Best Approach to Model and Design a Simple Four Sided Moment Frame Building in RAM SS

I was wondering if there is any literature on the best way to approach the design of a simple four sided moment frame building using RAM Structural System?

Thanks,

Scott

  • Right, when the design is controlled by something in the Frame module (e.g. drift or steel provisions) then the user has to manually change the size (using View/Update or Assign – Size) until everything works. “Optimizing” lateral members is tricky for a number of reasons. Take a simple moment frame example. Given a certain size for the beam and columns you get a certain distribution of forces. If you then select a member size that has the strength to resist those forces then you change the force distribution, not to mention the self-weight, so another analysis is required and another optimization and so forth.

    We could add an iterative member optimizer to handle such a thing, and we probably should (I’m sure that’s already on the enhancement list somewhere), but when you add optimization for drift, seismic provisions, and joint checks that could get overwhelming.



  • Ok, sounds great, but I currently have to manually select beams and columns based on the controlling criteria correct? Is there any thought of in the future having something like an auto-select list to base the iterations off of? Thanks for your speedy response.

  • It’s a little known fact that if the beams and columns are modeled as lateral members, but not assigned a specific size, the RAM Steel beam and column modules will pick a size for you, based on the same criteria used to select gravity members. So you can simplify your process and start with lateral members from the beginning. The thing to remember is that if circumstances change, like the criteria or loads, then you have to clear those sizes in Modeler in order to have the gravity modules select sizes again. Also note, the DataCheck will give a warning for unsized lateral members, but those warnings can be ignored.

    Regardless how the initial sizes are selected it’s always important to evaluate the design in RAM Frames Steel – Standard provisions if not also in the Seismic Provisions – where the gravity and lateral loads are considered together along with notional loads, P-Delta effects, etc.

    For a moment frame structure I would argue that the extra depth in the sections required to keep drift limits in check is more often than not the governing factor, however, so having the program select initial trial sizes to meet gravity design is not a lot of time savings. For drift sensitive structures the Drift Control mode of Frame is a powerful tool to help efficiently optimize the member area and inertia.



  • Yea, maybe I didn't explain my question correctly. Currently RAM SS optimizes gravity beams and columns using the RAM Steel Beam and RAM Steel Column Modules. It appears to me that there is currently no method to optimize a simple moment frame building other than inputting sizes by using the view/update under steel code checks in RAM Frame.

    My question is that is there a certain way I should approach that?  For instance should I put everything in as gravity, use the RAM Steel Beam and RAM Steel Column modules, and then go back to modeler and change all of the beams to lateral? My first question would be that if I do it this way will the sizes that were just found using the gravity loads still stay assigned to the beams/columns (I am assuming I need to freeze the design in the respective modules).

    Then after this step I would go into RAM Frame, run the analysis, load combinations, and then the Steel Designer, and I would have to go in an manually change the sections to meet the design loads imparted on them.  

    I have included my approach in number format below for ease of reading.

    1. Assign all beams and columns as gravity members.

    2. Design beams as gravity members using the RAM Steel Beam Module (Freeze design after it has been completed)

    3. Design Columns as gravity members using the RAM Steel Column Module (Freeze design after it has been completed)

    4. Go back to RAM Modeler and assign all frame members to be lateral.

    5. Go to RAM Frame and run the analysis, load combinations, and Steel Design processor

    6. Manually go an update beams/columns that fail during the member check under the steel post processor.

    I hope this better explains my question, if you need any further information please feel free to ask me a question back in the forum.

    If my approach is close to what I stated above, is there anything in the works in the future in RAM Frame that would allow the engineer to assign a set of beams that would be checked and the program would pick the most efficient beam?

  • There's really nothing special to it, just model what you have. If there are corner columns and you need to consider orthogonal effects, that's an option in the seismic load generator. Maybe I’m missing the heart of the question.