City highrises: Waiting for the Big One

Downtown San Francisco (Photo: Jim Wilson)

In today's NY Times: At Risk in a Big Quake: 39 of San Francisco’s Top High Rises

...Engineers have known about a major defect in certain steel-frame buildings since 1994, when shaking from the Northridge earthquake in Los Angeles fractured critical joints in more than 60 buildings, bringing at least one very close to collapse. The building code was rewritten to eliminate the flawed technique.

Yet nearly a quarter of a century later, California is still wrestling with what to do with the hundreds of buildings, many of them high rises, that were constructed during the more than three decades when the defective connection system was widely employed...

“This is an issue that structural engineers should have been dealing with continuously since the mid-1990s and we just dropped it,” said Keith Porter, an earthquake engineering expert who helped lead the United States Geological Survey study that published the list of San Francisco high rises. “We don’t know how to deal with a problem this big.”

Experts consider these buildings vulnerable to collapse only in extreme shaking caused by rare and powerful earthquakes, similar to the one that struck San Francisco in 1906.

The list, buried among the seismic calculations of an appendix in the U.S.G.S. report, includes around 40 steel-frame high rises clustered in downtown San Francisco and built between 1960 and 1994, the approximate years when the flawed technique was employed. There are more than 200 high rises in the city...

On the List

In April, the United States Geological Survey published a report with a list of high rises in downtown San Francisco that included 39 steel-frame buildings constructed between 1960 and 1994, the approximate years when a flawed welding technique was employed. The list was compiled with help from the Structural Engineers Association of Northern California.

1. Hartford Building, 650 California

2. Beal Bank Building, 180 Sansome

3. Bechtel Building, 50 Beale

4. 44 Montgomery

5. 425 California Street

6. 555 California Street

7. McKesson Plaza, One Post

8. Pacific Gas & Electric Building, 77 Beale

9. One Embarcadero Center, 355 Clay

10. Transamerica Pyramid, 600 Montgomery

11. 100 Pine Center, 100 Pine

See also City's highrise boom: Seismic safety "never a factor."