Showing papers on "Soil structure interaction published in 1984"

Evaluation of p-y relationships in cohesionless soils

Abstract: The practice of analyzing laterally loaded driven and bored piles often requires modeling of soil response in terms of uncoupled, non-linear unit load transfer functions. These functions, called p-y curves, are input into computer codes that use finite difference or finite element representations of beam behavior. This paper considers three semi-empirical procedures for constructing p-y curves: the soft clay method, the stiff clay method and a new method that intergrates relative pile-soil stiffness and soil degradability effects.

On the effective seismic input for non-linear soil-structure interaction systems

Abstract: Two equivalent semi-discrete formulations are presented for the problem of the transient response of soil-structure interaction systems to seismic excitation, considering linear behaviour of the soil material and arbitrary non-linear structural properties. One formulation results in a direct method of analysis in which the motion in the structure and the entire soil medium, rendered finite by an artificial absorbing boundary, is determined simultaneously. The other represents a substructuring technique in which the structure and the soil are analysed separately. The forces induced in the discretized system by the incident seismic motion are obtained as part of the general formulation by using the free-field motion of the unaltered soil as the earthquake input. It is shown that these forces act within the soil region in the direct method, but only on the soil-structure interface in the substructure formulation. Both sets of forces, however, involve only the displacements and tractions acting on the fictitious surface in the unaltered (linear) soil which coincides with the soil-structure interface of the complete system. It is shown, further, that the free-field displacements alone define a minimal set of data for evaluating the seismic response of the structure, since the tractions and displacements on that surface are interrelated. In practice, the minimal set must be obtained by extrapolating the available information, as the free-field ground motion at a site is usually specified at a single reference point.

The behaviour of a propped retaining wall: results of a numerical experiment

Abstract: The design of propped retaining walls is currently based on approximate limit equilibrium calculations. A factor of safety is used to ensure adequate stability and to restrict soil and wall movements to acceptable levels. No distinction is made for the type of construction, whether excavated or backfilled, or of the stress state in the soil prior to construction. In this Paper the finite element method is employed to investigate the influence of type of construction and of initial stress in the soil on the behaviour of single propped retaining walls. An elasto-plastic constitutive law is used to model the soil behaviour and a rigid prop is assumed to act at the top of the wall. The results of the investigation indicate that for excavated walls in soils with a high initial K0 value prop forces and wall bending moments greatly exceed those predicted by current design methods. In addition large soil and wall movements are experienced even at shallow depths of excavation. The behaviour is dominated by the ver...

Interface Model for Dynamic Soil‐Structure Interaction

Abstract: A simple thinlayer element is developed and used in a finite element procedure for simulation of various modes of deformanon in dynamic soilstructure interaction. The constitutive behavior of the i...

Hybrid FE Procedure for Soil‐Structure Interaction

Abstract: A stress hybrid finite element procedure is developed for nonlinear, elastic and elastic‐plastic, analysis of soil‐structure interaction including simulation of construction sequences. The procedure is compared with a number of closed‐form solutions and field problems, and provides satisfactory and improved evaluation of stresses and deformations as compared to the displacement procedure.

Experimental study of soil-structure interaction at an accelerograph station

Abstract: Forced harmonic vibration tests, using eccentric mass shakers, were conducted at the Jenkinsville, South Carolina, accelerograph station to determine the effect of soil-structure interaction on the motions recorded during four small magnitude earthquakes. The station consisted of a 4′ × 4′ × 2′ concrete pad that was embedded in a stiff clayey to medium sandy silt with a shear-wave velocity estimated at 500 fps. A five-foot-high wooden hut was attached to the pad and provided shelter to the SMA-1 accelerograph, which was bolted directly to the pad. The real parts of complex foundation impedance functions, which were obtained by solving the equations of motion for the vibration tests, were generally similar to the theoretical impedance functions for an embedded rectangular foundation. However, the imaginary parts, which are a measure of the foundation damping, were closer to the theoretical prediction for a surface foundation. The tests also showed that the soil-pad-hut system had two strongly coupled translational and rocking modes of vibration in the frequency range of 1 to 60 Hz. The first mode occurred at approximately 11 Hz (N40°W direction) and 17 Hz (N50°E direction) and involved mostly the response of the hut, while the second mode occurred at approximately 50 Hz in both directions and involved mostly the response of the concrete pad. Approximate transfer functions between the motions recorded at the station during the earthquakes and the free-field motions were computed from the experimental data. These functions showed significant amplification in the frequency band 20 to 50 Hz with a maximum amplification of 3 occurring at 50 Hz. Some measurable amplification also was observed at the fundamental natural frequencies in both directions. Calculations based on the transfer functions indicated that the average response spectra of the recorded earthquake motions were amplified by an average of about 30 per cent for frequencies greater than 15 Hz. These results suggest that careful attention must be given to the design of accelerograph stations if they are to record true ground motions over a wide frequency range.

Soil‐structure interaction effects on the steady‐state response of torsionally coupled buildings

Abstract: The work presented in this paper investigates the effect of the foundation flexibility on the coupled lateral-torsional response of single-storey buildings excited by translational ground motion. The eccentricity between the centre of mass and the centre of resistance is considered to be the only cause of coupling of the lateral and torsional response of the building. The study is confined to the steady-state response of rigidly supported and flexibly supported torsionally coupled buildings subjected to harmonic free-field ground displacement perpendicular to the direction of the eccentricity. In the case of the flexibly supported building the foundation medium is assumed to be an elastic homogeneous isotropic half-space. The effect of the controlling parameters on lateral-torsional coupling is investigated. It is concluded that for a particular range of values of these parameters (representing most cases of actual buildings) their effect on the coupling of lateral and torsional response is not qualitatively affected by increases in the flexibility of the foundation medium.

Coefficients of Soil Reaction for Buried Flexible Conduits

Abstract: A study is conducted to examine the parameters governing the coefficient of soil reaction k\dn normal to the surface of conduits as well as the coefficient k\ds tangential to the wall surface, and simple formulas are developed for their evaluation. Both circular and elliptical conduits are taken into consideration, as well as two types of soil, namely very dense and medium-dense fillings. The coefficients of soil reaction are obtained by relating the results of internal force components and conduit deformations calculated with rigorous finite element analysis to equivalent results obtained from the system modeling of the problem. The results show that the coefficients of soil reaction vary considerably around the conduit. They are dependent on the span of conduit, the depth of soil and the direction of action.

Finite element and Ritz vector techniques for the solution to three‐dimensional soil — structure interaction problems in the time domain

Abstract: A general time domain finite element formulation and several efficient numerical techniques are combined to form a new method of analysis for the solution of three‐dimensional soil‐structure interaction problems in the time domain. For elastic systems the method is a very cost effective alternative to the frequency domain approach. However, the major advantage of the new method is its ability to be extended to non‐linear behaviour such as separation of foundation and soil or non‐linear material. The general equations of motion for the linear cases are expressed in terms of the relative displacements of the soil‐structure system with respect to the displacements of the buried part of the structure (volume methods). This formulation allows the load vector to be an exclusive function of the free field accelerations at the foundation level. The non‐linear case requires that the equation of motion be established in terms of the total interaction displacements. The soil is modelled with three‐dimensional solid elements in the near field and axisymmetric elements in the far field. Coupling between the two systems is enforced by expanding the displacements of the solid elements in terms of the axisymmetric ones. Reduction in the number of degrees of freedom is achieved by the use of orthogonal sets of Ritz functions. The reduced system of equations is uncoupled and solved very efficiently using the complex eigenvectors. A numerical example consisting of the response of a structure resting on a homogeneous half‐space is solved using the new method and one of the approaches in the frequency domain. Results given by both methods are remarkably similar.

Seismic Response of Offshore Drilling Islands in a Centrifuge Including Soil-Structure Interaction

Abstract: Seismic tests on a centrifuged model of an offshore drilling island are described. The island consisted of an underwater berm supporting a rigid steel structure. The island was instrumented to record accelerations and porewater pressures at various locations in the berm and the accelerations and displacements of the rigid structure. Computer plots of the data were obtained during the test program, while the centrifuge was in flight, and a representative sample is presented for discussion. The tests were analysed using the computer program, TARA-2, which is based on a non-linear dynamic effective stress method for analysing response of soil-structure systems to earthquake loading. Comparisons between recorded and computed seismic response data are good and suggest that TARA-2 may prove a useful tool in evaluating the seismic response of drilling islands.

Three-dimensional nonlinear soil-structure interaction analysis of pile groups and anchors.

Abstract: Analysis and design of structures supported by geological media pose various complexities such as nonlinear behavior of supporting media, nature of loading, irregularities in geometry and boundary condition, and the interaction effects. It is extremely difficult to find closed-form solutions for such problems. So often, numerical techniques such as finite difference, finite element and boundary integral methods are used. In this research two soil-structure interaction problems are analyzed using the finite element method involving fully three-dimensional idealizations. In order to incorporate nonlinear behavior of a soil, a nonlinear elastic (hyperbolic model), and generalized single surface plasticity model including hardening are implemented in the finite element program for analysis of a pile group foundation, and an anchor in sands, respectively. The parameters required to define these models are determined from comprehensive laboratory stress-strain data obtained by using a multiaxial testing device. Typical stress paths are back predicted using the generalized plasticity model to verify that it is capable of predicting those paths, and is found to be satisfactory. In order to include the interaction effects resulting in relative slip and debonding or crack and openings at the junction between two dissimilar materials, the thin-layer element model is implemented. Load deformation behavior, force and stress distributions in various components of pile group foundation, and the anchor-soil system are predicted by using the numerical procedure. The predictions are compared with results from a model test for the pile group and field observations for the anchor problem; the comparisons are found to be satisfactory. The effects of soil nonlinearity and interface behavior are also delineated and it is found that their inclusion, particularly in case of anchors analysis, can substantially effect the behavior of the system. Detailed analysis of the results permits an increased understanding of the stress deformation mechanisms of the three-dimensional problems.

Winkler Soil Model for Axial Response Analysis of Pile Groups

Abstract: In this approach, the soil is idealized as a nonlinear Winkler model for a pile group attached to a group of piles. The model can account for pile-soil-pile interaction. Pile group responses are compared with those obtained idealizing the soil as an elastic continuous medium. The reponses are also compared with a full-scale field load test.

Along‐Wind Motion of Building on Compliant Soil

Abstract: Theoretical investigation is presented for the along‐wind motion of a multistory building under random wind load excitation, taking into account the effect of soil compliancy under the footing. Assuming that the super‐structure is composed of identically constructed story‐units and the soil behavior is characterized by a known frequency dependent impedance matrix, closed form solutions are obtained for the frequency response functions and the spectral densities of structural response. Numerical examples show that soil compliancy decreases the structural response of a moderately tall 10‐story building by about 17%, but increases the response of a more flexible 40‐story building by 21–22%. Some of the frequency response functions are found to be dominated not by the first mode; thus, spectral peaks can theoretically occur near some higher mode frequencies if sufficient wind energy is available around these frequencies. The Davenport spectrum used in the numerical examples, however, has a dominant peak at a ...

User's Guide: Computer Program for Soil-Structure Interaction Analysis of Axially Loaded Piles (CAXPILE).

Abstract: : This report documents a computer program--CAXPILE--for the analysis of axially loaded piles in which the load applied to the top of the piles is resisted by a combination of skin friction and tip bearing. The report: (a) Describes the pile-soil system and the assumptions used in the analysis, (b) Presents the procedures used to generate nonlinear force-displacement curves from soils data, (c) Outlines the method of solution, and (d) Presents example solutions obtained with the program. (Author)

Uncertainty in soil-structure interaction analysis of a nuclear power plant due to different analytical techniques

Abstract: This paper summarizes the results of the dynamic response analysis of the Zion reactor containment building using three different soil-structure interaction (SSI) analytical procedures which are: the substructure method, CLASSI; the equivalent linear finite element approach, ALUSH; and the nonlinear finite element procedure, DYNA3D Uncertainties in analyzing a soil-structure system due to SSI analysis procedures were investigated Responses at selected locations in the structure were compared through peak accelerations and response spectra

Dynamic response analysis of shizunai bridge damaged by the urakawa-oki earthquake of march 21, 1982

Abstract: On the morning of March 21, 1982, a severe earthquake of a magnitude of 7.1 on the Richter scale hit Urakawa-oki or off Urakawa, southern part of Hokkaido Island in Japan. It is reported by the Japan Meteorological Agency (JMA) that the hypocentral depth was 40km and the highest JMA seismic intensity was 6 at Urakawa town. Shizunai Bridge, located near the epicenter, sustained serious damages to 6 pier columns out of 8. Very heavy cracks occurred at 2 pier columns (Piers-3 and 6), and medium to minor cracks were observed at 4 pier columns (Piers-2, 4, 5, and 7). This paper briefly describes an outline of the Urakawa-oki Earthquake, damage features of Shizunai Bridge, and results of a dynamic response analysis of Shizunai Bridge, which was conducted for investigating the causes of damages to the bridge. Two different analytical models are employed for the dynamic analysis. The first is a model of the overall system involving the entire parts of the bridge, although the second is a model of Pier-3 which was most seriously injured. In the both cases, structural responses to seismic motions in the direction transverse to the bridge axis, are computed. In an analysis for the overall model, two abutments, 8 piers, and 9-span girders are considered as a lumped mass-spring system. Surrounding soils above the bedrock are also included in the system, and non-linear characteristics of soils are considered. All of structural parts made of steel and reinforced concrete are assumed as elastic members. From the analysis for the overall model, it is concluded that responses (ratios of acting forces to design forces) of Piers-3 and 6 (supporting two ends of continuous girders) which sustained heavy damages are extensive comparing with those of the other piers, and that horizontal forces analyzed for Piers-3 and 6 are higher than 2 times their design horizontal forces, respectively. Next, in the analysis of Pier-3 model, non-linear characteristics of the reinforced concrete pier column are considered. From the analysis, it is concluded that plastic state will extensively develop at a section of 4.0m above the bottom of the column, which well explains the actual behavior of Pier-3 during the earthquake. (Author)