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RE: Seismic Zones in Texas

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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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