"Richard Smith" wrote in message ...

Hi Jim - starting topic's own thread...



Hi Jim

Can you sketch?
That is always helpful. I do that even when it seems we all agree, as
it can be amazing how a sketch reveals that the impressions are not
the same.

I'm thinking - maybe weld some brackets on top of the channel with the
bolted flange faces facing.
I'd normally wish there could also be a flange underneath - but the
close-fitting "standard" carriage would collide with it, so not
possible.

That said: if I understand correctly (big "if") - the loading may be
"cantilever beam" - tension on top, compression underneath.
Extending out of the shed?
Suspended - near the door?
In which case flange on top, nothing needed underneath as compresses
together would be bril.

Load analysis of the section - as channels tend to twist under load,
and is singular, I wouldn't dare use Euler-Bernoulli beam calculation
as works for symmetrical beams.

Sorry verbal description is hard to "see".

Rich S

-----------------------------

The channels will be attached web to web, with the splice plate sandwiched
between them at the center, hanger plates between them at the ends and other
stiffening as needed, so they should behave as a single symmetrical I beam.
So far the 3" channel track hasn't noticeably twisted under a 1/2 ton load.

Any cantilever loading will be the channel's own weight while setting up
plus possibly the weight of one end post and diagonal braces if the opposite
loaded side post sinks into wet ground. The model is a beam with pinned
joints to columns at the ends. Assume the columns are pinned at the base and
could tilt inward if the beam sags, though they won't tilt out or laterally.

Really I just need a good bolt geometry for the splice plate so I can start
calculating stresses. I'm leaning toward two large bolts through the
channels' neutral axes beside the joint and two more at the outer ends of
the vertical splice plate, and welding reinforcements to the web around them
if necessary. Perhaps a grid pattern of more smaller bolts would be better?

It seems to me that the beam splices I've seen on bridges might weaken the
lower flanges if the bolts aren't sufficiently tight, and this track must be
disassembled repeatedly and probably sprayed with slippery rust inhibitor
wax. The splice plate I have now, from a local steel erector's scrap pile,
is 10mm thick, 150mm high and 700mm long.