Showing papers on "Soil structure interaction published in 2001"

Kinematic pile bending during earthquakes: analysis and field measurements

Abstract: The passage of seismic waves through the soil surrounding a pile imposes lateral displacements and curvatures on the pile, thereby generating ‘kinematic’ bending moments even in the absence of a su...

Cyclic macro-element for soil–structure interaction: material and geometrical non-linearities

Abstract: This paper presents a non-linear soil–structure interaction (SSI) macro-element for shallow foundation on cohesive soil. The element describes the behaviour in the near field of the foundation under cyclic loading, reproducing the material non-linearities of the soil under the foundation (yielding) as well as the geometrical non-linearities (uplift) at the soil–structure interface. The overall 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 generalised variables, i.e. in forces applied to the foundation and in the corresponding displacements. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. Mechanisms of yielding and uplift are modelled through a global, coupled plasticity–uplift model. The cyclic model is dedicated to modelling the dynamic response of structures subjected to seismic action. Thus, it is especially suited to combined loading developed during this kind of motion. Comparisons of cyclic results obtained from the macro-element and from a FE modelization are shown in order to demonstrate the relevance of the proposed model and its predictive ability. Copyright © 2001 John Wiley & Sons, Ltd.

Load transfer approach for laterally loaded piles

Abstract: A two-parameter model has been proposed previously for predicting the response of laterally loaded single piles in homogenous soil. A disadvantage of the model is that at high Poisson's ratio, unreliable results may be obtained. In this paper, a new load transfer approach is developed to simulate the response of laterally loaded single piles embedded in a homogeneous medium, by introducing a rational stress field. The approach can overcome the inherent disadvantage of the two-parameter model, although developed in a similar way. Generalized solutions for a single pile and the surrounding soil under various pile-head and base conditions were established and presented in compact forms. With the solutions, a load transfer factor, correlating the displacements of the pile and the soil, was estimated and expressed as a simple equation. Expressions were developed for the modulus of subgrade reaction for a Winkler model as a unique function of the load transfer factor. Simple expressions were developed for estimating critical pile length, maximum bending moment, and the depth at which the maximum moment occurs. All the newly established solutions and/or expressions, using the load transfer factor, offer satisfactory predictions in comparison with the available, more rigorous numerical approaches. The current solutions are applicable to various boundary conditions, and any pile-soil relative stiffness.

Nonlinear Analysis of Integral Bridges: Finite-Element Model

Abstract: Integral abutment bridges (IABs) are jointless bridges where the deck is continuous and connected monolithically with the abutment walls. The biggest uncertainty in the design of these bridges is the reaction of the soil behind the abutments and next to the foundation piles, especially during thermal expansion. This lateral soil reaction is inherently nonlinear and is a function of the magnitude and nature of the wall displacement. Handling the soil-structure interaction in the design of IABs has always been problematic, usually requiring iterative, equivalent linear analysis. This paper describes the implementation of a full 3D finite-element model of an IAB system which explicitly incorporates the nonlinear soil response. This paper also presents the results from a small parametric study on a sample bridge where the soil compaction levels in the cohesionless soils behind the wall and adjacent to the piles were varied. These results show that the level of compaction in the granular backfill strongly dominates the overall soil reaction, and that this reaction greatly impacts the overall structural response of the bridge system.

Ground response during pile driving

Abstract: The paper presents a synthesis of the field measurements obtained in a series of large-scale pile-driving tests. The field test was performed at the Chiayi-Taipo area of the high speed rail system currently under construction in Taiwan. The test project included a complete instrumentation of three precast concrete piles with a network of piezometers, inclinometers, level posts, and velocity sensors. The instruments were used to monitor the variations of the dynamic soil pore water pressure, lateral ground deformations, vertical surface displacements, and ground vibrations induced by the pile on the surrounding soil medium during the driving process. Based on the test results, a correlation between the pile-driving resistance and the geological condition of the test site is identified.

Dynamic Experiments and Analyses of a Pile-Group-Supported Structure

Abstract: Experimental data on the seismic response of a pile-group-supported structure was obtained through dynamic centrifuge model tests, and then used to evaluate a dynamic beam on a nonlinear Winkler foundation (BNWF) analysis method. The centrifuge tests included a structure supported on a group of nine piles founded in soft clay overlying dense sand. This structure was subjected to nine earthquake events with peak accelerations ranging from 0.02 to 0.7g. The centrifuge tests and dynamic analysis methods are described. Good agreement was obtained between calculated and recorded structural responses, including superstructure acceleration and displacement, pile cap acceleration and displacement, pile bending moment and axial load, and pile cap rotation. Representative examples of recorded and calculated behavior for the structure and soil profile are presented. Sensitivity of the dynamic BNWF analyses to the numerical model parameters and site response calculations are evaluated. These results provide experimental support for the use of dynamic BNWF analysis methods in seismic soil-pile-structure interaction problems involving pile-group systems.

Probabilistic critical excitation for MDOF elastic–plastic structures on compliant ground

Abstract: Earthquake ground motions and their effects on structural responses are very uncertain even with the present knowledge. It is therefore desirable to develop a robust structural design method taking into account these uncertainties. Critical excitation approaches are promising and a new random critical excitation method is proposed for MDOF elastic–plastic shear-building structures on compliant ground. The power (area of power spectral density (PSD) function) and the intensity (magnitude of PSD function) are fixed and the critical excitation is found under these restrictions. In contrast to linear elastic structures, transfer functions and simple expressions for response evaluation cannot be defined in elastic–plastic structures and difficulties arise in describing the peak responses except by laborious elastic–plastic time-history response analysis. Statistical equivalent linearization is used to estimate the elastic–plastic stochastic peak responses approximately. The critical excitation responses are obtained for several examples and compared with those of the corresponding recorded earthquake ground motion. Copyright © 2001 John Wiley & Sons, Ltd.

Application of Periodic Boundary for Large Pile Group

Abstract: Full-scale testing of a large pile group is economically not feasible. A concept based on a periodic boundary has been used to study lateral behavior of a large pile group. The approach and findings from anchorage design of a major suspension bridge in California are presented here. Using the repeating nature of soil's displacement field within infinite number of piles arranged in a regular grid pattern, soil-pile interaction phenomenon from the finite area enclosed by one periodic soil boundary effectively represents behavior of the entire pile group. A 3D finite-element analysis was used to create the soil-pile models in which the boundary conditions mimic the repeating nature of the infinite number of piles by slaving the boundary nodes. The soil resistance, as calculated from the finite-element method employing the periodic boundary, is compared with the empirical p-y curve approach for a single isolated pile to determine the group effects. Values of p-multiplier and y-multiplier have been obtained fo...

Full-height piled bridge abutments constructed on soft clay

Abstract: Full-height piled bridge abutments constructed on soft clay are prone to lateral soil–structure interaction effects resulting from placement of the retained fill, and associated deformation of the underlying soil. The interaction increases lateral structural loading and displacement, and hence may result in unserviceable behaviour of the abutment or bridge deck. A series of geotechnical centrifuge tests and finite element method analyses are reported, examining the effect of clay layer depth and the rate of embankment construction. Agreement of data from the two methods is good, and the results confirm the existence of established lateral soil–pile interaction in the clay layer. However, additional interaction effects associated with the retained embankment material were also identified, causing a significant additional component of lateral loading on the structure. Such interaction increases bending moments in the piles, which are therefore of concern. Many existing empirical methods attempt to estimate ...

Full-scale experimental studies of soil-structure interaction?A review

Abstract: This paper presents a review of full-scale testing of structures related to soil-structure interaction and associated phenomena. It starts with a review of the early research on soil-structure interaction (including the work of Suyehiro, Sesawa and Kanai, and Biot), and proceeds with studies of the Hollywood Storage Building, of Millikan Library in Pasadena, and more recent studies. The usefulness of full-scale testing is illustrated by presenting recent results for the Hollywood Storage Building by the authors. Finally, an analysis of general trends in full-scale testing and soil-structure interaction research is presented based on the number of publications on these topics in the Earthquake Engineering Abstracts database. This analysis shows that the number of papers on the general topic of soil-structure interaction peaked at 35/year during the late 1970s, and at present is only about 10/year. Papers dealing with experimental aspects of soilstructure-intersection do not exhibit major fluctuations, and since 1970 appear at an average rate of 3.3/year. Only about 1.2 papers/year deal with full-scale experiments , about 2/3 of the experimental papers being devoted to laboratory testing. The only year with five papers on full-scale tests involving soilstructure-interaction was 1975, and about 45% of the time there were no contributions on this topic recorded in this database. Obviously, the priorities in earthquake engineering research are not properly balanced, and this situation is alarming. While small-scale laboratory tests and computer simulations are useful for understanding selected phenomena in soil-structure interaction, they lack the completeness of the full-scale tests. Laboratory experiments are designed to measure what the researcher has decided to study and may lead to discovering new physics only by accident, while the as-built environment contains all the physical properties of reality. This paper also presents a discussion on various difficulties in interpretation of earthquake response data recorded in structures and the use of full-scale test data. The main difficulty appears to be nonuniqueness of the interpretation of these data due to inadequate strong motion instrumentation and lack of processed data recorded in structures with intermediate amplitudes (between strong motion and microtremor levels). Finally, it is recommended that soil-structure models be refined, and more detailed seismic monitoring instrumentation be installed in buildings, including rotational transducers which will measure point rotation and will help separate the contribution of foundation rocking and structural deformation from the total recorded response. 1 Professor, Civil Engineering Department, University of Southern California, Los Angeles, CA 90089, 2531, U.S.A. 2 Research Associate Professor 3 Ph.D. Candidate “Strong motion accelerograms properly interpreted are the nearest thing to scientific truth in earthquake engineering” (Duke et al. (1970).

Free‐vibration analysis of a three‐dimensional soil–structure system

Abstract: A procedure which involves a non-linear eigenvalue problem and is based on the substructure method is proposed for the free-vibration analysis of a soil-structure system. In this procedure, the structure is modelled by the standard finite element method, while the unbounded soil is modelled by the scaled boundary finite element method. The fundamental frequency, and the corresponding radiation damping ratio as well as the modal shape are obtained by using inverse iteration. The free vibration of a dam-foundation system, a hemispherical cavity and a hemispherical deposit are analysed in detail. The numerical results are compared with available results and are also verified by the Fourier transform of the impulsive response calculated in the time domain by the three-dimensional soil-structure-wave interaction analysis procedure proposed in our previous paper. The fundamental frequency obtained by the present procedure is very close to that obtained by Touhei and Ohmachi, but the damping ratio and the imaginary part of modal shape are significantly different due to the different definition of damping ratio. This study shows that although the classical mode-superposition method is not applicable to a soil-structure system due to the frequency dependence of the radiation damping, it is still of interest in earthquake engineering to evaluate the fundamental frequency and the corresponding radiation damping ratio of the soil-structure system.

Soil Pressure Measured at Various Fill Heights Above Deeply Buried Thermoplastic Pipe

Abstract: When a flexible pipe is installed in a dense soil fill, stress redistribution takes place around the pipe because of pipe-soil interaction. The degree of this interaction is considered to be influenced by the stiffness ratio between the pipe and its surrounding soil. Classical theory based on elastic solutions shows that in an ideal installation condition, the zone of the pipe-soil interaction may be confined to one to two pipe diameters from the pipe. In 1999 a research team from the Ohio Research Institute for Transportation and Environment installed a total of 18 instrumented thermoplastic pipes at the deep pipe burial project site in Albany, Ohio. These pipes were placed under either a 6.1-m or 12.2-m (20-ft or 40-ft) embankment fill. During the pipe backfilling and subsequent embankment fill placement, soil pressure cells were placed at different fill heights above selected test pipes to measure the vertical extent of the pipe-soil interaction zone. The field-measured vertical soil pressure compared well with the predictions made by the elastic solutions. Summarized here are the information and data related to the vertical soil pressure measurements made in the Ohio University field study.

Earthquake response analysis of the Hualien soil–structure interaction system based on updated soil properties using forced vibration test data

Abstract: This paper presents results of the earthquake response analysis on a large-scale seismic test (LSST) structure which was built at Hualien in Taiwan for an international cooperative research project. The analysis is carried out using a computer program which has been developed based on axisymmetric finite element method incorporating dynamic infinite elements for far-field soil region and a substructured wave input technique. The non-linear behaviour of the soil medium is taken into account using an iterative equivalent linearization procedure. Two sets of the soil and structural properties, namely the unified and the FVT-correlated models, are utilized as the initial linear values. The unified model was provided by a group of experts in charge of the geotechnical experiments, and the correlated model was obtained through a system identification procedure using the forced vibration test (FVT) results by the present authors. Three components of ground accelerations are artificially generated through an averaging process of the Fourier amplitude spectra of the ground accelerations measured near the test structure, and they are used as the control input motions for the earthquake analysis. It has been found that the earthquake responses predicted using the generated control motions and with the FVT-correlated model as the initial linear properties in the equivalent linearization procedure compare very well with the observed responses. Copyright © 2001 John Wiley & Sons, Ltd.

Soil-Structure Interaction Effects on Elastic and Inelastic Structures

Abstract: The paper presents a critical assessment of the currently prevailing view of structural engineers, as expressed in seismic codes, that the role of SSI is always beneficial for the design seismic forces developing in a structure. Using recorded strong ground motions and theoretical analyses it is shown that, in certain seismic and soil environments, an increase due to SSI in the fundamental period of a moderately flexible structure may have a detrimental effect on seismic demand, contrary to the conclusion drawn on the basis of idealized (“average”) code spectra. Using a simple 2-dof system and a number of actual ground motions as excitation, it is also shown that indiscriminate use of presently popular “geometric” ductility relations may lead to erroneous conclusions in the prediction of seismic performance of flexibly-supported structures. A significant case history, referring to the failure of the 630-m Fukae bridge section of the Hanshin Expressway Route 3 in Kobe (1995), further supports the main findings of the paper, by showing that soil-structure interaction may have played a decisive even if subtle role in that failure.

Energy Dissipation in Soil‐Structure Interaction

Abstract: Energy dissipation as a means of reducing the seismic response of structures has become a popular topic among researchers and structural engineers who have developed and implemented devices, such as friction dampers, fluid dampers, and isolators, in the design or retrofit of structures. However, a natural source of energy dissipation is the interaction between a structure, its foundation, and the supporting soil medium. To account for this frequency‐dependent energy dissipation in dynamic analysis based on modal superposition, relatively simple and practical systems‐identification methods are presented to estimate the composite modal damping ratios for the significant modes of vibration. SSI experiments and analysis of simple theoretical models using this method have yielded relatively large modal damping ratios in certain situations for structures such as short to mid‐rise buildings, short‐span bridges, flat bottom fuel storage tanks, offshore concrete gravity platforms, nuclear power plant cont...

Non-Linear Seismic Soil-Structure Interaction Analysis Based on the Substructure Method in the Time Domain

Abstract: This paper presents an idealized 2-dimensional plain strain finite element seismic soil-structure interaction (SSI) analysis based on a substructure method by using original software developed by the authors. To investigate the effects of SSI the following types of analysis were performed: linear SSI analysis and non-linear SSI analysis. For the same structure, analysis was carried out by the procedure without the consideration of soil-structure interaction. These computations were achieved for different peak accelerations: 0.15g, 0.30g and 0.45g. In another case for a different site soil with a shear wave velocity of 200, 300 and 500 m/s, a linear SSI analysis was performed. In the analysis, the radiation condition was fully accounted for, the soil plasticity was modeled with the Von Mises failure criterion, basemat uplift was not considered, and the action of gravity was not taken into consideration.

Dynamic behaviour of pile foundations in layered soil medium using cone frustums

Abstract: An analytical method using a cone model is developed to evaluate the impedance functions of pile foundations in a layered soil medium. The dynamic behaviour of piles depends on the nature of the interaction between the piles and the surrounding soil. The soil–pile interaction effect modifies the stiffness of the piles and generates damping through energy radiation to infinity. This modified complex stiffness is called the impedance function. A physical model called a cone frustum is developed to represent the layered soil medium. It is capable of incorporating the complexity of layered soil media and the complicated behaviour of propagating waves. The analytical tool is developed based on wave propagation principles.

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 understood and considered at the designing stage. A new physical model was developed in Amirkabir University of Technology to study the behavior of buried pipes under different loading conditions. 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 as well as monotonic loads can be generated and applied to the soil surface. The generated load can be applied on the pipe centrally or eccentrically. The radial deflections of the tested pipes 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 in the paper. Among them, the soil density and the pipe depth proved to be the most important factors affecting the soil-pipe interaction. The influence of the impact at the first cycle was also found to be one of the main factors affecting the pipe behavior.

Practical solutions to soil–structure interaction problems

Abstract: Interaction of a structure and its foundation with the soil is discussed in this paper, and some of the numerical and analytical methods that have been developed for the analysis of raft and piled raft foundations are presented. It is shown that the use of simple spring models for the soil behaviour can lead to erroneous result and it is recommended that their use should be discontinued. Simple finite layer techniques are also examined, and results are compared with those of three-dimensional finite element techniques. It is shown that the finite layer techniques can yield good results for displacements in the raft and for moments induced into the piles. It is also shown that the use of thin plate theory for the raft can give good results for thick rafts and can be used for raft and piled raft analysis. The effect of including the stiffness of the superstructure in the analysis of the foundation is examined, and it is shown that the type of structure and its stiffness can have an effect on the deformation of the foundation. Finally, an analysis of an instrumented structure is carried out, and it is shown that reasonably good predictions of the behaviour of the foundation can be made through the use of soil-structure interaction theory and finite layer techniques.

Buckling analysis of buried pipes subjected to fault movements

Abstract: Buckling responses of buried pipes to fault movement considering the interaction of pipes and soil are analysed, using the Finite Displacement Analysis Method with thin shell elements The analysis model of interaction of pipe and soil is presented The pipe is discretized into 4 nodes thin thin shell elements and the soil is modeled by nonlinear springs Some factors and parameter effects, such as material nonlinearity of the pipe and soil and the geometrical parameters of pipe are studied

Status of Seismic Response Analysis of Long-span Structures under Multiple Support Excitations

Abstract: A summary of status of researches in the field of multiple support excitations of long-span structures is presentedThe structural responses for unsynchronized motions,especially,including the interaction of soil-structure are introducedSome problems,which need further investigation,are suggested