XFrame2D - analysis

Hello there, I have a couple of queries related to XFrame2D:

  1. What exactly is meant under geometric non-linear analysis? Is it a full GNA or a linear analysis with initial imperfections?

  2. I have noticed that a tapered beams can be used which is great. But do you intend to include a haunch in the design of frames? I know that stiffness of connections is adopted in the analysis but it would be excellent to take into account additional stiffness of a haunch to a beam automatically from connection design. I am aware that a haunch can be substituted by a tapered beam but it is not so accurate and it means additional manual operation.

  3. If I have understood correctly, there is no LBA (Linear Bifurcation/Buckling Analysis) to check stability of frames. Do you intend to add stability checks to the program?

  4. We need to carry out a standard linear analysis of a frame without imperfections. So I have set up everything as required:

    But for some reason, I am still getting results with the initial imperfections in ULS, please see picture below:
    Could someone advise please?


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  1. Yes. It is a full GNA of course. And the global initial sway imperfections according to art. 5.3.4 are taken into account as well. See the background information in the manual.

  2. Of course the haunch is taken into account already. See image below. Even in combination with a tapered beam.

  3. Correct there is no LBA (Linear Bifurcation/Buckling Analysis) to check stability of frames. This is just a rough estimate of model buckling. There is no need for that at all since Euler buckling is included in the GNA analysis. The stiffness of each member is corrected (decreased) by the axial force in each iteration step. If Euler buckling occurs in one or more beams the global stiffness matrix of the structure becomes singular (reaches singularity) and/or node displacements become very large.
    Note that there is no need to check Euler buckling since this included in the GNA. The only omission here is the lack of initial bow imperfection. That is why you must check buckling in the steel check using the beam length as buckling length. Please read the background information in the manual and the Eurocode.
    The check of stability is done within 1) the analysis and 2) the member steel check according to Eurocode.

  4. Note that you should always take imperfections (global and bow imperfections) into account. For no tall buildings the influence of global imperfections could be limited. That is why you as an engineer can choose not to charge this. Note that our implementation of the steel check according to Eurocode is based on GNA only. The final calculation is a GNA.

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