17.13. Effective Modal Mass

Try these first

1. 1.

   Define effective modal mass.

   Hint

   Think about how modes influence overall behavior.

2. 2.

   What is the formula for calculating effective modal mass?

   Hint

   Consider the components involved!

3. 3.

   What does effective modal mass measure?

   • Total mass of the system
   • Contribution of each vibration mode
   • Damping ratio

   Hint

   Think about the role of vibration modes.

4. 4.

   True or False: The modal participation factor is squared in the effective modal mass calculation to emphasize larger contributions.

   • True
   • False

   Hint

   Recollect the formula discussed.

5. 5.

   A building's effective modal mass is calculated as follows for three contributing modes: Mode 1 (M_eff1 = 0.4), Mode 2 (M_eff2 = 0.36), Mode 3 (M_eff3 = 0.25). What is the cumulative effective modal mass? Next, if the total mass of the building is 1000 kg, how much mass is effectively accounted for?

   Hint

   Add up the effective masses first.

6. 6.

   If a system shows a modal participation factor of 0.9 and the effective modal mass calculated is 500 kg for the first mode, what is the effective modal mass considering all factors?

   Hint

   Calculate it step by step using the squared participation factor.