The Karabel Bridge in Northern Spain: Pillarless Construction thanks to Hangers
The Karabel Bridge is a new bridge in the Basque Region in northern Spain that crosses the Urumea River in the town of Hernani in the Karabel neighborhood. It replaces an old bridge with 4 massive stone pillars that often caused flooding because they narrowed the river bed. The new bridge crosses the river without any pillars so that future high water can flow freely through the area.
The new arch bridge has a free span of approximately 51.5m and was planned as a steel concrete composite structure. The bridge frame consists of steel, and the two arches that are inclined towards the outside reach a height of 8m above the bridge deck. The bridge deck itself was built using reinforced concrete after lowering and positioning the frame girder structure.
The bridge deck is supported by 18 hangers consisting of 64mm Ø, Type DST-520 M64, St 520/650 N/mm2 bar tendons. The bar tendons were produced by Daver Steel, DSC Spain’s exclusive partner, and supplied to the jobsite complete with assembled forks and pins. The tendons were equipped with turnbuckles that were used for the correct assembly and stressing of the hangers supervised by DSI specialists.
The entire steel composite structure of the bridge was preassembled on the Urumea River banks. Once completed, the 250t bridge was moved to its final position and placed on the abutments. Afterwards, the reinforcement was installed and the bridge deck concrete was poured. As soon as the reinforced concrete deck had reached the necessary strength, a DSI specialist once again checked the tension forces on each individual hanger.
Afterwards, the designer made some adjustments during which some tendons were restressed and others destressed. For this purpose, the Daver Steel system was used. In this system, two structures embrace the tendons in the turnbuckle zone, and two jacks produce a relative movement so that the turnbuckle is free to move for stressing or destressing the bar tendons.