Hi,
I am currently modelling a 4 story concrete building with a single core with two levels of basement.
I am trying to run the spectral analysis using AS1170.4 and I have set all my floor diaphragms to rigid diaphragm. The model dissipation for each direction has reached over 90%, however the issue I am running into is the rigid diaphragms which consist of concrete slab with thickness of at least 180mm deflect unrealistically. The shear walls between adjacent floors also experience rigorous deformation.
This only occurs in spectral analysis, the equivalent static earthquake cases do have a realistic deflected shape.
Just wandering what might be the cause of such issue.
Thanks
Try without considering sign. See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/4029/ram-frame---dynamic-analysis-faq