The OH-1 (tentative name) redevelopment project is a two-tower development in the Ohtemachi business district in Chiyoda-ku, Tokyo, Japan. It is one of the biggest urban development projects to be undertaken in Tokyo.
The site of the project was home to Mitsui and Co’s headquarters, which was demolished to construct the two towers. The office section of the mixed-use development will become Mitsui’s new headquarters.
Mitsui Fudosan is developing the project and construction commenced in May 2016. It is scheduled for completion in 2020. Mitsui is investing JPY120bn (approximately $1.23bn) in the project, while Mitsui Fudosan will invest JPY50bn (approximately $515m).
The development is expected to establish Tokyo as a cosmopolitan hub and cultural destination.
The OH-1 redevelopment is being carried out on a 20,900m² site, which will include towers A and B. The towers will have a combined floor space of 360,000m².
Tower A will be a 30-storey building with a height of 160m, while Tower B will be a 41-storey building with a height of 200m.
Skidmore, Owings and Merrill architects drew inspiration from the neighbouring Imperial Palace gardens to create the delicate exterior design.
The two towers differ in height, massing and materiality. Tower A’s design is inspired from traditional Japanese craftsmanship and woodworking techniques, while it uses a combination of granite and glass cladding.
Tower B’s design is a symbol of contemporary Japan and will be clad in steel and glass. The towers are designed to allow natural ventilation and incorporate a range of sustainable features that reduce energy usage.
The development will create commercial office space, a multipurpose hall, luxury hotel, retail spaces, and parking areas.
The multi-purpose hall of the development, including a 1,500m² foyer, will be located on the third floor of Tower A. It will be capable of accommodating business events, international conferences, musical performances, and entertainment activities.
The development also includes temporary accommodation facilities, which can be utilised in emergency situations. The facilities include space for 2,400 people, storage areas for emergency provisions, and emergency wells.
A state-of-the-art co-generation system will be installed in the development, which will use oil or medium-pressure gas. The system will be capable of providing power supply even in case of emergencies, ensuring business continuity.
A key feature of the project is the development of large landscaped public open space covering an area of 6,000m². The green space extending up to the Imperial Palace gardens and the nearby Masakado Shrine will be the biggest in the Ohtemachi district.
The public space will preserve and enhance the existing setting of the Masakado Shrine. It will feature a wooded area, including local tree species, a water feature, and a plaza to facilitate outdoor events.
The two towers will be fitted with advanced HiDAX-R oil dampers developed by Kajima Corporation to provide wind and earthquake resistance.
The state-of-the-art systems can protect against wind-driven motion and earthquakes of 7.0 intensity. They are also effective in preventing shaking caused by intensity 4-5 earthquakes or seismic motions.
The joint venture of Nikken Sekkei and Kajima Corporation was awarded a design and construction contract for the project.
The project is expected to improve the international competitiveness of Tokyo by creating an attractive urban space. It will also improve business continuity planning functions and disaster preparedness in the district by upgrading the district cooling and heating system.
The systems will be upgraded with anti-flooding and earthquake-proofing features. Efficiency improvements will also be undertaken to reduce carbon emissions by 1,000t a year.
Its development will also be integrated with Tokyo’s public transportation system. It will create a barrier-free pedestrian network linking with the subway concourse and provide direct access to multiple Metro lines.
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