Showing papers on "Soil structure interaction published in 1974"

Modal damping for soil-structure interaction

Abstract: Normal mode analysis for soil-structure interaction is an approximation. Its adequacy depends largely on the technique used to determine the overall modal damping values. A method is presented herein for the modal damping determination, based on the principle of transfer function matching at the natural frequencies of the interaction system. This method is physically realistic and consistent, and is shown to be adequate for engineering purposes.

Shear wave velocity and modulus of a marine clay

Abstract: A study was conducted on Boston Blue Clay to develop input for later soil amplification and soil structure interaction studies. The study consisted of (a) direct in situ measurement of the shear wave velocities by seismic cross-hole techniques, (b) obtaining samples of the soil from which to measure the properties necessary to calculate the modulus from empirical formulas, and (c) measurement of the shear modulus by torsional resonant column tests on undisturbed samples. These are all standard techniques in use in earthquake engineering, but, so far as the authors know, they have never before been applied to the Boston Blue Clay. It was the objective of the study to evaluate the accuracy of each of these methods and, if possible, to reconcile the differences in the data provided by each. Insofar as the exprapolated laboratory test results, the calculated results using Hardin's and Black's formula, and the in situ results were in close agreement, the authors concluded that the shear wave velocity of Boston Blue Clay was approximately 800 feet per second, which corresponded to a shear modulus of 17,000 psi. The three techniques for measuring shear wave velocity or shear modulus of the Boston Blue Clay agreed on an average value between 750 and 900 fps. To obtain this agreement it was necessary to recognize that present sampling procedures cause inevitable sample disturbance and that this must be taken into account in evaluating the results of laboratory tests. The most important effect was that of secondary compression, which increased the shear modulus 40 fps per log cycle of time. This was lost when samples were taken from the ground. The laboratory test data indicated that the ground shear wave velocity increased linearly with the logarithm of time and this fact could be used to extrapolate the correct value of shear wave velocity back to the age of the soil deposit. In the present case this was approximately 20,000 years. Failure to incorporate the effects of secondary compression could seriously affect the accuracy of laboratory evaluations of in situ moduli. When proper consideration was given to these effects, all three methods used gave consistent results.

Soil/structure interaction effects in geologic media

Abstract: This paper treats soil/structure interaction under earthquakes and military explosions. The main purposes of the analyses described in the present paper are to determine the motions inside the structure at the attachment points of equipment and to evaluate structural integrity. The analytic techniques which are frequently applied include closed‐form or transform techniques, lumped parameter methods, and finite‐difference and finite‐element methods. Closed‐form methods, in which an idealized foundation is assumed to rest on the surface of an elastic half‐space, are frequently applied to earthquake response of nuclear power plants and are the basis for choosing lumped stiffness and damping coefficients for lumped parameter methods. No such guidance is generally available for lumped interaction parameters for protective construction. Partly due to this gap in theoretical guidance and partly because protective structures and surrounding soil receive loads which require nonlinear soil properties to be considered, successive trials are needed for lumped parameter methods applied to protective structures. Partly to avoid this uncertainty, finite‐element methods are increasingly being applied to soil/structure interaction. The two main types of structures being investigated in this way are near surface silos and partially exposed radar and power plant structures. The present paper gives analyses using the methods and for the structures described above. In addition, the concept of a soil island is discussed, along with nonlinear soil properties, methods of accounting for slip and debonding at interfaces between soil and structure, nonreflecting boundaries, gravity loading, and models of the structure or structural elements.

Field performance of reinforced concrete pipe

Abstract: The field performance of a full-scale reinforced concrete pipe in an embankment installation is described. Normal stresses were measured by specially designed stress cells placed in the soil and at the soil-pile interface. Displacements in the soil were obtained by settlement plates, and the resulting data were used to calculate a settlement ratio that is in agreement with that anticipated for such an installation. In the pipe itself, diameter changes and strains in the concrete and reinforcing steel were monitored. Data were taken to investigate the response of the soil-pipe system to incremental increases in the height of cover and to the application of a live load under conditions of shallow cover. In general, the experimental measurements are mutually consistent, but they exhibit some differences from results predicted by plane strain finite element model that utilizes soil parameters obtained primarily from uniaxial strain tests.