Abstract
Soil-structure interaction (SSI) effects are typically neglected for relatively lightweight buildings that are less than two-three storeys high with a limited footprint area and resting on shallow foundations (i.e., not featuring a basement). However, when the above conditions are not satisfied, and in particular when large basements are present, important kinematic SSI may develop, causing the foundation-level motion to deviate from the free-field one due to embedment effects. In the literature, transfer function models that estimate the filtering effect induced by rigid massless embedded foundations are available to “transform” foundation-level recordings into free-field ones, and vice-versa. This work describes therefore a numerical study aimed at assessing potential limits of the applicability of such transfer functions through the employment of a 3D nonlinear soil-block model representing a layered soil, recently developed and validated by the authors, and featuring on top a large heavy building with basement. A number of finite element site response analyses were carried out for different seismic input signals, soil profiles and embedment depths of the building’s basement. The numerically obtained transfer functions were compared with the curves derived using two analytical models. It was observed that the latter are able to reliably predict the embedment effects in “idealised” soil/input conditions under which they have been developed. However, in real conditions, namely when a non-homogeneous profile with nonlinear behaviour under a given seismic excitation is considered, especially in presence of a basement that is more than one storey high, they may fail in capturing some features, such as the frequency-dependent amplification of the motion at the basement level of a building with respect to the free-field one.
Highlights
Soil-structure interaction (SSI) effects are typically neglected for relatively lightweight buildings that are less than two-three storeys high with a limited footprint area and resting on shallow foundations
The finite element site response analyses carried out in the present work aimed at capturing the kinematic soil-structure interaction effects due to a building’s basement, and at comparing the FE-based transfer functions derived from the results of such analyses with analytical counterparts available in the literature
While SSI effects are typically neglected for relatively lightweight and short buildings resting on shallow foundations, large heavy buildings feature a foundation-level motion that may significantly deviate from the free-field one
Summary
Soil-structure interaction (SSI) effects are typically neglected for relatively lightweight buildings that are less than two-three storeys high with a limited footprint area and resting on shallow foundations (i.e., not featuring a basement). The focus of other works was instead to assess if SSI effects could impact foundation-level recordings, which is the focus of the current endeavour Within the latter scope, Karatzetzou and Pitilakis (2018a) [7], using a 2D finite element soil-block model representing a linear homogeneous soil, observed that the peak acceleration of the foundation motion generally decreases with respect to the free-field one by 10%–15% on average for both squatty and slender structures and for soil profiles with soft to medium stiffness. A number of finite element site response analyses were carried out for different seismic input signals, soil profiles and embedment depths of the building’s basement In these analyses, the building’s total mass and weight were disregarded, so as to capture only the kinematic SSI effects; the actual stiffness of the structure and its basement/foundation was accounted for, together with the compression-only interface conditions between the latter and the surrounding soil.
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