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Re: ASCE 7-05

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On Oct 23, 2007, at 10:14 AM, Charles R. Ashley Jr. wrote:

I am trying to figure out what tragic wind event triggered these ridiculous revisions! I am sure there must have been a bus load of innocent children
involved, I just can't seem to find it.
Figure out how the original LRFD-only rules were developed and why Appendices 13 and 24 of Section VIII Div 1 of the ASME Code are linguistic nightmares and you'll probably find well-meaning members who feel that greater 'accuracy' trumps ease of interpretation and definitive language.

By way of a disclaimer, I confess I'm talking through my hat to a degree, because I haven't done an actual wind load structural problem in years. However I do have a pretty solid background in internal and external fluid mechanics, and I know for a fact that figuring aerodynamic loading on short prismatic shapes hasn't been rocket science for a long time. Especially for low speed flows at ambient conditions. It isn't terribly precise, but then neither is a lot of engineering analysis, despite what you hear from FEA developers. And it doesn't require CFD either, although test data and an undergraduate fluid mechanics course help.

I'd be real curious if anyone on the list has actually gone through the reasoning behind the new wind loading rules who would comment what the changes represent and why the changes were necessary. I did my own background checks on the ASME Code appendices I mentioned, and tracked though the Code arithmetic and found I could provide the same results in a far simpler form. It took me some time, but it's paid off handsomely. I also did some background checking on the AISC bolting design calculation. Turns out that those rules can likewise be greatly simplified and in fact generalized while still following the original principles. So can the rules for outstanding flanges.

The points made about balanced committee membership are taken, BTW, but my experience is that even one 'expert' on a topic can pretty much drive committee discussion in any direction he/she sees fit. If in addition they feel that order effects are nice to account for, second order effects are included even if the results only vanish into the white noise.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/



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