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Re: UBC 97 seismic section and NEHRP

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dhorning(--nospam--at)CH2M.com wrote:

>You're quite right, the 1997 seismic section is quite different, and is
>based on NEHRP.  Wait 'til you see IBC 2000.  One difference which may
>not be readily apparent is that 1997 gives loads at strength rather than
>service levels (that's why it's "R" and not "Rw").

Your right - its not readily apparent.  I missed it when recently comparing
the '94 and '97 seismic requirements for a project.  I wondered why seismic
seemed to increase so much (although '97 still governs over '94 for my
application).

Per the '97 UBC, 1629.1 states that "Where Allowable Stress Design is used,
the load combinations of Section 1612.3 shall apply."  Section 1612.3 has
two
alternate procedures for allowable stress design, but in both "E" is divided
by a factor of 1.4.  Thus the seismic loads given in Chapter 16 are 40%
higher
than required for allowable stress design.