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Monday, March 29, 2010

No Japanese ancient towers have collapsed in earthquakes

Tokyo Sky Tree, is being built as a new TV transmission tower in Sumida Ward of Tokyo, has attained a height of 338 meters on the morning of March 29 and has become the tallest tower in Japan, exceeding 333-meter high Tokyo Tower. It will be 634 meters tall and go into operation next spring.
Techniques of building Japanese ancient towers are utilized for building the latest ones.

Sorin(相輪), a nine-rings is on the top of five-storey pagoda and originally means a parasol, is used for building of Tokyo Sky Tree because a recent study proved that it is useful to weaken the wind resistance.

I heard that no tower in the Japanese temples has ever fallen down because by earthquakes. The ancient earthquake-resistant design has been adopted toward the new tower's building design.

Horyu-ji Temple Five-storied Pagoda(法隆寺五重塔), which was constructed of hinoki(Japanese cypress) about 1300 years ago, is the oldest tower in Japan. It has not been damaged at all even after nine times of severe earthquake with a Japanese seismic intensity of five.
Any towers of Japanese temples in Hyogo Prefecture where The Great Hanshin earthquake occurred in 1995 did not collapse then.

Why are the towers of Japanese temples so strong against earthquakes? The flexible structure of the towers is more resistant to earthquakes. The parts of the tower were piled up without being impregnably connected, so the tower can swing like a snake and it disperses the energy of earthquake. And a central pillar of the tower damps vibrations because it is not fixed in the ground.

Its flexible structure makes it possible to build a skyscraper where large earthquakes occur.
Kiyoshi Muto(武藤清) who was an architect investigated Kan'ei-ji(寛永寺) five-storied pagoda in Ueno after the Great Kanto Earthquake struck Kanto Region in 1923, because it was not damaged at all by the earthquake. As the result of investigation, he found the advantages of the flexible structure. However, the rigid structure theory was the mainstream of those days.

After World War II, the seismologists and the experts of earthquake-proofing in the U.S.A. suggested Japanese architects to adopt the flexible structure, but no one did it but him in Japan. In 1963 he published a book "Taishin-Sekkeihou(耐震設計法:The method of quakeproof design)" that insisted on applying the Japanese original flexible structure to building a skyscraper. Under the conduct of Sei Nikai who was an engineer of Kajima Corporation (founded in 1840), the Japan's first skyscraper "Kasumigaseki Building" was completed in 1968.

However, recently an experiment on quake-resistance of a five storied pagoda denied the effect of central pillar. Originally the towers in the Buddhist temples were built for keeping Buddha's bones, so its architecture should have come to Japan from India via China and the Korean Peninsula in the sixth century.

No one knows when, and where, and how the ancient earthquake-proofing technique was established because no ancient wooden tower exists in China and the Korean Peninsula and earthquakes hardly happened in these areas. Why are the towers of Japanese temples so strong against earthquakes? The answer is still a mystery.

On the other hand, wooden towers are weak against fire. Many of wooden towers were lost by fire and wars. Although some towers were terribly damaged by fallen trees when typhoons came, they were reconstructed as before; such as the five-storied pagoda of Murō-ji located in Nara prefecture.

The five-story pagoda of Senso-ji that is popular among tourists was destroyed by fire twice in the Edo era. After the reconstruction in 1648, it was not damaged by the Great Kanto Earthquake in 1923, but it was burned down again by World War II.
The tower rebuilt in 1973 was made of reinforced concrete. A stone that is engraved with a letter "塔 (tou, means tower)" was buried where the tower stood before the rebuilding.

As an aside, Kan'ei-ji five-storied pagoda stands on the site of Ueno Zoo now because the site of the temple was divided into some subdivisions in the Meiji Era.
At the main hall of Senso-ji, replacing roof tiles with ones made of titanium has been in the works as an earthquake countermeasure.

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