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.

What is claimed is: 
     
         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.