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RE: Who's using ASD or LRFD?

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>You're both right and wrong on this, Chris.
I figured as much (and no offense taken. I daresay we'd've had a lot less 
bickering over relative merits with a little more understanding of 
origins and differences). Just the same, how much difference can there 
be? No question that incorporating plastic bending response is a jump, 
but column response already includes the effects of yielding. Moreover 
tensile and shearing limit loads (excluding stability considerations) are 
pretty much defined by first yield. Not too much left beyond expanding 
the details, unless you start getting into real non-linear response like 
actual collapse loading. Specifically it doesn't sound like there's any 
big change in real safety margins, such as might require less explosive 
to be used in demolition.

>The 1999 LRFD Specification will have, among other things,
>explicit treatment of srength and stiffness requirements for stability
>bracing for beams, columns, frames, etc., a section on evaluation and load
>testing of existing structures, and a major improvement to fatigue
>provisions.
Is this going beyond the current practice of specifying limiting 
width/thickness ratios to stave off elastic buckling or are you getting 
into post-buckling strength or improved correlations of buckling response 
of thin elements? Maybe a little more detail on bracing stiffness 
requirements? 

Tell me a little more about the fatigue improvements. I presume this 
isn't going to incorporate anything too revolutionary like crack growth 
mechanisms and fracture mechanics, so it'll be an upgrade to the old way 
of specifying cyclic response based on construction details. Harking back 
to the SMRF problems with Northridge my guts tell me that a little more 
attention to basic fracture prevention in the area of weld quality and 
plastic response might also be on the way. 

This isn't to argue about which approach is better, because it's still 
not obvious to me that they're all that much different, at least in the 
results produced. The sorts of changes (especially fatigue and bracing 
provisions) you mentioned look like general improvements which aren't 
peculiar to LRFD and would be advisable for ASD design like the machinery 
and the associated structures I do. Which will likely always be based on 
elastic response. 

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