Scantlings methodology for recreational boats

Discussion in 'Class Societies' started by TANSL, Dec 21, 2013.

  1. rxcomposite
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    rxcomposite Senior Member

    AH- You were typing too fast. I understood it well, thank you. In the beam theory, there must a vertical component to handle the Vshear or vertical shear. I have studied the Vshear formula for several load models.

    For composite beam, is the vertical shear to be handled partially by 0/90 degree fabric, or just a medium density foam core?

    I guess my confusion lies in the Off Axis theory of composite and the castllagno's theorem whre if you apply a point load to the top member where the diagonals meet, the load is transferred (diagonally to the lower member) via the trusses.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Our paths crossed in cyber space.

    Forget what the beam is made from for now...where is the load and how does it get from A to B? Then this method of getting from A to B...can the material do this and not fail?

    Everything in structural analysis can be reduced to simple bending and shear..that's it. Followed by deflection checks.
     
  3. rxcomposite
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    rxcomposite Senior Member

    I misunderstood. You said you will correct, not add an explanation.

    Maybe I should review more carefully the formula stated in the rule where it shows how to meet the minimum web shear requirement in composites.
     
  4. rxcomposite
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    rxcomposite Senior Member

    Got it. Thanks
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    RX

    Shear stress is simply Force/Area.

    Thus once you can calculate the force, from the arrangement, the "area" becomes the important part. And linked to that is what material is it. Simple example:

    Shear in beams-diagonals.jpg

    The diagonal (strut/tie) are angled at 30 degrees. The load in the strut at 30 degrees, shall be different from that if 45 degrees, shall be different from that if 75 degrees. This has nothing to do with material. Just arrangement and orientation. This determines what the magnitude is...the magnitude is dictated by its arrangement.

    Once that is done...the tie/strut (or fibre) must now be selected to take said load and safely within limits of yield and buckling.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    There is your confusion. You don't need C's theorem.

    C's theorem is related to an ecstatic body with endless forces being applied and thus how to calculate the deflection of varying forces being applied from different directions? It links into strain energy.
     
  7. rxcomposite
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    rxcomposite Senior Member

    Got it. Simplifying thus, we have a truss bridge;
     

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  8. Ad Hoc
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    Ad Hoc Naval Architect

    Got it in one. If you use foam (like a solid web) just make sure the shear stress calculated, is below the design allowable for the foam. Otherwise ensure the fibres can take the load, that's it :)
     
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