 |
スクリプトは事前提出されたものですので、ビデオの音声とは異なる場合があります。 |
 |
Ancient Technology Living in Today's Society
National Institute of Technology, Kure College
“Wow, that was great!”“It was so high.”
“The view from the top was awesome!”
“I really wanna come back here again.”
“Me, too.”
“What? What's going on?”
“Is the ground shaking?”
“Yeah, it is!”
“This is quite big.”
“Look at that! Skytree is shaking, too.”
“Man, that was quite big.”
“Yeah, it was.”
“Why doesn't Skytree collapse under such big earthquakes here in Tokyo? “
“There must be a hidden secret in Tokyo Skytree.”
“Let's try to find it, shall we?”
We are the students from National Institute of Technology, Kure College. I'm Koki Miyamoto, I'm Natsuo Shirasu, I'm Masato Ueda. And we are studying architectural engineering.
Do you know how many times earthquakes occur in Japan every year? Including small earthquakes, more than a thousand earthquakes occur in Japan every year. So, for us, an earthquake is a very serious natural disaster. And, it is not unusual for buildings to collapse from big earthquakes. Therefore, in modern Japanese society where lots of high-rise buildings stand in a row, we have to build buildings which are resistant to large earthquakes.
Today, we are going to talk about the traditional earthquake-resistant technology that was used in ancient times.
We can find this technology in temples in Japan. There are lots of temples in Japan. And some of them have five-story pagodas. A five-story pagoda is built in the form of traditional Japanese architecture. The roofs have beautiful curved tips. And each tier is slightly smaller than the one below, making the form slender and elegant.
And we can enjoy its beautiful figure in each season. We would like to talk about the origin of the five-story pagoda. To find the origins of Japanese pagodas, we must go back to ancient India. So let's go to ancient India.
Here we are in Sanchi, India. This stupa was built in the 3rd century BC. This was built in order to keep the relics of Buddha in it. It is from this stupa that the design of Japanese pagodas came from. So now, let's go back to Japan.
Let me show you some examples of five-story pagodas which have not fallen down due to earthquakes over hundreds of years.
This five-story pagoda is located in Horyu-ji Temple in Nara. We call this Goju-no-To. This is a picture of Horyu-ji Temple. The building on the right is the five-story pagoda. It was built in the 7th century, and it is the oldest wooden building in the world. And it is 103.3ft high. After it was built, there were 46 earthquakes with magnitudes larger than 7.0 in Japan.
However, as far as we know, there is no evidence that this five-story pagoda has ever collapsed due to such large earthquakes.
“Is that really true?”
“It is quite surprising that Goju-no-To has endured so many earthquakes for 1400 years.”
“That's right. Not only Goju-no-To but also many other five-story pagodas in Japan have stayed standing over hundreds of years.”
Why could the five-story pagoda of Horyu-ji Temple resist falling down against such strong shocks? The key issue is its special structure. This pagoda has a shinbashira and a flexible frame. This is a shinbashira. A shinbashira means the central pillar of a pagoda. And it's located in the center of the pagoda. It is only fixed to the top of the five layers and it is not fastened to the pagoda itself. Some of them are embedded in the base, some are put on the base, and others are suspended. The shinbashira of Horyu-ji Temple doesn't even touch the ground! So how does it work?
We will show you a video of a simple model test we did. We young engineers also made the model and the shaking table by ourselves. This is the model of a five-story pagoda made with five bowls and a chopstick. As you can see, these bowls are ordinary miso-soup bowls we use every day.
The bowls represent each layer and the chopstick represents the shinbashira of a five story pagoda. And this is the shaking table.
Look at this picture. The left one has a shinbashira. The right one doesn't have one, and the middle one doesn't have a shinbashira either, but the bowls are taped to each other. Each model is put on the shaking table.
Now, let's shake these on the same cycle. (play video) As you see, the right one and the middle one collapsed. But the left one which had a shinbashira did not fall down. Why is the five-story pagoda which has a shinbashira stronger than the others?
When an earthquake occurs, the pagoda is initially shaken like this. In this case, if all the stories were shaken in the same direction, the center of gravity would shift and the pagoda would soon topple over.
But if there is a shinbashira, each story touches the shinbashira as it is shaken and the shift of the tower's center of gravity is reduced. Because of this, the shakes of the tower are not amplified. In other words, each story moves independently and the center of gravity doesn't shift so much. This minimizes the risk of the pagoda collapsing. It doesn't resist against the shaking because of its hard structure, but, instead, it parries the shaking force by using a flexible structure.
This seismic technology, based on the traditional pagoda, is incorporated into many new high-rise buildings in Japanese cities. A seismic technology with a shinbashira has also been applied to Tokyo Skytree which was completed three years ago. Tokyo Skytree is the highest broadcasting tower in the world. Thanks to the efforts taken by modern engineers, Skytree has achieved the height of 2080ft high with a shinbashira structure.
Let's compare Tokyo Skytree with other famous Japanese high-rise buildings. As you can see, Tokyo Skytree is overwhelmingly high, isn't it? The shinbashira of Tokyo Skytree showed its power during the earthquake that caused the meltdown of the reactor in Fukushima Nuclear Power Plant on March 11, 2011. The tower had already reached 2050ft high before that day. It was just after deactivating the safety system. However, the tower suffered no damage. How come? This technique, which was taken from the traditional shinbashira, is now supporting modern Japanese buildings.
“Wow, Skytree does have a hidden secret!”
“It is unbelievable that this technique, realized in the 7th century, was in play at 2080ft high, isn't it?”
“Yes, it is.”
“And we, young engineers, should inherit these techniques and develop them more for the next generation.”
“I think so, too.”
