Sitter Viaduct (Southeast Railway)

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Coordinates: 47 ° 24 ′ 2 "  N , 9 ° 19 ′ 30"  E ; CH1903:  742,384  /  251 691

Sitter Viaduct
Sitter Viaduct
Sitter Viaduct with Voralpen-Express, including the power station Kubel power plant, SBB-Sitterbrücke in the back
Convicted St. Gallen – Wattwil railway line
Subjugated Sitter
place St. Gallen
construction Stone arch bridge with fish belly girders
overall length 365 m
Longest span 120 m
height 99 m
building-costs 1.55 million francs
start of building 1908
completion 1910
location
Sitter Viaduct (Südostbahn) (Canton of St. Gallen)
Sitter Viaduct (Southeast Railway)

The Sitter Viaduct is a single-track railway bridge of the Südostbahn (SOB) over the Sitter near St. Gallen . It belongs to the St. Gallen – Wattwil railway line , which is used by the Voralpen-Express , among others . The 365 meter long viaduct of the former Bodensee-Toggenburg-Bahn (BT) is 99 meters high and is the highest railway bridge in Switzerland.

location

The machine house of the Kubel electricity works , the mouth of the Urnäsch and the wooden Kubelbrücke , over which the St. Gallen Bridge Path leads, are located under the SOB's Sitter Viaduct . The SBB's Sitter Bridge is around 400 meters downstream . The Sitter forms the border between the cantons of St. Gallen and Appenzell Ausserrhoden under the viaduct .

  • Floor plan of the Sitter Viaduct and the power station building

description

Voralpenexpress on the Sitter Viaduct. The two curves at the back on the St. Gallen Haggen side and at the front towards Herisau are clearly recognizable.

The viaduct consists of two foreshore bridges made of stone vaults and a 120 meter long steel riveted single lattice girder with a downwardly arched, maximum 12.5 meter high semi-parabolic girder ( fish belly girder ). The truss is still the most widely spanned girder of a Swiss railway bridge. The entire length of the bridge is at a gradient of 16 per mille. On the Herisau side , the iron intermediate girder is followed by two brick arches with openings of 25 meters and five arches of 12 meters, which are located in a curve of 350 meters radius. On the St. Gallen side there are four arches with a width of 25 meters in a curve with a radius of 1000 meters. All the pillar foundations could be set down on Nagelfluh . The pillar built right next to the Kubel power plant is 93 meters high and is the tallest structure in the city of St. Gallen . On the movable support on the Herisau side, the track is provided with a dilation device that allows the truss to expand by 140 millimeters.

The viaduct is a cultural asset of national importance with KGS number 8304.

planning

The originally planned straight line had to be abandoned due to objection from the Kubel power station, which also necessitated the construction of the 247-meter-long Sturzenegg tunnel southwest of the viaduct. The bridging of the Sittertobel went beyond the usual scope of a private railway . Three different projects were developed for the project:

  • A steel cantilever bridge with two end openings 98 meters wide and a central opening 147 meters.

  • A stone arch bridge with a main arch of 121.35 meters and vaults on both sides with a span of 25 and 12 meters.

  • A bridge with a steel semi-parabolic girder with a span of 120 meters and subsequent vaults with a span of 25 and 12 meters.

The choice was not easy for those responsible. The first two projects would have caused huge additional costs. Concerns about the large span of the main arch also arose in the second project. The project was realized with a steel lattice girder and subsequent vaults. Due to dam slides southwest of the viaduct, the structure had to be extended by two arches, each with a span of 12 meters. The bridge cost the then proud sum of 1.55 million francs.

construction

An truss subsequent vault with three-hinged arch: The two fighters joints are orange, the peak dyed light blue joint.
In June 1909 the construction of the more than 75 meter high scaffolding tower for the assembly of the truss was completed.
Wooden scaffolding tower for assembling the truss in February 1910.
View into the interior of the intermediate carrier.

The material for the construction of the bridge was brought from the St. Gallen freight yard to the eastern bridgehead by light rail . The stone vaulted bridges with 26,000 m³ of masonry were built in the traditional way at the time using two material ropeways and other ropeways that span the valley . The work was made more difficult by the building of the Kubel power plant and by the subsequent extension of the viaduct on the Herisau side.

The pillars and front walls are made of Schrattenkalk from Hohenems . Sandstone from Staad and Wienacht was used for the interior of the bridge . Sand and gravel were extracted directly in the Urnäsch and Sitter and processed with two stone crushers. For the lining of the vaults with sand-lime bricks from Regensberg , falsework was created, which were supported on both sides on steel girders built into the pillars. The two vaults adjoining the steel lattice girders were designed as three- hinged arches with two transom and one crown joint in order to avoid cracks in the masonry.

From summer 1908 to spring 1909 , the well-known master carpenter Richard Coray built a wooden scaffolding tower with a total height of 97.15 meters in the middle of the bridge for the installation of the 920-tonne truss . In the tower was a lift for ten to twelve people with a lifting height of 78.5 meters. The dimensions of the scaffolding tower were imposing. 1650 m³ of wood were used for its construction and it weighed almost 1400 tons. In November 1909, the scaffolding tower and the bridge withstood gale-force autumn storms.

In the fall of 1909, the Bell machine works began assembling the truss at a dizzying height. The mild steel plates riveted to with prepared red-hot rivets together. As soon as the steel intermediate girder was completed, it was set down on the main pillars. It lies on four granite blocks, each weighing 13.5 tons. Setting it down and fitting it onto the abutment at a dizzy height required sophisticated, courageous and precise engineering.

  • View from the Herisau abutment at the start of construction on May 5, 1908

  • A pillar was erected in July 1908. The stones were transported with the help of a freight train.

  • Electric drive stations for the two material ropeways leading over the Sittertobel.

  • A goods cart of the material ropeway on the Herisau side.

  • Work status as of August 1909, two 450-meter-long material ropeways run across the Sittertobel.

  • Status of work in October 1909 on the pillars on the Herisau side.

  • In January 1910, the 120-meter-long and 920-tonne steel middle section was assembled on the scaffolding.

  • Riveting work on the steel middle section at a height of almost 100 meters.

  • In autumn 1910 the scaffolding tower that was used to assemble the middle section was dismantled.

Conversions

Weight lever on the Herisau side to relieve the two abutment pillars.
Electric locomotives and multiple units have been running over the Sitter Viaduct since 1931, such as an SBB NPZ in 2012.

Soon after the start of operations, clearly perceptible depressions appeared on two of the vaults. Cracks formed in the vaults and the 90 and 60 meter high abutment pillars . These two pillars leaned against each other by 270 millimeters. To stabilize the structure, a bracing device, which is still effective today, was installed between 1920 and 1922, as it had already proven itself in the Eglisau Rhine Bridge . A weight lever generates a horizontal counter pressure of 2240 kilo Newtons [kN] to relieve the two pillars.

So that the Bodensee-Toggenburg-Bahn (BT) could start electrical operation on October 4, 1931, several catenary masts had to be installed on the viaduct .

Because a waterproof for road gravel lacked trough, water penetration caused frost damage . In the 1970s, BT built a gravel trough made of reinforced concrete over the stone vaulted bridges with moisture insulation on top. The trains, which have become increasingly heavier since the middle of the 20th century, made it necessary to reinforce the truss. Since the railway had to be maintained, the reinforcement work extended over the years 1978 to 1982. During this time, a complete repainting was also carried out. With the installation of an elastic track fastening, the noise of the trains traveling over the viaduct could be reduced. Because the Schrattenkalk from Hohenems proved to be insufficiently frost-resistant for the pillars and front walls, the main pillars were given a concrete coating.

swell

Web links

Commons : Sitterviadukt SOB  - collection of images