Suspension bridge, Trift glacier

The Trift glacier in proximity to the Swiss Susten pass is one of the most quickly melting glaciers in the Alps. Ladders as well as a path along the glacier provided access to the Trift lodge. In the meantime, however, a lake formed at this location. Since a detour would have been significantly longer and more difficult, the decision was made to cross the gorge at its narrowest with a suspension bridge. After five months of planning and construction, the first Trift bridge was opened in September 2004. Despite the simple and cost efficient construction mode, e.g. with recycled steel cables, the bridge was designed for long service. However, the planners had underestimated two factors. For one, the structure attracted far more visitors than originally expected. Beyond that, the bridge had been designed for wind speeds up to 120 km/h in ­relation to data from a nearby measurement station. However, the observation was made that gusts of wind in the narrow gorge reached wind speeds up to 200 km/h and resulting turbulences caused torsion within the construction. The decision was made to build a new bridge at a safe location, offset by 20 m and 30 m higher, with a simpler access path and also lower wind speeds due to the greater gorge width in this area. The construction principle remained, yet was adapted to the increased span and budget. A parabolic underspanned suspension stabilises the delicate construction and prevents uplift at extreme wind speeds. Two U shaped steel elements each placed at one third of the entire span provide additional stabilisation and also stiffen the suspension cables. After two years of planning and six weeks of construction the new, approximately 170 m long bridge spanning the Trift gorge at a height of almost 100 m above the lake was opened in summer 2009. The old bridge served as work platform. In a final step, the parabolic underspanning was tensioned. The old bridge was disassembled and transported for re-use at a new location only after the new bridge was completed. As Salbit bridge, it now connects two lodges in the nearby Göschener valley