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RE: Important Message: SEAINT Continues on LinkedIn SEAOSC group

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Bill,
There should be no residual stresses forming the stringer with heat.  Heat is often used to relieve stresses.  I would favor an HSS for the center stringer.  I don't know how you would characterize the laminate wood.  A custom wood laminate in the shape of a helix might be a big task.  But once formed, I don't think that there would be any more chance of residual stresses than you would get with any other wood laminate. 
 
I would go with the steel and if a wood look is desired, I would skin the HSS in wood. 
 
I don't know why you could not trust the output, but that depends on the model.  An unbalanced and a full balanced live load should cover it.  Be conservative on how much deflection you will allow. 
 
The Hyatt Regency in Kansas City had a cantilevered stairway.  It was tested with the full live load plus 70% and then 40% of the DL.  It was the old load test per ACI 318.  It passed and is still there today.  The skywalk that did not collapse was removed and a single walkway was installed that was supported from below.  The lesson here is to fabricate the stair based on you computer calculations, set it up in the shop, and test it.  Testing is a great sleep aid.   

Regards, Harold Sprague
 
> From: Bill(--nospam--at)AllenDesigns.com
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Important Message: SEAINT Continues on LinkedIn SEAOSC group
> Date: Fri, 25 May 2012 12:38:12 -0700
>
> Quick, before it closes down, I have one last question. I have a project
> with a circular stair. The owner wants a center stringer and otherwise open.
> I'm thinking tube or pipe, but in any case, it will follow the geometry of a
> helix.
>
> Questions:
>
> If the steel section is formed via heat, are there residual stresses or can
> I assume stresses are zero until I apply load onto the stringer? Same
> question if the stringer is formed with laminated wood.
>
> I know a helical spring only sees torsion, but that is because one end is
> moving with respect to the other. If I model this stringer, with the top and
> bottom preferably pinned (in x, y and z directions), can I trust the output
> if I have two load cases, full live load and unbalanced live load?
>
> Finally, is there a question I forgot to ask?
>
> Also, it would be a travesty not to acknowledge the work and foresight
> provided by Shafat Qazi and Dennis Wish in conceptualizing, launching and
> maintaining the best medium for structural engineers in my lifetime. Thank
> you, gentlemen!
>
>
> T. William (Bill) Allen, S.E. (CA #S2607)
>
> ALLEN DESIGNS
> Consulting Structural Engineers
> 32302 Camino Capistrano, #206
> San Juan Capistrano, CA 92675
>     V (949) 248-8588.F (949) 209-2509
>
>
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