Return to index: [Subject] [Thread] [Date] [Author]

RE: doubts in Pre-engineered metal building design

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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.
>
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org


* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 

* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org