All you say is of course true Dan and with a lever ratio like that I think it
would be really hard to keep bolts secure in the concrete.
I have misgivings though about having a swing moving out over the edge of a
concrete platform. Sounds to me like a good way to get a leg broken or someone
to get hit as the swing glides backward out over the open space.
----- Original Message -----
From: Dan Rossi
To: blindhandyman@yahoogroups.com
Sent: Wednesday, September 09, 2009 9:38 AM
Subject: Re: [BlindHandyMan] Calculating load capability
Nancy,
I agree that you probably don't have to worry about the posts snapping off
but remember that as the swing moves forward, the uprights are attempting
to pivot around the point where they cross the floor of the porch, meaning
that the bottoms of the posts are pulling away from the wall of the porch.
Not only that, but since the floor of the porch is the fulcrum, you have a
six foot lever arm above, and maybe a ten inch lever arm below, so the
force at the top of the uprights, as the swing moves forward, is
multiplied by about 7 times and that is a force attempting to pull the
bolts out of the porch wall.
I would think that sinking the posts into concrete a couple of feet down
would go a long way to helping the system be more structurally stable.
We've just had a discussion on the issues of burying posts or not, so you
can make your own decision on that point, but I think that it might be
prudent in this case.
As far as chain strength, the guys at any big box store should be able to
tell you what the relative strengths are of the various gauges of chain.
I don't have any real knowledge of that.
--
Blue skies.
Dan Rossi
Carnegie Mellon University.
E-Mail: d...@andrew.cmu.edu
Tel: (412) 268-9081
[Non-text portions of this message have been removed]
