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IBC Load combinations

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In the IBC the Basic Load Combinations (Section 1605.3.1) come from ASCE
7-98 Minimum Design Loads for Buildings and Other Structures, Section
2.4.1. The Alternate Basic Load Combinations come from UBC 97 Section
1612.3.2 (the 0.9D - E/1.4 combo was added in the Errata), and are more
traditional. It is probably more a matter of compromise rather than
"science", to include both sets of Load Combinations. They came from
different sources and are just different. Eventually it seems likely that
one set or the other will be removed from the IBC, but until then you are
free to use whichever set of combinations you want.
Allen Adams, S.E.
RAM International

From: "Jake Watson" <jwatson(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: IBC Load combinations

For those of you using the IBC, I am hoping you can clarify a load
combination.  Equations 16-12 (0.60D+0.7E) and 16-18 (0.90D+E/1.4) give
dramatically different results.  This can't be intented.  Any guidance would
be appreciated.

Jake Watson
Salt Lake City, UT

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