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Re: Curved Stair Stringer

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I would use a channel shape.  Together with the threads you realize a very
stiff stair assembly.
They put the channel in a 3 roll bending machine at a skew so they can bend
it following a helix path.  The legs of the channel are short so there are
no
big problems in bending them.

Regards,

Vlad
vcernescu(--nospam--at)banerjee.com

----- Original Message -----
From: "richard lewis" <rlewistx(--nospam--at)juno.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, September 25, 2003 1:16 PM
Subject: Re: Curved Stair Stringer


> It is 2 parallel stringers with the same center of radius at each of the
> curves.
>
> Rich
>
> On Thu, 25 Sep 2003 10:01:31 -0400 "Vlad Cernescu"
> <vcernescu(--nospam--at)banerjee.com> writes:
> > Is it a one stringer or two parallel stringers?
> >
> > Regards,
> >
> > Vlad
> > vcernescu(--nospam--at)banerjee.com
> >
> > ----- Original Message -----
> > From: "richard lewis" <rlewistx(--nospam--at)juno.com>
> > To: <seaint(--nospam--at)seaint.org>
> > Sent: Thursday, September 25, 2003 9:46 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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