Dimension from section modulus

Discussion in 'Education' started by Ghost Boy, Sep 18, 2020.

  1. Ghost Boy
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    Ghost Boy Junior Member

    Hello,

    I am a student of Naval Architecture. I am doing scantling of midship section. I have calculated section modulus for various member. I have to calculate the dimension of various member from this section modulus. I am badly in need of a chart, where I get the dimension regarding section modulus. Can you guys please help me?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    You calculate it by hand!
     
  3. Olav
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    Olav naval architect

    Ghost Boy,

    welcome to the forum.

    I assume you know the longitudinal bending moments due to hogging and sagging of the vessel. From there you can derive the required section modulus for your midship section.

    Also you should have calculated the required dimensions for the hull shell and any longitudinal and transverse members according to the design loads (static water pressure, slamming, wave impact, deck load,...).

    Using the parallel axis theorem you can now calculate the actual section modulus of your frame and then compare it to the longitudinal strength requirements.

    If it satisfies the requirement: Congratulations, you are done. If not: Beef up your structure (i.e. the longitudinal members) until it does.
     
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  4. Ghost Boy
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    Ghost Boy Junior Member

    Thank you :D
     
  5. Ghost Boy
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    Ghost Boy Junior Member

    Can you please tell me, how can I calculate it by hand?
    TIA
     
  6. Olav
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    Olav naval architect

    For simple rectangular cross sections, e.g. flat bars or shell plating: section modulus = (width * height)²/6

    For more sophisticated cross sections, e.g. bulb flats, angle profiles etc: divide the shape into simple shapes and again use Steiner's theorem. Alternatively have a look here for a table with section moduli of bulb flats.
     
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  7. Ghost Boy
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    Ghost Boy Junior Member

    Thank you again. can you please send me tables for angle and T section like this?
     
  8. Olav
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    Olav naval architect

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  9. Ghost Boy
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    Ghost Boy Junior Member

    thanks a lot
     
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