National

How does Tokyo Skytree stand up to typhoon winds?

by Oscar Boyd

STAFF WRITER

Record-breaking typhoon winds are bearing down on Tokyo, threatening to tear roofs from houses and rip up trees across the country. This is a problem for many buildings, but not for the Tokyo Skytree — the tourist attraction and broadcasting tower in Tokyo’s Sumida Ward.

At 634 meters tall, the Skytree became Japan’s tallest structure, and the tallest tower in the world, when it was completed in 2011.

Designed by architectural firm Nikken Sekkei, the tower was built to withstand Japan’s “severe natural environment,” with particular attention paid to the threat of earthquakes and typhoons.

To ensure its integrity during these extreme events, the tower uses two forms of vibration control system.

At its top, the Skytree has two tuned mass damper (TMD) systems installed by Mitsubishi Heavy Industries. One is at an altitude of 625 meters, weighing 25 tons, and the other is at an altitude of 620 meters and weighs 40 tons.

Together, these dampers act as reverse pendulums when the tower shakes, reducing vibrations caused by wind or earthquake — particularly important considering the tower’s vast height, but comparatively narrow base, just 70 meters in width on each side.

The second mechanism of wind and earthquake-proofing comes from the tower’s core column, an 8-meter-wide reinforced concrete cylindrical with a maximum thickness of 60 centimeters and a height of 375 meters. This is connected to the tower’s steel outer frame and is connected to oil dampers that help suppress vibrations through the column caused by wind or earthquake.

According to structural design documents, this core column reduces earthquake-related accelerations by up to 50 percent and wind-related accelerations by 30 percent.

To predict the forces the top of Skytree would come under, its architects installed a weather balloon to collect data on wind speeds. This data was used to ensure the tower exceeded government standards on building safety so that it would sustain “virtually no damage” winds strengths that are expected to occur once every 1,350 years.

Skytree is expected to perform with “elastic behaviour” even in winds that occur once every 2,000 years, allowing it to remain operational as a broadcasting tower even in these conditions.

The tower is also expected to be able to withstand a magnitude 7.3 earthquake within its immediate vicinity.