18.6. Modal Mass and Modal Contribution

Try these first

1. 1.

   What does modal mass represent?

   Hint

   Think about which mass is involved in the structure's response.

2. 2.

   Define modal contribution.

   Hint

   Consider how modes influence seismic events.

3. 3.

   What does modal mass signify in structural dynamics?

   • Total mass of the structure
   • Mass participating in a specific mode
   • Unrelated to seismic analysis

   Hint

   Connect it back to modes of vibration.

4. 4.

   True or False: The modal contribution is irrelevant for low-rise structures.

   • True
   • False

   Hint

   Reflect on the importance of all structures during dynamic analysis.

5. 5.

   Given a structure with varying modal contributions: Mode 1 contributes 40%, Mode 2 contributes 30%, and Mode 3 contributes 25%. Compute the total contribution and discuss implications for engineering assessments.

   Hint

   Add the contributions to find the total.

6. 6.

   In an analysis, a structure with a total of 5000 kg mass exhibits a modal mass of 4600 kg in the first three modes. What percentage of the total mass does this represent? Discuss the significance in designing for seismic responses.

   Hint

   Use the formula: (modal mass / total mass) * 100.