VOA标准英语2010年-Engineers Assess Damage from Haiti Ear

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"Earthquakes continue to surprise you. ... You can learn something new from each of them that will benefit future designs and future generations." — Brady Cox

The January 12 Haiti earthquake and its aftershocks killed or injured hundreds of thousands of people in the Caribbean island nation, mostly as a result of what engineers call structural¹ failure — buildings collapsing², roofs falling in, that sort of thing.

Although a fault line goes pretty much right through Haiti's capital city, Port-au-Prince, the natural disaster most Haitians worried about was hurricane.  The destructive tropical storms rake through the region every summer, and Haiti, a very poor country, was still cleaning up from a succession of severe hurricanes over the past two years.  The last big earthquake was in the 19th century. So it's not surprising that many buildings were not designed or built to withstand the shock.

Experts we talked to — who haven't seen the damage first-hand — agreed that an earthquake so close to the city, and so close to the surface, was bound to be destructive, but they say substandard buildings also explain much of the damage.

Civil engineering professor Anne Kiremidjian of Stanford University has been studying pictures from the earthquake zone, where she says masonry³, concrete frame, and adobe⁴ construction dominates.

"All three types of construction can be extremely vulnerable to earthquakes."

For example, she says masonry buildings — made of brick or concrete block — have to be properly reinforced.

"Just looking at the collapsed⁵ buildings that were built in masonry, I had to strain my eyes to see maybe one or two pieces of reinforcement, which is highly inadequate⁶."

Engineers normally plan buildings mainly for what they call the static load — the weight of the building and its contents, just sitting there. But an earthquake adds additional forces — back and forth⁷ shaking — and the building has to be designed to withstand it.

The building materials and techniques used in Haiti are not necessarily prone⁸ to failure, says structural engineering professor Clay Naito of Lehigh University in Pennsylvania. But construction has to be done right.

"Reinforced concrete is an excellent material for earthquakes. You can design structures out of reinforced concrete that work very well under very high earthquake demands. The problem is when you leave out the details," Naito said.

Details such as matching the strength of columns to the mass of the floors they're supporting.

International engineering teams will be traveling to Haiti to assess why the damage was so severe and widespread. Brady Cox is a civil engineering professor at the University of Arkansas. He has visited Japan and Peru after recent earthquakes there, and he'll be doing the same thing in Haiti.

"After every major earthquake we learn lessons that we use to refine our designs and building codes. And it's amazing — earthquakes continue to surprise you. After each one they all seem to have a signature and hopefully you can learn something new from each of them that will benefit future designs and future generations."

Engineers stress the importance of adopting a building code that would require features to make buildings less prone to earthquake damage.

Architecture professor Mary Comerio of the University of California at Berkeley notes that the costs of reconstruction⁹ in Haiti under much stricter building codes would be "astronomical¹⁰."

"If you think about a simple house costing maybe $10- or $20,000 in island terms, and then multiply that by a million, you're going to get some pretty big numbers very quickly. And that isn't counting all of the infrastructure¹¹, the public buildings, the schools, the government buildings, etc."  

But even modest changes in construction can significantly improve survivability. Clay Naito, the Lehigh engineer, says in earthquake-prone Japan, small changes were made in traditional building techniques with costs in mind.

"What they did to address that issue is come up with some standard designs which can be used in their current construction methods that could enhance them against earthquakes," Naito said. "And I think a similar type of approach could be done in Haiti."

But it will require that Haitians accept that earthquakes are a hazard they have to live with and plan for. And Anne Kiremidjian, the Berkeley professor, says that may be hard to do. 

"It's not just Haiti's problem," she stressed. "I think this is a worldwide problem. There was a study done that people tend to forget within 10 years that there was a devastating¹² earthquake. Or that there was a devastating event. If it doesn't happen frequently enough, people have a tendency to forget, and very often choose to forget." 

It's too soon to know whether, in the rush to rebuild the ruined Haitian capital, attention will be paid to the need to reduce the vulnerability of a city built on a fault line.