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Thread: Carrying capacity of an I beam

  1. #1
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    Default Carrying capacity of an I beam

    Hi, I am looking into using I beams to make a simple hoist for my home shop. Basically, two I beams in parallel to each other and another perpendicular one that rolls on the two parallel ones. Then a small electrical hoist, rated at 250Kg will roll on the perpendicular one. Given that all the I beams will be about 6m long, what size I beam must I use in order to be able to carry 250Kg's? The parallel I beams will share half of the total weight and the perpendicular I beam will carry the electrical hoist and the goods to be lifted.

    For example, If I use 100mm high, 5mm thick I beams, would that be sufficient?

  2. #2
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    Over 6mtr I would go with at least 150mm high beam because it will flex on it's own over that distance.
    For only 250kg a truss type setup would probably be better over 6mtr's with 2 angles welded at the bottom to allow the trolley to roll on.

    Dave

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    So use 150mm parallel I beams and a truss type construction that rolls on these beams... My ceiling height is very low, so would a truss type beam that is 150m or less have enough carrying capacity? Or maybe you are saying use truss type beams all around? I guess that would make the whole thing lighter as well, hmm...

    I am also thinking about how to make the two beams parallel. The building is a pre-fabricated one with modular wall segments. I wouldn't trust those walls to carry the beams. Even if they would carry, it would be too shaky and difficult to fix the beams to be precisely parallel.

    So I am contemplating to bore holes at the corners of the building into the concrete floor. Then place 90mm or so pipes into these holes, fix them there and then erect the I beams over the ends of these pipes. I would also be able to make them adjustable to a certain degree for parallelism.

    The movement of the hoist will be entirely human powered. So I guess it is necessary to use ball bearings at the moving places and to make everything precisely parallel.

    If I could do this right, it would make changing my lathe chuck a child's play. Also, putting the rotab on and off the mill would be so much easier. I also need to do work on my table saw to change the arbor. This will also allow me to lift the table of it, together with the motor trunnion, so I have access to the arbor

    But I also want to be certain that no part of this hoist falls on my head
    Last edited by taydin; 02-15-2011 at 07:53 AM.

  4. #4
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    But I also want to be certain that no part of this hoist falls on my head [/QUOTE]

    Not sure you are going to like some of the answers you will be getting. The structural engineering world is very conservative and asumes major liabilities. Flexing is your enemy here as it can induce inertia moments which are hard to control. Look around at some overhead set-ups and you will be surprized at how little they are actually rated for with a over design factor of 4 or 5. You may want to consider removable support legs to keep your design requirements reasonable for a HSM.

  5. #5
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    I would put a truss strap under each track beam.Maybe a 150mm standoff in the center with the strap welded to each end of the beam on the bottom.The strap would only need to be something like a flatbar,maybe 25x8mm or a 16mm round rod even would work.This would make the system much more ridgid.

    Since the running beam needs to be clear on the bottom,I would use a larger beam for it,say maybe a 150mm tall.

    I would also use chain and sprockets to keep the running beam parrallel to the track beams.
    I just need one more tool,just one!

  6. #6
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    Quote Originally Posted by taydin
    ....two I beams in parallel to each other and another perpendicular one that rolls on the two parallel ones. .... The parallel I beams will share half of the total weight and the perpendicular I beam will carry the electrical hoist.....
    If the electrical hoist will travel then when it is at one end of the perpendicular beam (the hoist beam) then the adjacent parallel beam will carry the full weight of the load.

    Because all your travel will be human powered you do not need the larger factors of safety of commercial installations where inertia has to be considered and that would especially be the case if you used a manual chain hoist. Sway considerations have to be considered and the top of your columns will need to be held laterally - possibly fastened to the building and maybe with aditional diagonal braces down to the ground.

    Because of your low headroom you may need to use a top running hoist beam and this then should not limit the depth of your track beams which, over a distance of 6m (almost 20 feet) would be better at 8" or 10" deep (200mm or 250mm). For beam lateral stabily wider flange beams are to be preferred. I wouldn't go smaller than 150mm high and wide and 6mm thick.
    Last edited by jep24601; 02-15-2011 at 09:37 AM.

  7. #7
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    Thanks for the responses guys, they all make quite sense...

    I can go with 200mm or even 250mm parallel beams to prevent the flex, because these will be leaning against the wall and won't be that much of a hindrance. Well, they will take away wall space. With this much height, I suppose the thickness can be reduced to maybe 4 or 5 millimeters.

    But for the movable beam, I really want to minimize the height. My milling machine top is very close to the ceiling. I would hate to have to turn the head in order to go over it and then re-tram it. Or I will have to put the milling machine at the limit of the hoist. Just move the hoist close enough to put on the rotab or work on the table.

    Actually as HAP has suggested, using a 100mm movable beam and a removable support leg close to where the lifting will take place sounds like a good compromise. With a support, much less than 100mm should work, too...

  8. #8
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    Taydin, you know that MIGHT be a good idea. Basically it is a gantry crane. They are, (or were,) used in shipyards, steel mills and LARGE fabrication plants. Mostly because they permit total access to the ENTIRE floor. You, on the other hand, want to painlessly change chucks on your lathe, mount a rotary table on your mill, and occasionally lift up your cabinet saw to tinker with it.What is the need for such a complex and expensive hoisting system?
    Alright, I said it. Now, I happen to have a 150mm I-beam 4 metres long holding up the roof over my garage door. It meets code for allowable deflection and we get quite a bit of snow here. For a 6 metre span, I would have required a 200mm beam, because of mid-point deflection limits. You are in the EXACT same position. A 250 kg point load, (when the load is on the hoist and the hoist is at one end, in the middle of one side.) There will be very little load sharing-you will have one-half the weight of the traveller plus all the load weight suspended at the mid-point of one beam.
    Is this REALLY what you want/need? If the answer is yes, then charge on, but grab your wallet! If, on the other hand, you decide on something a little less complex and a bit more economical, how about a rolling gantry?
    This would have a span to straddle your lathe, mill or saw, travel on four sturdy wheels or casters with locks, be a LOT lighter and about as manouverable as you need. Most of your design problems would vanish.
    Duffy, Gatineau, Quebec

  9. #9
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    Quote Originally Posted by taydin
    For example, If I use 100mm high, 5mm thick I beams, would that be sufficient?
    In a word, no.

    Bending capacity depends on material [1] and geometry [2].

    For the span and section size you quote, the deflection is 20mm when subjected to the (unfactored) load you describe [3]. That's far too much [4].

    Your section size is way too small and doesn't appear on standard section tables [5],[6].

    Have a play with some free beam analysis software [7] to get a feel for the section size you will need.

    Remember to factor your loads!


    [1] Steel. Young's modulus approx. 200 kN/mm2. http://www.engineeringtoolbox.com/yo...lus-d_417.html
    [2] For your beam Ixx = 256 cm4 http://en.wikipedia.org/wiki/Second_moment_of_area
    [3] Simply supported, central point load http://en.wikipedia.org/wiki/Euler–B..._beam_equation
    [4] Bottom of page 3. http://faculty.arch.tamu.edu/anichol...beamdesign.pdf
    [5] http://www.roymech.co.uk/Useful_Tabl..._dim_prop.html
    [6] http://www.engineeringtoolbox.com/am...ms-d_1318.html
    [7] http://sourceforge.net/projects/cbeam/files/

    Data file for above program with your input parameters

    #cba input file
    SPANS 6000.00
    ELASTICITY 2.10e+002
    INERTIA 2.56e+006
    CONSTRAINTS -1 0 -1 0
    LOADS 1 2 2.50 0.00 3000.00 0.00
    #gui values - ignored by cba
    UNITS kN mm
    MATERIAL Steel S235
    SECTION Isec 10 10 0.5 0.5
    SELFWT YES

  10. #10
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    Quote Originally Posted by Duffy
    Taydin, you know that MIGHT be a good idea. Basically it is a gantry crane. They are, (or were,) used in shipyards, steel mills and LARGE fabrication plants. Mostly because they permit total access to the ENTIRE floor. You, on the other hand, want to painlessly change chucks on your lathe, mount a rotary table on your mill, and occasionally lift up your cabinet saw to tinker with it.What is the need for such a complex and expensive hoisting system?
    Yes, the I beams cost about $1 per Kg here. I don't know how much each weighs, but they can easily weight 100Kg or more each. So it will be probably somewhere in the $700 area. A 2 ton engine hoist is more expensive than that here (I would need a 2 ton, because the boom would have to be extended almost to max in order to reach over the lathe and such. When the boom is extended like that, the carrying capacity drops to about 500Kg). And I don't have room for an engine hoist.

    Quote Originally Posted by Duffy
    Alright, I said it. Now, I happen to have a 150mm I-beam 4 metres long holding up the roof over my garage door. It meets code for allowable deflection and we get quite a bit of snow here. For a 6 metre span, I would have required a 200mm beam, because of mid-point deflection limits. You are in the EXACT same position. A 250 kg point load, (when the load is on the hoist and the hoist is at one end, in the middle of one side.) There will be very little load sharing-you will have one-half the weight of the traveller plus all the load weight suspended at the mid-point of one beam.
    Is this REALLY what you want/need? If the answer is yes, then charge on, but grab your wallet! If, on the other hand, you decide on something a little less complex and a bit more economical, how about a rolling gantry?
    This would have a span to straddle your lathe, mill or saw, travel on four sturdy wheels or casters with locks, be a LOT lighter and about as manouverable as you need. Most of your design problems would vanish.
    I considered using a rolling gantry, but I won't be able to store it inside. If I leave it outside, it'll have walked in a matter of days, even if I chain it somewhere

    My shop is in a rural area and far away from my house.

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