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Re: Curved Stair Stringer

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I had a similar situation, but I was allowed a single support at the joint
where the inner stringers met the intermediate landing.

For the stringers I'd use a rolled HSS, like a 12x2 or 12x4.  You also might
have to take into account the stabilizing effects of the stair treads,
landing, and inner stringer to make it work.

As for rolling, you might be surprised as to what is possible.  Call a steel
shaping company to find out what the radii are for different sized tubes.
I'd even suggest calling *several* companies, because they have different
machines with different capacities and abilities.  There are usually several
advertisements in Modern Steel Construction.

There's one in Kansas City called Shaped Steel, and the owner claims that
the radius of the pieces are within 1/16" when they leave his plant (he then
said the tolerance he guarantees is 1/4" after the pieces are mis-handled
all the way through the fabrication shop and at the job site).

Jason Kilgore
Leigh & O'Kane, L.L.C.

----- Original Message ----- 
From: "richard lewis" <rlewistx(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Thursday, September 25, 2003 8:46 AM
Subject: Curved Stair Stringer

> I looking for some tips for modeling a curved beam. I have an circular
> custom stair. It is supported at the 1st floor (slab on ground) and 2nd
> floor. It looks something like a slotted hole in plan. From the first
> floor it does a 1/4 turn. Then there is a straight run, then another 1/4
> turn back to the 2nd floor. I am supporting it with a tube at the second
> floor and anchoring it to the slab at the first floor. The tube will give
> me torsional resistance. The tube is about 16 ft. long and spans to 2
> perpendicular beams, one at each end. The beams then span to columns
> buried in the wall. Looking at this in plan view the 2nd floor beams
> would form an 'H' shape.
> I want to get feedback for modeling the stringers in a computer frame
> analysis. I guess my first impulse is to use short chord elements to
> simulate a curved member. I started doing this with 15 degree angles for
> the chords.  I would then uniformly load these members and have a fixed
> joint at the tube column at the 2nd floor. I guess the connection to the
> floor slab at the first floor would be pinned.  I would use a moment
> frame from the vertical legs of the 'H' shape to give me lateral
> stability. Any other suggestions for modeling this?
> I am wondering what would be the best section for a stringer.  Since it
> is a curved member it will have torsion.  Should I be using a closed
> section like a tube?  A tube might be hard to bend on the radius.  Should
> I make a closed section from welded curved plates?  Should I just use a
> single thick plate for a stringer?
> Thanks for your help.
> Rich

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