Langwieser Viaduct
| Langwieser Viaduct | ||
|---|---|---|
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| use | railroad | |
| Crossing of | Plessur, Sapunerbach | |
| place | Langwies | |
| construction | Reinforced concrete arch bridge | |
| overall length | 284 m | |
| width | 5 m | |
| Number of openings | 13 | |
| Longest span | 100 m | |
| Arrow height | 42 m | |
| Pillar strength | 1 m | |
| Arch thickness (vertex) | 2.1 m | |
| Arrow ratio | 2.38 | |
| Arch slenderness | 4 m | |
| height | 62 m | |
| building-costs | CHF 625,000.00 | |
| start of building | August 1912 | |
| completion | July 1914 | |
| opening | December 1914 | |
| construction time | about 2 years | |
| Status | in use | |
| planner | H. Schürch, K. Arnstein | |
| location | ||
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| Above sea level | 1317 m above sea level M. | |
| View from Langwies saddle | ||
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The Langwieser Viaduct is a single-lane railway bridge of the Rhaetian Railway (RhB) near Langwies , municipality of Arosa , in the canton of Graubünden in Switzerland .
Location and description
The viaduct is part of the narrow-gauge Chur – Arosa railway line . Immediately behind Langwies train station , it leads from the lower end of Unter Wis in a south-westerly direction to the south-east end of the Middle Prätschwald and crosses the Plessur and the Sapüner-Fondeierbach at a height of 62 m . The 284 m long structure is by far the largest bridge on the RhB. As a cultural asset of national importance, it is one of the most famous bridges in Switzerland and, as the first concrete railway bridge of this size, received worldwide attention. The younger brother of the Langwieser Viaduct is the Gründjitobel Viaduct with a span of 85 m and a length of 139 m , which is located approx. 1.8 km down the valley .
history
General
The line from Chur to the high-altitude spa town of Arosa was - apart from the Vereina tunnel from Klosters to the Engadine - the last stretch of today's RhB network to be built. It was realized between 1912 and 1914 by the private corporation Chur-Arosa Bahn (ChA) . For financial reasons, this merged with the RhB in 1942, as did the Bellinzona-Mesocco-Bahn and - one year later - the Bernina Railway . The railway line is 26 kilometers long and overcomes an altitude difference of 1154 meters. Due to the difficult terrain in the Schanfigg, it is extremely rich in engineering structures with 19 tunnels and 52 bridges. As with the recently built railway lines of the RhB trunk network , high architectural demands were placed on the design of the structural and engineering structures. To bridge the Plessur near Langwies, a large structure was required. Although the planners had also examined the option of a train station up in Langwies Platz - in order to cross the river further back in the Arosa Valley - the route with a "large bridge" was chosen.
The chief engineer of the railway construction, Gustav Bener , wanted, wherever possible, to use local natural stone for the bridges and retaining walls. Iron or concrete bridges should only be erected where stone vaults were out of the question due to the river profiles or insufficient load-bearing capacity of the building site or where good building blocks were missing. The latter was the case in Langwies. The upper Schanfigg consists of mighty moraine deposits ; Sand and gravel are plentiful, but suitable building blocks are in short supply. However, even with sufficient stone stocks, the high and long bridge as a stone structure would only have been very expensive to build. An iron construction could only have been transported over the winding and steep Schanfiggerstrasse from Chur in short sections and at great expense. For these reasons, the prevailing conditions almost forced reinforced concrete construction .
Organization of the construction site and construction process
The contract for the planning and execution of the viaduct was given to the Swiss-German company Züblin & Cie. Even before the railway company was founded, at the beginning of July 1912 . granted in Basel and Strasbourg. Due to the boldness and novelty of the building, they refrained from awarding a public contract and turned directly to an engineering office that was trusted to successfully implement such a project; The construction management had set very special guarantee requirements for the construction of the bridge, with a liability period of ten years for work and material. Züblin also received also awarded the contract for the construction of the railway section Palätsch -Langwies. The overall manager for planning and construction of the viaduct was engineer Hermann Schürch . The draft and the static calculations were carried out under Karl Arnstein in the technical office in Strasbourg. The construction management was carried out by engineer J. Müller, assisted by the local engineer-site managers A. Zwygart and J. Fleury.
In September 1912, the construction site set-up and foundation excavation began. The remote construction site could only be supplied from Chur by horse-drawn carriage across the street. A horse-drawn train with four horses could transport a maximum load of 2.5 tons, so that a total of around 1000 loads were necessary to build the bridge. Each of these trips took a day and a half. The hired carter Thomann designed a special frame that extended from the wagons over the horses to the front. In this way, the long reinforcing bars could be loaded and fixed for transport. The planum of the future Langwies station served as the installation site and was accessed via a cable car from the higher street. Large stocks of cement and reinforcing steel had to be built up, as at times the daily consumption on the construction site was twice as large as the possible supply. For the power supply, a three and a half kilometer long, provisional high-voltage line was built from the machine house in da Bünst of the Arosa power station to the construction site. A telephone system was also installed on site. The bridge construction site itself was served with a 340 m wide cable crane. The engineers regulated the workflow using a precisely worked out graphic construction program, from which the number of workers required and the material flows could be seen.
The early onset of winter in October 1912 delayed the foundation work in the area of the arch abutments, which included several construction phases. From the beginning of April 1913, the work could be continued. The foundations were completed by summer, after which the pillars and girders of the side openings on the Langwieser side could be concreted. At the beginning of September 1913, the wooden falsework for the main arch was completed, so that the latter was completely concreted just a month later. In 1914, the roadway over the arch and the side openings on the Arosa side were finally created. In October 1914, the bridge passed the final test: it sank by less than a millimeter when loaded with a steam locomotive and three heavily loaded freight cars. The building swallowed up a total of 250 tons of reinforcing iron and 7,469 m³ of concrete, 2,608 m³ more than initially planned due to the multiple cubic structures of the foundations. The total costs without the stockpile reinforcement and superstructure amounted to over CHF 625,000.
Technical design
Overview: Three-part, monolithic, elastic construction
In addition to the Langwieser and Aroser side openings, the viaduct consists of the 100 meter wide main opening with a large arch in between. The parts are separated by open joints in the roadway. The double pillars above the arch abutments continue this separation to the foundations. The joints allow the structure to be deformed with little constraint under temperature fluctuations and shrinkage . The bow reacts like an elastic spring and rises and falls accordingly in its middle part by around two centimeters between summer and winter. The three separate sections of the roadway are each held horizontally at one point in the longitudinal direction of the bridge. For the roadway of the main opening, this is at the connection to the arch apex; that of the Arosa side openings is fixed in the abutment , that of the Langwieser side in the mighty group pillar. The amount of change in length of the roadway increases with increasing distance from these fixed points. As the distance increases, the pillars become higher and therefore more elastic. The highest pillars for all three carriageway sections are the double pillars, and this is where the changes in length of the carriageway are greatest. This proportionality of the movement of the roadway and the height of the piers is one of the main conceptual features of the Langwieser Viaduct. It allows joints and bearings to be largely dispensed with. The resulting monolithic construction is still an ideal to be striven for in concrete construction today, since bearing structures and lane crossings could be possible weak points if there was insufficient maintenance.
Main arch
A second specialty of the Langwieser Viaduct is the formation of the arch. It is a clamped arch made of two upright ribs. This arrangement was unusual at the time of construction. The arched ribs are interconnected with sixteen strong crossbars. The whole thing forms a curved Vierendeel beam that ensures the lateral stability of the middle section. The construction method customary at the time with a single wide arch slab - a horizontal rectangular cross-section such as the Gründjitobel Viaduct - would have resulted in an unusually strong slab due to the comparatively high railway loads and the resulting bending stress on the arch, and thus an uneconomically heavy arch. The arched ribs with upright rectangular cross-sections, which are much stiffer compared to this training, would have led to high stresses due to temperature fluctuations in a flatter arch ; However, since the Langwieser Bogen has a large arrow height in relation to the span , these additional stresses are not significant. The goal of a hinge-free monolithic construction aimed at by the engineers has thus influenced the choice of the arch geometry and the cross-section.
Design of the individual parts
The design of the individual parts of the viaduct corresponds to the overarching conceptual requirements. This initially concerns the absorption of the lateral wind effects. The roadway acts as a horizontal beam to absorb the wind forces. The four-meter wide deck, together with the supporting longitudinal ribs as girders across the bridge axis, is much more rigid than in the vertical direction. Since the effects of the wind forces are also less than the vertical traffic loads, the roadway girder can span much larger spans in the horizontal direction than the distance between the pillars. In the transverse direction, the carriageway girders of the side openings are only supported on the end abutments, or rather the Langwies group pillar, and the outer double piers above the abutments. The carriageway girder above the arch guides the wind loads to the inner double pillars and to the apex of the arch. As a result, the pillars show very different designs in the transverse direction: the stabilizing double pillars have strong, full-walled panes in the transverse direction, while the other pillars - similar to the arch, only much slimmer - are divided into two stems and crossbars. They divert the wind forces downwards and upwards and are supported in the transverse direction by the deck girder. In the apex of the arch, the two arched ribs are raised above the roadway, which creates a good and secure connection between the two arched ribs over a longer distance. This is a structural peculiarity of the Langwieser Viaduct that cannot be found on any comparable bridge.
Falsework
For the falsework of the main arch, 800 cubic meters of logs from the nearby forests were used. The huge wooden fan was another impressive work of the Triner carpenter Richard Coray . The planning and construction of the scaffolding required extreme precision from everyone involved. Construction began on May 15, 1913, and was completed on September 6 of the same year. The construction of the falsework was based on the principle of the shortest possible force dissipation. In order to distribute the forces evenly across the scaffolding, concreting began not only from both sides, but also at the top of the vault. The weight of the freshly concreted arch was transferred to the scaffolding towers, which were also concreted, via the round wood beams of the fan. The actual deformations of the scaffolding ascertained in the process were significantly less than the predicted ones, as the scaffolding formed an arched structure with its wooden wreaths, which relieved the central fan. After the arch was merged on October 6, 1913, the falsework remained in place until the bridge was completed on July 1, 1914. The three scaffolding towers were blown up after the fan was dismantled, some remains of concrete can still be found in the Plessur today. A model of the falsework was in the Railway Museum in Zurich until 1959 .
Bridge-building and architectural significance of the viaduct
When it was built, the Langwieser Viaduct was the widest-span railway bridge in the world. It immediately became a very popular, often photographed building and a symbol of the Schanfigg valley . The architectural treatment is kept as simple as possible and essentially consists of the small protrusions on the pier heads. When the viaduct was designed, two construction methods for arch bridges in reinforced concrete emerged, which have continued to develop in parallel to this day. One principle is based on load-bearing panes and slabs ( Maillart - Menn line), the other (mainly represented in Switzerland by Alexandre Sarrasin ) uses rod-shaped elements for the arch, like the Langwieser Viaduct.
Both construction principles are innovations triggered by the material reinforced concrete. With them, the reinforced concrete freed itself to a certain extent from the models of the brick arched bridges. Of the latter, the Wiesener Viaduct and the Soliser Viaduct have some formal similarities with the Langwieser Viaduct. This stylistic relationship is not primarily justified for technical reasons, but is primarily due to the choice of the 100-meter span and the large arrow height: According to Schürch, a flatter, wider arch would have been more economical in Langwies, but the process of the complex approval process would have been included Do not want to complicate the Swiss Railway Department by deviating too much from existing spans. Since the supervisory authority found the span too wide, plans were drawn up on which it is given as 98 or 99 meters.
In 1908 the Züblin company built for the first time two reinforced concrete bridges with bar-shaped ribs on the Hungarian Fogaras - Kronstadt railway line near the Schinkatal in Transylvania. These works became the actual prototypes for the Langwieser Viaduct. The larger of these two bridges has a span of "only" 60 meters, which shows that the Langwieser Viaduct actually represented a breakthrough in the arched rib system in large bridge construction. It is therefore hardly missing in any textbook on reinforced concrete bridges.
Varia
On February 21, 1983, the Arosa firefighter Werner Wellauer crossed the bridge from Langwies train station with a fire truck to get to a house in flames in the middle Prätschwald. In spite of this daring intervention, the building burned down to the foundation wall due to the lack of sufficient extinguishing water, and since Wellauer could not turn the vehicle at the scene, he had to drive back over the viaduct in reverse.
On the occasion of the celebration of the 75th anniversary of the Arosa Railway in 1989, Florenz Schaffner, Arosa spa director and initiator of the Arosa Humor Festival , descended from the Langwieser Viaduct under the guidance of mountain guides. He carried a birthday cake and a large Arosa flag with him for the festival community waiting by the fireplace on the Sapünerbach.
Since the 100th anniversary of Arosa Energie in 1997/98, the viaduct, which was refreshed in 2009, has been illuminated at night during the winter season by hundreds of light bulbs attached to the structure that replicate the bridge silhouette, making it a tourist attraction. The bridge has no cantilever for pedestrians and is thus blocked for a corresponding use.
literature
- Ueli Haldimann , Tibert Keller, Georg Jäger : Experience the Chur-Arosa Railway - a stroll through the Schanfigg. AS Verlag & Buchkonzept AG, Zurich 2014, ISBN 978-3-906055-25-1 , pp. 74-77.
- Jürg Conzett: The Langwieser Viaduct - a monolithic elastic construction. In: Marcel Just, Christof Kübler, Matthias Noell (eds.): Arosa - The Modern in the Mountains. gta Verlag, Zurich 2007, ISBN 978-3-85676-214-8 , pp. 30–39.
- Reinforced concrete bridges on the Chur - Arosa branch line. In: Zentralblatt der Bauverwaltung, No. 28 of April 8, 1914, p. 220 ( digitized version )
- The RhB. Part 3: St. Moritz-Samedan-Zernez-Scuol-Tarasp, Pontresina-Samedan and Chur-Arosa: the RhB's electric locomotives. (= Eisenbahn Journal. Specials 4). Hermann Merker Verlag, Fürstenfeldbruck 1998, ISBN 3-89610-038-6 , p. 78 ff.
- Hans Hofmann: Chur-Arosa, from the construction and operation of the railway. 2nd Edition. Calanda Verlag H. Hofmann, Chur 1989/93, ISBN 3-905260-11-5 , p. 56 ff.
- Fritz Maron: Chur-Arosa Railway. In: From mountain farming village to world health resort Arosa. Verlag F. Schuler, Chur 1934, pp. 115 f., 120, 122.
- Ueli Haldimann (Ed.): Hermann Hesse , Thomas Mann and others in Arosa - texts and images from two centuries. AS Verlag und Buchkonzept, Zurich 2001, ISBN 3-905111-67-5 , p. 108 f.
- Hans Danuser : Arosa - as it was back then. Volume 2: 1907-1928. Self-published, Arosa 1998, p. 92 ff.
- Hans Danuser, Ruedi Homberger: Arosa and the Schanfigg. Self-published, Arosa 1988, p. 128 f.
- Hans-Bernhard Schönborn: The Rhaetian Railway, past and present. GeraMond, 2009, ISBN 978-3-7654-7162-9 , p. 119.
- Society for civil engineering (ed.), Peter Marti, Orlando Monsch, Massimo Laffranchi: Swiss railway bridges. 1st edition. vdf Hochschulverlag, Zurich 2001, ISBN 3-7281-2786-8 .
- Bruno Hitz, Rudolf Weber: Experience the Rhaetian Railway . Orel Füssli, Zurich / Wiesbaden 1988, ISBN 3-280-01849-8 .
- Rhaetian Railway (Ed.): Rhaetian Railway . Desertina, Disentis 1988, ISBN 3-907036-08-5 .
- Hans Domenig: From the Tingelzüglein to the high mountain railway. In: Terra Grischuna. 59th year, issue 1, Terra Grischuna Verlag, Chur 2000, ISSN 1011-5196 .
- Katharina Hess, Paul Emanuel Müller: About the wild Plessur. In: Terra Grischuna. 48th year, issue 1, Terra Grischuna Verlag, Chur 1990, ISSN 1011-5196 .
Individual evidence
- ^ Photo of the model of the former railway museum in Zurich (the museum holdings have largely been in the Swiss Museum of Transport in Lucerne since 1959 ).
- ^ Bernhard Studer: A century Arosabahn. In: railway magazine. Issue 5, 2014, p. 31.
- ↑ 100 years, 800,000 trains - one car. In: Southeastern Switzerland . July 25, 2012, accessed January 2, 2020 .
- ↑ Hans Danuser : Arosa - as it was back then. Volume 6: 1979-1995. Self-published, Arosa 2002, p. 157 f.
