Inclined stiffeners

Discussion in 'Class Societies' started by Roni, May 13, 2021.

  1. Roni
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    Roni Junior Member

    I'm working out scantlings in accordance to GL 2012 HSC rules. I was wondering what treatment is usually to inclined stiffeners, such as the one from the image:

    upload_2021-5-13_11-56-7.png

    Is it usual to calculate the second area moment of the inclined section or just simplify and do the calculations assuming a perpendicular stiffener with the web height and not web depth?

    Thanks a lot
     
  2. TANSL
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    TANSL Senior Member

    You should calculate properties of the inclinened section. Anyway, in such a rectangular shape, using web height could be enough.
     
  3. Roni
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    Roni Junior Member

    I've done some quick comparisons and just using the height instead of depth does give a smaller value for I (second area moment) than calculating I value for an inclined section. The larger the angle the greater the difference. I was also looking at the web shear area, and comparing the GL 2012 HSC, wich states in section C3.8.4.1:

    The web may be attached vertically or inclined to the
    attached shell (only the structural height times the
    thickness as effective shear area is to be considered)
    On the other hand DNVGL 2019 HSC rules state that:

    Where beams are inclined towards the attached plating, see Figure 12, the inclination shall be considered in an appropriate way when calculating the scantlings. Usually the web of a beam is contributing to the full depth of the beam, where the bending stiffness shall account only for a structural height as measured perpendicular to the attached plating.
    I know they are different rules, but was nonetheless curious on why the different treatments.
     
  4. TANSL
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    TANSL Senior Member

    I think that I do not fully understand what you want to compare, but the shear area is the same, whether the reinforcement is inclined or not, while the first and second moments of area change a lot with the angle formed by the reinforcement and its associated plate.
     
  5. Roni
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    Roni Junior Member

    If I'm reading the rules correctly the Gl 2012 rules states that I should consider the shear area = depth*thickness (form rule: "
    only the structural height times the thickness as effective shear area is to be considered"), while the DNVGL rules states that I should consider the shear area = height * thickness ("Usually the web of a beam is contributing to the full depth of the beam").
     
  6. TANSL
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    TANSL Senior Member

    I have always used, and I think it is the right thing to do, the actual area of stiffener.
    I think you should forget the GL regulation and use the last one from DNV-GL.
     
  7. Roni
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    Roni Junior Member

    The actual area of the stiffener does seem more correct and in line with beam theory.
     
  8. TANSL
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    TANSL Senior Member

  9. baeckmo
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    baeckmo Hydrodynamics

    That stiffener is subject to buckling, it will deform till it lies flat to the skin, unless it has a substantial flange that prevents the top part to deflect sideways. I have seen bottom panels completely "blown inwards" with that kind of "stiffener"; in my world it is to be avoided!
     
  10. Roni
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    Roni Junior Member

    I'm doing the dimensioning with as an exercise, but went with the L stiffener because local builders in the area said the much rather build that than a top hat.
     
  11. TANSL
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    TANSL Senior Member

    It is not the type of stiffener as such but the high value of the web height / thickness ratio that can promote buckling.
    The same can happen in a normal top hat if that ratio is high.
     
  12. Roni
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    Roni Junior Member

    There are buckling under shear criteria in the rules, they should cover that right?
     
  13. TANSL
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    TANSL Senior Member

  14. Alik
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    Alik Senior Member

    If You look at DNVGL 0342 standard, they have conversion method for inclined stiffeners. We did this for aluminium designs.
     

  15. Scarf
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    Scarf Junior Member

    For your question about effective shear area, the reason GL may be telling you to use height x thickness might be to remind you not to include the area of flange in your shear area.

    Some Rules have limiting web depth to web thickness ratios to comply with, which tries to ensure web stability against buckling. For deep webs tripping brackets can also be provided to prevent the girder twisting under load.
     
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