"Jim Wilkins" wrote in message news
"Carl Ijames" wrote in message
news
"Jim Wilkins" wrote in message news
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
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I have no idea what "standard practice" is for this, but I'll toss out
some thoughts. First, cut one of the 8' channels in half and make three
splices, where each splice is in the middle of an uninterrupted span of
the backing channel by tapping one channel and using flat head bolts.
That keeps the central web thickness constant and lets one channel serve
as the splice plate for the other side. That would probably handle your
current load but maybe not the full 1 ton (I get a maximum stress of 3100
psi with a 250 lb load in the center of a single 8' span, so you have
plenty of safety margin for your 500 lb load). Second, if you cannot use
a tie plate below the joint because of interference with the trolley but
have room above, add a short section of channel on top of the splice
instead of a flat tie plate, with bolts through the webbing. Doing both
should get you a full strength joint. You may only need to do this above
the central splice, not all three. Of course, how big and how many bolts
and how long the upper channel should be is left as an exercise for the
reader :-).
--
Regards,
Carl Ijames
My notes from a while ago give ~25 KSI and a sag of 1 in 145 for one
16' length of 4x5.4 channel with a 1000 Lb center load. It likely came
from an on-line calculator. I could buy a single 20' beam for the
track but I couldn't handle it by myself; the four separate pieces are
reasonable to lift on a stepladder since this is a temporary outdoor
installation when I use the sawmill.
I did a quickie setup with 8' of channel extending out 4' from the
shed to cut one 750# log into two lighter pieces and realized that the
16' track I hadn't completed could be suspended from the shed roof
beam at its center splice, which makes everything simple. With the
shorter track I had to set up an end support to bring the log out,
remove the support to cut, replace it to flip the log and remove it
again to size the second piece, as the log had been roughly squared
oversize before drying. An 8' track over the saw would let it pass the
end support, the other 8' gives 4' to pick up the logs in the shed
plus 4' out the other side to put the finished beams on a trailer.
The center-supported track is easy (except for erecting it) but I want
to consider how to splice a single span so I don't do anything
regrettable when drilling for the center-supported splice plate. I
think I'll drill the web and leave the flanges alone.
For the single span I can have a tie plate below but not above the
lower flange, so the cap screws will be in single shear, tapped into
the flange and probably the splice plate too, for better bearing. I
can afford the extra machining work and custom fitting on one small
home project that only I will assemble.
My understanding is that if the lower tension splice plate has about
the same cross-sectional area as the flanges, it will stretch at close
enough to same rate to distribute the load on the bolts evenly instead
of shearing them progressively. I think I should use only one row to
minimize lost area. I've been using Grade 8 3/8" bolts which are
smaller than the AISC manual lists.
I couldn't find where I saw how to arrange rivet holes to minimize
both the loss of strength and width of the joint. In this instance I
think I can just make the lengthwise bolt spacing and splice plate
longer.
-jsw
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I think I misunderstood your layout so I better stop "helping" :-). The
link you posted to a splice diagram showed an I beam, so I assumed you were
using two C channels back to back to simulate an I beam with a thick
vertical web. If that's the case I still think my three splice instead of
one layout would be almost as easy to assemble and would be stronger. Just
for confirmation, the program I use (Engineering Power Tools, free or
shareware for more features at
www.pwr-tools.com) gives peak stress 24.9 ksi
and 1.32" deflection for 1000 lbs at center and 16' span for one C channel.
--
Regards,
Carl Ijames