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RE: Seismic Zones in Texas

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Ken,

We are all getting old and the change coming down the pike is scary.  The
best thing to do is to run through the NEHRP with the new numbers, and
develop a degree of comfort before you are forced to.  The commentary will
explain all of the changes and reasons much better than I can.  

I am kind of the acid test.  If I can figure it out, you can rest assured
that you can too.

The base event will be the 2% in 50 years.  But when you boil the numbers
down, some base accelerations will go up and some will go down from the 1997
UBC.  By and large the base acceleration will be increasing.

The vast majority of the people developing the new code are practitioners.
There are some university professors and researchers, but there are not
many.  Every change to the code has solid well reasoned rationale.  The
changes are not arbitrary.

We authors (I chaired the nonbuilding structures section) are not perfect,
but the 1997 NEHRP Provisions and Commentary are well written with a lot of
thought, discussion, and debate.  Usability was a major theme throughout the
development process. 

The BSSC is having its meeting January 20-21 in Reno.  I would invite you to
attend.  It is generally quite a learning event.  I am sure Claret Heider of
the BSSC (she watches this list) would get you all of the information you
need, if you choose to come.

Regards,
Harold Sprague
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Kenneth Tarlow [mailto:ktarlow(--nospam--at)yahoo.com]
Sent: Thursday, January 07, 1999 6:03 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Seismic Zones in Texas







Dear Harold,

Does the IBC code raise the design standard to 5% in 50 years or the
975 year event?  In California this has been the level  for Hospitals
and Schools.

When I compare the force levels in the 1997 UBC with earlier
editions,(they are much more difficult to calculate and probably going
to create some big battles between plancheckers and engineers) I find
the force levels to be roughly the same.  Will the IBC code mean a
higher standard?

The funny thing about the USGS maps is that most or all structural
Engineers are not trained to use them.  The PGA is based on bedrock
not actual soil conditions.  If you were to look at a zip code in
Northridge you might get a PGA .4 or .5g.  We know from all the 
instermentation in the quake zone that the PGA's were much higher. 
The type of soil seems to play a large role in this.

Structural Engineers are not trained in shear wave mechanics.  This
new code is a result of the inaccuracy of the zone system we use
today.  However we are left with the same inacuracies, because the
specific information is not usable for the Structural Engineer.

All these problems are due to the Calculator.  The Engineers writing
these codes must have only experienced the calculate in his/her
academic and professional training. 

Is anyone else thinking this will be a disaster? or am I just getting
old and am afraid of change.

Ken Tarlow 

 
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