Analytical closed-form solutions to estimate the effect of soil-structure interaction on the fundamental period and damping ratio of buildings are a useful tool to correctly interpret data of real-time dynamic monitoring of single structures as well as to assess the vulnerability of classes of buildings located on different subsoils. Most of the existing formulae simplify the structure into a single degree of freedom system (SDOF) on a shallow circular footing resting on a half-space. Nevertheless, reliable equivalence criteria to assimilate a multi-DOF building to a SDOF, a foundation grid system to a single circular footing, as well as a layered soil profile to a half space, are still not trivial. The application of the analytical formulae to more complex foundation systems require the direct calculation of the foundation impedance functions that may be onerous and too long in the above-described applications. This paper re-elaborates the analytical impedance functions and the derivation of the fundamental period and foundation damping ratio proposed in the literature and adopted by seismic design codes, to obtain solutions in which period and damping directly depend on dimensionless ratios expressing the soil-structure relative stiffness and mass, the structural slenderness and the foundation embedment. The obtained formulae were applied to five masonry buildings located on shallow covers of soft clay in Southern Italy, where the natural periods were experimentally measured.

Rocking shallow foundations have seismic performance advantages over conventional fixed-base foundations; they can limit the inertial load transmitted to the structure as a function of the capacity of the foundation. Although previous experimental campaigns have highlighted the effectiveness of rocking foundations in practice, these have tended to focus on standalone simplified single-degree-of-freedom (SDOF) systems. Structures incorporating rocking foundations, such as bridges, are more complex than these simplified designs. In addition, limited experimental work has been performed to assess the influence of the soil’s degree of saturation on the seismic performance of rocking foundations, with most studies focusing on soil layers in dry or fully saturated conditions. The purpose of this research is to appropriately model and assess the behavior of a prototype bridge system, built to incorporate rocking foundations, and placed on unsaturated sandy silt layers. A series of dynamic centrifuge tests were performed on a single-span bridge with two foundations, subject to seismic motion in the longitudinal direction. The experimental program consisted of tests on dry, saturated, and two mixed saturated-unsaturated soil layers where the water table depth was lowered to a certain depth below the soil layer surface. The soil-structure system was subjected to a suite of scaled earthquake motions of varying intensities while the response was recorded. As the depth of the water table decreased, the settlement experienced by both foundations decreased, becoming less than the settlement experienced when the structure was placed in the dry soil layer. Furthermore, as the depth of the water table decreased, bridge deck drifts were found to reduce. This study highlights the performance of rocking foundations when implemented in bridge structures resting on soils with varying water table depths.

In bridge or large building projects, pile foundation design is commonly used to resist liquefaction. However, due to the complex mechanism of soil liquefaction, liquefiable soil layers are often addressed in practical design by reducing the modulus and strength of soil as seismic design parameters for pile foundations in the liquefied ground. Therefore, developing reasonable reduction factors becomes a major concern in geotechnical engineering. This study investigates the dynamic response of the single-pile-supported structures with different fundamental vibration periods (T=1.0 s and T=0.3 s) in liquefied soil layers during seismic motion. A series of 1g shaking table tests were performed to study the behavior of soil-pile-superstructure interaction during liquefaction, to clarify this complex mechanism, and to evaluate the seismic performance of pile foundations in liquefied soil layers. This paper provides a detailed description of the apparatus installation, model design, and input motion. Additionally, the preliminary test results are demonstrated and would be discussed.

The construction and popularity of multimegawatt offshore wind turbines (OWTs) are increasing globally because of their capacity to produce clean and green energy at a low cost. As many of these structures will continue to be installed in earthquake prone areas worldwide, it becomes necessary to develop a better understanding of the dynamic soil-structure interaction (DSSI) particularly the higher mode effects involved in the dynamic response. The main aim of this study is to perform a rigorous modal analysis of the NREL 5MW offshore wind turbine using several monopile foundation modeling techniques to show the higher mode effects. Furthermore, the different parameters such as diameter and embedded depth of the monopile and soil initial moduli affecting the dynamic characteristics are investigated. The study shows that higher modes need to be considered in order to obtain a more rational dynamic soil-structure interaction response of the system.

Physical properties of soil ground are generally varying spatially. However, in the seismic design of structures, especially nuclear power plants, the physical properties are considered conservatively even though their spatial variation is observed at the ground surrounding the foundations. In this study, to clarify the effect of spatial variations of relative density (Dr) of sand on the seismic behavior of the seawall pile foundation, two cases of the centrifugal shaking table experiment under centrifugal acceleration of 50 G were conducted. They had different spatial variations composed of two relative densities of sand; one was Dr = 103% with 80% of the volume occupation ratio, another one was Dr = 70%, which liquefaction strength ratio was the half that of Dr = 103%, with 20% of the volume occupation. Based on the experimental results, it was found that the effect of the different arrangements of the sand with Dr = 70% were negligible because similar dynamic response of excess pore water pressure, horizontal displacement of the seawall, and bending strain of the seawall pile foundation were observed in both cases.

Dynamic lateral earth pressure on walls is usually estimated by applying PGA-based conventional methods. However, those methods cannot consider soil-structure interaction (SSI), which affects the magnitude and distribution of the earth pressure. In this study, we analyzed the dynamic earth pressure on the basement walls of buildings, considering the soil-building interaction by using nonlinear numerical simulations in OpenSees. The numerical model was validated by comparing its results with the experimental data obtained from a centrifuge model test. A parametric study was performed, varying building height and width, basement depth, and geotechnical properties. The results showed that the inertial interaction of the building greatly increased the magnitude of earth pressure, while the kinematic interaction had a minor effect on the magnitude of earth pressure. The findings highlight the importance of incorporating the dynamic characteristics and inertia of buildings when predicting earth pressures on basement walls in practical design applications.

Pile foundations serve the purpose of transmitting structural loads from areas with low soil bearing capacity and stiffness to deeper soil or rock strata possessing greater bearing capacity and stiffness. The type and slenderness ratio (L/D) of the pile foundation, which supports mid-to-high-rise buildings, significantly influences the seismic response of the building during any seismic disturbance. The present paper investigates the influence of the slenderness ratio of piles on the seismic response of buildings through scaled-down model tests and numerical investigation. In this study, a scaled-down model featuring a 10-storey building and varying slenderness ratios (30, 40, and 50) for the pile foundation has been utilized. All the model tests are performed in the laminar shear box through shaking table tests, and the results obtained are validated using three-dimensional finite element analysis. All the models are subjected to sine sweep tests (for natural frequency prediction) and scaled-down input ground motions. The study has examined the seismic response of the building, which is characterized by the maximum lateral displacement, inter-storey drift, and the bending moment generated in the piles. It is found that the lateral displacement of the building supported on a pile foundation (L/D = 30) increases by 139.84% in comparison to fixed-base structures (FB). However, it is also found that the lateral displacement and inter-storey drift of the building supported on the pile (L/D = 50) have decreased by 10.79% and 21.48%, compared to those resting on piles with L/D = 30, respectively. Hence, it is concluded that the slenderness ratio of the pile foundation plays a significant role in the response of the building during seismic events.