What is Post-Tensioning?

Post-tensioning is a technique for making prestressed concrete, masonry, and other structural structural components. The term”processed” refers to infusing inner forces (or stress) into the masonry or concrete element when it is being constructed to counteract external loads imposed after the construction is placed in service. 

The internal forces are applied by tensioning high-strength steel that can be used before or after the concrete is installed. The process is known as pre-tensioning if the steel is stretched before concrete placement. The process is known as post-tensioning when the steel is tested after concrete placement.

Benefits of using prestressed concrete and masonry concrete

Engineers have long acknowledged the benefits of using prestressed concrete and masonry concrete. If a designer wants to reap the advantages, they should decide whether the structure will be built using the pre-tension or post-tension methods. 

Pre-tensioning typically occurs in a factory where concrete components are made in specially designed casting beds equipped with steel bulkheads that keep the steel in position while tension is applied. The concrete is then positioned around the steel pre-tensioned and allowed to set. 

The bulkheads’ steel is taken off, and the entire piece of precast concrete is brought to the project site for assembly. The process can be restricted to regular shapes or sizes that are easily moved.

What Does Post-Tensioning Do to Concrete and Masonry?

If a masonry or concrete component is being prestressed this way, the steel has been stretched, and the masonry or concrete has been compressed. The force of compression is used to crush or squeeze something, and tension is the force that pulls a thing apart. Concrete as building materials and masonry are sturdy in reduction. 

However, they are comparatively weak when it comes to tension. Steel, on the other hand, is highly durable under pressure. Putting the masonry or concrete into compression and then putting the steel in anticipation before any significant service loads are applied makes both building materials the most durable. This creates a stronger concrete or masonry component which is actively compressed and is more able to withstand tensile force.

One issue that happens to concrete floors or masonry walls is that they are exposed to forces that cause them to bend and be able to turn.

What equipment and materials are used for Post-Tensioning?

The fundamental component of a post-tensioning device is known as the tendon. A tendon for post-tensioning is made from one or more pieces of pre-tensioned steel, covered with a protective coating, and housed within sheathing or a duct. 

A tendon has anchors at both ends to transfer forces to the structure. Long tendons can also include intermediate anchors along their length. The steel used for prestressing could be a strong steel strand (typical for horizontal settings) or a strong steel bar (typical for vertical stages). Steel for prestressing is produced according to the applicable ASTM specifications.

Tension is applied to the prestressing steel using post-tension stressing jacks. The jack is positioned against any anchor inserted into concrete and pulls on the steel with a specified force. While tensioning occurs, the steel is stretched while the masonry or concrete element is extended. 

When the proper tensioning pressure is achieved, the steel used to prestress is fixed to the concrete. The anchors create a permanent mechanical connection that will keep the steel tension while the concrete is in compression.