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In a land swept by typhoons and shaken by earthquakes, how have Japan’s tallest and seemingly most breakable old buildings — 500 or so wooden pagodas, tower-shaped buildings — remained standing for centuries? Japanese scholars have been confused for ages about their stability.

For centuries, many attributed the resilience (抗震性) of pagodas to the massive trunk-like central columns known as shinbashira, which bends and swings during a typhoon or earthquake, just like a tall tree. But the amazing thing is that the shinbashira actually does not carry any load at all but is suspended from the top of the pagoda — hanging loosely down through the middle of the building. The weight of the building is supported entirely by twelve outer and four inner columns.

And what is the role of the shinbashira, the central column? The best way to understand the shinbashira’s role is to watch a video made by Shuzo Ishida, a structural engineer at Kyoto Institute of Technology. Mr. Ishida, known to his students as “Professor Pagoda” has built a series of models and tested them on a “shake-table” in his laboratory. In short, the shinbashira was acting like an enormous pendulum (钟摆). Under pressure, a pagoda’s loose floors could be made to slide back and forth independently. Viewed from the side, the pagoda seemed to be doing a snake dance — with each floor moving in the opposite direction to its neighbours above and below. The shinbashira, running up through a hole in the centre of the building, made it unlikely that individual storeys moved too far because, after moving a certain distance, they banged into it, passing on energy away along the column.

Another strange feature of the Japanese pagoda is that, because of the building tapers (锥形), with each floor plan being smaller than the one below, none of the vertical (垂直的) columns that carry the weight of the building is connected to its corresponding column above. In other words, a five-storey pagoda contains not even one column that travels right up through the building. More surprising is the fact that the individual storeys of a Japanese pagoda are not actually connected to each other. They are simply stacked one on top of another like a pile of hats.

The extra-wide eaves (屋檐) also play a part. Think of them as a balancing pole of tightrope-walkers. The bigger the mass at each end of the pole, the easier it is for the tightrope walker to maintain his balance. The same holds true for a pagoda. With the eaves extending out on all sides like balancing poles, the building responds to even the most powerful earthquake with a graceful swinging, never an abrupt shaking.

【语篇导读】本文是一篇说明文。作者讲述了不倒塔的原理结构。