Ten years of the Tokyo Skytree: ever-evolving technology

Never boring to watch, and powerful

The slender, futuristic design of the Skytree made some people uncomfortable at first, perhaps due to their attachment to the sleek shape of the Tokyo Tower. One thing is for sure, from now on the “Heavenly Tree” is fully integrated into the landscape of the capital.


View from the Skytree of the Hojomon Gate of Senso-ji Temple in Asakusa, beautiful harmony with traditional Japanese architecture.

The slender structure of the tower is a consequence of the restrictions of the site, stretched from east to west. The round base could not exceed a maximum diameter of 60 meters. Therefore, a triangular shape was adopted to extend each side to 70 meters to increase the strength of the structure.

However, a round shape was desirable in order to ensure smooth transmission of radio waves and a 360° view of the observation deck. That is why the triangular base gradually turns into a round one in front of the platform. Between them, the bearing axles are not straight, but slightly convex (mukuri) or slightly concave (sorry) as a Japanese sword, a traditional Japanese architectural figure to achieve greater rigidity.

On the first floor, at the
On the first floor, at the “group” entrance, visitors can see the western top of the tripod up close. The thickest steel frame has a diameter of 2.3 meters.

The view through the glass floor at level 340 of the observation deck allows you to perfectly see the gradual deformation of the overall structure, from a triangle to a circle.  The “sori” effect of the middle rib and the “mukuri” effect of the side ribs are also clearly visible.
The view through the glass floor at level 340 of the observation deck allows you to perfectly see the gradual deformation of the overall structure, from a triangle to a circle. The “sori” effect of the middle rib and the “mukuri” effect of the side ribs are also clearly visible.

This complex shape explains the variety of looks the Skytree can take on depending on the viewing angle. In some directions it will appear perfectly symmetrical, in others it gives the impression of leaning on one leg more extended than on the others, like a soldier in a “resting” position, in still others – with an inclination forward.

Its apparent simplicity explains why it has so quickly blended into the Tokyo landscape. But its subtle complexity and highly thoughtful design make you never tire of looking at it. The specifications called for a landmark in the landscape that “transcends time and space”. Built on such a small lot, it is certainly an architectural masterpiece.

(Left) A symmetrical silhouette from the Yanagshima Footbridge over the Kitajuukken-gawa River;  (Right) From the Sumida-ku Town Hall, he opens the lower part of the skirt on the left and creates the illusion of swaying hips on the right.
(Left) A symmetrical silhouette from the Yanagshima Footbridge over the Kitajuukken River; (Right) From the Sumida District Town Hall, he opens the bottom of his skirt on the left and creates the illusion of swinging on the right.

Revolutionary Seismic Damping Technology

To protect such a thin and slender structure from earthquakes, a revolutionary technology has been developed: shinbashiraor “pillar of the heart”.

Encased in a steel lattice that forms the main body of the tower, Skytree has a reinforced concrete column that houses stairs, elevators and other technical systems. This central concrete pillar is attached to the outer structure up to the lower third with fixed steel rods, and on the upper two thirds with oil shock absorbers that allow a certain play. In the event of an earthquake, the physical and mechanical differences between the two structures cause the central column to initiate vibrations somewhat later than the outer casing. towers, so that the forces that excite the two structures cancel each other out and drastically reduce the swaying of the top.

During the Great East Japan Earthquake on March 11, 2011, tremors of magnitude 5+ on the Japanese seismic scale were recorded in Tokyo. sindo. Skytree, which was still under construction at the time, was unaffected. Lightning rods were installed a week later, and upon completion, the tower reached a height of 634 meters. Konishi Atsuo, Chief Structural Architect at Nikken Sekkei, proudly stated, “We have evidence that the damping system is effective at both dampening strong long-term earthquakes (such as the March 11, 2011 earthquake) and pushing vertically against the tower. »

The central column is visible when looking up, here in front of the main entrance on the 4th floor.
The central column is visible when looking up, here in front of the main entrance at 4and scene.

Even brighter LED lights

Obviously, do not forget about lighting. At the time of construction, not a single large-scale structure in the world was completely illuminated by LEDs.

To achieve the color produced by conventional high intensity lamps, filters are used to block unwanted wavelengths. This drastically reduces light intensity, in addition to deteriorating over time. In LED lighting, the emission color is determined by the combination of compounds, so there is no waste, and LEDs provide energy savings of 40% in addition to high light intensity.

The Skytree project provided an opportunity to develop high power LED lighting technology that was still in its infancy. Since then, the number of large installations around the world that have switched to LED lighting has skyrocketed, and Skytree has been a major contributor to this.

The LEDs are located around the western tripod.  It remains small in size and very flexible.
The LEDs are located around the western tripod. It remains small in size and very flexible.

LEDs take up very little space, allowing them to be used for downward lighting, a rarity in building lighting. They are discreetly located under the observation deck and observation corridor, creating a magnificent gradient that resembles the snow-capped peak of Mount Fuji. Kaiho Koichi, lighting designer, said: “It’s not so much about the lighting, but about the coloring of the structure.” This concept is in perfect harmony with the Edo culture still very sensitive in the Sumida area.

In the case of a structure as large as the Skytree, “light pollution” also had to be considered. Indeed, the light must be controlled so that it does not go beyond the site, because otherwise it will cause inconvenience to the residents. However, the narrowness of the site made it difficult to control this parameter. Downward-facing LED floodlights have played their role in this sense, making it easier to control the dispersion of light.

For the first hour after sunset, the production remains sober, white with a beautiful gradient.
For the first hour after sunset, the production remains sober, white with a beautiful gradient.

LEDs do not emit ultraviolet rays, which means they do not attract insects that can cause damage.
LEDs do not emit ultraviolet rays, which means they do not attract insects that can cause damage.

When the tower opened, the lighting design was based on the concept of two color schemes that alternated daily: a very pale blue and a combination of purple and gold. For 5and anniversary, an orange has been added. In 2020, power upgrades made the lighting even brighter.

Skytree, now ten years old, continues to evolve and urban development of the surrounding city continues. A spokesman for Tokyo Skytree Town said: “The health crisis has resulted in a sharp drop in tourist numbers, but the support from the local community and areas along the rail line has been exemplary. This reinforces the feeling that we have done a good job by working locally and continuing to develop the territory in cooperation with the local community. »

For those who think “I’ve been there before”, we can’t recommend visiting Skytree again and walking around the area. You will definitely make new discoveries.

The photo was taken from the observation deck of the Asakusa Cultural and Tourism Center.
The photo was taken from the observation deck of the Asakusa Cultural and Tourism Center.


A roll of digital images of Sumida installed in the main lobby.

(Report, text, and photographs by Hashino Yukinori, Nippon.com. Cover photo: Purple and gold illumination of the Skytri tower in the aesthetic of Edo culture.)

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