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Ways of Strengthening Cantilever beams

  1. Dec 7, 2011 #1
    I am working on a design project and we have thought of cantilever beam to hold 1 ton mass spread along its span. I wanted to know what are popular ways to strengthen a cantilever beam to counter deflection and be able to hold objects loaded over it easily as I havent seen any mechanics of materials book talk about such ways.

    Any suggestions would be much appreciated

    Regards

    EDIT: Talking about mild steel angle iron beams
     
  2. jcsd
  3. Dec 7, 2011 #2
    What are the design restrictions/limits? Do you need to strengthen the beam itself, or can you add elements?
     
  4. Dec 7, 2011 #3
    1) Don't use angle iron to support a 1 ton load. Use rectangular tube steel
    2) Same question as pantaz
     
  5. Dec 7, 2011 #4
    We can add elements. The structure is 9 ft long. Inclusion of cross beams is not possible as the structure is holding material that would be dropped so we can add any elements only after certain intervals, approximately 1.5-2 ft.

    @Travis

    I though angle iron would be better. Any reasons you recommend rectangular steel tubes ?
     
  6. Dec 7, 2011 #5

    Mech_Engineer

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    The advantage has to do with the section modulus of the beam. If you have a cantilever beam that you can't add supporting elements to, then your only option is to size the beam's section modulus such that it is able to support the entire weight.

    The most efficient beams on a weight per section modulus standpoint have more material in areas of high bending stress (top and bottom), and less material where the bending stress is low (middle). Sections like an I-beam or rectangular tube are good candidates.

    http://en.wikipedia.org/wiki/Beam_theory
    http://en.wikipedia.org/wiki/Section_modulus
     
  7. Dec 7, 2011 #6
    I thought angle iron due to its height would prove good as it section modulus would be high after I-beam.

    well beam section aside, what are additive elements configurations that can serve to counter deflection and support weight ?
     
  8. Dec 7, 2011 #7

    Mech_Engineer

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    For a start you could support the beam at several points along its length with a compressive / tensile truss structure similar to that of a bridge.
     
  9. Dec 7, 2011 #8
    Yea, angle is good for support as it is good in bending, but for supporting a load you will have a good deal of torsion and you will likely twist your beam. Angle is better than flat plate, but not tube (after all, tube steel is basically just two angle pieces welded along the sides!) 2000lb is pretty heavy to be cantilevered...

    You have a sketch of the idea? It may just be me but I'm not clear on the application.
    Is the "structure" the support mechanism or the 1 ton load? Is the support structure 9 feet long or 9 feet tall? Or is it the load that is 9 feet?
     
  10. Dec 7, 2011 #9
    deflection is a function of f(E,I,M)
    your best shot would be to increase the moment of inertia by choosing between different types of beams that suit your need.
     
  11. Dec 7, 2011 #10

    I will surely upload the sketch soon.

    Actually it's our senior year design project of making a feeding system for Aluminum melting furnace. We have thought of making a rotating platform that would be 9ft long (not upwards tall) for holding the 30kg units of Al-chips, ingots and pipes which would then be rotated into the furnace and under the action of gravity, material will fall and be fed at once. The structure is essentially a cantilever beam made by joining two long 9ft beams separated by a distance of 3-4 feet, think of it as rectangle made by 9+9+3+3 feet of beams. It will be pivoted outside the furnace door

    Currently they are using labor to feed all this stuff which takes time, is hard for worker to withstand the heat. Our goal is to feed one tonne at once. The furnace has a door at its one end which slides up and exposes the opening resembling a window 11 ft wide and 40 inches high. You see we have limited space to enter the furnace so any other solution is ruled out like any conveyor etc.
     
  12. Dec 8, 2011 #11
    I am an engineer at an aluminum smelting/casting plant, so I know basically what you are trying to accomplish. I don't spend much time at our furnaces, though, so I'm not entirely sure how we reintroduce material. I am not sure I understand what you want to do with your cantilever, however. How does the beam allow the material to fall "under the action of gravity"?

    I'll just wait for the sketch.
     
  13. Dec 8, 2011 #12
    An important problem to overcome in any cantilever is the support, ie the connection to the supporting structure. Root stresses/forces are necesarily high here and usually need to be distributed (spread out) into the support in some way.
     
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