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Thread: Help on making ramps: aluminium tube deflection and welding

  1. #1
    Associate Engineer
    Join Date
    May 2018

    Help on making ramps: aluminium tube deflection and welding

    Hi. I am trying to make up 2 aluminium ramps out of aluminium and just wanted to double check that i was on the right track. I will be carrying granite benchtops on a trolley over them.

    I have narrowed it down to maybe using 4 65x3mm square tubes with radius corners and diamond security mesh welded on top.
    This has given the best deflection vs weight results while still being low profile.
    I figured i could weld the security mesh on top without weakening the underside of the beams.

    It is 6060 ali which is has 69.5 gpa or 69500 mm/2 modulus of elasticity.
    I have been given the moments of inertia from a spec sheet which look like lx mm4 and ly mm4.
    If it where a rectangle i would be using moment ly correct? This was 473924.0 mm4
    Ramp length is 3500mm with 100kg of force on each beam

    I have been getting deflections of 22mm with the single load calculator and 15 with the distributed load.
    The line load has been giving me crazy answers. Not sure of i am doing it right.
    I was diving the weight in KN by the contact in one direction that the trolley wheel makes with the ramp.

    Looks like 5356 is the wire to use with extruded ali but i also have 4043 which is less prone to cracking.

    The big one was how much deflection the beams can take before they get stressed so much that it causes fatigue.

    Any help or advice would be great.

  2. #2
    Administrator Kelly Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Line load is given in force/length and only application if you have a distributed load application. 22mm deflection seems like a lot - you need to determine the applied stress and compare to the yield stress of the material. Hopefully, you can get a factor of safety of about 1.5 or greater.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Lead Engineer Cake of Doom's Avatar
    Join Date
    Aug 2012
    Are you sure you've entered the right values? With 100 kg as a mid-span load with 3.5 m length, I get 0.16 mm deflection. That's not including self weight of section and and decking.

  4. #4
    Associate Engineer
    Join Date
    May 2018
    Thanks for the info Kelly. Exactly what i was after.
    Also the distance to the neutral plane is d/2 correct?

    I got the 22mm from the point load in the centre calculator.
    I used this as i thought worst case scenario the ramp will be loaded in the centre momentarily.
    The load will be on pneumatic wheels so doubt it would be the full 22mm.
    Are you suggesting to use the uniform loading calculator instead?

    Thanks for the replies.

  5. #5
    Lead Engineer
    Join Date
    Aug 2013
    Houston TX USA
    What is the length of the ramp and the center to center distance between the front and rear wheels on the cart? There are "Beams with two point loads" analysis equations available.
    Also, have you calculated the maximum bending stress vs. the maximum allowable yield stress for your ramp material for your load cases. All beam deflection equations assume the beam is still in the elastic bending range; even if the stress at that deflection exceeds the maximum allowable yield stress for the beam material.

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