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

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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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