A new cross-anisotropic elasto-plastic constitutive model is developed based on experimental observations of marine clay from the Gulf of Mexico. Standard triaxial and torsional simple shear tests performed on the aforementioned clay demonstrate that the soil exhibits a cross-anisotropic behavior with lower compressibility in the direction of the deposition than perpendicular to the direction of deposition. A new general cross-anisotropic model for the stress-dependent elastic moduli is presented. In agreement with experimental evidence, the model considers that the Young's modulus and the shear modulus of soil depend on the state of stress, while the three Poisson's ratios are practically constant. The expressions for the stress dependence of the moduli are derived by considering the conservation of energy. Numerical simulations of the undrained elastic reloading demonstrate that the development of pore water pressure depends significantly on the exact representation of the cross-anisotropic elastic parameters. The plastic model is developed based on the assumptions that the material behavior is time independent and that the interaction between mechanical and thermal processes is negligible. The model, having twelve parameters, consists of a failure function, plastic potential function (non-associated flow rule), yield function and hardening law. To describe the degree of cross-anisotropy at failure, a new four-parameter failure criterion is developed. The plastic potential function, having two parameters, determines the directions of the plastic strain increments which are assumed independent of the stress path leading to the current state of stress. The potential surface expands along its center line and may translate in the stress space. The yield criteria are associated with and derived from surfaces of constant plastic work. The yield-plastic work relation requires six parameters in which four parameters define the yield function and two parameters define the plastic work equation. For the special case of isotropic soil, all of the functions may be reduced to those of Lade's isotropic elasto-plastic model. Most of the elastic and plastic parameters can be easily determined by experimental results from standard triaxial tests, but a few parameters need advanced tests such as the torsional simple shear test on hollow cylinder specimens and the cubic triaxial test. Comparisons between results from computer simulation of tests and actual experimental data showed that the model is satisfactory in predicting the behavior of the tested clay under torsional simple shear and conventional triaxial compression and extension tests.

The objectives of the studies reported in this dissertation are: (1) to evaluate the dynamic impedance of horizontally inhomogeneous, thin soil layers and of piles embedded in such layers; and (2) to provide improved insight into the response of vertically excited piles bearing on a stratum of arbitrary stiffness. The dissertation consists of two major parts. The first part, reported in Chapters 2 through 5, deals with the analysis of the impedances of inhomogeneous soil layers. Vertical, torsional, and horizontal modes of vibration are investigated. Primary emphasis is placed on assessing the effect of the radial variation of the soil shear modulus. The numerical solutions for layer impedances are obtained for several different radial variations of the shear modulus, and are compared with each other and that applicable to a homogeneous soil. The importance of the inertial effects of the soil zone near the pile and the consequences of discontinuous radial variations of soil modulus are clarified. The layer impedances are then used to evaluate the manner and extent to which the dynamic stiffness and damping capacity of piles may be influenced by the weakening of the soil near the pile-soil interface. The second part of this dissertation, comprised of Chapters 6 and 7, deals with the dynamic impedance of a vertically excited pile which is driven through a uniform layer and bears on a stratum of finite depth and arbitrary stiffness. The solution takes due account of the variation of the soil reactions with depth by expressing them in terms of the characteristic functions of the two-layer medium. Comprehensive parametric studies are made to assess the effects of the various parameters involved and to evaluate the applicability of the solution based on the idealization of the soil medium as a series of thin horizontal layers. Comparisons are also made with previously reported solutions for statically and dynamically loaded piles. The results provide improved insight into the mechanism of soil-pile interaction.

Three interior and three exterior fiber reinforced slab-column connections were subjected to gravity loads and then tested under lateral load simulating earthquake forces. Test results were compared to previous tests on non-fiber slab-column connections. Addition of steel fiber to the concrete matrix greatly increased the ductility and the energy dissipation capacity of all specimens. Fiber reinforcement also enhanced the shear capacity of interior connections. The failure mode switched from punching shear in interior connections with small amount or no fiber reinforcement to flexure failure in interior connections with higher fiber reinforcement ratios. Fiber reinforcement apparently did not improve the shear strength of exterior connections. The optimum amount of steel fiber found through the tests was between 50 and 100 pounds of fiber per cubic yard of concrete.

A parametric study of the response of a class of linear secondary systems to earthquake excitations is made. The combined dynamical system studied consists of a single-degree-of-freedom oscillator attached to a continuous cantilever beam. The generalized differential equation governing free vibration is solved exactly for the modes of the combined system. Floor response spectra for records from the 1985 Mexico City and the 1940 El Centro earthquakes are presented in several formats. The floor response spectrum concept is an extension of widely used ground response spectrum concept and may provide useful insight into the behavior of linear secondary systems. The effects of each of the system parameters are examined. It is shown that the frequency characteristics of the excitation modify the relative importance of the system parameters. The study also demonstrates the effectiveness and limitations of the cascade approximation which is often applied as an approximate solution to the problem.

The studies reported herein are motivated by the need to gain improved understanding of the response to earthquakes of deeply embedded and underground cylindrical tanks storing nuclear wastes, and develop rational but simple methods of analysis and design for such systems. The first part of the study, reported in Chapters 2 and 3, is concerned with the dynamic modeling and response of soil-wall systems. Simple approximate expressions for the dynamic pressures and associated forces induced by ground shaking on a rigid, straight, vertical wall retaining a semi-infinite, uniform viscoelastic layer are developed, and comprehensive numerical data are presented which elucidate the effects of the numerous parameters involved. These solutions are then compared with those obtained by use of a popular approximate model, and the accuracy of the model is assessed. It is shown that the model may lead to substantial inaccuracies. The sources of the errors are identified, and a modification is presented that defines correctly the action of the system. The modified model is then used to evaluate the response of more involved soil-wall systems. The second part, comprised of Chapters 4 and 5, deals with the response to horizontal shaking of an upright, circular, rigid vault that is embedded in a uniform viscoelastic stratum of constant thickness and infinite extent in the horizontal plane. Both the vault and the stratum are presumed to be supported on a non-deformable base. Simple approximate expressions for the dynamic pressures and associated forces induced in the vault are developed, and comprehensive numerical solutions are presented. Furthermore, the accuracy of a popular model in which the medium is represented by a series of independent thin layers is investigated. The errors arising from such an idealization are identified, and a modification is proposed that describes correctly the behavior of the stratum. The last part, reported in Chapter 6, deals with the response to a lateral base shaking of a rigid cylinder containing a viscoelastic solid. Simple approximate expressions for the resulting dynamic wall pressures and tank forces are developed, and comprehensive numerical solutions are presented which elucidate the effects of the numerous parameters involved.

The punching shear strength of the slab usually governs the design of slab-column connections in regions of high seismicity. One method of increasing the shear capacity of the connection region is to increase the thickness of the slab using shear capitals. A shear capital is a thickened portion of the slab in the vicinity of the column used solely for improving the shear strength of the connection region. Three interior and three edge slab-column connections with different size shear capitals were tested under simulated earthquake type loading and compared to connections without shear capitals. Based upon the test results, the presence of a shear capital improves the strength and stiffness of a slab-column connection. A shear capital should be reinforced and have a sufficient length with respect to the depth of the slab when load reversals are expected.

A comprehensive study of the response of liquid storage tanks subjected to ground induced lateral excitations is presented. Wall flexibility affects the response coefficients of tall tanks significantly. In general, response coefficients for tanks are relatively insensitive to super-structure parameters. A simplified procedure for evaluating inertial interaction effects is considered. While foundation translation dominates the response of broad tanks, foundation rocking is important for tall tanks. Exact values and approximate expressions reveal that the effects of interaction are a function of the relative flexibilities of the medium and super-structure. Effects of ground motion incoherence are evaluated by formal stochastic and approximate semi-deterministic approaches. Kinematic interaction reduces the response of tanks. The reductions are generally small, particularly for tall tanks. Inertial interaction effects are generally substantially larger than corresponding kinematic interaction effects. Inertial interaction normally reduces the response of broad tanks, but can increase the response of tall tanks.

Two analytical closed-form solutions are developed for steady-state lateral response of earth and rockfill dams built in semi-elliptical canyons. In the first model, the canyon is assumed to be rigid, while the dam is idealized as a two-dimensional linearly-hysteretic elastic body deforming only in shear (shear beam). Both free and base-induced oscillations are studied for various canyon geometries. In the second model, the canyon is assumed to consist of flexible elastic rock, subjected to asynchronous excitation consisting of obliquely incident harmonic SH waves. The solution accounts in a rigorous way for the complex wave reflection, transmission and diffraction phenomena associated with the dam-filled canyon. The study focuses on the effects of: (a) the angle of incidence, (b) the impedance ratio and (c) the canyon narrowness. It is shown that the effects of radiation damping and ground motion spatial variability are very important.

Two new methods for the solution of problems involving material variability are proposed. Medium properties are modeled as second order stochastic processes defined by their mean and convariance functions. Both methods make use of the Karhunen-Loeve expansion which is a mean-square convergent orthogonal expansion of a continuous process in terms of a countable set of uncorrelated random variables. The first of the proposed methods relies on implementing the Karhunen-Loeve expansion for the medium property in conjunction with a Neumann expansion of the inverse operator. This results in an explicit expression for the response process as a multivariate polynomial functional of a set of uncorrelated random variables. The second method treats the solution process as an element in the Hilbert space of random functions, in which a sequence of projection operators is identified as the Polynomial Chaoses of consecutive order. The solution process is then determined by its projection onto the spaces spanned by these polynomials. These concepts can be construed as extensions of the deterministic finite element methods to the space of random functions. Both of the proposed methods are exemplified by three problems from the field of engineering mechanics. The corresponding results are found in agreement with those obtained by a Monte-Carlo simulation solution of the problems. In addition to the two methods mentioned above, a new formulation is presented for a class of problems involving deterministic media subjected to random external excitations. The formulation involves a combination of the boundary element method with the Karhunen-Loeve expansion for the exciting process. Namely, the boundary element method is used as a discretization tool to restate the problem as a set of discrete equations. Further, the Karhunen-Loeve expansion is utilized to represent the random processes in a manner conducing their optimal discretization.

This dissertation deals with two distinct topics: (1) The effects of soil-structure interaction, both kinematic and inertial, on the dynamic response of a variety of base-excited foundations and of simple structures supported on such foundations; and (2) the effects of fluid-structure interaction for relatively simple structural systems subjected to forces induced by waves and currents. A fundamental step in the analysis of a base-excited structure-foundation system is the evaluation of the transfer functions of its foundation motion. Defined for harmonically excited massless foundations, these functions relate the amplitudes of the components of foundation motion to those of the free-field ground motion at some reference or control point. These functions are evaluated for surface-supported circular and rectangular rigid foundations and for embedded square foundations considering a spatially varying, horizontal free-field ground motion. Consideration is also given to more complex ground motions defined stochastically by a local power spectral density function and a spatial incoherence function. An approximate analyses based on the Iguchi-Scanlan averaging technique is employed. The structures examined are considered to have one lateral and one torsional degree of freedom in their fixed-base condition. The response quantities examined include the ensemble means of the peak values of the lateral and torsional components of the foundation input motion and of the associated structural de formations. These responses are evaluated over wide ranges of the parameters involved and are compared with those obtained for no soil structure interaction and for kinematic interaction only. Simple, physically motivated interpretations are given for the observed differences. The studies of fluid-structure interaction include comprehensive analyses of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses are also evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this procedure. A simple approximation is included for the hydrodynamic modal damping values of multi-degree-of-freedom, stick-like systems.