Jim - if you can stick with the 500 pound load, try a 16 ft. 2x12. The
calculator here predicts a max stress of 725 lbs and .323 in. deflection.
Add a couple of "angle irons" to the sides maybe?
You'd be happier with one of those calculators on your computer. They
are quite handy for something like this.

Hul

Jim Wilkins wrote:
Is there a standard way to splice gantry hoist track made from two
channel sections? I'd like to make a 16' track from four 8' lengths of
C4 x 5.4 channel. The constraints are that the trolley wheels have to
roll inside the lower flange, which rules out this pattern:
https://www.researchgate.net/profile...101002@1470947
and a vertical plate or tee section extending below the lower flanges
can't block the HF 1 ton trolley. I've already turned its wheels down
to fit in 3" channel.

The immediate application has the splice plate suspended from a roof
beam and the outer ends supported by tripods, allowing 8' of clearance
for my bandsaw mill on one side and maneuvering room in the 4' wide
storage shed on the other, plus enough outside overhang to load the
cut timbers onto a narrow trailer.

The maximum load in this case will be under 500 lbs but I've been
struggling to use this problem as an exercise in designing a splice
that allows the full load capacity of the channels or 1 ton trolley on
a 16' span without interfering with the rolling trolley. I might be
able to shim up the lower fillets of a piece of scrap W6 x 9 beam so
the channel fits against the web and flanges. It looks like I have to
accept tapping the lower flanges of the channel and trimming the cap
screws flush inside.

-jsw