Hello, I have some questions regarding performing a Dynamic analysis in RAM elements to determine the natural frequency of a monumental stair. Following are the steps I have taken so far:
My questions are:
1. There's no particular reason why we elected to use a single mass matrix per model in Ram Elements, it's just simpler that way.
2. Generally, more mode shapes are required to capture a higher mass participation. Reducing the number of mass points is another strategy. Also make sure the masses are placed at nodes that have the potential to move.
3. There is a report Analysis - Dynamic analysis with period values (1/frequency values) for each mode shape. If the structure is no conducive to clearly directional modes then each mode will be somewhat a blend of drift and twist. There not much you can do about that other than revise the structure (or the masses).
See also: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/8162/ram-elements-dynamic-modal-analysis-faq