Situated in Tokyo’s Ueno Park, the main building of the National Museum of Western Art was designated as a UNESCO World Heritage Site in 2016 as one part of “The Architectural Work of Le Corbusier, an Outstanding Contribution to the Modern Movement.” The building was constructed in 1959, before the development of architectural technology for preventing the impact of earthquakes. It was later equipped with excellent measures to combat earthquakes, helping to save it from damage. The 2011 off the Pacific coast of Tohoku Earthquake brought significant damage to eastern Japan, though this building was almost completely unaffected. The precious works of art inside it similarly suffered almost no harm.
     The building had been standing for 52 years at the time of the earthquake, and was hit by tremors ranging from 5-higher to 5-lower on the Japanese seismic intensity scale. It only received very little damage despite these strong tremors, because seismic isolation technology almost completely stopped the building from shaking.

Seismic Isolation Technology Absorbs Earthquake Tremors and Prevent Buildings from Shaking

     What kind of technology is seismic isolation?
     There are three kinds of methods for protecting buildings from earthquakes: earthquake resistance, tremor control, and seismic isolation.
     Earthquake resistance involves reinforcing the building itself so that it will not be destroyed in the event of an earthquake.
     Tremor control involves incorporating vibration-absorbing devices within the structure of the building, preventing it from being ruined by earthquakes.
     Meanwhile, seismic isolation involves installing “seismic isolation devices” under the foundations of the building, rather than inside the building itself. This helps hold back earthquake tremors from reaching the building. Even if the surrounding area shakes from side to side, the seismic isolation devices work as a cushion to prevent vibrations from reaching the building. As a result, the building is less likely to be destroyed by the earthquake. This method does not completely prevent the building from shaking; rather, it slows down the vibrations of the earthquake, meaning that the building only moves back and forth slowly.

The Mechanism for Absorbing Vibrations

     Seismic isolation devices are made from material such as laminated rubber, produced by stacking sheets of rubber and metal on top of each other like a mille-feuille or custard slice. Even if the surrounding area trembles violently through the earthquake, the seismic isolation devices deform and absorb horizontal tremors, reducing the extent to which the building shakes.

     Seismic isolation technology has not spread much outside of Japan, but it gained rapid popularity in Japan following the Great Hanshin earthquake in 1995. The city of Kobe suffered extensive damage, but some buildings constructed with seismic isolation were not harmed at all. This led to an increase in interest about this technology. Similarly, buildings with seismic isolation suffered little damage in the Tohoku earthquake, demonstrating the advanced capabilities of this technology.

“Seismic Isolation Retrofitting”: Providing Seismic Isolation in Existing Buildings

     After the Great Hanshin earthquake, the National Museum of Western Art was examined for its earthquake resistance. This examination revealed that the building had less than half the earthquake resistance required by standards in Japan at the time.
     The National Museum of Western Art is a valuable building designed by Le Corbusier, one of the leading architects of the 20th century. It houses and displays many precious western paintings and sculptures dating from the Renaissance to the start of the 20th century, including Monet’s Water Lilies and Courbet’s Gypsy in Reflection. As such, it was essential to renovate the building to improve its earthquake resistance. It was common at the time to add earthquake-resistant walls and increase the thickness of pillars and beams to enhance buildings’ resistance to earthquakes. However, this kind of construction work would spoil Le Corbusier’s original design. The only way to improve the museum’s earthquake resistance while preserving its cultural value was to utilize seismic isolation technology.
     However, it is not easy at all to incorporate seismic isolation into an existing building like the National Museum of Western Art.
     In order to preserve the building’s design and functions, this process requires working with the foundations that support the building and replacing some of the foundations with seismic isolation devices while the existing building is standing on them. This is like changing the legs on a table while there are many objects placed on it.
     This advanced technology is called “seismic isolation retrofitting.” This technology is used to protect buildings that were constructed before seismic isolation techniques existed, and it was implemented for the first time in Japan at the National Museum of Western Art. After this, the technology was used in other buildings such as Osaka’s emblematic tower, Tsutenkaku, and the smaller building in the JP Tower in front of Tokyo Station that preserves part of the former Tokyo Central Post Office.
     The process requires lifting the entire building or digging up the surrounding area for working on the foundations, and so it involves highly advanced technology and significant costs.

Designated as a World Heritage Site After Undergoing Construction Work Requiring Advanced Technology

     The National Museum of Western Art has a complicated structure with an atrium in its center as well as some areas featuring basement floors. For this reason, the building was analyzed before construction by using refined techniques to check that the entire structure could hold up after the renovations were finished.
     The actual construction work involved installing seismic isolation devices underneath the existing foundations. More specifically, workers first removed the flooring around the building’s foundations, dug the areas surrounding the foundations, and then installed posts that would support it temporarily instead of the foundations. This was done by cutting the posts into round slices and inserting them one by one under the ground. The posts were cut into slices because there was little space underground and so workers were unable to install a machine to install posts. After this, the workers cut away the bottom of the foundations and installed seismic isolation devices. Finally, they cut up and removed the posts, and then restored the flooring to its original state.
     A total of 49 seismic isolation devices were needed for the entire building. Each device bears anywhere from approximately 140 to 300 tons. They can support the museum’s weight and withstand the force of earthquakes even when the building has moved 40 centimeters horizontally and the laminated rubber has deformed into a diagonal shape.
     Construction work began in May 1996, and was carried out for almost two years. In April 1998, the museum was reopened after successfully undergoing renovation to keep it safe and seismically isolated.
     During the 2011 Tohoku earthquake, the grounds of the National Museum of Western Art suffered tremors with a maximum acceleration of 265 cm/s². The seismic isolation devices absorbed the vibrations, lowering the maximum acceleration of tremors within the building to 100 cm/s², leading to almost no damage occurring in the museum.
     Later, in 2016, it was designated as a UNESCO World Heritage Site as one part of “The Architectural Work of Le Corbusier, an Outstanding Contribution to the Modern Movement.”