annular members such as rings and hoops. On the other hand, the material, diameter, number, and in the case of a plurality, the arrangement pitch, length (total length along the material axis of the PC steel material), etc. can be set as appropriate, and it includes a single configuration or a case where it is formed into a single and cylindrical shape. However, a case where a plurality of annular members are arranged such that their central axes are aligned on a common axis is a typical example. In this case, the common axis becomes the material axis of the annular reaction body.

[0023] As long as the spiral reaction body is configured to support the expansion force directed from the peripheral surface of the PC steel material in a direction perpendicular to its material axis with tensile force and adhesion to concrete or with elastic restoring force, and to generate a reaction force of the expansion force toward the PC steel material, the configuration is arbitrary, and it is the same as the annular reaction body (Reference invention) and the material, diameter, length, etc. can be set as appropriate. In the present invention, it is assumed that it is constituted by a coil spring .

[0024] Here, the tensile force means the tensile resistance of the spiral reaction body itself, and the adhesion to concrete means the reaction force acting from the concrete to the peripheral surface of the spiral reaction body against the above expansion force, and includes not only adhesive force but also frictional force.

[0025] In addition, the support mechanism of the expansion force in the spiral reaction body includes not only the case of supporting only with tensile force and adhesion to concrete or only with elastic restoring force, but also the case where they cooperate to support.

[0026] The prestress structure according to the present invention includes the case where it is constructed at the site where structures such as bridges are constructed, but a typical example is when it is adopted for precast concrete members manufactured in a factory. In particular, when these are manufactured as road bridge decks and joined and integrated, the joined portion can be resistant to bending without separately introducing tension.

Brief Description of the Drawings

[0027] [Fig. 1] It is a view of the precast concrete member 1 according to this embodiment. (a) is an overall longitudinal sectional view, (b) is a cross-sectional detailed view along line A-A, and (c) is an overall perspective view of the annular reaction body 4. [Fig. 2] It is a view showing the action of the precast concrete member 1. (a) is a longitudinal sectional detailed view showing how the tension of the PC steel wire 2 is transmitted to the concrete in the direction parallel to the material axis of the PC steel wire and in the direction perpendicular to the material axis, respectively. (b) is a cross-sectional detailed view along line B-B, showing how the component force in the direction perpendicular to the material axis of the PC steel wire 2 travels from the peripheral surface of the PC steel wire 2 in the radial direction centered on its material axis and is transmitted to the concrete as an expansion force. (c) is a partial cross-sectional detailed view along line B-B, showing how the above expansion force is tension-supported by the tensile strength performance of the annular reaction body 4 and how the reaction force is generated toward the PC steel wire 2. [Fig. 3] It is a view showing the reduction in tension transmission near the end of the precast concrete member together with a longitudinal sectional view. (a) is a view of a conventional precast concrete member, and (b) is a view of the precast concrete member 1 according to this embodiment. [Fig. 4] It is a view showing an example of constructing a road bridge floor slab 44 by joining the precast concrete members 1, 1 together. (a) is a side view of the state before joining as seen from the bridge axis direction, (b) is a side view of the state after joining as seen from the bridge axis direction, and (c) is a conceptual diagram of the bending moment generated in the road bridge floor slab 44. [Fig. 5] It is a view of the precast concrete member 1'. (a) is an overall longitudinal sectional view, and (b) is a side view as seen from the bridge axis direction when constructing a road bridge floor slab 61 together with the precast concrete member 1. [Fig. 6]FIG. 0 is a view showing the operation of the precast concrete member according to the second embodiment, (a) is a longitudinal sectional detail view showing how the tension of wire 2 from PC steel is transmitted to concrete in a direction parallel to the material axis of the wire from the PC steel and in a direction perpendicular to the material axis, (b) is a cross-sectional detail view along line C-C, showing how the component force in the direction perpendicular to the material axis of wire 2 from PC steel is directed from the peripheral surface of the wire from the PC steel in a radial direction centered on its material axis and transmitted to concrete as an expansion force, and (c) is a partial cross-sectional detail view along line C-C, showing how the above expansion force is supported by the tensile force and the adhesive force with concrete or by the elastic restoring force, and how the reaction force is generated toward wire 2 from PC steel.

Mode for Carrying Out the Invention

[0028] Hereinafter, embodiments of the prestress structure according to the present invention and a precast concrete member using the same will be described with reference to the accompanying drawings.

[0029] [First Embodiment] FIG. 1 shows a precast concrete member 1 according to this embodiment.

[0030] As shown in the figure, the precast concrete member 1 is a floor slab adopting a pretension method prestress structure, in which wire 2 from PC steel as PC steel material is embedded in concrete, and the tension introduced into the wire from the PC steel is transmitted to the concrete through its adhesion to the concrete.

[0031] Although not shown in the figure, wire 2 from PC steel may be appropriately arranged in a required number along the depth direction of the paper surface according to the width of the floor slab.

[0032] The precast concrete member 1 according to this embodiment is composed of two end sections 3a and 3b including the vicinity of each end of the PC steel wire 2, and an intermediate section 3c sandwiched therebetween. In the end section 3a, an annular reaction body 4 is arranged with its material axis positioned along the material axis of the PC steel wire 2.

[0033] The annular reaction body 4 is configured by arranging a plurality of, in this embodiment, four annular members 21 formed by bending flat steel into an annular shape so that their central axes are aligned on a common axis, and the common axis serves as the material axis of the annular reaction body 4.

[0034] The annular reaction body 4 may be interconnected with a connecting material so that the annular members 21 are spaced from each other, and appropriately positioned with a spacer so that the material axis coincides with the material axis of the PC steel wire 2 (both are not shown).

[0035] Note that the annular member may be formed of round steel or the like instead of flat steel as shown in the figure.

[0036] When the tensile force introduced into the PC steel wire 2 is transmitted to the concrete in the end section 3a, the annular reaction body 4 is configured to tensilely support the expansion force generated in a direction perpendicular to the material axis from the peripheral surface of the PC steel wire 2, so that the reaction force of the expansion force is generated toward the PC steel wire 2.

[0037] The number, arrangement pitch, or diameter of the annular members 21 may be appropriately determined according to how much improvement is desired in reducing the transmission of the tensile force in the vicinity of the material end including the end section 3a.

[0038] When manufacturing the precast concrete member 1, the PC steel wire 2 may be inserted into the annular reaction body 4 in advance and then the procedure may be the same as the conventional one.

[0039] The precast concrete member 1 according to this embodiment employs a pre-tensioning prestress structure, and the tension of the PC steel wire 2 is transmitted to the concrete through the adhesion between the PC steel wire 2 and the concrete. As shown in Fig. 2(a), the tension is transmitted to the concrete as a compressive force in the direction parallel to the material axis of the PC steel wire 2, while the component force in the direction perpendicular to the material axis is transmitted to the concrete as an expansive force.

[0040] Since the concrete inherently cannot be expected to have tensile strength, this expansive force not only causes cracks in the concrete but also reduces the adhesion between the PC steel wire 2 and the concrete, and ultimately leads to a decrease in the transmission of tension in the end section 3a.

[0041] In view of this point, in the precast concrete member 1 according to this embodiment, as shown in Fig. 2, an annular reaction body 4 is arranged in the end section 3a with its material axis positioned along the material axis of the PC steel wire 2. When the tension introduced into the PC steel wire 2 is transmitted to the concrete in the end section 3a, the expansive force (black arrows in Figs. 2(b) and (c)) transmitted from the peripheral surface of the PC steel wire 2 in the direction perpendicular to its material axis is tension-supported by the tensile strength performance of the annular member 21 as shown by the white arrow (large) in Fig. 2(c), and the reaction force of the expansive force is configured to be generated toward the PC steel wire 2 as shown by the white arrow (small) in the same figure.

[0042] Therefore, the concrete surrounding the PC steel wire 2 is restrained from deforming to bulge in the direction perpendicular to the material axis and is pressed against the PC steel wire 2, thereby increasing the adhesion.

[0043] Figure 3 shows the effect related to the reduction in the transmission of the tension force. In the case of a precast concrete member with a conventional prestress structure, as shown in Fig. (a) of the same figure, near the end of the PC steel material, since the expansion of the concrete cannot be suppressed, the adhesive force between the PC steel material and the concrete becomes small. Therefore, in the section from a certain distance away from the edge of the member to a certain position, the tension force of the PC steel material is not transmitted to the concrete at a sufficient magnitude (anchorage length L 1 ) and had to be treated as such.

[0044] On the other hand, in the precast concrete member 1 according to the present embodiment, as shown in Fig. (b) of the same figure, since the expansion of the concrete in the end section 3a is suppressed by the above-described annular reaction body 4, the anchorage length is L 2 and is shortened.

[0045] Figure 4 shows an example of constructing a road bridge deck using the precast concrete member 1.

[0046] To construct a road deck, as shown in Fig. (a) of the same figure, first, the precast concrete members 1, 1 are laid across the bridge girder 42. At this time, the precast concrete members 1, 1 are arranged such that the end sections 3a face each other through a clearance 41 for joining.

[0047] Next, as shown in Fig. (b) of the same figure, a joining structure 43 is appropriately applied to the clearance 41 to join the precast concrete members 1, 1 to each other to form a road bridge deck 44.

[0048] Fig. (c) of the same figure schematically shows the bending moment generated in the road bridge deck 44.

[0049] When constructing a road bridge deck by rigidly joining two precast concrete members, at the end of the road bridge deck, since there is no rotational restraint, the bending moment becomes zero. On the other hand, at the joint, since the ends of the respective precast concrete members are rotationally restrained, a certain bending moment is generated. However, in the precast concrete members 1, 1 according to the present embodiment, as shown in the figure, since sufficient tensile force is transmitted to the concrete extending in the end section 3a and a compressive force is introduced in advance, bending cracks are suppressed at the joint.

[0050] In addition, when constructing the joint structure 43, if ultra-high-strength fiber-reinforced concrete is used as its constituent material, bending cracks are also suppressed at the joint between the joint structure 43 and the precast concrete members 1, 1.

[0051] The mixing and construction methods of ultra-high-strength fiber-reinforced concrete may be appropriately determined with reference to the "Design and Construction Guidelines (Draft) for Ultra-High-Strength Fiber-Reinforced Concrete" issued by the Japan Society of Civil Engineers.

[0052] As described above, according to the precast concrete member 1 according to the present embodiment, the annular reaction body 4 whose material axis is positioned along the material axis of the wire 2 from the PC steel is arranged in the end section 3a, and when the tensile force introduced into the wire 2 from the PC steel is transmitted to the concrete in the end section 3a, the expansion force transmitted from the peripheral surface of the wire 2 from the PC steel in the direction orthogonal to its material axis is tension-supported by the tensile strength performance of the annular member 21, and the reaction force of the expansion force is configured to be generated toward the wire 2 from the PC steel. Therefore, the concrete surrounding the wire 2 from the PC steel is restrained from deforming so as to bulge in the direction orthogonal to the material axis and is pressed against the wire 2 from the PC steel, increasing the adhesive force. Therefore, the tensile force of the wire 2 from the PC steel is transmitted to the concrete as a compressive force with sufficient magnitude.

[0053] Therefore, the reduction in the transmission of the tension force in the end section 3a is suppressed, and even when the two precast concrete members 1, 1 are joined and integrated, it is possible to prevent bending cracks at the joint without separately introducing the tension force.

[0054] In this embodiment, the case where the PC steel material is the wire 2 rather than PC steel has been described. However, depending on the size of the precast concrete member, instead of the wire 2, PC steel bars may be used.

[0055] In addition, in this embodiment, the precast concrete member 1 is used for the floor slab. However, if it is necessary to suppress bending cracks at the end, it can be applied not only to the floor slab but also to members at any part such as column members and beam members.

[0056] In addition, in this embodiment, the configuration related to the precast concrete member has been described. However, for example, if it is long and thus the transportation cost is high, and even after subtracting the cost of introducing the tension force on-site, if it is economical as a whole, it may be constructed on-site as a prestressed structure.

[0057] In addition, in this embodiment, the annular reaction body 4 is provided only in one of the end sections 3a and 3b, i.e., the end section 3a. However, instead of this, a configuration in which the annular reaction body 4 is provided in each of the end sections 3a and 3b may be adopted. In this case, all the above-described modification examples related to the end section 3a are similarly applicable to the end section 3b.

[0058] FIG. 5(a) is a longitudinal sectional view showing a precast concrete member 1' in which the annular reaction bodies 4 are provided in each of the end sections 3a and 3b, and FIG. 5(b) is a side view showing an example in which a road bridge floor slab 61 is constituted by using the precast concrete member 1 and the precast concrete member 1'.

[0059] To construct the road bed slab 61, first, place the precast concrete members 1, 1', and 1 across the bridge girder 42.

[0060] At this time, the precast concrete member 1 located on the left side in the figure and the precast concrete member 1' located in the center are arranged such that the end section 3a of the precast concrete member 1 and the end section 3b of the precast concrete member 1' face each other with a clearance similar to the clearance 41. The precast concrete member 1' and the precast concrete member 1 located on the right side in the figure are also arranged such that the end section 3a of the precast concrete member 1' and the end section 3a of the precast concrete member 1 face each other with a clearance similar to the clearance 41.

[0061] Next, appropriately apply a joining structure 62 similar to the joining structure 43 to each clearance to join the precast concrete members 1, 1', and 1 to each other to form the road bridge bed slab 61.

[0062] With this configuration, since sufficient tensile force is transmitted to the concrete spreading in the end section 3a of the precast concrete member 1 and the end sections 3a and 3b of the precast concrete member 1', and a compressive force is introduced in advance, bending cracks are suppressed at the joint locations.

[0063] [Second Embodiment] Next, the second embodiment will be described. For components having substantially the same configuration as those in the first embodiment, the same numbers are assigned and their descriptions are omitted.

[0064] The precast concrete member according to the second embodiment has a spiral reaction body 61 arranged as shown in Fig. 6(a) instead of the annular reaction body 4 of the precast concrete member 1 described in the first embodiment. Similar to the annular reaction body 4, its material axis is positioned along the material axis of the PC steel wire 2.

[0065] The spiral reaction body 61 is composed of a steel coil spring and can be configured to mainly resist the above-mentioned expansion force with its elastic restoring force. Regarding the wire thickness and overall diameter, etc., it may be appropriately determined according to the degree of improvement of the reduction in the transmission of the tension force in the vicinity of the material end including the end section 3a.

[0066] In addition, the spiral reaction body 61 may be configured to resist the above-mentioned expansion force by the combined action of the tensile force of the wire itself and the adhesion to the surrounding concrete in addition to its elastic restoring force.

[0067] When the tension force introduced into the wire 2 from the PC steel is transmitted to the concrete in the end section 3a, the spiral reaction body 61 supports the expansion force generated in the direction perpendicular to the material axis from the peripheral surface of the wire 2 of the PC steel with the tensile force and the adhesion force to the concrete or with the elastic restoring force, so that the reaction force of the expansion force is generated toward the wire 2 from the PC steel.

[0068] When manufacturing the precast concrete member according to the second embodiment, since the spiral reaction body 61 can be arranged on the wire 2 from the PC steel so as to be wound around, different from the precast concrete member 1, the spiral reaction body 61 may be arranged on the wire 2 from the PC steel at an arbitrary timing before the concrete is placed.

[0069] The precast concrete member according to the second embodiment, similar to the precast concrete member 1 of the first embodiment, adopts a pre-tensioning prestressed structure, and the tension force of the wire from the PC steel is transmitted to the concrete through the adhesion between the wire 2 from the PC steel and the concrete. As shown in FIG. 6(a), the tension force is transmitted to the concrete as a compression force by the component force in the direction parallel to the material axis of the wire 2 from the PC steel, while the component force in the direction perpendicular to the material axis is transmitted to the concrete as an expansion force.

[0070] This expansion force not only causes cracks in the concrete because concrete inherently cannot be expected to have tensile strength, but also reduces the adhesion between the wire 2 and the concrete from the PC steel, and thus causes a decrease in the transmission of the tension force in the end section 3a.

[0071] In view of this point, in the precast concrete member according to the second embodiment, as shown in FIG. 6, a spiral reaction body 61 is arranged in the end section 3a such that the material axis is positioned along the material axis of the wire 2 from the PC steel. When the tension force introduced into the wire 2 from the PC steel is transmitted to the concrete in the end section 3a, the expansion force (black arrows in FIGS. 6(b) and 6(c)) transmitted from the peripheral surface of the wire 2 from the PC steel in a direction orthogonal to its material axis is supported by the tensile force and the adhesion to the concrete or supported by the elastic restoring force, and the reaction force of the expansion force is configured to be generated toward the wire 2 from the PC steel as shown by the white arrow (small) in FIG. 6(c).

[0072] Therefore, the concrete surrounding the wire 2 from the PC steel is restrained from deforming to bulge in the direction orthogonal to the material axis and is pressed against the wire 2 from the PC steel, thereby increasing the adhesion.

[0073] Also in the precast concrete member according to the second embodiment, similar to the explanation using FIG. 3, the suppressing effect of the reduction in the transmission of the tension force is exhibited, but the explanation thereof is omitted here.

[0074] Also, similar to the explanation using FIG. 4, a road bridge deck can be constructed using the precast concrete member according to the second embodiment. However, since the construction procedure and the action regarding the flexural crack are the same as those in the first embodiment, the detailed explanation is omitted.

[0075] As described above, according to the precast concrete member according to the second embodiment, the spiral reaction body 61 whose material axis is positioned along the material axis of wire 2 from PC steel is arranged in the end section 3a, and when the tension introduced into wire 2 from PC steel is transmitted to the concrete in the end section 3a, the expansion force transmitted from the peripheral surface of wire 2 from PC steel in a direction orthogonal to its material axis is supported by the tensile force and the adhesive force with the concrete or by the elastic restoring force, and the reaction force of the expansion force is configured to be generated toward wire 2 from PC steel. Therefore, the concrete surrounding wire 2 from PC steel is restrained from deforming so as to bulge in the direction orthogonal to the material axis and is pressed against wire 2 from PC steel, increasing the adhesive force. Therefore, the tension of wire 2 from PC steel is transmitted to the concrete as a compressive force with sufficient magnitude.

[0076] Therefore, the reduction in the transmission of tension in the end section 3a is suppressed, and even when two precast concrete members 1, 1 are joined and integrated, it is possible to prevent bending cracks at the joint without separately introducing tension.

[0077] Further, according to the precast concrete member according to the second embodiment, since the spiral reaction body 61 can be arranged on wire 2 from PC steel so as to be wound around it, it is possible to arrange the spiral reaction body 61 on wire 2 from PC steel at an arbitrary timing before concrete placement. Thus, the constraints during manufacturing are relaxed, and the manufacturing cost can be reduced.

[0078] In the second embodiment, the case where the PC steel material is wire 2 from PC steel has been described. However, depending on the size of the precast concrete member, PC steel bars may be used instead of wire 2 from PC steel.

[0079] Also, in the second embodiment, the precast concrete member is used for the floor slab. However, if it is necessary to suppress bending cracks at the ends, it can be applied not only to the floor slab but also to members at any part such as column members and beam members.

[0080] In the second embodiment, the configuration related to the precast concrete member has been described. However, for example, if the member is long and thus the transportation cost is high, and even after subtracting the cost of introducing the tensile force on-site, the overall cost is still economical, it may be constructed on-site as a prestressed structure.

[0081] In the second embodiment, the spiral reaction body of the present invention is a spiral reaction body 61 made of a steel coil spring, and mainly resists the above-mentioned expansion force with its elastic restoring force. However, alternatively, it is also possible to configure by arranging wire rods, for which elastic restoring force cannot be expected, in a spiral shape. Even in such a modified example, it is possible to resist the above-mentioned expansion force by the adhesion between the tensile force of the wire rod and the surrounding concrete.

[0082] In the second embodiment, the spiral reaction body 61 is provided only in one of the end sections 3a and 3b, i.e., the end section 3a. However, alternatively, it may be configured to provide the spiral reaction body 61 in each of the end sections 3a and 3b. In this case, the above-mentioned modified example regarding the end section 3a is equally applicable to the end section 3b.

[0083] Similar to the description in FIG. 5, a road bridge deck can be constructed using a precast concrete member provided with the spiral reaction body 61 only in one of the end sections 3a and a precast concrete member provided with the spiral reaction body 61 in each of the end sections 3a and 3b. Since the construction procedure and the action regarding flexural cracks are the same as those in the first embodiment, the description thereof is omitted here.

Explanation of Reference Numerals

[0084] 1, 1´ Precast concrete member 2 PC steel wire (PC steel material) 3a, 3b End sections 3c Intermediate section 3c 4 Annular reaction body 21 Annular member 61 Spiral reaction body

Claims

1. In a prestress structure in which PC steel materials such as wires made of PC steel are embedded in concrete that extends into two end sections including the vicinity of each end of the PC steel material and an intermediate section sandwiched between them, and the tensile force introduced into the PC steel material is transmitted to the concrete through adhesion with the concrete, a spiral reaction body whose axis is positioned along the axis of the PC steel material is disposed in at least one of the two end sections, when the tensile force is transmitted to the concrete, the spiral reaction body supports the expansion force directed from the circumferential surface of the PC steel material in a direction perpendicular to its axis with a tensile force and an adhesive force with the concrete or with an elastic restoring force, and generates a reaction force of the expansion force toward the PC steel material, so that the fixing length at the time of introducing the tensile force is shortened, The prestress structure is characterized in that the spiral reaction body is constituted by a coil spring.

2. A precast concrete member characterized in that the prestress structure according to Claim 1 is adopted.

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