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Architecture Engineering QUESTION #2355
Question 1
In seismic base isolation design, the primary purpose of installing isolation bearings at the base of a structure is to:
  • Increase the fundamental natural frequency of the structure to avoid resonance with ground motion
  • Shift the fundamental period of the structure to a longer period to reduce seismic forces and decouple structure from ground motion✔️
  • Increase the structural stiffness to limit inter-story drifts during earthquakes
  • Transfer seismic forces directly to the foundation without amplification
Correct Answer Explanation
Base isolation works by inserting flexible bearings (elastomeric or friction pendulum) between the structure and foundation. This elongates the fundamental period of the structure (typically to 2–4 seconds), placing it well beyond the dominant period of earthquake ground motion (0.1–1.0 s). This drastically reduces acceleration transmitted to the structure. The isolators accommodate large displacements at the isolation level while the superstructure moves as a near-rigid body.