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In the spider’s web. Stuttgart railway overpass cable-stayed with CFRP

A spectacular display of bridge-building took place in Stuttgart recently. For the extension of underground line U6 from Stuttgart-Fasanenhof to the airport, a 127-metre-long railway overpass owned by Stuttgarter Strassenbahnen AG (SSB) was inserted into place over the A8 motorway. Its hangers are composed entirely of carbon-fibre-reinforced polymer (CFRP). This ultralight and incredibly stable material was developed primarily by the Swiss Federal Laboratories for Materials Science and Technology (Empa). The intricate network arch bridge developed by Stuttgart-based engineering firm schlaich bergermann partner (sbp) consists of two parallel steel arches and a concrete deck stayed with CFRP hangers manufactured by Carbo-Link, Empa’s spin-off. Both the bridge arches and the deck were constructed directly beside the motorway. The 72 carbon hangers, which resemble a spider’s web, contribute only 1,675 kilograms to the bridge’s total weight of roughly 1,500 tonnes. Unlike a classic tied-arch bridge with vertical hangers, the suspender cables criss-cross each other diagonally to give the impression of a fine rope net. For railway bridges, it is particularly important for a network arch bridge to sag less than a tied arch bridge with vertical hangers so that the tracks do not bend as much when they bear the weight of a train. The wear of 100 years of railway operations had to be simulated with more than eleven million trial train runs in order to test the new type of material.

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