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Re: '97 UBC Design - Are you too old to change your ways???

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It is commonly reported that of the 20 billion in damage caused by the 
>earthquake, 15 billion was in residential construction.  Add to that 
>the fact
>that most of it was relatively new and we  have a justification for 
>change.  The
>Caltech/Curee rpoject on wood frame construction is a testamony to the 
>need for
>change.  I believe that the new provisions in the 97 UBC are in part 
>related to
>this experience.

I see this line of thinking as a weak, overly simplified  straw man
arguement.  Of the $15B, how much was non-structural damage unrelated to
structural strength?  How much was due to water damage, soil movements,
secondary fires, loss of use, temporary housing, and code-driven
upgrades?  Of the structural damage, what portion was for homes designed
and built before 1976?  How did homes built to the 1988-91 UBC's fare in
relation to others?  The overwhelming majority of structures and enclosed
space in the San Fernando Valley are residential.  Whatare the damage
costs relative to replacement costs, broken down into foundation,
structural, non-structural, and into structure types.   Without this
data, we are all just shooting in the dark.

The 1988 UBC was the ultimate result of ATC 3-6, published in 1976-78,
with a detailed commentary.  That commentary compiles statistical
arguements for adoption of the ATC provisions based on a statistically
low, but presumably acceptable probability of structural failure.  It
also compiles similar statistics for the probability of life losses and
injury.   It was an attempt to bring the statistical probability of
seismic failures to the same level as for wind or other natural hazards.

Using the ATC 3-6 Commentary statistics, a 30% increase in design base
shear, coupled with the other engineering provisions of that (proposed)
code (adopted in 1988), would reduce the chance of a structural failure
by a factor of over 10.  Not a tenth of previous codes.  This is a factor
of ten applied to structures designed and built to what eventually became
the 1988 UBC.

What we now have, as I see it, is a class of structures which may well be
grossly overdesigned for seismic hazards relative to all other hazards. 
This is no longer a minimum life safety code, it is a performance based
code with an implied level of performance far above life safety, and
totally out of kilter with other natural hazards. That is not logical or
consistent.   It will not prevent gross soil movements, water damage,
falling furniture, broken underground pipes, or restrain all your
groceries from disgorging themselves from cupboards and refrigerator.  It
won't keep your electricity, water, or other utilities from making your
home unlivable.  All these non-structural damages went into that $15B
figure, and none will be effected by the strength of shearwalls or
collector elements.

 If Code officials had actually known this, the 1997 UBC may never have
been adopted.  

Sorry for the rant.  I'll go quietly, now.

Russ Nester

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