deck structure analysis

Discussion in 'Boat Design' started by greycloud, Aug 14, 2014.

  1. greycloud
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    greycloud Junior Member

    Greatings every one

    I'm designing the carling for a winch that is to be fixed to a vessel's deck. the problem I'm facing is that the bending moment caused by winch operation will be applied mid plate. i looked in many references to find such a case of plate bending but i couldnt so hope someone can give any insight to solve this problem

    Thanks in advance
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

  3. greycloud
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    greycloud Junior Member

    ad hoc: thanks but my problem is only in analyzing the bending stress in the deck plate caused by the winch moment. the earlier thread u posted doesnt mention anything specific about my problem. I need any equation used or method for breaking down this problem into smaller pieces. the bolts and shear stresses are easy and dont cause me any trouble
     
  4. TANSL
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    TANSL Senior Member

    greycloud, I think you should better analyze the problem. The plate must support a shear stress generated by the way of working the winch.
     
  5. NavalSArtichoke
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    NavalSArtichoke Senior Member

    If you expect just the deck plate to resist the load from the winch, good luck!

    IMO, you should have the deck to which the winch is affixed reinforced with beams or framing below. The deck plate can act as the upper flange of such beams or frames.

    You haven't described the purpose of this winch or the amount of pull you hope to generate. Is this a small machine, like a line tugger, or something much larger, like an anchor handler?
     
  6. TANSL
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    TANSL Senior Member

    Agree. The calculation will allow you to determine whether to increase the thickness of the plate, or reinforce it underneath, or both at once. The important thing, imo, is to correctly analyze the problem and therefore give the plate the right solution. You can not treat a problem of shear stress, increasing, for example, the radius of gyration of "beam".
    Ad Hoc comprehensively analyzes the problem in the thread refrenced in post # 2.
     
  7. greycloud
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    greycloud Junior Member

    Tansl and Navalisartichoke: i know the plate alone will fail and i did mention in my first post that i'm designing the carling but i mentioned the plate because the structure is considered a plated structure.

    i'm well aware that there are shear stresses exerted on the plate and carling but my difficulty is in the bending stress. I'm asking for the way engineers analyze the bending stress in such case as you are experienced.
     
  8. greycloud
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    greycloud Junior Member

    the winch will pull a load of 40 tons it is relatively big
     
  9. TANSL
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    TANSL Senior Member

    It's clear that you know exactly what you're trying. But clarifies me a question, please, what is, for you, the bending stress and how it occurs?. I had never heard this kind of stress.
     
  10. NavalSArtichoke
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    NavalSArtichoke Senior Member

    I think I may be misunderstanding what you are calling a 'carling'.

    A 'carling' represents a longitudinal beam which runs along the edge of a hatch opening or other penetration in the deck. Does your winch sit atop some opening?

    In any event, we're probably going to be talking past one another unless you can provide some drawings or sketches which illustrate the structure atop which your winch will be placed.

    If the winch is pulling 40 tons, you probably should snag a naval architect or structural engineer to design this foundation, and not try to do it yourself if you have no training or experience.
     
  11. greycloud
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    greycloud Junior Member

    Sorry i didn't respond earlier i had a busy weak. hope u people are still around.

    TANSL: the bending stress in our case is the result of a varying line load creating a couple whos axis is parralel to the width of the plate.

    Naval:sorry looks like i used the wrong word here i meant stiffeners. i attached some sketches and drawings hope they help.
     

    Attached Files:

  12. Ad Hoc
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    Ad Hoc Naval Architect

    Then clearly you have not understood the link I posted.
     
  13. gonzo
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    gonzo Senior Member

    The drawing shows a force vector parallel to the deck. Is that the only direction it will have? Otherwise, you need to design for worst case scenario.
     
  14. greycloud
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    greycloud Junior Member

    AD Hoc: as u are an experienced member here I took another look at your thread. did u mean that i should neglect the plate and apply the loads to long and transverse beams and their supports? I respect your opinion.

    gonzo: the loads are actually perpindicular to the plate plane. perhaps the drawing was not so clear.so what do you think about this case?
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    It should not matter whether you consider me experienced or not, you need to comprehend the post, in the link I provided. It is not about me, it is about the information I posted.

    You have to address 2 issues 1) Bending and 2) shear..and if aluminium, 3) deflection.

    Follow the load path and that will tell you what you need to analyse; as noted in my link.
     
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