Efterspänning

Efterspänning is a Swedish term that translates to "post-tensioning" in English, a construction technique used to strengthen concrete structures. It involves tensioning steel tendons or cables after the concrete has hardened. This process is distinct from pre-tensioning, where the steel is stressed before the concrete is poured.

In post-tensioning, ducts or sheaths are embedded in the fresh concrete, and steel tendons are threaded through these ducts once the concrete reaches a sufficient strength. Hydraulic jacks are then used to pull the tendons to a predetermined tension. Once the desired force is achieved, the tendons are anchored at the ends of the structural element. The tension in the tendons creates compressive forces within the concrete, which counteract tensile stresses that will develop when the structure is in use. This allows for longer spans, thinner structural elements, and improved resistance to cracking and deflection.

Post-tensioning is commonly employed in bridges, parking garages, building slabs, and other structures where high performance and durability are required. The method offers advantages such as increased load-bearing capacity, enhanced fire resistance, and greater design flexibility. The anchoring systems and the grouting of the ducts after tensioning are critical steps to ensure the long-term effectiveness of the post-tensioning.