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Membrane fabric tidal wave barrier doubles as fair weather shelter.
By Chelan David
Since ancient times, ports and harbors in Japan have suffered frequent tsunamis, and the damage can be substantial. Tsunamis are not mere floods or tidal waves, but seismic sea waves caused by earthquakes or volcanic eruptions under the seabed.
In August of 2004, scientist Dr. Masataka Nagano proposed an idea to limit the havoc caused by tsunamis. His solution was to construct a simple barrier fence similar to a guardrail along the seaside as opposed to using a revetment composed of concrete.
Following the catastrophic Indian Ocean tsunami in December 2004—one of the deadliest natural disasters in recorded history, in which more than 200,000 people perished—the Japanese Ministry of Land, Infrastructure, Transport and Tourism decided to introduce Nagano’s idea. After months of study it was decided that the Port of Kushiro in the northeastern part of Hokkaido, the second largest of the four main islands of Japan, would be the ideal spot to erect a tidal wave barrier.
A whale of a barrier
Large tsunamis have been known to rise more than 100 feet, but the waves themselves don’t cause the most serious damage; rather, it’s the floating flotsam accompanying the waves, such as lumber, fishing boats and containers. The tidal wave barrier shelter conceived by Taiyo Kogyo Corp., Osaka, Japan, is designed to minimize damage by inhibiting the entry of floating obstacles while allowing seawater to pass through. It also protects houses and cars from being washed away by a tsunami’s undertow.
The barrier combines form and function. Under normal conditions, when there is no eminent danger of a tsunami striking, the shelter is used as a shade to block rain and sunlight. Its softly curved design represents two whales swimming closely together. The former mayor of Kushiro City, Yoshitaka Itoh, requested that the barrier feature a whale monument, as the giant marine mammal serves as a symbol of the port.
One of the obstacles that had to be overcome in developing and implementing the design, says Yukitoshi Maruyama, manager of Taiyo Kogyo’s Hiroshima sales branch, was finding a way to accommodate the scale and shape of the shelter within the limited budget and terms of official construction. Conveying the membrane structure’s safety attributes and potential for aesthetic beauty was also a challenge.
The tidal wave barrier shelter was intended to be impressive and serve as a symbolic monument at the entrance of the port; however, a heavy structure would have been difficult due to the geotechnical condition of the quay wall abutting the construction site.
The practical solution
A membrane structure served as a practical solution for the tidal wave barrier shelter because, as Maruyama puts it, “Even if a severe tsunami attacks and the shelter is destroyed and goes out, towns and houses are not destroyed due to the softness and harmlessness of the material.”
The light-storage membrane fabric used for the shelter was CMX270 Photoluminescence, a PVC-coated glass fiber fabric made by Hiraoka & Co. Ltd., Tokyo. In addition to its other attributes, it was chosen because it can absorb and emit light energy from the sun or lighting. “The fabric promises shade and UV protection during the day and a stunning visual effect at night,” says Maruyama. “After dark, the membrane glows with stored daylight, illuminating both interior and exterior. In case of a blackout, the shelter itself glows and provides light to surrounding areas.”
The base material is titanium oxide photocatalytic membrane, which utilizes TiO2 coating technology to ensure translucence and has excellent stain-proof properties. “The self-cleaning effects maintain the clean fabric surface that keeps high transparency of the fabric,” explains Maruyama.
A symbolic monument
Prior to the engineering work of the structure, the Japanese government established guidelines for the barrier to ensure it would function in the event of a tsunami. The basic concept, says Maruyama, was introduced from rock and mud flow prevention work in the region’s mountainous area. The conditions were tested using hydraulics simulation by what Maruyama calls a “semigovernment engineering organization.”
After the implementation study was completed, actual construction took place in two phases. The first phase began in April 2006 and was completed in June 2007. The final phase was completed in February 2008.
The shelter now serves as a community gathering place and has hosted several city events. “The fabric whale-shaped shelter now plays an important role for tourism and serves as a symbolic monument of the port,” says Maruyama.