This week’s Postcard Friday looks at a very unusual bridge, one that has a unique design but is located deep in the mountains. The bridge at hand is the Trisanna Bridge. It’s located in the Austrian Alps near the town of Pians in the state of Tyrol. It’s located next to the Wiesberg Castle, which dates back to the 1400s. Together, they make for a perfect photo opportunity, regardless from which angle.
The bridge itself was constructed by Ludwig Huss in 1884. It had a curved Whipple design. Huss had the challenge of building a structure that was high into the mountains. With a height of 86 meters (282 feet) above the ground, the bridge was one of the highest ever built in Austria during that time. The main span was supported by stone viaduct approach spans on each side of the river valley. With the main span being 120 meters (390 feet), the bridge has a total length of 211 feet (692 feet). It took Huss and crew two years to build the bridge, with it opening on 21 September, 1884. Because of concerns regarding the stability of the bridge, especially in the lower deck, an inverted arch featuring a Vierendeel truss design was added in 1922, thus the bridge had a belly-fish design with two different truss designs in one single span. To this day there has been no other bridge with such a design.
Sadly the contraption lasted only 42 years and in 1964, the bridge was replaced. While the stone approaches remained, a tireless effort was undertaken to lower the belly-fish span to the ground. Elevator scaffolding was installed on both ends of the span, while at the same time, the new span was constructed off-site. Once it was ready, it was lifted up on the north side of the scaffolding to the site of the old bridge. That span was then pushed off its foundation and was hoisted down slowly to the ground, where it was dismantled at the site with the bridge components hauled away. The new span was lifted onto the foundation and was attached to the railroad bed.
Today’s bridge still is one of the highest in Austria and it is still one of the most photographed structures in the Tyrol region. It’s popular because of its natural setting yet its history and design makes for stories to write about and topics to discuss in the engineering community. It is one of the forerunners of the high spans we see today but also one that is famous, not just for its design but also for how it was built.
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