Two Footbridges in Tokyo: Case Studies on the Relation Between Structure and its Form

The paper presents two footbridge projects recently constructed in Tokyo, Japan, with focus on the architectural and associated technical challenges. The first footbridge in Tokyo is located at the newly developed high-rise complex Toranomon and serves as an open plaza, spanning 35 meters in length and 20 meters in width between two buildings. The structure is a simply supported monocoque box girder with a folded plate geometry in the bottom flange. The piers, made of multi-faceted non-standard cross sections, are designed for ductile plastic behaviour and thus limit the horizontal reactions to the substructure in case of extreme earthquakes, resulting in exceptionally slender columns. The paper discusses the technical challenges in designing the plastic behaviour of the multi-faceted pier cross sections, including the physical loading cycle test of the scaled model. The second footbridge, the Shiokaze bridge, is situated in the coastal park in Odaiba, an artificial island in the Tokyo bay, connecting two sides of the park which are separated by the water. In plan, the deck alignment is gently curved towards the seaside to achieve a smooth transition to the primary undulating walkways of the park. The form of the arch bridge is determined through form-finding, eliminating unfavourable bending moment due to the geometric variation of the hanger angles. The paper discusses the process of form-finding and the materialization of the found form.