Architects and Structural Engineers:Daiichi-KobeAssociates,Fujita Corporation
The basic idea in the organization of space was to cover the central field with a circle with a diameter of 125m, freely arrange the other facilities on the periphery an cover those facilities with an irregular form, Instead of enveloping the entire domed space with one large structure ,the idea was to create a number of frameworks, each adapted to the shape of an internal space and then integrate them. This was to be “an indoor playground”, “a work of originality that combines advanced technology and the latest thinking” and “an energy saving facility that, for example, uses natural energy.” For these reasons, it was decided at a fairly early stage in the design process to give the building the image of a cloud floating above the earth.
To achieve this image, it was decided to make the large circular roof a double-layered air-inflated membrane structure and to cover the irregular peripheral portion with a single-layered membrane structure. All indoor spaces including the field are at normal pressure and doors and windows can be freely arranged because only the roof is a air-inflated membrane structure. A simple frame in the form of a truncated cone is introduced in the center to maintain the thickness and configuration of the double-layered air-inflated membrane. The arrangement is also effective acoustically, because the opening gives to the ceiling surface a naturally convex shape that scatters sound toward the periphery and reduces echoes.
The double-layered air-inflated membrane forming a “floating cloud” with a diameter of 107m was built by linking a framework in the shape of a truncated cone in the center and a ring truss with 48 upper radial cables and as many lower radial cables, covering them with PTEE coated glass fiber membrane and introducing air into the double-layered membrane to achieve an internal pressure of 300mmHG(in normal circumstances). This enormous disc-shaped roof with an outer diameter of 128m is held up at eight points along the ring truss by supports, each made up of three columns. Since the air-inflated membrane is supported by cables, no damage through contact will occur even in the case of deflation. The arrangement is also advantageous from the point of view of disaster prevention and evacuation. This structural system is called a “hybrid double-layered air-inflated structure” because it combines the merits of a wheel-type cable structure and a air inflated membrane structure , and the project is the first application of the system in the world.
The framework of the single layered membrane covering the irregular peripheral portion was made a simple lattice shell structure in which steel pipes are assembled in a grid using ball joints with a diameter of 350mm.
Construction of the dome took approximately 20 months. The procedure followed for constructing the main structure was as follows. First, simultaneously with the erection of the eight 3-column supports , the ring truss and the truncated cone shaped central ring were assembled in a low position where it was easy to work and were joined by upper cable and membranes. Next, the lower cables and membranes were attached to these cables and air was introduced inside. After sash and glass had been installed in the ring truss [weight: approximately 2400t], lift up to a height of 19m was carried out. The inner columns of the 3-clumn supports served as guides in this process. Finally, the irregular, single-layered membrane connecting the ring truss to the reinforced concrete canopy of the peripheral portion, on which work had been proceeding simultaneously, was constructed.