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Technical Features of External Prestressing
- Facilitating of concrete placing due to the absence of tendons in the webs, and ease for placing tendons.
- Improvement of conditions for tendon installation which can take place independently from the concrete works.
- Reduction of friction losses, because the unintentional angular changes, known as wobble, are practically eliminated. Furthermore, in case of the use of a polyethylene sheathing the friction coefficient is drastically reduced compared to standard internal and bonded prestressing using corrugated sheat metal ducts.
- Generally the webs can be made thinner, resulting in an overall lighter structure
- As an overall result, better concrete quality can be obtained leading to a more durable structure and facilitating execution.
Typical Applications for External Prestressing
Typical applications where external tendons are feasible, practical and economical, are:
- Repair work and strengthening of all kinds of structures
- Underslung structures - Precast segmental construction simple and continuous spans - Incremental launching procedure, in particular centric prestressing
The PBL multi strand anchorage systems can be used for external prestressing tendon
- The tendon is formed from plain 0.5” or 0.6” dia. strands according to ASTM 416 or BS standard
- The duct is from high density polyethylene and continuous from one anchorage to the other. The Tendon sheathing passes freely through intermediate diaphragms, respectively deviators, whereby a metal or HDPE sleeve provides the required reservation opening.
- A standard PBL multi strand anchorage assembly consisting of anchor head, wedges, anchor plate casting safely transfers the prestressing force to the end cross-beam
- The tendon is filled with cement grout after it has been tensioned. As no double pipe is provided at the anchor points through the end-diaphragms a certain bond between tendon and structure is created which hinders the replaceability. Depending on requirements, the anchor head may be protected by a cap, or alternatively the anchorage recess is filled with non-shrinkage concrete.
PBL GROUP LTD. PBL Group Building 8/11 Soi Vipavadi 44 Vipavadi Rangsit
Road, Jatujak, Bangkok 10900