The Sunniberg Bridge

Today we cycled down the valley to the next little town, passing the Sunniberg Bridge on the way. This bridge has become quite a landmark in the area, as it is an amazing engineering feat. It was designed by a Swiss engineer called Christian Menn, who won an award for its innovative design and aesthetically pleasing appearance.

It is a tall cable-stayed bridge, 526m long, 12m wide, with a longest span of 140m, and pylons up to 77m above ground level. Menn's adoption of the extradosed bridge form allows the deck to be more slender than in a conventional box girder bridge (because it's supported by cables from above), while the overall bridge doesn't spoil the beautiful mountain landscape (because the cables are at a much shallower angle than a conventional cable-stayed bridge). The extradosed bridge is really a special case of a post-tensioned bridge, where the cables are lifted out of the deck to allow the overall bridge deck to carry higher bending moments and shear forces at pier positions.

The bridge was designed without any expansion joints, which means that under temperature variations, the deck "breathes" i.e. sways sideways. The piers are designed with relatively slender bases to be flexible enough to withstand this movement, and along with the need to maintain highway headrooms, this leads to their distinctive and elegant Y-shape.

It took 2,5 years to build at a cost of SFr 17 million - and it was ironically opened by Prince Charles, that notorious foe of modern architecture!

The bridge is part of the Klosters bypass scheme, and leads into the Gotschna Tunnel which burrows through the mountain to allow the village to be bypassed by passing traffic. The tunnel is 4,2km long and was built at a cost of SFr211 million and took 8 years to complete.

No wonder Swiss engineers have such a stellar reputation and this bridge is studied by engineering students at universities all over the world!

More photos of the bridge can be seen here