Nonlinear response of superstructures influenced by frequency-dependent oscillations in impedance functions of pile groups embedded in a layered soil

Abstract eng:
This paper presents the effects of frequency-dependent oscillations in the impedance functions of a pile group embedded in a layered soil medium upon the dynamic nonlinear responses of structural systems. Single-degree-of-freedom systems with various natural frequencies and yielding strengths are taken into consideration for superstructures. The impedance functions in the horizontal and rotational directions evaluated by using the Flexible Volume Method are simulated based on a so called “Gyromass Element Method (GEM)”. This author proposed a simple parameter model that can simulate various types of frequency-dependent impedance functions by using a mechanical element called a "gyromass", a frequency-independent element defined as a unit system that generates a reaction force due to the relative acceleration of the nodes between which the gyromass is placed. This method can calculate the time-history response of inelastic structures supported by soil-foundation systems showing frequency-dependent oscillations in their impedance functions. In this study, responses of the superstructures evaluated by the GEM and by an approximate method using static impedance functions are compared. The numerical results show the tendencies of the responses of structural systems to be influenced by oscillations in the impedance functions, such that the oscillations may affect superstructures that have particular natural frequencies and yield strengths, and may affect the responses of inelastic structures more strongly than elastic structures.

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