Stem navel

A protruding nose is a longer, mostly pointed steel construction that is attached when bridges are pushed in immediately in front of the first part of the superstructure to be pushed in. It thereby reduces the overhanging length of the superstructure during the insertion process and thus the cantilever moment acting on it. While the new superstructure was only pushed forward over a small part of the span , the front nose is already supported on the next pillar .

Front anchor bolts are used in incremental launching and when building with advancing scaffolding.

A front beak consists of a truss construction or two full-wall longitudinal beams that are stiffened by horizontal and vertical braces. Large stem bolts can be subdivided for size adjustment and disassembled for transport. They should be as light as possible, which is due to the tapering or stepped shape.

Its lower edges are aligned according to the slope of the superstructure. The slack on the next pillar is compensated for by a hydraulic lifting device in the case of front-end beaks with a straight lower edge. A variant of the stem nose has a curved lower edge in which the sag is compensated for by lifting jacks placed on the pillar.

Front end bolts for prestressed concrete bridges differ in structural details from those for steel bridges.

A protruding nose has its most favorable static effect when its length in prestressed concrete bridges corresponds to approx. 60% of the maximum span. In the case of a steel superstructure with usually larger spans, this value is approx. 37% with shorter extension beaks.

Its use requires sufficient space for its assembly at the top of the first part of the superstructure. At the target abutment, it must be possible to push the stem through and there must be sufficient space for its dismantling.

Vorbauschnabel in 1870 during the construction of the Stadlauer Ostbahnbrücke

For the first time, a wooden front beak from the Benckiser brothers was used in 1859 when the Waldshut – Koblenz Rhine bridge was inserted, and then in 1861 when the entire Kehl Rhine bridge was inserted.

Web links

Commons : Vorbauschnabel - collection of images, videos and audio files

Individual evidence

^ Gerhard Mehlhorn, Manfred Curbach (Ed.): Handbook bridges . 3rd edition, Springer-Vieweg, Wiesbaden 2014, ISBN 978-3-658-03339-2 , p. 1012
↑ Tom Höhne: Development of a front end nose for the incremental pushing of large bridges . Diploma thesis at the Mittweida University of Applied Sciences (PDF; 6.2 MB)

[1] Gerhard Mehlhorn, Manfred Curbach (Ed.): Handbook bridges . 3rd edition, Springer-Vieweg, Wiesbaden 2014, ISBN 978-3-658-03339-2 , p. 1012

[2] Tom Höhne: Development of a front end nose for the incremental pushing of large bridges . Diploma thesis at the Mittweida University of Applied Sciences (PDF; 6.2 MB)