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FW: CMU Wall Design for Out-of-Plane Loads

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Kenny,

I've also struggled with this section of the code.  The conclusions that
I've reached are as follows:
1.  fa<.04fm'  OK to use strength design and slender wall analysis.
2.  fa>.04fm' and h/t<30  OK to use strength design and slender wall
analysis with deflection limitation.
3.  fa>.04fm' and h/t>30  Need to use ASD design and the analysis of forces
are to include "slenderness effects" (P-delta, variable moment of inertia
and load duration effects).

The 2000 IBC has raised the stress ratio limit to .05fm'.  The original
limit seemed arbitrary and indeed it is.  The limit was imposed because the
testing that validated the design procedure was modeled for light roof
loads.  Perhaps when new testing is performed, the design provisions can be
extended.

I hope this was helpful.

Curt La Count
Jacobs Engineering
Portland, OR

-----Original Message-----
From: Kenny Yip [mailto:kenny(--nospam--at)jeiwa.com]
Sent: Tuesday, March 04, 2003 4:26 PM
To: seaint(--nospam--at)seaint.org
Subject: CMU Wall Design for Out-of-Plane Loads


I posted the following question last Wednesday or Thursday, but so far no
one has ever responded it.  I think my question must be a challenging one.
I post it here one more time to see if I can be of any luck.

Dear Fellow Engineers:

Under section 2108.2.4.4 of 97UBC, there are seven equations (from 8-19 to
8-25) associated with walls having axial load of 0.04fm' or less.  I am
wondering if this set of formulas can be equally applied to the next
section (i.e. 2108.2.4.5) for walls with axial load between 0.04fm' and
0.2fm' and the slenderness ratio h/t does not exceed 30.  No equations,
other than (8-26), are given in this section.

My axial stress is 135 psi under service load (my fm' = 2500 psi), and h/t =
18.5.  I have talked to some engineers.  Some said that I can use those
equations and some told me that I can not use them.  What do you think?

I appreciate your informative advice.


Kenny Yip, P.E.
Jones Engineers
Bellingham, WA


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