Unbonded Post-Tensioning

Prestressed concrete has been around for years, and it serves as a more efficient, and reliable alternative to reinforced concrete. Prestressed concrete, as we know it, can be divided into 2 separate technologies, both offer significant material savings: pre-tensioned and post-tensioned concrete. Both technologies are commonly used in structural applications, however pre-tensioned concrete is usually precast at manufacturer’s plant and delivered to the building site, and post-tensioned concrete is cast on site.

SDS specializes in the design of post-tensioned concrete members therefore we will focus on this technological solution going forward.

Using post-tensioned systems, we introduce additional internal forces into the structural member. Those forces (bending moment and compression throughout the member) balance or counteract the effects of applied loading and self-weight of the member. Cables are stressed after concrete has gained sufficient compressive strength.

This beneficial effect results in better overall performance of the structure and extends the time between necessary maintenance works.

Tendons are stressed after concrete has reached sufficient compressive strength. Cables are later cut at stressing ends. This technology is less time-consuming compared to the bonded technology as it doesn't require the injection of grout into the cables. This solution is still relatively new yet widely used in building applications, mostly in the USA. Cables are delivered in bundles already covered in HDPE sheathing which also saves a significant amount of time compared to the bonded technology.

SDS specializes in both unbonded and bonded technologies, therefore we could advise you on selecting the structural solution most beneficial to your project.

• Formwork is installed in place to accomodate rebar, cables and concrete.

• Rebar and prestressing cables are laid out. Because prestressing balances a large portion of self-weight and external loading, the amount of rebar is usually limited to the minimum required by the building code.

• Concrete is poured.

• 3 to 4 days after the pour, cables are stressed, cut and stressing pockets are filled. The formwork and supports can be removed and transferred onto the next level.