I am running into a weird output from Ram Structural System's, RAM Frame module regarding total displacement/drift.
From my understanding, the Total Displacement at the roof level should equal the sum of the displacements of both the roof and second floor level and the story drift is the net difference between the two.
However, when I check the drift a point at the roof level the total displacement shown is only shown for the roof level and not for the entire building and I am getting a zero output for the lower second floor.
Vice versa, when I check the drift at a point for the second floor the total displacement shown is only for the second floor and I am getting a zero output for the roof level, which is not correct.
I am not sure what is wrong in the model. I have double and triple checked my inputs and outputs.
If anyone could shed some light on what I may be doing wrong that would be greatly appreciated.
Finally, just to give some background, the building is a two story building with a basement. The roof framing consists of metal deck over steel framing, and the second and first floors consist of slab on metal deck over steel framing (composite); My lateral system is Ordinary Steel Moment Frames.
I have also attached the model here for anyone who is brave enough to download and take a look.
Thank you in advance
-Warren 21116MT_06_Porsche Edison_Lateral_04-04-22.rss
In this model the diaphragms are rigid, but partial. If you request drift results at a point that is outside of the slab edge or inside of an opening at some level, then the displacement of that level/point is 0. Be sure to select points that are common on all levels to get relative story displacements.
Alternatively, use nodal displacements for points on your frames.
The ground level diaphragm won't move at all. See: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/18422/ram-frame---criteria---ground-level
Hello Seth,
Thank you for your prompt response.
Another question, are you suggesting that I should change my diaphgrams to semi-rigid and then re-run the analysis ?
In addition, when I select common points on all levels I still seem to get the same issue.
However, when I select a point on a specific frame I am getting the net displacement not on every frame. This is separate from using nodal displacement points on my frames.
Thank you
-Warren
No, I'm not suggesting a semi-rigid diaphragm, that's just an important detail when it comes to questions about drift.
All I am saying is that the exact plan location of the selected point for drift matters. Is it on the deck or not? If yes, then you should get deflection values, if not, then zero. Since your model has two partial levels that don't really overlap and then the ground level below that, I would not expect anything more than one set of drift values anywhere.
Hi Seth,
I trust this message finds you well.
I wanted to come back and shed some light on the situation as I found out what was really wrong with my model upon further inspection.
It appeared that the reasons I was not getting consistent drifts in my model from story to story was actually because my story labels did not match the floor type labels. This is a novice mistake on my part. However, I adjusted them to match and my drift values were correct in what I was expecting.
I just wanted to share that with someone in case anyone comes across this issue in the future.
Also, in hindsight, I should have checked my model more carefully.
Thanks again for all your help Seth,