Pretension is the technique in which we are imparting tension in strands before placing the concrete. A compressive force is therefore induced into the concrete. Hey, I am Krunal Rajput. The Man Behind CivilJungle. I started this site to spread knowledge about Civil Engineering.
I am a Degree Holder in Civil Engineering. The difference is that in pre-tensioned concrete, the tendons are tensioned prior to pouring of concrete while in post-tensioned concrete, tendons are tensioned after putting concrete. Your email address will not be published. Important Point. Pre-Tensioning Post-Tensioning 1 Pre-tensioning is done in the factories thus suitable for precast construction works Post-tensioning can be done in factories as well as on the site 2 In this type of concrete, the pre-stressing cables called the strands are tensioned before casting the concrete and then concrete is casted enclosing the tensioned cables.
In this type of concrete, the strands are enclosed within a duct in the form and then concrete is casted. The process of tensioning the strands is carried out after the concrete attains its sufficient strength.
In this method, products are changed according to a structure. Cables are used in place of wires and jacks are used for stretching. This method is developed due to bearing. Post-tensioning is preferred when the structural element is heavy. Search for:. No Pretensioning Post-tensioning 1 Pretension is the technique in which we are imparting tension in strands before placing the concrete.
In this type of concrete, the strands are enclosed within a duct in the form and then concrete is casted. The process of tensioning the strands is carried out after the concrete attains its sufficient strength.
Cables are used in place of wires and jacks are used for stretching. Post Views: Category Construction. Tags Post-tension Concrete Pretension concrete. Segregation and Bleeding of concrete — Causes and Mitigation. To pretension concrete the steel is first tensioned in a frame or between anchorages external to the member.
The concrete is then cast around it. After the concrete has developed sufficient strength the tension is slowly released from the frame or anchorage to transfer the stress to the concrete to which the tendons have by that time become bonded. The force is transmitted to the concrete over a certain distance from each end of a member known as the transfer length. Post-tensioned concrete is made by casting concrete that contains ducts through which tendons can be threaded.
An alternative is to cast the concrete around tendons that are greased or encased in a plastic sleeve. When the concrete has sufficient strength the tendons are tensioned by means of portable jacks. The load is transmitted to the concrete through permanent anchorages embedded in the concrete at the ends of the tendons. Ducts are usually grouted later or filled with grease to protect the tendons against corrosion.
In some applications the post-tensioning tendons are run alongside the concrete member. One advantage of post-tensioning is that it permits using tendons that are curved or draped. This can be achieved in pretension but not so easily. For pretension concrete the steel is the first tensioned in a frame or between anchorages external to the member, therefore the concrete is then cast around it. Post tensioned concrete is made by casting concrete that contains ducts through which tendons can be threaded.
Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.
Afterwards, once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or tensioned, and anchored against the outer edges of the concrete. Post-tensioning is a form of prestressing. Prestressing simply means that the steel is stressed pulled or tensioned before the concrete has to support the service loads.
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