Thursday 13 November 2014

Post Tensioned Concrete

Published by: Harga Besi Beton

Post-tensioning can be process of reinforcing and prestressing concrete. Stresses are delivered into the concrete applying bars or strands of steel while is it being conscructed. The strands of steel are usually utilized in horizontal construction for example foundations and beams. Steel bars are utilized for vertical purposes for instance columns and walls.

Standard steel strands used in post-tensioning use a tensile strength of 270,000 pounds/in². In contrast, an average non-prestressed piece of reinforcing includes a tensile strength of 60,000 psi. Strands typically have a diameter of 1/2 in. and therefore are stressed to a force of 33,000 pounds. The stresses delivered into the concrete offset the expected external loads the concrete will experience.

In post-tensioning the steel is held in a duct, which halts the steel and concrete from binding after the concrete solidifies. The steel are able to be stressed after concrete sets. Normally, this is accomplished in two phases. The first prestress used is up to 50% of the last force and this is completed when the compressive strength reaches 12-15N/mm².

Then 2nd phase is once the last stressing takes place and this is conducted when te concrete meets its design strength. The strands and bars are tensioned by stretching all of them with a hydraulic jack. They're then fixed in place by having an anchoring element, which holds the force in them for the life of the building. Post-tensioning permits te engineer to have all the advantages of using prestressed concrete while maintaining the freedom of constructing on site.

Concrete is extremely strong in compression and weak in tension. Steel on the other hand is quite strong in tension. By mixing the two materials we make a component, which is strong in both tension and compression. Additional advantages are available by using the steel to put the concrete into compression. This increases it's tensile strength, that allows for longer spans and thinner parts. It also helps to stop the formation of shrinkage cracks, which often stops moisture passing through the material.

The more the concrete is compressed, the more unlikely it's that cracking will happen. Using post-tensioned concrete permits flexible column spacing as well as structural depth.

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