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Thread: Problem transferring load from secondary beams to primary (steel building)

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    Default Problem transferring load from secondary beams to primary (steel building)

    Hello people this is my first post.
    I'm having this problem with RSAP2014.I made a steel building and i want the loads i have put to be transferred from secondary beams to primary ones.First of all i used the command divide in order to create the necessary nodes to my beams and this worked as i don't get any error messages during calculations.But when i checked the results i realized that no forces have been transferred from beam to beam.Here's a screenshot http://prntscr.com/2o9uo5 .As you can see the M,Q diagrams for the secondary beams are fine but can't say the same for the primary ones.Also using cladding doesn't help,cause this just distributes the load amongst all beams.Is there's something i need to with the nodes so that the program may understand what i wish to do?Generally i can't find some tool or command that it will make this kind of division to primary and secondary beams
    Also i'm curious why my slab diaphragm appears like that
    http://prntscr.com/2o9w8g
    Attached Images Attached Images

  2. #2
    I could stop if I wanted to kmarsh's Avatar
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    Default Re: Problem transferring load from secondary beams to primary (steel building)

    Hi Kostas,

    Both of these issues suggest that there are elevation differences between beams and secondary beams. How, exactly, that would happen by using divisions to add nodes, I'm not sure. I have a couple of suggestions for you:
    1. There is no need to divide the primary beams unless you are using division to give yourself snapping points for the secondary beams. Robot works on what I'm going to call a "super model" which is used by Robot to generate the final computational model (the one from which the matrix of equations is extracted and solved) Simply putting the end of a secondary beam along the same line as a primary beam will be enough for Robot to interpret that there is intended to be a connection there.
    2. I assume you may have had warnings during calculations indicating some instabilities? If so, and you opted to ignore those warnings, you will still get the model to solve but it will most likely be incorrect. Check the deflections of the nodes at the ends of the secondary members to see if the deflections are huge. If so, this will support the theory that there are small differences between the nodal locations and the line of the primary beam.
    3. try using the "Detailed Correct..." tool from the Edit menu. If you correct all framing members on this level "to plane" you should be able to remove any inaccuracies vertically between these members. If there continue to be inaccuracies, you can start aligning elements to line, or to vertical planes to get them all aligned. You can check these yourself by looking at the coordinates of the secondary beam end nodes and the primary beam end nodes.
    4. If you have checked the nodes, corrected the model and still cannot solve the problem, you might try opening the file in "Repair Mode" which can sometimes correct inconsistencies in the model if they are detected.

    If all of that does not work, you can post your model here and we can take a look at it to see what we can find.
    Thanks,
    -Ken
    Ken Marsh
    Owner, Marsh API

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    Default Re: Problem transferring load from secondary beams to primary (steel building)

    Hi

    It seems your slab diagram shows up like it does because you have calculation model setted as "rigid diagram" (or something similar). Try setting calculation mode to FE mesh and see if your slab still looks like same.

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    Default Re: Problem transferring load from secondary beams to primary (steel building)

    First of all thank you both for your time and your interest about my problem.jpo82 you're right i have set my slab as a rigid diaphragm as you said.i chose to do so cause i'm not interested in analyzing the slab itself but i'm only interested in its stiffening effect.the fact that it appears like that causes me only presentation problems so i was just wondering if there was a way to "hide" these lines that appear outside the building.
    Now as for my main problem with the loads everything is correct in terms of elevation kmarsh.i also tried your other suggestions(adding the secondary beams without using divide first and running the file in repair mode). Unfortunately nothing seems to work.The program refuses to realize that Fz from the secondary beams should be put on the primaries.Anyway i'll be posting the file and hope that someone can find a solution.
    Attached Files Attached Files

  5. #5
    I could stop if I wanted to kmarsh's Avatar
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    Default Re: Problem transferring load from secondary beams to primary (steel building)

    Hi Kostas,

    Well, we're one step closer... I noticed that you have all the slabs set to "Full Stiffening (Rigid Body)". The full rigid body stiffening is *literally* a rigid body. This is why no forces are being put into the primary beams. Change your panel calculation model to "Flexible Stiffening XY" as shown here:
    FlexibleStiffening.png
    and you will be closer to getting your model to perform like you want.

    If you'd like more information, I cover the topic of panel calculation models in detail in Robot Essentials.
    Let me know how that goes for you.
    Thanks,
    -Ken
    Ken Marsh
    Owner, Marsh API

  6. #6
    I could stop if I wanted to kmarsh's Avatar
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    Default Re: Problem transferring load from secondary beams to primary (steel building)

    Kostas,

    You had also asked about being able to turn the rigid diaphragm off in the view for visual clarity. You can find the visibility setting for those here:
    diaphragmlinks.png

    Hope that helps,
    -Ken
    Ken Marsh
    Owner, Marsh API

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