Final Report

AASHO Road TestHighway Research BoardNational Academy of Sciences - National Research Counci

Effects of Soil-Structure Interaction for Structures Subjected to Earthquakes

An extended summary is presented of a state-of-the-art report on the subject matter. The report parallels one presented at the Fourth U. S. National Conference on Earthquake Engineering, in May 1990

Dynamic Soil Pressures on Vertical Walls

A summary is presented of recently contributed simple approximate solutions for the dynamic pressures and the associated forces induced by ground shaking on rigid vertical walls. The walls are presumed to be either straight or circular in plan and to retain a uniform viscoelastic soil stratum of constant thickness and infinite extent in the horizontal direction. Both the walls and the stratum are considered to be supported on a non-deformable base undergoing a space-invariant, uniform horizontal motion. The effects of both harmonic and earthquake-induced excitations are examined, and comprehensive numerical data ate presented which elucidate the underlying response mechanisms and the effects and relative importance of the various parameters involved. A brief review is then included of available simple, approximate schemes for modeling the systems examined. Finally, the sources and magnitudes of the errors that may result from the use of these models are identified, and modifications are proposed with which the responses of the systems may be defined correctly. In the proposed modifications, the soil stratum is modeled by a series of elastically supported semi-infinite layers with distributed mass. The concepts involved are introduced for the straight wall and are then applied to the embedded cylindrical system

Dynamic stresses in an elastic half-space

This paper deals with the problem of time-varying point loads applied onto the surface of an elastic half-space and the stresses that such loads elicit within that medium. The emphasis is on the evaluation of the isobaric contours for all six of the stress components at various frequencies of engineering interest and for a full range of Poisson’s ratios. The extensive set of pressure bulbs presented herein may be of help in predicting the severity of dynamic effects in common practical situations in engineering—or even the lack thereof

Soil-structure interaction effects for laterally excited liquid-tank system

Following a brief review of the mechanical model for liquid-storage tanks which permits consideration of the effects of tank and ground flexibility, and lateral and rocking base excitations, the effects of both kinematic and inertia interaction effects on the response of the tank-liquid system are examined and elucidated. The free-field motion is defined by a power spectral density function and an incoherence function, which characterizes the spatial variability of the ground motion due to the vertically incident incoherence waves. The quantities examined are the ensemble means of the peak values of the response. The results are compared with those obtained for no soil-structure interaction and for kinematic interaction to elucidate the nature and relative importance of the two interactions. Only the impulsive actions are examined, the convective actions are for all practical purposes unaffected by both kinematic and inertia interactions. It is shown that the major reduction of the response is attributed to inertia interaction. 20 refs

Dynamic soil pressures on rigid vertical walls

A critical evaluation is made of the dynamic pressures and the associated forces induced by ground shaking on a rigid, straight, vertical wall retaining a semi-infinite, uniform viscoelastic layer of constant thickness. The effects of both harmonic and earthquake-induced excitations are examined. Simple approximate expressions for the responses of the system are developed, and comprehensive numerical data are presented which elucidate the effects and relative importance of the various parameters involved. These solutions are then compared with those obtained by use of a simple model proposed previously by Scott, and the accuracy of this model is assessed. Finally, two versions of an alternative model are proposed which better approximate the action of the system. In the first, the properties of the model are defined by frequency-dependent parameters, whereas in the second, which is particularly helpful in analyses of transient response, they are represented by frequency-independent, constant parameters

Influence of Higher Modes on Strength and Ductility Demands of Soil-Structure Systems

Due to the inherent complexity, the common approach in analysing nonlinear response of structures with soil-structure interaction (SSI) in current seismic provisions is based on equivalent SDOF systems (E-SDOF). This paper aims to study the influence of higher modes on the seismic response of SSI systems by performing intensive parametric analyses on more than 6400 linear and non-linear MDOF and E-SDOF systems subjected to 21 earthquake records. An established soil-shallow foundation-structure model with equivalent linear soil behaviour and nonlinear superstructure has been utilized using the concept of cone models. The lateral strength and ductility demands of MDOF soil-structure systems with different number of stories, structure-to-soil stiffness ratio, aspect ratio and level of inelasticity are compared to those of ESDOF systems. The results indicate that using the common E-SDOF soil-structure systems for estimating the strength and ductility demands of medium and slender MDOF structures can lead to very un-conservative results when SSI effect is significant. This implies the significance of higher mode effects for soil-structure systems in comparison with fixed-based structures, which is more pronounced for the cases of elastic and low level of inelasticity

Dynamics of solid-containing tanks

Making use of a relatively simple, approximate but reliable method of analysis, a study is made of the responses to horizontal base shaking of vertical, circular cylindrical tanks that are filled with a uniform viscoelastic material. The method of analysis is described, and comprehensive numerical data are presented that elucidate the underlying response mechanisms and the effects and relative importance of the various parameters involved. In addition to the characteristics of the ground motion and a dimensionless measure of the tank wall flexibility relative to the contained medium, the parameters examined include the ratio of tank-height to tank-radius and the physical properties of the contained material. Both harmonic and earthquake-induced ground motions are considered. The response quantities investigated are the dynamic wall pressures, the critical forces in the tank wall, and the forces exerted on the foundation. Part A of the report deals with rigid tanks while the effects of tank wall flexibility are examined in Part B. A brief account is also given in the latter part of the interrelationship of the critical responses of solid-containing tanks and those induced in tanks storing a liquid of the same mass density

Dynamic response of flexible retaining walls

Making use of an extension of a recently proposed, relatively simple, approximate method of analysis, a critical evaluation is made of the response to horizontal ground shaking of flexible walls retaining a uniform, linear, viscoelastic stratum of constant thickness and semiinfinite extent in the horizontal direction. Both cantilever and top-supported walls are examined. Following a detailed description of the method and of its rate of convergence, comprehensive numerical solutions are presented that elucidate the action of the system and the effects of the various parameters involved. The parameters varied include the flexibility of the wall, the condition of top support, and the characteristics of the ground motion. The effects of both harmonic base motions and an actual earthquake record are examined. Special attention is paid to the effects of long-period, effectively static excitations. A maximum dynamic response is then expressed as the product of the corresponding static response and an appropriate amplification or deamplification factor. The response quantities examined include the displacements of the wall relative to the moving base, the dynamic wall pressures, and the total wall force, base shear and base moment