Paul Crocker -
There is more in-depth discussion about the development of the 2/3 factor in
the Commentary to Appendix A in the NEHRP Provisions Commentary starting on
Page 287 in FEMA 303.
Fred Turner, Staff Structural Engineer, California Seismic Safety
Commission, 1755 Creekside Oaks Drive Suite 100, Sacramento, CA 95833
916-263-0582 Work Phone, 916-263-0594 Fax fturner(--nospam--at)quiknet.com
From: Sprague, Harold O. <SpragueHO(--nospam--at)bv.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Friday, May 05, 2000 6:48 AM
Subject: RE: NEHRP earthquake loading
>Look at page 37 of the NEHRP Commentary. The third paragraph of Section
>4.1.1 discusses the lower bound margin of collapse of 1.5. The 2/3 factor
>is the inverse of 1.5.
>> -----Original Message-----
>> From: Paul Crocker [SMTP:paulc(--nospam--at)ckcps.com]
>> Sent: Thursday, May 04, 2000 12:32 PM
>> To: 'seaint(--nospam--at)seaint.org'
>> Subject: NEHRP earthquake loading
>> In the '97 NEHRP, seismic design is based on 2/3 of the 2,500 return
>> earthquake (2,500 year return period = 2% probability of exceedance in 50
>> years). Does anyone know what rationale is used to justify the 2/3? I
>> read through the commentary, and can't seem to find anything about the
>> I assume either it was an arbitrary decision about the design level to
>> toward, or there is something specific about it that I am missing.
>> Paul Crocker