Seismic Soil-structure Interaction Analysis Research Articles

Large‐scale seismic soil–structure interaction analysis via efficient finite element modeling and multi‐GPU parallel explicit algorithm

AbstractAs urban population increases, integrated underground–aboveground complexes are being constructed at growing paces in major cities. The seismic analysis of such complexes is crucial for the safety and functionality in the threat of potential earthquake disasters. However, fine‐grained numerical modeling and analysis of such large and complex structures are still inefficient due to the consideration of the soil–structure interaction (SSI). To address this challenge, an efficient approach for numerical modeling of large‐scale seismic SSI analysis is presented in this paper to overcome the limitations of existing finite element analysis (FEA) software. Moreover, a multi‐graphic processing unit (GPU) parallel explicit algorithm is implemented for the nonlinear dynamic SSI problems to further increase the computational efficiency. A large underground–aboveground complex project in China is used as an example to demonstrate the capability of the integrated method. The accuracy and reliability of the multi‐GPU parallel explicit finite element algorithm for SSI analysis (GFEA‐SSIA) are verified through a comparative analysis of the linear‐elastic and nonlinear dynamic response of the building calculated by GFEA‐SSIA and common FEA software. Finally, the structural response and structural damage of the underground–aboveground complex are analyzed under multidirectional seismic motions, and the damage distributions of the structures are provided.

A new equivalent acceleration-based non-uniform response spectrum method for efficient seismic SSI analysis

A complex multiple-support response spectrum (CMSRS) method with a concise and universal expression is required to estimate the seismic responses of soil–structure interaction (SSI) systems under non-uniform seismic excitations to replace existing complex methods. This paper introduces and defines a new concept called equivalent acceleration of boundary load (EABL) that converts widely used equivalent loads into equivalent accelerations, and further develops an efficient CMSRS-EABL method for the seismic analysis of the SSI system. First, EABL offers three main benefits: it simplifies the expressions without sacrificing precision, extends the applicable scope of viscous-spring artificial boundary (VSAB) to all stress-type artificial boundaries, and presents dynamic equations in a familiar form. Subsequently, the CMSRS–EABL formula was successfully deduced based on the equivalent simplified dynamic equations. This formula significantly simplifies the traditional method by reducing the effective modal participation factors, mean-square-roots, and cross-correlation coefficients by 4, 5 and 15 items, respectively. Finally, a rectangular construction surrounded by a VSAB–soil combination was used as an example to illustrate the convenience of the developed CMSRS–EABL method and verify its precision. The results indicate that the proposed method is characterized by greater simplicity and ingenuity, and it is capable of high precision similar to that of the conventional methods. We believe this method will be of significant benefit in evaluating the anti-seismic performance of deeply buried and long-standing structures.

Seismic soil–structure interaction analysis of wind turbine support structures using augmented complex mode superposition response spectrum method

Abstract. In this study, the seismic soil–structure interaction (SSI) of wind turbine support structures is investigated based on the complex mode superposition approach. For accurate and efficient estimation of seismic loadings on wind turbine support structures, an augmented complex mode superposition response spectrum method (RSM) is developed, where the maximum shear force and bending moment of the non-classically damped system are analytically derived. An empirical formula of the modal damping ratios with a threshold value for the allowable damping ratio is also proposed to improve the prediction accuracy of the shear force acting on the footing. Furthermore, additional loadings to consider the contribution of the mass moment of inertia of rotor and nacelle assembly and P−Δ effect to the bending moment on the tower are analytically derived. The proposed formulae are first demonstrated upon a 2 MW wind turbine supported by two different types of foundations. A parametric study is then carried out by changing the tower geometries and soil conditions to propose the threshold value for the allowable damping ratio.

Seismic resilience of extra-large LNG tank built on liquefiable soil deposit capturing soil-pile-structure interaction

Assessment of seismic resilience of critical infrastructure such as liquefied natural gas (LNG) storage tanks, is essential to ensure availability and security of services during and after occurrence of large earthquakes. In many projects, it is preferred to build energy storage facilities in coastal areas for the ease of sea transportation, where weak soils such as soft clay and loose sand with liquefaction potential may be present. In this study, three-dimensional finite element model is implemented to examine the seismic response of a 160,000 m3 full containment LNG tank supported by 289 reinforced concrete piles constructed on liquefiable soil overlaying the soft clay deposit. The seismic soil-structure interaction analysis was conducted through direct method in the time domain subjected to the 1999 Chi-Chi and the 1968 Hachinohe earthquakes, scaled to Safe Shutdown Earthquake hazard level for design of LNG tanks. The analyses considered different thicknesses of the liquified soil deposit varying from zero (no liquefaction) to 15 m measured from the ground surface. The key design parameters inspected for the LNG tank include the acceleration profile for both inner and outer tanks, the axial, hoop and shear forces as well as the von Mises stresses in the inner tank wall containing the LNG, in addition to the pile response in terms of lateral displacements, shear forces and bending moments. The results show that the seismic forces generated in the superstructure decreased with increasing the liquefied soil depth. In particular, the von Mises stresses in the inner steel tank exceeded the yield stress for non-liquefied soil deposit, and the elastic–plastic buckling was initiated in the upper section of the tank where plastic deformations were detected as a result of excessive von Mises stresses. However, when soil liquefaction occurred, although von Mises stresses in the inner tank shell remained below the yield limit, localised stress concentrations were observed in the lower section of the tank near the base, increasing the risk of the elephant foot buckling. The lateral displacements, shear forces and bending moments in the piles increased with increasing depth of the liquefied soil. Indeed, increasing the pile lateral displacement amplified the bending moment at the pile head, thus resulting in increases in the pile bending moments especially when the liquefied soil depth exceeded one third of the entire soil deposit. In particular, the bending moment at the pile head exceeded the yield moment capacity of the pile and subsequent plastic hinges were formed. Moreover, when the thickness of the liquefied soil was more than half of the entire soil depth, the mobilised bending moments in the piles exceed the ultimate moment capacity of the pile and thus total failure of the piles were observed. In addition, in the absence of liquefied soil layer, the inertial interaction had a dominant impact on the pile response in this study. However, with increasing the thickness of the liquefied layer, further loads were developed in the piles due to amplified kinematic interaction, while the inertial interaction-induced loads decreased.

A Step-by-Step Probabilistic Seismic Soil–Structure Interaction Analysis with Ground Motion Incoherency for a Bridge Pier on Bored Pile Foundations

In current design practice, typical seismic design of bridges tends to use simplified approaches. On the opposite side, the most advanced seismic analyses currently used in practice in all the fields of structural engineering are probably the ones used for the design of nuclear facilities, which include soil–structure interaction and motion incoherency effects. From that category, the most modern methodology is the probabilistic approach, which has been added to the new ASCE 4 standard. This type of state-of-the-art analysis is carried out in ACS SASSI software on a typical concrete bridge structure with deep foundations. A comparison of the results with the deterministic SSI approach and the typical Eurocode design from previous studies is presented at the end. Major differences in behavior are highlighted, which impact the overall safety of the structure.

Soil-structure interaction analysis of Çelebiağa Mosque, Pertek-Türkiye

After the construction of the Keban Dam, some settlements with historical, cultural, and natural value were flooded. A scientific committee consisting of academicians and public authorities decided to the relocation of the buildings including the historical Çelebiağa Mosque. In this study, the seismic soil-structure interaction analysis of the historical Çelebiağa Mosque, which was dismantled and reconstructed in a separate region due to the construction of the Keban Dam was carried out. The analysis of the masonry mosque was performed with the SAP2000 finite element analysis software. The Winkler foundation model was used to idealize the soil environment on which the historical mosque was built. The effects of soil-structure interaction on historical masonry mosque were examined in terms of transmitted acceleration, response spectra, and lateral displacement at various heights of the structure. Depending on the results of the analysis, the effects of soil-structure interaction of a reconstructed historical masonry building were investigated. PGA was obtained as 0.51g at the flag level of the minaret under the Kocaeli earthquake and 0.94g under the Sivrice earthquake. Again, the maximum horizontal displacements of the minaret at the flag level were obtained as 11 cm and 8.5 cm under the Kocaeli and Sivrice earthquakes. The behavior of historical masonry structures under earthquake loads has been interpreted by considering the geological conditions.

Evaluation of Seismic Performance and Soil-Structure Interaction (SSI) for Piloti-Type Buildings considering Korean Geotechnical Conditions

Piloti-type structure is a popular architectural style consisting of only columns or minimum number of shear-resisting walls on the first floor. The large difference in lateral stiffness between the first and the upper floors makes the structure very vulnerable to earthquakes. Through the recent earthquakes in Gyeongju (2016) and Pohang (2017), due to such structural disadvantages, many damage cases have been reported, especially in low-rise piloti-type buildings with five stories or less. In this study, seismic soil-structure interaction (SSI) analysis is conducted on low-rise piloti-type buildings considering Korean geotechnical characteristics, and the effect is analytically evaluated. To achieve this goal, seismic SSI analysis applying the measured Gyeongju earthquake and design response spectrum (DRM) based on the architectural design codes are conducted by constructing three-dimensional structural analysis models with a five-story piloti-type building and four different soil properties: fill (FI), alluvial soil (AS), weathered soil (WS), and weathered rock (WR). From the analysis results, it is found that WS soil is largely affected by the seismic SSI, and the influence of the seismic SSI is different for each soil type regardless of the type of earthquake. Through the parameter study, simple and reasonable estimates are proposed to consider the SSI effect on the base shear in low-rise piloti-type buildings.

Correction to: Seismic soil-structure interaction analysis of structure with shallow foundation using response spectrum method

This erratum is being published to correct two reference mistakes and an equation symbol in the paper.

Nonlinear seismic soil-structure interaction analysis of nuclear reactor building considering the effect of earthquake frequency content

A three-dimensional nonlinear soil-structure interaction analysis is simulated in time domain in order to evaluate the behavior of a nuclear reactor building under different earthquake motions. The effects of earthquake frequency content and soil-structure interaction are taken into account by using three different ground motions and four different soil types. Viscous boundary and free-field column are used to absorb propagating waves and consider the free-field motion in the soil medium, respectively. Analysis of three cases are carried out: (i) linear analysis, (ii) nonlinear analysis with the bonded contact between superstructure and soil medium, and (iii) nonlinear analysis with the sliding contact between superstructure and soil medium. The results obtained from the time domain are validated by using a code in the frequency domain, and a good agreement is found between two methods. By changing the soil properties and ground motions, some comparisons of the nuclear reactor responses are made. It is concluded that both of soil-structure interaction and earthquake frequency content are highly sensitive to the behavior of nuclear reactor building under seismic loading. Also, this research leads to some new findings that are useful for practical applications while considering the soil-structure interaction and earthquake frequency content in nuclear structures.

Seismic soil–structure interaction analysis of structure with shallow foundation using response spectrum method

Seismic soil–structure interaction (SSI) of structure with shallow foundation is studied using response spectrum method (RSM). A SSI model is first constructed with the consideration of the coupling of horizontal and rocking motions of structural foundation. In this model, the structure is modelled by finite elements and the soil by the accurate lumped parameter model (LPM) based on rational approximation. The SSI model is a non-classically damped system due to introducing damping of LPM. Complex mode superposition RSM is subsequently applied to solve the non-classically damped SSI system under design response spectrum. Seismic responses of 3-story and 6-story shear structures on two types of sites are finally calculated using the SSI model and RSM. The numerical experiments indicate that RSM can be an effective tool to analyze seismic SSI of structure with shallow foundation, and some conclusions are drawn: (1) the coupling of horizontal and rocking motions of foundation should be considered for relatively high structure on soft soil site, (2) the rational-approximation-based LPM is more accurate than the simple one, (3) the over-damped case can be neglected in the complex mode superposition process although it arises at fundamental frequency, and (4) the quasi spectrum transform relationship can be used to obtain the relative displacement and relative velocity response spectra from the given absolute acceleration design response spectrum.

Response spectrum method for seismic soil–structure interaction analysis of underground structure

The response spectrum method (RSM) has been incorporated into many codes for seismic design of aboveground structures since 1950s. However, no RSM is presented in details for the seismic design of underground structures due to the complexity of seismic soil–structure interaction (SSI). In this paper, the RSM is developed for the seismic analysis of the underground structures including SSI. First, the underground design response spectrum is derived using two different procedures from the ground design response spectrum that is commonly available in most seismic design codes. Second, the SSI analysis model consisting of the underground structure and its adjacent soil is established with the roller side boundaries and the bottom boundary subjected to the underground response spectrum. Third, the RSM is applied to the SSI analysis model to estimate the structural response under the underground response spectrum. Finally, the numerical examples are presented to demonstrate the feasibility of the RSM for the SSI analysis model of underground structure.

A New Approach in Equivalent Spring-Dashpot Method for Seismic Soil-Structure Interaction Analysis of Long Bridges Including Non-uniform Excitations

This paper is conducted on evaluating the seismic responses of long bridges under the effect of the soil-structure interaction (SSI) and spatially varying earthquake ground motions (SVEGM). The commonly used spring-dashpot method for analysis of the pile-supported structures under the effect of (SSI) improves to a more capable model. Also, a comprehensive investigation of the dynamic response of a long bridge subjected to spatially varying earthquake ground motions (SVEGM) is performed based on a proposed analytical model which includes the effect of (SSI). The modeling methodology is discussed in detail. To emphasize the importance of the SVEGM and SSI, bridge responses are also determined for the uniform ground motion and fixed base cases. This study proposing a compatible analytical model concerns the relative importance of the SSI and SVEGM and shows that these effects cannot be neglected in seismic analysis and design of long bridges.

Seismic Soil–Structure Interaction Analysis of Concrete Gravity Dam Using Perfectly Matched Discrete Layers with Analytical Wavelengths

ABSTRACT For heavy structures like concrete gravity dams, soil–structure interaction has a great effect on the structural behavior. One of the important features of soil–structure interaction problems is absorbing boundary conditions for the unbounded soil domain. In this study, perfectly matched discrete layers with analytical wavelengths (AW-PMDLs), which was developed recently by the authors, is applied to concrete gravity dam analyses. Free-field motions during earthquakes with the presence of absorbing boundary conditions need to be included. A Free-field element is presented to take into account the free-field motions. The hydrodynamic pressure from the reservoir to the dam is introduced by using Westergaard added mass method. A procedure with the combination of the AW-PMDL elements, Free-field elements, and Westergaard added masses is proposed to analyze concrete gravity dams considering soil-–structure interaction. For the sake of numerical analyses, AW-PMDLs, Free-field elements, and Westergaard added masses are implemented by using user-defined elements (UEL) in ABAQUS. The validation of the proposed procedure is made by comparing the results with a previous study and the results obtained from SASSI, a program used to analyze the soil–structure interaction problems in the frequency domain. Then, the linear and nonlinear analyses of the dam system are observed for various soil stiffness. It can be seen that the nonlinear analyses need to be considered for a rigorous dam structure analysis.

Simple formulas for estimating a lumped parameter model to reproduce impedances of end-bearing pile foundations

The paper presents simple formulas to evaluate parameters of a lumped system reproducing the frequency-dependent dynamic stiffness of end-bearing pile foundations. The model can be implemented in commercial finite element software and allows performing inertial soil-structure interaction analyses of structures considering the coupled roto-translational, vertical and torsional behaviour of the soil-foundation system. Pile groups arranged in a square layout are considered; the soil profile is constituted by a homogeneous deformable soil layer overlying a bedrock where piles are socked for a fixed length. Formulas are calibrated with a nonlinear least square procedure, based on data provided by an extensive non-dimensional parametric analysis of the soil-foundation systems, performed with a Winkler's type model, previously developed by the authors, which assumes soil and piles to behave linearly. Firstly, the suitability of the adopted numerical tools in capturing the dynamic stiffness of end-bearing foundations is proven. Then, capabilities of the proposed formulas in estimating parameters of the best lumped systems are shown, and, for some case studies, comparisons of non-null terms of the impedance matrix obtained through the best lumped system, the one computed through the formulas, and the impedances resulting from the dynamic analyses, are presented. Finally, some applications of the proposed formulas in the framework of the seismic soil-structure interaction analysis of bridges are shown to demonstrate the capability of the adopted lumped system and the formula efficiency in assuring a reliable evaluation of the superstructure seismic response, with respect to that obtained from a more rigorous approach.

Seismic Response Characteristics of a Piled Raft in Clay

This paper presents a study on three-dimensional seismic soil–structure interaction analysis of a piled-raft (PR) foundation in clay by the substructure approach. Two different pile modeling techniques were adopted and compared with centrifuge shaking table test results reported in the literature. The effect of pile spacing on dynamic impedances, kinematic response parameters, axial pile forces and bending moments of PRs is studied. It is found that the presence of a rigid raft on a pile group results in significant variation in vertical and horizontal dynamic stiffness after a dimensionless frequency ([Formula: see text] value of around 0.22. The influence of raft on kinematic response parameters at the top of raft is found to be significantly influenced by pile spacing beyond a dimensionless frequency ([Formula: see text] value of 0.4. The axial forces generated at the pile heads of a PR–structure system during seismic shaking are quantified using a new dimensionless factor, and are found to be significantly influenced by the pile spacing. Pile layout in the PR system is found to play an influential role in seismic response as well as pile bending moment for a structure–PR–soil system studied.

Time domain stochastic finite element simulation towards probabilistic seismic soil-structure interaction analysis

This paper exploits the recent advances in the field of stochastic finite elements in time-domain simulation of the seismic behavior of soil-foundation-structure systems in three-dimension considering the soil parameters to be heterogeneous, anisotropic, non-Gaussian random fields, structural material parameters to be non-Gaussian random variables, and earthquake motion to be a non-stationary random process. Both the formulation and its implementation are discussed. Scalable numerical schemes for distributed memory parallel computing of hundreds of millions stochastic degrees of freedom, that may arise for any typical uncertain soil-structure interaction (SSI) problem, are presented. Although the presented approach allows for treatment of material nonlinearity, behaviors of only linear systems are illustrated in this study. Through comparisons of the stochastic SSI analysis results with that of the deterministic SSI, deterministic rigid base structural response history, and 1-D deterministic geotechnical site response analyses, and through an extensive parametric study by varying the input uncertainty parameters, the shortcomings of the conventional deterministic approaches are highlighted.

Establishing Outcrop Time Series at Various Depths in a Nonlinear Soil Column: An Iterative Approach

Seismic soil-structure interaction (SSI) analysis of nuclear facilities is an important consideration during design and retrofit. SSI tools used in the nuclear industry are currently based on an equivalent linear (EL) approach. Procedures for developing input ground motion for EL approaches are well established. However, the procedures for establishing input ground motion for nonlinear soil-structure interaction (NLSSI) analysis of nuclear facilities are not well established. A collaborative research group at Idaho National Laboratory has recently developed analytical methods and numerical tools for using NLSSI analysis for nuclear facility seismic calculations. NLSSI analysis for a nuclear facility allows for calculation of seismic wave motion through a near-field soil domain using either (a) vertically propagating shear and compressive waves, which is the current industry practice, or (b) a three-dimensional nonvertical wave field. This technical note presents an iterative procedure for establishing outcrop motion at a depth in the soil column for NLSSI analysis that uses vertically propagating shear waves. The approach presented in this technical note starts with a known ground motion at the surface that is deconvolved to a depth, and then the obtained motion is convolved up to a different desired location of input for the NLSSI model. To demonstrate the validity of the approach, a finite element soil column that is representative of a nuclear facility site in the United States is used to produce compatible outcrop seismic time series for reduced nonlinear soil mesh depths. The developed approach for reducing the nonlinear soil column model depth is a two-step iterative method. The first step is establishing an outcrop time series at the lowest depth considered that produces the top-of-soil response spectrum of an actual recorded ground motion. The second step is providing compatible outcrop time series at a shallower depth based on the information from the first step. A comparison of the 5% damped response spectrum from the resulting acceleration time series based on the iterated outcrop motions and the original acceleration time series is conducted. The study shows that the proposed iterative approach produced comparable results within 1% range of the original recorded time series results when sufficient iterations were performed.

Soil-structure interaction and motion incoherency effects on a concrete bridge with deep foundations

The paper presents a seismic SSI study that has been conducted for a 242 m long concrete bridge in Braşov, that has deep foundations on drilled piles. The structure is typical for Romania and highly used throughout the country. The seismic soil-structure interaction were performed using the state-of-the-art ACS SASSI software. The soil-structure interaction analyses were performed for both coherent (synchronous) and incoherent (non-synchronous) seismic inputs. The main focus of the study is to evaluate the effects of soil – structure interaction and of the seismic motion incoherency on the bridge dynamic response. The paper includes comparisons of results obtained using the Eurocode 8 analysis procedures and the state-of-the-art seismic soil-structure interaction analysis using ACS SASSI. The final conclusions indicate the limitations of the current bridge design soil-structure interaction modelling and the simplified motion spatial variability modelling in Eurocode 8. Furthermore, the future directions of the research study are presented.

Earthquake input for finite element analysis of soil-structure interaction on rigid bedrock

When using the finite element method to analyze seismic soil-structure interaction (SSI) problem on rigid bedrock, several methods have been developed to input earthquake on the lateral boundary of finite element model. These boundary conditions include the free boundary, the viscous-spring (VS) boundary, the tied degrees of freedom (TDOF) boundary and the free-field loading combined viscous-spring (FFL-VS) boundary. Their accuracy and location should be investigated. In this paper, the formulations and ABAQUS implementations of these boundaries are given. The accuracy properties of these boundaries are then compared by numerical examples including the free-field and SSI problems. The comparison studies indicate that the free and VS boundaries failed to reproduce the free-field and SSI responses when a relatively small size SSI model is employed. The TDOF and FFL-VS boundaries can simulate the exact free-field response and have good performances in seismic SSI analyses. The FFL-VS boundary is more accurate than the TDOF boundary. The appropriate locations for the TDOF and FFL-VS boundaries depend on the SSI model. A simplified approach is developed for appropriate boundary location. This approach is applicable to the FFL-VS boundary but not to the TDOF boundary due to the former more accurate than the latter.

Regional subsidence effects on seismic soil-structure interaction in soft clay

Regional subsidence effects on dynamic soil properties and ground layering deformation are often ignored in practice, when dealing with seismic soil-structure interaction analyses. Nevertheless, these effects can substantially change the frequency content and spectral accelerations in both free field and in the soil-structure system. Pore pressure variations over the project economic life are due to both regional subsidence as well as dissipation of excess pore pressure caused by the structure weight. These variations lead to changes in effective stresses, which in turn, modify the dynamic properties such as shear wave velocity distribution and modulus degradation and damping curves, as well as soil layer thickness and shape. These changes can be substantial in highly compressible very soft clay, such as that found in Mexico City valley. This paper presents a numerical study on the seismic response of a conventional five-story building supported by a compensated box foundation built in soft clay, considering these effects. Three-dimensional finite difference models were developed with the software FLAC3D. Initially, the evolution of effective stresses with pore pressure was established based on in-situ piezometer measurements of an instrumented site, and laboratory data. Then, changes in dynamic properties were taken into account based on the results gathered from series of resonant column tests conducted for several effective consolidation stresses, and a PS suspension logging test. The static behavior of the soil-structure system was assessed. For the cases studied herein, the complex interplay between soil nonlinearities, which lead to fundamental period elongation of the soil deposit, Tp, and the overall tendency of ground consolidation to shorten it, controls the variations in the spectral ordinates depending on how close Tp is of the predominant period of the excitation.