Big ones, actually. I need two pieces of steel tubing, each 25 feet long, with an OD of approximately 1 inch, and a wall thickness of at least 1/8 inch (or maybe solid-steel rods, if they're cheaper). The goal is to have something very stiff, since it will be supporting a lateral load of 200+ pounds.
Not being an expert, but needing something weather-resistant, I assume I can either buy stainless steel, or a less-expensive steel that I'll need to paint to keep it from rusting in the rain.
Does anyone know where I can buy something like this (preferably without spending a fortune)? It isn't the sort of thing Home Depot carries!
Maybe some more information about the intended use would help. Does it have to be a seamless length? Exactly what is the support and where is the loading? 25 feet of 1" tubing with an 1/8" wall would be pretty flexible.
Did you watch Monster House this week? They did a patio cover where the fabric slid up on cable in 2' widths. I didn't catch all the details, but it looked pretty cool (and maybe easier to handle than 1 huge sheet).
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Joel. phx
I have an 18' x 45' pool and rolling the solar cover on the 19'x4" aluminum tube is a royal pain in the AZ.
So we have a 25' (300") beam supported at the ends and with 200# load uniformly (assumption!) distributed along its length. 1" OD, 1/8" wall would be grossly overstressed and even in a super alloy would be like spaghetti.
2" OD, 1/4" wall is more to the point but even it would have over 4" deflection at the center. BeamOut (0 150 300)(30E6,I_tube 2 .25)Beam 0 300(0 300,200÷300) pos'n pt. distrib shear bend. slope def'l force force stress stress 0 -100 0.6667 -143.6 0 0.04656 0 150 0 0.6667 0 -13970 0 4.365 300 -100 0.6667 0 0 -0.04656 0
Ted: Thanks for the bending analysis! Very useful. Looks like I should go for a 2" diameter, with 1/4 inch walls, if I can find such a thing.
Brian: Yes, the wind is definitely an issue. That's why I'm using 1/8 inch steel cables to support the canopy. The cables are attached to steel posts bolted onto concrete-filled masonry fence pillars. The canopy is already up, so I can see what the wind does. What's missing is the ability to roll it up for storage, which is what I'm trying to work out now.
ATP: Measure a similar canopy? I'm afraid this one is sui generis (one of a kind). Haven't seen any others like it.
Thompson family: Local gas company for 40-foot steel pipes? Interesting idea, although it looks like I'll need a larger diameter.
Paul: 21 feet by 4.5 inches? That's quite a tube! Unfortunately it has the wrong dimensions for this project.
I was hoping a suggested vendor, but no such luck yet. Maybe this is the wrong group. Is there a rec.crafts.longsteelpipes?
Stiffness varies as the square of radius so 2" OD will be 4x stiffer than 1" OD. You're "winding a web" which helps. As the pipe deflects toward the load, distribution of tension in the web will transfer load to the less-deflected pipe closer to the bearings.
You can buy 20 foot lengths of pipe at a steel yard, Nominal 1-1/2" pipe is 1.900 OD, nominal 2" pipe is 2.375 OD. In the 2" pipe, std and schedule 40 pipe has wall thickness of .154", and weighs 3.65 lb/ft, schedule 80 is .218" wall and weighs 5.02 lb/ft. (These figures from a chart my steel suppier hands out.) I'd expect to pay about 40 cents a pound in Minneapolis. I'd think that std/schedule
40 would be quite sufficient for your job.
Joining two lengths in the middle to get your 25 feet would be no problem. I'd machine an insert 6" long from smaller pipe, plug it in and buttweld the joint. A good welder could probably do it on V-blocks and probably wouldn't need the insert to keep things straight, but that's how I'd do it for strength and staightness. Grind the weld flush so it doesn't make a track in the middle of the fabric.
You might even find galvanized pipe. If not, for rustproofing, I'd paint it with a zinc-rich primer like "instant cold galvanize" from LPS. If you have a W. W. Grainger near you, their house brand "Dem-kote" is just as good and somewhat cheaper. This stuff meets some mil-specs for rust resistance and costs less than $5 a can. Aside from the mil-spec claim, it works. I've been using it for 25 years on various fabricated steel objects that don't need to be pretty. Pretty it ain't (matte gray finish that doesn't always level out well) and it doesn't accept topcoats well at all, , but it does do a good job of preventing rust.
Shake the can and rattle the ball within every 30 seconds. I'm not kidding! The zinc dust settles fast in the can if you don't, then the nozzle plugs and that can is done working.
Not true, Don. Stiffness is the reciprocal of deflection - more stiffness = less deflection. Deflection is inversely proportional to moment of inertia, I, so stiffness is directly proportional to I. For a solid round rod, I is proportional to D^4. For a thin walled tube, I is proportional to D^3. For 1.5 and 2" pipe, neither case applies so we have to deal with the details.
Comparing 1.5 and 2" schedule 40 pipe, Nominal OD wall ID I 2 2.375 0.154 2.067 0.6657 1.5 1.9 0.145 1.61 0.3099
giving a ratio for I of 2.15 so the 2" would be a bit more than twice as stiff.
Personally, I'd prefer to avoid welding at the point of maximum stress (the middle in this case although using your procedure should be more than adequate. I'd probably weld 5' on the end of a 20' length.
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