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Re[2]: Frank's Houses and Earthquakes

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     The Philippines lie in the so-called Pacific ring of fire. Frequent 
     earthquakes occur here and our structural engineers normally do not 
     design our masonry units to be part of the structural system. What we 
     normally would do is to allow the masonry wall to crack but not 
     collapse by providing enough reinforcements into the columns and the 
     floor slab. Fatal incidences usually occur in the provinces where 
     fly-by-night small contractors use bamboo slats to hold the walls in 
     place.
     
     The separation of the masonry wall from the structural system though 
     is an expensive item usually frowned upon by the building owners. What 
     the ACI should do to help us out here is to provide us, especially in 
     the Asian region, a standard detail to follow showing separation of 
     the masonry wall from the main structural system. Base from my 
     experience, adherence to a published standard is a strong weapon 
     against stingy building owners.
     
     
     jerome


______________________________ Reply Separator _________________________________
Subject: Re: Frank's Houses and Earthquakes
Author:  MIME:cejn(--nospam--at)engmail.newcastle.edu.au at INTERNET
Date:    5/25/98 1:48 AM


Dear Frank,
     
The death rate from the Tashkent earthquake in the centre 47 sq kilomrtes, 
about 20 sq miles was 1 in 3.  Look at your family of say 5 kids grand 
children etc and subtract off 30 percent.  Poorly constructed masonry can 
survive an earthquake seen it plenty.  It is plain dumb luck that it was 
built in right place so not get a full load or its on rock.
     
The problem with masonry is it very rapidly climbs as a killer in 
earthquakes.  Of course they only lost 256,000 in Tashkent.
     
I refer you to JSCE  V0l 11 No 4 p 155s-163s and also to the latest National 
geopgraphic on the earthquakes in the pacific northwest.
     
Of course your right your chances of dying in an earthquake are remote 
unless your in the wrong place at teh wrong time.  Then the odds are 
appalling.
     
     
     
John Nichols.
     
At 14:28 22/05/98 -0400, you wrote:
>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
>
>
>
>