The Ribcage concrete bridges, Leidschenveen, 1998-2002
Our winning entry to an international competition to design 50 concrete bridges for Leischenveen([a Vinex development near Leidschendam/The Hague) was based on modern concrete technology. After analysing the mechanical behaviour of various bridges, we arrived at a new design with a varying cross-section in concrete. The span is supported by a concrete ‘spine’ which reaches maximum height in the middle of the span and flattens out at the bearing ends, thus following the moment curve. The changing cross-section of the pre-stressed tension cables fits in well with this concept: the tension strands are gathered in the narrow middle section and fan out at the bearing ends. Slender transverse ribs stiffen the bridge and allow the highly economic use of materials: even at maximum traffic load, the bridge only needs to be 100 mm thick at the edges. The distinctive spine with its changing profile, and the cross-ribs which also vary in height, are clearly recognizable as a reflection in the water surface.