Need a book? Engineering books recommendations...

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

Re: Inverted tapered steel girders

[Subject Prev][Subject Next][Thread Prev][Thread Next]
> From: Jim Wilson <wilsonengineers(--nospam--at)yahoo.com>

> A pre-engineered type metal has roof girders that taper from an estimated
> 24" at the ends to 48" at mid-span.  Girders are 12ft on center and
> support gage metal C-channels.  The span is approximately 70ft.  The
> girder top flange is level.  The beam is spliced at midspan with
> connection angles welded to the flanges and bolts (in tension) tieing the
> lower flanges together.  There is no web connection.  There are no
> diaphragms or braces between members.  The building is in central NJ.

Ideal model will exhibit very low shear at centre and the current
connection may be adequate for shear and moment. However, no web
connection or stiffening is questionable for a 48" deep section.

>   This looks like a potential stability problem to me, but because of the
> taper and the splice, I'm not sure how to verify or quantify this.  Is
> anyone familiar with such beam configurations?

My first concern is uplift (bottom chord compression) in the centre of
the span. Other concerns follow from the actual configuration of the
assembly (e.g. moment or simple connections at the columns, etc).

Under gravity loads, there may actually be adequate torsional restraint
from the purlins bearing on the top flange AND from the dead load of the
bottom half of the rafter.

>   I understand that the metal building manufacturers that made this type
> of member are no longer in business, but that's hear-say.  I did not note

That's very common. It also happens that some manufacturer's
didn't/don't have state-of-the-art engineering.

> a manufacturer on the building, and I can't re-visit the site to look for
> this info.

Some manufacturers provide a ridge cap at the endwall gable with the
company name. Anybody nearby could check this. After that, it depends on
WHY you need to review the beam. Is this a renovation project or is it
being reviewed for commercial reasons?

>   I would like to recommend someone to the Owner so that these members can
> be reviewed further.  Perhaps an experieneced metal building design
> engineer has seen this before.  Any help will be much appreciated.

I have not seen this particular form. There are as many possibilities as
there are manufacturers. 

Paul

-- 
R. Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ado26(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   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 
******* ****** ****** ****** ******* ****** ****** ********