Feed armor
A feed scaffold , also called a feed scaffold, is used to create the superstructure of long prestressed concrete bridges in sections. In 1959 this construction method was first used in Germany by the Strabag company at the Kettiger slope bridge near Andernach . In the not far away Krahnenberg Bridge , planned by Hans Wittfoht and Polensky & Zöllner from 1961 to 1964 , the construction was further developed into a single-phase telescopic scaffold without special front girders, which served as a model for numerous other variants.
The free exciting falsework is usually hydraulically movable Stahlrüstträgern, nowadays usually truss that an entire bridge span span support free. There is also a trailer at the rear and a front nose so that the armor is always supported on two pillars while it is being moved. The longitudinal beams can be arranged above the superstructure to be produced. In this variant, the formwork scaffolding is attached to the main girder and must be opened to move it in order to be able to pass the pillars. It is also possible, however, for the steel scaffolding girders to be located below or, in the case of the T- beam, to the side of the superstructure, with the formwork construction resting on it. But then the formwork has to be lowered, separated and shifted transversely so as not to collide with the pillars when shifting lengthways. In the case of high piers, the prop scaffolding is usually supported directly on them, for example with support brackets; for low piers, shoring towers can also be used.
With this construction method, the bridge superstructure is concreted on site. After the concrete has hardened, the formwork is lowered and the feed armature is shifted by one production cycle, usually one field. A feed armament is mainly used for long bridge constructions where the incremental launching method is not possible or uneconomical. These include prestressed concrete bridges with highly variable cross-sections, such as haunches .
For large spans and long superstructures, as was the case for the first time with the Rombachtal Bridge , a pre-stressed concrete trough with a steel front end was used as a feed scaffold , which was demolished after the bridge was completed. Alternatively, only the longitudinal girders of the Kassemühle viaduct were made from prestressed concrete.
It should not be confused with the prefabricated scaffolding developed in France between 1963 and 1966 for the construction of the superstructure from prefabricated segments .
literature
- Karl Heinz Holst, Ralph Holst: Bridges made of reinforced concrete and prestressed concrete - design, construction and calculation . Ernst & Sohn Verlag, Berlin, 2004, ISBN 3-433-02837-0
- Hans Wittfoht: The use of feed armor in bridge construction. In: IABSE congress report = Rapport du congrès AIPC = IVBH Kongressbericht, Volume 9, 1972, on e-periodica.ch (PDF; 8.0 MB)
Web links
Individual evidence
- ↑ Erwin Beyer, H. Thul: Hochstraßen. Planning, execution, examples . 2nd Edition. Beton-Verlag, Düsseldorf 1967.
- ^ Christian Menn: Reinforced concrete bridges . Springer-Verlag, Vienna, New York 1986, ISBN 3-211-81936-3 , p. 36