Nishizawa explains the special features of traditional Japanese architecture. Foremost is the temple’s wooden construction, designed to flex in an earthquake. The seemingly decorative penetrating tie beams attaching the roof to the outer posts, and two lots of three-layer inner supports, have a functional purpose: Each one is a mini shock absorber. The heavy roof, which sits on wooden columns, reinforces the structure and provides stability. (There is however, a risk that roof tiles may fall in an earthquake, killing anyone standing too close.) Each column sits on top of its own stone base but is not fixed to it. The reasoning is that in an earthquake one column may be nudged off its base but not all of them. The building hops and skips. It will therefore be easier to repair.
The students have built an elaborate 6½ foot-tall wooden model of a traditional three-story pagoda, and are conducting experiments to measure how it responds to earthquakes. They place it on a “shaking table” and attach it to two sets of hydraulic rams on two axes. One will shake the model up and down and the other from side to side, simulating the vertical and lateral force of a 7.3 magnitude earthquake.
Three, two, one, shake! The pagoda sways and bends but stands up well. Each floor seems to move independently, so the quake forces are displaced and isolated. The strain on the first floor level is many times more than the posts could normally endure, says Professor Nishizawa. However, with this multi-level structure if one post were to be dislodged the structure could collapse, so it is vital that the whole structure is stacked properly.
The flexible wooden column that runs up through the structure, called a shinbashira, culminates in a decorative finial at the very top of the pagoda called a sorin. This is considered a symbol of Buddha’s grave. It, too, plays an important structural role: It moves sideways and absorbs the force, preventing the structure from swaying too much.
Tokyo’s new 2,080ft Sky Tree, Japan’s tallest tower, also uses old technology in the form of a flexible central column.