Jännitteistystä

Jännitteistys, often translated as prestressing or pre-tensioning in English, is a structural engineering technique used in concrete construction. It involves intentionally inducing compressive stresses into the concrete before or during the application of external loads. This is typically achieved by stretching steel tendons or wires to a high tension. In pre-tensioning, the steel is tensioned before the concrete is poured. Once the concrete has hardened sufficiently, the tension in the steel is released, transferring its force to the concrete as compression. In post-tensioning, ducts are placed within the concrete formwork, and the steel is tensioned after the concrete has hardened. The ducts are then typically filled with grout to bond the steel to the concrete.

The primary benefit of jännitteistys is to counteract the tensile stresses that occur in concrete under load. Concrete is strong in compression but weak in tension. By introducing pre-compression, the concrete can resist tensile forces more effectively, allowing for longer spans, thinner structural elements, and reduced cracking. This technique is widely used in bridges, beams, slabs, and other structural components where significant loads are expected. The controlled application of internal compressive forces significantly enhances the durability and load-carrying capacity of concrete structures.