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RE: Steel Moment Frames in Seismic Zone 0

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Bill,

First read the quote:
"Structural engineering is the art of molding materials we don't wholly
understand, into shapes we can't fully analyze, so as to withstand forces we
can't really assess, in such a way that the community at large has no reason
to suspect the extent of our ignorance." Jim Amrhein

Now the bad news.  It is true.  You must consider seismic.  I would suggest
that you get the NEHRP Provisions and Commentary.  The good new is that the
NEHRP is free.

When we look first at geology and seismology, we are looking at our time of
studying, measuring, and quantifying earthquakes relative to the geologic
time of the creation of the faults, escarpments, and other things that cause
the ground to shake, we only have a snapshot in geologic time.  What is the
recurrence of New Madrid Fault?  What is the ground shaking capacity of the
Meers Fault?  What happens to structures when subjected to significant
vertical accelerations?  What is the response spectra for distant long
period events?  And what about inadvertent shaking due to explosions?  

Then we look at how structures respond to earthquakes.  It was not that long
ago that SMRF's were relatively easy to design.  We did not have to look at
weld ductility or prequalified connections.  There was a time that we just
threw an arbitrary lateral load on the building, designed a lateral force
resisting system that kind of made sense, and that was a seismic design.  We
were wrong.

When the provisions were developed for the NEHRP, some of these arguments
were made.  The Provisions were approved by people not only living on shaky
ground, but also by those of us who live in a more stable geologic region.
We just were coming to grips with the "extent of our ignorance".  The added
seismic design and construction provisions for low seismic areas is a
reflection of what is perceived as good practice, of very little cost, and
what we don't know.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	Bill Polhemus [SMTP:bill(--nospam--at)polhemus.cc]
> Sent:	Saturday, July 20, 2002 9:37 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Steel Moment Frames in Seismic Zone 0
> 
> Okay, dumb question time (I seem to be the one that brings them up, so
> other
> people don't have to. C'mon, you know who you are!)
> 
> Anyway, I haven't had time to catch up with the IBC as yet, though I do
> have
> a copy sitting here looking pretty. I remember hearing that seismic design
> is going to HAVE to be considered even in places were it never was before
> (i.e. Zone 0/Zone 1). Is this true?
> 
> It appears from Charlie's response to Mark that this is the case. I know I
> could just crack open the UBC and start reading (and I've even purchased
> several of the supplemental publications such as the "Structural/Seismic
> Design Manual for IBC Vol. 1," so I could go there as well).
> 
> But I like the capsule descriptions that folks like Charlie and Harold
> always give.
> 
> Thanks.
> 
> 
> William L. Polhemus, Jr. P.E.
> Polhemus Engineering Company
> Katy, TX, USA
> Phone (281) 492-2251
> FAX (281) 492-8203
> email bill(--nospam--at)polhemus.cc
> 
> -----Original Message-----
> From: Carter, Charlie [mailto:carter(--nospam--at)aisc.org]
> Sent: Saturday, July 20, 2002 9:17 AM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Steel Moment Frames in Seismic Zone 0
> 
> >I am preparing to design a 4 story moment
> >frame office building on the east coast
> >(seismic zone 0) and was wondering what
> >other folks have been doing.
> >What are some other engineers in this area
> >requiring?  What is standard practice?
> 
> It all depends upon the R factor you select (or are permitted to select in
> the applicable building code)....
> 
> 

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