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RE: Beam design

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Santhosh,

First, I will agree that my personal belief is that if you cannot do it by
hand (FEA/stiffness method type analysis of large structures being a clear
exception...doing such by hand would take way too long and could be
construed as torture under anyone's standards, Geneva conventions or not)
than you really should not be doing by computer.

Second, I will say that I agree with Michelle that there are likely quite
a few members in your structural system that likely should have minimal to
no axial load in them (i.e. what I might call "neglagable" axial load).
This is where care must be used in making use of analysis results
(regardless of what analysis package you use...you appear to be using
STAAD).  Analysis results will give information based upon what
assumptions and decisions that you make and if you are not careful then
you can end up things like axial where maybe it should not be or could
realistically be neglected.

Now, I don't know what you modelled nor what assumptions that you made
when creating your analysis model.  Thus, it is possible that the "beam"
members that you have in your model have significant (i.e. not neglagable)
axial and that they SHOULD have those axial loads (i.e. maybe you are
modeling a moment frame).  So, while it is possible that maybe you have
some members that really don't have or should not have axial load, I will
assume that you do have some elements that require design for both axial
load and flexural loads.

So, that being the case, I will again agree with Michelle...codes do NOT
have interaction charts or examples, etc.  Such things are "tools" that
help engineers "apply" the code provisions.  In other words, interaction
charts or exmaples are items that essentially put the code provisions to
work in format that makes your life (and mine and all other engineers)
easier.  And like any tool, they must be used with caution as they can be
used incorrectly.  Thus, I will offer my belief again that if you cannot
do a design by hand, then you should not really being using "tools" (i.e.
tables, charts, computers, etc) or at a minimum you should be using them
with extreme care.

Now, as to doing the design, I would encourage you to put a little effort
into learning a little bit on your own first.  This will mean picking up
and reading a text book or looking at some examples in some publication.
You have not said whether your beams are concrete or steel (or something
else).  So, even if someone wanted to guide you to a design procedure,
they would have to give you more than one as while many of the basic
principles are similar for both concrete and steel for designing a beam
with axial load, the "devil is in the details" (as the saying goes).

So, I would suggest taking a look at a textbook on either concrete or
stell design.  If you are looking at steel members, then the AISC manual
has some examples (as well as some "tools") for designing beams with axial
loads (or columns with bending loads).  For concrete, a textbook is likely
your best solution, but I believe that you could look at something like
the PCA Notes on the use of ACI 318.  I also believe that many concrete
textbooks will have some "generic" column interaction (P-M interaction)
curves that you could use as "tools".

If after you have read a little bit and tried to learn a little bit on
your own, but still don't understand some things about designing for both
axial loads and flexural loads, then you will likely get more helpful
responses if you come back and ask specific question about specific things
that you don't understand.

And while I won't say it as harshly as others, you could also take a class
or two that covers such material.  While I am not a person that believes
that everything needs to be learned in school (engineers need to be ready
and willing to learn new stuff "on the job" that was not covered in school
due to time, etc.), it is certainly a good way to learn some stuff for the
first time for many people.

I will agree to some degree with those who seemed liked they responded
somewhat harshly in the form that I do believe that I don't really like
really general questions when asked in such a way that it appears that the
person asking may not have even bothered to spend a little time trying to
figure stuff out on their own (I am not sure if I consider this to be true
in this case or not).  I am a strong believer that one should try to
figure stuff out some on their own before asking for help.  Too many times
we get lazy and just assume that someone else will "spoon feed" us
something when we likely could have figured it out on our own with a
little effort.

So, I encourage to read a little but feel free to come back with some
specific questions if you need/want.

Regards,

Scott
Adrian, MI


On Tue, 24 Jan 2006, Michelle Motchos wrote:

> My 2cents- I agree this is a scary conversation. What happened to good
> mentoring (but that is a completely different diatribe)...
>
> Santhosh, The code does not "give charts only for bending moment
> capacity" (at least not here in the US) because the codes contain
> equations, not design aids (which are included for convenience "The
> Manual" assuming you are working in steel).  Fundamentally, you need to
> read the code sections on combined forces and apply the equations for
> the frame members receiving axial loads and moments. As an aside, unless
> every member you are analyzing is part of a lateral frame it is unlikely
> that all the framing members would be subjected to axial loads in
> everyday design. From my experience the load is generally assigned to
> the diaphragm in the infill framing areas and they are designed for
> bending only. That would be a modeling issue in stadd and about all I
> use it for is single plane truss design so I can't provide much other
> guidance.
>
> Michelle Motchos, PE
> Stevens & Wilkinson of SC
> PO Drawer 7. Columbia SC 29202-0007
> www.sc-sc.com
> mmotchos(--nospam--at)sw-sc.com
>
>
>
> -----Original Message-----
> From: Gary [mailto:gloomis(--nospam--at)masterengineersinc.com]
> Sent: Tuesday, January 24, 2006 12:57 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Beam design
>
> That is very dangerous - letting the computer do it.  If you can not
> design a beam manually then you should never allow the computer do it.
> How do you if the computer is right?
>
> Gary
>
> -----Original Message-----
> From: Kevin Below [mailto:kbelow(--nospam--at)genio.ca]
> Sent: Tuesday, January 24, 2006 12:17 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Beam design
>
> Santhosh, it sounds like you might benefit from the Staad post-processor
> which does the design for you.  It is called Staad.etc.
> I don't use Staad, et least not yet, but I think it will probably show
> you the calculations involved, and you will be able to observe and
> understand the process.
>
>
>
> génio experts-conseils inc.
> Kevin D. Below, ing., Ph.D. en Structures
> 290, rue Seigneuriale
> Beauport, QC G1C 3P8
> Tél. : (418) 660-6969 poste 272
> Fax : (418) 660-6463
> kbelow(--nospam--at)genio.ca
>
>
> -----Original Message-----
> From: Santhosh Kumar Yedidi [mailto:sant527(--nospam--at)gmail.com]
> Sent: 24 janvier 2006 00:09
> To: seaint(--nospam--at)seaint.org; ShermanWC(--nospam--at)cdm.com
> Subject: Re: Beam design
>
>
> Dear Sherman,
>
> Can you please help regarding the beam design issue. I understood the
> procedure of how to do beam design with axial force. I am working in a
> consulting firm. We analyze any frame structure using staad. After staad
> analysis, we get the member end forces. All member end forces also
> contain an axial component irrespective of being a beam or column.  So
> all beams contain an axial component. Then our beam theroy is not so
> useful. because codes give charts only for bending moment capacity.
>
> So my question is why those people havent thought about this issue of
> axial force. Can you suggest some generalization, which would help me to
> design the beams using beam theory rather than again analysing each beam
> seperately for combined axial and moment.
>
>
> On 1/10/06, Sherman, William <ShermanWC(--nospam--at)cdm.com> wrote:
> >
> > Bill Cain: that is an unfair comment.  Rizmirza provided a valid
> > response relating to concrete design for flexure and axial loads - I
> > didn't learn that method in school, but learned it "on the job".  And
> > a "basic structural analysis course" will not tell you how to design
> > steel or concrete for such combined loads if it only covers
> > "analysis".
> >
> > Santhosh: you need to be clearer about what you are asking.  Are you
> > looking for detailed methods for a given material vs general analysis
> > of combined loads?  Are you talking about steel design or concrete
> > design or another material?  Your original question is hard to answer
> > without understanding more detail of what you want to determine.
> >
> >
> > William C. Sherman, PE
> > (Bill Sherman)
> > CDM, Denver, CO
> > Phone: 303-298-1311
> > Fax: 303-293-8236
> > email: shermanwc(--nospam--at)cdm.com
> >
> >
> >
> >
> >  ________________________________
> >  From: bcainse(--nospam--at)aol.com [mailto:bcainse(--nospam--at)aol.com]
> > Sent: Tuesday, January 10, 2006 12:20 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Re: Beam design
> >
> >
> >
> >
> >
> > Santhosh-
> > I would strongly advise you to enroll immediately in a basic
> > structural analysis course. This question is too basic for you to be
> > doing any design work. Regards,
> > Bill Cain, S.E.
> > Berkeley CA
> >
> > -----Original Message-----
> > From: Santhosh Kumar Yedidi <sant527(--nospam--at)gmail.com>
> > To: seaint(--nospam--at)seaint.org
> > Sent: Tue, 10 Jan 2006 11:08:18 +0530
> > Subject: Re: Beam design
> >
> >
> > Exactly this is the answer I am waiting for, but then when you do a
> > frame analysis all the members have axial force value. So then
> > everything has to be designed as a column only. Thats why I was asking
>
> > this question.
> >
> > On 1/9/06, David Topete <davetopete(--nospam--at)yahoo.com> wrote:
> > > Turn the beam 90 degrees and it becomes a column with bending.
> > >
> > > Santhosh Kumar Yedidi <sant527(--nospam--at)gmail.com> wrote:
> > > How to do beam design with axial forces acting.
> > >
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