strength of inch plate?

Hi all, Am hoping to build a couple of stands for sitting dump truck bodies on, the bodies weight somewhere between 60 and 80tonne. I want them up on stands so
i can get to the bottom of them as well as the top as we need to get a crane in every time we roll them over. I had in mind to build a 'triangle' shaped stand so that the part contacting the body would be as thin as possible and allow the best access for welding. I had no fixed height in mind, but was thinking either short enough to sit on a chair under the body while welding, or tall enough to stand under the body while welding. a triangle seems like the strongest shape, and i was hoping to not do any internal gussets/bracing except for two pieces of RHS somewhere at mid height to get the tines of a forklift into.
Anyone with a bit more knowledge than I've got who can tell me what size of material I'll need to support these bodies? There will be two stands, and a max body weight of 80 tonnes, so lets be on the safe side and say that each stand must hold a minimum of 60 tonne. will inch plate get me there or do i need to be thinking more like 40mm?
Thanks, Shaun
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This kind of support really needs to be engineered. You might find a unit you can copy at a local mine site. My concern with single stands is that you have to ensure the ground underneath does not shift or sink. I have seen concrete slabs start to sink under large loads like that. For such loads I would consider sawhorse designs made out of six inch rectangular tube with half inch wall. Two sawhorse style stands would provide you with eight contact points with the ground. If one or two locations should sink or crack it is no big deal. Four separate stands gives you a one in four chance of settling. The sawhorses give you one in eight. The other thing to consider is that when turning and settling the load onto the horses you could give the supports a shock/impact load double or triple the static load without actually dropping it. To make proper supports you will have to spend big dollars on material. Either get an engineer or ask the manufacturer of the dump boxes. They might supply you with a design for a reasonable charge. Randy

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On Mon, 07 May 2007 09:04:03 GMT, "Shaun Van Poecke"

Remember a credo that has been modified time and again, yet still stands everywhere: The demands of the job are never so urgent that we can not take the time to do the job safely.
I can guarantee if your insurance carrier gets wind of this plan first they'll go white as a ghost, then they'll be calling as soon as they get over the shock.
You need to have any work stands like this done locally by a registered structural engineer who can look at all the details, and give you certified plans with his seal on them, meaning he's willing to stake his reputation on them - would /you/ go under an 80-ton truck body supported only by matchsticks? I sure as hell wouldn't.
If these supports give way it wouldn't be very healthy at all for the guy under there welding on the bottom side - Worse, he's going to be so busy concentrating on making a good weld he might miss the initial warning signs of the collapse till the work starts moving in front of his mask...
Seriously, if this was my problem I'd put in a requisition to buy or lease a bigger crane for the shop, so you don't have to call an outside firm every time you want to flip a body over or hoist in a fresh slab of wear steel. And do your welding work from the top or side, where there's much less crush hazard. If you want two people working at once, put it on it's side, and leave the crane attached so it can't roll.
Besides, with overhead welding and cutting there's a much higher chance of getting white-hot Slag Dingleberries dropping and bouncing into places you /really/ don't want them.
"AAUGH! My Biscuits are Burning!!!" ;-P
--<< Bruce >>--
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wrote:

Thanks for the suggestions Bruce. We dont have any local structural engineers, and the ones who are distant prefer to sign off on work that to actually do any of it themselves. If they design something and it doesnt 'fit' then they have to pay for the cost of materials/alterations to be done. To give you some idea of the cost involved, a simple drawing in autocad (basically measuring up then drawing) with no engineering work costs somewhere between AU$5,000-AU$7,000 - with no liability. Getting something as basic as a stand measured, designed, engineered then drawn would likely cost more than my entire years wages. I was hoping to go with something a bit more substantial than mathcsticks in the end though. I usually start my viewpoint on these things by looking at the chassis and pivots on the actual truck being used. If the truck can hold the tray at only 4 pivot points (2 hinges and two ram attachments) fully loaded up at a couple of hundred tonnes, then a similar structure has an excellent chance of supporting the same tray empty.

We have a few cranes that are big enough for this, but its an ongoing refurbishment contract, and last time i checked the cost of a 50T crane came in at about AU$500,000. A 130 tonner costs a fair bit more than that. We hire our cranes out on site, and if we were to have them in the shop 7 days a week holding up trays while they were being welded then I'd probably lose my job, just shortly before everyone else in the shop lost their job due to the company going bankrupt. After having analysed the situation, a stand seems like the most logical way to go, for many reasons. It just needs to be made right.

Ive done my share of overhead, and burnt more parts of myself than i care to mention in the process ;-) Thankfully the guys on this crew wont have it quite so hard as i did..... they'll have fully enclosed speedglass helmets withforced air respirators (almost like air con for your head), hoods, leather jackets, aprons and spats. Best of all, they'll be welding with 715 supercore wire and a 75%argon 25%CO2 shielding gas giving some of the easiest spatter free vertical up/overhead that there is to be had. Almost makes me want to go back to welding. Nah.
Shaun
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Shaun: Some thoughts / questions:
1. How do you propose to get the dump off the truck without a crane or other lifting device? (I must have missed that part of the thread.)
2. Your analysis of the fact that the truck can support the dump at only four points when loaded is essentially correct. A suitable stand can be designed if given a little thought.
3. For a 80 ton (assume 2200 lbf. ton) dump, that's about 200,000 lbf. total. Most steels can carry 200,000 psi in compression. So if your "stand" was simply steel plates stacked up to the height you needed you would be fine from a compression stand point. Simply make the footprint of the stand big enough to reduced the floor weight to an acceptable level while assuming each stand takes the full 200,000 lbf.
4. Side loads, as stated preveously, will kill you. Literally. Keep the stands low as possible. Tie the stands together with rod or cable to prevent them from sliding out with respect to each other. Consider safety cables attached to the building if you don't have a crane in case the dump decides to move off the stands.
5. Consider renting the crane to proof your design. Lower the dump and balance it on a single stand. If the stand supports the weight for 15 minutes you're probably OK to use them 4 at a time.
6. If you are going to use a truss design (tripod) then the legs of the tripod should be made from material no smaller in diameter than the diameter of the pivot pins when the dump is attached to the truck. Hollow tubing is Ok, but the wall thickness should be at least 20% of the OD (SWAG). It should go without saying that the legs of the tripod should be welded or otherwise connected together to a common base so they can't splay out.
Hope you can find some useful nuggets here. Good luck.
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On Tue, 08 May 2007 12:30:54 GMT, "Shaun Van Poecke"

Okay, but IMO the tone everyone here read into your initial posting was "No Worries, we just need to prop it up on a couple of sawhorses, and it's good to go!" And since we have a pretty good idea just how heavy the beds on a mine dump truck are, you can see why we got just a wee bit concerned... ;-)
DISCLAIMER: I've dealt with this kind of problem, but not anywhere near on this scale. My 'big gun' is only a ~225A MIG.
I would approach this as a one-piece frame that hits all four truck chassis mount points at once with round tubing saddles hitting the same contact points, vertical square/rect tubing posts down, and a simple square tubing frame flat on the floor.
Some big pieces of heavy plate to spread the weight out onto the floor slab evenly at each corner would be prudent, and put two knee braces at 90-degrees on the outside angles of the posts to leave the inside work area clear.
ASCII Art, sectional view:
DUMPTRUCKBED O O | | /| |\ / | | \ ======J======______ _______ concrete floor slab or compacted gravel base
If they make different sized beds (or different truck makers that use different bed dimensions) and the one work stand needs to be adjustable to fit them, cut the four base frame tubes at the four (ADJ) points and make slide joints that will couple any torsion across.
I was going to say nested 'seamless' square tubing (like a trailer hitch receiver), but I don't know how big they make it. If the tubing is big enough, you can get your arm in there with a small 4" angle grinder and knock the inside seam flat.
And put a 'floor' of thin plate or heavy expanded metal on top of the workstand's base tubing as a walk surface for the workmen.
If it's a one piece braced stand and overbuilt by a decent margin, that will greatly reduce the odds of the loaded stand unintentionally turning into a parallelogram. || to // to _ _ with lots of screaming and running like a bad Godzilla movie...
(Oxymoron - Like there's ever been a good Godzilla movie?) :-P
Oh, and if the stand is square and sturdy the truck bed should stay square too, which is kind of important if you find you have to cut the entire bottom sheet out and start over. At this scale you can't just "warm it up with a Rosebud, get out the Big (Fine) Hammer and give it a whack" to get it back on the truck chassis.
--<< Bruce >>--
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wrote:

"I just don't understand how that could have happened - the guys on RCM sain one inch plate should be fine"
John Martin
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It is hard for me to imagine a better solution than trying to find something ready made and designed for the task.
i
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Id agree with you in normal situations; i rarely have made a tool for a job that couldnt be bought, not even for the (sadistic) pleasure in it. I wouldnt waste my time builsing stands for my car, even though i could easily make stands that are better than anything i could buy in my local auto store, and i dont even have to pay for materials. Its just *easier* buying stuff.
But when it comes to something like this, there just isnt that much available. I dont know what the situation is like in the states, but even in a town like the one im living in, surrounded by nothing but desert and mines for the next day's drive, there isnt that much *really* heavy equipment around, despite being surrounded by 240tonne dump trucks. What most places do is pretty much what some of the guys on RCM have done; pass the buck. They say they cant handle it, havent got the cranes, havent got the stands, havent got the experience, havent got the labour.
I work at the biggest shop for about 1200 miles. But even we dont have the stuff to deal with this job. Yeah, We've got a few cranes, a few 50 tonners and a 130 tonne. Despite calling around to the other shops that were 1200+ miles, All they could tell me is that they had to build their own stuff. I could have said that we couldnt deal with it either, but I think we can. By following appropriate safety procedures and taking things one step at a time, im sure we'll get there.
I dont come from an engineering background myself, i come from a boilermaking background. I was lucky enough to get a chance to move up into managing projects this year, and im doing the best that i can. Around here (as im sure it is in most places) many supervisors are well behind the eight ball when it comes to project management. Materials are ordered after they are needed, drawings are examined when the shop staff dont know whats going on, plans are drawn up after the fact.
I try to be a bit more proactive.... This project isnt coming up for another month or so, but im trying to get in early, think about the logistics of how to handle the job, what equipment and consumables to use, materials that will need to be ordered, as well as the nitty gritty of who will be doing what, and in what order. Rest assured, RCM wont be the final say on what happens, especially in terms of safety ;-)
But its still a good place to start. For stands above 750kg (1650lbs) in australia they require engineers certification. 60 tonnes well exceeds that. But the usual process is for someone involved in the actual work to draw something up, run it by an engineer who will either approve it, or give some suggestions about what needs to be changed. Once the engineer signs off, neither the specs, the material or the process can be changed. The SWL as specified by the engineer must be welded onto the stand.
Calling around to suppliers was my first port of call, then i asked others who were doing the same or similar work. RCW was my next port of call, then i asked contacts i know locally who have had some experience in the past. Coming up next will be an educated guess based on all these factors plus my own experience, then flipping through some engineering books. Then submit the drawing to an engineer, see what the feedback is, if good, go ahead.
If someone ends up crushed (most likely to death) because of something i design that an engineeer signs off on then the engineer will be going to prison, not me. Getting engineers to sign off on things releases my duty of care, which is all that anyone cares to do in this day an age of so called 'safety awareness', but that kind of safety is only a way of looking out for number 1 as far as i can see. The way i see it, I wouldnt want to get crushed to death (or even hurt at all!) myself, and I'd have a pretty hard time living with myself if someone else suffered because of my effort or lack thereof, so i put the time in and find out as much information as i can before going ahead with anything.
Shaun
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Try sci.engr.joining.welding and those boys have a lot of experience.
Welders are a "different" lot. If it was me doing what you are doing, the job would be done already, and either success or failure would be achieved. Lots of us welders just "fly by the seat of our pants" and try things.
In your post, the thing not stated as being a sure thing, and IMHO, is very important is: how high will these be? If you are intending to make them one foot tall, that is worlds away from them having to be six feet tall. The shorter the better. Even if the welder has to be inconvenienced to weld in the overhead position. This is no big deal to a real welder, but they are becoming harder and harder to find in today's job market. Do all the welding you can in the flat position.
The specificity of your placement system now comes into play. You said "crane", but there's a world of difference between a crane on treads, one on wheels with outriggers, and a gantry crane. A lot of difference in the way they handle loads, and the sensitivity of handling materials. Call it "touch", or whatever, but when it comes to moving such big things, a smooth lift with smooth movement is preferable to herky jerky.
Now, lastly. I think for what you want to do, pyramid shaped would be monstrously strong, as you would have the pyramid outer structure's support, and could also put in vertical gussets. The compression strength of anything is incredible on end, as evidenced by the difficulty of breaking an egg in your hands by squeezing on the ends. But then, something as simple as a tic-tac-toe box on end would be incredibly strong, too.
Iggy made an outstanding suggestion in that you buy something preengineered for the purpose. I know in some cases, these things are made up as they go along, and are really one of a kind, but you might find Iggy's suggestion to be the shortest time wise, and the most efficient cost wise.
Personally, I would not hesitate to make some pyramid shaped or tic-tac-toe supports, with fork attachments for moving. I just wouldn't cut anything out of the supports for forklift tines, but rather add them on in the form of channel, or do the simple thing and make a dolly to roll them around, and a short chain to lift them off the dolly. You already have a crane. Maybe even make it hydraulic so you can pump it up, roll it, then drop it in EXACTLY the right spot. Or even roll them under the dump body as it is lowered by the crane.
One inch steel is GAWD awful strong in compression strength. It's just the sideloading you have to watch out for. I would use a welding positioner, in your case, the crane. You have it, and it's free, where a welding positioner would cost more. Do HOT welds in the flat position, and pour the metal in there, 7018 being my favorite, but in this case, even 9018 or 11018.
Have someone who at least is proficient in engineering help you arrive at a configuration as to angles and reinforcement and safe working loads.
But, I would think a baseplate, pyramid, and internal compression bracing of 1" steel would be adequate for what you want to do. I like the tic-tac-toe box, too.
And remember that the more you use, the more you divide by. IOW, four supports will hold 1/4 the weight, where three would support more weight for each support.
Lastly, don't forget that if you can leave the crane attached, that the crane will be supporting some of the weight, and the stands won't be holding all that much.
Lots of things to consider. To a welder, it's like a puzzle. Let's try this.
Hmmmmmmmmmmm. That didn't work worth a flip. Where did it fail? Lets try that ........
Welders love puzzles. We're problem solvers while everyone else is standing there scratching The Twins.
Keep us posted.
Steve
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What Steve said.
i

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Thanks John, Im sure you blindly follow every bit of advice you hear too ;-)
Shaun
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Those are big loads but I'm less worried about the strength of the assembly than I am about the side loading when setting the assembly down, the base to height ratio, and the surface you are setting these down on. Even if you are working on 10" of reinforced poured concrete, I'd have some issues of point loads, tipping, etc. If you are working on any sort of soft surface exposed to the elements, you need some serious review of what you plan on doing.
As others have said, buy off the shelf or get an engineer in to review and sign off on what you do. Really cheap compared to the alternatives.
Shaun Van Poecke wrote:

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If I was forced at gunpoint to make something like that (say 2 feet tall), and if I had no access to an engineer, I would simply stack squares of plywood, 1.5-2 ft in size, glued one to another, lying horizontally on top of another, and put a 1" steel plate on top.
My preference would be to just buy something off the shelf.
i

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Then you might have gotten shot in the head ;-)
I had a talk today with another local business owner who had done this sort of work in the past, he said avoid timber at all, even hardwoods as these sort of weights will make timber explode. If they sold 60 tonne stands on the shelves, I'm sure I could talk our accounting department into buying a few.
Shaun
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Right. Wood timbers can take a few hundred pounds per square inch perpindicular to the grain (actual number is a function of species, grade, and condition) and they don't take point loads well (they crack and split) Much stronger in axial compression.
Shaun Van Poecke wrote:

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Shaun Van Poecke wrote:

That business sounds like they don't have a clue what timber can do. Maybe visit a shipyard where they are laying a ships keel and take a look at the the WOOD blocking they are using. The entire ship gets built on that timber. When complete there is FAR more than 60 tons on it and it doesn't move. Might compress it some.
--
Steve W.
Near Cooperstown, New York
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Also note that plywood does not have the same structure as timber. (due to crosscrossed layers of wood)
If I had a 20 ton shop press, I would be tempted to make a model of a plywood block that I mentioned above -- appropriately reduced in size for the reduction of load -- and apply the press to such a block.
i
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Steve W. wrote:

I'm glad it wasn't just me that was confused. Cribbing is the material of choice for most large load temporary support. If it will hold up a freeway section or a ship keel, I'm sure it would work for 60 tons.
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I'm sure, though, that certain woods are better than others. I know some of the lighter stuff crushes easily. Oak palettes are certainly better than pine ones. Someone who's really familiar with shipyards ought to know that.
Steve
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