Showing papers on "Soil structure interaction published in 2000"

Modeling lateral soil-pile response based on soil-pile interaction

Abstract: Although most designers prefer the p-y curve method as compared to elastic continuum or finite-element analysis of laterally loaded pile behavior, the profession has reached a state where it is tim...

Coupled BEM/FEM approach for nonlinear soil/structure interaction

Abstract: A general coupled boundary element/finite element formulation is presented for the investigation of dynamic soil/structure interaction including nonlinearities. It is applied to investigate the transient inelastic response of structures coupled with a halfspace. The structure itself and the surrounding soil in the near field are modeled with finite elements. In this part of the model inhomogeneities and an elastoplastic material behavior with hardening effects can be taken into account. The remaining soil region, i.e. the elastic halfspace, is discretized with the boundary elements. Thus wave radiation to infinity is included in the model. In representative examples it is shown that the methodology is computationally powerful and can be used efficiently for the nonlinear analyses of complex soil/structure interaction problems.

Seismic Soil-Structure Interaction in Buildings. I: Analytical Methods; Seismic Soil-Structure Interaction in Buildings. II: Empirical Findings

Abstract: The two papers describe trends of the apparent system periods, , and damping factors, , in recorded response of 56 ˜˜ T z0 buildings (A1 to A45, and B1 to B14 in Table 1 of part II) to 15 California earthquakes. The building, foundation, and soil are viewed as an equivalent linear system, excited by horizontal ground motion. Only inertial interaction is considered as ‘‘the more important effect for foundations without large, rigid base slabs or deep embedment’’ (by allowing one translation and rocking of the foundation). The kinematic interaction (modification of the free-field motion by the foundation in absence of inertial forces) is neglected as ‘‘second order.’’ Rocking and torsional excitation components of the incident motion, differential motions of extended foundations, warping of flexible foundations, and nonlinear soil response due to soilstructure interaction (SSI) are not mentioned. The papers aim to verify the ‘‘simplified analytical procedures similar to those in the BSSC and ATC codes.’’ This discussion (1) requests some clarifications; (2) suggests that time-dependent changes in (caused by nonlinear response of soil during SSI) should ˜ T have been included in the analysis; and (3) comments on the conditions when kinematic SSI should not be neglected. In view of the bold simplifications adopted in parts I and II, one would expect at least fair to good agreement of the predicted trends with the data, as a proof (albeit qualitative and rough) that the assumptions are justified. However, as the authors admit, there is ‘‘significant scatter in the data.’’ Table 1 in part II lists the confidence (A-acceptable; L-low) characterizing the quality of the available geotechnical data and the accuracy of identification. An L was assigned 15% of the 44 cases with base acceleration 0.25g. Does the proposed simplified analysis break down for progressively larger strains in the soil, e.g., base accelerations >0.15g?

Inelastic Seismic Response of Bridge Drilled-Shaft RC Pile/Columns

Abstract: An analytical model based on a Winkler beam is used to represent the lateral force response of a reinforced concrete (RC) pile in cohesionless soil. An inelastic finite-element analysis was performed on the structure, using as the pile constitutive model the section moment-curvature relationship based on confined stress-strain relationships for the concrete. Parameters varied were pile head restraint (free and fixed head), height of pile head above grade level, and soil stiffness. Linear, bilinear, and hyperbolic soil models were examined. The analysis showed that shear would be significantly underpredicted by an elastic analysis, as inelastic behavior moved the point of maximum moment in the pile shaft closer to the surface, thus reducing the shear span. Maximum moment depth in the pile shaft and plastic hinge length were also shown to be strongly dependent on soil stiffness, and in the case of fixed-head piles, on abovegrade height of the superstructure. Linear soil models were shown to be adequate for most cases of pile/column design.

Seismic response and damage analysis of buildings supported on flexible soils

Abstract: The investigation reported in this paper studies the effects of soil–structure interaction (SSI) on the seismic response and damage of building–foundation systems. A simple structural model is used for conducting a parametric study using a typical record obtained in the soft soil area of Mexico City during the 1985 earthquake. Peak response parameters chosen for this study were the roof displacement relative to the base and the hysteretic energy dissipated by the simple structural model. A damage parameter is also evaluated for investigating the SSI effects on the seismic damage of buildings. The results indicate that in most cases of inelastic response, SSI effects can be evaluated considering the rigid-base case and the SSI period. Copyright © 2000 John Wiley & Sons, Ltd.

Finite Element Study of a Geosynthetic-Reinforced Soil Retaining Wall With Concrete Block Facing

Abstract: This paper focuses on the results of finite element modeling of a full-scale, concrete-block, geosynthetic-reinforced soil retaining wall constructed at the Public Works Research Institute in Japan. A nonlinear hyperbolic geosynthetic model was incorporated into a computer program that is capable of simulating soil-structure interaction behavior. The soil was simulated using a hyperbolic model while the block-block and soil-block interactions were simulated using interface elements. Comparison of numerical and measured experimental results indicated that the finite element model is capable of simulating the construction behavior of concrete-block geosynthetic-reinforced soil structures.

A boundary element method for the static analysis of raft foundations on piles

Abstract: This paper presents a Boundary Element Method formulation for the static analysis of piled rafts in which all the interactions between the plate, the pile and the soil are simultaneously considered In this approach the soil is treated as an elastic linear homogeneous half space, the plate is assumed to be thin and both are represented by integral equations Each pile is represented by a single element and the shear force along it is approximated by a second-degree polynomial The pile-tip stress is assumed to be constant over the cross-section The cap–soil interface is divided into triangular elements and the contact pressure is assumed to vary linearly across each element The vertical displacement of each node in the plate and in the piles is represented by an integral equation so that a set of linear equations is obtained involving the tractions and displacements at all nodal points on all the interfaces From these equations the nodal displacements and the overall stiffness of the system can be calculated Numerical results are presented and they correspond closely to those obtained by other authors

Variations between Foundation‐Level and Free‐Field Earthquake Ground Motions

Abstract: Strong motion data from sites having both an instrumented structure and free-field accelerograph are compiled to evaluate the conditions for which foundation recordings provide a reasonably unbiased estimate of free-field motion with minimal uncertainty. Variations between foundation and free-field spectral acceleration are found to correlate well with dimensionless parameters that strongly influence kinematic and inertial soil-structure interaction phenomena such as embedement ratio, dimensionless frequency (i.e., product of radial frequency and foundation radius normalized by soil shear wave velocity), and ratio of structure-to-soil stiffness. Low frequency components of spectral acceleration recorded on shallowly embedded foundations are found to provide good estimates of free-field motion. In contrast, foundation-level peak ground acceleration (both horizontal and vertical) and maximum horizontal velocity, are found to be de-amplified. Implications for ground motion selection procedures employed in attenuation relations are discussed, and specific recommendations are made as to how these procedures could be improved.

Modelling non‐linear ground response of non‐liquefiable soils

Abstract: A non-linear finite element (FE) model is presented to account for soil column effects on strong ground motion. A three-dimensional bounding surface plasticity model with a vanishing elastic region, appropriate for non-liquefiable soils, is formulated to accommodate the effects of plastic deformation right at the onset of loading. The elasto-plastic constitutive model is cast within the framework of a FE soil column model, and is used to re-analyse the downhole motion recorded by an array at a Large-Scale Seismic Test (LSST) site in Lotung, Taiwan, during the earthquake of 20 May 1986; as well as the ground motion recorded at Gilroy 2 reference site during the Loma Prieta earthquake of 17 October 1989. Results of the analysis show maximum permanent shearing strains experienced by the soil column in the order of 0.15 per cent for the Lotung event and 0.8 per cent for the Loma Prieta earthquake, which correspond to modulus reduction factors of about 30 and 10 per cent respectively, implying strong non-linear response of the soil deposit at the two sites. Copyright © 2000 John Wiley & Sons, Ltd.

Soil structure interaction of bridges for seismic analysis

Abstract: The current state-of-practice in soil structure interaction analysis and the latest approaches for analyzing large pile groups for bridge design is the focus of this report. Ground motion aspects for seismic design and soil structure interaction for typical foundations are described. The experience gained from the seismic retrofit and new design applications for major toll bridges in California provides the basis for this report.

Soil-structure interaction of buried pipes under cyclic loading conditions

Abstract: The safety of lifelines, as the most important urban facilities, under different conditions highly depends on the safe design and performance of these buried structures. This cannot be achieved unless their actual behaviors are well realized and considered at the designing stage. To study the behavior of buried pipes under different loading conditions, a new physical model was developed in Amirkabir University of Technology. The model is capable of simulating and monitoring flexible pipes under different conditions. The depth and the position of the buried pipes as well as the type and density of the surrounding soil can be changed and controlled. The cyclic loads with different amplitudes, and cycles as well as the monotonic loads can be generated and applied on the soil surface. The generated load can be applied on the pipe centrally or eccentrically. The radial deformations of the tested pipes as well as the shear and normal stresses on the boundaries of the soil trench were measured by a special probe and data acquisition system developed for this model. A series of different tests were carried out to study the soil-pipe interaction. The main factors affecting the behavior of these buried structures were studied and described in the paper. Among them the soil density and the pipe depth proved to be the most important factors affect the soil-pipe interaction. The influence of the impact at the first cycle was also found one of the main factors affecting the pipe behavior. There are also many other results the descriptions and discussion about which are given in the next sections.

Development and field testing of multiple deployment model pile (mdmp)

Abstract: A model pile is a calibrated tool equipped with instrumentation capable of monitoring the pile/soil interaction over the pile history. Monitoring includes the installation, pore pressure dissipation combined with consolidation and soil pressure equalization, and ultimately the pile behavior under loading and failure. The model pile installation and soil structure interaction simulate the actual field conditions of full-scale piles. As such, the obtained information can be utilized directly (e.g., skin friction) or extrapolated (e.g., pore pressure dissipation time) to predict the soil's response during full-scale installation. The Multiple Deployment Model Pile (MDMP) was developed as an in situ tool for site investigations. The MDMP instrumentation is capable of monitoring the pile/soil interaction throughout the life cycle of a driven pile: (1) dynamic force and acceleration readings at the pile top and along the pile during driving; (2) pore water pressure and radial stresses during equalization; and (3) skin friction, end-bearing resistance, and local (subsurface) displacement during static loading. These measurements allow the observation of pile capacity gain (a.k.a. "set-up" or "freeze") and accurately monitor the load-transfer relations. The MDMP was successfully deployed twice in Newbury, MA during March 1996. The obtained dynamic measurements allowed the evaluation of the pile's static capacity and clarified the difficulties associated with dynamic analysis of small-scale penetration. Pile capacity gain with time was examined based on normalization procedures developed by Paikowsky et al. (1995). The excess pore water pressure dissipation, variation of radial effective stresses, and pile capacity gain with time were determined for the two tests. The obtained results show that the MDMP is capable of providing accurate soil-structure interaction relations during static load testing. The measurements indicate a complex mechanism governing capacity gain that combines pore pressure dissipation and radial stress redistribution over time. These findings are used to predict the time-dependent behavior of full-scale instrumented piles and to re-evaluate the capacity gain phenomenon. The obtained results explain some unanswered questions and allow the development of procedures incorporating pile capacity gain in design and construction.

Soil-structure interaction of buried structures

Abstract: This paper, authored by a member of the Transportation Research Board Committee on Subsurface Soil-Structure Interaction, provides an overview of current trends and future developments affecting the soil-structure interaction of buried structures. The analysis, design, and performance of buried structures associated with transportation facilities require an understanding of this interaction. Buried structures usually cannot resist the loads to which they are subjected without utilizing the strength of the surrounding soil in a complex interaction. The soil-structure interaction of a buried structure is affected by the structure's material composition, size, and stiffness; by the method of construction in the field; by the type of and placement of backfill material; and by the external loading.

Soil-structure interaction effect on active control of multi-story buildings under earthquake loads

Abstract: A direct output feedback control scheme was recently proposed by the authors for single-story building structures resting on flexible soil body. In this paper, the control scheme is extended to mitigate the seismic responses of multi-story buildings. Soil-structure interaction is taken into account in two parts: input at the soil-structure interface/foundation and control algorithm. The former reflects the effect on ground motions and is monitored in real time with accelerometers at foundation. The latter includes the effect on the dynamic characteristics of structures, which is formulated by modifying the classical linear quadratic regulator based on the fundamental mode shape of the soil-structure system. Numerical result on the study of a -scale three-story structure, supported by a viscoelastic half-space of soil mass, have demonstrated that the proposed algorithm is robust and very effective in suppressing the earthquake-induced vibration in building structures even supported on a flexible soil mass. Parametric studies are performed to understand how soil damping and flexibility affect the effectiveness of active tendon control. The selection of weighting matrix and effect of soil property uncertainty are investigated in detail for practical applications.

Overview of seismic research for nuclear power plant

Abstract: Seismic analysis is one of the major problems in the design of nuclear power plant. This paper is intended to look at some of the areas (definition of design earthquake parameters, seismic calculation theory, soil-structure interaction, floor accelerogram and floor response spectra, seismic analysis of structures, foundations, foundation structures, underground structures and equipments etc.), the progresses that have been made in these areas, and the remaining issues in need of further research.

Simulation Method of Soil Boundary Condition in Shaking Table Tests of Soil-Structure Interaction

Abstract: Through comparing several boundary simulation methods used in past tests, this paper draws a conclusion that the effect of the flexible boundary box is satisfactory According to the practical conditions of the test, a flexible boundary model box is designed the results of three free field shaking table tests show that the response of the point away from the boundary for some distance matches that of the center point of the soil surface This testifies that the influence of the boundary on the soil inside is small and the test box satisfactorily decreases the boundary effect on sesmic response of the soil As a result, the simulation design of the soil boundary is successful, which provides good conditions for shaking table tests of Soil Structure Interaction system

A model to analyze a buried structure response to surface dynamic loading

Abstract: A relatively simple model of a buried structure response to a surface loading that can simulate a possible opening and closure of a gap between the soil and the structure is presented. Analysis of the response of small and medium scale buried roof slabs under surface impulsive loading shows that the model\'s predictions are in fairly good agreement with the experimental results. Application of the model to a study case shows the relative influence of system parameters such as, the depth of burial, the arching coefficient, and the roof thickness, on the interface pressure and on the roof displacement. This model demonstrates the effect of a gap between the structure and the soil. The relative importance of including a gap opening and closure in the analysis is examined by the application of the model to a study case. This study results show that the deeper the depth of burial, the longer the gap duration, and the shorter the duration of the initial interface impact, while the higher the soil\'s shear resistance, the higher the gap duration, and the shorter the initial interface impact duration.