Earthquake's Unusual Pattern Stumps Many Engineers in Japan

Article excerpt

IT'S HARD TO WALK anywhere in this city and not see evidence of the awesome forces unleashed by the magnitude 7.2 earthquake that ripped through the city before dawn a week ago.

Wooden and concrete buildings lie in piles of rubble. Others tilt at impossible angles and will be razed. Elevated highways and overpasses collapsed.

Japan believed it was ready for a major quake. It wasn't ready for this.

"The human brain has a limit, but nature doesn't," said Yoshihiro Takeuchi, chairman of the Earthquake Damage Investigation Committee for the Japan Institute of Architecture.

For Takeuchi, an engineering professor at Osaka Institute of Technology, the shattered landscape is a laboratory that contains specimens of everything he has studied - and at least one phenomenon rarely spotted in his visits to quake sites in Japan and elsewhere.

"The characteristic of this quake is the middle floors of buildings collapsing," he told The Associated Press on Sunday during a tour of some of Kobe's worst-hit areas. "In past quake history, we haven't seen this before . . . except for a few isolated examples."

The Sakura Bank building lost its fourth floor; the old city building its sixth. Part of the fifth floor of Nishishimi Hospital, in another neighborhood, collapsed.

In each case, there seemed to be little other structural damage; it was like a sandwich from which one slice of meat disappeared.

Takeuchi theorized that this quake simultaneously thrust upward and sideways, hence the wide cracks in sidewalks and the shift upward or downward of some buildings by two feet or more.

This motion also may have doomed some of the highways, which had been such a source of pride for Japanese engineers. After interstates were toppled in California quakes, they bragged that such a thing couldn't happen in Japan.

"All the people saying that have received a shock," Takeuchi said.

Japan has different construction standards for highways and buildings. The huge pillars supporting raised roads consist of concrete cores surrounded by vertical steel rods that are then wrapped with vertical steel hoops and surrounded by another coat of concrete.

In Kobe, many ruptured, the reinforcing rods snapped like matchsticks.

The horizontal-vertical movement probably was to blame, but only detailed studies will tell, Takeuchi said. He doesn't foresee major changes to standards but said the disaster could yield new construction techniques.

Most of the quake's energy was released just below the city on what had been considered a relatively inactive fault line. It still is uncertain whether two of the Earth's plates ground against each other, or one pushed over the other. …