Showing papers on "Soil structure interaction published in 1988"

Soil-structure-interaction analysis in time domain

Abstract: The procedures to perform nonlinear soil-structure-interaction analysis in the time domain are summarized. The nonlinearity is restricted to the structure and possibly an adjacent irregular soil region. The unbounded soil (far field) must remain linear in this formulation. Besides the direct method where local frequency-independent boundary conditions are enforced on the artificial boundary, various formulations based on the substructure method are addressed, ranging from a discrete model with springs, dashpots and masses to boundary-element methods with convolution integrals involving either the dynamic-stiffness coefficients or the Green's functions in the time domain via the iterative hybrid-frequency-time-domain analysis procedure with the nonlinearities affecting only the right-hand side of the equations of motion.

Isolation of soil‐structure interaction effects by full‐scale forced vibration tests

Abstract: SUMMARY Forced vibration tests designed to isolate the effects of soil-structure interaction are described and the results obtained for the nine-storey reinforced concrete Millikan Library Building are analysed. It is shown that it is possible to determine experimentally the fixed-base natural frequencies and modal damping ratios of the superstructure. These values may be significantly different from the resonant frequencies and damping ratios of the complete structure-foundation-soil system. It is also shown that forced vibration tests can be used to obtain estimates of the foundation impedance functions. In the case of the Millikan Library it is found that during forced vibration tests the rigid-body motion associated with translation and rocking of the base accounts for more than 30 per cent of the total response on the roof and that the deformation of the superstructure at the fundamental frequencies of the system is almost entirely due to the inertial forces generated by translation and rocking of the base. Full-scale forced vibration tests are commonly used to determine the natural frequencies, modal damping values and mode shapes of structures. The frequent practice in interpreting the results of forced vibration tests is to neglect the effects of the interaction between the structure and the soil. Such a simplifying assumption may lead to serious errors in that resonant frequencies, energy dissipation and other dynamic characteristics of the complete structure-foundation-soil system are ascribed to the superstructure. The typical result is that the fixed-base natural frequencies of the structure are underestimated while the energy dissipation in the structure is overestimated. The principal objective of this study is to analyse in detail the effects of soil-structure interaction during forced vibration tests. In particular, an attempt is made at extracting structural characteristics, such as fixed- base natural frequencies and energy dissipation mechanism, as well as foundation-soil characteristics, such as foundation impedance functions, from forced vibration test results which involve the complete structure-foundation-soil system. Although a large number of theoretical studies of the interaction between structures and the supporting soil have been made and a variety of sophisticated analytical models have been proposed, the experimental study of the interaction phenomenon has been very limited. The second objective of this study is associated with the need of illustrating the interaction effects under controlled experimental conditions. For the purpose of this study the nine-storey reinforced concrete Millikan Library Building was selected as the experimental site. The Millikan Library has been the subject of a large number of forced vibration tests (Kuroiwa,12 Jennings and Kuroiwa,9 Trifunac,19 Foutch et al.,' Luco et al.,'3) and ambient vibration tests (Blandford et al.,' Trifunac,19 McLamore," Udwadia and Trifunac20). Accelerograms for the 1968 Borrego Mountain, 1970 Lytle Creek and 1971 San Fernando earthquakes have been recorded in the Library and a

Behaviour of diaphragm walls in clay prior to collapse

Abstract: Centrifuge model tests have been used in an attempt to gain a coherent view of the soil-structure interaction behaviour following the excavation of soil in front of a pre-constructed wall. Excavation was simulated by the removal of a suitably heavy fluid from a preformed cavity. The broad replication of stress magnitudes and stress paths permitted the full representation of wall deformation, soil strain and swelling, completing a 50 year full-scale lifespan in under 24 hours of continuous centrifuging. Measurements were made of soil displacement vectors, pore water pressures, wall displacements and bending moments together with forces in props when they were present. These have made possible the validation of simplified ‘geostructural mechanisms’ which offer the same degree of advantage to the designer as does the idealization of heam behaviour encapsulated in engineer's beam theory. A serviceability criterion for soil or wall displacements can be entered into simplified admissible strain fields appropria...

Soil Parameters for Design of Buried Pipelines

Abstract: This paper presents the table of recommended design parameters for soil, shows their physical significance, and compares the resulting stiffness and strength for the variety of soil and compaction levels tested. These results are useful for estimating soil properties and for judging the benefits of compaction, as well as for use in finite element analysis.

Dynamics of Soil-Base-Isolated-Structure Systems

Abstract: A study of the effects of soil-structure interaction on the dynamic response of linear base-isolated structures is presented. The structures are supported at the surface of a homogeneous and viscoelastic half-space and are excited at the foundation. The conditions under which the interaction effects are of sufficient importance to warrant consideration in design are defined. These conditions appear to be different than corresponding conditions for conventional structures, and in particular, the interaction effects in base-isolated structures are not as important as those in conventional structures.

A plane strain soil‐structure interaction model

Abstract: A plane strain model for dynamic soil-structure interaction problems under harmonic state is presented. The boundary element method is used to study the response of a homogeneous isotropic linear elastic soil. The far field displacement at the free surface is approximated by an outgoing Rayleigh wave. The finite element method is used to describe the response of the building, of the foundation and possibly of a finite part of the inhomogeneous non-linear soil. Two coupling procedures are described. The model is applied to a problem previously studied in the antiplane case. Incident P, SV and Rayleigh waves are considered. The results show an amplification and an attenuation of the structure motion with frequency when incident Rayleigh waves and P, SV body waves are respectively considered.

Analysis of pile group by infinite layer method

Abstract: This Paper presents an infinite layer method for the analysis of the settlement interaction between piles embedded in layered soil. In this method, the soil, which can have properties varying with depth, is divided into a number of infinite layers whereas the pile is divided into the same number of solid bar elements, which deform as a rigid section in the horizontal plane. Based on the single pile model, the increase in settlement of each pile due to interaction with the adjacent pile was calculated by an iteration procedure and is expressed in terms of an interaction factor. The influence of the layered soil, pile spacing and pile stiffness on the interaction effect is also examined. Assuming that the principle of superposition is applicable, the interaction between piles in a pile group can then be easily evaluated. The effect of the rigidity of the pile cap on the load distribution among the piles and the settlement of the foundation system has also been investigated. L'article presente une methode po...

Modified calculation of pile-group settlement interaction

Abstract: A procedure that allows for the influence of the greater soil-mass stiffness between piles is described for calculating group settlement interaction factors. For the calculation of the settlement of a pile due to the presence of an adjacent pile, a weighted average of the soil moduli near the pile and between the piles is used with the classical Mindlin equation of elasticity. This procedure leads to decreased interaction between piles, and therefore to smaller group settlement and more uniform distributions of load, than are obtained by the conventional analysis in which the soil-mass modulus is assumed to be equal to the soil modulus near each pile. When applied to a recent series of field tests, the modified procedure is found to predict the group performance more closely than does the conventional procedure.

Implementation of effective seismic input for soil−structure interaction systems

Abstract: A previously introduced method for transmitting effective seismic excitation to a discretized soil-structure system implemented. The method permits free-field excitation of a linear soil system to be specified within the regie of computation, arbitrarily close to a zone that includes the (possibly non-linear) structure and local subgrade and bae, thus eliminating the need to transmit the seismic excitation through artificial boundaries. This approach is demonse through a numerical example comprising a linear, two-dimensional system. Some comments also are made on the rere efficiencies of various local absorbing boundaries.

Centrifuge modelling of sand embankments and islands in earthquakes

Abstract: The bumpy road shaking table system at the Cambridge geotechnical centrifuge was used to conduct an experimental investigation into the effects of earthquakes on sand embankments and islands. The results of the study show that, when a loose or medium dense embankment or island is subjected to an earthquake, positive pore pressures are generated, particularly at the crest. This pore pressure generation softens the embankment and lowers its resonance frequency, resulting in liquefaction and decoupling of surcharge motions from crest motions in the extreme case. When a dense embankment or island is subjected to a strong earthquake, spiky acceleration records are observed at the shoulders of the embankment or island. These records may be attributed to the propagation of dilation fronts through the sand which is in a state of cyclic mobility. If a rigid surcharge is present on the crest, the interaction of the embankment or island with the rigid surcharge gives rise to surcharge accelerations which are charact...

Numerical studies of soil–structure interaction using a simple interface model

Abstract: The effect of interface roughness in problems of soil–structure interaction is demonstrated using a simple finite element interface model. Three examples of geotechnical interest are presented to d...

Wave and earthquake response of offshore structures with soil-structure interaction

Abstract: Dynamic response of offshore structures to random sea waves and strong earthquake motions is investigated. Sea waves are modelled by Bretschneider's wave energy spectrum and ground motions are represented by Kanai's power spectrum. Governing equation of motion is obtained by the substructure method. Response analysis is carried out using frequency-domain random vibration approach. Wave responses are found to be generally larger whereas seismic responses are smaller when soil-structure interaction effects are considered. Reliability studies show that earthquake loadings provide comparable results to those of wave loadings, but the latter have more significant effects on response evaluations because of the longer duration time.

Soil/structure/interaction aspects for jackup platforms

Abstract: The paper deals with the integrated behaviour of the structure and the foundation soil for independent-leg-supported jackup platforms With the traditional wedged shape of the leg foundations (spud cans), the foundations stability of the platform is achieved by vertical preloading Common practice has been to preload to a level equal to the maximum vertical leg force in the design storm Since the actual storm loading includes horizontal forces and possible moments in combination with the vertical force the soil is likely to be loaded into the plastic large strain area The consequences may vary from slight or insignificant leg penetrations and redistribution of leg reaction forces to catastrophic foundations stability problems The paper deals with important aspects of the soil structure interaction as overall platform stability, foundation stiffness and structural response A general description of the soil structure interaction aspects is given, including a discussion of todays practice of operating jackup rigs Simple analytical models for soil structure interaction are described The effects of various soil conditions, foundation geometries, preload level etc on overall stability and structural response are given by examples

Model behavior of prestressed tie-back

Abstract: Tie‐back walls are frequently used presently for the support of deep excavations, yet soil‐structure interaction under “service” conditions is not really understood. This study is an attempt to analyze the problem using the results of experimental work by the writer. Soil and wall movements, variations in anchor prestress, as well as sand stresses on the wall were measured on a small scale physical model. Numerical parametric analyses of soil‐structure interaction based on a Winkler model were also made by varying soil stiffness, soil properties, and anchor prestress values to fit the model tests. Results were subsequently extrapolated to real size. It was shown that the soilwall‐anchor interaction was profoundly influenced by an increase in the anchor prestress, which generally led to a large reduction of the associated tie‐back displacements. This should be attributed to the force equilibrium on the wall, which was shown to differ markedly from the one used by conventional limit equilibrium design.

Soil bridge abutment interaction

Abstract: Presented herein are analyses of 6 bridge approaches Lateral movement and settlement of the foundations and embankments are discussed Results of slope stability and finite element analyses are related to measured movements A graph for predicting approach pavement settlement is included A theoretical approach model was used to run an extensive series of finite element analyses Movements resulting from these analyses are presented with several variable model conditions Variable conditions include embankment and foundation configuration, soil cohesion, and soil friction angle (A)

Probabilistic evaluation of soil-structure interaction in liquefaction. proceedings of the sixth international conference on numerical methods in geomechanics, 11-15 april 1988, innsbruck, austria. volumes 1 - 3

Abstract: A method is proposed here to estimate structural damage considering the generation and dissipation characteristics of excess pore water pressure generated due to earthquake shaking. Anisotropic stress is used in the formulation. The residual and consolidation settlement are estimated accordingly. The information on differential settlement is used to develop a damage criterion. The influence of structural rigidity on the structural damage potential is also evaluated. A probabilistic model is developed to study the risk of structural damage since a considerable amount of uncertainty is associated with most of the parameters in the model. The methodology is illustrated with the help of an example. (Author/TRRL)

3-dimensional seismic responses of a gravity-type steel offshore platform with emphasis on soilstructure interaction

Abstract: Three-dimensional seismic analysis of a gravity-type steel platform, which is proposed for oil production and storage at marginal offshore fields, is carried out. The present structure is characterized by a massive top deck, a six-leg flexible tubular framed jacket, and a wide spread out base tank. The interest for investigation is, therefore, placed on the dynamic interaction of the structure with soils at site. Different modleings are taken for structural parts in view of the accuracy for response analysis. The dynamic substructure method is applied to advantage for evaluating the soil-structure Interaction effectively. Through the numerical computation, some useful informations are derived for the seismic design of the concerned offshore structure.