esijännitettyihin

Esijännitettyihin is a Finnish term that translates to "prestressed" in English. It refers to a method of construction where a material, most commonly concrete, is intentionally subjected to compressive stress before it is subjected to external loads. This pre-compression is achieved by introducing tension into reinforcing elements, such as steel tendons, and then anchoring them in place. When the tension in the tendons is released, they exert a compressive force on the concrete.

This technique is widely used in civil engineering, particularly in the construction of bridges, beams, and slabs. The primary benefit of prestressing is to counteract the tensile stresses that would otherwise develop in these structures under load, especially in the bottom portion of a beam. By pre-compressing the concrete, the structure can carry heavier loads and span longer distances than would be possible with conventional reinforced concrete. It also improves durability by reducing cracking and increasing resistance to environmental factors like corrosion.

There are two main types of prestressing: pre-tensioning and post-tensioning. In pre-tensioning, the tendons are stretched and anchored before the concrete is cast. Once the concrete hardens, the anchors are released, and the tendons transfer their tension to the concrete. In post-tensioning, the tendons are placed within ducts in the concrete after it has hardened, and then tensioned using hydraulic jacks. The tendons are then anchored, and the ducts are often grouted to bond the tendons to the concrete.