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RE: Any Young Engineers Out There?

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Jeremy,

You are 100% correct in your statement as things stand right now (i.e.
1989 ASD spec and 1999 LRFD spec).  For the specs that is "legal" force
right now, there are some rather large differences.  That is because ASD
has not been updated in more than a decade.  Think of ASD as an old Dodge
Charger from the 1970s or so...using "old" technology such as carbirators
and drum brakes, etc.  In the mean time, LRFD is like a Ford Mustang.  It
has consitantly gotten the latest in technology applied to it and thus
recent models have had things like disc brakes and fuel injection, etc.

That is until now...

Just like Dodge "revived" the Charger and updated it with new technology,
AISC has revived ASD with updated information and knowledge.  The point is
that the 2005 combined AISC spec (both ASD and LRFD) is done in a form so
that they are virtually interchangable.  This is where to some degree my
car analogy falls apart as a Dodge Charger and as Ford Mustang are not
really interchangable.  But for ASD and LRFD under the 2005 spec (as I
understand it at least...haven't looked too closely at it yet), the point
is that they are virtually the same thing except that on the demand side
(i.e. loads) you have load factors (or more specifically load factors
that are generally other than 1.0) for LRFD and there is a "modification"
factor on the capacity side that "converts" between LRFD and ASD.

The point is that you will see those additional "checks" now for ASD that
has traditionally only been seen in the LRFD design.

As to thickness of the manual, that has relatively little to do with
additional checks/differences between the ASD spec and the LRFD spec(s).
FWIW, the 1989 ASD spec in my 9th edition manual is roughly 110 pages.
The 1986 LRFD spec in my 1st edition LRFD (could be considered 10th
edition overall) manual is roughly 135 pages.  The 1999 LRFD spec in my
3rd edition LRFD manual (could be considered 12th edition overall) is
rougly 190 pages (counting similar content in all...such as table of
contents, glossary/nomenclature, etc).  So, even going from the roughly
110 pages of the 9th edition spec to the roughly 190 pages of the 12th
edition spec, that is maybe a 1/4" or less of "thickness" difference
(assuming that they use the same thickness paper....which is NOT the
case...the 11th edition [2nd edition LRFD - aka "Silver Book"] used a
heavier bond paper than pervious manuals...the 12th edition went back to a
lighter papar that might be lighter than the 9th ASD or 1st LRFD
editions).  So, the point is that the differences in the code have
relatively little impact on the overall thickness of the manuals.  The
thickness of the manual is more a function of the what the over all
content is in them and the newer manuals have quite a bit more "stuff" in
them (FWIW, the 3rd edition LRFD/12th overal manual included the 2000 LRFD
spec for steel HSS sections, which had previously been in a seperate
manual...and I am sure there is other "stuff" in it that was note in the
previous manuals).

But, there still is a significant difference between the "thickness" of
the 1989 ASD spec (even if you add the roughly 30 or so pages of
Supplement No. 1 from 2001) and the 1999 LRFD spec.  And that difference
in thickness is due to all the "updated" technology that has been put into
LRFD that has not been put into ASD...until now (i.e. the 2005 combined
spec).

Regards,

Scott
Adrian, MI


On Tue, 24 Jan 2006, Jeremy White wrote:

> LRFD is more than just applying load factors, though.  I believe it includes
> addition checks (ductility), additional equations, etc. (that's why the book
> is so much thicker)
>
> - Jeremy White
>
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Tuesday, January 24, 2006 2:53 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Any Young Engineers Out There?
>
> Ya, but they will be taking it off that shelf in the not so distant
> future.  This difference this time is that future model building codes
> (i.e. starting with 2006 IBC, I believe) will not longer reference the
> 1989 AISC ASD spec as "permitted"/"legal" design.  All current codes
> that I aware of that are in effect (i.e. legally adopted by local
> jurisdications) still reference the 1989 AISC ASD spec (sometimes they
> also reference the Supplement 1 to the ASD spec that was officially
> released in December 2001 although it did not really modify all that much)
> along with a version of the LRFD spec.  Thus, you can right now "legally"
> design using the 1989 ASD spec.  This is largely due to AISC not updating
> the ASD spec and not being able (or wanting to...maybe) "kill" it from the
> model building codes.
>
> That is until now...
>
> Now they have an updated spec that updates both ASD and LRFD and that is
> what will be referenced in future model (i.e. IBC) building codes.  And
> when that happens, we will all be "forced" (although I have no doubt that
> some will continue to use "old" ASD) to use the new spec.  Now, it will
> not happen right away cause even once a model building code adopts the new
> spec (which I believe that the 2006 IBC has done), it takes time for many
> local jurisdictions/states to adopt that model building code.
>
> So, enjoy your reprieve and relish your last, limited time with 1989 ASD
> (and thus "Green Book") spec.  You will likely be delving into the 2005
> ASD/LRFD spec relatively soon, be that either in the form of a free PDF
> from AISC or in your brand spaking new 13th edition AISC manual (assuming
> that they ever ship them...sorry Charlie...could not help myself <grin>).
>
> Now, the interesting question I think is: how many people will make the
> switch to LRFD when they are force to learn the new 2005 ASD/LRFD spec?
> After all, the only really difference between "using" ASD and LRFD will be
> whether or not you want to put load factors on your load calculations on
> the "demand side".  The "capacity" side of the equation will be virtually
> identical.
>
> Regards,
>
> Scott
> Adrian, MI
>
>
> On Tue, 24 Jan 2006, Polhemus, Bill wrote:
>
> > Here's the question that I want to see answered...and mark my words, it
> > will probably be asked before a year has gone by:
> >
> > "How many engineers here--regardless of age--took one look at the new
> > Thirteenth Edition AISC Manual of Steel Construction, put it up on their
> > bookshelves and went right back to the Ninth Edition?"
> >
> > (N.B. It's gonna take forty years traveling in the wilderness, like
> > Moses and the children of Israel, before the last vestiges of the ASD
> > Idolatry are snuffed out).
> >
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