Mysteries of Japanese pagodas
By Edwin Karmiol
TOKYO - Despite being built without nails or
reinforcing metal parts, some 400 wooden multi-story
Buddhist pagodas across Japan have, throughout the
centuries, withstood destructive earthquakes and
powerful typhoons. Modern builders are now using
computers in an effort to apply the ancient building
techniques to today's highrises.
the aftermath of the 1995 Great Hanshin Earthquake in
Hyogo prefecture, less than 600 kilometers southwest of
Tokyo, all 15 three- and five-story pagodas in the
devastated areas remained undamaged despite being buffeted.
While more recently built structures were falling around
them, these magnificent old pagodas remained intact.
The sturdiness of these structures is due to
their flexibility, achieved through their assembly
method. In fact, during tremors and powerful winds, the
tiers of the pagodas move independently as if performing
an ancient snake dance.
Engineers at Takenaka Construction Co
have, through computer simulation, confirmed how the 7th
century, five-story pagoda at Horyuji temple in Nara
prefecture could resist an earthquake as strong as the
one that destroyed parts of the city of Kobe in 1995.
Toshiharu Hisatoku, until
recently an executive architect with Takenaka Corp and
leader of the quake-simulation project, explained the
mechanism that allowed the 32.55-meter-tall, 305-tonne
pagoda to survive for the past 1,300 years.
The existing pagoda, along with
other Buddhist temples at the site, was founded by
the emperor's son, Prince Regent Shotoku (574-622),
but was reconstructed around 711 after the original one burned down.
Fire is the only natural enemy of these
edifices built of strong Japanese cypress wood.
five tiers of that pagoda, and in all pagodas, are
structurally independent from one another. A central
pillar, or shimbashira, standing on a base stone
extends up to the spire but does not support the
framework, roof, or any other parts of the structure.
It is the inner and outer posts around the
central pillar that are instrumental in supporting the
weight of each story independently. Consequently, the
fifth-floor roof is supported by posts resting on the
base rafters of the fourth floor while the latter posts
sit on the third floor's base rafters.
This, said Hisatoku, "imparts a great flexibility to the
structure as the overhanging eaves function like a
mobile, creating a counterbalanced lever".
case of an earthquake or typhoon, each of the pagoda's
five tiers vibrates and moves alternately in the
opposite direction - so that when the first story of the
pagoda sways to the left, the second floor swings to the
right, and the third story rocks in the opposite
direction, and same with the other floors.
snake-like movement re-establishes the balance of the
structure in a natural way. Moreover, the central column
serves as a stopper for the base rafters battering
against it whenever they are swaying too violently. This
movement prevents the pagoda from staggering too far out
of line and collapsing.
Yoneko Oyama, a resident of the
city of Nara, says: "It gives me a sense of
security; it is well designed." Oyama, who teaches
volunteer tour guides
in Nara, adds that most Japanese people are unaware
of the anti-earthquake properties of the pagodas.
"My students are amazed when I
familiarize them with such details. I feel some
responsibility to teach them about the meaning of
pagodas. I relay this information to them in the hope
that they will pass it on to the younger generation,"
simulated experiments, Hisatoku's team entered seismic-wave data to
trigger a major "quake" measuring 7.2 on the
Richter scale directly beneath the Horyuji temple pagoda.
It also programmed the computer to simulate horizontal
and vertical tremors at a rate of 0.9 times per second and
2.5 times per second, respectively. Despite the
magnitude of the "quake", the pagoda's top tier
oscillated horizontally only 38 centimeters.
It is believed
that structures topple when they move horizontally by
one-50th to one-30th of their height. It is also
believed that the looseness and mobility of the joints
in wooden structures help absorb the earthquake's
violent energy, keeping it from toppling.
results convinced Hisotaku that "even wooden houses
could resist earthquakes if they are built with the same
elastic characteristics intrinsic to the pagodas".
Reinforcing the flexibility theory,
are observations by Tsunekazu Nishioka, a temple
carpenter who has supervised the restoration of a
pagoda. "The building looks very sturdy and solid, but
if you give it a good shove with your hand while the
pagoda is still under construction, the whole structure
sways back and forth. If it doesn't, the building is no
good," he said.
Taking their inspiration from the
earthquake-resistant features of pagodas, Japan's
leading construction companies have borrowed and
improved these techniques in modern
construction. Highrise structures are now being gradually
outfitted with the most advanced anti-earthquake
Takenaka Corp's 161-meter-high
Applause Tower in Osaka, 550km southwest of Tokyo, which
was completed in 1992, has a heliport on top of the
tower that has incorporated a 480-tonne active mass
damper (AMD) system. The computer-activated AMD can
absorb the swaying of a building in case of strong winds
and earthquakes. Whenever the sensors, located on
different floors, detect tremors, the data are relayed
to a computer system that triggers the actuator to shift
its weight in the opposite direction of the seismic
Takenaka says this helps reduce the
earthquake and strong wind vibrations by 50 percent. The
AMD concept is based on the pagoda's "snake dance", says
engineers have drawn practical ideas from the pagoda's
resistance to earthquakes, even if they are still not
sure of having probed all its secrets. "It is doubtful that the
carpenters who build the pagodas knew themselves how to
make them quakeproof. It is maybe sheer luck," said
(Inter Press Service)