Arch bridge over the river Butrón in Gatika (Bizkaia)

Abstract

The unique medieval castle of Butron is located in the municipality of Gatika, in the Historical Territory of Biscay, within one of the last meanders of the Butron river, before the estuary of Plentzia. The ancient masonry bridge connecting the castle and the opposite bank of the river, apart from being a hydraulic obstacle favouring the flooding of the alluvial plain in the area, presented a high risk of collapse. The municipal administration decides to reconstruct the ancient bridge, building a reinforced concrete arch bridge, with a single span of 23 m and a rise-to-span ratio of 1/6,57. This structural typology was chosen because of its ability for ensuring hydraulic section, and as a reminiscence of the ancient bridge. This humpback profiled structure is an example of an arch solving, in our days, a clearance in the range of very short spans.