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Frank's Houses and Earthquakes

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Frank Lew said: "The reality is that only a very small percentage of such
housing stock ever sustain any earthquake damage, even of the cosmetic
variety, during their service life.  This is true even in urbanized Zone 4
country like the Los Angeles and San Francisco areas.  My mother-in-law's
twostory house in Oakland was one of many that were hastily built in 1907 to
help meet the demand for housing after the '06 S.F. event.  It has a brick
foundation, no anchor bolts or hold downs, and wouldn't calc out or meet
today's codes.  Yet, in it's 91 years of existence, the only damage have some
minor plaster cracks in one living wall, caused by the Loma Prieta event. I've
lived in five non-engineered houses, all located in the Bay Area and within a
few miles of the Hayward and San Andreas faults.  Those houses have
experienced several earthquakes that have caused damage in the region, but
none of those houses sustained any damage."

Frank -  I am surprised by your statements particularly since you are such a
noted and experienced structural engineer and retired building official. No
two earthquakes are alike, so just because your family's old houses survived
some moderate, distant earthquakes, it is no indication that they will survive
future events.

Are you saying that since your family experienced no damage from major
earthquakes in the past 91 years in the Bay Area, that houses with incomplete
load paths pose acceptable risks? 

The average earthquake recurrence interval for the East Bay is roughly 220
years give or take 100 years or so. Your family's experience fortunately fell
between earthquakes in a quiescent period of seismic activity after the great
1906 earthquake. The latest research indicates that the Northern Segment of
the Hayward Fault (near your current residence in Orinda) is overdue for a
characteristic major earthquake. Aren't you at all concerned about this risk?

In recent years, you've volunteered many hours to develop residential retrofit
provisions for ICBO. Do you feel that your work that helped create Appendix
Chapter 5 of the Uniform Code for Building Conservation was worth the time and
effort? 

In 1996, the Association of Bay Area Governments estimated that 150,000
housing units will be uninhabitable after a Hayward Earthquake event. An event
on just the Northern Segment of the Fault will dislocate some 80,000 housing
units. The Peninsula Segment of the San Andreas Fault could generate roughly
40,000 lost housing units. Note that these estimates are for losses only from
shake damage and do not included losses from fire, liquefaction, or
landsliding. 
Do you dispute these figures? 

You, Frank, are correct in noting that only a small fraction of all homes in
the Bay Area will be uninhabitable. There are roughly 5 million people in 1.7
million housing units in the Bay Area. A 150,000 loss is about 9 percent of
the housing stock for the entire Bay Area - comparable to that 8 percent lost
in Watsonville in the Loma Prieta Earthquake. In the East Bay alone, the
percent loss may be as high as 10 to 20 percent . Assuming 2.5 persons per
household, that could be 375,000 homeless. 

Are you aware of the social and economic disruption in Watsonville from their
recent 8 percent loss of housing stock? 

Do you consider a 2 to 20 percent loss of housing in the Bay Area "very
small?" 

Do you think it will be easy for the East Bay to absorb these housing losses
within a reasonable time frame? Where are they all going to go?

A preliminary survey this spring by ABAG shows an encouragingly high number of
homes in Alameda have been retrofitted. Do you think governments and insurance
companies should continue to encourage retrofits? 

Aren't we continuing to add to our seismic risk with new housing that will
also likely be uninhabitable after earthquakes? 

What steps do you think we should take to manage this risk? Are we really
doing all that we can? 

Now Frank, aren't you just a bit glad you are no longer Chief Building
Official of Contra Costa County in the East Bay? 

Seriously now Frank...

>From Fred, your shadow in Sacto