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RE: Effective Peak Acceleration to Velocity Related Acceleration

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The building codes in the US are in the process of changing on many
fronts in this regard.  There are no zone designations in the ASCE 7-95
nor in the NEHRP Recommended Provisions and this will hold true for the
IBC due out in April 2000.  New maps are nearing the end of the
development stage for the NEHRP.  We are changing the probability basis
of the maps from 10% of exceedence in 50 years to 2% in 50 years.  The
new maps will indicate spectral accelerations.

Note in the Blue Book Commentary it states that the PGA is not a
consistent scaling factor for the seismic spectral acceleration values.

I would recommend that you read:
1.  SEAOC Recommended Lateral Force and Requirements (Blue Book)
commentary C104.2
2   NEHRP Recommended Provisions .... and Commentary (1994 is out now
1997 due out probably in Jan 1998)
3.  ATC-3-06

Use the 1997 UBC Appendix as a guide.  There are many sites throughout
the Middle East that have been assigned a UBC zone.  You should be able
to extrapolate from the assigned values shown.

Regards,
Harold Sprague
Black & Veatch

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From: kassamem(--nospam--at)aramco.com.sa
To: seaoc(--nospam--at)seaoc.org
Subject: Effective Peak Acceleration to Velocity Related Acceleration
Date: Monday, September 22, 1997 6:52AM

I am looking for any formulas or rule of thumb to convert "Peak Ground "
accelerations to "Effective Peak Velocity Related Accelerations ". I
have ASCE 7-93 which provides definition of these accelerations, i.e Aa
and Av, the difference being the periods.

Actually I have a "Seismic Response Assessment Report" from a consultant
done long time ago for my project, located in Middle East. This
consultant is no longer providing any services to the project.

The report states  "For 1000 Average Return Period (criteria for this
project), the computed Mean Peak Ground Acceleration is 0.183g". The
report also provides Mean Ground Accelerations for other return periods
 - 500 years is 0.127g, 5000 years is 0.354g and 10,000 years is 0.452g.
It does not provide any information on Velocity Related Acceleration.

How does one determine the Equivalent UBC Zone with the above
information ? Is it UBC Zone 2B or Zone 3 ?  (UBC Return Period is 475
years versus 1000 years on my project). The AISC Seismic provisions and
ASCE categories is based on "Effective Peak Velocity Related
Accelerations". UBC Zoning is also based on this.

Is it safe for me to assume that this site (not located in US) is
equivalent to UBC Zone 2B ? According to "Project Guidelines" prepared
prior to my arrival on the project, the site was classified as UBC Zone
3. From my drawing reviews, detailing of concrete structures, ductility
requirements, for Zone 3 has not occurred. It is a Lump Sum Turn Key
Contract and the Contracor is trying to convince the owner that
detailing for UBC Zone 2B is adequate and that there was an error in the
"Project Guidelines". The majority of the structures that get effected
are concrete and some steel connections are doubtful.

Any comments or words of wisdom

Eqbal M Kassam, P.E