Showing papers on "Soil structure interaction published in 2002"

Stochastic Finite-Element Analysis of Seismic Soil-Structure Interaction

Abstract: A procedure is presented for the probabilistic analysis of the seismic soil-structure interaction problem. The procedure accounts for uncertainty in both the free-field input motion as well as in local site conditions, and structural parameters. Uncertain parameters are modeled using a probabilistic framework as stochastic processes. The site amplification effects are accounted for via a randomized relationship between the soil shear modulus and damping on the one hand, and the shear strain of the subgrade on the other hand, as well as by modeling the shear modulus at low strain level as randomly fluctuating with depth. The various random processes are represented by their respective Karhunen-Loeve expansions, and the solution processes, consisting of the accelerations and generalized forces in the structure, are represented by their coordinates with respect to the polynomial chaos basis. These coordinates are then evaluated by a combination of weighted residuals and stratified sampling schemes. The expansion can be used to carry out very efficiently, extensive Monte Carlo simulations. The procedure is applied to the seismic analysis of a nuclear reactor facility.

Modelling of nonlinear dynamic behaviour of a shallow strip foundation with macro-element

Abstract: A new nonlinear soil-structure interaction macro-element is presented. It models the dynamic behaviour of a shallow strip foundation under seismic action. Based on substructured methods, it takes into account the dynamic elastic effect of the infinite far field, and the material and geometrical nonlinear behaviour produced in the near field of the foundation. Effects of soil yielding below the foundation as well as uplift at the interface are considered. Through the concept of macro-element, the overall elastic and plastic behaviour in the soil and at the interface is reduced to its action on the foundation. The macro-element consists of a non linear joint element, expressed in the three degrees of freedom of the strip foundation, reflecting the limited bearing capacity of the foundation. This model provides a practical and efficient tool to study the seismic response of a structure in interaction with the surrounding soil medium. Applications to a bridge pier show the potentialities of this kind of model.

Numerical modelling of group effects on the distribution of dragloads in pile foundations

Abstract: Negative skin friction on pile foundations, predicted from the results of numerical analyses, is presented. Soil slip at the pile–soil interface has been found to be the most important factor in governing pile behaviour in consolidating ground. Reduction in dragload is predicted for piles in a group owing to interaction between soil and pile. It has been demonstrated that the group effect depends not only on the configuration of the pile group, but also on soil slip along the pile–soil interface, governed mainly by the interface friction coefficient and the soil settlement. Various factors should be included in an evaluation of the group effect, including the pile spacing, the number of piles in a group, the relative location of piles in a group, the pile type, the pile installation method, the surface loading and the stiffness of the soil. Existing design approaches result in overprediction of dragload for a single pile and of group effect for a pile group. Back-analysed dragloads and group effects consi...

Movements in the Piccadilly Line tunnels due to the Heathrow Express construction

Abstract: This paper presents the results of analyses of monitoring records taken from inside one of the existing Piccadilly Line tunnels during the construction of three station tunnels at the Heathrow Express Central Terminal Area. The monitoring data allow a detailed picture of the way in which existing segmental concrete-lined tunnels behave as a result of tunnelling works below. Settlement curves at critical construction stages are presented. It is shown that the computed ‘volume loss’ varied between 1·3% and 2·5%. Long-term settlement records indicate that the maximum settlement increased by 27% for a period three years after tunnel completion. This result is compared with earlier findings from the Heathrow trial tunnel. Asymmetry of the settlement troughs caused by the outer tunnels, constructed after the central concourse tunnel, is discussed, and asymmetry parameters are defined from a number of case histories. The relationship of asymmetry parameters to pillar width between tunnels is presented and discus...

A Study of Soil-Reinforcement Interface Friction

Abstract: An important design parameter of reinforced soil structures is the friction mobilized between the soil and reinforcement elements, i.e., the pullout friction. The most commonly adopted method to identify this friction is a special test setup, i.e., the pullout test. Compared to the results of the pullout test, the direct shear test gives much smaller values. In this paper the mechanism of interaction between a soil and rigid planar as well as nail reinforcement is investigated. It is found that the mobilized friction between soil and reinforcement is influenced by the elastic parameters of the soil and its dilatancy angle. A simple approach is proposed from which the pullout friction can be estimated from the direct shear coefficient of friction between soil and reinforcement and the friction angle and dilatancy angle of the soil, all of which can be determined by direct shear tests. The results of the proposed model are in good agreement with results of pullout tests from the literature.

Load transfer curves along bored piles considering modulus degradation

Abstract: The load-transfer (or t-z) curve, which reflects the interaction between a pile and the surrounding soil, is important for evaluating the load-settlement response of a pile subjected to an axial load using the load-transfer method. Preferably, the nonlinear stress-strain behavior of the soil should be incorporated into the t-z curve. This paper presents a practical approach for the estimation of t-z curves along bored piles by considering the nonlinear elastic properties and modulus degradation characteristics of the soil. A method for evaluating the modulus degradation curve from the results of a pressuremeter test is proposed. The results of load tests on one instrumented bored pile in Piedmont residual soil in Atlanta and another in the residual soil of the Jurong Formation in Singapore provide verification of the validity of the proposed approach.

Flexural strength and ductility of extended pile-shafts. i: analytical model

Abstract: An analytical model, based on the commonly used equivalent cantilever concept, is developed for assessing the local ductility demand of a yielding pile-shaft when subjected to lateral loading. For elastic response of the pile-shaft, an equivalent depth-to-fixity is assumed, which can be derived by equating the lateral stiffness of the cantilever to that of the elastic soil-pile system. In adapting the equivalent cantilever model to yielding pile-shafts, however, the depth-to-maximum-moment is assumed to occur at a depth above the depth-to-fixity. The lateral strength, which depends on the depth-to-maximum-moment, is determined using the flexural strength of the pile and the ultimate pressure distribution of the soil. By assuming a concentrated plastic hinge rotation at the depth-of-maximum- moment, a kinematic model relating the local curvature ductility demand to global displacement ductility demand is developed. The kinematic relation is shown to depend on the aboveground height, depth-to-maximum-moment, depth-to-fixity, and equivalent plastic hinge length. The model is illustrated using a pile-shaft embedded in cohesive and cohesionless soils.

Soil structure interaction analysis: modeling the interface

Abstract: The sand–structure interface, developed under monotonic loading, was modeled based on physical observations. The model takes into account the macroscopic conditions to yield a general constitutive ...

Effects of Space Distribution of Excitation on Seismic Response of Arch Dams

Abstract: The effects of the ground motion spatial variation and of the canyon geometry on the dynamic response of arch dams during the event of an earthquake is studied in this paper. The seismic response of a dam subject to time harmonic longitudinal, shear, and Rayleigh waves impinging the dam site from different directions is analyzed. Several canyon and reservoir geometries are considered. A three-dimensional boundary element model which allows for the rigorous representation of the dynamic interaction between the dam, the foundation rock, and the water is used. The foundation rock is modeled as a uniform viscoelastic boundless domain where the incident traveling wave field is defined by its analytical expression, which may include any spatial variation. The obtained results show the importance of three-dimensional effects which are many times neglected.

Influence of soil-structure interaction on pounding response of adjacent buildings due to near-source earthquakes

Abstract: A numerical approach to analyse pounding responses of adjacent buildings on subsoil to earthquakes is presented. The nonlinear calculation of the soil-structure system is performed subsequently in the Laplace and the time domain. The adjacent buildings and the subsoil are described by finite elements and boundary elements, respectively. In the numerical investigation the effect of Kobe, Northridge and Chi-Chi near-source earthquakes is considered. The result reveals that both the subsoil and long-period pulses in the ground motions can increase the pounding potential of buildings. In addition, poundings can amplify the induced floor vibrations. In contrast, soil-structure interaction has reduction effect on the induced vibrations. In order to estimate the distance required to prevent pounding the influence of the soil-structure interaction is significant.

Effects of wave passage on the relevant dynamic properties of structures with flexible foundation

Abstract: An evaluation of the wave passage effects on the relevant dynamic properties of structures with flexible foundation is presented. A simple soil–structure system similar to that used in practice to take into account the inertial interaction effects by the soil flexibility is studied. The kinematic interaction effects due to non-vertically incident P, SV and Rayleigh waves are accounted for in this model. The effective period and damping of the system are obtained by establishing an equivalence between the interacting system excited by the foundation input motion and a replacement oscillator excited by the free-field ground motion. In this way, the maximum structural response could be estimated from standard free-field response spectra using the period and damping of the building modified by both the soil flexibility and the travelling wave effects. Also, an approximate solution for the travelling wave problem is examined over wide ranges of the main parameters involved. Numerical results are computed for a number of soil–structure systems to identify under which conditions the effects of wave passage are important. It comes out that these effects are generally negligible for the system period, but they may significantly change the system damping since the energy dissipation within the soil depends on both the wave radiation and the diffraction and scattering of the incident waves by the foundation. Copyright © 2001 John Wiley & Sons, Ltd.

Simplified analysis of layered soil-structure interaction

Abstract: The interaction of an arbitrary structure with its foundation soil is treated by representing the stratified soil with the end of a linear elastic half space model with specific geometrical and elastic properties for its layers. The proposed procedure is based on a purely analytical treatment of the underlying soil model, as well as on the use of a structural model with fictitious supports inserted at the contact nodes of the foundation elements with the soil surface. The availability of a general purpose finite element program is a prerequisite in order to carry out the analysis of the structural model. The analysis for an arbitrary static loading is performed by using the stiffness matrices of the soil surface and of the structure with respect to their contact nodes. This approach provides a flexible framework to perform parametric studies to include the variability of soil properties. Three numerical examples are presented and the results are compared wiht those based on Winkler’s assumption of modulus of subgrade reaction.

Three-Dimensional Analysis of Lateral Pile Response using Two-Dimensional Explicit Numerical Scheme

Abstract: A procedure for exploiting a two-dimensional (2D) explicit, numerical computer code for the 3D formulation of dynamic lateral soil-pile interactions is considered. The procedure is applied to two models using simultaneous computation of a series of plane strain boundary value problems, each of which represents a horizontal layer of soil. The first model disregards the shear forces developed between the horizontal layers, and may be considered as a generalized Winkler model. The second model takes account of these forces by coupling the behavior of the horizontal layers. Several verification problems for a single pile and pile groups in a homogeneous soil layer modeled as a viscoelastic material were solved and compared to known solutions in order to assess the reliability of the models. Excellent agreement was observed between results of the present analyses and existing solutions.

Elastic wave propagation in a 3-D unbounded random heterogeneous medium coupled with a bounded medium. Application to seismic soil–structure interaction (SSSI)

Abstract: We present a sub-structuring method for the coupling between a large elastic structure, and a stratified soil half-space exhibiting random heterogeneities over a bounded domain and impinged by incident waves. Both media are also weakly dissipative. The concept of interfaces classically used in sub-structuring methods is extended to ‘volume interfaces’ in the proposed approach. The random dimension of the stochastic fields modelling the heterogeneities in the soil is reduced by introducing a Karhunen–Loeve expansion of these stochastic fields. The coupled overall problem is solved by Monte-Carlo simulation techniques. A realistic example of a large industrial structure interacting with an uncertain stratified soil medium under earthquake is finally presented. This case study and others validate the presented methodology and its ability to handle complex mechanical systems. Copyright © 2002 John Wiley & Sons, Ltd.

Minimum Depth of Soil Cover above Soil–Steel Bridges

Abstract: Soil–steel bridges are built of flexible corrugated steel panels buried in well-compacted granular soil. Their design is based on the composite interaction between the soil pressures and the displacements of the conduit wall. The structure failure could be initiated by shear or tension failure in the soil cover above the steel conduit. The provisions for design given in different codes, such as the Canadian Highway Bridge Design Code, managed to avoid some of the problems associated with the failure of soil above soil–steel bridges by requiring a minimum depth of soil cover over the crown of the conduit taking into consideration the geometric shape of the conduit. However, the present code requirements for a minimum depth of cover were developed for a maximum span of 7.62 m and using nonstiffened panels of 51 mm depth of corrugation. The effect of having larger spans or using more rigid corrugated panels has not been examined before and is the subject of this paper. The present study uses the finite-eleme...

Effect of soil-structure interaction on seismically isolated bridges

Abstract: The objective of this study is two-fold: first, to assess the effects of soil-structure interaction (SSI) on the response of seismically isolated bridge piers and, second, to develop a method that ...

Modeling of dynamic soil-structure interaction by ANSYS program

Abstract: Based on shaking table model test and using general - purpose finite element program ANSYS, some issues about modeling of Soil -Structure lnteraction(SSI) system are discussed in this paper. These issues mainly include simulation of flexible soil container, selection of dynamic constitutive model of soil, simulation of the changing - status nonlinearity of soil - structure interface, meshing, consideration of gravity, treatment of reinforcements in structure, using of symnietry principle and so on. As a result, some computational results of acceleration time -history of 551 system are given in this paper. Comparison between computer and test results shows that acceleration time -history curves of corresponding points are coincident approximately, and it is verified that the simulation methods in this paper are rational and the model is feasible.

3d finite element analysis of large dynamic machine foundation considering soil-structure interaction

Abstract: This paper presents three dimensional finite element method for analysis of dynamic response of large dynamic machine foundation considering soil-structure interaction Dynamic machine foundation and its surrounding rock are taken as an integrated coupling object Machine foundation is regarded as viscoelastic body to reflect deformation of foundation Viscous-spring artificial boundary is constructed which can simulate not only the radiation damping of semi-infinite soil, but also the elasticity recovery capacity of the far field media on the boundary The equivalent spring solid element is constructed for implementing the artificial boundary with commercial FE program Analysis of dynamic response of Yanshan LDPE project is performed by the method Quantitative analysis of major factors which affect dynamic response of large machine foundation is performed by numerical experiments and some useful conclusions are drawn

Yielding from field behavior and its influence on oil tank settlements

Abstract: One of the problems of major concern in designing large oil storage tanks is the interaction with the foundation soil, particularly in terms of differential settlements. Ultimate or serviceability limit states can be reached due to nonallowable local displacements along the tank perimeter. This paper presents experimental data obtained during the construction of a thermal power plant in Northern Italy. The performed analyses have been particularly devoted to highlighting the occurrence of local soil yielding and its influence on the performance of oil tank structures. The analyses address the influence of local soil yielding on excess pore pressure response as well as on the trend of lateral displacements and perimeter differential settlements. As soon as the soil reaches a yielding condition, significant changes occur in terms of the overall soil-structure interaction phenomena, with consequences mainly in the displacement patterns and rates. The obtained evidence reported in the paper is aimed to focus the attention of the designer on the need to properly detect the stress history of the soil deposit.

Tunnelling in soils - ground movements, and damage to buildings

Abstract: Tunnelling through soils results in ground loss, causing surface settlements and transverse movements. When the tunnel drive passes below an existing structure, it is important to estimate the effects upon the structure. However, the Greenfield deformations should not simply be imposed upon a structure, because the structure contributes to a stiffening of the ground. A computational three dimensional soil-structure interaction analysis is required, to obtain detailed stress-deformation response of the influence of tunnel construction on existing buildings. As an example, the case of the CAIRO metro tunnel is analysed. The numerical simulations presented here take into account the physics of the problem: face supporting, over cut and conical shape of the machine, the injection of grout in the annular void and its consolidation. After a precise description of the principles of excavation process simulation, the authors analyse not only the effect of final settlements on the existing buildings but also the stress induced in the structures during the passage of the tunnel boring machine.

Improving the Response of Soil-Metal Structures during Construction

Abstract: For economic reasons, manufacturers of soil-metal bridges have strived to build these structures under the shallowest possible depth of soil cover, below the one allowed by codes of practice. For such structures, special analysis is needed to circumvent or prevent the formation of failure mechanisms that may be triggered during construction or when subjected to traffic loads. Therefore, special features, such as transverse stiffeners attached to the metal shell and the use of thrust concrete beams, may be required to assist the corrugated metal shell in carrying the loads. In this paper, a novel design is proposed for such structures in which the surrounding soil is reinforced and the metal shell is tied into the soil. A finite-element analysis of long span soil-metal structures with shallow soil cover is carried out using these two designs. The analysis is verified and substantiated using field data obtained during the construction of an 18 m soil-metal bridge. Comparing the structural response from the two designs shows that the latter design can lead to a superior structure.