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Re: Rigid vs Flexible residential diaphragm discussion

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>The construction of pressure vessles and pipes is, in 
>my opinion, much more controled than the work done by contractors on 
>buildings in the field. 
Point taken. In fact the pressure vessel codes in particular address 
fabrication as much as design. Moreover the inspection issues are also 
addressed. The fact that there seems to be relatively little control of 
building, especially residential construction scares hell out of me. Here 
in Minnesota we're seeing structural problems with new homes and not just 
cheap construction but new make-believe manor homes selling for 200-500 
grand. It's not ultimate failure, but details like joints that separate 
over time and leak or ventilation problems leading to trapped moisture or 
backdrafting. In fact a SE colleague of mine told me flat out that he 
simply wouldn't buy a house that wasn't at least 15 years old. 

But inspection is another issue. I still get the message that Code 
provisions for basic design are flawed or unacceptable to the SE's whose 
practice really depends on them. (Or maybe the other way 'round) It 
doesn't seem that the notion of a diaphragm, which isn't anything new, 
should be exciting such comment. I really don't understand why this 
wasn't worked out in the Committee structure, based on test results or 
the principles of basic mechanics, then submitted for peer review. Steel 
construction, certainly the ASD provisions, are just that. (And I note 
that the ASD column methodology is sound enough to carry into LRFD with 
only a 1.4 bugger factor applied to jibe with the LRFD load factor) I 
don't do wood frame design, but it's been around for centuries and 
follows the same laws of mechanics that we all know and love. It's not as 
linear or elastic or even isotropic like steel, but engineers have made 
ships and airplanes and bridges out of the stuff. Why the problems 
defining diaphragm action in residential construction? It just seems like 
someone isn't minding the store.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)