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Earthquake force considered in load combination (IBC2000)

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E is as defined in Section 1617.1, specifically Equation 16-29. QE is the
design seismic force (based on the full dead load mass, plus a portion of
Live Load and Snow Load in some cases - see Section 1617.4.1 for the
definition of W). Furthermore, you have to include the -0.2SDSD term, which
further reduces the Dead Load. So for Formula 16-12 you have: 0.6D -
0.7(0.2)(SDS)(D) + 0.7(rho)QE. There has been a lot of discussion (and
complaint) about the conservative nature of this combination, but that is
what the Code says. Note that IBC 2003 is the same, so the code-makers have
not been persuaded to change it.
Allen Adams, S.E.
Chief Structural Engineer
RAM International


From: "Ali Karimzadegan" <karimzadegan(--nospam--at)pidec.com>
To: "SEAINT" <seaint(--nospam--at)seaint.org>
Subject: Earthquake force considered in load combination (IBC2000)

	In the IBC 1605.3.1 equation 16-11 we have load combination of
0.6D+0.7E in which the dead load factor reduced significantly w.r.t. UBC97.
Now the question is that whether E (in this load combination) shall be
calculated based on the 0.6 dead weight of structure or E should be based on
the full weight and if it is based on full weight then it seems that this
load combination is over conservative and I can not understand the logic
behind it. Please clarify.

Regards,
A. Karimzadegan
M.S. C.E.
PIDEC
Shiraz - Iran
T : +98-711-2270120
F : +98-711-2299412
e-mail : karimzadegan(--nospam--at)pidec.com <mailto:karimzadegan(--nospam--at)pidec.com>


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