3D dynamic soil-structure interaction in layered, fluid-saturated, poroelastic half-space

Recent studies on design optimization of steel frames considering soil-structure interaction have focused on static loading scenarios, and limited work has been conducted to address the design optimization under dynamic soil-structure interaction. In the present work, first, a platform is developed to perform optimization of steel frames under seismic loading considering dynamic soil-structure interaction (SSI) in order to quantify the effects of earthquake records on the optimum design. Next, verification of the adopted modeling technique is conducted using comparison of the results with the reference solution counterparts in frequency domain. For time history analyses, records from past events are selected and scaled to a target spectrum using simple scaling approach as well as spectrum matching technique. For sizing of the steel frames, a recently developed metaheuristic optimization algorithm, namely exponential big bang-big crunch optimization method, is employed. To alleviate the computational burden of the optimization process, the metaheuristic algorithm is integrated with the so-called upper bound strategy. Effects of factors such as the building height, presence of soil domain, and the utilized ground motion scaling technique are investigated and discussed. The numerical results obtained based on 5- and 10-story steel braced frame dual systems reveal that, although dynamic SSI reduced the seismic demands to some extent, given the final design pertains to different load combinations, the optimum weight difference is not considerable.

Dynamic soil-structure interaction (SSI) effects have always been important in the context of assessing the seismic safety and vulnerability of large and complex infrastructures such as bridges, dams, power plants, industrial units etc. Although SSI problem has been under intensive investigations in the past several decades, relatively little is known about the SSI in the case of multi-layered half-space. Majority of previous researches dealing with SSI problems were conducted for rather simple soil profiles: elastic half-space, a soil layer bonded to rigid base, or a soil layer overlying elastic half-space. Very few papers appeared in the literature tackle the SSI problem having two or more soil layers overlying elastic half-space. This is probably due to the substantial computational effort required. Advantages and limitations of widely used current approaches such as finite element method (FEM), boundary element method (BEM) and thin-layer method (TLM) are discussed. Sponsored by the Science Foundation of Sino-German Center researches into SSI on layered soil carried out at Dalian University of Technology are briefly introduced. An advanced approach for dynamic SSI analysis of structures on multilayered half-space is proposed, which circumvent difficulties encountered by FEM, BEM and TLM with relative ease. The governing wave motion equations are solved in the frequency-wave-number domain analytically. The precise integration method (PIM) is employed to perform integration to obtain numerical results. Very high accuracy can be achieved. Analytical solution of wave motion equation is written in dual vector form, which enables efficient and convenient assembling of two adjacent layers into a new one without losing effective digits. Formulations dealing with dynamic impedance of arbitrary-shaped foundation on isotropic as well as arbitrary anisotropic multi-layered soil are presented. The solution is not difficult to extend to problems dealing with foundation embedment and throughthe- soil coupling of two or more foundations. Numerical results validate efficiency and accuracy of the proposed approach.

This study investigates model errors caused by the rigid-foundation assumption in dynamic Soil-Structure Interaction (SSI), which has been widely accepted in the past decades to reduce computational effort. A linear two-dimensional model is used for a qualitative analysis that compares the dynamic responses of a rigid system, comprising a rigid foundation embedded in a layered half-space with a superstructure mounted on top, and a corresponding flexible system with the same parameters but a flexible foundation with a variable stiffness. The Indirect Boundary Element Method combined with non-singular Green’s functions of distributed line loads is employed to calculate the system responses accurately. Transfer functions computed for a range of parameters show that the rigid-foundation assumption leads to overestimating the system natural frequency and changes the peak deformations to a different extent. It is also shown through a case study of 42 earthquakes that the rigid-foundation assumption may either overestimate or underestimate the system responses by up to approximately 50%, and in some cases even by approximately 100%, depending on the frequency content of excitation and SSI dynamic characteristics.

The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the finite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave field on the nodes of the substructure composed of elements that contain artificial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artificial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplified by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verified by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.

Experimental and analytical studies were conducted to determine dynamic soil–structure interaction characteristics of a single‐span, prestressed‐concrete bridge with monolithic abutments supported by spread footings. The experimental programme, consisting of harmonic forced vibration excitation of the bridge in the transverse and longitudinal directions, revealed the presence of four modes in the frequency band, 0 to 11 Hz, and the onset of a fifth mode at 14 Hz, the highest frequency attained during the tests. The fundamental mode at 4.7 Hz was the primary longitudinal bending mode of the deck and had a relatively low damping ratio (ζ1), that was approximately 0.025 of critical. The second and third modes at 6.4 Hz and 8.2 Hz were the primary twisting modes of the deck which involved substantial transverse rocking, transverse translation and torsion of the footings. As expected, the damping ratios associated with these two modes, ζ2 = 0.035 and ζ3 = 0.15, were directly related to the relative amounts of deck and footing motion. The fourth mode at 10.6 Hz was the second twisting mode of the deck and involved relatively little motion of the footings and abutment walls, which was consistent with the low damping, ζ4 = 0.02, observed in this mode. The response data at 14 Hz suggested that the fifth mode beyond this frequency was the second longitudinal bending mode of the deck involving longitudinal translation and bending of the abutment walls.A three‐dimensional finite element model of the bridge, with Winkler springs attached to the footings and abutment walls to represent the soil–structure interaction, was able to reproduce the experimental data (natural frequencies, mode shapes and bridge response) reasonably well. Although the stiffnesses assigned to the Winkler springs were based largely on the application of a form of Rayleigh's principle to the experimental data, these stiffnesses were similar to theoretical foundation stiffnesses of the same size footings on a linearly elastic half space and theoretical lateral stiffnesses of a rigid retaining wall against a linearly elastic backfill.

An indirect boundary element method to model the 3-D scattering of elastic waves in a fluid-saturated poroelastic half-space

Dynamic soil-structure interaction models for fragility characterisation of buildings with shallow foundations

Seismic design and analysis of underground structures

Quantifying dynamic soil-structure interaction for railway induced vibrations

The influence of dynamic soil–structure interaction (SSI) on simply supported railway bridges is investigated. Impedance functions are calculated considering shallow foundations in soil strata limited by bedrock. The impedance functions are coupled to bridge models, and the assembled soil–bridge systems are investigated addressing the modal properties. A parametric study is performed on a large set of soil–bridge systems. Finally, the response to train loading is analysed. The study shows that the effects of SSI are essentially different depending on whether radiation damping is active or not. Shorter bridges are often affected by radiation damping and the response due to train loading may be significantly reduced when SSI is considered. However, for longer bridges (>15 m) the effect of SSI is often small. Due to the stiffness reduction of the impedance, some bridges may even have a detrimental effect from SSI and a reduction of the traffic speed is obtained.

The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector antenna is investigated. The main free vibration characteristic of an antenna is natural frequency. The analysis model simulated with fixed base condition and soil structure interaction. A parametric study is conducted to understand the antenna structure soil behavior (soil structure interaction (SSI)) by changing the antenna orientation, soil properties with impedance functions (spring constants) as per ASCE 4-16 and 3D (three dimensional modeling of founding medium) model methods. To address this problem, Finite Element Method is used to model soil structure interaction analysis of antenna structure with foundation by MSC PATRAN & NASTRAN using direct method and impedance method. The soil considered as homogeneous and analyzed for shear wave velocity (Vs) 100 m/s, 180 m/s, 250 m/s, 450 m/s, 760 m/s for antenna with 90° elevation. To study the embedment effect, soil around the footing and pedestal is considered. The frequency results are compared for antenna with four orientations with Vs 100 m/s soil properties. Considerable reduction in frequency observed with soil structure interaction in higher modes. Soil structure interaction study in antennas helps in finding what extent the natural frequency falls when the soil interaction is incorporated in the model.

This paper presents the results of 3D nonlinear finite element modeling of seismic soil-foundation-structure interaction in fully integral abutment bridges using HP steel piles as bridge foundations. The soil’s stiffness has a significant effect on load distribution when the soil, HP piles, abutment, and superstructure act as a combined system to resist seismic forces on the bridge. Due to the lack of knowledge on dynamic soilstructure interaction during earthquakes, the real world design procedures are kept simple and conservative. A deeper understanding of soil-foundation-structure interaction mechanism will facilitate sustainable bridge design by optimizing the sizes of structural members and increasing the service life of bridges. In this paper, the seismic soil-structure interaction mechanisms are investigated for the bridge longitudinal direction as well as for the bridge transverse direction. Both simple span and two-span bridges are analyzed using the finite element program ANSYS. The research findings will provide the theoretical support to sustainable bridge design by optimizing the size and orientation of HP steel piles in fully integral abutment bridges.

Real-time dynamic hybrid testing for soil–structure interaction analysis

Soil-structure interaction (SSI) plays a critical role in evaluating seismic performance and guiding damping design in earthquake-prone regions. This study investigates the influence of damping layers placed between the half-space and the foundation on dynamic SSI and the seismic response of the superstructure under plane SH waves. Therefore, an analytical solution is developed by coupling the wavefunction expansion method with the transfer matrix method, and it is verified by reducing the model to a published exact solution when the damping layers become sufficiently small. Parametric analysis reveals that seismic damping layers have a significant effect on the displacement response of both the foundation and superstructure, as well as the surface ground motions. Increasing the shear wave velocities and the number of damping layers, while decreasing the layer thickness, can attenuate the seismic response of the foundation and superstructure. In addition, the surface ground motions exhibit strong sensitivity to the incident angles. The results show that the structural response under earthquake excitation can be effectively mitigated by appropriately designing seismic damping layers. They also provide valuable insights for seismic design and earthquake resilience, extending and advancing previous analytical DSSI studies.

Offshore wind turbines (OWTs) have emerged as one of the most sustainable and renewable sources of energy. The size of OWTs has been increasing, which creates more challenges in the design of foundations due to the potential higher‐mode effects involved in the dynamic soil‐structure interaction (DSSI) response. Several foundation modeling techniques are available for calculating the OWT fundamental frequency; however, their capability to predict the higher modes by considering real geometric configurations is unclear. The main aim of this study is to perform a rigorous modal analysis of the NREL 5MW reference OWT to investigate the higher mode effects using the 3D finite element method. A detailed parametric analysis is also performed to study the effects of soil inhomogeneity, initial soil modulus, and the monopile dimensions (diameter, thickness, and embedded pile depth) on higher modes' natural frequencies and effective mass participation ratios. The study shows that dynamic soil‐structure interaction has a significant role in modal response and the simplified foundation models are not accurate enough. Given the significant contribution from higher modes, they should not be simply ignored in the OWT design, particularly in earthquake‐prone zones.