Showing papers on "Soil structure interaction published in 1976"

Pore-water pressure changes during soil liquefaction

Abstract: An analytical procedure is presented for evaluating the general characteristics of pore-water pressure buildup and subsequent dissipation in sand deposits both during and following a period of earthquake shaking. It is shown that in layers of fine sand, excess hydrostatic pressures may persist for an hour or more after an earthquake. However evidence of subsurface liquefaction may not appear at the ground surface until several minutes after the shaking has stopped and the critical condition at the ground surface may not develop until 10 min-30 min after the earthquake. However, for coarse sands and gravels with an impedance of drainage due to the presence of sand seams or layers, pore pressures generated by earthquake shaking may dissipate so rapidly that no detrimental build-up of pore pressure or a condition approaching liquefaction can develop. Improving the drainage capability of a sand deposit may thus provide an effective means of stabilizing a potentially unstable deposit. Analyses of the type described also provide the means for assessing whether subsurface liquefaction will have any serious effects on structures supported near the ground surface.

Seismic wave effects on soil‐structure interaction

Abstract: One of the most common hypotheses implicit in the seismic analyses of structures is that the earthquake input motion is identical at all points beneath the structure. Very little experimental evidence presently is available to supplant this viewpoint. However, one may infer a spatially distributed surface motion of the soil if the earthquake is simply assumed to consist of a complex of surface waves traversing the plan of the structural site. Under these conditions, as shown in the paper, the effects of passing waves must be integrated over the structural area to obtain their net effects as exciting functions to the structure. When this is done for individual Fourier components of the quake, one important result is the diminution or ‘self-cancelling’ effect of some inputs, particularly for those waves the wavelengths of which are comparable to the dimensions of the structure, or shorter. Another important effect is the torsional excitation of the structure. The present paper is not necessarily aimed at replacing present analysis methods but at discussing some of the effects which will inevitably be entrained by the introduction of any information or hypotheses regarding the spatial distribution of earthquake motions. This analysis tends to suggest why higher frequencies are of lesser importance for a structure having a large rigid foundation.

Tall Buildings under Five-Component Earthquakes

Abstract: In design, earthquakes are often idealized as having a single horizontal component which can act in two orthogonal directions. The present note examines the influence of other components. Free-field motion is taken as having two horizontal translational and three rotational components and is averaged over the building.s base. Soil-structure interaction is otherwise ignored. Vertical translation is not dealt with because the present building idealization does not lend itself. In the absence of adequate records, ground motion is assumed to coincide with theoretical solutions for regular homogeneous formations. The building is idealized as linear, uniform, and admitting shearing and torsional deformations.

Effect of Backfill Compaction of Design Criteria for Hardened Facilities: Results of Soil-Structure Interaction Calculations for Dry Types 1 and 2 Backfill Materials

Abstract: : The results of a series of two-dimensional plane-strain, dynamic finite element, structure-medium interaction code calculations are presented. These calculations parametrically investigated the effect of variations in constitutive properties of the backfill region around a hypothetical, shallow- buried protective structure. Two parameter studies were conducted on this plane-strain idealization of a simple buried structure while under a long duration local surface air-blast loading: The first investigated differences in the dynamic response of the structure under this loading due to changing the surrounding backfill from a dense (or well-compacted) glacial till to the same material in a loose (or poorly compacted) condition; The second is identical with the first except that dense and loose clay shale materials were simulated. The calculations indicated that, for the particular idealized problem investigated, the use of loose rather than dense backfill results in (1) increased deflections across backfill sections; (2) increased loads on, deflections of, and thrusts, shears, and bending moments within the structure, and (3) increased amplitudes of the shock spectra for points on the inside surface of the structure.

Seismic ssi of nuclear power plant structures

Abstract: Nuclear power plant structures are massive structures typically embedded at a considerable depth in a soil deposit. An important aspect in the seismic design of these structures is the evaluation of the dynamic interaction between the structure and the soil. This paper presents the results of a study conducted to evaluate seismic SSI effects for a partially embedded massive nuclear plant structure using the finite element method of analysis. The analyses were carried out using the finite element program LUSH which incorporates the use of variable modulus and variable damping in the soil. The high frequency ranges, which must be considered in the study of SSI for nuclear power plants, are also adequately accounted for in the computer program used. Several significant parameters that could affect seismic SSI are examined. Consideration was given to parameters affecting: (1)Accuracy; (2)core storage requirements; and (3)execution time.