Forspændte

Forspændte is a Danish term meaning pre-tensioned or prestressed. It is the past participle form of the verb forspænde, to prestress or apply pre-tension. In engineering and construction, forspændte components are elements whose internal tensile force is introduced before they are loaded in service, in order to improve structural performance, increase load capacity, and control cracking.

There are two main techniques: forspænding (pre-tensioning) done before casting a concrete member, and efterspænding (post-tensioning) performed after casting. In pre-tensioning, tendons are laid out and tensioned, then concrete is cast around them; after curing, tendons are released and transfer stress to the concrete. In post-tensioning, tendons are placed within the hardened member and tensioned using jacks, with the stress anchored by plates. The Danish term for the latter is efterspænding.

Applications include prestressed concrete beams, slabs, cables in suspension systems, and ground anchors. The use of forspændte elements improves stiffness, reduces member size, and limits crack widths under service loads. It is common in modern bridges, parking structures, and high-rise floors.

History: The technique was developed in the early 20th century, with French engineer Eugène Freyssinet among pioneers; nowadays it is standard in many parts of the world.

Etymology: from for- (pre) + spænde (to tighten). In Danish, forspændte is typically used as an adjective describing a component that has been prestressed.