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RE: '97 UBC Design - Are you too old to change your ways???[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: '97 UBC Design - Are you too old to change your ways???
- From: "Jeffery Seegert (x 485)" <jbseegert(--nospam--at)matrixti.com>
- Date: Thu, 23 Sep 1999 08:05:21 -0400
HERE! HERE! Well Said! -----Original Message----- From: r nester [mailto:rnester(--nospam--at)juno.com] Sent: Thursday, September 23, 1999 3:56 AM To: seaint(--nospam--at)seaint.org Subject: Re: '97 UBC Design - Are you too old to change your ways??? 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 ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.
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