Located in Tokyo’s Ueno Park, the main building of the National Museum of Western Art was declared a UNESCO World Heritage Site in 2016 as part of Le Corbusier’s architectural work, an excellent contribution to the modern movement. The building was designed in 1959, before the advent of architectural technologies to deter earthquakes. Later, it was built with excellent measures to tackle earthquakes, helping to save it from destruction. The 2011 Pacific coast of Tohoku Earthquake did major damage to East Japan, but this building was almost entirely untouched. Likewise, the precious works of art inside it have suffered almost no damage.
The building had been standing at the time of the earthquake for 52 years, and was struck by earthquakes ranging from 5-upper to 5-lower on the Japanese seismic scale.Despite these powerful tremors, it suffered relatively little damage, since the seismic insulation technology almost completely prevented the building from trembling.
Seismic Isolation Technology Absorbs Earthquake Tremors and Avoids Shaking Buildings
There are three types of strategies to protect structures from earthquakes: earthquake protection, tremor control, and seismic isolation. Earthquake resistance means strengthening the structure itself so that it can not be demolished in the case of an earthquake.
Tremor management requires the incorporation of vibration-absorbing equipment within the foundation of the building, preventing it from being damaged by earthquakes. In the meantime, seismic insulation requires the construction of “seismic isolation systems” beneath the foundations of the structure, rather than within the structure itself. This helps to hold back earthquake tremors from reaching the building.
The mechanism for the absorption of vibrations
Seismic insulation systems are made of material such as laminated rubber, which is created by stacking sheets of rubber and metal on top of each other like a mille-feuille or a custard slice. And if the surrounding area trembles violently as a result of the earthquake, the seismic shielding systems distort and withstand horizontal tremors, minimizing the degree to which the structure shakes.
Seismic isolation technology has not spread much outside Japan, but has gained rapid prominence in Japan following the Great Hanshin Earthquake of 1995. The town of Kobe sustained substantial damage, but some buildings with seismic insulation were not at all affected. This has contributed to an rise in demand in this technology. Similarly, houses with seismic insulation experienced no damage as a result of the Tohoku earthquake, demonstrating the advanced capabilities of this equipment.
Retrofitting seismic isolation
After the Great Hanshin earthquake, the National Museum of Western Art was examined for its resistance to earthquakes. This analysis showed that the building had less than half of the earthquake resistance needed by Japanese standards at the time.
The National Museum of Western Art is a valuable building designed by Le Corbusier, one of the most influential architects of the 20th century. It houses and shows many precious western paintings and sculptures from the Renaissance to the beginning of the 20th century, including Monet ‘s Water Lily and Courbet’s Gypsy in Contemplation. As such, it was necessary to renovate the building in order to enhance its earthquake tolerance. It was popular at the time to install earthquake-resistant walls and increase the thickness of the pillars and beams to increase the resistance of buildings to earthquakes. However, this kind of building would ruin Le Corbusier ‘s initial style. The best way to boost the earthquake resistance of the museum while maintaining its cultural significance was with the use of seismic isolation equipment.
In order to maintain the architecture and functions of the structure, this phase involves dealing with the pillars that support the structure and replacing some of the pillars with seismic shielding systems while the current building is already standing on them. This is like changing the legs on a table, when there are a lot of objects on it.
This innovative method is called ‘seismic insulation retrofitting.’ This method is used to secure structures that were designed prior to the existence of seismic insulation techniques and was first used in Japan at the National Museum of Western Art. The technology was then used in other structures, such as Osaka’s emblematic tower, Tsutenkaku, and the smaller JP Tower building in front of Tokyo Station, which retains part of the old Tokyo Central Post Office.
The method includes moving the entire structure or digging the surrounding area to work on the foundations, which thus includes technologically sophisticated equipment which substantial costs.
Designated as a World Heritage Site after building work is ongoing, requiring sophisticated technologies
The National Museum of Western Art has a large structure with an atrium in its middle, as well as several sections of basement floors. For this cause, the building was evaluated prior to completion using refined methods to check if the whole structure could be preserved once the repairs had been completed.
The actual building work included the installation of seismic insulation systems beneath the current structures. More accurately, the workers first removed the floor around the base of the building, dug the areas around the base, and then placed the posts that would protect them temporarily instead of the foundations. This was achieved by splitting the posts into circular slices and putting them under the ground one by one.
The posts were sliced into strips since there was no underground space and the staff were unable to install a rig to install the posts. After that, the staff cut the bottom of the base and mounted seismic insulation equipment. Finally, they cut and replaced the posts, and then returned the floor to its original condition.