Hopper Split Barge Scantling Calculation

Discussion in 'Class Societies' started by QUICKNAVAL, Sep 27, 2013.

  1. QUICKNAVAL
    Joined: May 2012
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    QUICKNAVAL Junior Member

    Anyone can help me this...

    I have doubts regarding this formula (from class) in solving the thickness of the hopper well (plating).

    Actually it is a rescantling calculation of an existing hopper split barge. That's
    i why refered class rules in solving the thickness of the hull plating. Why the required thickness of the strength deck (t=8.177mm) is much bigger compare to hopper well plating (t=6.861mm). And the existing hopper plating (t=24mm), why it is so thick?

    The deadweight of the split barge is just 1500 tonnes,,, and the cargo area is 12 m x 34m.

    And what is the safety factor to be used for manual calculations of each member?

    Attached is the midship section and hull scantling calculation.

    Your help is much appreciated.

    Thank you.
     

    Attached Files:

  2. french44
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    french44 Junior Member

    check on the rules that you use if you don't have additional for this part of the ship. In general you have a special chapter for.
     
  3. TANSL
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    TANSL Senior Member

    Answering to your questions would be a job, not difficult, but hard. Will need to check that you are correctly applying the C.S. Regulation and the specific chapter refers to this type of boat, it would be necessary to make many mathematical operations and .... in this moemnto not worth it.
    I advise you not to go so fast and before you start crunching numbers, you should design an appropriate structure for the problems with the boat. Eg
    - Large deck openings that require profiles in "T" very strong in the contours of the opening.
    - How are you going to unload the load?. Maybe you need bottom doors.
    - You may need the hopper has an horizontal part, at its bottom.
    - Inclined pillars completely lose their effectiveness.
    - The ship's longitudinal strength perhaps force you to put some more longitudinal girder on the bottom.
    - And many more "small" things.
    So, think about the elements of the structure and how they connect to each other and then starts with the calculations.
    I remain at your disposal for anything you need, if it is within my knowledge.
     
  4. QUICKNAVAL
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    QUICKNAVAL Junior Member

    Actually the formulas in my calculation is based on IACS class,,,ship for dredging activity (to be specific a split hopper dredger).



    See attached file.
     

    Attached Files:

  5. TANSL
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    TANSL Senior Member

    It seems strange that in the calculation of the hopper is not taken into account the weight of the material to be stored in it.
    There are usually 2 or 3 formulas for calculating the thickness of a plate as well as the minimum thickness formula. You should choose the greater thickness obtained with them. You've only used the minimum thickness value. Search for some other formula.
    Are you sure to properly use the values ​​of "L" and "s"?
    I insist: reviews the structure which, in my opinion, is not correct.
     
  6. french44
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    french44 Junior Member

    that you use is for hull not for the inner plate of cargo , you may have a special part for that, in BV is in special ship and dredger
     
  7. QUICKNAVAL
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    QUICKNAVAL Junior Member

    L - is the length of the vessel and "s" is the spacing of longitudinals in the hopper. I did the manual calculation of this hopper plate, and i come up to 16 tonnes/m2 loading. I think this load is safe for a 12mm hopper plate (above) and 150mm X 90mm x 9 AB (under)., unsupported span at 2m and longitudinals spacing is 550mm.

    The cargo area is just 400 sq.m. and the required deadweight is 1500 tonnes. I think the 16 tonnes/m2 has greater margin already.
     
  8. TANSL
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    TANSL Senior Member

    I think that a load of 9 or 10 ton/m2, assuming a hopper's height about 4 m would be more than enough.
    Unsuported span of 2 m, is very large. You should think of beams with intermediate supports every, for example, 500 mm (every frame).
    The resulting thickness must be increased so as to compensate the abrasion caused by the load. C.S. rules will tell you how much you should enforce this compensation.
    Again I suggest you study the structure that, in my opinion, is not correct.
     

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  9. french44
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    french44 Junior Member

    the density is in general from 1.3 t/m3 to 1.5 t/m3 , the spacing of 500 mm is good and no more than 800 mm . in addition you have ragging so you have to increase the thickness about 20/30 % (experimental value if you don't want to change the plate too quickly) in addition the corrosin value from the rules is for hull in this case with ragging the protection (paint when the ship is new) stay no more than one week so if you want to be quiet increase the class value by 15 %. I have try several solutions and one is doing good results is to calculate the structural with normal load and to fit hardox plate and the top on the structural plate. So we never change the structural plate only the hardox plate , it's quick and easy.
     

  10. QUICKNAVAL
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    QUICKNAVAL Junior Member

    Is this a right a right idea, that i should get the maximum moment (considering the load and the weight of the vessel, and the buoyancy), then divide it to the allowable hull bending stress (235MPa), in order to get the required section modulus of the hull. And then compare it to the actual section modulus of the half midship section (considering it was open, or the hull split into two sections).
     
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