Re: Information on earthquake-proof buildings

No building is ever designed to be "earthquake proof" in the sense that it 
will never be damaged in any earthquake.  Recent earthquakes have shown 
that ground shaking can be intensified by a number of factors beyond the 
size of the quake itself.  To make a quake-proof building would make it too 
expensive and difficult to use to be practical.  Instead, what engineers 
strive for is "earthquake-resistant" buildings.  These are buildings that 
may suffer damage, but will safeguard the lives (and to a lesser 
degree, the property) of those inside the building and near the building on 
the outside.

The major hazards to life are total or partial collapse of the building and 
falling pieces from the structure, including broken glass.  In 
quake-prone areas, new buildings are designed and old buildings are 
renovated to avoid either of these problems.

Collapse can come from several causes.  Older, unreinforced masonary 
buildings pose the greatest risk as even modest shaking wil break the 
mortar and cause the building to literally go to pieces.  The heavy 
masonary then comes crashing down on occupants and passers-by.  
Stell-reinforced concrete is a much safer material.  Some construction 
techniques, however, can lead to the separation of floors from walls and 
the collapse of a building into a pancake-like stack of rigid floors. 
Another major collapse hazard is the presence of "soft" first floors.  
Appartments may be built over a garage level or stores, for example.  The 
first level has few walls and large openings and is unable to resist the 
side-to-side shaking in a quake.  Wood-frame structures are the most 
resistant to shaking damage, though occupants are still at risk from 
falling objects inside and the building may be shaken off its foundation, 
rupturing utility lines.  In addition to shaking, buildings and their 
occupants are at risk from secondary effects of earthquakes including gas 
leaks and the resulting explosions and fires.

Each time a major quake occurs, engineers learn more about how to design 
buildings.  Unfortuantely, they usually learn this by studying badly 
damaged buildings.  Buildings in quake-prone areas are being fitted with 
instruments to measure shaking and to allow engineers to better predict 
building response a design safer buildings.  Most earthquake safety 
improvements are implemented by changes in building codes.  Older 
structures usually do not meet modern codes and take advantage of new 
knowledge.  They can be very expensive to upgrade, but the alternative may 
be even worse.

Techniques in current use include base isolation, diagonal bracing, and 
passive damping.  Base isolation works by separating the building from the 
moving ground.  Teflon pads, large rollers, springs or other devices allow 
the ground to move under the foundation without transmitting all of that 
motion to the building (sort of like pulling the tablecloth out from under 
the plate and having the plate stay still). Diagonal bracing helps resist 
shearing forces that come from the swaying motion of a shaken building:

  ____             _____
 |    | shear->   /    /
 |____|          /____/

Passive damping has been pioneered, as have many earthquake engineering 
advances, by the Japanese.  It involves using a variety of techniques to 
absorb shaking energy within a building.  Some techniques use building 
materials that will deform, but not break.  Others isolate large masses 
such as the HVAC equipment from the rest of the building (using rollers 
or springs as in base isolation) and use those masses as a counter-balance 
to reduce building sway.

The USGS web site has some information at: http://quake.wr.usgs.gov/prepare/factsheets/SaferStructures/

A good list of web resources is available at: http://quake.wr.usgs.gov/prepare/structures.html

A site from the American Plywood Association gives a good overview of 
quake-resistant home building.  Of course, they do emphasize the value of 
plywood in such construction. http://www.mcvicker.com/twd/apa/eqguide/eqguid01.htm

A search on the keywords "earthquake resistant building" turned up all 
sorts of sites from people offering quake-resistant domes for houses to 
companies offering quake-proofing services to information sites such as the 
USGS sites above

David Smith
La Salle University, Philadelphia PA