ERROR when run analysis on RM

Hi all! I modeling a curve steel bridge but non-composite with deck. When I run analysis on RM, i have errors:  Negative pivot: Node...global DOF (1).... Help me please!! .

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  • Hi Phu,

    Nice long bridge project.

    You get a negative pivot error anytime there're equation system instabilities at a specific node, indicating the Degree Of Freedom that causes this conditions. You might need to revise your boundary conditions in the support hinges, i.e. the translational and rotational releases as this displacement’s components are not automatically checked in the input, just in the calculations. Another common mistake that causes this type of error is to forget some Elements activation. Other option is related to the evaluation of the load applied.

    Check your error/warnings log file.

    In your specific case it only happens in the Influence lines evaluation where you assigned traffic lanes to the beam elements 10083-10202 and the errors are either at other active nodes that are not connected to the structure so cannot be loaded or calculated: 15083-15703,16203, 16703,10120,11190; or at the beginning or end nodes of the structure:10083, 11083, 10203,11203 where you might need to modify your influence line to be a little bit shorter.

    I believe most of those errors happens due to the concept of the non-composite deck characteristic. After pouring the slab the top elements should be connected to the beams and not just work totally independently? You had created a series of different nodes for these concrete slabs and, in it might be the case that they should be the same nodes of the original steel girders and of the resulting composite steel and concrete beam. Then the traffic load shall be applied in the composite elements.

    If you have more doubts I suggest you to send us a Service Request.

    Thanks,

    Marcos Beier

    marcos.beier@bentley.com

    Senior Technical Support Engineer, Bridge

    MSc., Structural Analysis Specialist, Civil Engineer, RM Bridge Enterprise

    Bentley Systems Inc.

    www.bentley.com.br

    Answer Verified By: PHU TANGOC