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Re: Site Built Spiral Stair Case

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I did one of these. Huge pain in the ass and not worth the fee.

I ended up using plywood laminations to make stringers and had to use rods under the treads to get the torsion to work out.

Analyze in Risa (or similar) and get your stresses down. Watch deflections and IIRC one of the stringers (the outer one) was hard to get to work together with the inner stringer.

My advice - use steel and wrap in fake wood.

-gm

On Tue, Sep 2, 2008 at 2:54 PM, David Fisher <dfisher(--nospam--at)fpse.com> wrote:
Looks more like an art than a science to me...

David L. Fisher SE PE
Senior Director

The Fisher Companies Ltd. - Cayman
372 West Ontario Chicago 60610
75 Fort Street Georgetown Grand Cayman BWI
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-----Original Message-----
From: Michel Blangy [mailto:mblangy(--nospam--at)satco-inc.com]
Sent: Tuesday, September 02, 2008 4:00 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Site Built Spiral Stair Case

Perhaps, but how to assign allowable stresses to such an extraordinary
creation? In my estimation it would be easier to put a value on the beauty
of the heavens.

-----Original Message-----
From: Garner, Robert [mailto:rgarner(--nospam--at)moffattnichol.com]
Sent: Tuesday, September 02, 2008 1:34 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Site Built Spiral Stair Case


Let's see if I can confuse things.  A spiral like this is essentially a
coil spring.  Coil springs translate linear motion along their axis into
torsion of the coils.  It doesn't sound like you will have a
torsion-resisting section unless you can box the thing somehow.  Are you
creating a spiral box-beam?  That should work.  Or at least be
analyzable.

Bob Garner, S.E.

-----Original Message-----
From: Michel Blangy [mailto:mblangy(--nospam--at)satco-inc.com]
Sent: Tuesday, September 02, 2008 12:57 PM
To: Seaint@Seaint. Org
Subject: Site Built Spiral Stair Case

An Architect wants to use a method I've never seen before to construct
site
built spiral stair cases. We do a lot of tight radius spiral staircases
here
in southern California residences. Typically, the outer and inner
supports
of the treads are continuously supported by tightly spaced studs. The
idea
now is to line the inside face of the spiral with multiple layers of
plywood, glued and screwed in place and then, after the glue has had
time to
cure, the plywood and interior support studs are to be cut parallel to
the
tread nose line at some depth creating a spiraling plywood beam. I have
no
clue as to how to calc this out, but the architect has seen several
constructed and swears they are quite solid. How might one spec a load
test
for such a thing and does this test indemnify the EOR? What other
concerns
if any would you have?

Thanks in advance,

Michel



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