Viaduct over River Ulla: An Outstanding Composite (Steel and Concrete) High-Speed Railway Viaduct

The viaduct over River Ulla is located in the Atlantic High Speed Railway Line between A Coruna and Pontevedra, in the northwest of Spain. Its location, close to the firth of Ulla, in a landscape of outstanding natural beauty and strong environmental constraints, was the object of a tender among the most renowned Spanish structural specialists. The solution chosen was a 1620 m long viaduct, with three main spans of 225 + 240 + 225 m and several approaching spans of 120 m length each, which meant a main span being about 20% longer than the Nantenbach bridge in Germany, the current world record in High Speed Railway composite steel and concrete truss girder beam bridges. The main spans have been designed with a double composite steel and concrete truss deck, with double composite action in hogging zones, and a total depth ranging from 9,15 m at the mid-span section to 17,90 m at the section over the piers. The adjacent spans that give access to the depth-varying main ones have been designed with constant depth. This article describes the structural conception of the bridge and the three different constructive processes that had to be used due to the access and the environmental restrictions.