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Re: Diaphragm Calculations

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Dennis:

The implied units on the coefficient 0.188 are 1/ft.  This is one of 
those cases where the equation results are only valid if appropriate 
units are used.  As both a structural design engineer and a Mathcad 
user, I also run into this type of difficulty.  The source of the 
trouble is that many of our design "equations" are not derived 
mathematically but are instead simply the result of curve fitting 
applied to empirical data.  Consider for instance the ACI truism that 
the square root of something in psi units is also in psi units; 
Mathcad doesn't "understand" this.  The reality (call it unfortunate 
if you want) is that everyone who uses such a "data-fit" equation 
must confirm whether the equation is units consistent (can be used in 
Mathcad directly) or units dependent (requires creative conversion).

-Mike


***************
>  Regarding the 0.188 number in the third part of the equation:
>  The number is a constant and not related to units.
> ************************************************
> <Dennis Responds>
> Then please tell us how the units balance so that we can explain this to 
> Mathcad that automatically converts and issues an error when units do not 
> match?
> When looking at the basic terms 0.188 L en,
> L = feet
> en = in
> 
> en is taken from Table 23-2-K "en" Values (inches) for use in calculating 
> Diaphragm Deflection due to nail slip (structural I).
> 
> Once again, the units do not balance since this term yields either in^2 or 
> ft^2 and all other terms are in inches.

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201