On Sun, 7 May 2006 22:13:35 -0700, "Steve B"
wrote:


"Don Foreman" wrote

I am now thoroughly confused. I envisioned a 150" high upside-down L,
like a gallows. The stuff about pins at top and bottom, saddle,
concrete base and 8x8 post has me baffled.


Follow me:

Three pieces:
one 150" long
one 48" long
one 21" long, each end cut on the diagonal

Assembled as you say, a gallows

Two pins welded along the center axis top and bottom of the 150" piece

The "gallows" sill sit into a receiver hole in a metal receiver that is
encased in in a concrete base.

The top pin will go into a short extension that comes off a beam end that
sticks out past the 8x8 vertical roof support at the corner of the deck.

Got it, thanks! The column is restrained from lateral movement by
vertical pins at top and bottom.

Cranking the formulae from Machinery's Handbook thru MathCAD, using a
150 lb load hanging from a 3 foot horizontal beam at the top, it
looks like the peak bending stress in the column is about 2000 PSI --
minimal for steel. Peak lateral deflection in the column looks
like about 0.294 inches at a distance of about 92" down from the top.
This isn't completely accurate, is a bit pessimistic, because I
treated the load moment as a single lateral 900-lb load 6" down
from the top pin to produce the moment. If I got me sums right,
looks like you should be in good shape. I figure a 1/2" dia top pin
will see shear stress of about 4000 PSI, again very modest for steel.

Because it is at the corner of the top deck, it can rotate about 270
degrees.

A hoist is placed at the end of the gallows arm.

When I get it up, I shall post it to the mailbox.

I'm just mounting a swinging gallows arm on two pins.

Steve