Incremental launching
With timed shifting method is called a production method of bridges.
The construction of the connected bridge superstructure (multi-span girder) takes place in sections behind an abutment in a production facility, which is also referred to as a "clock basement". After the completion of a bridge section, it is moved (“pushed in”) over the pillars together with the sections previously produced in order to be able to produce the next section (cycle). The method is used in particular for longer bridges with a straight or almost circular floor plan and with uniform crests or tubs in elevation.
history
A forerunner of the process was that used in the USA for the construction of trestle bridges such as B. the Portage Bridge applied method to deliver the building material on the completed track up to the bridge and lower the parts with a mobile crane to their place of installation. As soon as the first pillar was finished, the deck girder and the track were built to it. Then the next pillar was built, which in turn was connected to the track, and so on.
In 1856 an anonymous author mentioned in a specialist journal the previous method used in the construction of lattice girder bridges , namely preparing the individual lattice girders next to the bridge and then driving them to the designated place by car over light scaffolding. He then suggests that the whole bridge be put together on dry land and then pushed over to its place.
This proposal was implemented between 1856 and 1858 by the Benckiser company in Switzerland when building lattice bridges over the Thur near Andelfingen ZH , over the Emme near Derendingen SO and over the Aare near Bern .
During the construction of the first Grandfey Viaduct near Freiburg in Switzerland between 1857 and 1862, Ferdinand Mathieu , the chief engineer of the French iron and later steel company Schneider & Cie. , Le Creusot , insert the lattice girder over six pillars up to 75 m high. The lattice girder beam pushed over the valley served as a crane for building the first and then the next pillar.
Benckiser pushed in the entire superstructure at the Waldshut – Koblenz Rhine bridge (1858–1859) and at the Kehl Rhine bridge (1858–1861). Shortly afterwards, the method was repeated by the forerunners of the companies Fives-Lille and Etablissement Cail in the construction of the Viaduc de Busseau and then routinely used by Schneider & Cie in the construction of numerous iron bridges throughout Europe, including the first Stadlauer Ostbahnbrücke in Vienna.
This type of production was initially used in particular for iron and steel bridges . In the prestressed concrete construction , the bridge over the Río Caroní was pushed in for the first time in Venezuela in 1962 with the help of slide bearings and a front end navel . For the construction of the Wildbichler Bridge , a motorway bridge over the Inn in Kufstein , Fritz Leonhardt and Willi Baur optimized this construction method and developed the incremental launching technique that is still used today. The Taubertal Bridge was the first bridge built in Germany using this method.
Description of the procedure
In the incremental launching process in prestressed concrete construction, instead of the production of bridges on teaching or advancing scaffolding, there is factory production in repetitive stages. The superstructure is built in short sections (cycles) in fixed formwork behind the abutment . The individual sections are concreted directly next to one another and connected to one another in a rigid manner with tensioning cables . The hardened new bridge section is then raised a few millimeters and moved forward by one cycle length together with the other already completed cycles in the direction of the bridge axis. This is done using hydraulic presses and PTFE slide bearings. After that, the next section is made in the same place in the same formwork. Usually one cycle per week is produced. At the foremost section, a steel stem is mounted in order to reduce the cantilever moments that occur when moving until the supports are reached . In particular, hollow box cross-sections are suitable for incremental pushing. The process is very economical because of its short transport routes, small equipment pools, good formwork and armament utilization and recurring work processes. The disadvantage is that the cross-section of the superstructure has to remain unchanged due to the process and therefore the construction height required for the largest span is decisive.
The sliding in of steel bridges in sections (one also speaks of “launching” here) or steel girders of composite bridges works in the essential steps analogous to incremental pushing in prestressed concrete construction. In contrast to this, however, the production of the cycles only relates to the assembly of carrier parts. The actual production of the steel structure takes place in the factory. Due to the mostly much lower weight of the parts, a front nose is often not necessary. The sections can also have different lengths here. The size and mass of the individual parts is usually limited by the means of transport to the construction site.
Recent developments
With the contact method (concrete construction) , as it was used for the Schnaittach viaduct , it is now possible for the first time to also build bridge superstructures with a variably curved plan axis (e.g. a clothoid ). An approximation polygon replaces the variably curved site plan axis, which the individual superstructure cycles follow like a link chain with different articulation angles. The cycle production system is made rotatable in plan and possibly also tiltable. When a new cycle is concreted onto the superstructure that has already been created, the kink angles are set that result from the calculation of the approximation polygon. In the simplest case, the lateral and height deviations of the superstructure from the end position that occur during the advance are compensated for by transversely displaceable sliding bearings on the pillars, in the case of a variable gradient by hydraulically height-adjustable bearings with a corresponding control.
literature
- Eugen Brühwiler, Christian Menn: Reinforced concrete bridges . Springer-Verlag Vienna 2003, ISBN 3-211-83583-0 .
Web links
- Construction process for bridge construction ( Memento from June 11, 2007 in the Internet Archive ) (PDF file; 9.54 MB)
- 3D animation of the incremental launching process on YouTube
Individual evidence
- ↑ Overview of the railways under construction in Switzerland. : Allgemeine Bauzeitung , year 1856, pp. 2–7, 133–139 (online at ANNO ).
- ↑ Suggestion for rolling over the lattice walls without scaffolding. : Allgemeine Bauzeitung , year 1856, p. 135, drawing on sheet 29 (online at ANNO ).
- ↑ Ulrich Boeyng: The railway bridge over the Rhine between Waldshut and Koblenz. A monument to the history of technology . In: Preservation of monuments in Baden-Württemberg , 19th year 1990, issue 3, pp. 135–140. ( PDF file, 1 MB )
- ↑ Bernard Marrey: Les Ponts Modern; 18 e –19 e siècles. Picard éditeur, Paris 1990, ISBN 2-7084-0401-6 , p. 210
- ↑ Historical plan drawing on cnum.cnam.fr
- ↑ Reinhard Maurer: Prestressed concrete bridges. In: Civil engineering. 10/2005, p. 577 ( Memento of the original from January 15, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
