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You are to design a tension member

  1. Sep 27, 2010 #1
    You are to design a tension member....

    You are to design a tension member (square rod) with a cross section to carry a mass of 575 000 kg with a safety factor of 2 against yield and a safety factor of 3 against static fracture (overload).

    a) What is the design stree that you will use for the application? Why?

    b) What are the appropriate bar dimensions for use?


    =============================================================

    FS = UTS / R

    [sigma] = F / Ao

    Ao = L * w

    ======================================================

    FS = 1279MPa / 3 = 426.33333... MPa ~ 426 MPa
    that's the design stress considering static fracture

    FS = 862 / 2 = 431 MPa
    that's the design stress consider yield stress/strength

    So, I'm considering using a design stress that is the average of these two values, which would be: 429 MPa

    I'm just confused, because we haven't done anything like this in class.

    Now for part b)

    [sigma] = F / l*w

    F = 575 * 103(kg) * 9.81(m/s2)
    F = 5.641 MN (mega Newtons)

    429 = 5.641 MN / Ao

    Ao = 13148.6014 MM (mega meters? I'm not sure about the units on this one)

    l = w = 6574 MM

    Please help and thank you; ie, does this look right to you?
     
  2. jcsd
  3. Sep 28, 2010 #2
    Re: You are to design a tension member....

    Of the three stresses (426, 429 & 431) you have calculated only one gives a safety factor of 3 against fracture.

    Which one is it?

    This is the only one which satisfies both the safety factors of at least 2 and at least 3.

    I'm sure if you check the units of (426, 429 & 431) in part (b) you will be able to calculate a more sensible area.
     
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