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

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Russ-
Good post, you can count me as one who agrees with
your observations.

Lynn

r nester wrote:
> 
> It is commonly reported that of the 20 billion in damage caused by the
> >Northridge
> >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
> rnester(--nospam--at)juno.com