Ganter Bridge

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The Ganter Bridge, for a size comparison: There is a truck in the middle of the bridge
Ganter Bridge

The Ganterbrücke ( Valais German " Ganterbrigga ") is part of the Simplon Pass road of Nationalstrasse 9 and is located in the municipality of Ried-Brig in the canton of Valais in Switzerland . It is a cultural asset of regional importance and with the KGS no. 9077 listed in the list of cultural assets in Ried-Brig . From 1980 until the opening of the Poya Bridge in Freiburg in 2014, it was the bridge with the largest span in Switzerland.

history

The old Ganter Bridge

In the middle of the 20th century, the Simplon Pass road was added to the national road network of Switzerland as a winter-safe connection between northern Italy and Ticino with the Valais. The section between Brig and Gondo was expanded into two lanes as a 3rd class national road in the 1960s and 1970s, and new sections were laid out. About halfway between Brig and the top of the pass, 10 km south of Brig, the road leads through the steep, deeply cut Gantertal. The Ganterbach was originally crossed on a small bridge on the valley slope, followed on the right side of the valley by a 1.5 km long section of road that is at risk of rock falls. The Old Ganter Bridge (Ganterbrigga) is about 800 meters upstream (east) of the new bridge. This was built in the course of the construction of the Simplon Street by Napoleon Bonaparte 1801-1805. The old bridge had a central part made of wood so that it could be destroyed more quickly. The stone arch was installed later.

The new route alignment crosses the Gantertal before the geologically problematic section with the new large bridge, which shortened the length of the road by 1.7 km. In order to avoid the difficult founding conditions in the valley, the canton originally planned a tunnel, the cost of which was estimated at around 50 million Swiss francs. Because of these high costs, Christian Menn was asked for an alternative proposal. After examining the local conditions, Menn proposed a preliminary design for a cable-stayed bridge , which impressed the canton so much that he commissioned the design without holding a competition for the project.

The construction of the bridge lasted from late summer 1976 to December 1980. Due to the climatic conditions, the bridge could only be built eight months a year. The construction costs amounted to 23.5 million Swiss francs.

construction

In the bridge area, the S-shaped road route at the northern abutment consists of a right curve of 200 m radius, followed by a 225 m long, straight middle section and merging into a left curve with also 200 m radius. The longitudinal slope of the roadway, which is 1450  m above sea level. M. is mostly around 5% towards the south. Two 3.75 m wide lanes with 0.75 m wide edge strips on both sides and 0.5 m wide curbs are transferred.

Foundation and substructure

Side view of the Ganter Bridge

The difficult subsoil had a significant impact on the bridge construction and required as few foundations as possible and consequently large spans. The northern rock valley slope is very steep with an average incline of around 45 ° and shows strong signs of weathering on the surface. This resulted in the base of the slope on the Ganterbach as the location of the highest pillar S3 and the bridging of the steep slope with a large span of 127 m. The southern slope of the valley is inclined by about 25 ° and, from a depth of around 40 m, consists of decomposed and weathered slate rock with little load-bearing capacity, over which there is a loose rock cover that moves between 6 and 10 mm towards the valley every year.

The two pillars S2 and S3 on the north side of the valley are clamped in foundations in the rock. The 124.5 m high S3 pillar between the upper edge of the foundation and the roadway level has external dimensions of 12.0 × 10.0 m at the foot. The three pillars S4 to S6 arranged in the southern slope of the valley have floating shafts as foundations. The dimensions of the shafts resulted from load balancing, i.e. H. the weight of the excavated ground was about the same as the pillar load from the dead weight of the bridge. For the heaviest pillar S4, this resulted in a foundation depth of almost 40 m with a shaft diameter of 12.4 m. The pillars are slidably mounted on the shaft head plates with two Neo-pot plain bearings each . However, the bearings on pillars S4 and S5 are blocked as planned. To compensate for the slope movements, the pillars can be pushed back into their original position by pressing. The bearings of pillar S4 are designed for a displacement of 50 cm and have a diameter of 2.7 m and a load-bearing capacity of 10500 t.

In order to minimize the creeping movements of the slope, extensive surface and deep drainage was installed.

superstructure

The structure is 678 m long and has eight fields with spans (from south to north) of 35 m, 50 m, 80 m, 127 m, 174 m, 127 m, 50 m and 35 m. Except for the edge pillar S1, all pillars are monolithically (rigidly) connected to the superstructure, which means that the building system is a seamless, continuous frame system with a curved floor plan in the longitudinal direction .

The main opening with a span of 174 m was chosen so that it lies exactly in the middle of the straight road section. The 127 m long side openings are arranged in the curves. The superstructure is a box girder , prestressed lengthways and crossways , 10 m wide and between 2.5 m and 5.0 m high. The bridge girder is reinforced in the three main fields with flat inclined braces, which are designed as tension washers due to the curved side fields. The drawing pulleys consist of tendons , which are embedded in subsequently produced thin-walled concrete panels and anchored to the 15-meter pier heads.

As a mixture of a prestressed girder bridge and a stay cable bridge, the building structure can nowadays also be referred to as an extradosed bridge . The main pillars of the seamless eight-field frame are a maximum of 150 m high.

The superstructure of the main spans was built using cantilever . The piers S4 to S6, which were articulated in the final state, were provided with a provisional foot restraint.

Repairs from 2006 to 2008

Between 2006 and 2008 the bridge was renovated for a total of 10 million francs. On the one hand, the roadway was renewed and the insufficient covering of the reinforcement replaced. At the same time, the bridge piers on the south side were shifted to the south by up to 105 mm. The next adjustment of the bridge piers is planned for 2050. In addition, Webnet rope nets were installed as a barrier for those at risk of suicide.

Trivia

The song “Ganterbrigg - Alterschtatzion” by the Valais singer Sina and also the song “Dr Bus” by the Valais hip-hop combo Jess-g-Gott deal with the suicide issue in connection with the Ganterbrücke.

literature

Web links

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

Coordinates: 46 ° 17 ′ 47 "  N , 8 ° 3 ′ 3"  E ; CH1903:  six hundred and forty-seven thousand one hundred seventy-one  /  127403