ultimate strength of a stiffened panel project

Discussion in 'Materials' started by mesut, Sep 22, 2009.

  1. mesut
    Joined: Nov 2008
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    Location: portugal

    mesut initialstability_1983

    hello all,

    i will have a project regarding utimate strength of a simple stiffened panel,and i have already generated the relevant macro in ansys for that.

    for ultimate strength calculation ,i am using so-called Fi method in which we have Gmax/Gyield which is supposed to be under 1 but somehow it is a little bit above 1 .i do not know what is the problem, i have been working on it but i could not.

    i hope the explanation was clear.is there anybody here have done this sort of project before? i would be greatful if somebody help me out on this issue

    kind regards,
    mesut.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    what is the purpose of the project, to mimic theory using FEA or to calculate an actual structure?
     
  3. mesut
    Joined: Nov 2008
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    mesut initialstability_1983

    hello

    i am calculating the actual structure which consists of one plane with an associated web and flange.it is simple.i modeled it in ansys using APDL, and i have implemented ultimate strength formulas(Fi method) in the macro,but frankly i am not comfortable with those formulas,too
    is it possible to send me the relevant ultimate strength formulas? some links..

    the purpose of this project is to find the ultimate strength of the panel changing the dimensions and utilizing Monte Carlo simulation,By the way do you have any information about monte carlo simulation? if you send it to me,i would be grateful.

    many thanks
    kind regards,
    mesut.
     
  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    mesut

    There are endless papers on such topics, many by the Koreans. Some really excellent papers. If you have access to a library, you should be able to find in many quality journals.

    However, I am still unsure of what your objective is, other than being able to demonstrate that you can do it too? If that is the case, then you shall need several of those very good papers, not to mention a copy of "Theory of Plates and Shells" by Timoshenko.

    As for the Monte Carlo method, any good statistic book will give you what you need. Although I have no idea why you have selected this method for assessment. Perhaps this is linked with your 'motivation' for the research.
     
  5. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    Ultimate strength

    Mesut,

    I think you are oversimplifying the problem if you are writing a program.

    I beleive you are looking for the "behaviour" of the panel in the environment it will be used for, not merely the ultimate strength.

    You will be looking for load bearing and stiffness of the panel.

    First, ultimate strength is defined as compression or tension. The values are different. Then there is manufacturers published data and the safe load you use for calculations. Usually 90% of the published data.

    In a uniformly loaded stiffened panel, one side is under compression, the other side is under tension depending on the position away from the neutral axis and the direction of load.

    This will determine the strain.

    The Gmax/Gyield you are referring to must be the stress to strain ratio, usully expressed as a fraction or decimal and is usually less than one. If it is unity, it will fail as the applied stress is equal to the strain. Do not confuse with Safety Factor as it is expressed in whole numbers. A safety factor of 2 means a stress to strain ratio of 0.5 or 1/2.

    Even when the stress to strain ratio is satisfied, you have to satisfy the ratio of span to deflection. the distance a panel will deflect from the horizontal when a vertical load is applied. Usually, this is 1/50 or 1/100. Engineering formulas apply depending on use such as Naval, Civil, or Mechanical.

    As one author says"you can build it mighty strong but not mighty stiff". Load bearing and stiffness are not the same.

    You also have to consider the material you have to use. Metal has uniform strength in all directions, wood in one direction, composites in the direction of the fiber the material runs. With composites, you have to calculate individual layers and its distance away from the neutral axis.

    Lastly, you have to consider how the end of the panel is fixed. Rigid, cantilever, simply supported, or combinations? This is standard mechanical or civil engineering formulas. Again, where do you intend to use it?

    Hope it helps.
     
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  6. mesut
    Joined: Nov 2008
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    Location: portugal

    mesut initialstability_1983

    Hello All,

    Thank You For Your Help And Sorry About Beİng Late To Respond To You Sİnce My Computer Were Crushed And I Have Been Tryİng To Handle İt.
    İ Am Not Deep İn Marİne Structure, İ Am Just A New Begİnner Student Who Wants To Study İn Marİne Structure.

    İ Wİll Use İt İn Naval.consider That One Steel Panel Associated Wİth A Web And İts Flange İs Being Extracted From A Shİp And Being Analyzed ,the Panel Is Simply Supported.frankly I Am Confused With Rotations And İ Have Just Constrained The Plate Not The Flange And Web.İ Am Not Sure About That.if You Want İ Can Send The Image To Your E-mail Address To Determine The Boundary Conditions.

    Thank You Very Much

    Kind Regards,
    Mesut.
     

  7. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    mesut
    yes, just send me a PM with the details/images...and i'll have a look
     
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