Showing papers on "Soil structure interaction published in 1999"

Seismic Soil-Pile-Structure Interaction Experiments and Analyses

Abstract: A dynamic beam on a nonlinear Winkler foundation (or “dynamic p-y”) analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 002 to 07g The soil profile consisted of soft clay overlying dense sand Site response and dynamic p-y analyses are described Input parameters were selected based on existing engineering practices Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems

Seismic soil-structure interaction in buildings. II: Empirical findings

Abstract: System identification analyses are used to evaluate soil-structure interaction effects for 77 strong motion data sets at 57 building sites that encompass a wide range of structural and geotechnical conditions. Kinematic interaction effects on the "input" motion at the bases of structures are found to be relatively modest in many cases, whereas inertial interaction effects on the structural response to these motions can be significant. To quantify inertial interaction effects, fixed- and flexible-base modal vibration parameters are used to evaluate first-mode period lengthening

Nonlinear ground response at lotung lsst site

Abstract: A fully nonlinear finite-element (FE) model is developed to investigate the impact of hysteretic and viscous material behavior on the downhole motion recorded by an array at a large-scale seismic test site in Lotung, Taiwan, during the earthquake of May 20, 1986. A stick model with the same spatial interpolation accuracy as a three-dimensional FE model is used for vertical wave propagation analysis. The constitutive model is based on a three-dimensional bounding surface plasticity theory with a vanishing elastic region, and accounts for shear stiffness degradation right at the onset of loading. The model is cast in a time-domain nonlinear FE code SPECTRA and is used to analyze the 1986 earthquake data. It is shown that the recorded downhole motion of Lotung was dominated by nonlinear response. Results of the fully nonlinear analysis are compared with the predictions of the program SHAKE so that the performance of the nonlinear model may be assessed relative to that of an equivalent linear model.

Dynamic response of a pile in a multi-layered soil to transient torsional and axial loading

Abstract: The dynamic response of an elastic pile subjected to transient torsional and axial loading is considered. The pile is embedded in a multi-layered elastic soil. The stress field in a soil is simplified by following the existing solutions for a pile subjected to static torsional and axial loading. The dynamic equilibrium equation of soil is solved in the Laplace domain by using analytical techniques. The soil resistance is coupled into a one-dimensional governing equation of a pile segment and an analytical solution is presented. An impedance matrix can then be derived for a pile segment relating end stress resultants to the displacements. Non-homogeneous initial conditions of the pile are considered. The impedance matrices of pile segments are assembled by following the concepts of finite element method to analyse a pile embedded in a multi-layered soil. The treatment of soil base response is also discussed. Time domain solutions are obtained by using a numerical Laplace inversion procedure. The extension ...

Lateral Vibration and Internal Forces of Grouped Piles in Layered Soil

Abstract: Simplified analytical models are developed for the lateral harmonic response of single piles and pile groups in layered soil. Pile-to-soil interplay is represented by a dynamic Winkler formulation based on frequency-dependent springs and dashpots. For pile-to-pile interaction, the wave field originating from each oscillating (“source”) pile and the diffraction of this field by the adjacent (“receiver”) piles are considered. The response of single piles and pile pairs is evaluated both numerically (through a transfer-matrix formulation) and analytically (introducing an efficient virtual-work approximation). Closed-form solutions are obtained: (1) for the impedance of single piles; (2) for the dynamic interaction factors between two piles; and (3) for the “additional” internal forces (“distress”) developing in grouped piles because of pile-to-pile interaction, a phenomenon frequently ignored in current methods of analysis. Both swaying and rocking vibrational modes are considered. The effect of pile length ...

Three-dimensional dynamic soil-structure interaction analysis in the time domain

Abstract: A new numerical procedure is proposed for the analysis of three-dimensional dynamic soil-structure interaction in the time domain. In this study, the soil is modelled as a linear elastic solid, however, the methods developed can be adapted to include the effects of soil non-linearities and hysteretic damping in the soil. A substructure method, in which the unbounded soil is modelled by the scaled boundary finite-element method, is used and the structure is modelled by 8-21 variable-number-node three-dimensional isoparametric or subparametric hexahedral curvilinear elements. Approximations in both time and space, which lead to efficient schemes for calculation of the acceleration unit-impulse response matrix, are proposed for the scaled boundary finite-element method resulting in significant reduction in computational effort with little loss of accuracy. The approximations also lead to a very efficient scheme for evaluation of convolution integrals in the calculation of soil-structure interaction forces. The approximations proposed in this paper are also applicable to the boundary element method. These approximations result in an improvement over current methods. A three-dimensional Dynamic Soil-Structure Interaction Analysis program (DSSIA-3D) is developed, and seismic excitations (S-waves, P-waves, and surface waves) and externally applied transient loadings can be considered in analysis. The computer program developed can be used in the analysis of three-dimensional dynamic soil-structure interaction as well as in the analysis of wave scattering and diffraction by three-dimensional surface irregularities. The scattering and diffraction of seismic waves (P-, S-, and Rayleigh waves) by various three-dimensional surface irregularities are studied in detail, and the numerical results obtained are in good agreement with those given by other authors. Numerical studies show that thc new procedure is suitable and very efficient for problems which involve low frequencies of interest for earthquake engineering.

Effect of liquefaction on lateral response of piles by centrifuge model tests

Abstract: This article presents work conducted on the effect of liquefaction on lateral pile response. Many existing bridges are founded on piles driven through loose sand that may liquefy during earthquake shaking. Both lateral stiffness and lateral capacity of piles (friction or end-bearing) are very sensitive to the properties of the surrounding soil. In current seismic analysis procedures, the effect of soil on lateral response is incorporated through nonlinear distributed soil springs along the pile within a beam-on-elastic foundation formulation. The pressure-deflection curves characterizing those springs, called p-y curves, depend on pile diameter, soil properties, and state of effective stresses. Therefore, it is of great interest to evaluate the influence of the pore water pressure buildup in the sand due to the shaking on the p-y curves controlling the lateral response of the pile during the rest of the shaking. This is being done in this project by means of centrifuge model testing at the Rensselaer Polytechnic Institute 100 g-ton geotechnical centrifuge in Troy, New York. It is expected that this will result in a proposed guideline for seismic analysis of piles in liquefying sand.

Seismic Earth Pressure on Retaining Structures

Abstract: A simple kinematic method to predict the seismic earth pressure against retaining structures is developed. The fundamental solution to the free-field seismic response considering nonlinear, plastic behavior of soil is included in the retaining wall analysis for the first time. Perturbation to the free-field response caused by soil-structure interaction effects for different types of wall movement is considered. Results from this kinematic method are compared with those obtained from finite-element analysis and observed from laboratory shaking table tests performed on model retaining walls.

Seismic effectiveness of tuned mass dampers considering soil–structure interaction

Abstract: This paper presents how soil–structure interaction affects the seismic performance of Tuned Mass Dampers (TMD) when installed on flexibly based structures. Previous studies on this subject have led to inconsistent conclusions since the soil and structure models employed considerably differ from each other. A generic frequency-independent model is used in this paper to represent a general soil–structure system, whose parameters cover a wide spectrum of soil and structural characteristics. The model structure is subjected to a stationary random excitation and the root-mean-square responses of engineering interest are used to measure the TMD's performance. Extensive parametric studies have shown that strong soil–structure interaction significantly defeats the seismic effectiveness of TMD systems. As the soil shear wave velocity decreases, TMD systems become less effective in reducing the maximum response of structures. For a structure resting on soft soil, the TMD system can hardly reduce the structural seismic response due to the high damping characteristics of soil–structure systems. The model structure is further subjected to the NS component of the 1940 El Centro, California earthquake to confirm the TMD's performance in a more realistic environment. Copyright © 1999 John Wiley & Sons Ltd.

An efficient approach for settlement prediction of pile groups

Abstract: The paper presents exact closed form solutions for estimating the settlement of single and group piles in non-homogeneous soil, using a load transfer approach derived from elastic continuum theory. The effects of load transfer factor have been explored in detail to account for the effect of a finite depth of compressible soil and non-homogeneity of soil profiles. Interaction factors between pairs of piles, and overall settlement ratios for pile groups of various geometries, are evaluated from the solutions and are shown to be consistent with those obtained from a full boundary element approach. The solutions are in the form of Bessel functions. However, to facilitate evaluation, a simple program called GASGROUP has been developed. The program can be readily used to predict the settlement of large pile groups. The analysis is quick and efficient, and can be run in a personal computer even for a group of 700 piles. The program is used to predict the single and group pile responses for a number of actual pil...

Vertical and rocking impedances for rigid rectangular foundations on soils with bounded non-homogeneity

Abstract: The vertical and rocking response of rigid rectangular foundations resting on a linear-elastic, compressible, non-homogeneous half-space soil model is studied. The non-homogeneity is described by a continuous yet bounded increase of shear modulus with depth. The mixed boundary value problem is solved by means of the semi-analytical method of the subdivision of the foundation/soil contact area whereby the influence functions for the sub-regions are determined by integration of the corresponding surface-to-surface Green's functions for the particular soil model. Impedance functions are given for representative values of the non-homogeneity parameters, the Poisson's ratio and the foundation geometry over a wide range of frequencies. Significant features associated with the soil non-homogeneity are pointed out.

Variational solution for vertically loaded pile groups in an elastic half-space

Abstract: This paper presents a variational approach that can be used to analyse vertically loaded pile groups in soil modelled by an elastic half-space. With use of a variational approach, both the displacements and shear stresses of group piles are each represented by a finite series. The principle of minimum potential energy is used to determine the response of pile groups. Good agreement between the present analytical method and other numerical methods is observed for the behaviour of pile groups. The theoretical predictions compare reasonably well with field measurements.

Use of sparse iterative methods for the resolution of three‐dimensional soil/structure interaction problems

Abstract: In this paper we present a study of the performance of sparse iterative solvers regarding the resolution of three-dimensional and non-linear problems encountered in soil/structure interaction. It is composed of two parts. In the first one, we present briefly iterative methods and preconditioners used in this study, then we analyse their performance on three soil/structure interaction problems: a shallow foundation under a vertical loading, a single pile subjected to a lateral loading and the construction of a lined tunnel in a soft soil. Tests are performed assuming an elastic–perfectly plastic constitutive law for the soil material with a non-associated Mohr–Coulomb flow rule. Copyright © 1999 John Wiley & Sons, Ltd.

Simulation analyses of buildings damaged in the 1995 Kobe, Japan, earthquake considering soil–structure interaction

Abstract: A series of studies was conducted on three buildings of steel reinforced concrete structures with RC shear walls damaged in the 1995 Hyogo-ken Nanbu earthquake. These buildings are located in an area where structural damage centred around. Two of these buildings suffered severe damage, while the third was not structurally damaged. Our studies deal with site inspections, including micro-tremor measurement of buildings, the evaluation of input motions, and the response analyses considering soil-structure interaction. The results of simulation analyses of the two severely damaged buildings correspond to their actual damage state. From the response analyses of the one slender building with no structural damage, it was concluded that uplifting is the main reason it did not suffer any structural damage. Through these studies, the importance of soil-structure interaction and effective input motion is fully understood.

A coupling model of FE–BE–IE–IBE for non-linear layered soil–structure interactions

Abstract: A coupling model of Finite Elements (FEs), Boundary Elements (BEs), Infinite Elements (IEs) and Infinite Boundary Elements (IBEs) is presented for analysis of soil–structure interaction (SSI). The radiation effects of the infinite layered soil are taken into account by FE–IE coupling, while the underlying bed rock half-space is discretized into BE–IBE coupling whereby the non-horizontal bed rock surface can be accounted for. Displacement compatabilities are satisfied for all types of aforementioned elements. The equivalent linear approach is employed for approximation of nonlinearity of the near field soil. This model has some advantages over the current SSI program in considering the bed rock half-space and non-vertical wave incidence from the far field. Examples of verification demonstrate the applicability and accuracy of the method when compared with the FLUSH program. Finally, the effects of the relative modulus ratio Er/Es of rock and soil and the incident angles of non-vertical waves on the responses of the structure and the soil are examined. Copyright © 1999 John Wiley & Sons, Ltd.

Laboratory studies of dynamic shaft resistance response of a vibro-driven model pile in granular soil by varying the relative density

Abstract: The complexity of driveability prediction of vibro-driven sheet piles can be subdivided into three main parts: vibro-driver, soil, and sheet pile related parameters. This paper describes a series of laboratory tests in which one of the main soil related parameters was studied. The objective of the tests was to study the induced volume changes along the shaft and its effect on the static and dynamic load-displacement relationships at three relative densities. The paper also provides a discussion of the volume change mechanisms in light of the present results.

Vertical excitation of stochastic soil-structure interaction systems

Abstract: This paper considers two stochastic models for a soil-structure interaction problem with vertical propagation of P waves during strong earthquake motion. These models include the horizontal and vertical spatial variability of stiffness of the soil medium. The first model involves a two-dimensional stochastic Winkler foundation, which takes into account the horizontal variability of the soil. This model elucidates some experimental results obtained on a nuclear power station physical model built in Hualien (Taiwan). The second model is developed as a continuum system of random columns involving, this time, horizontal and vertical random characteristics of the soil medium. For both models a statistical analysis was performed with respect to determining probabilistic properties resonance frequencies and amplitudes of the corresponding transfer functions. The theoretical development and numerical results demonstrate the importance of considering soil variability for geotechnical design applications.

Dynamic soil–structure interaction effects on the seismic response of suspension bridges

Abstract: A stochastic approach has been formulated for the linear analysis of suspension bridges subjected to earthquake excitations. The transfer functions of various responses have been formulated while including the effects of dynamic Soil-Structure Interaction (SSI) via the use of the fixed-base modes of the structure. The excitation has been characterized by the 'equivalent stationary' processes corresponding to the free-field motions at each support and by an assumed coherency function between these motions. The proposed formulation considers the non-stationarity in the structural response due to sudden application of excitation by considering (i) the time-dependent frequency response functions, and (ii) the order statistics formulation for the peak factors in evolutionary response processes. The formulation has been illustrated by analysing the seismic response of the Golden Gate bridge at San Francisco for two example excitations conforming to USNRC-specified design spectra. The significance of various governing parameters on the dynamic soil-structure interaction effects on the seismic response of suspension bridges has also been studied. It has been found that the contribution of the vertical component of ground motion to the bridge response increases with increasing soil compliance. Also, the extent to which the spatial variation of ground motion affects the bridge response depends on how significant the SSI effects are.

Stochastic analysis of seismic structural response with soil-structure interaction

Abstract: The most important features of linear soil-foundation-structure interaction are reviewed, using stochastic modeling and considering kinematic interaction, inertial interaction, and structural distortion as three separate stages of the dynamic response to the free-field motion. The way in which each of the three dynamic stages modifies the spectral density of the motion is studied, with the emphasis being on interpretation of these results, rather than on the development of new analysis techniques. Structural distortion and inertial interaction analysis are shown to be precisely modeled as linear filtering operations. Kinematic interaction, though, is more complicated, even though it has a filter-like effect on the frequency content of the motion.