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RE: PL stair stringer

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Brad,

Reference "Metal Stairs Manual", National Association of Architectural Metal
Manufacturers.  You won't find a very sophisticated technique, but it has
been used for a lot of years.    They just drop the allowables to 20 ksi for
plate stringers.  The problem is very complicated in that the treads act as
stiffening elements for the stringers, but the stiffening elements do not
extend up into the compression zone of the plate.  The ability to stiffen
the stringer also varies with the tread types.  Pan stringers provide more
stiffening than open grate treads.  

Generally I assume the NAAMM technique is accurate for metal pan stairs.
But I use channels for open grating treads.  You can spend a huge amount of
time in modeling and designing and get a result that is no better than the
NAAMM technique.  I use the NAAMM technique in practice until I get
something that makes me nervous.  Then I design it, have it constructed, and
load test it.  Every strange design that I have seen that was tested, proved
the NAAMM to be O.K.

There is only one problem.  I have not been able to contact NAAMM in Chicago
at 312-922-622 or at http://www.naamm.org/.  Maybe one of our AISC
colleagues can shed some light on the current disposition of NAAMM.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Brad Friederichs [SMTP:brad(--nospam--at)vesolutions.net]
> Sent:	Monday, March 13, 2000 9:08 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	PL stair stringer
> 
> Fellow Engineers,
>  
> How are plate stringers for stairs designed for bending (incl lateral
> stability)?
>  
> What equation is used for lateral torsional buckling?
>  
> Thanks for your help.
>  
> Brad Friederichs