Showing papers on "Soil structure interaction published in 2003"

Inelastic dynamic analysis of RC bridges accounting for spatial variability of ground motion, site effects and soil–structure interaction phenomena. Part 1: Methodology and analytical tools

Abstract: During strong ground motion it is expected that extended structures (such as bridges) are subjected to excitation that varies along their longitudinal axis in terms of arrival time, amplitude and frequency content, a fact primarily attributed to the wave passage effect, the loss of coherency and the role of local site conditions. Furthermore, the foundation interacts with the soil and the superstructure, thus significantly affecting the dynamic response of the bridge. A general methodology is therefore set up and implemented into a computer code for deriving sets of appropriately modified time histories and spring–dashpot coefficients at each support of a bridge with account for spatial variability, local site conditions and soil–foundation–superstructure interaction, for the purposes of inelastic dynamic analysis of RC bridges. In order to validate the methodology and code developed, each stage of the proposed procedure is verified using recorded data, finite-element analyses, alternative computer programs, previous research studies, and closed-form solutions wherever available. The results establish an adequate degree of confidence in the use of the proposed methodology and code in further parametric analyses and seismic design. Copyright © 2003 John Wiley & Sons, Ltd.

Kinematic soil-structure interaction from strong motion recordings

Abstract: Earthquake strong motion recordings from 29 sites with instrumented structures and free-field accelerographs are used to evaluate variations between foundation-level and free-field ground motions. The focus of the paper is on buildings with surface and shallowly embedded foundations. The foundation/free-field ground motion variations are quantified in terms of frequency-dependent transmissibility function amplitude uHu. Procedures are developed to fit to uHu analytical models for base slab averaging for the assumed conditions of a rigid base slab and a vertically propagating, incoherent incident wave field characterized by ground motion incoherence parameter k. The limiting assumptions of the model are not strictly satisfied for actual structures, and the results of the identification are apparent k values ~denoted k a) that reflect not only incoherence effects, but also possible foundation flexibility and wave inclination effects. Nonetheless, a good correlation is found between k a values and soil shear wave velocity for sites with stiff foundation systems. Based on these results, recommendations are made for modifying free-field ground motions to estimate base slab motions for use in response analyses of buildings.

Soil–structure interaction in yielding systems

Abstract: The effects of soil–structure interaction in yielding systems are evaluated, including both kinematic and inertial interaction. The concepts developed previously for interacting elastic systems are extended to include the non-linear behavior of the structure. A simple soil–structure system representative of code- designed buildings is investigated. The replacement oscillator approach used in practice to account for the elastic interaction effects is adjusted to consider the inelastic interaction effects. This is done by means of a non-linear replacement oscillator defined by an effective ductility together with the known effective period and damping of the system for the elastic condition. To demonstrate the efficiency of this simplified approach, extensive numerical evaluations are conducted for elastoplastic structures with embedded foundation in a soil layer over elastic bedrock, excited by vertically propagating shear waves. Both strength and displacement demands are computed with and without regard to the effect of foundation flexibility, taking as control motion the great 1985 Michoacan earthquake recorded at a site representative of the soft zone in Mexico City. Results are properly interpreted to show the relative effects of interaction for elastic and yielding systems. Finally, it is demonstrated how to implement this information in the context of code design of buildings. Copyright © 2003 John Wiley & Sons, Ltd.

Inelastic dynamic analysis of RC bridges accounting for spatial variability of ground motion, site effects and soil-structure interaction phenomena. Part 2: Parametric study

Abstract: The methodology for dealing with spatial variability of ground motion, site effects and soil–structure interaction phenomena in the context of inelastic dynamic analysis of bridge structures, and the associated analytical tools established and validated in a companion paper are used herein for a detailed parametric analysis, aiming to evaluate the importance of the above effects in seismic design. For a total of 20 bridge structures differing in terms of structural type (fundamental period, symmetry, regularity, abutment conditions, pier-to-deck connections), dimensions (span and overall length), and ground motion characteristics (earthquake frequency content and direction of excitation), the dynamic response corresponding to nine levels of increasing analysis complexity was calculated and compared with the ‘standard’ case of a fixed base, uniformly excited, elastic structure for which site effects were totally ignored. It is concluded that the dynamic response of RC bridges is indeed strongly affected by the coupling of the above phenomena that may adversely affect displacements and/or action effects under certain circumstances. Evidence is also presented that some bridge types are relatively more sensitive to the above phenomena, hence a more refined analysis approach should be considered in their case. Copyright @ 2003 John Wiley & Sons, Ltd.

Finite element parametric study of the behavior of segmental block reinforced-soil retaining walls

Abstract: Geosynthetic-reinforced-soil retaining walls with modular-block (segmental) facing have gained wide popularity because of their satisfactory performance and aesthetic appearance. A better understanding of the deformation of this wall system requires an analytical tool that is capable of considering the properties of soils, geosynthetic reinforcement, and soil–structure interactions in a realistic manner. In this paper, a validated finite element procedure was used with a hyperbolic soil model for conducting a series of analysis under working-stress conditions. The effects of the length, spacing and stiffness of reinforcement, the width, interaction and connection strength of the modular block, and the backfill and foundation soil properties were investigated. The deformation and lateral stress at the wall face, vertical stress along the base of the wall and the strains developed in the geosynthetic reinforcement are discussed. All design parameters were found to affect the wall performance with a certain ...

Large displacement behaviour of a structural model with foundation uplift under impulsive and earthquake excitations

Abstract: This paper considers the dynamical behaviour of a structural model with foundation uplift. The equations of motion of the system considered are derived for large displacements thus allowing for the eventual overturning of the system. The transition conditions between successive phases of motion, derived in terms of the specific Lagrangian co-ordinates used in the formulation of the equations of motion, present innovative aspects which resolve some previously inexplicable behaviour in the structural response reported in the literature. The dynamical behaviour of the model is considered under impulsive and long-duration ground motions. The minimum horizontal acceleration impulses for the uplift and the overturning of the system are evaluated in analytical form. The sensitivity of the model to uplifting and to overturning under impulsive excitations is established as a function of few significant structural parameters. Numerical applications have been performed changing either the structural parameters or the loading parameter, in order to analyse several dynamical behaviours and also to validate the analytical results. For earthquake ground motions the results, reported in the form of response spectra, show that linearized models generally underestimate, sometimes significantly, the structural response.

Centrifugal modeling of seismic behavior of large-diameter pipe in liquefiable soil

Abstract: This study focused on the behavior of a large-diameter burial pipe with special reference to its stability against flotation subject to soil liquefaction. Centrifugal modeling technique was used where the results are presented for a total of eight shaking table tests conducted on the burial pipe in a laminar box under 30g gravitational field. The ground was prepared with Nevada sand at a relative density of 38% and shaken with a sinusoidal wave at an amplitude of 0.5g. The use of a viscous fluid in a saturated soil deposit satisfied the time scaling relationships of both dynamic and dissipation phenomena. The centrifugal modeling technique simulated flotation of pipeline as the soil liquefied. A technique that used gravels and geosynthetic material was used to mitigate flotation. The response of the soil deposit, in terms of acceleration and excess pore pressure, was investigated. The uplifting of the pipe, earth pressure response and ground surface deformation were also presented. Based on the test results, a design procedure was proposed for the burial pipe in resisting flotation due to soil liquefaction. The deadweight and stiffness of the gravel unit, which was confined by geosynthetic, were important items in design.

Experimental study of boundary effects in dynamic centrifuge modelling

Abstract: Dynamic centrifuge modelling has been established as a powerful tool for studying soil–structure interaction problems under earthquake loading. Increasingly complex models are being tested in centrifuges all around the world in an attempt to understand real structure behaviour under earthquake loading. However, there is a need to model the field conditions correctly in these centrifuge models. In a geotechnical centrifuge, the space available to model real situations is not infinite, and it is necessary to enclose the model within the finite boundaries of a container. The boundary effects of the soil container are important and can lead to inaccurate simulation of a field situation that has infinite lateral extent. The equivalent shear beam (ESB) model container used in dynamic centrifuge testing is built to achieve the same dynamic response as the soil sample to minimise the boundary effects. A series of dynamic centrifuge tests involving loose and dense, dry and saturated models of homogeneous horizonta...

Numerical Analysis of Tall Buildings Considering Dynamic Soil-Structure Interaction

Abstract: Three-dimensional finite element analysis in time domain on dynamic soil-pile-structure interaction of a practical engineering is carried out in this paper. General-purpose finite element program A...

Effects of soil spatial variability on soil-structure interaction

Abstract: Many physical systems in general, and soil materials in particular, exhibit relatively large spatial variability in their properties, even within so-called homogeneous layers. Physical descriptions of this spatial variability are not feasible owing to the prohibitive cost of sampling and uncertainty induced by measurement errors. This variability is widely dealt with as uncertainty in soil properties. Probabilistic methods currently used to represent this uncertainty often suffer from many limitations. For instance, they often only account for uncertainty in estimating the average soil properties. A probabilistic approach was developed here to investigate the effects of soil heterogeneity and provide practical recommendations and guidelines to account for these effects in routine engineering design. -- There are still many unknown consequences of spatial variability. It is shown here that natural variability of soil properties within geologically distinct and so-called uniform layers affects soil behaviour. This study found that the phenomena governed by highly nonlinear constitutive relations are the most affected by spatial variability of soil properties. The bearing capacity of shallow foundations and lateral interaction loads of buried pipelines are functions of soil shear strength and, therefore, are governed by highly nonlinear stress-strain relationships. -- The effects of soil heterogeneity were investigated for a strip foundation placed on elastic perfectly plastic soil and subjected to vertical loads. From a comparison of Monte Carlo simulations, accounting for the spatial variability of soil strength, and deterministic analyses assuming uniform soil properties, it was found that the soil heterogeneity changes the mechanical behaviour of foundations. A parametric study was performed to quantify the effects of soil heterogeneity parameters on foundation response; the studied cases were pre-designed using statistical methods (Design of Experiments, DOE). It was observed that soil strength's degree of variation and probability distribution, which characterize the amount of weak pockets of soil, have the most effects on the foundation behaviour for the range of parameters considered. Correlation distances also affected the variability of foundation responses owing to local averaging effects. -- The results of the parametric study are presented as simple regression equations (response surfaces) to estimate probabilistic characteristics of foundation responses - namely mean and coefficient of variation of bearing capacity and bearing pressures at damage criteria. They were used to calibrate partial design factors for limit state design methods, LSD, and estimate characteristic values for routine engineering design. The results, in terms of regression equations, can also be employed directly in level II & III reliability analysis methods. -- A similar study with a limited scope was performed for lateral loading of a buried pipeline. Only one burial depth (geometrical configuration) was taken for the pipeline. Among the probabilistic characteristics of soil considered here, the degree of variability of soil strength was found to be the most significant factor affecting pipeline response. The response and failure mechanism of a laterally loaded buried pipeline is complicated and is dependent on several deterministic factors such as burial depth, pipe-soil interaction coefficients, and soil weight. The study could be further developed to account for other probabilistic characteristics and deterministic parameters, and their corresponding interactions.

Soil arching over deeply buried thermoplastic pipe

Abstract: Soil arching associated with buried thermoplastic pipe is discussed. First, the soil arching phenomenon is described. Then two different approaches are mentioned from the literature to represent the degree of soil arching (or vertical arching factor). The elastic solutions of Burns and Richard are revisited to derive expressions for the vertical soil arching factor for buried pipe. Comparison of the elastic solutions and field soil pressure cell readings reveals the importance of incorporating a bending stiffness parameter. With this finding, the AASHTO method for calculating the load on buried pipe is evaluated against the elastic solutions. The analysis reveals that the AASHTO method is conservative, overestimating the load on thermoplastic pipe by up to 30%. Further evidence to support the finding is found within the strain gauge readings taken on the pipe walls in the field. Therefore, alternative equations derived directly from the elastic solutions are recommended to predict the load on buried therm...

Earthquake response analysis in the time domain for 2D soil–structure systems using analytical frequency-dependent infinite elements

Abstract: This paper presents a time domain method for soil–structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating analytical frequency-dependent infinite elements for the far-field soil region. Equivalent earthquake input forces are calculated based on the free-field responses along the interface between the near- and far-field soil regions using the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far-field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil–structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space, and results are compared with those obtained by the conventional method in the frequency domain. Copyright © 2003 John Wiley & Sons, Ltd.

A seismic free field input model for fe-sbfe coupling in time domain

Abstract: A seismic free field input formulation of the coupling procedure of the finite element (FE) and the scaled boundary finite-element (SBFE) is proposed to perform the unbounded soil-structure interaction analysis in time domain. Based on the substructure technique, seismic excitation of the soil-structure system is represented by the free-field motion of an elastic half-space. To reduce the computational effort, the acceleration unit-impulse response function of the unbounded soil is decomposed into two functions; linear and residual. The latter converges to zero and can be truncated as required. With the prescribed tolerance parameter, the balance between accuracy and efficiency of the procedure can be controlled. The validity of the model is verified by the scattering analysis of a hemi-spherical canyon subjected to plane harmonic P, SV and SH wave incidence. Numerical results show that the new procedure is very efficient for seismic problems within a normal range of frequency. The coupling procedure presented herein can be applied to linear and nonlinear earthquake response analysis of practical structures which are built on unbounded soil.

Buckling analysis of high-temperature pressurized pipelines with soil-structure interaction

Abstract: High-temperature pressurized pipelines design requires special attention, as restrained thermal stresses are high. Due consideration should be given to thermal expansion, as stresses in bends of expansion loops are significant. Also, the modelling of the soil-pipe interaction using soil characteristics, especially friction and lateral resistance, is important when analyzing high-temperature pipelines. This paper describes a numerical procedure for the analysis of global and local buckling behavior of high temperature pressurized buried pipelines. Results of finite element calculations are presented and discussed.

Time domain earthquake response analysis method for 2-D soil-structure interaction systems

Abstract: A time domain method is presented for soil-structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating infinite elements for the far field soil region. Equivalent earthquake input forces are calculated based on the free field responses along the interface between the near and far field soil regions utilizing the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil-structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space with the assumption of the linearity of the near and far field soil region, and results are compared with those obtained by the conventional method in the frequency domain.

Mode acceleration approach for generation of floor spectra including soil-structure interaction

Abstract: A mode acceleration formulation is presented for the transfer function of absolute acceleration response of a single-degree-of-freedom oscillator which is supported on a base-excited, classically damped and flexible-base primary system. The primary system response has been described in terms of fixed-base primary mode shapes, with the response in last few modes assumed to be pseudo-static. Base flexibility has been assumed to be described by complex-valued impedance functions, and the effects of kinematic interaction have been assumed to be negligible. The proposed formulation can be used within the framework of any power spectral density function-based random vibration approach to generate floor response spectra of desired level of confidence. A numerical study is carried out with the help of an example primary system and band-limited white noise to illustrate the proposed formulation. It has been shown that the proposed formulation gives very accurate estimates of floor response spectra if pseudostatic response is assumed to be in those primary modes only which are stiff enough to the base excitation. It has also been shown that neglecting soil-structure interaction may give too overconservative or unconservative estimates, depending on the damping ratio, natural period, and location of the oscillator, energy distribution in the excitation process, and shear wave velocity of soil.

Soil Structure Interaction in Practice

Abstract: Seismic incidents of recent decades have evoked extensive studies focusing on the effects of Soil-Structure Interaction (SSI) Rodriguez and Monies [1] evaluated the importance of SSI effects on the seismic response and damage of buildings in Mexico City during the 1985 earthquake A simple structural model was used to conduct a parametric study using a representative record obtained in the soft soil area of Mexico City The results indicated that in many cases of inelastic response, SSI can be evaluated considering the rigid-base case and the amplified period of the SSI system A similar procedure can be followed to assess seismic damage in multi-story buildings supported on flexible soils Literature in the area is rather extensive This brief introduction gives only a flavour of issues in recent studies on the topic Based on an observation on the damage pattern caused by the 1994 Northridge earthquake, that is that the number of severely damaged buildings was reduced in areas where the surface soil experienced some form of non-linear response, Trifunac and Todorovska [2] studied the effects of non-linear soil response They attempted to quantify the relationship between the density of red-tagged buildings and the severity of shaking, including the density of breaks in water pipes as a variable specifying the level of strain in the soil

Modelization of Dynamic Soil-Structure Interaction Using Integral Transform-Finite Element Coupling

Abstract: The aim of this work is a reliable modelling of the wave propagation in dynamic soil-structure interaction. A small FEM domain will be introduced to model the structure and its surrounding area, while The Integral Transform Method (ITM) is used to model the Half-space. With this Coupling Method (ITM-FEM) there is no more limitation in case of local irregularities.