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# rho or omega?

• To: seaint(--nospam--at)seaint.org
• Subject: rho or omega?
• From: Darrell Hambley <dth(--nospam--at)red.primextech.com>
• Date: Mon, 25 Oct 1999 10:46:25 -0700

```I submitted a set of calculations for a residential home and they said I
need to show what I used for rho (equation 30-1 in '97 UBC). I used
equation 30-2 with omega instead because it seemed a worse case (2.8 for
omega instead of a default value of 1.5 for rho).
Now I'm confused as I read the UBC further. If anyone can answer a few of
these questions I'd be really grateful!
1. When do you use 30-2 instead of 30-1? "E" (in equ 30-1) is for elements
according to 1630 but, according to 1630.3.1 omega (in equ 30-2) is for
"specific elements" also. They're both for elements. What's the difference?
2. Now please look at 1632, equ 32-1(elements). Fp=4*Ca*I*W which is 1.44W
in zone 3. That's a big number! Paragraph 1630.1.1 defines Eh as equal to V
or Fp. I don't like that word "or". Which one do I use? Is it implied that
one value is for the structure as a whole and the other is for a specific
element?
3. The 1.4 factor...  E/1.4 from 1612.3.1 will lower the value of E of equ
30-1, (E=pEh) but now equation 30-2 is still larger so question 1 above
still confuses me... When do I use equ 30-2?