Method of constructing post tension RCC slab

In this construction video tutorial, you will learn how post tension RCC slabs are built up as well as how post tensioning is performed and benefits of post tensioning process.

POST TENSION SLAB: It refers to the slab that is tensioned as soon as the slab is developed. Reinforcement is arranged to avoid the compression.

In Post tension slab, cables or steel tendons are utilized to substitute the reinforcement. Post-tensioning offers a solution to get rid of the natural weakness of concrete in tension as well as optimize its strength in compression.

In concrete structures, this is obtained by arranging high-tensile steel tendons/cables in the element prior to start the casting. If the concrete attains the required strength, the tendons are pulled with special hydraulic jacks and retained in tension with specially designed anchorages which are attached at each end of the tendon.

It creates compression at the edge of the structural member that increases the strength of the concrete for resisting tension stresses.

If tendons are correctly curved to a specific profile, they will exert, other than compression at the perimeter, a useful ascendant set of forces (load balancing forces) that will neutralize applied loads, alleviating the structure from a portion of gravity effects.

In this type of concrete slab, cables are affixed in place of reinforcement. In Steel reinforcement the gapping among bars is 4inch to 6inch while in Post tension slab the gapping is in excess of 2m.

Go through the following video tutorial, to get more details on post tension slab.

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Published By

Rajib Dey

www.constructioncost.co

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Post-tensioning and its phases

The ducts for the tendons (or strands) are arranged together with the reinforcement prior to the casting of concrete in post-tensioning systems.

The tendons are arranged in the ducts as soon as the casting of concrete is completed. The objective of duct is to avoid connection among concrete and the tendons throughout the tensioning operation.

Contrary to pre-tensioning, the tendons are pulled with the reaction that operates against the hardened concrete. It is defined as bonded post-tensioning when the ducts are filled with grout. The grout belongs to a neat cement paste or a sand-cement mortar that comprises of proper admixture.

In unbonded post-tensioning, the ducts are not at all grouted and the tendon is set in tension individually with the end anchorages. In the sketch given below, there is a schematic illustration of a grouted post-tensioned member. The profile of the duct is based on the support conditions. For a simply supported member, the duct contains a sagging profile among the ends. For a continuous member, the duct bends in the space and hogs over the support.

The following figures demonstrate the assessment of ducts in a box girder of a simply supported bridge. The second image demonstrates the end of the box girder as soon as the post-tensioning of some tendons is completed.

Given below, the different phases of the post-tensioning operation :-

1) Casting of concrete.
2) Arrangement of the tendons.
3) Arrangement of the anchorage block and jack.

4) Use tension to the tendons.
5) Seating of the wedges.
6) Cutting of the tendons.

The stages are demonstrates schematically in the following figures. Once a tendon is anchored at one end, the tension is employed at the other end with a jack.

The tensioning of tendons and pre-compression of concrete happen concurrently. A system of self-equilibrating forces forms once the tendons are expanded.

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Published By
Rajib Dey
www.constructioncost.co
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