Splicing gantry track

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:

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 =============================================

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 :-).

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

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 =============================================

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

gives peak stress 24.9 ksi and 1.32" deflection for 1000 lbs at center and 16' span for one C channel.

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 Wilk> Is there a standard way to splice gantry hoist track made from two

Your assumption is correct, two channels back to back with sections of

3/8" plate between them at the ends as hangers and as splices between 8' lengths. The 3" x 16' track I've been using to move logs in and out of a shelter hangs from a roof beam at the center splice and this 4" x 16' one will too, in another shed that has become storage for squared timbers. At this point creating a 16' free span gantry from the 4" channels is just a design exercise, to see what I could make from my materials.

I do like your idea of staggering the joints but it prevents assembling the four channels as two separate 8' sections with higher load capacity than the 3" channel I'm using now, one to load the trailer and the other to unload and stack, and I don't have another piece of 4" channel to cut in half. My 3" and 4" channels came from a stack of used pallet rack parts at a surplus store that closed. The nearest metal dealer recently quoted me $120 for a 4" x 20' channel, cut in half so I could bring it home.

I have extra 3" channel and 3.5' of W6x9 beam that I picked up to reinforce the splice somehow, perhaps bolted on top to go with a plate under the tension flange, but that challenges my limited ability to calculate and I have no idea how to figure the assembly's resistance to buckling, I proof test my homebrew hoists on a stump with a 1000 Kg crane scale.

Thanks for confirming my numbers on the stress and deflection of the

4" channel. I'm never sure I didn't miss something with those calculators. Is it true that the peak stress on two channels would be half as much, and acceptable for the working load?

-jsw

I had cut some wide, 2.0" thick oak planks and did consider them to strengthen the gantry track.

"This calculator can also be used to measure beam deflection. Because beams are typically positioned on edge, use "thickness" to represent beam depth and "depth" to represent the thickness of the beam." It accepts the non-standard dimensions of unplaned wood from my sawmill.

The issue I didn't mention here is clearance height under the existing shed roof beams, as the timbers are stacked almost as high as I could get them with 3" channel for the gantry track.

-jsw

Your assumption is correct, two channels back to back with sections of

3/8" plate between them at the ends as hangers and as splices between 8' lengths. The 3" x 16' track I've been using to move logs in and out of a shelter hangs from a roof beam at the center splice and this 4" x 16' one will too, in another shed that has become storage for squared timbers. At this point creating a 16' free span gantry from the 4" channels is just a design exercise, to see what I could make from my materials.

I do like your idea of staggering the joints but it prevents assembling the four channels as two separate 8' sections with higher load capacity than the 3" channel I'm using now, one to load the trailer and the other to unload and stack, and I don't have another piece of 4" channel to cut in half. My 3" and 4" channels came from a stack of used pallet rack parts at a surplus store that closed. The nearest metal dealer recently quoted me $120 for a 4" x 20' channel, cut in half so I could bring it home.

I have extra 3" channel and 3.5' of W6x9 beam that I picked up to reinforce the splice somehow, perhaps bolted on top to go with a plate under the tension flange, but that challenges my limited ability to calculate and I have no idea how to figure the assembly's resistance to buckling, I proof test my homebrew hoists on a stump with a 1000 Kg crane scale.

Thanks for confirming my numbers on the stress and deflection of the

4" channel. I'm never sure I didn't miss something with those calculators. Is it true that the peak stress on two channels would be half as much, and acceptable for the working load?

-jsw ===================================================

First, the usual disclaimer, I'm not an engineer and this isn't professional advice :-). But I've read a lot and done a lot of calculations on mechanical prototypes I was designing that worked as designed. Yes, if you put two channels in parallel with the same total load the peak stress is cut in half. For 1000 lb concentrated at the center of an 8' span a single 4" channel will deflect 0.165" and peak stress will be 12.5 ksi, and a 3" channel will deflect 0.383" and have peak stress 21.7 ksi. Adding a second

4" channel cuts the deflection to 0.083" and the peak stress to 6.3 ksi, and the doubled 3" deflection and stress become 0.191" and 11 ksi. That says that the 4" channel is almost twice as strong so one 4" channel is worth almost two 3" channels. How about if you bolt a 4' piece and an 8' piece of 4" channel to an 8' piece, back to back with the ends flush at one end. That gives you your desired doubled 4" x 8' channel with 4' extra sticking out one end, which doesn't hurt so long as you have room in your shed for it to still fit. Then take the other 4' x 4" channel and bolt it with ends flush to the other 8' channel, and then bolt on a 4' piece of 3" channel with the bottom flanges aligned so the crane trolley can roll the entire length. If your doubled 3" channel is sufficient now, this should be more than enough, and you can unbolt the 3" channel and bolt together the 4" assemblies to make the full 16' span with staggered joints.

Whenever you have a live load, like people walking on a deck or lifting a load that is moving and bouncing, the usual rule of thumb is to triple the load to calculate the peak stress. Then apply whatever safety factor you feel appropriate. For something used once with no one anywhere near that can get hurt I might go down to 2x but for this I'd go at least 4x - remember, I'm not a professional. So if your beam steel is rated at 25 ksi yield I'd keep the peak stress below 25 ksi/12 = 2.1 ksi, maybe less. Others might say that is way too conservative but I never, ever want anything I'm walking under to fall on me :-). Running those numbers in reverse for the 4" channels, 2.1 ksi / 6.3 ksi * 1000 lbs = 333 lbs for a rated load for your 8' span 4" assembly. I said I was conservative.

I could if I found some extra 4" channel, but I have only four 8' pieces and want to pair them into two separate gantries, one to load and the other to unload the trailer. For the squared timber shed application two doubled 8' channels joined at a suspended splice plate is the easy answer. The 3/8" plates between the outer ends of the channels are the cut-off end tabs that attached the channel to the pallet rack columns, and make perfect centerline hangers to shackle the ends to the tripods. I have a scrap 3/8" plate that's a good size for the center splice and hanger without cutting it.

I have one manual chain and one electric cable hoist. The manual one is much too slow to shock load the track. The HF 1300# electric hoist starts with a sharp jerk as you mentioned, but the impulse doesn't seem as bad as the hoist nears its capacity. I bought it so I could lift and stack the timbers from a distance in case the loaded gantry collapsed.

The HF hoist itself works fine but its pipe mount is sketchy and completely unsuited to being suspended from a gantry trolley without some custom metalwork. I welded a squared U frame that bolts to the hoist from heavy angle and made axles and wheels that ride on the 3" channel track, though it turns out not on the 4" channel. That was the

2015 project where I asked about press-fitting bearings into precisely bored recesses.

-jsw

Wouldn't an asymmetrical section tend to twist and buckle as its deflection increased?

These gantries are set up temporarily outdoors on the bare ground and need a leveling adjustment to keep the load from moving by itself, either a tripod whose legs I can move in or out, or a large forged turnbuckle hung from a braced post. . In both cases the channel ends can rotate to some extent, more so with the tripod where the channels hang from chain. A stiffer top connection that constrained channel rotation wouldn't adapt to the uneven ground, plus it would add an unknown amount of cantilever loading that reduces the column strength of the tripod legs which are

8' chain link fence posts or 2" x 10' EMT for lightness. A stronger tripod of 2" x 10' water pipe legs is too top-heavy to set up safely.

-jsw

Have you tried calling OSHA about it? They _love_ this kind of thing.

So you're butting C channel back to back and end to end to get the length and profile you want? If I had 6 pieces, I'd think about bolting (and welding?) two of them on top offset by 4', but I'm not sure I'd call it 1T-ready, since it only adds single flange support.

Resolves to

. But, looking for the word "channel", I found the paper, clicked to DL, and it brought up the abstract with jpgs. He bolts the shit out of that I-beam, doesn't he? ;)

The center support helps immensely, depending on the amount of support it can lend.

Will there be clearance space to add web splice plates since you already pared down the wheels for the narrower beam flanges?

Oh, right. Using C, you can shim/splice between for center strength, then reposition the extra washers on the trolley to compensate.

A 3/8" thick plate or turnbuckle eye between the channels is included in the original design.

That (slightly) modified trolley is derated to stay with 3" channel unless I need to move a light load like the

Wouldn't an asymmetrical section tend to twist and buckle as its deflection increased?

These gantries are set up temporarily outdoors on the bare ground and need a leveling adjustment to keep the load from moving by itself, either a tripod whose legs I can move in or out, or a large forged turnbuckle hung from a braced post. . In both cases the channel ends can rotate to some extent, more so with the tripod where the channels hang from chain. A stiffer top connection that constrained channel rotation wouldn't adapt to the uneven ground, plus it would add an unknown amount of cantilever loading that reduces the column strength of the tripod legs which are

8' chain link fence posts or 2" x 10' EMT for lightness. A stronger tripod of 2" x 10' water pipe legs is too top-heavy to set up safely.

-jsw ===============================================

Yes, twisting is always a concern and my suggestion would probably make it more susceptible. Whether or not that would be the limiting factor in loading, I can't say.

Jim - sounds like the 3 or 4 inch channels are the best fit considering the dimensions of the shed.

Hul

Jim Wilk> > Jim - if you can stick with the 500 pound load, try a 16 ft. 2x12. > > The

In case you haven't followed the disconnected details, I have a good scheme to erect gantry hoist tracks 8' out and in from the roof beam over the shed entrance. The beam was sized to support its share of a foot of solid ice on the roof, 60 Lbs/sq'.

I'm less sure of how I might splice the four 4" x 8' channels into a

16' track that isn't supported in the middle, not that I need to right now, but I don't want to rule it out in the future by drilling holes for the center-supported splice plate that would interfere with an unsupported splice. My question was a fishing trip for ideas.

I think the answer is to drill the web to bolt to the center splice/hanger plate and leave the flanges untouched for now.

-jsw

That thought completely missed me the first run through, likely because you said you turned the wheels to narrow it. It evidently narrowed my 3D mockup.

She's a dilly! Boilerplate web design. What can you say? Or maybe Chinese Sumo wrestlers are picky about their wives' weight.

I couldn't remember the word "sumo" so I googled "japanese wrestler". One of the pics which came up was Asuka, a female, which led to the red latex EVA plug suits. I'm happy to have gone off on that tangent.

Isn't cosplay wonderful?

So are you making a 16' track, or keeping two 8-footers? I'm getting dizzy here.

That won't do at all, though it's lovely. Opposing warlord guards on the castle wall would see a -polished- grappling hook, so it needs to be black. But I already have one, hanging by the front door in case the dam upstream gives out and I need to grapple into heights in a hurry. Now to lose 40# so my arms will lift me...

Look at this inexpensive darling:

Idly fascinating.

Jim - for the free center 16 ft version, take a look at an I beam with the two channel (4 all total) pieces within it in place of the 3/8 in. center support. Cleareance on the bottom could be a problem and the lack of a horizontal surface on the inside of the I beam flanges too. But an I beam in the center gives a greater strength for the greater stresses. You could get a 6 ft I beam and make it even longer...

Hul

Jim Wilk> > Jim - sounds like the 3 or 4 inch channels are the best fit

I bought a 3.5' length of W6 x 9 (?) for the purpose when I got the channel. This morning I used the 25% Labor Day coupon on another HF 1 Ton Push Trolley which fits pretty well on the 4" channels with the W6 sandwiched between. Spacing the channels 3/8" apart moves them off the lower web fillet. The flanges are parallel, not tapered. It helps to finally have all the pieces to play with.

I get a maximum stress of 17.5 KSI for a W6 x 9 16' long, center loaded with 2000 Lbs, compared to 12.5 KSI for two parallel 4" channels. I could abut the upper channel flanges and reinforce the tension side joint with a splice plate, then struggle with moment of inertia calculations for the combination. thanks

-jsw

Jim - you said that the flanges are parrallel; is that the channel stock or the I beam?

Hul

Jim Wilk> > Jim - for the free center 16 ft version, take a look at an I beam > > with the