Early warning device and ductility control method for prestressed FRP reinforced structure

1. A tensioning screw early warning device for a prestressed FRP reinforced structure, comprising a fixing plate, an FRP strip having a first end and a second end, a self-locking plate having two sides, an anchoring plate having two sides that are oriented in a same direction as the two sides of the self-locking plate, at least one tensioning screw, a plurality of nuts and expansion bolts, wherein the fixing plate and the anchoring plate are located on the two sides of the self-locking plate; the first end of the FRP strip is fixedly connected to the fixing plate, and the second end of the FRP strip is fixedly connected to the self-locking plate; the at least one tensioning screw passes through the self-locking plate and the anchoring plate; the plurality of nuts are in threaded connection to the tensioning screw, and the plurality of nuts are configured to lock on the two sides of the self-locking plate and on the two sides of the anchoring plate; the expansion bolts are configured to fasten the fixing plate, the self-locking plate, and the anchoring plate on a concrete matrix; and a through hole for mounting one of the expansion bolts that is on the self-locking plate is an oblong hole, and the oblong hole is disposed in parallel with the tensioning screw.

2. A single-screw early warning device for a prestressed FRP reinforced structure, comprising a fixing plate, an FRP strip having a first end and a second end, a self-locking plate having two sides, an anchoring plate having two sides having two sides that are oriented in a same direction as the two sides of the self-locking plate, a tensioning screw, a plurality of nuts and expansion bolts, wherein the fixing plate and the anchoring plate are located on the two sides of the self-locking plate; the first end of the FRP strip is fixedly connected to the fixing plate, and the second end of the FRP strip is fixedly connected to the self-locking plate; the tensioning screw passes through the self-locking plate and the anchoring plate; the plurality of nuts are in threaded connection to the tensioning screw, and the plurality of nuts are configured to lock on the sides of the self-locking plate and on the two sides of the anchoring plate; the expansion bolts are configured to fasten the fixing plate, the self-locking plate, and the anchoring plate on a concrete matrix; and a through hole for mounting one of the expansion bolts that is on the self-locking plate is an oblong hole, and the oblong hole is disposed in parallel with the tensioning screw.

3. The single-screw early warning device for a prestressed FRP reinforced structure according to claim 2 , wherein both the fixing plate and the self-locking plate are provided with two strip-shaped grooves parallel to each other, the strip-shaped grooves are used for the FRP strip to pass through, and the first and second ends of the FRP strip are respectively fixedly connected to the fixing plate and the self-locking plate through a self-locking winding structure.

4. The single-screw early warning device for a prestressed FRP reinforced structure according to claim 3 , wherein the self-locking plate is T-shaped and comprises a connecting section and a fixing section, wherein the fixing section is perpendicular to the connecting section and is symmetrical about the connecting section, the connecting section is used for connecting the first end of the FRP strip to the fixing plate, the connecting section is provided with the strip-shaped grooves, and the fixing section is provided with the oblong hole.

5. The single-screw early warning device for a prestressed FRP reinforced structure according to claim 3 , wherein an edge of the FRP strip is a smooth transition structure.

6. The single-screw early warning device for a prestressed FRP reinforced structure according to claim 2 , wherein a center line of the FRP strip coincides with a center line of the tensioning screw.

7. The single-screw early warning device for a prestressed FRP reinforced structure according to claim 2 , wherein a length of the oblong hole is greater than twice a maximum elongation of the tensioning screw.

8. A ductility control method for a prestressed FRP reinforced structure, characterized by using the single-screw early warning device according to claim 2 and comprising:

S1. fastening the anchoring plate on the concrete matrix through the expansion bolt;

S2. fastening the first and second ends of the FRP strip on the fixing plate and the self-locking plate respectively; and

S3. passing the tensioning screw through the anchoring plate and the self-locking plate, passing one of the expansion bolts through a midpoint of an oblong hole on the self-locking plate and fastening the tensioning screw to the concrete matrix,

using a first of the nuts which is on said one of the expansion bolts to mutually lock the tensioning screw and the self-locking plate without tightening the first nut on the self-locking plate and, at the same time, tightening a second one of the nuts which is on said one of the expansion bolts on the fixing plate,

then, while applying a predetermined range of tensioning force, using a third one of the nuts to mutually lock the tensioning screw and the anchoring plate; and

then stopping application of the predetermined range of tensioning force.

9. The ductility control method for a prestressed FRP reinforced structure according to claim 8 , wherein step S2 both includes fastening the first and second ends of the FRP strip respectively on the fixing plate and the self-locking plate through in a self-locking winding manner.

10. A dual-screw early warning device for a prestressed FRP reinforced structure, comprising a fixing plate, an FRP strip having a first end and a second end, a self-locking plate having two sides, an anchoring plate having two sides that are oriented in a same direction as the two sides of the self-locking plate, a tensioning plate having two sides that are oriented in a same direction as the two sides of the self-locking plate, a tensioning screw, a plurality of nuts and expansion bolts, wherein the tensioning plate comprises a first tensioning plate and a second tensioning plate arranged in parallel; the fixing plate, the self-locking plate, the anchoring plate, and the tensioning plate are sequentially arranged from left to right; the first end of the FRP strip is fixedly connected to the fixing plate, and the second end of the FRP strip is fixedly connected to the self-locking plate; the tensioning screw passes through the self-locking plate, the anchoring plate, and the tensioning plate; the plurality of nuts are in threaded connection to the tensioning screw, and the plurality of nuts are configured to lock on the two sides of the self-locking plate, on the two sides of the anchoring plate, and on the two sides of the tensioning plate; the expansion bolts are configured to fasten the fixing plate, the self-locking plate, and the anchoring plate on a concrete matrix; and a through hole for mounting one of the expansion bolts that is on the self-locking plate is an oblong hole, and the oblong hole is disposed in parallel with the tensioning screw.

11. The dual-screw early warning device for a prestressed FRP reinforced structure according to claim 10 , wherein both the fixing plate and the self-locking plate are provided with two strip-shaped grooves parallel to each other, the strip-shaped grooves are used for the FRP strip to pass through, and the first and second ends of the FRP strip are fixedly connected to the fixing plate and the self-locking plate through a self-locking winding structure.

12. The dual-screw early warning device for a prestressed FRP reinforced structure according to claim 11 , wherein the self-locking plate is T-shaped and comprises a connecting section and a fixing section, wherein the fixing section is perpendicular to the connecting section and is symmetrical about the connecting section, the connecting section is used for connecting the first end of the FRP strip to the fixing plate, the connecting section is provided with the strip-shaped grooves, and the fixing section is provided with the oblong hole.

13. The dual-screw early warning device for a prestressed FRP reinforced structure according to claim 11 , wherein an edge of the FRP strip is a smooth transition structure.

14. The dual-screw early warning device for a prestressed FRP reinforced structure according to claim 10 , wherein a center line of the FRP strip coincides with a center line of the tensioning screw.

15. The dual-screw early warning device for a prestressed FRP reinforced structure according to claim 10 , wherein a length of the oblong hole is greater than twice a maximum elongation of the tensioning screw.

16. A ductility control method for a prestressed FRP reinforced structure, characterized by using the dual-screw early warning device according to claim 10 and comprising:

S1. fastening the anchoring plate on the concrete matrix through one of the expansion bolts;

S2. fastening the first and second ends of the FRP strip on the fixing plate and the self-locking plate respectively; and

S3. passing the tensioning screw through the self-locking plate, the anchoring plate, and the tensioning plate, mutually locking the tensioning screw and the self-locking plate by a first one of the nuts, and mutually locking the tensioning screw and the tensioning plate by a second one of the nuts;

S4. enlarging distance between the tensioning plate and the anchoring plate, thereby pulling the tensioning screw to apply a predetermined range of tensioning force, and mutually locking the tensioning screw and the anchoring plate by a third one of the nuts, and finally stopping the pulling; and

S5. mounting said one of the expansion bolts on the concrete matrix through the oblong hole of the self-locking plate, centering the expansion bolt in the oblong hole of the self-locking plate while said one the expansion bolt is unlocked and untightened, and then fastening the expansion bolt while centered in the oblong hole.

17. The method for improving ductility of the FRP reinforced structure and achieving overload early warning according to claim 16 , wherein step S2 includes fastening the first and second ends of the FRP strip respectively on the fixing plate and the self-locking plate in a self-locking winding manner.

18. The ductility control method for a prestressed FRP reinforced structure according to claim 16 , wherein step S4 includes enlarging the distance between the tensioning plate and the anchoring plate by a hydraulic jack.

19. The ductility control method for a prestressed FRP reinforced structure according to claim 16 , wherein step S4 includes passing a third tensioning screw through the tensioning plate and and mutually locking the third tensioning screw and the tensioning plate by a fourth one of the nuts, and enlarging the distance between the tensioning plate and the anchoring plate by pulling one end of the third tensioning screw away from the anchoring plate.