Showing papers on "Soil structure interaction published in 1991"

Empirical spatial coherency functions for application to soil-structure interaction analyses

Abstract: The spatial coherency of strong ground motion from fifteen earthquakes recorded by the Lotung LSST strong motion array is analyzed. The earthquakes range in magnitude from 3.7 to 7.8 and in epicentral distance from 5 to 80 km. In all, a total of 533 station pairs are used with station separations ranging from 6 to 85 meters. Empirical coherency functions for the horizontal component S‐waves appropriate for use in engineering analyses are derived from these data. The derived coherency functions are applicable to all frequencies and to separation distances up to 100 m. For these short station separations, the coherency decreases much faster with increasing frequency than with increasing station separation. The computed coherencies indicate that at high frequencies (>10 Hz) over 25 percent of the power of the ground motion is random for station separations greater than 30 m.

Three-dimensional nonlinear study of piles

Abstract: The main objective of this work is to examine the effect of nonlinear soil behavior on the axial and lateral response of piles to monotonic and cyclic loading with a view towards developing simplified, yet realistic models for representing pile‐soil‐pile interaction effects. The specific role of pile‐soil slippage and separation, and the overall nonlinear soil behavior on the response of single piles and pairs of piles is studied by means of a three‐dimensional finite element elastoplastic model that includes interface elements for representing slippage and pile‐soil separation. Numerical results indicate that material nonlinearity can significantly affect pile and soil response. Pile‐soil slippage is dominant under purely axial loading, while for lateral loads pile‐soil separation and generalized inelastic soil deformation are the crucial factors. In fact, ignoring these sources of nonlinearity can lead to greatly overestimating the amount of interaction between piles. Guided by the results of this work,...

Kinematic Seismic Response of Single Piles and Pile Groups

Abstract: This paper presents a comprehensive set of dimensionless graphs that could be readily utilized in practical applications A comparative study of these graphs leads to interesting conclusions that may contribute towards an improved appreciation of the nature of seismic pile-soil-pile interaction The graphs should be of practical value in determining the 'effective' seismic input motion at the base of structures, if the free-field motion is known The discussion of the study results focuses on elucidating the role of the key parameters, and aims at developing engineering insight into kinematic soil-pile and pile-pile interactions during earthquakes

One-dimensional analysis of soil plugs in pipe piles

Abstract: Under static loading in compression, open-ended piles may fail in a plugged mode, with the soil plug moving with the pile, or in an unplugged mode, with shear failure occurring between the soil plug and the pile shaft. It may be shown that, under drained loading conditions, the former mode of failure will generally occur, because arching action within the pipe pile leads to high frictional capacity of the plug. However, under faster rates of loading relevant to the offshore environment, the increase in effective stresses within the soil plug is limited and the plug capacity is significantly lower. The Paper presents a simple one-dimensional analysis of the soil plug under partially drained conditions. The analysis has been implemented numerically, and the resulting program used to derive design charts which give the plug capacity as a function of the soil plug parameters and the rate of loading. These design charts are presented in appropriate non-dimensional form, with example calculations included for t...

Behavior of pile plug in sandy soils during and after driving

Abstract: When open-ended piles are driven into the soil, a soil column is created inside. The advance of the soil column with respect to the pile penetration reflects the mode of pile penetration in the soil and influences the pile-soil interaction during and after installation. Formation of the soil column inside open-ended model and large scale experimental piles was analysed at four sandy sites. The incremental filling ratio was found to be linked to the impact characteristics. The influence of the soil column on driving results as on static results was evaluated and discussed. In contrast to the driving results, the static loading results were not changed by the removal of the soil column. The plugging effect was explained by an exponential cumulation of stresses inside the piles.

Pile-cap-pile-group interaction in nonhomogeneous soil

Abstract: A numerical method of analysis is presented to study the behavior of vertically loaded pile groups embedded in a nonhomogencous soil with the pile caps in contact with the ground. The considered soil profiles consist of soil with Young's moduli increasing linearly with depth. Parametric solutions are presented to show the influence of the distribution of the soil Young's moduli on the behavior of the groups. For the nonhomogeneous‐soil profiles considered, the effect of the cap in contact with the ground has a small influence on the stiffness of the group compared to the case without a ground‐contacting cap. The load carried by the cap, as expected, is significantly affected by the distribution of the soil Young's moduli. Case studies of field tests in clay show that the consideration of the nature of the soil inhomogeneity at the sites better models the behavior of pile groups with ground‐contacting caps.

Seismic Response of Transamerica Building. I: Data and Preliminary Analysis

Abstract: The objective of this paper is to present preliminary analyses of a set of acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake (Ms=7.1) from the 60story vertic...

Performance Assessment of Tunnels in Cohesionless Soils

Abstract: The ground behavior near circular tunnels in cohensionless soils, including the initial elastic response, the intermediate yielding, and the ultimate collapse, is explored in detail. Different modes of tunnel behavior are identified and the conditions for their occurrence are estimated using analytical solutions. The results compare well with those from finite‐element analyses, model tests, and field measurements. The ground convergence curve concept is applied as an analytical tool to interpret the response of the ground to tunneling. It is demonstrated that this method quantitatively relates the development of pressure on the lining to the tunnel wall displacement for the entire spectrum of the ground behavior, and thus provides an optimum design tool for lining pressure or ground‐displacement control. The validity and limitations of currently available lining design models are also addressed.

Analysis of Blast‐Loaded, Buried RC Arch Response. I: Numerical Approach

Abstract: The physical processes that govern the dynamic interaction between a soil continuum and an abutting or embedded structure are very complex and, often, highly nonlinear, requiring a numerical approach for the solution of such problems. Given the scarcity of experimental studies relative to any particular combination of structure, soil, and loading, the development of efficient analytical/computational tools is important in order to: (1) Understand the complex nonlinear response observed experimentally; (2) perform parametric studies; and (3) develop design guidelines. The approach outlined in this paper represents one attempt at expanding the state‐of‐the‐art in dynamic soil‐structure interaction modeling. In this approach, a hybrid numerical method, which merges the finite difference technique with the finite element method, is combined with a nonlocal continuum damage/plasticity model for concrete, a viscous cap plasticity model for dry sand, and an elastic/strain hardening plasticity model for steel, as...

Structural Control Including Soil‐Structure Interaction Effects

Abstract: The effects of soil‐structure interaction on the form of the control rule and on the effectiveness of active control of the seismic response of structures are examined. The structure is modeled as a uniform shear beam supported on a rigid foundation embedded in an elastic soil. The seismic excitation is represented by vertically incident shear waves. Active control in the form of an absorbing boundary located at the top of the structure is considered. The active absorbing boundary cancels the reflection of waves at the top of the structure and eliminates resonance within the superstructure. It is found that the form of the control rule changes as a result of the rocking of the foundation associated with the kinematic and inertial interaction. However, the effectiveness of this form of active control remains unchanged or is improved when soil‐structure interaction effects are included.

Analysis of Blast‐Loaded, Buried RC Arch Response. Part II: Application

Abstract: A hybrid numerical approach, which combines the finite difference technique and the finite element method, is coupled with a nonlocal continuum damage/plasticity model for plain concrete, a rate‐dependent cap model for soil, and an elastic/strain hardening plasticity model for steel. The resulting approach is applied in the analyses of two shallow buried reinforced concrete arches that were blast loaded (using explosive‐generated pressures applied to the soil surface) in separate test programs. The geometry and structural detailing of the two specimens are different, as are the soil properties, depths of burial, and the surface blast pressures. The comparisons between the predictions and the test results are shown to agree well overall. The numerical results are discussed in light of the test data in order to better understand the structural mechanisms that develop during testing. The discrepancies between the test data and the numerical results are discussed and corrections to the model are proposed.

Analysis of ground response data at Lotung large-scale soil- structure interaction experiment site. Final report

Abstract: The Electric Power Research Institute (EPRI), in cooperation with the Taiwan Power Company (TPC), constructed two models (1/4-scale and 1/2-scale) of a nuclear plant containment structure at a site in Lotung (Tang, 1987), a seismically active region in northeast Taiwan The models were constructed to gather data for the evaluation and validation of soil-structure interaction (SSI) analysis methodologies Extensive instrumentation was deployed to record both structural and ground responses at the site during earthquakes The experiment is generally referred to as the Lotung Large-Scale Seismic Test (LSST) As part of the LSST, two downhole arrays were installed at the site to record ground motions at depths as well as at the ground surface Structural response and ground response have been recorded for a number of earthquakes (ie a total of 18 earthquakes in the period of October 1985 through November 1986) at the LSST site since the completion of the installation of the downhole instruments in October 1985 These data include those from earthquakes having magnitudes ranging from M{sub L} 45 to M{sub L} 70 and epicentral distances range from 47 km to 777 km Peak ground surface accelerations range from 003 g to 021 g for the horizontal componentmore » and from 001 g to 020 g for the vertical component The objectives of the study were: (1) to obtain empirical data on variations of earthquake ground motion with depth; (2) to examine field evidence of nonlinear soil response due to earthquake shaking and to determine the degree of soil nonlinearity; (3) to assess the ability of ground response analysis techniques including techniques to approximate nonlinear soil response to estimate ground motions due to earthquake shaking; and (4) to analyze earth pressures recorded beneath the basemat and on the side wall of the 1/4 scale model structure during selected earthquakes« less

Simplified procedure for evaluating earthquake loading on piles. de mello volume; a tribute to professor dr. victor f. b. de mello in honor of his contribution to the development of geotechnical engineering in latin america

Abstract: In this paper a simplified procedure for evaluating earthquake loading on piles is presented. From the illustrative examples it has been found that maximum surface seismic displacement first depends on the maximum first natural period of the overburden when excited through its lower boundary by a horizontal seismic disturbance. Maximum shear wave velocity of the overburden becomes a very important design parameter, calling for a reliable seismic surveying as to define an average value of maximum shear wave velocity and values for the coefficients of variation. The use of compatible strain material properties, referring to damping and stiffness calls for appropriate laboratory tests conducted in the expected strain range. Applying a minoration factor to the shear wave velocity one tries to cover in a simplified criterion the dispersion on strain dependent material properties. For damping, the minoration factor is implicit in the load factor usually applied to the spectral accelerations. When studying the interaction of piles with the seismic moving soil it must be remembered that the prevailing mechanism is different from that produced by lateral external loading at the pile head. Relative deflections of the pile to its embedding moving soil are usually smaller and in the elastic domain. For the covering abstract of this book see IRRD 836508. (Author/TRRL)

Analysis of ground response data at Lotung large-scale soil- structure interaction experiment site

Abstract: The Electric Power Research Institute (EPRI), in cooperation with the Taiwan Power Company (TPC), constructed two models (1/4-scale and 1/2-scale) of a nuclear plant containment structure at a site in Lotung (Tang, 1987), a seismically active region in northeast Taiwan The models were constructed to gather data for the evaluation and validation of soil-structure interaction (SSI) analysis methodologies Extensive instrumentation was deployed to record both structural and ground responses at the site during earthquakes The experiment is generally referred to as the Lotung Large-Scale Seismic Test (LSST) As part of the LSST, two downhole arrays were installed at the site to record ground motions at depths as well as at the ground surface Structural response and ground response have been recorded for a number of earthquakes (ie a total of 18 earthquakes in the period of October 1985 through November 1986) at the LSST site since the completion of the installation of the downhole instruments in October 1985 These data include those from earthquakes having magnitudes ranging from M{sub L} 45 to M{sub L} 70 and epicentral distances range from 47 km to 777 km Peak ground surface accelerations range from 003 g to 021 g for the horizontal componentmore » and from 001 g to 020 g for the vertical component The objectives of the study were: (1) to obtain empirical data on variations of earthquake ground motion with depth; (2) to examine field evidence of nonlinear soil response due to earthquake shaking and to determine the degree of soil nonlinearity; (3) to assess the ability of ground response analysis techniques including techniques to approximate nonlinear soil response to estimate ground motions due to earthquake shaking; and (4) to analyze earth pressures recorded beneath the basemat and on the side wall of the 1/4 scale model structure during selected earthquakes« less

New method of time-dependent analysis for interaction of soil and large-diameter flexible pipe

Abstract: Design equations have been developed to predict the pre-yield deflections, stresses, and strains in buried flexible plastic pipes over time. The solutions consider the effects of creep in the pipe material and the surrounding soil and backfill, the water table, arching, and variable bedding conditions. These equations are obtained by regression analysis, and results are generated using a finite element program. The design equations predict pipe deflections that are consistent with those obtained in the field over a period of time. It is shown that the arching of soil surrounding a pipe can be quantified to further appreciate its cause and effects. The ratio of the pipe's vertical deflection to its horizontal deflection is shown to be an ambiguous way of defining the structural integrity of nonrigid pipes. Strain level may be a better indicator of the structural integrity of the pipe than pipe deflection, because it considers both the bending moments and the thrust in the pipe wall and can be measured against the allowable strain for that particular pipe material. Vertical pipe deflections predicted by the design equations for different depths of cover as well as for different time periods are shown to match field measurements well.

A residual force finite element approach to soil–structure interaction analysis

Abstract: An iterative process based upon a hybrid ‘residual force’ method is presented for solving elasto–plastic soil–structure interaction problems. In this approach the soil and the structure are treated as separate bodies and related only by compatibility of displacements and equilibrium of forces at the soil–structure interface. This scheme enables a significant improvement in numerical stability and rate of convergence over the conventional initial stress method. It is also shown that various interface conditions such as shear failure, slip and breakaway, and frictional and dilatant behaviour can be readily accounted for. Some practical aspects associated with the proposed scheme are emphasized for a number of numerical examples.

Three dimensional soil‐structure interaction analysis: deformable structures in multilayered soil mass

Abstract: A new hybrid method based on three‐dimensional finite element idealization in the near field and a semi‐analytic scheme using the principles of wave propagation in multilayered half space in the far field is proposed for the dynamic soil‐structure interaction analysis. The distinguishing feature of this technique from direct or indirect boundary integral techniques is that in boundary integral techniques a distribution of sources are considered at the near field boundary. Strengths of these sources are then adjusted to satisfy the continuity conditions across the near‐field/far‐field interface. In the proposed method unknown sources are placed not at the near field boundary but at the location of the structure. Then the Saint‐Venant's principle is utilized to justify that at a distant point the effect of the structure's vibration can be effectively modelled by an equivalent vibrating point force and vibrating moment at the structure's position. Thus the number of unknowns can be greatly reduced here. For soil‐structure interaction analysis by this method one needs to consider only three unknowns (two force components and one in‐plane moment) for a general two‐dimensional problem and six unknowns (three force components and three moment components) for a general three‐dimensional problem. When a vertically propagating elastic wave strikes a structure which is symmetric about two mutually perpendicular vertical planes the structure can only vibrate vertically for dilatational waves and horizontally for shear waves. Under this situation the number of unknowns is reduced to only one whereas in boundary integral and boundary element techniques the number of unknowns is dependent on the number of nodes at the near field boundary, which is generally much greater than six. Several example problems are solved in this paper using this technique for both flexible and rigid structures in multilayered soil media.

Results and analysis of soil‐structure interaction experiments performed in the centrifuge

Abstract: In this paper a centrifuge model that is capable of realistically representing soil-structure systems subjected to earthquake-like excitation is used to create a data pool which demonstrates the influence of (i) the frequencies of the structure, (ii) the foundation embedment and (iii) the foundation shape on radiation damping and soil-structure interaction effects for a structure on a semi-infinite soil layer over bedrock. The centrifuge model used in this study was developed and validated by the authors in an earlier publication,1 and employs an internal method of earthquake simulation, and the clay-like material, Duxseal, to absorb wave reflections at the boundary of the soil sample. The results of the experimental study are used to compute damping and stiffness values of a two-degree-of-freedom piecewise-linear numerical model of the soil-structure systems. The experimental parameter values are then compared to the values computed using classical text book formulae. The analysis demonstrates the value of the experimental data in validating and developing soil-structure interaction theory, and confirms the accuracy of classical text book formulae in the linear range.