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RE: NEHRP earthquake loading

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Paul,

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.

Regards,
Harold Sprague


> -----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
> period
> 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
> have
> read through the commentary, and can't seem to find anything about the
> 2/3.
> I assume either it was an arbitrary decision about the design level to
> work
> toward, or there is something specific about it that I am missing.  
> 
> Paul Crocker