structural analysis using class rule

Discussion in 'Class Societies' started by naserrishehri, Jan 11, 2015.

  1. naserrishehri
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    naserrishehri Senior Member

    dear friends
    How can i satisfy the classification society that the strength of 2nd deck in the attached drawing is enough to carry the movable pontoon deck?
     

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  2. TANSL
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    TANSL Senior Member

    The best thing to do is to place longitudinal girders in the deck 2, similar to the ones in the main deck. These girders should be assumed supported by transverse bulkheads (web frames) as the ones on the left side of your picture.
    So you have to study a beam of length equal to the distance between bulkheads (2.4 m). You can assume its ends are fixed. In your drawing, you have an uniform load of 2.84 tons / m ???. (note the width of the attached plate to calculate the actual load on the beam)
    Calculate the maximum flexural bending moment in the beam (pl ^ 2/12 pl^2/8 if you want to be conservative), and give it a modulus (first momento of transversal area) so that the maximum stress in the cross section of the girder not exceed the maximum allowable stress for CS.
     
  3. naserrishehri
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    naserrishehri Senior Member

    the class request to issue calculation as per their rule's formula but i do not know which part of the rule i should refer?
     
  4. TANSL
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    TANSL Senior Member

    You can use the formula for deck longitudinal girders. Instead of the regulatory design load, you can use the load that you have calculated on the deck, if greater than the required by the rules.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    All Class rules have cargo/concentrated loads requirements.

    However, in the absence of any, you can simply design it from 1st principals.
     
  6. naserrishehri
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    naserrishehri Senior Member

    dear tansl
    when i use deck plate thickness formula then the deck load caused by weight gets bigger than class deck load calculation.
    it means i should increase the connection area of movable deck and 2nd deck.but it's impossible.
    do you have another solution?
     
  7. TANSL
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    TANSL Senior Member

    Dear friend, we should clarify two things. The first is that the plate alone can never withstand the loads on the deck; have to put a girder similar as in attached figure. So what you need to calculate is the longitudinal reinforcement (girder + attached plate) that supports the deck cargo. The second thing to note is that the design loads proposed by CS Rules are the minimum values according to CS should be applied. That is, the designer can put the load he wants or needs, provided that not less than indicated in the rules.
    All that said, must correctly calculate the load on the girder. Suppose that in the second deck between 2 webs (spaced every 2.4 m), there are 5 cars of 2600 kg each placed there. This deck panel has to endure therefore 13000 kg. That is, each girder will hold 6500 kg. As the length of the girder is 2.4 m, the load is 6500 / 2.4 = 2708 kg / ml. That is the design pressure. If we consider the acceleration due to waves, we could consider a design load of 8500 kg / ml, for example. And now, use the formula that tells you the modulus for reinforcements (noty for plates).
    Hope this help.
     

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  8. naserrishehri
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    naserrishehri Senior Member

    DEAR TANSL
    thanks a lot for your kind advise.
    please see the attachment, what is your idea about the new longitudinal girder above the 2nd deck?
     

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  9. TANSL
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    TANSL Senior Member

    I think the right thing is to do something completely similar to what is on the main deck, so that the 2nd deck is flush.
     
  10. naserrishehri
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    naserrishehri Senior Member

    it's too difficult fabrication and welding inside the tank.i want to calculate section modulus of the L.type longitudinal girder as per CS rule and choose the best girder thickness.
     
  11. TANSL
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    TANSL Senior Member

    Yes, that is right. The flange of the girder is more effective than the web, so, if you can, increase the thickness and width of the flange.
    The solution to your sketch does not convince to me, but only you know what you can and can not do. However, think on another solution, for example, put guirders flange under the deck but outside the tank.
     
  12. naserrishehri
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    naserrishehri Senior Member

    DEARTANSL
    can i consider the inner side plate as a longitudinal girder in my calculations?
     
  13. TANSL
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    TANSL Senior Member

    I do not understand properly. Does a sketch?.
    (Do we use the e.mail?)
     
  14. naserrishehri
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    naserrishehri Senior Member

    DEAR TANSL
    please see the attachment.
    i want to consider inner side bulkhead of the side tank as a longitudinal deck
    girder in my calculation.
     

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  15. TANSL
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    TANSL Senior Member

    You can do this but you must calculate the bulkhead considering the load the second deck transmits (in the plane of the bulkhead) and hydrostatic load (perpendicular to the bulkhead and increasing downward) due to the water contained in the tank. That loads system I do not know whether it is covered in formulas provided by the Rules of the CS.
     
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