Tokyo-Skytree-2012-Kakidai-CC-BY-SA

Tokyo Skytree – Ancient earthquake resistant technology in the worlds tallest radio tower

The Tokyo Skytree is the tallest broadcasting tower as well as the second tallest structure in the world standing 2080 feet tall (634 meters). On February 29, 2012 its construction was completed.

Engineers say the Skytree will be able to withstand even the strongest of earthquakes because they incorporated a traditional building technique in the structure: Shinbashira. The term shinbashira was originally used in construction and means a „central pillar.“ It refers to a central pillar at the core of a pagoda or similar structure. This earthquake resistant technology can be dated back to the 6th century AD.

The pagoda of the Buddhist temple Hōryū-ji („Temple of the Flourishing Law“) is widely acknowledged to be the oldest wooden building existing in the world with it’s shinbashira coming from a tree felled in 594 AD.

Records show that, even though Japan is an earthquake prone nation, only two of the pagodas have collapsed during the past 1,400 years due to an earthquake.

Tokyo Skytree is perhaps the first modern building to draw on this design idea and make use of a shinbashira for earthquake resistance. At the center of the tower stands a 375-meter steel-reinforced cylinder, fully 8 meters across and weighing 11,000 metric tons. The bottom third of this cylinder—up to 125 meters—is fixed solidly to the surrounding structure. In its upper two-thirds, meanwhile, up to its full height of 375 meters, it is not welded to the tower. The unattached portion of the shinbashira can swing freely, its movement absorbed by oil dampers between it and the surrounding beams. When an earthquake brings horizontal shaking, the shinbashira sways at a different frequency from that of the tower, counteracting the shaking and bringing the structure back to a stable state. This construction can reduce lateral motion by up to 50%.

The shinbashira was put to the test before Tokyo Skytree was even finished. When the Great East Japan Earthquake struck on March 11, 2011, the tower was still under construction, but the shake-reduction technology worked as planned, and all construction staff members on site were safe that day. The structure was also unscathed, and just a week later, on March 18, workers affixed the lightning rod to the top of the tower, bringing it to its full height of 634 meters.

 

=> Read the full article with more information about the Tokyo Skytower at nippon.com

The multi-story pagoda came from China to Japan during the sixth century CE.