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RE: Value for EI in tall wall

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I often will either use an upper or lower bound to speed up calculations. In this particular stiffness calculation you are using the EI to determine P critical. The 0.1 will give you the lowest EI and the lowest P critical and thus the most conservative answer. The 0.4 limit is just so the equations don't get you into an area of P critical unsubstantiated by empircal testing.

Harold Sprague

From: "Joe Grill" <jgrill(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: RE: Value for EI in tall wall
Date: Thu, 5 Aug 2004 11:49:51 -0700

Thanks, I have been able to put that together and you have confirmed that
for me. I guess my next question would be is it O.K. to use the upper bound
value or when is it and when is it not a good idea.

I have once again inherited a project that I have to go through.  It is a
custom home that is to be manufactured with "insulating concrete foam walls"
(ICF walls).  I have a design manual published by PCA with some good
information and design examples. They list the Equations that I mentioned in
my earlier post, but (without explanation) use the upper bound value, where
the example in the Notes on 318-99 uses the lower bound value again without
explanation.  It makes quite a difference in the design of these walls.  I
can't seem to make up my mind as to which and when.

Joe Grill

-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)]
Sent: Thursday, August 05, 2004 10:21 AM
To: seaint(--nospam--at)
Subject: RE: Value for EI in tall wall


0.1 is the lower bound of EI and 0.4 is the upper bound of EI

Harold Sprague

>From: "Joe Grill" <jgrill(--nospam--at)>
>Reply-To: <seaint(--nospam--at)>
>To: <seaint(--nospam--at)>
>Subject: Value for EI in tall wall
>Date: Wed, 4 Aug 2004 16:25:30 -0700
>I have a tall concrete wall that will fall in to the range of design by the
>magnified moment method.  On page 23-2 of the Notes on 318-99 there are
>equations for determining EI. I can't decide what's what with that string >of values. The following example shows e/h=1.04 therefore, the portion of
>the equation with the e/h becomes negative and doesn't satisfy the
>condition.  Because of that they use the equation with the .1 factor to
>determine EI, but when does the equation with the .4 factor come in.  I'm
>Joe Grill

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