gempa & building code jepang

24Mar11

gempa bumi dan tsunami di jepang kemarin memberikan banyak pelajaran kepada kita. semangat gambaru, tidak mengeluh berkepanjangan, organisasi penyelamatan yang rumit tapi terbukti berjalan .. sampai bertahannya gedung-gedung tinggi terhadap gempa berskala 9 richter. belasan tahun sebelumnya, saat gempa besar menghantam kobe, asosiasi profesi di jepang mencanangkan perubahan dan perbaikan mendasar pada perhitungan struktur tahan gempa, serta memberlakukan building code yang sangat ketat. ini merupakan salah satu hal hal penting yang menyelamatkan jepang pada gempa dan tsunami kemarin ..

Japan’s Strict Building Codes Saved Lives

By James Glanz and Norimitsu Onishi
The New York Times
Published: March 11, 2011

Hidden inside the skeletons of high-rise towers, extra steel bracing, giant rubber pads and embedded hydraulic shock absorbers make modern Japanese buildings among the sturdiest in the world during a major earthquake. And all along the Japanese coast, tsunami warning signs, towering seawalls and well-marked escape routes offer some protection from walls of water.

These precautions, along with earthquake and tsunami drills that are routine for every Japanese citizen, show why Japan is the best-prepared country in the world for the twin disasters of earthquake and tsunami – practices that undoubtedly saved lives, though the final death toll is unknown.

In Japan, where earthquakes are far more common than they are in the United States, the building codes have long been much more stringent on specific matters like how much a building may sway during a quake.

After the Kobe earthquake in 1995, which killed about 6,000 people and injured 26,000, Japan also put enormous resources into new research on protecting structures, as well as retrofitting the country’s older and more vulnerable structures. Japan has spent billions of dollars developing the most advanced technology against earthquakes and tsunamis.

Japan has gone much further than the United States in outfitting new buildings with advanced devices called base isolation pads and energy dissipation units to dampen the ground’s shaking during an earthquake.

The isolation devices are essentially giant rubber-and-steel pads that are installed at the very bottom of the excavation for a building, which then simply sits on top of the pads. The dissipation units are built into a building’s structural skeleton. They are hydraulic cylinders that elongate and contract as the building sways, sapping the motion of energy.

Of course, nothing is entirely foolproof. Structural engineers monitoring the events from a distance cautioned that the death toll was likely to rise as more information became available. Dr. Jack Moehle, a structural engineer at the University of California, Berkeley, said that video of the disaster seemed to show that some older buildings had indeed collapsed.

The country that gave the world the word tsunami, especially in the 1980s and 1990s, built concrete seawalls in many communities, some as high as 40 feet, which amounted to its first line of defense against the water. In some coastal towns, in the event of an earthquake, networks of sensors are set up to set off alarms in individual residences and automatically shut down floodgates to prevent waves from surging upriver.

Critics of the seawalls say they are eyesores and bad for the environment. The seawalls, they say, can instill a false sense of security among coastal residents and discourage them from participating in regular evacuation drills. Moreover, by literally cutting residents’ visibility of the ocean, the seawalls reduce their ability to understand the sea by observing wave patterns, critics say.

Waves from Friday’s tsunami spilled over some seawalls in the affected areas. “The tsunami roared over embankments in Sendai city, washing cars, houses and farm equipment inland before reversing directions and carrying them out to sea,” according to a statement by a Japanese engineer, Kit Miyamoto, circulated by the American Society of Civil Engineers. “Flames shot from some of the houses, probably because of burst gas pipes.”

But Japan’s “massive public education program” could in the end have saved the most lives, said Rich Eisner, a retired tsunami preparedness expert who was attending a conference on the topic at the National Institute of Standards and Technology in Gaithersburg, Md., on Friday.

In one town, Ofunato, which was struck by a major tsunami in 1960, dozens of signs in Japanese and English mark escape routes, and emergency sirens are tested three times a day, Mr. Eisner said.

Initial reports from Ofunato on Friday suggested that hundreds of homes had been swept away; the death toll was not yet known. But Matthew Francis of URS Corporation and a member of the civil engineering society’s tsunami subcommittee, said that education may have been the critical factor.

“For a trained population, a matter of 5 or 10 minutes is all you may need to get to high ground,” Mr. Francis said.

That would be in contrast to the much less experienced Southeast Asians, many of whom died in the 2004 Indian Ocean tsunami because they lingered near the coast. Reports in the Japanese news media indicate that people originally listed as missing in remote areas have been turning up in schools and community centers, suggesting that tsunami education and evacuation drills were indeed effective.

Unlike Haiti, where shoddy construction vastly increased the death toll last year, or China, where failure to follow construction codes worsened the death toll in the devastating 2008 Sichuan earthquake, Japan enforces some of the world’s most stringent building codes. Japanese buildings tend to be much stiffer and stouter than similar structures in earthquake-prone areas in California as well, said Mr. Moehle, the Berkeley engineer: Japan’s building code allows for roughly half as much sway back and forth at the top of a high rise during a major quake.

The difference, Mr. Moehle said, comes about because the United States standard is focused on preventing collapse, while in Japan — with many more earthquakes — the goal is to prevent any major damage to the buildings because of the swaying.

New apartment and office developments in Japan flaunt their seismic resistance as a marketing technique, a fact that has accelerated the use of the latest technologies, said Ronald O. Hamburger, a structural engineer in the civil engineering society and Simpson Gumpertz & Heger, a San Francisco engineering firm.

“You can increase the rents by providing a sort of warranty — ‘If you locate here you’ll be safe,’ ” Mr. Hamburger said.

Although many older buildings in Japan have been retrofitted with new bracing since the Kobe quake, there are many rural residences of older construction that are made of very light wood that would be highly vulnerable to damage. The fate of many of those residences is still unknown.

Mr. Miyamoto, the Japanese engineer, described a nation in chaos as the quake also damaged or disabled many elements of the transportation system. He said that he and his family were on a train near the Ikebukuro station when the earthquake struck. Writing at 1:30 a.m., he said that “we are still not far from where the train stopped.”

“Japan Railway actually closed down the stations and sent out all commuters into the cold night,” he said. “They announced that they are concerned about structural safety. Continuous aftershocks make me feel like car sickness as my family and I walk on the train tracks.”



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