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Quake prep still issue 20 years later

New technologies make it possible to prepare homes for the next ‘big one’ but CA homeowners slow to change.

BY ZACHARY HOFFMAN | SAN FRANCISCO | October 16, 2009

On Oct. 17, 1989, the eyes and ears of the world were trained on San Francisco for the third game of the World Series of Baseball, recalls Art Agnos, mayor of San Francisco at the time. “Instead of seeing the players running onto the field what the world saw was a lot of shaking.”

“I was on my way into the baseball stadium and was greeted by emergency personnel,” said Agnos.

This year marks the 20th anniversary of the Loma Prieta earthquake that killed 63 people and caused nearly $10 billion in damages across the Bay area. The magnitude 6.8 earthquake lasted for 15 seconds, but in that time the region learned how unprepared it is for large earthquakes.

“Loma Prieta really exposed the vulnerability in the Bay area,” said Jack Boatwright, geophysicist for the United States Geological Survey (USGS) and resident San Franciscan. “The difficulty with earthquakes from an engineering point of view and a scientific point of view is that we always learn something we didn’t know.”

After the earthquake, the city passed a $100 million bond to assist private homeowners to retrofit older masonry buildings for safety in future events.

“We had been learning for some time that we should be building to new seismic standards,” said Agnos. “The major damage was not dealt to the modern high rises, the main damage was in the old, old construction throughout the city.”

But still today, retrofitting older structures remains one of the main problems in preparing for future earthquakes, even though the cost per household is relatively low.

Boatwright said, “The difficulty is convincing, often homeowner by homeowner, that they should take on these retrofits.”

Still, every year codes are changed, earthquakes teach new lessons and new building methods are developed to combat violent shaking.

Researchers at Stanford University have developed a new framing structure that can be easily retrofitted into existing buildings that transfers the damaging energy of an earthquake into replaceable fuses instead of the structure itself, much like electrical fuses protect electronic equipment from energy surges.

“The whole landscape,” said Greg Deierlein, the professor at Stanford’s Department of Civil and Environmental Engineering who led the team, “is to design for reparability, to think about where there is damage and factor in rapid repair.”

"By prolonging the longevity of buildings, you have a really positive sustainability impact,” Deierlein said.

Laura Adleman of the San Francisco Department of Emergency Management said, “Generally speaking we want people to be occupying safe buildings, the fewer buildings that are vulnerable the better… recovery is a large issue and housing is only a small portion of that.”

Deierlein believes that the concept of this controlled rocking system can be adapted for use on bridge structures; in fact, there are those in the engineering world using the same concept for bridge design.

The new design allows structures to rock off of their foundations within the confines of “shoes,” and when the earthquake ends, steel tendons act in an elastic manner to snap the structure back to its pre-quake, plum position.

This is in contrast to conventional structural systems, where damage occurs in the main structural members that can be expensive and difficult to repair and replace.

Deierlein said. “Existing systems can be left with large permanent drifts (leaning buildings) that may make repairs prohibitive and lead to demolition of the building.”

As these types of breakthroughs are made, they are slowly integrated into building codes and retrofits as more data supports their advantage.

But says Boatwright, “The difficulty with earthquakes is that we always learn something we didn’t know.”

“One is never ready for a disaster,” Agnos said, “That’s why they are called disasters because there is complete devastation; you just have to deal with as best you can when it comes.”

“I think San Francisco is as prepared as any city can be to deal with the first 48 hours until help arrives from outside resources,” said Agnos.


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