Unbonded Pt Slab Design

By Author: Darmesh
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Unbonded PT slab design is a single-strand system. Its applications include slabs-on-grade, structural mats and raft footings, circular fluid tanks and tilt up walls. Because the unbounded tendon is small in diameter as well as light and flexible, it can make maximum use of the entire depth of concrete slab, making it particularly well suited to thin slabs, and the time and the cost associated with grouting is eliminated.
Unbonded post-tensioned slab concrete differs from bonded Post Tensioned (Concrete) Slab by providing each individual cable permanent freedom of movement relative to the concrete. To achieve this, each individual tendon is coated with grease (generally lithium based) and covered by a plastic sheathing formed in an extrusion process. The transfer of tension to the concrete is achieved by the steel cable acting against steel Anchor Plate embedded in the perimeter of the slab. The main disadvantage over bonded post-tensioning is the fact that a cable can distress itself and burst out of the slab if damaged (such as during repair on the slab).
The advantages of this system-
The ability to individually ...
... adjust cables based on poor field conditions
The procedure of post-stress grouting is eliminated.
The ability to de-stress the Tendons before attempting repair work.
The ability to achieve longer clear spans.
Unbonded post-tensioning tendons are commonly used in parking garages as barrier cable. Also, due to its ability to be Stressing and then de-stressed, it can be used to temporarily repair a damaged building by holding up a damaged wall or floor until permanent repairs can be made. The Long span beam & slab possible with post tension reinforcement provide the advantage of additional versatility in column layout and is also adaptable to irregularly shaped floor plans. Flat plates and Unbonded PT slab design reinforcement has been used in offices, apartments, condominiums, and parking structures.

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