TENDON ANCHORAGE AND CONSTRUCTION METHOD OF A PRE-STRESSED CONCRETE STRUCTURE

Abstract

An anchorage includes a bearing plate arranged in an end portion of a concrete structure with an insertion hole formed therein and formed with a through hole connecting to the insertion hole. A sleeve is inserted through the insertion hole and the through hole, with one end portion of the sleeve disposed on the outside of the structure. A tendon is inserted within the sleeve, with one end portion of the tendon disposed on the outside of the structure. A locknut is engaged with the one end portion of the sleeve and in contact with the outer surface of the bearing plate. A PC grout fills the insertion hole and the sleeve. Before filling, the tendon is applied with tension and, after strength expression of the PC grout, the tension is released. The tendon undergoes a Poisson effect to expand radially outward and compression stress occurs in the PC grout.

Claims

1. A tendon anchorage comprising: a bearing plate arranged in an outer end portion of a concrete structure with an insertion hole formed therein and formed with a through hole connecting to the insertion hole of the concrete structure; a hollow sleeve inserted through the insertion hole of the concrete structure and the through hole of the bearing plate, one end portion of the sleeve put on the outside of the concrete structure; a tendon inserted within the sleeve, one end portion of the tendon fixed to the concrete structure and the other end portion of the tendon put on the outside of the concrete structure; a locknut engaged with the other end portion of the sleeve, which is put on the outside of the concrete structure, and in contact with the outer surface of the bearing plate; and PC grout filling the insertion hole and the sleeve, wherein before filling with the PC grout, the other end portion of the tendon is pulled outward by a tensioning device with the one end portion being fixed so that the tendon is applied with tension and, after expression of a predetermined strength in the PC grout, the tension is released by the tensioning device, and the tendon undergoes a Poisson effect to expand radially outward and compression stress occurs in the PC grout between the expanding tendon and the sleeve.

2. The tendon anchorage according to claim 1, wherein the tendon is a continuous fiber-reinforced polymer strand.

3. The tendon anchorage according to claim 1, wherein a hollow sheath tube is embedded in the concrete structure, and the hollow space of the sheath tube is used as the insertion hole.

4. The tendon anchorage according to claim 1, wherein the compression stress p occurring in the PC grout and calculated by the following equation 1 is 20 to 60 MPa: p=φ/2×v×(0.7×εu)×(t×E)/(R×R) (Eq.1), where φ, v, εu, R, t, and E represent, respectively, the diameter of the tendon, Poisson's ratio of the tendon, tensile strain with guaranteed ultimate load of the tendon, inner radius of the sleeve, thickness of the sleeve, and elastic coefficient of the sleeve.

5. The tendon anchorage according to claim 1, wherein at least one of the inner surface and the outer surface of the sleeve is made concavo-convex.

6. The tendon anchorage according to claim 1, wherein the bearing plate arranged in the outer end portion of the concrete structure consists of a single continuous plate, not plural plates.

7. The tendon anchorage according to claim 1, wherein a plurality of convex shear keys are provided on a surface of the bearing plate opposed to the concrete structure, and recesses that the shear keys enter are formed in positions corresponding to those of the shear keys on a surface of the concrete structure opposed to the bearing plate.

8. A tendon anchorage comprising: a pair of locknut-and-bearing-plates arranged, respectively, in the end portions within a concrete structure and each formed with a through hole; a hollow sleeve engaged with each of the pair of locknut-and-bearing-plates and connecting to the through holes; a tendon inserted through the through hole of each of the locknut-and-bearing-plates in the end portions within the concrete structure and the hollow sleeve, the end portions of the tendon put on the outside of the concrete structure; and PC grout filling the sleeve, wherein before the PC grout filling the sleeve and concrete forming the concrete structure being placed, with one end portion of the tendon being fixed using a fixing device, the other end portion of the tendon is pulled outward by a tensioning device so that the tendon is applied with tension and, after expression of a predetermined strength in the PC grout and the concrete, the tension is released by the tensioning device, and the tendon undergoes a Poisson effect to expand radially outward and compression stress occurs in the PC grout between the expanding tendon and the sleeve.

9. The tendon anchorage according to claim 8, wherein the tendon is a continuous fiber-reinforced polymer strand.

10. The tendon anchorage according to claim 8, wherein the compression stress p occurring in the PC grout and calculated by the following equation 1 is 20 to 60 MPa: p=φ/2×v×(0.7×εcu)×(t×E)/(R×R) (Eq.1), where φ, v, εu, R, t, and E represent, respectively, the diameter of the tendon, Poisson's ratio of the tendon, tensile strain with guaranteed ultimate load of the tendon, inner radius of the sleeve, thickness of the sleeve, and elastic coefficient of the sleeve.

11. The tendon anchorage according to claim 8, wherein at least one of the inner surface and the outer surface of the sleeve is made concavo-convex.

12. The tendon anchorage according to claim 8, wherein the sleeve is formed with a filling hole for the PC grout to fill the sleeve and an air discharge hole for air to be discharged.

13. A construction method of a pre-stressed concrete structure using a post-tensioning system, comprising: arranging, in an end portion of a concrete structure with an insertion hole formed therein, a bearing plate with a through hole connecting to the insertion hole of the concrete structure; engaging a locknut with one end portion of a hollow sleeve; inserting the sleeve through the through hole of the bearing plate into the insertion hole of the concrete structure and placing the locknut engaged with the one end portion of the sleeve on the bearing plate; inserting a tendon into the sleeve; fixing one end portion of the tendon; placing a tensioning device in the other end portion of the tendon; with the tendon being applied with tension, filling the insertion hole of the concrete structure with PC grout such that the PC grout also fills the clearance gap between the sleeve and the tendon inserted into the sleeve; and after the PC grout reaching a predetermined strength, releasing the tension within the tendon.

14. A construction method of a pre-stressed concrete structure using a pre-tensioning system, comprising: providing a formwork; installing, in each lateral end portion within the formwork, a hollow sleeve and a locknut-and-bearing-plate engaged with the sleeve such that the locknut-and-bearing-plate comes into contact with each lateral end portion within the formwork; inserting a tendon through installation holes formed in the lateral end portions of the formwork into the formwork and putting the end portions of the tendon out through the respective lateral end portions of the formwork, while within the formwork, inserting the tendon into the sleeve installed in each lateral end portion within the formwork; placing a fixing device in one end portion of the tendon put out of the formwork through one lateral end portion of the formwork; placing a tensioning device in the other end portion of the tendon put out of the formwork through the other lateral end portion of the formwork; applying the other end portion of the tendon with tension using the tensioning device; with the tendon being applied with the tension, filling the sleeve in each lateral end portion within the formwork with PC grout; placing concrete within the formwork; and after the PC grout and the concrete reaching a predetermined strength, releasing the tension within the tendon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 is a cross-sectional view showing how pre-stress is introduced into a concrete structure using a post-tensioning system.

[0073] FIG. 2 is a cross-sectional view showing how pre-stress is introduced into a concrete structure using a post-tensioning system.

[0074] FIG. 3A is an enlarged cross-sectional view showing a tendon in a tensioned state together with a surrounding sleeve and PC grout filling the sleeve.

[0075] FIG. 3B is an enlarged cross-sectional view showing a tendon in a tension-released state together with the surrounding sleeve and the PC grout filling the sleeve.

[0076] FIG. 4 is a cross-sectional view of a first example showing how pre-stress is introduced into a concrete structure using a post-tensioning system.

[0077] FIG. 5 is a cross-sectional view of a second example showing how pre-stress is introduced into a concrete foundation structure using a post-tensioning system.

[0078] FIG. 6 is a cross-sectional view of a third example showing how pre-stress is introduced into a PC composite bridge using a post-tensioning system.

[0079] FIG. 7 shows a process of manufacturing a pre-stressed concrete structure member using a pre-tensioning system.

[0080] FIG. 8 shows a process of manufacturing a pre-stressed concrete structure member using a pre-tensioning system.

[0081] FIG. 9 shows a process of manufacturing a pre-stressed concrete structure member using a pre-tensioning system.

[0082] FIG. 10 is a partially enlarged plan view showing an enlarged version of one end portion of the concrete structure member shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] FIGS. 1 and 2 are cross-sectional views showing how pre-stress is introduced into a concrete structure using a post-tensioning system. A concrete structure introduced with pre-stress is called pre-stressed concrete structure. FIG. 3A is an enlarged schematic cross-sectional view showing a tendon (a stressing member, a tensioning member) in a tensioned state to be described below together with a surrounding sleeve and PC grout filling the sleeve. FIG. 3B is an enlarged schematic cross-sectional view showing a tendon in a tension-released state together with the surrounding sleeve and the PC grout filling the sleeve as well as compression stress (double-headed arrows) occurring in the PC grout.

[0084] As will be described in more detail below, the tendon is provided within the concrete structure to introduce pre-stress into the concrete structure. When one end (fixing end) of the tendon is fixed and the other end (tensioning end) is pulled outward, the tendon is applied with longitudinal tension. A fixing device for fixing one end of the tendon is shown schematically in FIGS. 1 and 2. A tensioning device for pulling the other end of the tendon is not shown in FIGS. 1 and 2. Specific examples of the fixing device and the tensioning device will hereinafter be described.

[0085] Referring to FIG. 1, a metal or polyethylene cylindrical sheath tube 5 is embedded in the concrete structure 2. The hollow space of the sheath tube 5 is used as an insertion hole 4 through which a sleeve 7 to be described below is inserted. The sheath tube 5 may employ, for example, a spiral sheath with its inner and outer peripheral surfaces made concavo-convex.

[0086] A metal bearing plate 3 is provided on the upper surface of the concrete structure 2. The bearing plate 3 is formed with a cylindrical through hole 3a having a diameter approximately equal to the outer diameter of the sheath tube 5 provided in the concrete structure 2, and the sheath tube 5 is also inserted through the through hole 3a of the bearing plate 3. The insertion hole 4 (hollow space of the sheath tube 5) is opened outward at the upper end face of the bearing plate 3. The through hole 3a of the bearing plate 3 may be formed to have a diameter slightly greater than the outer diameter of the sheath tube 5.

[0087] A metal cylindrical rigid sleeve 7 is inserted through the insertion hole 4. The sleeve 7 has an outer diameter smaller than the insertion hole 4 (inner diameter of the sheath tube 5). An annular clearance gap is formed between the sheath tube 5 and the sleeve 7 in a cross-sectional view. The inner and outer peripheral surfaces of the sleeve 7 may also be made concavo-convex (e.g., threaded). Both the inner and outer peripheral surfaces of the sleeve 7 are preferably made concavo-convex, though may be either the inner or outer peripheral surface of the sleeve 7. For the sleeve 7, a metal member having a rigidity in the circumferential direction tolerable the compressive stress 18 occurred in a PC grout 15 described later can be used. The rigidity of the sleeve 7 can be adjusted by the rigidity of the adopted metal member itself and the wall thickness thereof.

[0088] An upper end portion of the sleeve 7 extends above the bearing plate 3 and a screw thread 11 is formed on the outer peripheral surface of the upper end portion of the sleeve 7 extending above the bearing plate 3. A locknut 8 with a screw thread formed on the inner peripheral surface thereof is threadably mounted on the upper end portion of the sleeve 7 with the screw thread 11 formed on the outer peripheral surface thereof and engaged tightly with the outer peripheral surface of the sleeve 7 in contact with the upper surface of the bearing plate 3.

[0089] The tendon 1, which has a diameter smaller than the inner diameter of the sleeve 7, is inserted through the hollow space 6 of the sleeve 7 extending from the locknut 8 through the bearing plate 3 into the concrete structure 2. An annular clearance gap is also formed between the tendon 1 and the inner peripheral surface of the sleeve 7 in a cross-sectional view.

[0090] The tendon 1 can employ a continuous fiber-reinforced polymer strand composed of one core strand and multiple (e.g., six) side strands twisted around the core strand. The tendon 1 and the core strand and the side strands forming the tendon 1 each have an approximately circular shape in a cross-sectional view (not shown). Also, the core strand is arranged at the center of the tendon 1 and the multiple side strands are positioned to surround the core strand in a cross-sectional view. The tendon 1 has a diameter of about 5 mm to 40 mm, for example.

[0091] The core strand and the side strands constituting the tendon 1 each form a resin containing fiber bundle obtained by bundling, into a cross-sectionally circular shape, multiple (e.g., several tens of thousands of) elongated continuous carbon fibers impregnated with thermosetting resin or thermoplastic resin for curing. Each of the carbon fibers is very thin, having a diameter of 5 μm to 7 μm, for example. The tendon 1 may be said to be made of Carbon Fiber Reinforced Plastics. Aramid fiber or glass fiber may be used in lieu of carbon fiber. Epoxy resin or vinyl ester resin, for example, is used as the thermosetting resin. Polycarbonate or polyvinyl chloride, for example, is used as the thermoplastic resin.

[0092] One end (lower end in FIG. 1; fixing end) of the tendon 1 extending downward from the lower surface of the concrete structure 2 is fixed by a fixing device 12. The other end (upper end in FIG. 1; tensioning end) of the tendon 1 extending upward from the locknut 8 is pulled (also referred to as “applied with tension”) upward by a tensioning device (not shown). Since the one end (fixing end) of the tendon 1 is fixed, when the other end (tensioning end) of the tendon 1 is pulled, a longitudinal tensile force (also referred to as tensioning force) is applied to the tendon 1 and stress corresponding thereto occurs within the tendon 1. The tendon 1 stretches in proportion to the stress and cross-sectional contraction occurs (the diameter of the tendon 1 contracts). In FIG. 3A, the tendon 1 (its thickness) before being pulled in the longitudinal direction is indicated by broken lines.

[0093] As shown in FIGS. 2 and 3A, PC grout 15 fills the sleeve 7 with the tendon 1 kept in a tensioned state. Referring to FIG. 2, the PC grout 15 fills not only the sleeve 7 but also the sheath tube 5.

[0094] Referring to FIGS. 2 and 3B, after the PC grout 15 is cured and a predetermined strength is expressed, the tension within the tendon 1 by the tensioning device is released. The tendon 1, when applied with tension by the tensioning device, stretches in the longitudinal direction (axial direction) and thereby tensile strain occurs in the longitudinal direction. When the tension within the tendon 1 is released, a Poisson effect occurs in the tendon 1 and expansive strain by the Poisson's ratio occurs circumferentially outward of the tendon 1 (in the direction perpendicular to the axis), whereby the tendon 1 expands circumferentially outward. That is, comparing FIGS. 3A and 3B, when the tension within the tendon 1 is released, the tendon 1 contracts in the longitudinal direction (L1>L2), while expands in the radial direction (D1<D2). It is noted that how the tendon 1 contracts and expands is drawn with considerable emphasis in FIGS. 3A and 3B. As a result, as schematically shown in FIG. 3B, predetermined compression stress 18 occurs in the PC grout 15 filling the clearance gap between the tendon 1 and the sleeve 7. This compression stress 18 causes the tendon 1 to be anchored reliably to the sleeve 7. In addition, since the tension within the tendon 1 is released and the tendon 1 contracts in the longitudinal direction, the locknut 8 threadably coupled to the upper end portion of the sleeve 7 is urged against the bearing plate 3 (tensioning reaction force) and pre-stress occurs in the concrete structure 2. The tendon 1 is thus anchored reliably within the concrete structure 2 and the structural performance of the concrete structure 2 is improved with the pre-stress introduced.

[0095] Specific examples of a concrete structure introduced with pre-stress will hereinafter be described with reference to FIGS. 4 to 10.

FIRST EXAMPLE

[0096] FIG. 4 shows a first example, illustrating in detail examples of a fixing device and a tensioning device for applying tension to a tendon. FIG. 4 does not show a sheath tube that is provided to allow an insertion hole within the concrete structure.

[0097] Referring to the left part in FIG. 4, the fixing device includes a bearing plate 23A provided at one end (left end in FIG. 4) of the concrete structure 22, a locknut 28A, a ram chair 38, an anchor head 39, a friction sheet and blade net 41, and a wedge 40. A sleeve 27A is inserted through a sheath tube (insertion hole) that is embedded in the concrete structure 22, and a tendon 21 is inserted through the sleeve 27A. The sleeve 27A is inserted through the through hole of the bearing plate 23A, and a leading end portion thereof is put on the outside of the bearing plate 23A. The locknut 28A is threadably mounted on the leading end portion of the sleeve 27A that is put on the outside of the bearing plate 23A.

[0098] The ram chair 38 is installed on the bearing plate 23A in a manner surrounding the locknut 28A. The ram chair 38 has an insertion hole at its center through which the tendon 21 is inserted, and a leading end portion (fixing end) of the tendon 21 is inserted through the insertion hole of the ram chair 38 and put on the outside of the ram chair 38.

[0099] The anchor head 39 is installed on the ram chair 38. The anchor head 39 has an insertion hole through which the leading end portion of the tendon 21 is inserted and a hollow space tapered for wedge into which the wedge 40 is pushed. The leading end portion of the tendon 21 that is put on the outside of the ram chair 38 is inserted through the insertion hole and the hollow space of the anchor head 39 to extend out of the anchor head 39. The friction sheet and blade net 41 is wound around the leading end portion of the tendon 21 that is put on the outside of the anchor head 39 and the exterior thereof is covered with the wedge 40, and the leading end portion of the tendon 21 covered with the wedge 40 is pushed into the hollow space of the anchor head 39. The leading end portion of the tendon 21 is anchored reliably within the hollow space tapered for wedge of the anchor head 39.

[0100] The friction sheet and blade net 41 is put on the outer peripheral surface of the leading end portion of the tendon 21 covered with the wedge 40 to reduce the clamping force of the wedge 40 against the tendon 21.

[0101] Referring to the right part in FIG. 4, the tensioning device includes a bearing plate 23B provided at the other end (right end in FIG. 4) of the concrete structure 22, a locknut 28B, ram chairs 31, 32, a ring nut 33, an expansion material filling sleeve 34, a tension bar 35, a center hole tensioning jack 36, a wedge 42, and an anchor head 43.

[0102] A sleeve 27B is inserted through an insertion hole of the concrete structure 22, and a tendon 21 is inserted through the sleeve 27B. The sleeve 27B is inserted through the through hole of the bearing plate 23B and put on the outside of the bearing plate 23B. The locknut 28B is threadably mounted on the leading end portion of the sleeve 27B that is put on the outside of the bearing plate 23B.

[0103] The first ram chair 31 is installed on the bearing plate 23B in a manner surrounding the locknut 28B. The first ram chair 31 has an insertion hole at its center through which the tendon 21 is inserted, and a leading end portion (tensioning end) of the tendon 21 is inserted through the insertion hole of the first ram chair 31 and put on the outside of the first ram chair 31.

[0104] The expansion material filling sleeve 34 is fabricated in a factory and provided on the leading end portion of the tendon 21 that is put on the outside of the first ram chair 31. Expansion material fills the expansion material filling sleeve 34 and provides expansion pressure of the expansion material to anchor the expansion material filling sleeve 34 reliably to the leading end portion of the tendon 21. The outer peripheral surface of the expansion material filling sleeve 34 is threaded, through which the ring nut 33 is fixed to the expansion material filling sleeve 34.

[0105] The second ram chair 32 is overlaid on the first ram chair 31 in a manner surrounding the ring nut 33 and the expansion material filling sleeve 34. The second ram chair 32 also has an insertion hole at its center through which the tendon 21 is inserted, and a leading end portion (tensioning end) of the tendon 21 is inserted through the insertion hole of the second ram chair 32 and put on the outside of the second ram chair 32.

[0106] The center hole tensioning jack 36 is installed on the second ram chair 32. After the installation of the center hole tensioning jack 36, the tension bar 35 is engaged with the inner thread of the expansion material filling sleeve 34. The leading end portion of the tendon 21 passes through the center hole tensioning jack 36 to be anchored to the leading end of the ram of the center hole tensioning jack 36 using the wedge 42 and the anchor head 43. When the center hole tensioning jack 36 is actuated and the tendon 21 is applied with tension, the center hole tensioning jack 36 moves away from the second ram chair 32. Since the center hole tensioning jack 36 is connected with the above-described expansion material filling sleeve 34 by the tension bar 35, the expansion material filling sleeve 34 also moves away from the first ram chair 31 by the tension bar 35. When a predetermined tensioning force is applied to the tendon 21, the ring nut 33 that is placed on the outer peripheral surface of the expansion material filling sleeve 34 is fastened and thereby fixed and anchored to the first ram chair 31. When the ring nut 33 is fastened, the tensioning force is maintained at the tensioning end by the first ram chair 31, the expansion material filling sleeve 34, and the ring nut 33. Thereafter, the center hole tensioning jack 36 is de-actuated, the center hole tensioning jack 36, the tension bar 35, and the second ram chair 32 can be uninstalled. The center hole tensioning jack 36, the tension bar 35, and the second ram chair 32, after uninstalled, can be used to apply tension to a tendon 21 at another location.

[0107] PC grout fills the insertion hole (sheath tube) of the concrete structure 22 with the tendon 21 kept in a tensioned state. The PC grout also fills the sleeves 27A, 27B. Before filling with the PC grout, seal may be applied around the bearing plates 23A, 23B so that the PC grout cannot leak out of the bearing plates 23A, 23B. After the PC grout is cured and a predetermined strength occurs, the tendon 21 is cut off in the vicinity of the locknut 28A, 28B and thereby the tension is released. As described above, when the tensioning force is released, predetermined compression stress occurs in the PC grout filling the clearance gap between the tendon 21 and the sleeves 27A, 27B, and the compression stress causes the tendon 21 to be anchored reliably to the sleeves 27A, 27B. In addition, tensioning stress is introduced into the concrete structure 22 via the bearing plates 23A, 23B.

SECOND EXAMPLE

[0108] FIG. 5 is a cross-sectional view showing how pre-stress is introduced into a concrete foundation structure using a post-tensioning system. Also in FIG. 5, a sheath tube is not shown. This presents an anchoring construction method that is hard to achieve with a related-art method and can specifically be utilized, for example, as a construction method for efficiently and reasonably anchoring a steel tower portion of a power transmission tower foundation to a concrete foundation.

[0109] FIG. 5 is a vertical cross-sectional view of a portion of a columnar or rectangular concrete foundation structure 52. The concrete foundation structure 52 shown in FIG. 5 is embedded in the ground and has an elongated shape in the depth (vertical) direction.

[0110] The concrete foundation structure 52 shown in FIG. 5 is a pre-stressed concrete foundation structure in which pre-stress is introduced in the vertical direction. Power transmission tower foundations have conventionally and frequently employed rebar-reinforced concrete structures. However, a pre-stressed concrete structure may be employed with the view to an improvement in the performance and/or functionality.

[0111] The foundation base plate 55 of the concrete foundation structure 52 shown in FIG. 5 corresponds to the above-described bearing plate, not including separate bearing plates provided correspondingly for the respective tendons but including a single thickened bearing plate used in common with the multiple tendons. The foundation base plate 55 plays another role. That is, a power transmission tower foundation truss (a columnar pipe or an angle bar, for example, is used) is welded onto the foundation base plate 55 via a reinforcement plate such as a shear plate (not shown). Since the power transmission tower is applied with a group of loads including its own dead load, wind load, earthquake load, etc. that acts on the wires and/or the tower, it is necessary to transmit such an external force to the concrete foundation structure built in the ground to thereby maintain the stability of the foundation with a reaction force from the ground. That is, a strong cross-sectional force such as a horizontal shear force, a pull-out force, and a bending moment acts on the foundation base plate that is installed on the concrete foundation through the tower foundation truss.

[0112] As a method for anchoring a steel truss tower to a concrete foundation, there has conventionally been employed a construction type in which an anchor-shaped steel truss reinforced with a shear plate at the leading end of the steel truss tower is embedded directly into a cast-in-place concrete foundation and reinforced therearound with reinforcing steel bars to integrate the tower foundation truss and the concrete foundation.

[0113] In the related-art anchor foundation type, since the anchor portion is installed in an inclined manner into the concrete foundation, it is very difficult to ensure accuracy for the installation. It is particularly necessary to install the steel truss tower not vertically but in an inclined manner and further at an installation accuracy of as high as 3 to 5 mm. This suffers from some problems that a specialized installation technique that only a limited number of construction vendors can support is required and that it results in an increase in the installation cost.

[0114] The foundation base plate 55 shown in FIG. 5 has a structure installed horizontally and directly on the upper surface of the concrete foundation structure 52 and directly utilizing tensioning forces within the tendons 51 to resist various active loads from the upper part of the power transmission tower. The power transmission tower truss is fabricated in a manner inclined with respect to the foundation base plate 55. A tensile force, a shear force, and a bending moment then act on the foundation base plate 55 as a major cross-sectional force.

[0115] A working procedure for introducing pre-stress into the concrete foundation structure 52 shown in FIG. 5 will be described in sequence and also the synergy with the present invention.

[0116] The fixing end portion of each of the tendons 51 will first be described. In the concrete foundation 52 shown in FIG. 5, the fixing end of the tendon 51 is not fixed by a fixing device. That is, the insertion hole (sheath tube) through which the tendon 51 is inserted is not formed entirely from one end (upper end) to the other end (bottom end) of the concrete foundation 52, but formed to a middle portion of the concrete foundation 52. This is for the reason that since the bottom surface of the concrete foundation 52 shown in FIG. 5 is in contact with the supporting ground, even if the sheath tube may be inserted to the bottom surface of the concrete foundation 52, there is no space or working space to anchor the tendon 51 to the concrete foundation 52 using a fixing device.

[0117] There has been an untwisting-type anchorage (Japanese Patent No. 6442104) practiced as a structure for anchoring one end (fixing end) of a tendon 51 within a sheath tube (insertion hole) provided in a concrete foundation 52. The untwisting-type anchorage 53 is obtained by untwisting the twisted side strands (loosening the twisted side strands) that form the tendon 51 along a predetermined length and filling the clearance gap (space) formed thereby with resin mortar or cement mortar. The tendon 51 is inserted through the untwisting-type anchorage 53 formed at one end into the sheath tube provided in the concrete foundation structure 52. Before tensioning of the tendon 51, PC grout 56 fills the space around the untwisting-type anchorage 53 to thereafter be cured. With strength expression in the PC grout 56, the one end portion (fixing end) of the tendon 51 is anchored (fixed) reliably to the concrete foundation 52.

[0118] Before the tendon 51 is inserted into the sheath tube, the foundation base plate 55 is installed. The foundation base plate 55 plays a role as a bearing plate as well as of fixing the tower foundation truss to transmit a cross-sectional force acting on the tower foundation truss to the concrete foundation. That is, a shear force and a pull-out force act on the foundation base plate 55.

[0119] The tendon 51 is applied with upward tension using a tensioning device described with reference to FIG. 4. After tensioning operations for all the tendons 51, PC grout (not shown) fills the sheath tubes and the sleeves 57 to thereafter be cured. After strength expression in the PC grout, the tensioning forces are released. As mentioned above, since the sleeves 57 are anchored reliably to the tendons 51, the tensioning forces are transmitted through the locknuts 58 engaged with the sleeves 57 to the foundation base plate 55, whereby the foundation base plate 55 is urged against the upper surface of the concrete foundation 52 and thus pre-stress is introduced into the entire concrete foundation 52. In addition, predetermined compression stress occurs in the PC grout filling the clearance gap between the tendons 51 and the sleeves 57, and the compression stress causes the tendons 51 to be anchored reliably to the sleeves 57.

[0120] The present invention being applied, the concrete foundation 52 shown in FIG. 5 can show a more critical synergy. As mentioned above, a shear force and a pull-out force act on the foundation base plate 55. First, if the acting drawing force is weaker than the sum of the tensioning forces, the foundation base plate 55 cannot be deformed upward according to the principle of pre-stress. It is therefore only required to set a design tensioning force greater than the maximum pull-out force.

[0121] Next is a resistance mechanism of the foundation base plate 55 by a shear force. Since compression stress due to the tensioning forces acts between the foundation base plate 55 and the upper surface of the concrete foundation 52, the product of the compression stress and the friction coefficient therebetween serves as a shear resistance. Further, in a method for increase in the shear resistance, convex portions such as, for example, round steels protrude from the lower surface of the foundation base plate 55 as shear keys 59, while recessed portions are provided in the upper surface of the receiving concrete foundation 52, such that the convex portions and the recessed portions are engaged with each other. This allows the sum of (the cross-sectional area of each convex portion)×(the shear resistance stress of each convex portion) to be considered as shear resistance (design resistance).

[0122] It is noted that before installation of the foundation base plate 55, filler/curing agent such as epoxy resin or grout mortar may be put in the recessed portions so that the convex portions and the recessed portions are in constant contact with each other.

THIRD EXAMPLE

[0123] FIG. 6 shows a case where an example according to the present invention is applied a PC composite bridge. The PC composite bridge is a pre-stressed concrete bridge constructed by fabricating a main girder portion and a floor slab portion forming the pre-stressed concrete bridge separately on site or in a PC factory and, in a working field, first installing the main girder portion and thereon the floor slab portion and then joining the main girder portion and the floor slab portion.

[0124] Referring to FIG. 6, the PC composite bridge shown in FIG. 6 includes an I-shaped main girder portion 63 and a floor slab portion 66 fixed on the upper surface of the main girder portion 63. It is noted that the main girder portion 63 may have not only an I shape but also a U shape, to both of which the technique according to the present invention is applicable. A tendon can be used for (1) joint between the main girder portion 63 and the floor slab portion 66, (2) shear reinforcement by vertical tensioning of the main girder portion 63, and (3) a shear reinforcement bar of the main girder portion 63.

[0125] The main girder portion 63 includes a web 63A extending straight-forward vertically, a head portion 63B formed integrally with the upper surface of the web 63A, and a leg portion 63C formed integrally with the lower surface of the web 63A. A sheath tube (not shown) is provided in the web 63A and the head portion 63B, and a vertically extending insertion hole is ensured by the sheath tube. On the other hand, the sheath tube (insertion hole) is provided to a middle portion of the leg portion 63C.

[0126] A box-shaped portion (recessed portion) 60 is formed in the upper surface of the floor slab portion 66, and a bearing plate 69 with a through hole opened therein is installed on the bottom surface of the box-shaped portion 60. The sheath tube is inserted from the bearing plate 69 to the lower surface of the floor slab portion 66 to ensure an insertion hole.

[0127] After multiple main girder portions 63 are provided with spacing therebetween, a vent (temporary bridge pier) (not shown) is provided between adjacent ones of the main girder portions 63. After the multiple main girder portions 63 and the multiple vents are joined and applied with tension in the bridge axial direction, the floor slab portions 66 are installed. Upon installation of the floor slab portion 66, sealing materials 64A are provided on either side of the upper surface of the main girder portion 63 and non-shrink mortar 64B is placed between the sealing materials 64A, onto which the floor slab portion 66 is installed (wet-joint construction method). A tendon 61 with a sleeve 67 and a locknut 68 provided in one end portion thereof and a factory-processed untwisting-type anchorage 62 provided at the other end thereof is inserted through the box-shaped portion 60 of the floor slab portion 66 into the sheath tube of the main girder portion 63. The untwisting-type anchorage 62 at the other end of the tendon 61 reaches the leg portion 63C of the main girder portion 63. Before tensioning of the tendon 61, PC grout 65 fills the space around the untwisting-type anchorage 62. With strength expression in the PC grout 65, the other end portion (fixing end) of the tendon 61 is fixed reliably to the main girder portion 63, as described with reference to FIG. 5. Thereafter, with the same construction method as that described with reference to FIG. 5, the tendon 61 is applied with upward tension using a tensioning device. With the tendon 61 in a tensioned state, PC grout fills the sheath tube and the sleeve 67 to thereafter be cured. After strength expression in the PC grout, the tension within the tendon 61 is released. Predetermined compression stress occurs in the PC grout filling the clearance gap between the tendon 61 and the sleeve 67, and the compression stress causes the tendon 61 to be anchored reliably to the sleeve 67. In addition, tensioning load is transmitted to the locknut 68 and the bearing plate 69, whereby pre-stress is introduced into the floor slab portion 66 and the main girder portion 63.

[0128] In this third example, synergies with the present invention are as follows.

(1) First Synergy

[0129] In this third example, pre-stress is required to be distributed in the wet-joint portions 64A, 64B between the floor slab portion 66 and the upper end portion of the main girder portion 63. In the present invention, since the bearing plate 69 has an effect of distributing a tensioning force, required pre-stress can be looked for in the wet-joint portions 64A, 64B. In addition, since the bearing plate 69 can achieve a significantly small-sized structure compared to related-art tensioning end portions, anchoring jigs can be accommodated within the floor slab portion 66.

(2) Second Synergy

[0130] The tendon 61 within the main girder portion 63 contributes to the joint between the main girder portion 63 and the floor slab portion 66. Further, the tendon 61 is arranged vertically along the web 63A, with the ends thereof being anchored to the concrete (the floor slab portion 66 and the main girder portion 63), to effectively serve as a shear reinforcement bar. In general, shear reinforcement bars are disadvantageous in that a bending hook or the like is required for concrete anchoring to result in a need for additional processing cost and/or extra length for anchoring, that is, additional material cost. In this third example, shear reinforcement can be provided only with the straight portion of the tendon 61, leading to cost reduction.

(3) Third Synergy

[0131] There are three methods for shear reinforcement of the main girder portion 63: (i) arranging a shear reinforcement bar, (ii) applying tension to the main girder portion 63 in the bridge axial direction, and (iii) applying vertical tension to the main girder portion 63. Among these methods, (i) method of arranging a shear reinforcement bar is most frequently employed due to its working easiness and the like. (ii) Method of applying tension in the bridge axial direction is the second most-employed one. In a pre-stressed concrete bridge, tension is naturally applied in the bridge axial direction and thereby a shear reinforcement effect can necessarily be expected. (iii) Shear reinforcement method of applying vertical tension to the web 63A is hardly employed for the reason that it has working difficulty. However, in this third example, the vertical tensioning effect that is applied to the joint between the main girder portion 63 and the floor slab portion 66 can be taken into design consideration as a shear reinforcement effect of the main girder portion 63. The vertical tensioning effect can significantly increase load capacity against shear force and/or occurrence of oblique crack as well as reduce the width of oblique crack.

FOURTH EXAMPLE

[0132] FIGS. 7 to 10 show processes of manufacturing a pre-stressed concrete structure member using a pre-tensioning system. FIGS. 7 to 9 show layouts in a side view of a PC production line in a PC factory for manufacturing a pre-stressed concrete structure member. FIG. 10 is a partially broken plan view showing an enlarged version of one end portion of the concrete structure member shown in FIG. 8.

[0133] In a general PC production line using a pre-tensioning system, an abutment for taking a reaction force of a tensioning force is provided and the tensioning force undergo fixing anchoring and tension anchoring, respectively, on the fixing side and the tensioning side to manufacture a PC concrete member using a pre-tensioning system. The fixing anchoring and the tension anchoring are here conventionally implemented and will not be described herein.

[0134] In a general pre-tensioning system, such a locknut-and-bearing-plate 75 and a sleeve 73 as shown in FIGS. 7 to 9 do not be provided in a member end portion. Accordingly, upon releasing a tensioning force in a member end portion, out-of-adhesion may occur between the tendon 71 and the concrete to result in that (i) if the tendon 71 is a PC steel strand (the diameter of the PC steel strand is represented by φ), it is impossible to expect pre-stress introduction from the end portion to the point of 65φ and (ii) if the tendon 71 is a continuous fiber-reinforced polymer strand (the diameter of the continuous fiber-reinforced polymer strand is represented by φ), it is difficult to expect pre-stress introduction from the end portion to the point of 50φ.

[0135] The example of manufacturing a pre-stressed concrete structure member using a pre-tensioning system shown in FIGS. 7 to 9 is directed to the case where the member has a relatively small length. This is for the reason that since as described above, presetting the locknut-and-bearing-plate 75 and the sleeve 73 according to the present invention allows pre-stress to occur in the member end portion, effective pre-stress can be expected over the entire length of the member even if the member may be relatively short.

[0136] A working method according of a fourth example will be described. Basically, multiple (three in FIGS. 7 to 9) formworks 70 are arranged in line with spacing therebetween on a base, and a set of locknut-and-bearing-plate 75 and sleeve 73 engaged therewith is arranged in a manner contacting closely to each of the lateral end portions within each formwork 70. The tendon 71 is inserted so as to penetrate all the three formworks 70. The tendon 71 is inserted through the hollow spaces of all the sleeves 73 and the through holes of all the locknut-and-bearing-plates 75 that are arranged in lateral end portions within the formworks 70. It goes without saying that holes through which the tendon is inserted are opened in lateral end portions within the formworks 70. It is noted that the sleeve 73 is formed with a PC grout filling port and an air discharge port as will be described below.

[0137] Referring to FIG. 7, a tensioning abutment 76 and a tensioning jack 78 are provided at one end (tensioning end) (right part in FIG. 7) of the tendon 71 put on the outside of one of the three formworks 70 located at one end (right end in FIG. 7). Also, a fixing abutment 77 and a fixing device 79 are provided at the other end (fixing end) (left part in FIG. 7) of the tendon 71 put on the outside of one of the three formworks 70 located at the other end (left end in FIG. 7). With the other end being fixed by the fixing device 79, when the one end of the tendon 71 is pulled by the tensioning jack 78, a predetermined tensioning force is introduced into the tendon 71.

[0138] Referring to FIG. 10, a PC grout filling port 73a and an air discharge port 73b are opened in the sleeve 73. PC grout (not shown) fills the sleeve 73 through the PC grout filling port 73a and air within the sleeve 73 is discharged through the air discharge port 73b. This causes the PC grout to fill the clearance gap between the sleeve 73 and the tendon 71 inserted through the sleeve 73.

[0139] Referring to FIG. 8, after the PC grout filling the sleeve 73, concrete 72 is placed within the formworks 70. The PC grout and the concrete 72 are cured until expression of a predetermined strength.

[0140] Referring to FIG. 9, after the PC grout and the concrete 72 reaching a predetermined strength, the tendon 71 is released on either outside of each formwork 70. The tensioning force within the tendon 71 is loosened (released) and pre-stress is introduced into the concrete 72 within each formwork 70. In addition, predetermined compression stress occurs in the PC grout filling the clearance gap between the tendons 71 and the sleeves 73, and the compression stress causes the tendons 71 to be anchored reliably to the sleeves 73. Thereafter, when the formworks 70 are removed, a concrete structure (pre-tensioned member) into which pre-stress is introduced using a pre-tensioning system is completed.

[0141] With the foregoing series of operations, even a short member can be introduced efficiently with tensioning stress equally through the end portions thereof. In fabrication of a general pre-tensioned member, since there is a risk for the occurrence of fracturing cracks in a member end portion, the tendon is unbonded by a length of 20 to 30φ in the member end portion. Comparatively, in this case, since the locknut-and-bearing-plates 75 are provided in the end portions, such a risk cannot occur.

Comparison with Existing Techniques
(1) Post-tensioning System with Bearing Plate and Expansion Material Sleeve

[0142] Existing techniques suffer from three problems as described above under the foregoing condition.

(i) Limitation on Tensioning of Lengthy Structure

[0143] To address this problem, in the present invention, the expansion material sleeve used for tensioning, which is eventually removed from the tensioning end portion of the structure, has an increased length and/or multiple expansion material sleeves are provided, and tensioning load by the tensioning jack is changed to get rid of the limitation on the length of the tendon. That is, in the present invention, since anchoring the tendon of the continuous fiber-reinforced polymer strand is eventually completed with the sleeve and the locknut engaged with the sleeve, upon completion, only the locknut of the anchoring portion can protrude from the tensioning end portion as shown in FIG. 1 or the anchoring portion cannot protrude at all as shown in FIG. 6.

(ii) Protrusion of Tensioning End Portion

[0144] In the present invention, the anchorage of the tensioning end portion and/or the fixing end portion can basically fulfill their functions within the concrete structure as shown in FIG. 1. In addition, the locknut can be thinned through creative design. As shown in FIG. 6, a box-shaped portion may be provided so that a component is accommodated within the concrete not to protrude at the end portion.

(iii) Adjustment of Tendon Length

[0145] On working site, the length of a tensioning target is sometimes required to be changed for various reasons. There are two coping methods according to the present invention.

Method A

[0146] The expansion material sleeve is fabricated to have an increased length. Since the ram chair shown in FIG. 4 can be divided into several pieces, the length of the ram chair is adjusted as appropriate, so that the factory-fabricated expansion material sleeve can be utilized adequately.

Method B

[0147] No factory-fabricated expansion material sleeve is used. The tendon of the continuous fiber-reinforced polymer strand, when carried into the site, is cut into a necessary length on site. The method of anchoring of the fixing end portion and the tensioning end portion basically employs the system including a friction sheet, a blade net, and a wedge as shown in FIG. 4. This method allows the anchoring position to be determined according to the on-site working conditions, which makes it possible to respond to a change in the length of the tendon. Even in such a case, applying the present invention allows the tension anchoring position to be set arbitrarily at the working end face, providing no working limitation.

(2) Pre-Tensioning System

[0148] Problems concerning the pre-tensioning system are as described above. To address these problems, in the present invention, even a short member can be introduced with predetermined pre-stress between the end portions as described above. It is also possible to eliminate a risk of splitting crack occurrence in a member end portion, which has been a working risk in the case of a related-art pre-tensioning system.