Formwork anchor

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Systematic structure of a form anchor.
1: Threaded rod
2: Nut
3: Formwork
4: Connection cone
5: Cladding tube
6: Concrete
The visible holes in the formwork anchors as an architectural design element. Tadao Andō , Azuma House
Open shuttering hole and associated sealing plug

A formwork anchor is a connecting element that connects two formwork panels . If the fresh concrete is poured into the formwork , it does not yet have the strength of the later component, but exerts pressure on the formwork. When shuttering a wall, the vertical formwork panels are therefore connected to one another. The connecting element, the formwork anchor, is located inside the concrete component.

The formwork anchor consists of several parts. The actual load transfer function is performed by a steel threaded rod. On each side it protrudes through a hole in the formwork, where it is secured on the outside by a nut . If the steel rod should be able to be removed again after the formwork has been stripped, it is inserted into an empty pipe that remains in the concrete component. A metal or plastic cone connects the empty pipe to the formwork on the sides so that the liquid concrete cannot leak out of the hole in the formwork. After removal, the formwork anchor leaves a hole in the finished component that can be closed or plastered with a plug / plug.

In order to ensure properties such as impermeability to water, fire resistance or soundproofing despite the penetration of the concrete component, there are different designs of the cladding tube. In the case of carpentry-made formwork, the exact position of the formwork anchors can be determined on site by drilling holes in the formwork panels. With modern system formwork, the holes are already specified. A simpler form of connecting formwork panels is by means of wire ( tie wire , hence the name "tie hole"), which is passed through holes in the formwork and remains in the component. The problem with the use of tie wire as an anchor is the risk of corrosion and, as a result, of the concrete flaking off, accompanied by a loss of strength.

Formwork anchors are standardized in DIN 18216 .

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