Tank On Deck

Discussion in 'Class Societies' started by naserrishehri, Jul 17, 2013.

  1. naserrishehri
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    naserrishehri Senior Member

    DEAR FRIENDS
    I 'm going to instal a tank by bolt on ship's main deck .
    which calculation shall be issued to the class except stability ?
     
  2. MikeJohns
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    MikeJohns Senior Member

    Tank design, method of affixing the tank, Deck loading adequacy or supporting structure such as a pillar and framing.
     
  3. naserrishehri
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    naserrishehri Senior Member

    would you please issue the rule name and chapter or part no?
     
  4. MikeJohns
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    MikeJohns Senior Member

    Sorry naserrishehri but its a 'specific' calculation for all Class I know of.

    So you'll need to ascertain that the structure can support the tank withing the fatigue allowance.
     
  5. TANSL
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    TANSL Senior Member

    I'm not really sure it's necessary to study fatigue.
    I think it is much simpler: the total loads on the deck, taking into account the accelerations in the tank area, should not lead to stresses in excess of the maximum allowable by the Classification Society.
     
  6. daiquiri
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    daiquiri Engineering and Design

    That is my opinion too. Design loads, together with maximum allowable stresses already include the fatigue and dynamic effects of ship motions.

    For example, when looking at Lloyd's, I think that Naserrishehri should refer to the Part 3, Chapter 3. The table 3.5.1 gives design loads to be considered, depending on the type of cargo. In particular, Item "b" (Cargo decks - Special cargo) gives the permissible cargo loading and equivalent permissible cargo head. The effects of sloshing are also considered in that chapter.
    Another Chapter to look into could be the Chapter 9 (Special Features).

    Naserrishehri: the best thing for you, IMO, would be to place a call or send an e-mail to the chosen Class Society and establish with them the proper way of proceeding with the scantling. You might perform formally the most correct and precise structural calculations for this case, but if they don't like them or disagree with your engineering choices and underlying assumptions, it would be all useless.

    Cheers
     
  7. MikeJohns
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    MikeJohns Senior Member

    Same thing. That's what the allowable stress is set to so I'm just using the term interchangeably sorry if it was not clear. Not a full S-N study just design to the fatigue limit which is also the allowable stress.
     
  8. MikeJohns
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    MikeJohns Senior Member

    I would usually just sign off on the design and carry the can or the tank:)

    But it's very hard to give any more advice without the details. eg does this ship go to sea, is it a barge in sheltered water ? And always best just to go and talk this over with the class society. I was presuming this was a student assignment ??
     
  9. naserrishehri
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    naserrishehri Senior Member

    what i found from above :
    After stability and deck loading calculations , i shall refer to a formula which issue by class
    and calculate an excess force due to ship acceleration . this formula may be is different by
    each class .
     
  10. daiquiri
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    daiquiri Engineering and Design

    Naserrishehri,
    I suggest you to call the technical office of the Classification Society and discuss it with them.
     
  11. naserrishehri
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    naserrishehri Senior Member

    daiquiri
    you are right.
     
  12. TANSL
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    TANSL Senior Member

    naserrishehri, naturally it makes sense to talk to the Classification Society. But do not need to find a special formula to calculate the beam. What you have to do is to study a beam subjected to loads, one of which is the weight of the tank. Discuss with the CS if, for example, consider an acceleration of 3g seems right, and they also discussed the degree of fixation of the ends of the beam. Known all this, calculate the section modulus of the beam, calculate the maximum bending moment, calculate the maximum stress in the beam and check how it is in relation to the maximum allowable by the CS.
    In all cases, if you do not want to follow the formulas of the CS, you can make a "direct calculation", according to the traditional strength of materials, meeting the general criteria of the CS, and submit it for approval.
     
  13. naserrishehri
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    naserrishehri Senior Member

    Dear TANSL
    Suppose that i found deck load . my 40tonnes cargo is going to be bolted on a seat and that seat shall be welded on the weather deck with a small connection area (for example :L100X100X10 and some bracket ) .
    How do i find deck load due to this cargo ?
     
  14. TANSL
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    TANSL Senior Member


  15. naserrishehri
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    naserrishehri Senior Member

    DEAR TANSL
    Please find the attachment for cargo drawing .
     

    Attached Files:

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