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Re: Story Drift: 1994 UBC vs. 1997 UBC
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- Subject: Re: Story Drift: 1994 UBC vs. 1997 UBC
- From: Seaintonln(--nospam--at)aol.com
- Date: Thu, 12 Aug 1999 23:35:53 EDT
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
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