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RE: Simplified Seismic Design Trends

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Good post Jim.

I'll only add that perhaps we should consider a "code change" if the
resultant knowledge shows the force to be, oh say, 15% different either way.
Otherwise it ain't broke.

Barry H. Welliver
barrywelliver2(--nospam--at)earthlink.net
 

-----Original Message-----
From: Jim Persing [mailto:jpersing(--nospam--at)fhoarch.com] 
Sent: Monday, May 12, 2003 6:35 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Simplified Seismic Design Trends

Scott,

I think I should have been more clear about what I consider "simplified"
methods.  What we have in the codes now that is labeled simplified is not
what I had in mind.  What we had as standard code requirements about a dozen
years ago is what I would call a simplified design.  I do not use the
current simplified methods in the code.

I have waded through pages of ASCE wind data, charts, factors, etc. and have
come up with loads that are less than a pound per square foot different than
using the tables in the UBC.  I think it is obvious from some recent
postings that we don't even agree on when a building is enclosed or not.  If
we don't know that why do we think that we can design buildings for wind
loads to a tenth of a psf and say that it is either right or wrong?  I think
one of your points is that being less "conservative" means being more
accurate.  I don't necessarily agree with that.  And I think that it has
been seen over the years that that is not necessarily so.  I believe that we
can save owners more money by spending more time designing details that are
more cost effective to build than by spending our time figuring out time
consuming ways to shave a few pounds off the design loads.

We have become "load" engineers, not building design engineers.  And the sad
thing is that the old codes that had basic values are generally very close.
I agree that seismic design has evolved, as it should have, as we learn more
with each earthquake but just because we have computers doesn't mean that it
should be a requirement to use them to design the simple items.  Another
recent posting regarded the definition of grade to determine seismic forces
for equipment.  Why have the codes become so convoluted so that something
that should be so simple cannot be understood by all of us?  Why is it when
our clients want to know the effects on a wood stud wall of increasing the
building height a little bit we can't give them an answer in 3 minutes but,
instead, have to go to wind and seismic load spreadsheets, interaction
equation spreadsheets, factor tables, reference codes -- who can design a
wood stud without a computer?

Well -- this has been too long.  I apologize -- except to Dennis :-)

Jim Persing, PE

> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Monday, May 12, 2003 4:31 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Simplified Seismic Design Trends
>
>
> I would argue a little caution.  In general, "simplified" design
> procedures tend to mean that more generalized engineering
> assumptions need
> to be made which tends tends to result in more conservative
> designs (good
> from an engineering point of view).  While this is
> potentially good from
> an engineering point of view from both cost/time and
> potentially safety
> (assuming some of those "generalized engineering assumptions" don't
> include anything that would result in unsafe assumptions), it
> typically
> means that construction costs will be higher as typically more
> "conservative" designs tend to result in things like more material and
> other construction related costs.  And like it or not,
> constructions costs
> tend to be MUCH more significant than design costs...from the point of
> view of the client who is paying both costs.
>
> Thus, the question becomes one of can you justify the cost to
> your client
> to build the project WHILE also justifying the your cost to
> produce the
> design.  You might save TONS of time with a more simplified
> design but end
> up producing designs that cost significantly more to construct.  Thus,
> while you might be able to lower cost of design services to the client
> (or just increase your profit without lower the client's
> cost), clients
> may ultimately pass you by to go with someone who charges
> them a little
> more (or the same amount) to get a design that costs
> significantly less to
> build.
>
> The point is that simplified design, while nice and desirable for many
> reasons (less engineering time involved, less likely for
> misinterpretations/mistakes to be made, etc), also has some downsides
> that you need to be aware of.
>
> HTH,
>
> Scott
> Ypsilanti, MI
>
>
> On Mon, 12 May 2003, Jim Persing wrote:
>
> > Barry, I totally agree with you.  And ditto for wind.  The
> more simplified
> > provisions should be the code and what we have now should
> be in an appendix
> > for use by those who can justify the expense for their
> larger projects.
> >
> > We should be spending more time designing structures and less time
> > calculating loads.
> >
> > Jim Persing, PE
> >   -----Original Message-----
> >   From: Barry H. Welliver [mailto:barrywelliver2(--nospam--at)earthlink.net]
> >   Sent: Saturday, May 10, 2003 6:28 AM
> >   To: Seaint Listserv
> >   Subject: Simplified Seismic Design Trends
> >
> >
> >   I'm looking for some help in identifying any movements or
> trends to
> > support a simplification in seismic design. I recognize
> that we have efforts
> > to that effect in the building code (and they are greatly
> appreciated by
> > small budgeted projects) and am interested in both participating and
> > encouraging these endeavors.
> >
> >
> >
> >   While one mans simple is another's complex, it does seem
> to me that the
> > trend in code making is a both/and mentality. It's
> wonderful that we have
> > both researchers and practitioners hammering out rules, but
> I fear we've
> > lost the ability to distill what we know and focus on
> getting the most for
> > our design dollars. Perhaps I've developed this sinking
> feeling based on
> > comparisons between my practice 20+ years ago and today.
> I've been (and
> > continue to be) an ardent supporter of EQ code evolution
> and think for the
> > most part the directions have been justified. I get
> frustrated however by
> > the quickly adopted provisions which get universally
> applied to general
> > building design and then get massaged with additional
> formulation and
> > exceptions. (EOR = End of Rant)
> >
> >
> >
> >   Of late I've been coming back to the thought... if
> Einstein can boil
> > science down to E=mc2, then surely mere structural
> engineers can aim toward
> > M=wl2/8.
> >
> >
> >
> >   Your comments and suggestions would be appreciated.
> >
> >
> >
> >   Barry H. Welliver
> >
> >
> >
> >
>
>
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