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Re: doubts in Pre-engineered metal building design

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Yes, I was ripping metal buildings in general, because of some unpleasant
experiences with them in the past.  Does that make them all under-designed?
No.  Do they generally base their designs as tight to the code requirements as
allowed?  From what I've dealt with, yes.  In some cases, such as snow loads,
the code minimum is not what is commonly used in some areas, particularly
because of roof failures.  That doesn't mean I multiply by 10.  I just don't
take the code allowance for snow being blown off  (Ce=1.0 instead of 0.7).  I
don't question that economics plays a huge role in design but, sometimes it
pays to put some extra capacity in a building before it is built, rather than
after it falls down.  I believe it is referred to as engineering judgment.  As
far as Z-purlins go, most designs for a metal building that I've seen have them
being loaded on the flanges (metal deck bearing on the top, bottom bearing on
the support frame), with no blocking at the support to prevent rolling.  Again,
my comments are based more on personal experience than an overall indictment of
metal buildings.  But, hey, you get what you paid for...

Mark Nowmos

"Effland, Greg" wrote:

>
> Answers to original questions:
>
> Q1.All the joints of the lean-tos connected to main frames are pinned and
> the
> main frame will take care of moments.is this ok in stability point of view.
>
> A1. This frame is stable as long as the attaching frame is stable.  The
> theory is no different then that of a braced frame... some frame parts
> "lean" onto another system (Bracing, rigid frame, etc.).
>
> Q2.soldier columns are provided when the c/c of frames exceeds more then 40
> feet in order to break the girt span.this soldier column base is pinned.is
> this ok
>
> A2. Yes this is ok if the top detail is correct.  Typically the soldier
> column, intermediate sidewall column, or any other name it might be called
> is designed as a simple span "beam."  Typically it should see only very
> minor vertical loads.  The base is usually pinned and the top connection,
> depending on forces, may have a "king post" or other horizontal beam and
> bracing to strut the top loads out of the column back into the next frame.
> If light loads exist some manufacturers may attempt to handle the loads at
> the top without a king post.  I would probably space the columns not more
> than +- 30 ft apart.  To use AISI Section C3.1.3 the girts must be span < 33
> ft (screw fastened panel, and other requirements also apply).  If the span
> exceeds 33 ft then make sure the girts were designed to AISI C3.1.2.
>
> Metal Building Defense:
> I'll try to not get too defensive... :-)
>
> As far as being skeptical, I guess that is good to be skeptical of every
> building anyone designs/checks.  It is the job of every structural engineer
> to provide for the safety of our designs.  Keep in mind that the mere fact
> that you may put extra cost and weight into a building does not necessarily
> make it better.  Hopefully if the owner wants a 1 ton crane in a building in
> a Zone 1 seismic area you don't design for a 20 ton crane in a Zone 4 area.
> If you don't design to the letter of the code how do you design?  Do you
> take all of your results and multiply by 10?
>
> An analogy... if you were to but a pickup truck, do you buy the heaviest and
> most expensive with the largest engine that is currently made?  Probably
> not...  Why?  Because other things come in to play...  what do I need to do
> with it... Am I going to pull a 30 ft trailer?  Do I want to pay $3000 to
> get a 454 or larger engine... Those same economic principals apply to
> buildings... don't buy a sears tower if you only need a sears store... make
> sure the building fits what is required... If you want extra capacity then
> ask for it, increase the loads, modify the specifications, say you want a
> maximum 60% CSR, etc.
>
> Just wanted to emphasize that metal buildings produced by a reputable
> company are designed to meet the requirements of the code, loadings, and
> owner's criteria all at a safe level.  Z-Purlins have many years or testing
> and field experience to justify their use.  The part to be paranoid about
> cold formed members is if you have to hand calculate effective properties as
> this could take days per section by hand (small exageration). :-)
>
> Using Shear Flow Theory... Z-Purlins due to their shape, when a vertical
> load is applied in plane with the web, will tend to translate laterally were
> as C-Purlins/Girts will tend to torsionally rotate.  So if torsion is of
> concern then be more wary of C-Sections.
>
> My 2 cents worth,
> Greg Effland, P.E.
>
> -----Original Message-----
> From: Mark Nowmos [mailto:mnowmos(--nospam--at)compuserve.com]
> Sent: Monday, May 14, 2001 1:06 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: doubts in Pre-engineered metal building design
>
> Be very skeptical.  These manufacturers design to the tightest of what the
> code allows.  And some of them seem to design in a vacuum, I believe the
> psychological term is "solipsism", where the outside world is just a fantasy
> envisioned by the beholder.  Check all their numbers.  I get the feeling
> that they have people just plugging numbers into a design program, with no
> review by an actual engineer.  Perhaps I'm being cynical or paranoid, but
> the use of Z-sections makes me cringe (especially when they are not
> laterally braced for torsion).
>
> Mark Nowmos (not a fan of these cheap, to-the-letter-of-the-building-codes
> buildings)
>
> Bill Polhemus wrote:
>
> >
> > Not sure as to the origin of your question.
> >
> > Are you trying to DESIGN a metal building? Or are you simply skeptical of
> > the standard metal building design approach and details?
> >
> > If the former, are you working as a consulting to a M.B. manufacturer?
> >
> > If the latter, I would point out that metal building folks have been in
> > business a LONG time, and I would venture to say that the established
> > manufacturers--and there are a surprising number of them--have this down
> > pat.
> >
> > William L. Polhemus, Jr., P.E.
> > Polhemus Engineering Company
> > Katy, Texas
> > Phone 281-492-2251
> > Fax 281-492-8203
> >
> > -----Original Message-----
> > From: HAMID [mailto:hamid(--nospam--at)dishnetdsl.com]
> > Sent: Saturday, May 12, 2001 12:04 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: doubts in Pre-engineered metal building design
> >
> > Hi every one
> > I have some doubts regarding pre enginnered metal building design.
> >
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