# Earthquake Engineering Questions and Answers – Response Spectra

This set of Earthquake Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Response Spectra”.

1. Which of the following gives the number of independent displacements required to define the displaced position of the mass with respect to its original positions?
a) Elasticity
b) Stiffness
c) Offsets
d) Degrees of freedom

Explanation: Degrees of freedom are the set of independent displacements or rotations which can fully define the displaced position of the mass relative to their original position. A vertical cantilever which has its mass concentrated at its tip can be idealized as a single degree of freedom (SDOF) system. The DOF can be represented by the lateral displacement u of the mass.

2. Which of the following statement is true?
a) Acceleration spectrum is a plot of natural period of vibration versus value of damping
b) Acceleration spectrum is a plot of amplitude of vibration versus peak absolute acceleration
c) Acceleration spectrum is a plot of natural period of vibration versus peak absolute acceleration
d) Acceleration spectrum is a plot of amplitude of vibration versus natural period of vibration

Explanation: Acceleration spectrum is a plot of natural period of vibration versus peak absolute acceleration of oscillator mass. The natural period of vibration is for a single degree of freedom system which has a specific value of damping. The value of peak absolute acceleration of oscillator mass used in this spectrum is subjected to a base acceleration equal to earthquake accelerograms.

3. A perfectly rigid structure has infinite time period.
a) True
b) False

Explanation: A perfectly rigid structure has its time period as zero. The natural frequency for rigid structure is infinite. When the structure is rigid and the time period is zero, it moves in unison with the ground and the acceleration in such case is termed as zero period acceleration.

4. At what period does the amplification factor reach its maximum value?
a) Sub-soil period
b) Long period
c) Zero period
d) Short period

Explanation: The amplification factor reaches a maximum value at sub-soil period. In between two extreme periods, the spectral acceleration at any specific period is a constant multiplier of peak ground acceleration, which is known as amplification factor. The amplification factor increases with increase in period, reaches maximum at sub-soil period and then decreases with further increase in period.

5. Who popularized the interaction between structural systems and ground acceleration?
a) Wegener
b) Housner
c) Basu
d) Esteva and Villaverde

Explanation: Housner popularized the interaction between structural systems and ground acceleration. Wegener proposed the theory of plate tectonics. Basu carried out the evaluation of ground acceleration using Bayesian analysis. Esteva and Villaverde derived the attenuation relationships for peak ground motions.

6. Which of the following is the PGA for a perfectly rigid structure?
a) Zero period acceleration
b) Zero frequency acceleration
c) Infinite period acceleration
d) Infinite amplitude acceleration

Explanation: The value of peak ground acceleration for a perfectly rigid structure is known as zero period acceleration. Zero period acceleration is the value of spectral acceleration when time period is zero. The time period is zero for a perfectly rigid structure and the structure moves in unison with the ground.

7. Which of the following statement is true for amplification factor?
a) The amplification factor for alluvium site condition is lower than that of rocky site conditions at short periods.
b) The amplification factor for alluvium site condition is higher than that of rocky site conditions at short periods.
c) The amplification factor is same for alluvium site condition and rocky site conditions at short periods.
d) The amplification factor is same for alluvium site condition and rocky site conditions at long periods.

Explanation: The amplification factor varies depending on the type of site conditions. The amplification factor for rocky site conditions is higher than that of alluvium site conditions at short periods. Whereas at long periods, the amplification factor for rocky site conditions is lower than that of alluvium site conditions.

8. Which of the following was used by Housner to report the interaction between structural systems and ground acceleration?
a) Response spectrum
b) Deterministic approach
c) Probabilistic approach
d) Design spectrum

Explanation: Housner popularized the interaction between structural systems and ground acceleration through response spectrum. These interactions were reported for the earthquake engineers. It reflects the amplitude of ground motion, frequency content and the effect of consequent filtering by the structure.

9. The response of a structure to ground motion vibrations does not depend on the mode of construction.
a) False
b) True

Explanation: The response of a structure to ground motion vibrations depends on many factors and one of them being the mode of construction. Other factors are type of foundations, materials used, form and size of construction and duration and characteristics of ground motion. The mode of construction should be such that the structure should not settle, liquefy or slide during earthquake ground vibrations.

10. Which of the following does not affect the value of amplification factor?
a) Time period
b) Site conditions
d) Hypocentral distance

Explanation: The amplification factor is not dependent on wind load. The amplification factor varies with the change in time period. The amplification factor for rocky site conditions is higher than that of alluvium site conditions at short periods and vice-versa at long periods. The amplification factor is inversely proportional to the hypocentral distance.

Sanfoundry Global Education & Learning Series – Earthquake Engineering.

To practice all areas of Earthquake Engineering, here is complete set of Multiple Choice Questions and Answers.

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