# Ram Elements Dynamic Analysis

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:

• I have rotated the model so that the Z-direction is "Up and Down" and the X-direction is "Sided to Side".
• Defined an X and Z direction dynamic load case in the load conditions module. For each load case I set the "Earthquake Scale Factor to 1.0, the damping ratio to 1% and set the direction to 0 degrees and 90 degrees for the X-direction and Z-directions respectively.
• Added mass loads to the nodes in the Z and X direction.
• The dynamic analysis has been run with the CQC method, with 10 modal shapes and considering node mass only.

My questions are:

1. Why are the mass loads not load case specific? The inputted masses appear to be included in all load cases?
2. I am getting about 30 percent participation in the X-direction and 70 percent participation in the Z-direction. When I turn mass loads off in the X-direction I get 100% mass participation in the X-direction. How do I get 100% mass participation in each direction?
3. Is there a way to get the natural frequency (or period) for each modal shape in each direction? When I turn on Finite Elements Model and view the modal displacements and deflection I am given 10 periods, which do not appear to be direction specific.

Thank you

Parents
• 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).