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Re: Minimum (or zero?) Temperature Reinforcement

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Walter,

Some more thoughts on unreinforced concrete construction. 

Buildings with unreinforced concrete walls were built in southern CA in a 
period of transition from unreinforced brick.  I'm guessing that they were 
built in the period approximately between the Santa Barbara Earthquake of 
1925 and the Long Beach Earthquake of 1933.  Wall thicknesses generally 
matched the those commonly used for brick at the time, 12" to 13" for 
commercial buildings.  Wall heights were in the range of 12 to 15 feet 
(height-to-thickness ratios in the range of 11 to 15).  Anchored to 
diaphragms, it seems that unreinforced concrete walls of H/t ratios like this 
should perform reasonably well in seismic zones: 6" walls with 7.5 feet 
between ground floor and diaphragm anchorage.  Perhaps your research can 
establish the suitability of thinner walls.  Cracks may be pointed and 
covered with plaster after the concrete cures.

The walls of a house in Pasadena CA with unreinforced concrete walls built 
before 1920 look as if they were built 10 years ago, while a house nearby of 
similar age with steel reinforced walls has countless areas of spalling, 
cracks, and rust stains.  I like the idea of small houses with unreinforced 
concrete walls, and think is worthy of further research.

Nels Roselund
Structural Engineer