Showing papers on "Soil structure interaction published in 1977"

Transmitting boundaries: A comparison

Abstract: The use of discrete models for the dynamic analysis of a contiuum requires the existence of a finite domain with well defined boundaries. When these boundaries do not exist naturally but have to be artificially imposed it may be necessary to apply appropriate conditions on forces or displacements at the boundary nodes to reproduce the physical behaviour of the actual problem. In the solution of soil structure interaction problems these conditions are simulated through the use of transmitting boundaries. In this paper several of these boundaries are evaluated comparing the results they produce in the amplification of seismic motions, the determination of foundation stiffnesses and the structural response. The distance of the boundaries to the zone of interest, the level of excitation (influencing the amount of internal soil damping), the geometry of the problem (finite soil layer versus a half-space) and the relative frequency of the structure with respect to the soil and the specified motion are all parameters which must be taken into account for this evaluation.

Contact stresses and ground motion generated by soil‐structure interaction

Abstract: A study has been made of the dynamic contact stresses that the foundation of a nine-storey reinforced concrete building exerts on the soil during forced vibration tests. The effects of the flexibility of the foundation on the contact stress distribution and on the force-displacement relationship for the foundation have been examined in an attempt at testing several simplifying assumptions commonly used in soil-structure interaction studies. Comparisons of calculated and observed ground displacements induced by soil-structure interaction in the immediate neighbourhood of the building have also been presented.

Seismic response due to travelling shear wave including soil‐structure interaction with base‐mat uplift

Abstract: The seismic response due to a travelling shear wave is investigated. The resulting input consists of a translational-and a torsional-acceleration time history, which depend on the ratio of the wavelength to the dimension of the footing. A nuclear reactor building is used for illustration. The combined result of the translational and torsional elastic response (the latter arises even in an axisymmetric structure) will not, in general, be larger than that encountered in the case of a spatially uniform earthquake. If the footing slips or becomes partially separated from the soil, a non-linear dynamic analysis has to be performed to determine the response. Substantial motions in all three directions will take place. The peak structural responses and the floor-response spectra are found to be highly non-linear for high acceleration input values.

Nonlinear soil-structure interaction of skew highway bridges

Abstract: Presented in this report is a study of the behavior of short, skew highway bridges interacting with their surrounding soils during strong motion earthquakes. The first part of the study defines a three-dimensional, nonlinear mathematical model for the complete bridge-soil system while the second part develops the associated computer program for carrying out time-history dynamic response analysis. The mathematical model consists of (1) linear, elastic, three-dimensional solid finite elements representing backfill soils and abutment walls, (2) linear, elastic prismatic beam elements representing the bridge deck, pier columns, and pier caps, (3) nonlinear friction elements representing the discontinuous behavior of separation, impact, and slippage at the interfaces between backfills and abutment walls, and (4) discrete translational and rotational linear springs representing foundation flexibilities at the bases of supporting columns. In developing the computer program for time-history dynamic response analysis, considerable effort was spent in achieving computational efficiency. Special programming techniques including the use of matrix reduction procedures, iteration procedures, and variable time steps were used.

Soil‐structure interaction at higher frequency factors

Abstract: Approximate solutions to the forced vibrations of a rigid circular plate attached to the surface of an elastic halfspace are presented for large values of the frequency factor. These results are important when solving soil-structure interaction problems when such problems involve high-frequency factors. This situation arises when high-frequency components of earthquakes are associated with a relatively rigid foundation of a large base and located on a soft terrain. Similar situations occur in cases of blast loadings and impact and in the foundations of large high-speed machinery. These solutions are used to solve the problem of the motion of a rigid mass on an elastic halfspace subjected to steady state and transient horizontal accelerations. From these results, it is deduced that a large rigid mat foundation located on soft terrain significantly attenuates input accelerations and consequently may be useful as the foundation of large massive rigid structures such as nuclear power station. /Author/

Seismic Soil-Structure Interaction Effects at Humboldt Bay Power Plant

Abstract: The results of a study of the distribution of ground motions and structural response in the Humboldt Bay Nuclear Power Plant during the Ferndale earthquake of June 7, 1975 are presented. Based on a knowledge of the motions recorded at the ground surface in the free-field, computations are made to determine the characteristics of the motions likely to develop at the base of the buried reactor caisson at a depth of 85 ft (26 m) below the ground surface and within the Refueling Building at the ground surface level. The computed motions are shown to be in reasonably good agreement with those recorded at these locations in the same earthquake.

Soil-structure interaction effects at the Humboldt Bay power plant in the Ferndale earthquake of June 7, 1975

Abstract: The distribution of ground motions and structural response in the Humboldt Bay Nuclear Power Station during the Ferndale earthquake of June 7, 1975 is analyzed. Based on a knowledge of the motions developed at the ground surface in the free-field, computations are made using an idealized complete interaction procedure based on finite element analysis, to determine the characteristics of the motions likely to develop at the base of the Refueling Building at a depth of 85 ft below the ground surface and within the Refueling Building at a depth of 85 ft below the ground surface and within the Refueling Building at the ground surface level. The computed motions are shown to be in reasonably good agreement with those recorded at these locations in the same earthquake. In addition, the recorded motions are compared with those computed by an analysis procedure which generally meets existing requirements of the Nuclear Regulatory Commission and it is shown that the regulatory requirements lead to an entirely adequate but not excessively conservative margin of safety based on the motions recorded in this event.

An investigation of the effectiveness of existing bridge design methodology in providing adequate structural resistance to seismic disturbances, phase iii: nonlinear soil-structure interaction of skew highway bridges

Abstract: Four different mathematical model elements are incorporated into the three dimensional computer program which possess the capability of performing linear or nonlinear-time-history dynamic response analysis. Solid finite element modelling is used for the backfill soils and the abutment walls. The bridge deck, pier columns and pier caps are modelled using prismatic beam elements. A frictional element is used to model the discontinuous behavior at the interfaces of the backfill soils and abutments. Boundary elements provide foundation flexibility at the base of columns supported on either piles or spread footings. In the nonlinear mathematical model the effects of separation, impact and slippage at the interfaces between the abutment walls and the backfill soils are taken into consideration. Computational efficiency is achieved through the use of mathematical techniques including matrix reduction procedures, interaction procedures and variable time steps. A number of analytical solutions are carried out considering a skewed three-span bridge with backfill soils. Different mathematical models are used to study the parameters which may influence the seismic response of the bridge. /Author/

Analysis and Measurement of Soil Behavior Around Buried Concrete Pipe

Abstract: A piece-wise linear finite-element model of a buried concrete pipe and the surrounding soil is used to analyze the behavior of a soil-pipe system for both a trench and an embankment installation. Soil moduli for the various soils comprising each installation were determined from uniaxial strain tests, and they are considered to be functions of the major principal stress and the initial dry density. Values of Poisson's ratio were determined from triaxial tests with lateral strain measurements. Based on an extensive set of data from uniaxial strain tests on compacted and undisturbed soils, formulations-are proposed to predict the constrained modulus from a knowledge of various soil index properties. Predicted soil stresses and deformations, interface stresses, and pipe deformations were compared to actual measured values from two field installations, and the results substantiate the adequacy of the approach.

Structure foundation interaction and soil creep

Abstract: An examination of the effect of soil creep on structure foundation soil interaction with regard to variation of differential settlement of columns, bending moments in the structure and column loads is presented. The structures considered are three bay portal frames with pin based columns, the foundations considered are strip footings of finite length, and the soil is regarded as being a linear viscoelastic continuum of infinite depth. The adopted cree function is almost linear with log time and thus has the same general form as that commonly observed in laboratory tests. The purpose of the paper is to indicate, in terms of the relative stiffnesses of the structure, foundation and soil, which situations will lead to significant deterioration in conditions for the structure with elapse of time. The effects of changes in most of the parameters of the problems are discussed. Thus the results presented should enable estimates to be made of the changes in the various interaction effects with time, when the creep properties of the soil have been determined.

Parameter estimation from non-normal modes of soil-structure interaction

Abstract: The damping in soil-structure interaction problems is known to be not proportional; thus, the mode shapes are not normal. Parameters may be estimated, however, including those associated with damping, if use is made of phase angle information. Two examples of this interaction are considered. In the first example, a one-story relatively flexible building, the interaction coefficients are estimated. Soil parameters are identified in a second example of a stiff structure modeling a nuclear reactor containment vessel. Modal information is used in both instances.

Assessment of seismic wave effects on soil-structure interaction

Abstract: It is normally assumed in the seismic analysis of structures that the free-field motion which is used as input is the same for all points on a given level beneath the foundation mat This represents a simplification, as not all particles of soil describe the same motion simultaneously As the foundation mat of the structure is rigid in the horizontal direction, it will tend to average the ground motion Abandoning the assumption of the uniformity of the input motion may lead to a reduction of the translational motion which a foundation mat will experience, as the displacement components will cancel each other to a certain extent This is of considerable interest for the design of nuclear power plants which are very stiff, large structures To investigate these effects, the extremely complex phenomenon of the passage of a seismic wave has to be simplified considerably It is the purpose of this paper to determine if wave passage effects can be determined from the simplified analyses currently used