# RE: ACI318-99 load combination question

• To: seaint(--nospam--at)seaint.org
• Subject: RE: ACI318-99 load combination question
• From: "Lutz,James" <JLUTZ(--nospam--at)earthtech.com>
• Date: Wed, 23 Aug 2000 17:12:11 -0700
```Equation 9-6 governs. U=1.05(D+T) is what you would get from equation 9-5 if
there were no live load, which is an unconservative load factor. Equation
9-6 creates a lower bound of a 1.4 load factor for "T" effects.

I think the fluid load needs to be considered for all load combination
equations, not just the few that are mentioned in the commentary. For
equations 9-2, 9.2.3, and 9-5, however, I think the 1.4F goes inside the
parentheses to be multiplied by the .75 reduction factor when wind or
seismic effects on the fluid, which are part of the E loads.

-----Original Message-----
From: Zachary Goswick [mailto:ZachG(--nospam--at)angusyoung.com]
Sent: Wednesday, August 23, 2000 2:57 PM
To: 'seaint(--nospam--at)seaint.org'

Does anybody know whether equation 9-6 "U=1.4(D+T)" or the commentary on the
same section saying equation 9-6 is "U=1.05(D+T)" is correct?  It appears to
me that they are saying two different things, or am I not seeing this
correctly?

Also, I am looking at section 9.2.5 and reading that 1.4F should be added to
ALL combinations that have live load in them.  The commentary says use just
two equations "U = 1.4D + 1.7L + 1.4F" and "U = 0.9D + 1.4F".  This does not
seem to me to be ALL of the combinations with live load in them.  Wouldn't
this be all of the combinations given in paragraphs 9.2.1 through 9.2.7. as
follows?

U = 1.4D + 1.7L + 1.4F                          - from equation 9-1
U = 0.75(1.4D + 1.7L + 1.7W) + 1.4F             - from equation 9-2
U = 0.75(1.4D + 1.7L + 1.7(1.1E)) + 1.4F        - from paragraph 9.2.3
U = 1.4D + 1.7L + 1.7H + 1.4F                   - from equation 9-4
U = 0.75(1.4D + 1.7T + 1.7L) + 1.4F             - from equation 9-5

It appears as if the second equation given by the commentary would not even
be included in what the actual code says.  Am I reading this incorrectly?
Can anybody shed some light on these issues?

I can figure out what would be the worst cases, but I am just trying to

Zachary Goswick
zachg(--nospam--at)angusyoung.com

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