Building tension

Post-tensioning is used on 90% of bridge projects in the UAE.

Post-tensioning, which has been around since the 1940s gained popularity in the Gulf, particularly in Dubai, only about ten years ago.

It is now widely accepted as one of the most intelligent techniques in construction with improvements being made on the concept almost every year.

What is bonded post-tensioning?
“Bonded post-tensioning describes the method of applying compression after pouring concrete and the curing process,” explains VSL Middle East civil engineer, David Grattaux.

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“The concrete is cast around plastic, steel or aluminium curved ducts, to follow the area where otherwise tension would occur in the concrete element.”

In lay terms, the process involves a set of ‘tendons’, similar to steel cables, which are then fished through the duct and concrete poured. Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react against the concrete member itself.

The tendons are then stretched; they are wedged in position and maintain tension after the jacks are removed, transferring pressure to the concrete. The duct is then (coated, grouted) to protect the tendons from rust.

This method is commonly used to create monolithic slabs for house construction in locations where expansive soil create problems for the typical perimeter foundation.

All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab, which supports the building without significant flexure. Post-tensioning is also used in the construction of various bridges, both after concrete is cured and by the assembly of prefabricated sections.

“Post tensioning has become an extremely popular method of construction over the last ten years, as it substantially reduces the amount of raw product [concrete] that is needed for any project, which reduces cost, ground loading, is more environmentally friendly and it allows the architect a free reign,” adds Grattaux.

“Post-tensioning generates excellent condition in the structure, enabling efficient use of building materials while controlling deformations under service conditions.”