Another steel channel load question

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A horizontal box tube channel, 2" square, 1/8" wall that is 9' long, and supported only at the ends: how much weight can be safely suspended from it's center? I looked online for structural info on box channel, but could not find the asnwer.    I guess another way to think of it would be how much force applied to the center, would it take to bend that 2x2 box channel, supportedonly at the ends.PrimeWeld 225X TIGMillermatic 180 MigLincoln IdealArc 250Thermal Dynamics Cutmaster 42Cut50 Plasma cutterCraftsman(1980) buzzbox purchased new
Reply:It usually takes very little weight to get something to "bend", the real question is how much deflection is acceptable. You'd want less deflection for say a trolly crane than you would for say a floor joist..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Good point. Deflection that doesn't result in beam failure, would not be of concern. The application is where a 9' piece of 2x2x1/8 is securely attached to the lift arms of a 9000 lb automotive lift. The center of that box channel has a lifting strap around the center, with the 2 hooks attached to the load to be lifted. The load, in this case, would be no more than 400 lb.PrimeWeld 225X TIGMillermatic 180 MigLincoln IdealArc 250Thermal Dynamics Cutmaster 42Cut50 Plasma cutterCraftsman(1980) buzzbox purchased new
Reply:Set your 9' tube on a couple of 4x4's short pieces with your desired clear span and stand on it on center. If you want more weight have the girlfriend jump into your arms. IF girlfriend is stronger, you jump into her arms .

  How much weight are you consider and what's the intended use ? Might be a better design available .
Reply:

Originally Posted by BD1

Set your 9' tube on a couple of 4x4's short pieces with your desired clear span and stand on it on center. If you want more weight have the girlfriend jump into your arms. IF girlfriend is stronger, you jump into her arms .

  How much weight are you consider and what's the intended use ? Might be a better design available .
Reply:I was typing as you posted. As for the tube, you could make a truss design which would help too if this is a more than once use. Heck, DSW and HIS WALLET is 400 pounds, that's nothing !


Reply:It takes an infinitely small amount of force to make something bend an infinitesimally small amount.  Just like DSW said.  Just because you can't see the deflection, doesn't mean it isn't there.  Nothing is infinitely stiff.  How much deflection is acceptable?  Are the ends simply supported underneath, or are they rigidly fixed into a structure?  It actually makes a difference between the two.

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Reply:God I wish my wallet weighed that much. I fall under what would be called the "working poor"..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:@ Will S - focus on deflection first, then stress.  You'll want to conservatively limit your span's deflection to L/360. You ellude to the ends being simply supported, or perhaps one end is moment resistant?  A free body diagram (sketch with loads) would help you/others to "see" the problem.A quicklook structural member calculator available at Structural Calculator. Note, calculator states for galvanized products.Recommend you dig a bit deeper into understanding the pedigree of the calculator.  You should understand the terms F, M, EI, stress, etc before you blindly use ANY online calculator to "prove" your structure is sound and safely supports the static/dynamic loading conditions {design intent}.My on the napkin calc, not taking into account any intermediate bracing, yields ~ 160lbs max vertical load for L/360.Last edited by ManoKai; 06-27-2016 at 07:23 PM.Reason: 1) Note, 2) HandCalc"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:Google "beam deflection calculator."  FWIW, with parameters given I make over half an inch center deflection and 30ksi peak stress which (if correct) would be considered pushing your luck.
Reply:Thank you all for your input. I was using a length of 1/8" wall box channel since that's what I thought I had. Turns out it is 3/16 wall, so that's a bit better. I'll use an inverted truss, with either a piece of flat bar or rod, as that will increase load capacity/safety margin.Now, just so it's better understood, what I'm doing is using this 2x2 box channel to bridge from one lift arm to the other, on a 9000# automotive hydraulic lift. I'm welding 24" pieces of 2" tubing, at the ends of the 9' channel, effectively making it an elongated U shape. The short pieces will fit into the 2" receptacles of the lift arms, where the lift pads normally go. We will attach a lift strap around the center of the 9' span, to lift a 400# outboard motor about 4". I need to replace the tilt-tube on that engine, and there is isn't enough clearance to do it with the engine mounted to the transom. Should take about 15 minutes, then we'll lower it back down, and re-install the 4 engine-mounting bolts. This is a one-time project, and I might have used my forklift tines on my tractor, but the loader hydraulics has developed a leak, and the FEL won't stay where I put it, even with no load.I decided to fab this, to use on an automotive lift, and since where the lift is, there is no fork lift or loader available, in the future, so this might come in handy lifting something out of a pickup truck bed, to set on a dolly. Appreciate all the replies and info provided.Last edited by Will S.; 06-27-2016 at 08:26 PM.PrimeWeld 225X TIGMillermatic 180 MigLincoln IdealArc 250Thermal Dynamics Cutmaster 42Cut50 Plasma cutterCraftsman(1980) buzzbox purchased new
Reply:From MonoKai's calculator: I get 1,093 lbs with 2" square 12 gauge and 9' span. The 1/8" would be stronger and your 3/16" better yet.The 12 ga is 0.109 ".The calculator didnt say whether L360 or not. Im assuming it is L360. For anyone not knowing L120, L240 or L360. Its stands for 1" deflection in 120", 240" or 360".  Or 10', 20' 0r 30'.Your truss would help but wouldnt be needed according to the calculator.
Reply:Thanks! Appreciate the post.PrimeWeld 225X TIGMillermatic 180 MigLincoln IdealArc 250Thermal Dynamics Cutmaster 42Cut50 Plasma cutterCraftsman(1980) buzzbox purchased new
Reply:@ Insaneride - believe you didn't apply the L/360 criteria when you ran the online calculator. Saw your answer in the report when L/360 was not/not applied.ReRip it and see what the detailed report outputs you.Last edited by ManoKai; 06-28-2016 at 04:41 PM."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:

Originally Posted by Oscar

...Nothing is infinitely stiff...
Reply:Isn't L/360 deflection for floor spans? For lifting I normally use L/600. I've seen some gantries cranes at L/900. Either way if your deflection is below the yield... it might bend but will spring back when the weight is removed. Do you math and decide what your comfortable with.


Reply:

Originally Posted by forhire

Isn't L/360 deflection for floor spans?....
Reply:I reripped it with the L 360 selected. I get 1,764 lbs and 6 gauge (0.203"). The op's 3/16" is 0.1875". The 0.1875" is close to 7gauge Will S, if your going to remove multiple motors then I would add the truss. Can you move the lift arms closer to each other?An L\600 would be 1" deflection for 50 foot span. The L\900 would be 1" for 75 feet. The 1" is measured at mid point.Last edited by Insaneride; 06-29-2016 at 09:38 AM.
Reply:file:///C:/Users/204042821/Downloads/Warren%20C.%20Young-Roark's%20Formulas%20for%20Stress%20and%20Strain%2  0(2001).pdfThis is awesome resource if you're willing to dig through some technical jargon.  I could try to put together an excel sheet that made inputs / outputs simple to use.  Is there a place on this site that would store such things?  It would be really nice if someone wanted to actually code the equations so that you could calculate using an online tool.I don't understand the L/600 or whatever.  That's not the language that I speak. But if you want to know the amount of stress you are creating and compare it to the maximum amount of stress the part can take or if you want to calculate how much deflection will occur, this book has equations for all those things.cheers,
Reply:Roark's Formulas for Strain and Strain (7th ed, 2002)"Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:

Originally Posted by Insaneride

I reripped it with the L 360 selected. I get 1,764 lbs and 6 gauge (0.203"). The op's 3/16" is 0.1875". The 0.1875" is close to 7gauge Will S, if your going to remove multiple motors then I would add the truss. Can you move the lift arms closer to each other?An L\600 would be 1" deflection for 50 foot span. The L\900 would be 1" for 75 feet. The 1" is measured at mid point.
Reply:try this                           http://webstructural.com/beam-designer.htmlpiece of soapstonetape measurechipping hammer (wire handle type)tip cleaners
Reply:This is truly a funny thread

9 foot span, 2" sorta tubing

Wouldn't consider springing for a piece of 3" HSS, that would be way too simple

The long, and short of it..........only thing that matters is whether the doggone thing will stress beyond 36K at full midpoint load, and yield.  To be safe, cut your stress factor back to maybe around something in the 20K range, and get to work

3x3 11ga (approx. .125 wall thickness) will support a 1K midpoint load (9' span) with bending stress of around 20K, and deflection of less than 1/2".  


  That's about maybe $20 worth of tubing

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Reply:Or use a wood 2x4

"Any day above ground is a good day"

http://www.farmersamm.com/
Reply:

Originally Posted by Will S.

A horizontal box tube channel, 2" square, 1/8" wall that is 9' long, and supported only at the ends: how much weight can be safely suspended from it's center? I looked online for structural info on box channel, but could not find the asnwer.    I guess another way to think of it would be how much force applied to the center, would it take to bend that 2x2 box channel, supportedonly at the ends.