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# tank wall spiral stair

## tank wall spiral stair

(OP)
I need to tell our fabrication dept. the correct diameter to role several 20' lengths of 1 1/2" sch. 40 pipe so they will fit as a hand rail for the tank stairway I designed. Tank dia.=46.15',tank height=46', stair stringer angle = 35 deg., stair height (vert.) 34'. I can't find a formula to figure this one out.

Thanks, John

### RE: tank wall spiral stair

Here is what I would do.
The angle of the projection of the stair on the horizontal plane is:
Assuming the stair is 3' wide, the radius at the handrail is
r=46.15'/2+3'=26.075'
The arc length of the horizontal projection of the handrail is
l=α*r=26.9'
The developed length of handrail is now:
L=√(l2+h2)=43.4'
And don't forget to add provisions for intermediate and end floors! prex

http://www.xcalcs.com
Online tools for structural design

### RE: tank wall spiral stair

There is a mistake in my previous post: the first formula should be:
α=34'/tan35°/(46.15'/2)=2.104
and the final result becomes
L=64.6'

prex

http://www.xcalcs.com
Online tools for structural design

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