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Re: IRAN QUAKE/can we discuss ths?

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Nels,
 
Excellent summary of the problems and underlying basis for their continuance.  This is why I indicated that it is the local engineering community that needs to help develop even rudimentary modifications to the local building practices to help begin mitigation.  Only the local engineers are familiar with the style of local construction.
 
We may not mandate retrofit of dwellings, and as you indicate we are fortunate in the way our typical dwellings are constructed, but we do study and learn from the failures of our residential structures modifying the codes and requirements as a result.  I did not mean to give the impression that I expected an immediate fix and massive retrofit effort was possible, only that the first steps need to be taken.
 
----- Original Message -----
Sent: Tuesday, December 30, 2003 9:29 PM
Subject: Re: IRAN QUAKE/can we discuss ths?

Paul,
 
Seismic hazard reduction in 3rd-world countries is a massive problem -- I don't think application of modern construction techniques to residential construction are a reasonable option in those countries.  The tremendous number of victims in the Bam Earthquake indicate to me that most were probably killed or injured in their homes.  What's to be done about mitigation of residential seismic hazards in a town with enough adobe houses to kill 50,000 people in an earthquake?  How about a quick course in Fundamentals of Seismic-resistant Adobe Dwelling Construction -- who knows enough about that subject to present such a course -- to folks who are largely illiterate [I assume]?.
 
Even in the US, there are no mandatory ordinances for seismic upgrade of dwellings -- not even for URM residences.  [Fortunately, our houses are usually built of light-weight materials, so that, for us, residential damage only rarely results in collapse or fatalities].
 
Worldwide, probably the most commonly used residential building material is earthen [adobe or some traditional variation -- it's just dirt, nothing else].  Vernacular residential construction in most areas of the world cannot take advantage of modern light-weight construction materials -- those materials just are not available.  Earthen construction is labor-intensive, but labor is more easily acquired than the materials that we are familiar with.  And, it's no use asking, "What are the structural engineers doing there?"  Even in the US, most houses are not designed by engineers.  In many areas of the world, the traditional methods of earthen construction are commonly understood and used by almost everyone in the community and soil is one  material that is readily available -- often the neighborhood, or the extended family will work together on building a new earthen house, using the methods learned from the previous generation -- in  just the way that the previous generations learned how to build their houses.  No other building material is readily available; no engineering is expected or available.
 
It seems to me that the best first approach to seismic hazard mitigation for new home construction in poor areas of the world where people have no choice but to live in earthen buildings would be to start by studying the traditional methods of a given district, and then develop and disseminate easy-to-understand and easy to communicate guidelines that could, with small modification to the traditional methods, incorporate seismic stability into the local traditional dwelling construction.  The  guidelines would include wall and opening proportions to maximize in-plane shear resistance; rules for height-to thickness ratios to promote wall stabilities; making use of light-weight materials for roof construction [to the extent available]; and details for interconnection of the walls to the roof.   High priority for a poor district would probably need to be to find a locally reasonable way of to minimize massive material overhead by building roofs of light-weight materials able to resist loads in tension and/or flexure [instead of using such heavy assemblies as vaulted adobe roofs, or branch-and twig-supported packed soils roofs].  It seems pretty likely that every local area will have its own unique best-solution to seismic hazard mitigation -- you and I will never visualize the needs from our desks.  Easy solutions are not available and the folks who take on the responsibility of solving these problems have staggering difficulties to overcome.
 
If a retrofit technology were at hand, it is likely that, for a family who is scratching just to keep from starving, retrofit would have very low priority -- after all, in any given community, a damaging earthquake is a very rare event and would be seen as posing very little urgency [death by ill-health or starvation is likely much more probable than death caused by earthquake shaking].  Even in southern California, where, in the last 100 years, damaging earthquakes have occurred every 20 years or so, most people have not experienced personal danger in an earthquake.  So, many building owners continue to resist earthquake hazard mitigation, and most people have not retrofit their homes for seismic hazard reduction using available voluntary retrofit methods.  It only takes a short time after an earthquake before the ground seem very firm again, and preparation of structures for future quakes begin to take lower priority.  In any case, useable retrofit methods for 3rd-world nations would probably vary widely from region to region because of variations in local construction styles and reasonably available strengthening materials.
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net