15.5.1. First Mode Shape

Try these first

1. 1.

   Define 'mode shape'.

   Hint

   Think about how a structure deforms when it vibrates.

2. 2.

   Why is the first mode shape important in seismic analysis?

   Hint

   Consider what happens during an earthquake.

3. 3.

   What best describes the first mode shape?

   • A localized deformation pattern.
   • The global movement of the entire structure.
   • The pattern of vibration without external forces.

   Hint

   Think about the first movement patterns seen in structures.

4. 4.

   True or False: The first mode shape corresponds to the lowest natural frequency of a system.

   • True
   • False

   Hint

   Consider which frequency typically is addressed first in analyses.

5. 5.

   A 10-story building experiences its first mode shape with uniform displacement across all floors. If the natural frequency is measured at 0.5 Hz, what implications does this have for the potential sway during seismic events?

   Hint

   Consider how low frequency affects movement during ground shaking.

6. 6.

   How would changing the material of a structure from steel to concrete affect its first mode shape and natural frequency?

   Hint

   Think about stiffness and its impact on vibrations.