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RE: We're Not Getting Older, We're Getting DUMBER

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Eric,
It wasn't a paper, just a conversation about the pro's
and con's of ASD vs LSD, in which I favoured ASD as I
design a lot of cranes and runways.  The towers were
quoted as an example on the side of LSD.  See e-mail by
Bob Shaw.
Gary

On 26 Jan 2006 at 8:53, Eric Ober wrote:

> I don't think I would take the position of saying one is better than the
> other.  However, there are situations where ASD is inappropriate (second
> order elastic frame analysis, seismic design, etc.) without what I
> consider headaches.  Once you modify the method for certain
> circumstances, the ASD design process starts to look a lot like LRFD.  I
> admit that I use ASD all of the time since that is what was expected of
> me from day one on the job.  Personally, I didn't find the leap
> 'backwards' to ASD that painful since I had a good understanding of
> 'limit states' to be checked in design and found that I was doing the
> same thing in ASD, just with a little twist.
> 
> As to the other post you made regarding the tower failure, I'd really
> like to see the paper where the statement is made that the cause of
> failure is LRFD versus ASD.  Does it exist in print?  In my experience,
> structural failures generally fall under a lack of understanding of the
> demands on a structure, poorly implemented construction, or poor design
> and detailing.  None of these have anything to do with the actual design
> methodology, if properly applied.
> 
> Eric
> 
> Eric R. Ober, PE, SE
> Associate
> Holbert Apple Associates
> Olney, Maryland
>  
> 
> -----Original Message-----
> From: Gary Hodgson & Associates [mailto:ghodgson(--nospam--at)bellnet.ca] 
> Sent: Thursday, January 26, 2006 8:37 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: We're Not Getting Older, We're Getting DUMBER 
> 
> Despite my earlier e-mail, I remain unconvinced that LSD
> is better than ASD.  I think that if the professors and
> others had put the effort into ASD that they invested in
> LSD, it would have been just as effective. I also do
> cranes and runways, etc and I much prefer ASD.  The
> problem up here is that the people on the code
> committees have bought the party line and made LSD
> mandatory.
> Gary
> 
> On 25 Jan 2006 at 23:11, Christopher Wright wrote:
> 
> > 
> > On Jan 25, 2006, at 2:11 PM, Eric Ober wrote:
> > 
> > > I'm sure there are other reasons but I can't think of them at the
> > > moment.
> > I confess, I'm not convinced. Calculation of live loading is 
> > independent of the methodology used to determine response to the
> loads. 
> > Anything modification you can make for load assessment (demand,
> right?) 
> > you can do for both limit analysis and elastic analysis. The P-delta 
> > effect is another matter. I presume you're saying that you do P-delta 
> > analysis only to determine changes in ultimate loading and that 
> > structural deformations aren't considered to have an effect under 
> > service loading.
> > 
> > As I said, professionally it's a matter of only cultural interest. 
> > Virtually all of my AISC related stuff has to do with machinery like 
> > cranes and crane supports. where service loading governs. I' done have
> 
> > any quarrel with the need for limit analysis for some structures in 
> > some situations--seismic response being the best example I can think 
> > of--but I've never (and still haven't) seen a persuasive argument for 
> > the LRFD approach as a replacement for working stress methods. If
> there 
> > were holes in the ASD approach they need to be fixed, and if the 
> > approach itself is clearly invalid then replace the whole thing--no 
> > question about that. But that isn't what happened when LRFD was 
> > mandated, and I think recent history of the AISC rules teaches us a
> lot 
> > about code promulgation and the role of the profession as a whole.
> > 
> > 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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