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RE: effective length factor for sway moment frames? K for frames with partially restrained connections?

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No. There are more than two types of FEA programs for structural analysis.

K fector is governed by a PDE. Apply FEM to formulate it, and solve it.
Output is K.  No massage is necessary. No initial imperfection is required,
either. No alignment charts. That is the one I mentioned for FEA of K
factor.

WD


> ----------
> From: 	Effland, Greg[SMTP:geeffland(--nospam--at)butlermfg.com]
> Reply To: 	seaint(--nospam--at)seaint.org
> Sent: 	Monday, April 02, 2001 11:58 AM
> To: 	seaint(--nospam--at)seaint.org
> Subject: 	RE: effective length factor for sway moment frames?  K for
> frames with partially restrained connections?
> 
> In clarification of my previous answer, there are two seperate programs
> types that are called FEA.  
> 
> The first are programs like RISA, STAAD, STRUDL, etc. that I consider
> "stiffness analysis" programs.  These programs, use a matrix stiffness
> analysis of one type or another and typically determine the results based
> upon an elastic analysis.  Through the use of a P-delta analysis you could
> massage out factors similar to k factors.  I think Scott had mentioned the
> fact that most of these just pull their k-factor out of a table from AISC
> (that's my understanding also).
> 
> The second are programs like ADINA or others that typically model using
> meshes etc. Programs of this type can typically take effects such as local
> buckling, initial imperfections, etc. into account which physically
> determine the actual in-place K factors (kind of an oxymoron statement
> since
> K-factors are approximations to adjust our imperfect equations to more
> accurately model physical performance).  These programs also typically
> take
> more time to model since the imperfections and etc. must be entered.  How
> do
> you know what imperfections will exist in the field???  I never get
> advanced
> notice for fork lifts running into columns or somebody going crazy with a
> cutting torch.
> 
> Most of us use computer programs of some type to design our buildings,
> bridges, etc...  To a computer, looking up a K-factor in a table is as
> quick
> or quicker than trying to model inelastic or nonlinear behavior.  Ever had
> a
> program tell you a member had 300" of deflection (typically because
> something was entered wrong)...  even if entered correctly, could that
> member really deflect 300" without breaking, yielding, etc. and how would
> this affect the other results...
> 
> ***
> My point is that there are tools or methods that can deliver more
> *precise*
> approximations.  But more *precise* numbers are not always more
> *accurate*.
> ***
> 
> As far as Scott's original question, it is my understanding that the use
> of
> a p-delta (2nd order) analysis does not completely eliminate the need for
> the use of K-factors (definitly room for interpretation).  I would tend to
> agree with Mr. Geschwindner who responded in MSC.
> 
> 
> Greg Effland, P.E.
> 
> -----Original Message-----
> From: Waterman Drinkwater [mailto:Drinkwater(--nospam--at)EQUATION.COM]
> Sent: Friday, March 30, 2001 11:32 AM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: effective length factor for sway moment frames? K for
> frames wit h partially restrained connections?
> 
> 
> We are not discussing which field of computing can have assumption. In
> fact,
> all engineering computing has assumptions.
> 
> What kind of assumption is for FEA of K factors? It is the ordinary
> structural theory. If you can accept those ordinary theory for daily
> structural analysis, there is nothing wrong to apply the same theory to
> analyze K factors. Those analytic results are much more reliable and
> accurate than those from alignment charts.
> 
> FEA of K factors does not require any extra input data. The same set of
> data
> for "ordinary structural analysis" is sufficient for analysis of K
> factors,
> and you can get the output. The cost is much less than applying the
> alignment charts. A pentium II 300MHZ can analyze 200 members' K in 1
> minute. If applying alignment chart, how much time is necessary?
> 
> 
> 
> 
> 
> > ----------
> > From: 	Effland, Greg[SMTP:geeffland(--nospam--at)butlermfg.com]
> > Reply To: 	seaint(--nospam--at)seaint.org
> > Sent: 	Friday, March 30, 2001 10:50 AM
> > To: 	seaint(--nospam--at)seaint.org
> > Subject: 	RE: effective length factor for sway moment frames?  K for
> > frames wit h partially restrained connections?
> > 
> > I agree that FEA might be more accurate than the old alignment charts
> > (actually the use of K factors in general is an assumption) but I have
> to
> > agree with Charles on this one.  The results of any computer program are
> > only as good as the input information, assumptions made within the
> > program,
> > and how accurate they are for that particular case.  To my knowledge all
> > FEA
> > programs are based upon assumptions, otherwise all physical testing
> would
> > be
> > unnecessary.  The point I think Charles was making is that this is a
> > complex
> > system in general... it is not like looking at bending on a flat plate.
> > How
> > many times has anyone analyzed a pinned base plate with more than 2
> anchor
> > bolts/rods?  Even with 2 anchor bolts this is not a true pinned
> > connection...  Besides, the numbers are statisically massaged after
> > physical
> > testing to achieve a best fit line or curve... this always leaves some
> > cases
> > that don't exactly agree with the reported findings.  Again, I agree
> with
> > Charles the resulting answer whether reported in 4 or 6 decimal places
> is
> > only as good as the assumptions which are never perfect.  Key here is to
> > make as good of assumptions as possible and go on... unless you want to
> > take
> > a year or more to design 1 frame.
> > 
> > my 2 cents worth anyway,
> > Greg Effland, P.E.
> > 
> > 
> > -----Original Message-----
> > From: Waterman Drinkwater [mailto:Drinkwater(--nospam--at)EQUATION.COM]
> > Sent: Friday, March 30, 2001 9:16 AM
> > To: 'seaint(--nospam--at)seaint.org'
> > Subject: RE: effective length factor for sway moment frames? K for
> > frames wit h partially restrained connections?
> > 
> > 
> > Theoretical results satisfy all the governing conditions. The
> theoretical
> > K
> > factor is theoretical exact. They are more reliable than the ones from
> > alignment charts. Those alignment charts were introduced before
> computer.
> > For the time being, almost every structural engineer has a computer for
> > analysis. Why should we keep applying those inaccurate charts?
> > 
> > When computers were not available for most structural engineers,
> engineers
> > used some approximate methods, for example, two cycles, to analyze frame
> > structures. No one uses two cycles since computer is everywhere. All the
> > results are theoretically analyzed on computers. FEA of K factors is a
> > must.
> > 
> > 
> > 
> > > ----------
> > > From: 	Charles Espenlaub[SMTP:Cespenlaub(--nospam--at)martinaia.com]
> > > Reply To: 	seaint(--nospam--at)seaint.org
> > > Sent: 	Friday, March 30, 2001 9:03 AM
> > > To: 	seaint(--nospam--at)seaint.org
> > > Subject: 	RE: effective length factor for sway moment frames?  K for
> > > frames wit h partially restrained connections?
> > > 
> > > If it is a "theoretical" analysis, you may get "an" exact value.  But
> > > since
> > > theory is based on educated assumptions, the exact value you get may
> > not,
> > > and probably will not, be the "exact" value that occurs in nature.
> Just
> > > because a computer can give you a four digit answer, does not mean,
> > > necessarily, that it is the right answer.
> > > 
> > > 
> > > Charles F. Espenlaub, III, P.E.
> > > Martin-Espenlaub Engineering
> > > Tel  215-665-8570
> > > Fax 215-561-5064
> > > 
> > > 
> > > 
> > > -----Original Message-----
> > > From: Waterman Drinkwater [mailto:Drinkwater(--nospam--at)EQUATION.COM]
> > > Sent: Thursday, March 29, 2001 4:55 PM
> > > To: 'seaint(--nospam--at)seaint.org'
> > > Subject: RE: effective length factor for sway moment frames? K for
> > > frames wit h partially restrained connections?
> > > 
> > > 
> > > Try theoretical (FE) analysis. You may get the exact value.
> > > 
> > > WD
> 
>