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RE: Story Drift: 1994 UBC vs. 1997 UBC

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See revised calculations at:

Still, Dm > 0.025 * h (slightly, but this is a fairly low stressed shear


Bill Allen, S.E.
Laguna Niguel, CA

> -----Original Message-----
> From: Seaintonln(--nospam--at) [mailto:Seaintonln(--nospam--at)]
> Sent: Thursday, August 12, 1999 8:36 PM
> To: seaint(--nospam--at)
> Subject: Re: Story Drift: 1994 UBC vs. 1997 UBC
> Bill,
> I reviewed your calc's on your website and have the following
> comments:
> 1. When I created this model in Excel I found that the units
> of the terms do
> not balance. The first term, for example, 8fvh^3/EAb is not
> intended to be
> converted to comparable units as Mathcad would do
> automatically. This is one
> of those examples that I wrote about in the Mathcad / Excel Thread.
> I received a number of responses to my previous threads as to
> how the units
> balanced and one or two list members sent me a complete
> breakdown as to how
> to the Algebra from 5wl^4/384EI converted to this formula
> above. The problem
> was that Mathcad converted the units which inflated the
> results - the results
> should be in the following units:
> fv = psi
> h = ft
> E = psi
> A = in^2
> b = ft
> The inclination is to convert feet to inches and, in this
> case, would inflate
> the answer by a factor of 12.
> The next issues is the Load per nail that you use. This
> should be the actual
> nail load based on the actual shear in the panel rather than
> the allowable
> capacity of the plywood - therefore, your load per nail
> should be somewhat
> less. This is moot since you might be assuming that your
> demand is equal to
> your capacity in this example.
> I might be wrong on this one, but the t for a non-structural
> grade 3/8" thk
> panel should be 0.298" rather than 0.373. I did not take the
> time to check my
> spreadsheet, but this is what I get off the lookup tables.
> Again, I might be
> the one who is wrong here.
> The nail elongation term is another one where the units are
> not suppose to
> balance. the results are to be in inch-feet but assumed
> inches. Again, this
> is an emperical formula and nobody to date has been able to
> tell me why
> constants of 1/feet was not used to clarify this. This might
> yield an error
> of 12 times in Mathcad.
> If you are interested in the translation from the normal simple span
> deflection formula to the first term of this deflection formula (the
> deflection in the chords) I can provide it to you.
> Let me know if I have made this clear - I think others are
> making the same
> mistakes.
> Dennis