# Earthquake Engineering Questions and Answers – MDOF System – Soil Structure Interaction Effects

This set of Earthquake Engineering Multiple Choice Questions & Answers (MCQs) focuses on “MDOF System – Soil Structure Interaction Effects”.

1. When is Soil-Structure Interaction necessary to be considered?
a) When superstructure is more flexible and soil underlying the foundation is stiff
b) When the superstructure is stiff and soil underlying the foundation is flexible
c) When both superstructure and soil underlying the foundation are flexible
d) When both superstructure and soil underlying the foundation are stiff

Explanation: When the superstructure is stiff and soil underlying the foundation is flexible then, the seismic waves propagating through the soil changes the properties of the soil and then soil structure interaction is required to be considered.

2. What are the two types of Soil Structure Interaction?
a) Direct and Indirect Interaction
b) Direct and Inertial Interaction
c) Kinematic and Indirect Interaction
d) Kinematic and Inertial Interaction

Explanation: When the changes due to discontinuity in medium of wave propagation and due to wave propagation in elastic medium is considered, then it is called Kinematic Interaction. When the deformation and stresses in the soil due to vibration of the structure is considered, then it is called inertial interaction.

3. What are the two approaches adopted for dynamic analysis including Soil Structure Interaction effects?
a) Direct and Indirect Approach
b) Direct and Substructure Approach
c) Substructure and Indirect Approach
d) Substructure and Superstructure Approach

Explanation: Direct Approach is based on including the soil medium in the mathematical model developed for dynamic analysis. The Substructure approach includes determining foundation input motion, frequency dependent impedance functions and computation of response of structure on frequency dependent soil springs.

4. When will the solution from the Direct approach and Substructure approach be identical in dynamic analysis including Soil Structure Interaction effects?
a) When the Structural Foundation is perfectly rigid
b) When the Soil underlying the foundation is perfectly rigid
c) When the Super-structure is perfectly rigid
d) When the Super-structure is flexible

Explanation: When the substructure or the structural foundation is perfectly rigid, then the effect of the finite element discretization done in the direct approach match with the effect of soil springs in the Substructure Approach.

5. What is the common numerical trick to force the lower modes of the combined soil–structure system to correspond to the deformations in structural system?
a) Consider the soil medium to be denser than foundation
b) Consider soil medium to be rigid
c) Consider soil medium to be massless
d) Consider soil medium to be flexible

Explanation: Considering the soil medium to be massless forces the modes for soil deformation to move to the higher end of the eigen spectrum, thereby providing structural modes at the lower end of the eigen spectrum.

6. The change in material properties leads to scattering of seismic waves at the soil-foundation interface.
a) True
b) False

Explanation: The change in material properties lead to scattering, diffraction, reflection and refraction of the seismic waves at this soil-foundation interface. It changes the nature of ground motion at that point from what would have otherwise observed in the absence of structure and foundation.

7. What are the Impedance functions in Substructure Approach represented by?
a) Linear and Rotational Soil Springs
b) Linear and Rotational Foundation Springs
c) Only Linear Soil Spring
d) Only Rotational Soil Spring

Explanation: The Linear and Rotational springs have complex stiffness denoted by $$\bar{k}_u$$ and $$\bar{k}_0$$ respectively. The damping of soil deposits is contained in the imaginary component of the impedance functions.

Sanfoundry Global Education & Learning Series – Earthquake Engineering.

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