Thread: How much can I safely lift on this structure?

Hi Bryan,
No it's not a skillion roof, it's just like yours with different trusses. The picture was only to show the truss design, & I wouldn't lift much with that hoist. It's great for lifting cement mixer in & out of the trailer, welder likewise. I also use it to lift the ride on mower up to a vertical position to change the blades, I don't think this is unsafe as when the mower is vertical, 100% of the weight is through the front wheels onto the cement floor. the hoist would only have a few kilos keeping it there. I have suspended 750 Kgs from the roof trusses using a 1 ton chain block. But only to lift the load 50mm above the ute bed, remove ute & lower to machinery skates. "Gallegos" hoist is what I was trying to say, legs spread at the bottom, triangulated at the top, & most importantly, horizontal beam on TOP of the legs. While I am typing, I have some serious concerns regarding the electric hoists on Ebay (the same as the one in my picture.) The spool end of the shaft is mounted in a bearing that is fitted into a depression in the end plate, providing it stays there it could support the design load. The other end of the shaft taking the load is mounted in the gear box fitted to the motor, this is only held to the mounting frame by 2 bolts threaded (in tension) to the aluminum motor frame. If these bolts stripped, it would allow the motor to drop & that would release the other end bearing from its seat & gravity would win. I have strengthened mine by just putting a simple strap to support the motor, as this is much further away from the spool, the load is less than on the motor bolts. The side straps look like about 30mm x 3mm & the bottom is about 40mm x 16mm solid bar. The top of the straps fold over about 50mm on top, but I was concerned that they might spread, so I just tacked a piece of 12mm square tubing to stop that. The motor had a cast block with a depression already there, so I just turned up a bolt with a blunt cone on its end. I tightened the bolt by hand & then gave it another 1/2 a turn with a spanner & locked it up. Its just a fluke that the only pic I had of the roof truss included the hoist. I do know where you can get fantastic cast iron wheel in Adelaide but they wont be cheap, the have polyurethane tyres with 2 ball races & can each support 400Kgs.
tinkera

I am wondering if this I-beam be strong enough for the task?
Steel and Containers - Retaining Wall Beams

Jackaroo, thanks for the link. The biggest size listed is 150mm. Based on Gorbel's specs, and on the assumption I-beams is I-beams, 6 inches will give you a 1 ton rating up to a span of 12 feet, or 4.2m. That would be more than enough span but not enough weight for me. I'd like at least 2T. Why shortening the span doesn't appear to increase the rating is puzzling. But increasing the beam depth does. So I would need 8" according to Gorbel.

Originally Posted by Bryan

Why shortening the span doesn't appear to increase the rating is puzzling. But increasing the beam depth does.

1 ton is the max point load of the flange? Increased beam depth will also have a thicker flange.
Well thats my guess

Stuart

Originally Posted by Bryan

Jackaroo, thanks for the link. The biggest size listed is 150mm. Based on Gorbel's specs, and on the assumption I-beams is I-beams, 6 inches will give you a 1 ton rating up to a span of 12 feet, or 4.2m. That would be more than enough span but not enough weight for me. I'd like at least 2T. Why shortening the span doesn't appear to increase the rating is puzzling. But increasing the beam depth does. So I would need 8" according to Gorbel.

A shorter length beam would give an increase in weight. You just need to find the right information.

I just realised that I have mentioned triangulated support above my lifting beam. Nobody mentioned this! Is this due to not picking it up or just being polite? This would of course be pointless. The support is below the beam. A 125mm length of pipe welded under centre and reo stretched over this from end to end. 50mm of weld each side at the ends plus some on to the pipe end.

Dean

Originally Posted by Oldneweng

Is this due to not picking it up or just being polite?

We try to be a polite lot

Another guess at the load not changing with span is that its the SWL of the hoist trolley

Stuart

Yeah I was being polite. Glad to hear it's actually the right way.

When I made my gantry I was appalled at the price of UB's, so I welded my beam/truss from 50x50x2 RHS, I beefed up the top member that has the trolley running on it to 4mm wall. The gantry will straddle a truck, clear span is 2600.

There are pluses and minuses to doing it this way. The main downside is that the truss being made from light tube needs to be a lot deeper, which can be a problem if you are scratching for height. The truss is 400 deep when I would have probably got away with a 200UB. The upsides are that the finished truss is light and manageable for 1 man and that you can tuck the chain block up inside, which saves a bit of height.

Thinking about beam or truss strengths in general, you need to know how much the beam will bend at its design load, you can have a situation where a beam safely supports a load but at the same time bends alarmingly. This is particularly important for gantries, because as the beam bends so the legs splay which throws more load onto the beam etc.

Originally Posted by Bryan

Jackaroo, thanks for the link. The biggest size listed is 150mm. Based on Gorbel's specs, and on the assumption I-beams is I-beams, 6 inches will give you a 1 ton rating up to a span of 12 feet, or 4.2m. That would be more than enough span but not enough weight for me. I'd like at least 2T. Why shortening the span doesn't appear to increase the rating is puzzling. But increasing the beam depth does. So I would need 8" according to Gorbel.

it's a long long time since I last did the sums, but beam size for lifting point loads depends on
acceptable deflection of the beam -- which is usually set very low, something like a 1mm deflection over 3m span
flange buckling -- I don't recall how to calculate this but from memory, a UC is not as strong as a UB because the UC has a wider flange which buckles more easily
web buckling -- again I don't recall how to calculate this but it's a critical failure mode, when the web starts to buckle the beam can suffer catastrophic failure
vertical supports
the connection between the supports and the beam

oh, and I-beams are not I-Beams, for one the steel strength varies (250 and 350 are the two grades which stick in my memory), then the rolling profile can be different between manufacturers and countries
because of this I'd be very cautious using a catalog from another country

Excellent info guys. I may not reply in detail to every post - shed time and computer time are both a bit scarce for me right now - but I am reading carefully and appreciate it, and I hope others may find it useful too. Will try to catch up on some replies later.

Originally Posted by Bryan

Jackaroo, thanks for the link. The biggest size listed is 150mm. Based on Gorbel's specs, and on the assumption I-beams is I-beams, 6 inches will give you a 1 ton rating up to a span of 12 feet, or 4.2m. That would be more than enough span but not enough weight for me. I'd like at least 2T. Why shortening the span doesn't appear to increase the rating is puzzling. But increasing the beam depth does. So I would need 8" according to Gorbel.

I did a quick check and a 150UB14 should be good for about 2t with a span up to 2700mm being a little conservative.

Originally Posted by bob ward

Thinking about beam or truss strengths in general, you need to know how much the beam will bend at its design load, you can have a situation where a beam safely supports a load but at the same time bends alarmingly. This is particularly important for gantries, because as the beam bends so the legs splay which throws more load onto the beam etc.

For short spans deflection is not usually an issue so personally I would just design for strength and not worry about it. You can check it but I never bothered. The legs and their connection to the beam should be designed for a bit of bending regardless to cope with side loads like if it is moved while loaded or used to not lift vertically. Its likely these loads are not going to be very large but I chose to add bracing between the legs and the beam anyway to strengthen it there on mine.

Originally Posted by ian

it's a long long time since I last did the sums, but beam size for lifting point loads depends on
acceptable deflection of the beam -- which is usually set very low, something like a 1mm deflection over 3m span
flange buckling -- I don't recall how to calculate this but from memory, a UC is not as strong as a UB because the UC has a wider flange which buckles more easily
web buckling -- again I don't recall how to calculate this but it's a critical failure mode, when the web starts to buckle the beam can suffer catastrophic failure
vertical supports
the connection between the supports and the beam

oh, and I-beams are not I-Beams, for one the steel strength varies (250 and 350 are the two grades which stick in my memory), then the rolling profile can be different between manufacturers and countries
because of this I'd be very cautious using a catalog from another country

Good point on the sections from other countries. Typically australian hot rolled sections are 300 or 350MPa and colled rolled like SHS and RHS are 350 or 450MPa but if you are using old material or are not sure of the origin assume 250.

Deflection limits are usually suggested to be L/250 for most beams (length of the beam divided by 250 ie 1mm for a 250mm long beam) but I think it might be L/500 or L/1000 for crane beams. Generally deflection limit are more about making it look right... going over them may not effect the strength but can make it look 'funny' and people will inevitabley comment on it.

If you use sections that are compact these are limited by strength of the material not buckling of the flange or web. The steel tables i listed before state whether a section is compact or non compact. Stick with compact sections (which most are) and youre good. The only thing to add to this is to be take care how you load the beam as localised loading can invalidate this. Running a trolley on or slinging over the top flange of a beam which is in compression can cause enough localised bending that it will buckle. This can be allowed for by adding stiffeners between the flanges if its loaded at a single point or using flat bar to thicken the top flange for a trolley. This could also be a problem if you make a truss style beam using RHS if the top section isnt heavy enough or the bracing is too far apart.

Also found the steel table for RHS and SHS http://www.edconsteel.com.au/library...d_sections.pdf

Hope this info helps

Bob Ward, nice fab work. You're obviously confident in your welding. I'm only a 'farm gate' sort of welder so I'd have some qualms about tackling that type of structure. I just rang my nearest steel supplier about universal beam. He told me in 150mm it comes in 14 or 18 kg/m, and 200mm in 16, 18 and 22 kg/m. So that obviously relates to the cross-sectional area. He quoted 18kg/m at $40/m in either size. He didn't know about Mpa ratings. So I don't know what you were quoted Bob, but that doesn't sound too bad to me. I mean I would expect to invest a few hundred dollars in material for this, maybe $500 with wheels and paint? How much do you reckon you spent on tube?

Originally Posted by bob ward

When I made my gantry I was appalled at the price of UB's, so I welded my beam/truss from 50x50x2 RHS, I beefed up the top member that has the trolley running on it to 4mm wall. The gantry will straddle a truck, clear span is 2600.

There are pluses and minuses to doing it this way. The main downside is that the truss being made from light tube needs to be a lot deeper, which can be a problem if you are scratching for height. The truss is 400 deep when I would have probably got away with a 200UB. The upsides are that the finished truss is light and manageable for 1 man and that you can tuck the chain block up inside, which saves a bit of height.

Thinking about beam or truss strengths in general, you need to know how much the beam will bend at its design load, you can have a situation where a beam safely supports a load but at the same time bends alarmingly. This is particularly important for gantries, because as the beam bends so the legs splay which throws more load onto the beam etc.

This is not the ideal design for a truss. The vertical tubes on the truss should be at 45 deg and touch one another so there is no cross beam without a angled beam above it. Using this form of triangulation will add enormous strength. A friend of mine told me many years ago that to determine a good design for structural work such as this, start by visualising the design with hinges at each join. Draw it or even model it with mechano etc. The truss in the above design would fold up like a card table. Triangulate the truss and it will not budge. The angle can be adjusted to suit the length of the truss. Have a look at a roof truss for a house, built out of timber. All triangles. I am trying to find an example but my internut service is running verrry slooow. If you see this post consider it lucky, or not!

Found one.

Truss Sample.jpgNot exactly as described but this is a vastly stronger structure. Picture this with hinges at each joint!

Dean

Originally Posted by gallegos

This is the gantry i built for my shed out of left over 100UC i had from a job. It breaks into 3 parts and i can change the length of the top beam if need be. From memory i think its good for about 2t. <snip> I built it specifically to move my lathe around.
Attachment 284750

Gallegos, what are the height and span of your design? Have you ever found these dimensions limiting? My current thinking is minimum span would be to clear a trailer, so say 2.4m, and clearance under the roller door is about 2.65 so under beam height would be 2.5 at best. Which sounds pretty skinny for a mill, even on a trailer. And no good for a truck. Sounds like you weren't interested in vehicle loading.

I was going to ask about the beam but I think I get it. Once I zoomed in I could see the bolts. You've doubled the centre section and bolted the ends to the braces. Looks real sturdy.

And I think I like the A frames instead of the usual inverted T with bracing. But if I wanted height adjustment I would need the verticals.

Hey Greg, can we see your Rolls?