I have a stair that I'm concerned may be susceptible to vibrational issues. I've often used RAM Elements to model a variety of stair configurations under gravity loads and ELF seismic loading, but can it also be used to check for vibration? Most of the information I'm finding online references using SAP to find the natural frequency for use in the AISC DG11 procedures, but DG11 also says that "several commercially available programs provide convenient features for computing the FRF magnitude". I know Elements can determine mode shapes via eigenvalue analysis, but what about the natural frequency? Any guidance on feasibility and/or ways to translate the procedures in the design guide to comparable inputs in Elements would be much appreciated. For instance, the amount of frictional damping on a stair plays a big role, and there's a damping input in the Earthquake Acceleration tab, but can any of the dynamic analysis functions for seismic loads be used for human-induced vibration, or would that not be applicable Thanks!
Jason
You can get the horizontal mode shapes for the stair structure overall if that's what you need. https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/8162/ram-elements-dynamic-modal-analysis-faq
Following this...
The DG11 gives a frequency range for vertical frequency as well as horizontal frequency. How can we go about obtaining the horizontal frequency from an Elements model?
We rotated the physical model and swapped the mass directions in this case.
So when you say rotating the model to have +z up, is there a way to define what axis is vertical, or are you using the rotate command to rotate the physical model? Then would you manually change TY masses to be TZ? Loads defined globally like self-weight would need to be changed to the new vertical axis and so forth?
I was helping another user with a similar question today, and we ended up rotating the model 90 degrees so that the +z axis is up (or +x). This makes it work better with Ram Elements eigen solution.