Cross Country Ski Bridge Pradella

Walter Bieler, Reto Ziridel

Subject | Because of its many mountain river valleys, its vast forests and its wet climate, Switzerland has a centuries-old tradition of bridge-building. This encompasses in particular timber bridges, in all shapes and sizes but always with a roof and side cladding to protect the timber. However, such covered structures were regarded as too heavy - both physically and visually - for modern bridge designs. Open, slimmer structures were called for, utilizing all the possibilities of modern technology. For instance, instead of a roof, the surfacing to the bridge deck can meet the function of providing protection for the loadbearing timber construction. Unprotected secondary members, e.g. balustrading, are regarded as expendable items and are designed to be easily replaced. This was the approach taken by Walter Bieler and his engineering team in their efforts to continue the development of modern timber bridge-building.

Design | Local power company Engadiner Kraftwerke AG wished to erect a crosscountry ski bridge over the River Inn about 3 km downstream of Scuol. A design using two 8-m-deep timber girders had already been devised for this purpose, but Walter Bieler's involvement subsequently resulted in a new design in 1990. The positions of the abutments and intermediate piers were retained but instead of the girder merely a 1.70-m-deep bridge beam was proposed which, with the side planking to protect the beams, appeared to be an extraordinarily light and delicate structure, fitting in well with the surrounding landscape. This design was finally approved not only because of the 46% reduction in building costs but also because the structural concept required far fewer loadbearing members and connectors, and thus promised to be a low-maintenance design less prone to corrosion.

Location

Pradella, near Scuol, Switzerland

Client

Engadiner Kraftwerke AG, Zernez, Switzerland

Structural Engineer Walter Bieler Ing. SIA, Ingenieurbüro für Holzkonstruktion, Bonaduz, Switzerland Assistant

Marcus Schmid, Dipl.-Arch. ETH/SIA.

Design

Reto Zindel, Dipl.-Arch. ETH/ SIA., Chur, Switzerland

Timber Construction Malloth + Söhne, St Moritz, Switzerland

Date of Completion 1990

Costs

The cost, including the deck surfacing but excluding the concrete works, was about 460 000 Swiss Francs.

Structure [ The bridge comprises four 200-mm-wide glulam beams placed at 1000 mm centres over the three spans of 21.50 + 42.0 + 21.50 m. The most favourable and cheapest solution was to employ the cantilever girder principle, i.e. the end spans cantilever 7 m beyond the piers and carry the 28-m-long centre section via two 20 mm dia. bolts per joint. Tensile forces are transferred to the beam ends

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