The chapel is situated at one of Japan’s leading resort hotels, Bella Vista Soa and Marina, Onomichi which overlooks the Seto Inland Sea.
Two interlinking spirals
Inspired by a flying ribbon, two spiral staircases start at different locations before ascending and connecting at the 15.3m high rooftop platform to form a single ribbon, symbolising two paths ending in marriage. The intertwining stairways also form the roof, eaves and walls, enclosing the central space that can seat up to 80 guests.
With just four connections where the inner and outer spirals meet, the two spirals mutually support each other and create a self-standing structure.
Structural model with 3D torque
Our structural engineers foresaw that when shoring was removed the building would undergo rotational sagging of up to 30mm under its own weight. So a structural model was made applying the same amount of reverse torque as the predetermined natural rotational force, the amount of possible deformation calculated through computer simulation.
As a result, the studs, which were deliberately angled for construction, became perpendicular at the time of completion, and stayed within a 2/1,000 margin of error between floors.
In order to reduce cost and construction time, a spiral steel tube approximately 280m long and 318.5mm in diameter that had been designed to form a single uninterrupted free curve, was replaced with 88 joined sections of different two-dimensional arcs, with radius ranging from 1.5m to 9m. The difference (10mm maximum) from the actual free curve was compensated for by the base material of the finish, resulting in the seamless flow of a helical curve.
Ribbon Chapel seamlessly integrates architecture and engineering to create a building of unprecedented composition. Arup provided structural, geometric, mechanical and electrical engineering, lighting design and acoustic consulting services to realise this delicate yet bold design.
The project has bagged multiple honours, including the Overall Winner of the LEAF Awards 2015, the Grand Award of Japan Commercial Environment Design Association Awards 2014, the Japanese Society of Steel Construction Outstanding Achievement Award 2015, and the Japan Society of Seismic Isolation Award 2015.
In particular, Arup’s Ikuhide Shibata, the project director, received the Japan Structural Designers’ Club Design Prize in 2015 for his outstanding contribution in realising this masterpiece.