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Bending Moment of a beam with mass under & above water.

  1. Mar 31, 2009 #1
    1. The problem statement, all variables and given/known data
    Please refer to the uploaded images. (there are two images)

    When the right of the weight is lifted up,
    I need to know the formula to calculate the bending moment of the beam according to the rest of parts I have and how to calculate the suitable size of the beam to be used.

    As the bending moment is at its maximum when one of the weight is lifted out of the sea, the rest of the bending moment measurements are not neccessary for me to find out.

    I could only know how to calculate the easy question on bending moment. This one is too tough for me.. Let's assume the buoyancy force is 40N.. Volume of buoyancy is 1000m^3

    2. Relevant equations
    M = Force x distance
    Volume of buoyancy is 1000m^3
    buoyancy force is 40N
    Mass = 40kg

    3. The attempt at a solution
    Moment of Mass = 40kg *9.81 m/s^-2* 30m = 11.72 KNm
    Moment of the structure (horizontal, above water)= 10 * 9.81 * 45 = 4.41 KNm
    Moment of the structure (vertical, above water) = 10 * 9.81 * 40 = 3.92 KNm
    Moment of the structure (horizontal, under water)= 10 * 9.81 * 22.5 = 2.21 KNm (how to deduct the buoyancy force??)
    Moment of the structure (vertical, under water)= 10 * 9.81 * 22.5 = 2.21 KNm (how to deduct the buoyancy force??)

    Total M = 12.75KNm

    In this case, how do I relate to the size of the stainless steel to be use ? what is the suitable diameter?
     

    Attached Files:

  2. jcsd
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