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Moment capacity using LFD and LRFD

Pradeepa Mayakrishnan
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In LEAP Bridge, when comparing the results for Moment Capacity of prestressed beam using LFD and LRFD, the amount of prestressing strands contribute to the capacity for the former one is drastically reduced with latter one at the same location?.Why there is difference in As for the same location in both approach?

LFD

LRFD

Thank you.

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  • 0 Offline

    Hi Pradeepa,

    The issue is related to accounting for the Development length.

    The calculation differs between LFD and LRFD code and that's the reason there is a major difference in Area of Prestressing Tendon.

    I hope it helps.

    Please let me know if you need any additional information.

    Thanks & Regards,

    Vinay

  • 0 Offline in reply to Vinay mysore

    PDF

    Hi Vinay,

    This is Hamid from EAC Consulting Inc. A member of our team had raised a question regarding the difference between the pre-stressing area  considered by LEAP Bridge when two different approaches of LRFR or LFR are used in load rating; and you had kindly responded to her. 

    We performed further calculations (please see the attachment), and found that the development length does not highly depend on the selection of the approach; and both LRFR and LFR result in the same development length. Our calculation also shows that the "effective pre-stressing area" at the considered location (H/2 where H is the beam depth) is also nearly the same for the two approaches. Our calculation results in an effective pre-stressing area which is the same as that computed by LEAP Bridge when LRFR approach is used, but what we obtained for LFR is significantly greater than the value reported by LEAP Bridge for LRF.

    We would much appreciate if you could kindly help us understand the reason behind this discrepancy.

    Regards, 

    Hamid Anajafi, PhD, P.E.

    Senior Structural Engineer 

    EAC Consulting, Inc.

    5959 BLUE LAGOON DR, SUITE 410, MIAMI, FL 33126

    305.265.5400 • 305.265.5464 (direct)

    hanajafi@eacconsult.com

  • 0 Offline in reply to Hamid Anajafi

    Hi Dr. Hamid,

    Based on the screenshot provided on the communities, that was my first observation.

    Please email me the LFD and LRFD leap files so that i can test this issue on my machine.

    Please let me know version you are working on. 

    Please email me the hand calculation as it will help me in my investigation.

    My email is "Vinay.Mysore@Bentley.com".

    Thanks,

    Vinay

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