Located next to the Atomic Bomb Dome, a UNESCO World Heritage Site, Orizuru Tower, named after the folded paper crane, has become a symbol of peace in its own right and a must-see destination in Hiroshima.

The building was renovated and seismically retrofitted from an existing building completed in 1978. Arup provided total structural engineering and building physics analyses to help realise this unique city icon.

While the majority of the 14-storey building houses office spaces, the first and top floors are designed for tourists - the first floor offers cafés and shops and the rooftop observation deck provides panoramic views of the city. One of the most distinctive features of the building is a collection wall of paper cranes which can be seen from the street. 

Seismic performance beyond regulation

The original steel embedded reinforced concrete structure was built before the major code revision in 1981, and therefore the structure had only up to 50% of the seismic capacity required by the latest building code. 

After the renovation, this building has achieved the seismic performance that is 1.5 times as what is required in the current code, even after inserting an observatory at the roof level.

Fitting the new into the old

The new spiral slopes on the east side and the extended balcony on the west side of the building are used as reinforcing elements. The heavy concrete walls have been replaced with light weight glass curtain walls. 

The new reinforcing steel framing is tied to the existing framing with high tension steel bars. This new portion has an independent pile foundation to transfer the loads safely into the ground.

Energy-efficient office spaces

By studying the seasonal prevailing wind and carefully conducting CFD analyses, our building physics specialists suggested the optimum locations for the façade openings to maximise natural ventilation. 

During mid-seasons, the south-west wind produces cross ventilation throughout the office spaces from the south side to the north side when the north-west façade is closed. This is an attempt to create energy efficient office spaces that reflects the environment outside, in contrast to the fully closed air-conditioned spaces.