際際滷

際際滷Share a Scribd company logo

Post-tensioning in Prestressed Concrete

D
Davinderpal Singh

This document discusses post-tensioning devices and systems. Post-tensioning involves applying tension to tendons placed in ducts within hardened concrete. There are two main types: bonded uses grout in the ducts while unbonded does not. Key devices include ducts, anchoring devices, jacks and optional couplers and grouting equipment. Common anchoring principles are wedge action, direct bearing and looping wires. More than 64 post-tensioning systems have been patented worldwide with the Freyssinet system most common in India.

1 of 32
POST-TENSIONING DEVICES AND SYSTEMS PRESENTATION BY- DAVINDERPAL SINGH
POST-TENSIONING THE TENSION IS APPLIED TO THE TENDONS AFTER HARDENING OF THE CONCRETE. MINIMUM GRADE OF CONCRETE USED IS 30 MPa. DUCTS ARE PROVIDED IN THIS TYPE OF PRESTRESSING.
POST-TENSIONING IN POST-TENSIONING SYSTEMS, THE TENDONS ARE PLACED IN DUCTS AFTER THE CASTING OF CONCRETE. THE DUCT PREVENTS BOND BETWEEN CONCRETE AND THE TENDONS DURING THE TENSIONING OPERATION. UNLIKE PRE-TENSIONING, THE TENDONS ARE PULLED WITH THE REACTION ACTING AGAINST THE HARDENED CONCRETE.
POST-TENSIONING TYPES IF THE DUCTS PROVIDED ARE GROUTED THEN IT IS CALLED BONDED POST-TENSIONING. AND IF DUCTS ARE NOT GROUTED THEN IT IS CALLED UNBONDED POST-TENSIONING. TENDON IS HELD IN POSITION BY END ANCHORAGES.
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
POST-TENSIONING STAGES The various stages of the post-tensioning operation are summarised as follows. 1) Casting of concrete. 2) Placement of the tendons. 3) Placement of the anchorage block and jack. 4) Applying tension to the tendons. 5) Seating of the wedges. 6) Cutting of the tendons.
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
POST-TENSIONING STAGES
POST-TENSIONING ADVANTAGES The relative advantages of post-tensioning as compared to pre-tensioning are as follows. Post-tensioning is suitable for heavy cast-in- place members. The waiting period in the casting bed is less. The transfer of prestress is independent of transmission length.
POST-TENSIONING DISADVANTAGES The relative disadvantage of post-tensioning as compared to pre-tensioning is the requirement of anchorage device and grouting equipment.
DEVICES The essential devices for post-tensioning are as follows. 1) Casting bed 2) Mould/Shuttering 3) Ducts 4) Anchoring devices 5) Jacks 6) Couplers (optional) 7) Grouting equipment (optional)
ANCHORAGE DEVICES In post-tensioned members the anchoring devices transfer the prestress to the concrete. The devices are based on the following principles of anchoring the tendons. 1) Wedge action 2) Direct bearing 3) Looping the wires
WEDGE ACTION The anchoring device based on wedge action consists of an anchorage block and wedges. The strands are held by frictional grip of the wedges in the anchorage block. Some examples of systems based on the wedge-action are Freyssinet, Gifford-Udall, Anderson and Magnel- Blaton anchorages
18
Post-tensioning in Prestressed Concrete
DIRECT BEARING The rivet or bolt heads or button heads formed at the end of the wires directly bear against a block. The B.B.R.V post-tensioning system and the Prescon system are based on this principle.
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
LOOPING THE WIRES The Baur-Leonhardt system, Leoba system and also the Dwidag single-bar anchorage system, work on this principle where the wires are looped around the concrete. The wires are looped to make a bulb.
Post-tensioning in Prestressed Concrete
COUPLERS The couplers are used to connect strands or bars. They are located at the junction of the members, for example at or near columns in post-tensioned slabs, on piers in posttensioned bridge decks. The couplers are tested to transmit the full capacity of the strands or bars.
Post-tensioning in Prestressed Concrete
MORE THAN 64 SYSTEMS HAVE BEEN PATENTED ACROSS THE WORLD. FREYSSINET SYSTEM IS COMMONLY USED IN INDIA.
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
Post-tensioning in Prestressed Concrete
31
Post-tensioning in Prestressed Concrete

More Related Content

Post-tensioning in Prestressed Concrete

  • 2. POST-TENSIONING THE TENSION IS APPLIED TO THE TENDONS AFTER HARDENING OF THE CONCRETE. MINIMUM GRADE OF CONCRETE USED IS 30 MPa. DUCTS ARE PROVIDED IN THIS TYPE OF PRESTRESSING.
  • 3. POST-TENSIONING IN POST-TENSIONING SYSTEMS, THE TENDONS ARE PLACED IN DUCTS AFTER THE CASTING OF CONCRETE. THE DUCT PREVENTS BOND BETWEEN CONCRETE AND THE TENDONS DURING THE TENSIONING OPERATION. UNLIKE PRE-TENSIONING, THE TENDONS ARE PULLED WITH THE REACTION ACTING AGAINST THE HARDENED CONCRETE.
  • 4. POST-TENSIONING TYPES IF THE DUCTS PROVIDED ARE GROUTED THEN IT IS CALLED BONDED POST-TENSIONING. AND IF DUCTS ARE NOT GROUTED THEN IT IS CALLED UNBONDED POST-TENSIONING. TENDON IS HELD IN POSITION BY END ANCHORAGES.
  • 7. POST-TENSIONING STAGES The various stages of the post-tensioning operation are summarised as follows. 1) Casting of concrete. 2) Placement of the tendons. 3) Placement of the anchorage block and jack. 4) Applying tension to the tendons. 5) Seating of the wedges. 6) Cutting of the tendons.
  • 13. POST-TENSIONING ADVANTAGES The relative advantages of post-tensioning as compared to pre-tensioning are as follows. Post-tensioning is suitable for heavy cast-in- place members. The waiting period in the casting bed is less. The transfer of prestress is independent of transmission length.
  • 14. POST-TENSIONING DISADVANTAGES The relative disadvantage of post-tensioning as compared to pre-tensioning is the requirement of anchorage device and grouting equipment.
  • 15. DEVICES The essential devices for post-tensioning are as follows. 1) Casting bed 2) Mould/Shuttering 3) Ducts 4) Anchoring devices 5) Jacks 6) Couplers (optional) 7) Grouting equipment (optional)
  • 16. ANCHORAGE DEVICES In post-tensioned members the anchoring devices transfer the prestress to the concrete. The devices are based on the following principles of anchoring the tendons. 1) Wedge action 2) Direct bearing 3) Looping the wires
  • 17. WEDGE ACTION The anchoring device based on wedge action consists of an anchorage block and wedges. The strands are held by frictional grip of the wedges in the anchorage block. Some examples of systems based on the wedge-action are Freyssinet, Gifford-Udall, Anderson and Magnel- Blaton anchorages
  • 18. 18
  • 20. DIRECT BEARING The rivet or bolt heads or button heads formed at the end of the wires directly bear against a block. The B.B.R.V post-tensioning system and the Prescon system are based on this principle.
  • 23. LOOPING THE WIRES The Baur-Leonhardt system, Leoba system and also the Dwidag single-bar anchorage system, work on this principle where the wires are looped around the concrete. The wires are looped to make a bulb.
  • 25. COUPLERS The couplers are used to connect strands or bars. They are located at the junction of the members, for example at or near columns in post-tensioned slabs, on piers in posttensioned bridge decks. The couplers are tested to transmit the full capacity of the strands or bars.
  • 27. MORE THAN 64 SYSTEMS HAVE BEEN PATENTED ACROSS THE WORLD. FREYSSINET SYSTEM IS COMMONLY USED IN INDIA.
  • 31. 31