# Dimension from section modulus

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

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1. Joined: Oct 2019
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### Ghost BoyJunior 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. Joined: Oct 2008
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You calculate it by hand!

3. Joined: Dec 2003
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### Olavnaval 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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### Ghost BoyJunior Member

Thank you

5. Joined: Oct 2019
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### Ghost BoyJunior Member

Can you please tell me, how can I calculate it by hand?
TIA

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### Olavnaval 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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### Ghost BoyJunior Member

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

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### Olavnaval architect

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### Ghost BoyJunior Member

thanks a lot

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