Quasi-Kinematic Response of Embedded Foundations: Evidence of Foundation Mass Effect From Numerical Analyses and Instrumented Structures

Abstract

Abstract. Experimental and theoretical studies on soil-structure interaction (SSI)

Analytical expressions relating free-field and foundation ground motions in buildings with basement, considering soil-structure interaction

“…As shown, according to the ground type classification of Eurocode 8 [39] and the V s30 value, all the sites belong to ground type C. The fundamental period of the buildings was calculated through modal analysis for the buildings located in Greece, whereas the period of the ROB building was obtained from [25]. The resulting fundamental periods were also compared with other works which deal with the same sites [6,40] and reasonable agreement was confirmed. It should be noted that the examined sites were checked for possible contamination of the free-field motion from the response of the structure through the site selection criteria reported in [25].…”

“…The convolution of the transfer functions (rotational and translational) and the free-field ground motion defines the foundation input motion (FIM) in frequency domain. Subsequently, inertial SSI follows, which involves replacement of the foundation and surrounding soil by frequency dependent impedance functions which were computed herein per [17] based on foundation footprint and embedment dimensions, similarly to [6] and [40] where the CO and LAB buildings modeling was studied respectively. Implementation of such impedance functions on buildings foundations consisting of embedded grid of strip footings may be justified by the fact that the grid of strip footings along with the basement perimeter walls bound together by the bottom and top slabs of the basement, form a very stiff box-type structure that could be considered rigid.…”

“…However, the response at the base of the structure, that is, its foundation, is further modified due to the response of the superstructure and the inertial loads which are transferred back to the foundation. This inertial interaction has been found to affect the foundation motion only in a limited frequency range around the fundamental frequency of the structure [3], nevertheless, for structures with massive foundations it may strongly affect the response of the coupled soil-structure system [5][6][7].…”

Improved correlation between foundation and free‐field ground motions through strong motion recordings and kinematic soil–structure interaction analyses

“…In case of structures with massive foundations, the inertial effect may be extremely important as well. [5][6][7] In the context of the well-known sub-structuring method of SSI analysis, kinematic and inertial interaction, although they occur simultaneously, they are decoupled and treated at successive steps. The frequency-dependent response amplitude of the FIM over that of the free-field is usually described by means of a transfer function in the frequency domain and is approximately equal to unity for low frequencies, while reducing with increasing frequency, at least for uniform soils.…”

“…3,4 Many studies have investigated rigid foundations of various shapes, embedded or lying on the surface of a uniform or layered half-space, excited by vertically propagating, or inclined wave fields. [5][6][7][8][9][10][11][12] Inertial interaction includes replacement of the soil surrounding the structure by frequency-dependent impedance functions, which define the features of frequency-dependent, coupled spring and dashpots placed at the soil-foundation interface. The parameters affecting the properties of impedance functions in frequency and time domain are reported in the literature.…”