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Engineering crane (math problem like hell)

  1. Jul 19, 2011 #1
    crane:
    http://tinypic.com/view.php?pic=2ywiidh&s=7

    Lifting:
    http://tinypic.com/view.php?pic=309ok06&s=7

    Determine the length of each chain sling that will hold the transformer, if the safe working load in each sling is not to exceed 150 kN. (H3.1)

    Calculate the maximum stretch in the lifting cable when the transformer is just being lifted off the barge 40 m below the bridge deck (i.e. static load) and the boom is at 60°, using a Ø15 mm steel cable (if young’s Modulus for steel is 210 Gpa’s).

    Calculate the maximum acceleration of the lifting operation, if the maximum breaking stress in the cable was not to exceed 1.867 Gpa’s
    [Remember F = m (g + a)]

    Calculate the pressure in the two hydraulic ram pistons, when the boom is stationary at 45°. The pistons are mounted 3m forward of the boom and 2.12 m up the boom and they have a diameter of Ø100 mm.
     
    Last edited: Jul 19, 2011
  2. jcsd
  3. Jul 19, 2011 #2
    This should really be in homework questions. Also those numbers seem slightly funny to me, the breaking load is too high, but that's what the problem says lets run with it.


    First of all, if this is a cable how will it be loaded? And how do you relate the breaking stress to a force.


    Also is that pic posted the full question? Does it tell you what you are lifting?
     
    Last edited: Jul 19, 2011
  4. Jul 19, 2011 #3
    well the load is carried by slings which each can only carry 150kN and i have no idea this is why i need help revising :S that is the info givin Calculate the maximum stretch in the lifting cable when the transformer is just being lifted off the barge 40 m below the bridge deck (i.e. static load) and the boom is at 60°, using a Ø15 mm steel cable (if young’s Modulus for steel is 210 Gpa’s). with it and its funny to u because im from australia and it stinks here ;l ur lifting a 30 tonne transformer
     
    Last edited: Jul 19, 2011
  5. Jul 19, 2011 #4
    It would help if you posted the full question. There was vital information missing from the OP that is needed to answer it.
    There is also information missing about the exact lifting arrangement. Ie, how the slings carry the load into the cable.

    Also as you've said this is a revision question, we can't just do the working for you, but we will go through the question step by step.
     
  6. Jul 19, 2011 #5
    THANK YOU THANK YOU THANK YOU saving my life im so nervous for exams
     
  7. Jul 19, 2011 #6
    Can you post the full question? With ALL the relevent information you have.
     
  8. Jul 19, 2011 #7
    there thats everything on paper i c infront of me that is all that is givin to me
     
  9. Jul 19, 2011 #8
    There was nothing written about the 30 ton load on the picture you posted, there is also nothing showing how the slings carry the transformer.

    EDIT: I see you've edited the original question, and added some stuff. Is that all of it?
     
  10. Jul 19, 2011 #9
    the 2nd url shows it srry if its a bother im just stressing over exams like hell
     
    Last edited: Jul 19, 2011
  11. Jul 19, 2011 #10
    That's ok, the 2nd link shows the rest of the information that's needed. This may take a while as i'm going to be doing it and asking you the questions i'd be asking myself.

    Starting from the 1st question.

    1. Determine the length of each chain sling that will hold the transformer, if the safe working load in each sling is not to exceed 150 kN. (H3.1)

    The diagram shows a bridle with 4 chain members going to each corner, with a central lifting point for the main cable.

    What can we assume about the load in each of those 4 members?
    How must each of the members be loaded?

    Hint: you can treat one side as a 2D problem because a beam is used, so there is an angle in 1 direction only.

    If the lifting point are 4m apart, what would changing the length of each member alter?
     
  12. Jul 19, 2011 #11
    yay moments i can do that if a beam is used we could use a 2D diagram so that means because a beam is used and they have to be all equal right? o.o
     
  13. Jul 19, 2011 #12
    Ignore the beam. It's not part of the question so we just assume it's strong enough.
    Also each of the members are flexible like a rope, so we can't transfer any moments. We can only load a rope in one way - tension. Which means the load in the rope must be axial.

    Correct, all the loads in the 4 chains have to be equal. This means we can devide the to total 30 tonne load into 4.

    Draw a FBD/picture of the 2D problem, and from the load we worked out find the tension in the chains for a given angle.
     
  14. Jul 19, 2011 #13
  15. Jul 19, 2011 #14
    Yep, if you pick an angle between the two ropes. You can work out the tension in each member. (As they are symmetrical, you only need to work out one)
     
  16. Jul 19, 2011 #15
    if all equal then 60?
     
  17. Jul 19, 2011 #16
    Although the loads are equal and each length is equal, the angle doesn't have to be 60 degrees. You can have really long members, meaning the angle is less, or really short ones giving a large angle.

    But try working out the tension with angle of 60 degrees. See how that compares to the maximum allowed.

    How would you work it out?
     
  18. Jul 19, 2011 #17
    ugh help? :|
     
  19. Jul 19, 2011 #18
    see i need help with this part 2 :| im so gonna fail </3
     
    Last edited: Jul 19, 2011
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