What is tensioning?
Tensioning is a construction technique that stresses a concrete column to reduce the traction load it is submitted to.
Tensioning consists of a procedure where the cable, stays or steel bar throughout a concrete column is pulled to pre-tension it (in the plant) or post-tension it (on site).
How cable tensioning works
This action includes increasing interior cable tension and pulling on it (therefore, both techniques are included under the term tensioning). The name comes from the nautical term related with ropes, as they are tensioned to adjust their internal tension and to control their resistance to other elements.
Both pre-tensioned concrete and post-tensioned concrete are subjected to pressure they can withstand, while the steel nerves are submitted to traction force. Steel performs well under traction, especially braided steel cable.
Concrete’s resistance to traction is an order of magnitude (approximately ten times) smaller than its resistance to pressure. Here at Tecpersa we use these techniques in construction to increase material quality and duration.
Pouring is done after tensioning. The concrete hardens over the pre-tensioned framework. That way a strong link is made between the cables and the concrete. A strong hold. Nevertheless, the piece cannot always be constructed at the plant.
The concrete is poured and a cannulated free nerve is used to insert the tensioned cable. If the tensed steel is anchored to one of the sides it is called a “passive anchor”. The remaining free anchors are referred to as active because the cable will slide over them until reaching the elongation and tension calculated in the design phase. The grip is what happens on the sides.
The combination of a tensed cable or “tendon” plus concrete equals a pre-tensioned or post-tensioned structure. Almost all types of construction are made with one of these two options. Tensioning at the plant is easier, while tensioning on site requires more attention.