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Review of Dynamic Soil-Structure Interaction Models
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Neighbouring buildings, even though disconnected from the structural viewpoint, may interact through the underlying soil especially when they are founded on very soft soils. Despite some pioneering studies since the early 1970’s, structure–soil–structure interaction has yet to be further investigated to reveal the effects that could be exerted on both the static and dynamic response of nearby structures. The present work aims at expanding the theoretical knowledge on this phenomenon through an extensive parametric study based on a truly 3D continuum approach solved through the Flac3D finite difference software. The impedance functions of two closely-spaced shallow foundations have been numerically calculated by varying the distance between the nearby footings and the subsoil configuration (homogeneous or layered). The numerical results have elucidated important effects of cross interaction between two neighbouring foundations. The static stiffness reduces, and this effect is increasingly significant as the foundations are closer whatever the subsoil conditions are. The dynamic coefficients increase with respect to those corresponding to the single footing over halfspace. Such effect is less important for the layer-over-halfspace soil configuration, for which the dynamic coefficients are mainly affected by the frequency response of the stratum. Finally, in the realm of the sub-structure approach, a novel simplified design approach, based on group factors for closely-spaced shallow foundations, was proposed to compute the soil-foundation impedance matrix englobing the foundation–foundation interaction in addition to the soil–foundation interaction.
The present article aims to provide an overview of the consequences of dynamic soil-structure interaction (SSI) on building structures and the available modelling techniques to resolve SSI problems. The role of SSI has been traditionally considered beneficial to the response of structures. However, contemporary studies and evidence from past earthquakes showed detrimental effects of SSI in certain conditions. An overview of the related investigations and findings is presented and discussed in this article. Additionally, the main approaches to evaluate seismic soil-structure interaction problems with the commonly used modelling techniques and computational methods are highlighted. The strength, limitations, and application cases of each model are also discussed and compared. Moreover, the role of SSI in various design codes and global guidelines is summarized. Finally, the advancements and recent findings on the SSI effects on the seismic response of buildings with different structural systems and foundation types are presented. In addition, with the aim of helping new researchers to improve previous findings, the research gaps and future research tendencies in the SSI field are pointed out.
In dynamic soil-structure interaction problems, involving the coupling of structure, foundation and soil, the use of a nonlinear macro-element modelling approach may result particularly advantageous not only to consider nonlinear effects and thus avoid the introduction of possible bias in seismic risk assessment analyses, especially when ground motion intensity levels are high, but also to greatly reduce the heavy computational effort required by 3D finite element soil-block models. In this work, a footing macro-element that models the soil nonlinear behaviour at near-field, as well as the far-field dynamic impedance and energy dissipation through radiation damping, is verified against results obtained from the analysis with OpenSees of a 3D nonlinear soil-block model, itself verified through cross-checks and cross-modelling efforts with equivalent-linear analyses in STRATA and nonlinear analyses in DEEPSOIL. Considering two soil profiles of different complexity and two records of different intensity, one of which leads to extensive soil nonlinearity, the soil-block is verified first. Then, the macro-element model, available in SeismoStruct, is verified against the soil-block model in terms of structural response of a single-degree-of-freedom (SDOF) system as well as near-field soil-footing behaviour.
Tuned mass dampers (TMDs) are widely implemented in many types of structures, such as tall buildings, wind turbines, towers, and bridges, to enhance the structural performance subjected to seismic and wind loading. In the present study, we aim to comprehensively investigate the effectiveness of TMD, by performing seismic vulnerability assessment of a 20-story steel building equipped with TMD and considering the soil-structure interaction (SSI) effects. A suite of high-fidelity three-dimensional nonlinear finite element simulations—in which nonlinear constitutive models are adopted for both structural components and soil, and Domain Reduction Method (DRM) and Perfectly Matched Layer (PML) are utilized to inject the seismic ground motions and represent the semi-infinite contents of the soil media, respectively—are conducted to obtain the structural responses. Finally, the performance of TMD is examined by comparing the fragility curves obtained under different conditions, i.e., with and without TMD, with and without SSI. It is observed that the TMD can notably decrease the structural demands, while the SSI effects can increase the fragility of structures, especially under strong earthquakes.
Soil-structure interaction (SSI) effects are usually omitted in the seismic vulnerability analyses of buildings. However, it has been proved that they might notably affect their seismic performance. In fact, European seismic codes establish that they should be included in the analyses of certain structures: with considerable second order (p-Δ) effects or mid/high-rise buildings. These characteristics are shared by reinforced concrete (RC) buildings in Portugal, which represent a considerable amount of its building stock. Moreover, a significant percentage (50%) have been constructed prior to restrictive seismic codes, i.e., without adequate seismic design. To obtain reliable results when including the SSI effects, the state-of-the-art reveals that a proper modelling of soil and foundations should be carried out. Nevertheless, most of the related studies are based on ideal structural and soil configurations. In addition, it has been found that there is a lack of studies and guidance, even in codes, on the quantification of the SSI effects. Therefore, this paper focuses on quantifying the SSI effects in RC buildings seismic vulnerability analyses by means of two approaches: the Beam on Nonlinear Winker method (BNWM) and the direct modelling of soil. The aim is to propose a method to practically include the SSI effects and to thoroughly characterise the soil behaviour. The method has been applied to a case study RC mid-rise building of Lisbon. A clay-type soil commonly found in Lisbon has been characterised, carrying the analyses out under undrained conditions. 3D finite elements procedures have been proposed to reproduce the complex soil nonlinear constitutive law to represent the behaviour of the entire system (soil + foundation + structure) as realistically as possible. The results have been compared in terms of the seismic safety verification and the fragility assessment. The results have shown that the modal behaviour and the deformed shape of the building are the same with and without the SSI. Nonetheless, it has been demonstrated that increasing the soil flexibility leads to higher periods and higher seismic damage. For this case study, the maximum capacity of the models can be reduced by up to 15% if the SSI effects are considered.
In this paper the seismic response of linear behaving structures resting on compliant soil is addressed through the application of the Preisach formalism to capture the soil nonlinearities. The novel application of the Preisach model of hysteresis for nonlinear soil-structure interaction problems is explored through the study of the seismic response of a real structure. Through a harmonic balance procedure, furthermore, simplified nonlinear springs and dashpots are derived in closed form for a ready and accurate evaluation of the nonlinear soil-structure interaction response. The selected case study is the bell tower of the Messina Cathedral in Italy. The Bell Tower hosts the largest and most complex mechanical and astronomical clock in the world and it has been recently equipped by a permanent seismic monitoring system. A pertinent finite element (FE) model including the superstructure and the soil underneath, has been defined using authentic drawings and engineering design reports. The modal properties of the FE model have been compared with the experimental ones, identified from environmental noise recorded through the seismic monitoring system. Furthermore, the FE model has been validated by means of acceleration time histories recorded at different floors during two independent seismic events. A nonlinear incremental dynamic analysis of the Bell Tower has been also performed. The seismic response obtained by the complete FE analysis, has been compared with the proposed Preisach lumped parameter model, assembled with nonlinear springs and nonlinear dashpots. The results are well in agreement, offering an alternative promising strategy for the nonlinear soil-structure interaction studies.
3D dynamic interaction of two adjacent elastic foundations embedded in a finite layered soil region rested in a homogeneous elastic isotropic half-space with a transient dynamic source is studied. The hybrid computational model, the corresponding numerical scheme and the accompanied software are developed, verified and inserted in detail parametric study. The hybrid approach is based on (a) finite element method (FEM) describing the scattered wave field in a finite layered soil profile with two foundations; (b) boundary element method (BEM) considering waves radiating from a dynamic transient source in elastic semi-infinite range. The aim is to propose an efficient hybrid methodology for evaluation of the dynamic response of a foundation-soil-foundation system, taking into account (a) the whole wave path from the dynamic source, through the layered soil region, till the underground structures; (b) the damage state of the geological material. The BEM model is based on the 3D elastodynamic fundamental solution in Fourier domain and it is applied in order to obtain frequency-dependent stiffness matrix and load vector of the dynamically active semi-infinite geological zone. Once the BEM model is formulated, it is inserted as a macro-finite element in the FEM software package ABAQUS. The frequency-dependent FEM model describing the wave field in finite layered soil profile with two elastic foundations is realized by ABAQUS. Solutions in time domain are obtained through application of the inverse fast Fourier transform. As a final result an efficient hybrid model comprising all in one: dynamic (seismic or other type) source-homogeneous elastic half-space-finite heterogeneous by layers and foundations soil profile, is presented. Parametric study illustrating the sensitivity of the dynamic field to key factors such as the type and properties of the load, the soil layering, the material properties of the far- and near-field soil regions, the damaged state of the geological material and the foundation-soil-foundation interaction is shown and discussed.
Investigating the nonlinear dynamic response of reinforced concrete (RC) structures is of significant importance in understanding the expected behavior of these structures under dynamic loading. This becomes more crucial during the design of new or the assessment of the existing RC structures that are located in seismically active areas. The numerical simulation of this problem through the use of detailed 3D modeling is still a subject that has not been investigated thoroughly due to the significant challenges related to numerical instabilities and excessive computational demand, especially when the soil–structure interaction (SSI) phenomenon is accounted for. This study aims at presenting a nonlinear simulation tool to investigate this numerically cumbersome problem in order to provide further inside into the SSI effect on RC structures under nonlinear dynamic loading conditions. A detailed 3D numerical model of full-scale RC structures considering the SSI effect through modeling the nonlinear frame and soil domain is performed and discussed herein. The constructed models are subjected to dynamic loading conditions and an elaborate investigation is presented considering different type of structures, material properties of soil domains and depths. The RC structures and the soil domains are modeled through 8-noded hexahedral isoparametric elements, where the steel bar reinforcement of concrete is modeled as embedded beam and truss finite elements. The Ramberg–Osgood constitutive law was used for modeling the soil domain. It was shown that the SSI effect can significantly increase the flexibility of the system, altering the nonlinear dynamic response of the RC frames causing local damages that are not observed when the fixed-base model is analyzed. Furthermore, it was found that the structures founded on soft soil developed larger base-shear compared to the fixed-base model which is attributed to resonance phenomena connected to the SSI effect and the imposed accelerograms.
This paper reports a comprehensive study including detailed experimental, theoretical, and numerical analyses to evaluate the performance of two predominant soil-structure interaction models, i.e., Winkler model and Pasternak model, in predicting the Predominant Natural Frequency (PNF) of structures partially embedded in soils. For the evaluation, PNF-based scour detection, a non-destructive testing technique that has been receiving increasing attention, was adopted. First, a series of lab experiments was conducted using idealized piers partially embedded in two representative soils, i.e., a sand and a clay, to measure the PNF-scour depth relationship. Next, a mathematical model was established and numerically implemented to predict the PNF of the idealized piers for scour detection. The soil-structure interaction was formulated using the Winkler model, which only considers the modulus of subgrade reaction for soils, and the Pasternak model, which considers the shear interaction in addition to the modulus. The numerically computed PNFs were then compared with those from the experiments in this study and those from a documented field test. Our results clearly show that when structures are partially embedded in soils, the Winkler model yields a better PNF prediction than the Pasternak model, regardless of the types of test piers and soils. This finding is different from those obtained in the dynamic response of structures resting on or fully embedded in an elastic foundation (i.e., not partially embedded), where the Pasternak model yields more realistic results than the Winkler model due to its consideration of the continuity of foundation media via the shear interaction. Due to the shear interaction, the PNFs predicted with the Pasternak model in this study are about 24-38% and 31-39% higher than the predictions with the Winkler model and the measured PNFs, respectively.
This paper presents a new direct modeling approach to analyze 3D dynamic SSI systems including building structures resting on shallow spread foundations. The direct method consists of modeling the superstructure and the underlying soil domain. Using a reduced shear modulus and an increased damping ratio resulted from an equivalent linear free-field analysis is a traditional approach for simulating behavior of the soil medium. However, this method is not accurate enough in the vicinity of foundation, or the near-field domain, where the soil experiences large strains and the behavior is highly nonlinear. This research proposes new modulus degradation and damping augmentation curves for using in the near-field zone in order to obtain more accurate results with the equivalent linear method. The mentioned values are presented as functions of dimensionless parameters controlling nonlinear behavior in the near-field zone. This paper summarizes the semi-analytical methodology of the proposed modified equivalent linear procedure. The numerical implementation and examples are given in a companion paper.
Usually for modeling of soil in a direct soil–structure interaction (SSI) problem, the equivalent linear soil properties are used. However, this approach is not valid in the vicinity of a foundation, where the soil experiences large strains and a high level of nonlinearity because of structural vibrations. The near-field method was developed and described in a companion paper to overcome this limitation. This method considers the effects of large strains and suggests a shear modulus and a damping ratio further modified in the near-field of a foundation. Validity and performance of this approach are evaluated, application examples are explained and the results of a parametric study about the role of soil and structure parameters in the extent of SSI effects on the nonlinear seismic response of structures are presented in this paper. One real existing and five, ten, fifteen and twenty story moment-resisting frame steel buildings with two different site conditions corresponding to firm and soft soils are considered and the responses obtained from the near-field method are compared with the recorded and rigorous responses. Moreover, various SSI modeling techniques are employed to investigate the accuracy and performance of each approach. The results show that the near-field method is a simple yet accurate enough approach for analysis of direct SSI problems.
In selecting the type of foundation best suited for mid-rise buildings in high risk seismic zones, design engineers may consider that a shallow foundation, a pile foundation, or a pile-raft foundation can best carry the static and dynamic loads. However, different types of foundations behave differently during earthquakes, depending on the soil–structure interaction (SSI) where the properties of the in situ soil and type of foundation change the dynamic characteristics (natural frequency and damping) of the soil–foundation–structure system. In order to investigate the different characteristics of SSI and its influence on the seismic response of building frames, a 3D numerical model of a 15-storey full-scale (prototype) structure was simulated with four different types of foundations: (i) A fixed-based structure that excludes the SSI, (ii) a structure supported by a shallow foundation, (iii) a structure supported by a pile-raft foundation in soft soil and (iv) a structure supported by a floating (frictional) pile foundation in soft soil. Finite difference analyzes with FLAC3D were then conducted using real earthquake records that incorporated material (soil and superstructure) and geometric (uplifting, gapping and P−Δ effects) nonlinearities. The 3D numerical modeling procedure had previously been verified against experimental shaking table tests conducted by the authors. The results are then presented and compared in terms of soil amplification, shear force distribution and rocking of the superstructure, including its lateral deformation and drift. The results showed that the type of foundation is a major contributor to the seismic response of buildings with SSI and should therefore be given careful consideration in order to ensure a safe and cost effective design.
This note outlines the theoretical development of a new subgrade model with inherent spring coupling called the modified Kerr-Reissner (MK-R) model. The MK-R model is a novel hybrid that synergistically combines the advantages of mechanical and simplified-continuum subgrade models with the specific objective of producing a model that is straightforward to implement in routine practice.
This paper presents a simple and stable procedure for the estimation of periods and dampings of piled shear buildings taking soil-structure interaction into account. A substructuring methodology that includes the three-dimensional character of the foundations is used. The structure is analyzed as founded on an elastic homogeneous half-space and excited by vertically incident S waves. The strategies proposed in the literature to estimate the period and damping are revised, and a modified strategy is proposed including crossed impedances and all damping terms. Ready-to-use graphs are presented for the estimation of flexible-base period and damping in terms of their fixed-base values and the system configuration. Maximum shear forces together with base displacement and rocking peak response are also provided. It is shown that cross-coupled impedances and kinematic interaction factors need to be taken into account to obtain accurate results for piled buildings.
There has been a rapid development of the nuclear industry on account of climatic change caused by global warming. The most favorable rocky sites for nuclear power plants are exhausted worldwide, and now nuclear facilities are proposed on soil sites. In a soil site, a combined piled raft foundation (CPRF) system can provide the desired level of performance for a nuclear structure under seismic loading conditions. The combined system of the nuclear structure with the CPRF involves complex dynamic interactions between the pile, soil, raft, and the superstructure. In the existing literature, the dynamic behavior of the CPRF system supporting massive and stiff structures is not well studied and investigated. Due to the highly nonlinear dynamic characteristic of the CPRF system supporting massive and stiff reactor buildings, this paper adopts interface nonlinearities (separation and sliding) through the master and slave concept, concrete and reinforcement material nonlinearities through the concrete damage plasticity model for piles and superstructures, and an equivalent linear approach considering soil degradation and damping with Mohr–Coulomb post yielding hardening behavior for the soil. After the successful validation of the modeling approach with the results of the experimental testing, the different aspects of the CPRF of reactor building are investigated, such as amplification, pile and raft behavior, pile–raft coefficient, separation and sliding, contact pressure, nonlinearity in the piles, and the response of the superstructure. This study indicates that the peripheral piles of the CPRF system could prevent the separation of the raft from the soil. The numerical result shows that damage in the CPRF system occurs near the top portion of the pile. The presented procedure to develop the combined model for the seismic analysis in the time domain could help to formulate guidelines for safety-related nuclear structures resting on the CPRF system.
Explicit dynamic calculations are required in various standards for bridges on high-speed lines to ensure normative limits. This dynamic analysis is based on the resonance phenomena between the train crossing and the frame's natural frequencies in bending. It is obvious that, especially here, an exact determination of the natural frequencies in the numerical models is important for determining the resonance speed, as there is no conservative consideration in dynamics. Furthermore, considering radiation damping based on soil-dynamic approaches can noticeably reduce the maximum amplitudes at the resonance point when simulating train crossings. However, due to the massive dimensions of structural members and a large number of constraints, the dynamic system of railroad frame bridges is usually not clearly to be identified. Hence, a prediction of natural frequency and radiation damping are currently large uncertainties for the design of frame bridges, making dynamically good-natured behaviour, characterised by large damping, particularly desirable. This paper examines the dynamic behaviour of embedded frame bridges, including the effect of soil-structure interaction, under 2D and 3D numerical approaches. Different modelling methods with respect to the unbounded domain and the satisfaction of the Sommerfeld's radiation condition are compared: (1) direct modelling using tuned damper elements, (2) coupled BEM-FEM, and (3) simplified substructure method. It is shown that the coupled FEM-BEM approach reproduces the relationships of three-dimensional dynamic soil-structure interaction (SSI) more accurately than a planar FEM approach since the SSI does not result independently of the chosen modelling method, which is reflected in divergent radiation damping. Furthermore, the governing rigid body modes can be identified using a simplified substructure method. The following parameters influencing the SSI are investigated and discussed in detail: (a) influence of the soil stiffness; mainly described by the ratio between the natural frequencies of the frame and the soil-abutment system, (b) layering of the underlying soil, (c) degree of superstructure clamping, and (d) material properties of the backfill. It is shown that the natural frequencies react robustly to the SSI and are thus mainly influenced by the structural stiffness of the frame. In contrast, radiation damping exhibits various dependencies. In particular, the superstructure slab's clamping ratio and the vertical rigid-body mode frequency (direct relation to soil stiffness) should be mentioned here, significantly influencing the vibrating system. Finally, based on these results , a recommendation for the dynamic design is given.
The soil-structure interaction is an integral part of the seismic evaluation, especially for structures with variable embedment depths. The purpose of this work is to ensure the adequacy of the small scaling factor in the dynamic analysis and study the seismic behavior of tall building with considering variable embedment depths and soil structure interaction effects. Therefore, scaled model tests of a 15-story steel structure were performed using shaking table tests and numerical simulations. Three scaled earthquake records, namely: Chi-Chi (1999), Northridge (1994), and Kobe (1995), were selected. The numerical scaled coupled models were implemented with Plaxis 3D software and validated with the experimental observations. Afterward, the experimental and numerical results of scaled models were verified with prototype models to ensure the adequacy of the small scaling coefficient. The results generated from small-scale models derived from experimental and numerical simulations were in good agreement. In addition, these results achieved good accuracy with full-scale field conditions in the seismic analysis. Therefore, a small geometric scaling coefficient of 1:50 achieved good accuracy for buildings with embedded parts to represent the dynamic behavior of structures. Within the frame results, it is noted that the SSI has an essential role in amplifying the lateral deflection of structures compared with a fixed base and thus the embedded depths significantly affect the lateral seismic response of the considered structures.
Regarding the unpredictable and complex nature of seismic excitations, there is a need for vulnerability assessment of newly constructed or existing structures. Predicting the seismic limit-state capacity of steel Moment-Resisting Frames (MRFs) can help designers to have a preliminary estimation and improve their views about the seismic performance of the designed structure. This study improved data-driven decision techniques in Python software, known as supervised Machine Learning (ML) algorithms, to find median IDA curves (M-IDAs) for predicting the seismic limit-state capacities of steel MRFs considering Soil-Structure Interaction (SSI) effects. For this purpose, Incremental Dynamic Analyses (IDAs) were performed on the steel MRFs from two to nine-story elevations modeled in Opensees subjected to three ground motion subsets of Far Fault (FF), near-fault Pulse-Like (PL) and No-Pulse (NP) suggested by FEMA-P695. The result of the analysis confirmed that there is no specific model for predicting the M-IDA curve of steel structures; therefore, the best developed ML algorithms to reduce a complex modeling process with high computational cost using 128,000 data points were proposed. To provide convenient access to prediction results, Graphical User Interface (GUI) was developed to predict Sa(T1) of seismic limit-state performance levels with a large database based on prediction models.
SSI and site amplification effects are investigated as influences on the seismic fragility of existing reinforced concrete moment-resisting frame and dual frame-wall system buildings supported on shallow foundations without interconnecting beams. We build upon a holistic methodology that accounts for site amplification and soil–foundation–structure interaction effects using a modular approach. We calculate fragility curves based on nonlinear dynamic analyses for various building structural typologies and geometries, infill conditions, code provisions, and soil profile materials and dynamic characteristics. We demonstrate that site amplification during earthquakes may significantly increase the fragility of the soil–foundation–structure system, which is reflected in its vulnerability. Moreover, SSI is especially prevalent for buildings on soft soil profiles and might modify their fragility. We propose a modular method to include site amplification and/or soil–structure interaction effects in a large-scale earthquake vulnerability assessment using fragility modifiers, which we express using an easy-to-code equation form.
The aim of the study is to evaluate the 3D dynamic response of a finite geological region containing two structures and rested on a semi-infinite elastic layered half-space with a dynamic source radiating transient waves. The hybrid modelling approach is applied. It is based on the decomposition of the whole domain under consideration into two sub-regions: a finite-sized near-field elastic isotropic zone with two containment structures and the open semi-infinite far-field layered region. The far-field zone is a semi-infinite elastic isotropic arbitrary layered medium where the near-field finite geological region is located on. The 3D hybrid computational tool is based on the boundary element method (BEM) for the far-field layered zone and the finite element method (FEM) for the finite near-field domain. The model for the semi-infinite layered zone is further extended by the incorporation of a new condensation algorithm which makes it possible to handle 3D wave propagation through arbitrary layered half-space. The condensation algorithm is developed to avoid high computational memory cost while retaining the compatibility with the hybrid FEM-hosted procedure which facilitates the useful solution for the practical three-dimensional engineering problems. The BEM model of the dynamically active far-field zone is inserted as a macro-finite element (MFE) in the FEM commercial program ABAQUS. The accuracy and convergence study of the hybrid numerical scheme is presented. Numerical simulations convincingly illustrate that the dynamic response of structure-soil-structure system depends on different key factors and their mutual interplay. These factors are arbitrary layering of the far-field geological zone, the characteristics of the dynamic source, the site effects phenomena, the structure-soil-structure dynamic interaction, the type and geometrical disposition of foundations and structures and the 3D features of the dynamic motion.
This paper is dedicated to evaluate the nonlinear Soil–Structure Interaction (SSI) impact on the earthquake-based response of vertically irregular reinforced concrete (RC) moment resisting frames. The main contribution of this paper is to evaluate the seismic performance of RC structures with 5 and 10 stories considering a number of key parameters including irregularity ratio, soil type and the vertical safety factor (FSv) of the foundation. In this regard, the beam on nonlinear Winkler foundation (BNWF) scheme is used for the modeling of shallow foundations resting on a semi-infinite sandy medium. Vertical irregularity is considered by using a tall ground story in the RC frames. The models are subjected to 15 earthquake ground motions for conducting nonlinear dynamic time-history analyses to capture the seismic demands of soil–structure systems. The results demonstrate that considering SSI influence reduces the seismic demands in the lower stories, which is more evident in the case of soft soils (site class E). Moreover, a rational relationship between the maximum inter-story drifts and the response of the foundations is observed. It is also concluded that for both regular and irregular structures, lower values of the FSv lead to a considerable decrease in the structural demands (story drifts) and an impressive growth in transient and residual foundation settlements.
This paper focuses on reviewing some classical soil-structure interaction models (SIMs) based on different superstructures and soils and strives to establish the relations between the soils and SIMs according to the American Society for Testing and Materials (ASTM) D2487-11 standard for soil classification. The SIMs with different superstructures, such as beams, plates, and shells, are reviewed. Since the mechanics properties of the superstructures are important, theories of the classical beams, plates, and shells are reviewed. The mechanics properties of several element-specific soils in the ASTM D2487-11 standard are revealed and utilized to establish the relations between the soils and SIMs. A generalized SIM that can be reduced to many classical SIMs is used to classify the existing SIMs with different superstructures. Based on the soil mechanics theory, some new explanations in this work provide some insights into the classical SIMs, e.g., the Pasternak model. Soil elasticity is divided into transverse elasticity and torsional elasticity, and the explanations are provided based on the soil mechanics theory. The Winkler–Terzaghi model that combines the Winkler and Terzaghi models is developed to illustrate the SIMs. Based on the combined Winkler–Terzaghi model, some new SIMs
are created for the specific soils in ASTM D2487-11. Based on the extended Hamilton’s principle, the forced vibration equations of the SIMs are created. The relations between soil classification and the SIMs established in this work can facilitate selection of an appropriate SIM for design and research in civil engineering, mechanical engineering, and petroleum engineering.
Steady state harmonic response of nonlinear soil-structure interaction problems is addressed in this paper. Due to well-known stiffness degradation phenomenon, the steady-state study is referred to small-medium strain condition whereas no significant pore water pressure change is observed (e.g. clayey soils and sands in drained conditions). A novel cyclic hysteretic model based on the Preisach formalism is proposed to describe the cyclic behavior of soil-foundation interaction. Through a harmonic balance procedure, furthermore, the steady state response of nonlinear soil-structure interaction problems is determined. Equivalent amplitude-dependent stiffness and damping have been derived in closed form to reliably describe the nonlinear soil-structure interaction phenomenon. Those expressions are function of the elastic foundation soil stiffness, the maximum attainable horizontal force and the moment capacity of the foundation. Furthermore, handy expressions of the equivalent fundamental period and damping, also dependent from the level of the excitation, are also derived. The proposed hysteretic model, moreover, has the advantage to be easily calibrated to match the modulus reduction and damping curves determined either from numerical or experimental tests. Numerical applications and comparisons with more advanced models and experimental data available in literature are also presented.
An empirical method for the evaluation of moments and contact pressures due to subgrade reactions is presented for combined footings conforming to certain stipulated limitations regarding continuity, rigidity, and variations in loading or column spacing. The values, although developed for continuous beam footings, can also be applied to grid or mat foundations. The results obtained by the empirical method are compared with those obtained by elastic analysis and are found sufficiently accurate for practical purposes.
In this paper, a numerical tool based on the Monkey-tail fundamental lumped parameter model is proposed for the simulation of dynamic soil-structure interaction (SSI). The proposed model has been implemented in the OpenSees finite element environment where the input parameters are merely function of the soil properties. The ease of use, accuracy and versatility of the proposed model is demonstrated in order to encourage its use within, among others, the practicing engineers’ community. Furthermore, the influence of the SSI and local soil conditions (i.e., site effect) on the seismic response of two 5-storey steel moment-resisting frame buildings has been investigated. Preliminary results shed light on the influence of these two geotechnical aspects on the structural seismic response where peak floor displacements and inter-storey drifts considering the SSI are even larger in the lower stories than those of the fixed base case. Furthermore, the results revealed the dependence of the soil amplification factor on the fundamental period of vibration, seismic intensity level and soil stiffness which are not taken into account by the current European design codes.
Non-linear analysis of soil structure interaction problem is still an active field of research due to development of useful interface element between the soil–soil and soil–structure. In this paper a focused review on coupled finite element modeling of soil structure interaction (SSI) system with soil non-linearity and interface element modeling is discussed. The non-linearity in soil is reviewed with various available constitutive models, whereas the Interface modeling is reviewed with zero thickness and thin layer elements, which is proposed by many researchers from 1970 to till date with special emphasis on behavior of superstructure. Further the paper discusses on the occurrence of ill conditioning due to significance of interface thickness and selection of normal and tangential stiffness during interface modeling. In addition to above, some special interface element (different degree of freedom on top and bottom face of element) in non-linear SSI is also reviewed. Therefore the attention is on advantages and disadvantages of the discussed methods according to their applicability, accuracy and caliber to idealize the superstructure and soil.
This paper evaluated the seismic performance of hypothetical tall buildings by estimating intensity measures, engineering demand parameters, and earthquake-induced losses using a soil–structure interaction (SSI) numerical framework. Numerical models for 40-story buildings were developed using OpenSees to study their seismic performance under the following modeling and building configuration conditions: (1) fixed-base structural model, (2) model including SSI effects, (3) fixed-base model with shear walls, and (4) model including shear walls and considering SSI effects. The buildings were assumed to be supported on subsurface conditions typical of downtown Los Angeles. The natural period of the soil profile was parametrically studied; the larger its natural period, the lower were the seismic demands of the building. The inclusion of shear walls caused a reduction of the natural period of the building and computed settlements in relation to the buildings without a shear wall system. Considering SSI effects in the modeling approach changed the computed seismic demands of the tall buildings in terms of maximum interstory drifts, peak story horizontal accelerations, and seismic-induced settlements. Computed median direct economic losses for the 2,475-year mean return period increased as much as 33% by considering SSI effects in the numerical analyses in relation to building losses ignoring those effects.
Dynamic Soil–Structure Interaction (SSI), involving the coupling of structure, foundation and soil, is a crucial and challenging problem, especially when soil nonlinearity plays an important role. This paper shows the impact of adopting different SSI models on the assessment of seismic fragility functions. The linear substructure approach is
initially adopted by implementing two different models, the first of which is one-dimensional and includes, between the foundation node and the ground, a translational elastic spring and a dashpot, whose stiffness and
viscous damping are retrieved from the real and imaginary parts of the dynamic impedance at the first natural frequency of the structure. The second and more refined model is a Lumped-Parameter Model (LPM) accounting for frequency dependence of the impedance. In order to explore the sensitivity of fragility functions to the linearity assumption, an additional approach, including soil nonlinearities, is employed. A nonlinear footing macro-element is adopted to model the near-field behaviour by condensing the entire soil-foundation system into a single nonlinear element at the base of the superstructure. Energy dissipation through radiation damping is also accounted for. The superstructure response is simulated in all approaches as a simple nonlinear single-degree-of-freedom (SDOF) system. The comparison between the adopted approaches is evaluated in terms of their effects on the characterisation of fragility functions for unreinforced masonry buildings (URM) on shallow foundations.
Joint analysis of hazard and fragility is becoming a widespread and unavoidable tool to estimate losses caused by earthquakes. The application of such analysis to buildings on soft soil is improved when the dynamic soil - foundation - structure interaction is considered, since both the reference hazard on site and the structural performance are modified by soil compliance. This study investigates and compares the site-specific seismic demand required to squat or slender masonry towers settled on stiff or soft soil. To this aim, 96 non-linear dynamic analyses were performed on 3D models, including soil, foundation and structure and excited by fourteen unscaled records of real earthquakes. Distributions of the equivalent bending rotation of structure and of peak and residual rotations of foundation were calibrated on numerical results and convoluted with the hazard curves of three Italian cities, to compute the mean annual rate of exceeding different values of structural and foundation demand. The resulting curves highlight that soil deformability enhances the bending demand and produces a not negligible permanent tilt in towers.
The process of soil response influencing motion of the structure and vice-versa is termed as soil-structure interaction (SSI). SSI has been traditionally considered to be beneficial to seismic response of a structure. It has been suggested that ignoring SSI in design practice leads to a conservative design. It is evident from the design codes which either allow a reduction of the overall seismic coefficient on account of SSI or suggest it to be ignored altogether. However observations from some of the past seismic events such as 1989 Loma Prieta earthquake and 1995 Kobe Earthquake show evidences of detrimental nature of SSI in certain circumstances. Recent studies have also been able to justify such possibilities. As a consequence of this dissent among the research fraternity, there is a lack of adequately formulated design guidelines. Though advances have been made in developing methods to solve an SSI problem, incorporating SSI in design practice has been a rarity. The present paper attempts to summarize various approaches to include SSI in analysis of structures and guidelines outlined in prominent seismic codes. The significance of such a study lies in the need for selection of appropriate approach. A review of contemporary research in field of SSI is also presented at the end.
Viscoelastic treatment has traditionally been used in industrial applications to reduce structural noise and vibration by dissipating part of the strain energy. Constrained-layer damping (CLD) treatments usually dissipate more energy than free-layer damping treatment (FLD), but its design must be integrated in the design process of the structure to be damped. Parametric studies are then necessary to determine the optimal viscoelastic material forming the CLD treatment, and the optimal placement and thickness of the layer. For structures with complex geometry, 3D finite elements are required and a change in the thickness or the placement of the viscoelastic layer implies a complete remeshing of the structure, which represents a significant additional computational cost in the parametric study. The goal of this work is to present a new strategy to model efficiently thin constrained viscoelastic layers. Two interface finite elements, based on a surface representation of the damping layer, are proposed. The first one is a joint element using relative displacements at the interface, and the second one is an original zero-thickness element which makes use of a volumetric integration. These elements are validated by comparison with 3D finite elements. Results show that the proposed interface elements allow a good representation of the damping layer's behaviour, especially for thin layers. Moreover, this modelling approach can be efficiently used in the context of parametric optimisation.
We present the results of nonlinear dynamic analyses performed on reinforced concrete (RC) moment resisting frames (MRFs). The analyses were performed considering SSI by means of both a plane-strain soil-structure finite element model approach and a structure-on-springs approach. The results show that the complete FE model approach may produce significant differences in the evaluation of the seismic demand, in terms of maximum inter-storey drift, with respect to the fixed-base structure and to the structure-on-springs approach, mainly because of the different incorporation of the damping in the two modeling approaches. Differences in the soil properties, the seismic design level of the structures and the modeling technique of SSI effects are reflected as reduction in the seismic demand with respect to a fixed-base model, up to 50% in maximum inter-story drift ratio and up to 20% in maximum base shear for the complete FE model and up to 20% in both maximum base shear and maximum inter-story drift ratio for the simplified BNWF model.
Soil-structure interaction (SSI) analysis is generally a required step in the calculation of seismic demands in nuclear structures, and is currently performed using linear methods in the frequency domain. Such methods should result in accurate predictions of response for low-intensity shaking, but their adequacy for extreme shaking that results in highly nonlinear soil, structure or foundation response is unproven. Nonlinear (time-domain) SSI analysis can be employed for these cases, but is rarely performed due to a lack of experience on the part of analysts, engineers and regulators. A nonlinear, time-domain SSI analysis procedure using a commercial finite-element code is described in the paper. It is benchmarked against the frequency-domain code, SASSI, for linear SSI analysis and low intensity earthquake shaking. Nonlinear analysis using the time-domain finite-element code, LS-DYNA, is described and results are compared with those from equivalent-linear analysis in SASSI for high intensity shaking. The equivalent-linear and nonlinear responses are significantly different. For intense shaking, the nonlinear effects, including gapping, sliding and uplift, are greatest in the immediate vicinity of the soil-structure boundary, and these cannot be captured using equivalent-linear techniques.
Adopting the most accurate and realistic modelling technique and computation method for treatment of dynamic soil–structure interaction (SSI) effects in seismic analysis and design of structures resting on soft soil deposits is one of the most discussed and challenging issues in the field of seismic design and requalification of different structures. In this study, a comprehensive critical review has been carried out on available and well-known modelling techniques and computation methods for dynamic SSI analysis. Discussing and comparing the advantages and disadvantages of employing each method, in this study, the most precise and reliable modelling technique as well as computation method have been identified and proposed to be employed in studying dynamic SSI analysis of structures resting on soft soil deposits.
The classical Winkler model treats the soil as a discrete medium, which is its most severe limitation. In order to model the continuity of the soil medium, attempts have been made to interconnect the Winkler springs by structural elements such as stretched membrane, beam, plate, shear layer, etc. In the present paper, this interconnection is achieved by springs themselves, giving rise to an intermeshed spring model. Such a model is developed numerically and implemented in the finite element code. A number of examples involving beams, plates and shells and their combinations 'on elastic foundation' have been analysed using this model. The model shows considerable promise to serve as an improved tool in soil-structure interaction analysis.
A method resembling the well-known moment-area procedure is presented for the solution of beams on an elastic foundation. Esse ntially it is an extension, adaptation, and systematization of the famed Vianello-Stodola procedures as are very briefly mentioned by August Foppl and Miklos Hetenyi. Because of the inherent power of these procedures, reasonably accurate results are obtained simply and quickly. The difficult mathematics that occur in the usual analytical solutions are completely avoided.
A superposition principle is employed to study the infinite plate reinforced by a centrally loaded finite beam where both rest on a Winkler foundation. The problem is intended to relate to a floating arctic ice ridge embedded in an ice sheet. The ridge is loaded vertically by a vessel breaking ice in a bending mode. After formulating the beam and plate problems separately, connectivity conditions are imposed to link the two parts. The Fourier transform of the plate equations provides the solution technique. Computation of the resulting integrals are completed by the Fast Fourier Transform algorithm. An application to arctic ridges provides the ridge and sheet properties necessary for the finite ridge solution to be essentially the same as that of the infinite ridge. Then the infinite ridge is considered and the proportion of the load isostatically resisted by the ridge and the sheet determined.
The Nuclear Regulatory Commission (NRC) regulation 10 CFR Part 50 Appendix S requires consideration of soil-structure interaction (SSI) in nuclear power plant (NPP) analysis and design. Soil-structure interaction analysis for NPPs is routinely carried out using guidance provided in the ASCE Standard 4-98 titled “Seismic Analysis of Safety-Related Nuclear Structures and Commentary”. This Standard, which is currently under revision, provides guidance on linear seismic soil-structure-interaction (SSI) analysis of nuclear facilities using deterministic and probabilistic methods. A new appendix has been added to the forthcoming edition of ASCE Standard 4 to provide guidance for time-domain, nonlinear SSI (NLSSI) analysis. Nonlinear SSI analysis will be needed to simulate material nonlinearity in soil and/or structure, static and dynamic soil pressure effects on deeply embedded structures, local soil failure at the foundation-soil interface, nonlinear coupling of soil and pore fluid, uplift or sliding of the foundation, nonlinear effects of gaps between the surrounding soil and the embedded structure and seismic isolation systems, none of which can be addressed explicitly at present. Appendix B of ASCE Standard 4 provides general guidance for NLSSI analysis but will not provide a methodology for performing the analysis. This paper provides a description of an NLSSI methodology developed for application to nuclear facilities, including NPPs. This methodology is described as series of sequential steps to produce reasonable results using any time-domain numerical code. These steps require some numerical capabilities, such as nonlinear soil constitutive models, which are also described in the paper.
Seismic vulnerability analysis of structures is usually accomplished without regard for soil-structure interaction (SSI). This is while accounting for SSI can result in variation of intensity and distribution of seismic vulnerabilities especially when a more rigorous analysis is implemented by nonlinear modeling of both structure and its underlying soil. This study moves in the same direction. Reinforced concrete buildings being 3, 5, 6, 8, 9 stories high, resting on soft and very soft soil types, once with moment resisting and once with concrete shear walls are considered. Twenty suits of 10 ground motions (200 records) consistent with 5 buildings with two different lateral load bearing systems on two types of soils are selected and scaled for nonlinear dynamic analysis of buildings. The analysis is once implemented for fixed-based and once for flexible-base buildings. The results show that contrary to the common belief, with a flexible-base, the location of maximum drift shifts to the first story where the most intensive vulnerability is observed. SSI changes the pattern of distribution of vulnerability especially for the beams of shear wall buildings and intensifies the seismic vulnerability on soft soils.
This work studies the structure-soil-structure interaction (SSSI) effects on the dynamic response of nearby piled structures under obliquely incident shear waves. For this purpose, a three-dimensional, frequency-domain, coupled boundary element - finite element (BEM-FEM) model is used to analyse the response of a configuration of three buildings aligned parallel to the horizontal component of the wave propagation direction. The SSSI effects are studied in terms of the maximum shear force at the base of the structures in both frequency- and time-domains. The results are presented in a set of graphs so that the magnitude of the interaction effects in configurations of buildings with similar vibration properties depending on the distance between them and the angle of incidence can be easily estimated. These results show a high influence of the wave type and angle of incidence on the interaction effects, not always corresponding the worst-case scenario with the commonly assumed hypothesis of vertical incidence. It is found that for configurations of non-slender structures, the SSSI effects can significantly amplify or reduce the single building maximum response depending on the separation between structures and excitation.
The dynamic response of a wind turbine on monopile is studied under horizontal and vertical earthquake excitations. The analyses are carried out using the finite element program SAP2000. The finite element model of the structure is verified against the results of shake table tests, and the earthquake response of the soil model is verified against analytical solutions of the steady-state response of homogeneous strata. The focus of the analyses in this paper is the vertical earthquake response of wind turbines including the soil-structure interaction effects. The analyses are carried out for both a non-homogeneous stratum and a deep soil using the three-step method. In addition, a procedure is implemented which allows one to perform coupled soil-structure interaction analyses by properly tuning the damping in the tower structure. The analyses show amplification of the ground surface acceleration to the top of the tower by a factor of two. These accelerations are capable of causing damage in the turbine and the tower structure, or malfunctioning of the turbine after the earthquake; therefore, vertical earthquake excitation is considered a potential critical loading in design of wind turbines even in low-to-moderate seismic areas. Copyright © 2015 John Wiley & Sons, Ltd.
Numerical modeling and simulation of clay brick masonry infilled in a reinforced concrete frame (RC frame) subjected to blast loading has been presented in this paper. The pressure loading generated in blast shock has been applied on the masonry and the reinforced concrete frame and time history analysis has been made using ABAQUS finite element software package. The slip and separation at the joints of RC frame and masonry occurring during blast loading due to large difference in their stiffness has been modeled using contact algorithm. The study of the infilled brick masonry has been carried out with elasto-plastic strain hardening model using Mohr-Coulomb yield and failure criterion and contact algorithm for modeling contact behaviour at the interface of masonry wall and RC frame. The non-linearity in RC beam/column has been modelled using concrete damaged plasticity model. The parameters for non-linear finite element modeling of masonry have been experimentally determined. In order to gain confidence in the analysis, the proposed constitutive models have been validated with available experimental results on infilled masonry walls. The parametric study has been made for surface blast of 100 kg TNT at a detonation distance 20, 30 and 40 m for 340 mm and 235 mm thick masonry walls with three grades of mortar infilled in a RC frame. The effect of variation of contact friction between mortar and RC elements on the behaviour of masonry walls has also been studied.
An analysis and implementation of the thin-layer element of Desai et al. for interfaces and joints shows that the planar approximation of the element treated as a solid element can provide satisfactory simulation of the finite-sized interface zone, and in the limit, its results approach those from the zero-thickness element. Advantages and limitations of the thin-layer element are identified, and it is implemented in a nonlinear finite element procedure with the hierarchical single surface plasticity model. The computed results are compared with those from laboratory tests on joints in concrete with different asperity angles. The nonassociative version provides highly satisfactory correlation with laboratory observations.
Traditionally fragility curves of reinforced concrete (RC) buildings are estimated with the assumption of fixed base structures. The objective of the present research is to study whether soil-structure interaction (SSI) and site effects may affect the seismic performance and vulnerability of reinforced concrete moment resisting frame (MRF) buildings and consequently modify the fragility curves. SSI is modeled applying the direct one-step approach considering either linear elastic or nonlinear soil behavior while site effects are inherently accounted for. To further examine the contribution of site and SSI effects, a two-step uncoupled approach is also applied, which takes into account site effects on the response of the fixed base structure, but neglects SSI effects. Additional analyses are performed investigating the influence of the soil depth and stratigraphy under nonlinear soil behavior on the seismic response and fragility of RC buildings. A 9-story RC MRF designed with low seismic code provisions is adopted as a reference structure. A comparative dynamic analysis is performed highlighting various trends in the seismic response of the considered SSI and fixed base systems. Fragility curves are derived as a function of rock outcropping peak ground acceleration for the immediate occupancy and collapse prevention limit states for the fixed base and SSI models based on the statistical exploitation of the results of incremental dynamic analysis (IDA) of the given structural systems. Results show the significant role of SSI and site effects under linear or nonlinear soil behavior in altering the expected structural performance and fragility of high-rise fixed base structures.