Showing papers on "Soil structure interaction published in 1985"

Dynamic soil-structure interaction

Abstract: Keywords: Interaction-sol-structure Reference Record created on 2004-09-07, modified on 2016-08-08

Simplified Earthquake Analysis of Structures with Foundation Uplift

Abstract: Simplified analysis procedures are developed to consider the beneficial effects of foundation‐mat uplift in computing the earthquake response of structures, which respond essentially as single‐degree‐of‐freedom systems in their fixed‐base condition. These analysis procedures are presented for structures attached to a rigid foundation mat, which is supported on rigid foundation soil or flexible foundation soil modeled as two spring‐damper elements. Winkler foundation with distributed spring‐damper elements, or a viscoelastic half‐space. In these analysis procedures, the maximum earthquake‐induced base shear and deformation for an uplifting structure are computed directly from the earthquake response spectrum. It is demonstrated that the simplified analysis procedures provide results for the maximum base shear and deformation to a useful degree of accuracy for practical structural design.

Non‐linear soil‐structure‐interaction analysis using dynamic stiffness or flexibility of soil in the time domain

Abstract: The basic equation of motion to analyse the interaction of a non-linear structure and an irregular soil with the linear unbounded soil is formulated in the time domain. The contribution of the unbounded soil involves convolution integrals of the dynamic-stiffness coefficients in the time domain and the corresponding motions. Alternatively, a flexibility formulation for the contribution of the unbounded soil using the dynamic-flexibility coefficients in the time domain, together with the direct-stiffness method for the structure and the irregular soil can be applied. The dynamic-stiffness or flexibility coefficient in the time domain is calculated as the inverse Fourier transform of the corresponding value in the frequency domain. The dynamic-stiffness coefficient's asymptotic behaviour for high frequencies determines the singular part whose transformation exists only in the sense of a distribution. As the dynamic-flexibility coefficient converges to zero for the frequency approaching infinity, the corresponding coefficient in the time domain is simpler to calculate, as no singular part exists. The salient features of the dynamic-stiffness and flexibility coefficients in the time domain are illustrated using a semi-infinite rod with exponentially increasing area. The dynamic-flexibility coefficients in the time domain are calculated for a rigid circular disc resting on the surface of an elastic halfspace and of a layer built-in at its base. Material damping is also introduced using the three-parameter Kelvin and the Voigt models.

Non‐linear soil‐structure‐interaction analysis using green's function of soil in the time domain

Abstract: The contribution of the (linear) unbounded soil to the basic equation of motion of a non-linear analysis of soil-structure interaction consists of convolution integrals of the displacement-force relationship in the time domain and the history of the interaction forces. The former is calculated using the indirect boundary-element method, which is based on a weighted-residual technique and involves Green's functions. As an example of a non-linear soil-structure-interaction analysis, the partial uplift of the basemat of a structure is examined. As the convolution integrals have to be recalculated for each time step, the computational effort in this rigorous procedure is substantial. A reduction can be achieved by simplifying the Green's function by ‘concentrating’ the region of influence. Alternatively, assuming a specified wave pattern, a coupled system of springs and dashpots with frequency-independent coefficients can be used as an approximation.

Beam on Generalized Two‐Parameter Foundation

Abstract: A method for analysis of beams bearing on a ground surface is presented. The method is based on treating the soil medium as a generalized two-parameter model. The inputs required for the model are dimensions and material properties only, which usually are known before the analysis. This contrasts to other two-parameter models in which the parameters are based upon assumed soil displacement distributions that may be difficult to predict before the analysis. Analyses show the new two-parameter model can yield responses of loaded beams reasonably close to those computed by using continuum solutions or a finite element method.

Influence of foundation flexibility on soil‐structure interaction

Abstract: The effect of the base mat flexibility on seismic soil-structure interaction is studied for an axisymmetric reactor building on a soft and a stiff soil. As a preliminary step, the dynamic response of a massless flexible circular plate with two rigid concentric walls, through which the plate is loaded, is analysed. The response of the plate is found to depend on the plate flexibility, the load distribution and the frequency of excitation. For practical, in-phase load distributions, the response of the flexible plate is close to that of a rigid plate at low frequencies, but deviates at high frequencies. Including the flexibility of the mat has hardly any effect on the frequencies and damping of the fundamental rocking and vertical modes of the reactor building. This is the case for soft and stiff soil conditions. However, the flexibility of the mat strongly affects the first and higher structural deformation modes. In both cases the amount of energy dissipated in the soil is a significant percentage of the total dissipation, and is essentially unaffected by the mat flexibility.

Nonlinear Hysteretic Dynamic Response of Soil Systems

Abstract: A simplified analysis procedure for the nonlinear hysteretic dynamic response of soil or structural systems, or both, is presented. The method is based on a Galerkin formulation of the equations of motion in which the solution is expanded using basis functions defined over the spatial domain occupied by the soil system. The basis functions are selected as the normal eigenmodes of the linearized problem. The hysteretic stress-strain behavior is modeled by using elastoplastic constitutive equations based on multi-surface kinematic plasticity theory. Accuracy and versatility of the technique are demonstrated by applying it to analyze the nonlinear dynamic response of an earth dam. The dam is modeled as a one-dimensional hysteretic shear wedge. Parametric studies assessing the influence of the nonlinearities on the response are presented. Finally, comparisons are made with results obtained through a more elaborate finite element representation of the dam.

Seismic Response of Pile Supported Cooling Towers

Abstract: An analytical method is developed to determine the seismic response of rotational shell structures, such as cooling towers, supported by deep foundations in the form of long piles. The substructure deletion method is employed through the development of a dynamic boundary system at the contact area between the superstructure and the substructure. A new mathematical formulation compatible with the shell deformation is developed to deal with the rigid body motions due to the negation of the fixed base assumption. Two pile foundation cases are considered in order to examine the effect of soil-pile-structure interaction on the seismic response of cooling towers.

Soil-Pipeline Interaction During Ground Movement

Abstract: The problem of the elastic interaction is examined between a pipeline or a group of connected flexible connected pipelines and the surrounding soil medium, which is induced by ground movement. The pipeline is modelled as a structural element in which flexure takes place only in the longitudinal direction. An approximate method for estimating the flexural moments that are induced in the vicinity of a transition zone is presented. The techniques proposed in the paper can be used to examine the flexural interaction between both near surface and deeply embedded pipelines located in a transition zone.

Interaction of soil and buried rigid structure. proceedings of the eleventh international conference on soil mechanics and foundation engineering, san francisco, 12-16 august 1985

Abstract: Deep mixing method has been applied in Japan to reinforce soft clay by manufacturing an extraordinarily stiff treated soil mass in-situ. Interaction of soft alluvial soil and the treated soil walls resting on reliable stratum is investigated to improve current design procedure. It is known from the centrifuge model test that the external forces are carried solely by the treated soil walls, that the magnitude and distribution of contact pressures at the surface of treated soil mass are dependent on the magnitude of factor of safety against external stability, and that the pressures change with time due to consolidation process of soft soil. For the covering abstract of the conference see IRRD 287689. (Author/TRRL)

Non-iterative method for the analysis of soil-structure interaction. proceedings of the eleventh international conference on soil mechanics and foundation engineering, san francisco, 12-16 august 1985

Abstract: A procedure for the combined analysis of structure and soil, which consists in establishing compatibility between structure and soil displacements, is presented. Structure deformations are calculated as a function of soil reactions and settlements of soil are found as a function of loads applied to it (these loads are equal to the soil reactions, with opposite sign), employing the concept of influence values. Finally a simple example of application is included, to illustrate the method. For the covering abstract of the conference see IRRD 287689. (Author/TRRL)

Reliability evaluation of containments including soil-structure interaction

Abstract: Soil-structure interaction effects on the reliability assessment of containment structures are examined. The probability-based method for reliability evaluation of nuclear structures developed at Brookhaven National Laboratory is extended to include soil-structure interaction effects. In this method, reliability of structures is expressed in terms of limit state probabilities. Furthermore, random vibration theory is utilized to calculate limit state probabilities under random seismic loads. Earthquake ground motion is modeled by a segment of a zero-mean, stationary, filtered Gaussian white noise random process, represented by its power spectrum. All possible seismic hazards at a site, represented by a hazard curve, are also included in the analysis. The soil-foundation system is represented by a rigid surface foundation on an elastic halfspace. Random and other uncertainties in the strength properties of the structure, in the stiffness and internal damping of the soil, are also included in the analysis. Finally, a realistic reinforced concrete containment is analyzed to demonstrate the application of the method. For this containment, the soil-structure interaction effects on; (1) limit state probabilities, (2) structural fragility curves, (3) floor response spectra with probabilistic content, and (4) correlation coefficients for total acceleration response at specified structural locations, are examined in detail. 25 refs., 21more » figs., 12 tabs.« less

BOSEF: Beam on Swelling Elastic Foundation.

Abstract: : This study developed an improved methodology for studying the behavior of moderately loaded mat foundations on expansive soils. A computer program BOSEF (Beam on Swelling Elastic Foundation) was prepared that includes modelling of the following phenomena: (1) Two-dimensional steady-state moisture flow through foundations soils; (2) Computation of subgrade distortion resulting from changes of soil moisture and total or applied stress; and (3) Soil structure interaction of a loaded beam resting on distorted subgrade. The methodology does not require calculation of suitable edge moisture penetration distances, which is a major obstacle for the use of previously published simplified design methods. Comparisons of computed displacements were made with two test cases for which data were available. The results of this research show that program BOSEF yields meaningful insights into the behavior of mat foundations on expansive soils. Recommendations are proposed to modify the computer program to better simulate performance of mat foundations on expansive soils. (Author)