Architect: Grimshaw Architects
Constructeur: WS Atkins UK en Ingenieursbureau Amsterdam
In June 1997, Grimshaw was appointed as architect for the development's first two bridges, following an international design competition. The bridges are central to the IJburg development's success in that they function as the main 'umbilical cords' to the existing Amsterdam infrastructure. In line with the policy on environmental alternatives to car congestion, they each accommodate two tramlines, two cycle paths and pedestrian footpaths, as well as several lanes of traffic, mains drainage and other public utility services. These requirements necessitated considerable design co-ordination.
The main bridge is 250m long and links the first of the islands to the mainland. It has been designed to reflect this landmark status and to acknowledge the transition from old to new land. It is 30m wide and has two decks. These are divided to leave appreciable gaps with views of the water below, ensuring that travellers experience their passage as a bridge and not a causeway.
In profile, the bridge is an undulating wave-like form, with two arches linked by a counter-arch. As the arches are fabricated from faceted lengths of steel box girder and the connections between elements are expressed, the structure is sinuous and elegant, as befits its landmark status and context.
The main arches work quite conventionally, but the counter-arch, while visually continuous with the other two, functions as a bowstring truss. It is in compression, but reads visually as if it were hanging in tension, merely touching the water.
Each arch and deck segment was prefabricated from steel and delivered to site by barge before being finally craned into place. Concrete abutments, central supports and the bridge deck topping were mainly constructed insitu. A key engineering challenge was to ensure that no lateral forces were transferred from the arch bearings to pile caps owing to the delicate nature of the geology below. For this reason arches are tied using post-tensioned steel cables and rest on sliding bearings.