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Code for Thought

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Fred,

Comments from Seismic Zone 2!

Maybe, maybe, if California does end up with zones of moderate seismicity, it 
will be beneficial for us outside of California that have to justify why we 
need certain requirements.  It is well known that all of California had been 
zoned 3 or 4 so as not to deal with the question of zone 2.  It is also well 
known that SEAOC's position regarding seismic design stops at the interface 
of seismic zone 3 with 2.

With the adoption of the 1985 UBC, the seismic provisions for zone 2 have 
practically been eliminated.  A prime example has to do with reinforced 
masonry that you mentioned.  Pre-1985 the UBC required that "all concrete and 
masonry the resists seismic forces meet the requirements for reinforced 
concrete or masonry."  The requirements for reinforced masonry were a minimum 
of .002 times the cross-sectional area of the wall --- You are familiar with 
the requirements.  With the 1985 UBC seismic zone 2 was lumped with seismic 
zone 1 and the reinforcing was changed to essentially unreinforced masonry 
based on a small series of tests for HUD for *small* single story masonry 
homes.  Test reports emphasized that the results were limited, 2500 sf max 
house, single story, etc., however, these restrictions appear nowhere in the 
UBC.

Just because there are rebars in a wall doesn't mean that it is reinforced 
masonry.  The criteria that I learned in school for the difference between 
unreinforced concrete and reinforced concrete is that the strength of a 
reinforced beam, wall, etc., should be at least 1.25 times the calculated 
strength of an unreinforced element.  That requirement, which was to prevent 
sudden failure at the same time of the reinforcing *and* concrete/masonry, 
seems to have been forgotten.

Seismic Zone 2 requirements should be closely akin to Seismic Zone 3 
requirements.  We have had, and will have earthquakes of the same magnitude 
that is experienced in Seismic Zone 3, except that we don't have them as 
often, at least not as often in the past 112 years.

It is with a wee bit of hope that California will adopt moderate earthquake 
zones so that the benefits will spill over to us.

It is a bitter fight to fight against local modifications to the building 
code that will permit mud adobe, burnt adobe, unreinforced masonry, and straw 
bale construction and loose.  While I, and many other structural engineers 
would not think of designing to the inadequate requirements that are now 
permitted in the UBC, there are some who will conform only to what is 
required by the code.

I will get off my soap box now!

A. Roger Turk, P.E.(Structural)
Tucson, Arizona