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SD-Lecture10-Review-of-Seismic-Concepts

SD-Lecture10-Review-of-Seismic-Concepts - Soil Dynamics...

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Soil Dynamics Lecture 10 A Review of some Basic Concepts of Vibrations

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Question #01. For a single-degree of freedom system, the natural period T is, I. The inverse of the natural frequency, II. Equivalent to the linear natural frequency, III. Expressed in Hertz (Hz). Answers: I II III I and II
Answer to Question #01. a) I only. For a single-degree-of-freedom system, the natural period T is the time in which the system completes one cycle of oscillation. The natural period T is the inverse of the natural frequency, which is expressed as, T = 1 / f

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Question #02. What is the spectral acceleration of a single-degree-of-freedom system? A. It is the minimum acceleration experienced by the system in response to a perturbation. B. It is the average acceleration experienced by the system in response to a perturbation. C. It is the maximum acceleration experienced by the system in response to a perturbation. D. It is the absolute acceleration experienced by the system in response to a perturbation.
Answer to Question #02. C. The maximum vibration of a single-degree-of-freedom system is measured in terms of acceleration, velocity or displacement. The maximum acceleration experienced by the system in response to a disturbing force is known as the spectral acceleration .

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Question #03. For the following harmonic oscillator, how is the stiffness best described? A. The stiffness is best described as the force acting on the ideal linear spring. B. The stiffness is best described as the force deflecting the spring a distance of 1 unit. C. The stiffness is best described as the magnitude of the spring deflection. D. The stiffness is best described as the reciprocal of deflection.
Answer to Question #03. B. Hooke’s law relates the amount of deflection of an ideal linear spring to the force applied to it. It is expressed as F = k x The stiffness k is the force that deflects the spring a distance of 1 unit.

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Question #04. When does the natural period of a building coincide with an earthquake’s period? A. They coincide when the natural frequency is at its maximum. B. They coincide when the acceleration is at its maximum. C. They coincide when the displacement is at its maximum. D. All the above are right.
Answer to Question #04. B. When the building’s period coincides with an earthquake’s period, resonance occurs. At resonance the acceleration response is at its maximum.

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Question #05. The period of a structure is correlated with the, I. The mass of the structure, II. The stiffness of the structure. Answers: A. I only. B. II only. C. I and II. D. None of the above.
Answer to Question #05. C. As the weight of a structure increases, the period of vibration becomes longer. For example, steel or reinforced concrete structures tend to have higher periods of vibrations compared with timber structures.

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SD-Lecture10-Review-of-Seismic-Concepts - Soil Dynamics...

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