Ten years of the Tokyo Skytree tower: constantly evolving technology

Never boring to watch, and powerful

Skytree’s slender, futuristic design initially made some people uncomfortable, perhaps due to their attachment to the sleek shape of Tokyo Tower. One thing is certain, from now on, “The Celestial Tree” is completely integrated into the landscape of the capital.


View from Skytree on the Hôzômon gate of the Sensô-ji temple, in the Asakusa district, a beautiful harmony with traditional Japanese architecture.

The slender structure of the tower is a consequence of the constraints of the site, stretched from east to west. A circular base could not have exceeded a maximum diameter of 60 meters. Therefore, a triangular shape was adopted to widen each side to 70 meters to increase the strength of the structure.

However, a circular shape was desirable in order to ensure smooth transmission of radio waves and a 360° view of the viewing platform. This is why the triangular base gradually transforms to become circular before the platform. Between the two, the carrying axes are not straight but slightly convex (mukuri) or slightly concave (sori) like a Japanese sword, a traditional Japanese architectural figure to achieve greater rigidity.

On the ground floor, at the “groups” entrance, visitors can see the western summit of the tripod up close.  The thickest steel frame has a diameter of 2.3 meters.
On the ground floor, at the “groups” 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 makes it perfectly visible the gradual deformation of the overall structure, from a triangle into 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 makes it perfectly visible the gradual deformation of the overall structure, from a triangle into 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 appearances that the Skytree can take depending on the angle of view. In some directions it will appear perfectly symmetrical, while in others it gives the impression of resting on one leg more outstretched than the others like a soldier in a “resting” position, in still others it has a leaning forward.

Its apparent simplicity at first glance explains why it blended so quickly into the Tokyo landscape. But its subtle complexity and its very elaborate 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 plot, it is definitely an architectural masterpiece.

(Left) Symmetrical silhouette seen from the Yanagishima Footbridge over the Kitajukken-gawa River;  (Right) From the town hall of Sumida-ku ward, he opens the bottom of his skirt on the left, and gives the illusion of swaying his hips on the right.
(Left) Symmetrical silhouette seen from the Yanagishima Footbridge over the Kitajukken River; (Right) From the town hall of the district of Sumida, he opens the bottom of his skirt on the left, and gives the illusion of being swayed on the right.

A revolutionary technique for damping seismic vibrations

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

Encased inside the steel lattice that forms the main body of the tower, the Skytree has a reinforced concrete column, which houses the stairs, elevators, and other technical systems. This central concrete pillar is attached to the external structure, up to the lower third by fixed steel bars, and on the upper two thirds by oil shock absorbers which allow a certain play. In the event of an earthquake, the physico-mechanical differences between the two structures cause the central column to initiate oscillation somewhat later than the outer body of the tower, so that the forces that agitate the two structures cancel each other out and drastically reduce the sway of the top.

In the Great East Japan Earthquake of March 11, 2011, Tokyo recorded tremors with an intensity of 5+ on the Japanese seismic scale shindo. Skytree, still under construction at this time, suffered no damage. The lightning rods were installed a week later, and the tower reached 634 meters when completed. Konishi Atsuo, Chief Structural Architect for Nikken Sekkei was able to proudly state, “We have had evidence that the damping system is effective both in damping strong long-period earthquakes (such as the earthquake of March 11, 2011), only the small rapid jolts vertically to the tower. »

The central column is visible when you look up, here in front of the main entrance on the 4th floor.
The central column is visible when you look up, here in front of the main entrance of 4e stage.

Ever brighter LED lights

Obviously no question of forgetting the question of lighting. At the time of construction, no large-scale structure in the world was lit entirely by LEDs.

To obtain a color given by conventional high-intensity lamps, filters are used which block unwanted wavelengths. This drastically reduces the light intensity, in addition to deteriorating over time. With LED lighting, the color of the emission is determined by the combination of the compounds, so there is no waste, and LEDs represent a 40% energy saving in addition to providing high light intensity.

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

The LEDs arranged around the west tripod.  It remains small in size and highly flexible.
The LEDs arranged around the west tripod. It remains small in size and highly flexible.

LEDs have a very small footprint, which allows their use for downlighting, a rare arrangement in building lighting. They are discreetly placed under the observation deck and the viewing corridor, producing a splendid gradient reminiscent of the snow-capped peak of Mount Fuji. Kaihô Kôichi, the lighting designer, said: “It’s not so much about illuminating as it is about coloring the structure”. This concept is in perfect harmony with the culture of Edo still very sensitive in the district of Sumida.

In the case of a structure as large as Skytree, “light pollution” also had to be taken into account. Indeed, the light must be controlled so as not to leave the site, because in the opposite case, it would constitute a nuisance for the residents. However, the narrowness of the site made controlling this parameter tricky. LED projectors, directed downwards, have played a role in this sense, facilitating the control of light diffusion.

During the first hour after sunset, the staging remains sober, white with a beautiful gradient.
During the first hour after sunset, the staging remains sober, white with a beautiful gradient.

LEDs do not emit ultraviolet rays, and therefore do not attract insects, which could cause damage.
LEDs do not emit ultraviolet rays, and therefore do not attract insects, which could cause damage.

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

Now ten years old, Skytree continues to evolve, and the urban development of the surrounding town continues. As a Tokyo Skytree Town spokesperson states: “The health crisis has led to a drastic drop in tourist numbers, but the support from the local community and neighborhoods along the railway line has been exemplary. This reinforces the feeling that we have done a good job working on a local basis, and continuing to develop the area in collaboration with the local community. »

For those thinking “I’ve been there before”, we can’t recommend paying Skytree another visit, as well as a walk around the surrounding neighborhoods. You are sure to make new discoveries.

Photo taken from the observation deck of the Asakusa Culture and Tourism Center
Photo taken from the observation deck of the Asakusa Culture and Tourism Center

“Sumida's digital emaki”, installed in the main entrance hall.
A roll of digital images of the Sumida, installed in the main entrance hall.

(Report, text and photos by Hashino Yukinori, Nippon.com. Title photo: Purple and gold lighting of the Skytree Tower, in the aesthetics of Edo culture)

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