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Shrinkage Strain Load & Moment capacity error - LBC Substructure

William Shekarchi
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I have bent that is being constructed in two phases so some shrinkage will happen on the first phase before the next phase is constructed. In the final condition, I could assume the entire shrinkage strain is applied to both sections but that will be very conservative. Is there a way to differentiate the strains in the final model?

I also noticed that the shrinkage strain causes tension in the bent cap but the moment capacity is not reduced based on a P-M diagram. Is this correct? If so, why is this not accounted for?

Thanks,

Will

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    Currently there is no option in the program to differentiate the strains in the final model.

    I would suggest to input average Shrinkage Strain value so that it won't b be conservative and you should be able to check the forces and reactions in the Analysis TAB to make it is within limits.

    Currently LEAP Concrete does not design the column in tension and also the program does not show anything
    in the interaction diagram for a column in tension.

    As per the RCpier user manual.
    Only the axial force and moments in the global X and Z-direction are used for the column design. A moment
    interaction diagram is constructed for each combination. The capacity of a column is determined by the method
    described on page HC-17 from RCpier Tutorial Manual.

    Tutorial Manual is available in this path C:\Program Files\Bentley\LEAP Bridge Concrete CE V21\Help\US

    For additional information related to Creep and shrinkage please check the Bentley Communities link.

    https://communities.bentley.com/products/bridge_design___engineering/w/bridge_design_and_engineering__wiki/15681/creep-and-shrinkage-values

    Answer Verified By: William Shekarchi 

  • 0 Offline in reply to Vinay mysore

    Thank you for the response. My next option was to use a weighted average strain similar to what you suggested.

    The P-M interaction I mentioned was actually for the bent cap but since the columns do not account for tension then it is clear the bent cap will not as well. Depending on the level of tension, the moment capacity could be greatly over-estimated.

    On a side note, the beta factor for the simplified method should be reduced (between 0 and 2) based on the amount of axial tension in the bent cap in accordance with ACI methods. The simplified method is giving much greater results than the general MCFT.

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  • 0 Offline in reply to Vinay mysore

    Thank you for the response. My next option was to use a weighted average strain similar to what you suggested.

    The P-M interaction I mentioned was actually for the bent cap but since the columns do not account for tension then it is clear the bent cap will not as well. Depending on the level of tension, the moment capacity could be greatly over-estimated.

    On a side note, the beta factor for the simplified method should be reduced (between 0 and 2) based on the amount of axial tension in the bent cap in accordance with ACI methods. The simplified method is giving much greater results than the general MCFT.

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