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  • 1.  HOW TO CALCULATE THE EQUIVALENT MOMENT OF INERTIA FOR A GRADED-THICKNESS CIRCULAR COLUMN?

    Posted 12-03-2018 12:12 PM
    If I have a thin-walled steel tubular circular column with graded-thickness along its longitudinal axis. How can I get the equivalent moment of inertia for the whole column?

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    Qusay Al-Kaseasbeh S.E., S.M.ASCE
    Grand Forks ND
    (701)885-2412
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  • 2.  RE: HOW TO CALCULATE THE EQUIVALENT MOMENT OF INERTIA FOR A GRADED-THICKNESS CIRCULAR COLUMN?

    Posted 12-03-2018 06:38 PM
    Edited by Tirza Austin 12-03-2018 06:38 PM
    One option could be to divide whole column in segments, estimate the average moment of inertia of each segment based upon given dimensions and integrate along the length for the given loading condition to find out the deflection at selected location along the length. You may have to go back to your Mechanics of Materials Textbook and look at one of the methods given to integrate along the segmented column, or Another Option Google out for the 4th Edition of the Standard Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Appendix B3 for tapered poles. You may have to search for a bit in the web, but if you do not find a specific formula, then use your good friend textbook of strength of materials and set up something n Excel or so.

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    Pedro Munoz Ph.D., P.E., M.ASCE
    Principal
    PRM Engineering, LLC
    Methuen MA
    (978)7388001
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    Original Message


  • 3.  RE: HOW TO CALCULATE THE EQUIVALENT MOMENT OF INERTIA FOR A GRADED-THICKNESS CIRCULAR COLUMN?

    Posted 12-04-2018 07:44 AM
    Edited by Tirza Austin 12-04-2018 07:43 AM
    Moment of Inertia for circular object is measured with respect to the polar axis.

    I  =  ∫ r2 ∂A

    for circular object, the voided part is considered weightless and cannot contribute to the moment of inertia.

    Therefore,      I  =  π (D4 - d4 ) /32

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    Olusegun Afolabi P.E., M.ASCE
    University of Lagos
    Lagos
    234803 4248600
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    Original Message


  • 4.  RE: HOW TO CALCULATE THE EQUIVALENT MOMENT OF INERTIA FOR A GRADED-THICKNESS CIRCULAR COLUMN?

    Posted 12-04-2018 07:53 AM
    Edited by Tirza Austin 12-04-2018 07:53 AM
    This requires special consideration as stiffness is different at each end, so the off diagonal terms are different in you stiffness matrix. Depending on the variation, the difference could be significant. Suggest to model as separate elements if you software doesn't support members with variable section.

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    Gregory Shafer P.E., M.ASCE
    BRIDGE TECHNICAL MANAGER
    Ellicott City MD
    (410) 480-0967
    BRIDGE TECHNICA
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    Original Message


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