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RE: Torsion in steel stair channels

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Regarding the connection of the pipe to the flange of the channel, I analyze this considering two “crescents” of weld. I let AutoCAD determine the section properties for me once I’ve drawn the weld correctly. Yes, it’s usually marginal. Sometimes (depending on spacing), I’ll go to a thicker wall, smaller O.D. pipe to get just a little more weld.

 

The torsion is a different issue, but I use the AISC design guide for that. If you’ve really got a problem, maybe you can enhance the connection between the stair treads (metal welded to the stringers with 1” at top, bottom and web, right?) and make them work as “torsion bars”. Just a thought.

 

T. William (Bill) Allen, S.E. (CA #2607)

V/F (949) 248-8588

San Juan Capistrano, CA

http://www.AllenDesigns.com

-----Original Message-----
From: DSmith7367(--nospam--at)aol.com [mailto:DSmith7367(--nospam--at)aol.com]
Sent: Friday, April 23, 2004 6:23 PM
To:
seaint(--nospam--at)seaint.org
Subject: Torsion in steel stair channels

 

We see a lot of stee stairs with steel pipe posts welded to the top flange of the stringer channel.  It is not uncommon to see a std. pipe (O.D. = 1.90") welded to and overhanging the 1.5" flange of an MC12x10.6.

 

Obviously, the stress in the pipe post at this point will not be developed.  How about the flange and web of the channel?  If we increase the width of the channel flange, there is now the problem of developing the torsion/bending moment in the channel flange and web.  If you take a strip of web over say 18" and try to carry the force, it will require a thick web and thus heavy channel.

 

Considering torsional restraint from the top flange and a portion of the web does not give much help.  How are these stringer/post assemblies analyzed?  I see such light channel stringers that I feel sure that they have not been checked except for just stair loads.

 

Any comments on this would be appreciated.