Cerradura Stress-Ribbon Footbridge. Iznajar (Spain)

A 25.00 m span stress ribbon footbridge is projected in ‘La Cerradura’ recreational area, located on the end riverbed of the Iznajar reservoir, in the province of Granada, Spain. Footbridge allows the access to both river banks, and additionally provides beautiful views of the cliff and the valley. On the other hand, structure allows access to the area all over the year, since present existing path is free of the reservoir action only in summer season, increasing in this manner, the value of this natural area for visitors. Among the studied solutions, the winner was a 25.00 m span stress-ribbon footbridge with two Vierendeel truss ramps for access anchored each 3.00 m against the cliff. The deck of the stress-ribbon is formed by a concrete slab 0.20 m deep and 3.50 m wide. The deck was suspended on two bearing tendons 19C15, and post-tensioning was applied with seven tendons of 7C15. The deck has been assembled from precast segments that are hung on temporary erection cables and removed after post-tensioning of the deck with the internal tendons. The maximum slope of the stress-ribbon is very limited by aesthetic reasons, so the deck is stressed by a large horizontal force that has to be transferred to the soil. The abutments need to transfer into the soil, by rock ground anchors, very large horizontal forces. The Vierendeel truss of 1.50 m deep fits perfectly to the topography of the rock, configured as a genuine way in the air. The whole work gets a perfect adaptation to the environment where it’s located.