"Christopher Tidy" wrote in message
...
SteveB wrote:
Thanks for your input, Chris. This is going to be mounted at a corner,
and needs to swing in through the handrail, so a stiffleg is out because
it would hit the building.

I get a better idea what you need now. I'm sorry this thread has turned
into a flame war about mathematics with which none of use are entirely
familiar. It does muddy the waters.

I can see that a stiff leg is out of the question. Is your building
wooden, brick, stone or what? 200 lb is not an enormous load and I think
it might be possible to attach the davit to the building without the long
vertical column. If you do a Google image search for "wall crane" and
"wall hoist" you'll see pictures of cranes which are attached directly to
the structure of a building. Some of these are quite hefty.

As I suggested (but it got lost in the argument somewhere) I think the
weakest feature of your design is that the load will be attempting to bend
the vertical column. I'm not a structural engineer, but my intuition is
generally good and this is fairly clear I think. If you took a long length
of box section, clamped one end to the bed of a pick-up and leant on the
other end, it would deflect quite a bit. But if you push on the end of the
section, as if you were trying to push the pick-up along, it would be much
harder to buckle it. So basically you could build something like one of
those wall cranes, but have a column below which carries compression only.
I did a little ASCII sketch (turn the fixed font on now):

-|\ -|\
| \ | \
| \ | \
-|---\ |---\
| |
| |
| -|
| |
| |
| |
| |
_|__________________________|_______
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

My preference is for the design on the left, as it avoids bending the
column. But I do think my original suggestion of an 8" deflection without
stand-offs is inaccurate. Given Ned's estimate, plus perhaps a little
extra flexibility in the mountings, 1" to 2" seems more reasonable. But
that's still a bit bouncy for my liking as flexing can cause problems such
as pivots jamming, etc.

I'd be interested to see pictures and drawings. Feel free to post them
online or e-mail them to the above address (remove NOSPAM). Good luck and
let us know how you get on.

Best wishes,

Chris


The problem with the drawing I provided is that it is waaaaaaaaaaaaaay
out of scale. The top triangle is 1 foot x 3 foot x the hypotenuse.

Your idea of putting the second standoff at the base of the triangle won't
work, because of the following configuration:

Starting from the base it goes something like this -from ground up, the
first six feet is sonotube, next foot is joisting, next eight foot is column
hooked directly to top of deck joisting, top foot is beam sitting on top of
eight foot column. There's no straight continuous piece in the whole deal.

That is why I wanted the majority of the weight to be transferred vertically
to the base of concrete in Sonotube. The standoffs are just to keep the
load from swinging as I swing it in over the handrail.

My main concern was how much the 14' vertical would flex under a 200# load.

Steve