This dissertation is composed of two parts. In the first part, a comprehensive study is made of the harmonic response of a rigid mass or a mass-sprint system supported on a pile driven in a homogeneous elastic medium. The objectives are to assess the effects of the various factors that affect the response of the system. The second part deals with the harmonic response of rigid and elastically supported simple systems on pile groups. The main aim is to incorporate pile-to-pile interaction and investigate its effect on response of such systems. The system is shown to respond essentially as a viscously damped single-degree-freedom oscillator. Plots are presented for the amplification factor and the resonant frequency of the system. With the information presented herein significant aspects of the dynamic response of vertically and laterally excited simple structure-pile systems may be evaluated readily.

The existing equivalent frame methods for lateral displacement analysis of flat-plate structures are one-value stiffness models which do not reflect the realistic response of structures. Based on the experimental data, the procedure for predicting the drift response of flat-plate structures is reviewed and an approach is proposed which accounts for the changes in the stiffness during the loading history. The application of the suggested procedure is demonstrated through examples. Punching failure in a flat-plate structure greatly changes the overall stiffness and results in moment redistribution between various members of the structure. This effect needs to be considered in the nonlinear analysis of flat-plate structures subjected to earthquake loading. A numerical procedure to account for the localized punching failure in calculating the response of flat-plate structures is developed. Furthermore, a hysteresis model suitable for slab-column connections is proposed on the basis of test results and implemented in a nonlinear dynamic analysis program.

This thesis deals with the effects of soil-structure interaction, both kinematic and inertial, on the responses of seismically excited rectangular foundations and simple structures supported on such foundations. The ground motion considered is defined stochastically by a local power spectral density function and a spatial incoherence function. The structures examined are considered to have one lateral and one torsional degree of freedom in their fixed-base condition. The response quantities investigated include the ensemble means of the peak values of the lateral and torsional components of the foundation input motion and of the associated structural deformations. These responses are evaluated and compared with those obtained for no soil-structure interaction and for kinematic interaction only. The information and concepts presented elucidate the nature and relative importance of the two effects and make it possible to assess readily the influences of the more important parameters involved.

The in-plane cyclic response of reinforced concrete frames with unreinforced masonry infill was studied. Four full-scale reinforced concrete frame assemblies with masonry infills were designed and tested under reversed cyclic loading. The effect of panel aspect ratio and the stiffness of the infill relative to the frame were studied in terms of stiffness, strength, energy dissipation and failure mode. Based on the test results, an equivalent diagonal compression strut model was developed to represent the behavior of masonry infill bounded by a reinforced concrete frame and a simplified method for the linear-elastic analysis of R/C frames with masonry infills proposed. Using the experimental load-deformation plots, the hysteretic parameters relating to stiffness degradation, strength deterioration and pinching of the hysteretic loops were identified. These may be used to define the behavior of confined infills for the non-linear analysis of the infilled frames.

The aseismic design of large structures may need to account for the nonstationary and the multivariate aspects of strong ground motions. These aspects influence both the time and the spatial variation of the dynamic response of the structure. Current techniques for treating this problem have considerable limitations. An approach is developed in the thesis for addressing this issue based on energy considerations. Estimates of evolutionary seismic auto- and cross-spectra are obtained. It is assumed that the available accelerograms are realizations of broad-band stochastic processes. By analyzing the output of lightly damped linear systems excited by these processes, estimates are obtained for the associated auto and cross spectral density functions. The proposed estimation techniques have two main advantages. Firstly, the evolutionary auto- and cross-spectra can be estimated without having to assume a specific form for the evolutionary spectrum. Secondly, with the evolutionary auto- and cross-spectra determined, the moments of structural responses to these stochastic seismic models, which are functions of time, can be approximated from the spectra without having to resort to simulation. The proposed method is further extended to provide for situations where not enough data are available to accurately assess the stochastic character of the ground motion. Based on a stochastic interpretation of ground accelerations, a weighted least squares method is used to estimate the coefficients of a commensurate model from the responses of a lightly damped linear system excited by these accelerograms.

Nine steel specimens, each containing a small hole have been tested under three sets of variable amplitude loadings to determine the effect of amplitude variability on fatigue life. Twenty-three constant amplitude tests have also been run at basically four different combinations of mean stress and stress range to determine the S-N curve and to check the variable amplitude test results against a commonly used analytical technique--the Rayleigh approximation. The analytical prediction is based on an S-N curve corrected for the effect of mean stress. The specimens consist of hot rolled A36 Grade 81A steel bar stock of dimension 0.75 inch by 1.50 inch. The loading gives a uniform bending moment about the axis of minimum moment of inertia and the small central hole is orthogonal to this axis. The stochastic loadings used in this study are so-called pseudo-narrowband loadings. The loadings vary from broadband to extremely narrowband. (Abstract shortened with permission of author.)

In order to determine the seismic response of existing reinforced concrete non-ductile flat-plate buildings, four reinforced concrete slab-column connection subassemblies designed for gravity load only were built at half-scale of prototype structure, and tested at Ryon laboratory of the Rice University. Each specimen had two exterior and one interior connections. The variables included the presence of spandrel beam, magnitude of gravity load, and reinforcing arrangement. The behavior of entire subassemblies and the individual connections under the cyclic loading was studied in terms of failure mode, stiffness, ductility, shear capacity, and moment transfer capacity in the two loading directions. Based on the test results, a procedure to predict the flexural and shear strengths of the interior and exterior connections is recommended. A hysterestic model for non-ductile slab-column connections is proposed. This model reflects the unsymmetrical moment transfer behavior of non-ductile connections. Furthermore, the model is incorporated in a non-linear dynamic analysis program and a typical flat-plate building is analyzed to demonstrate the application of the analytical model.

The effect of transient high temperature in the uniaxial compressive strength of high strength concrete was investigated. The temperatures studied varied from 100$\sp\circ$ to 800$\sp\circ$C. The presence of loads in a structure was simulated by preloading the test specimens during the heating period. Results showed that exposure to temperatures between 100$\sp\circ$ and 300$\sp\circ$C decreased the compressive strength of high strength concrete by 15 to 20 percent. For temperatures between 400$\sp\circ$ and 800$\sp\circ$C,the compressive strength of concrete decreased to thirty percent of that at room temperature. One third of the preloaded specimens failed explosively during the heating period. In the remaining specimens the presence of a preload had a beneficial effect and a smaller loss of strength was observed compared to unstressed specimens. Exposure to high temperature caused the modulus of elasticity to decrease in all specimens regardlessly of the preload condition and the strength of concrete.

Constitutive models in soil mechanics are used to determine theoretical solutions to a host of geotechnical engineering problems such as pile-soil interaction, pile installation, short and long term stability, consolidation and foundation problems, etc. A fundamental component of the numerical formulation of the constitutive equations is the development of the elastoplastic tangent stiffness matrix. The numerical formulation of the elastoplastic matrix for a work hardening/softening material, as applicable to a general purpose finite element computer code, has been attempted by the author. The derived tangent stiffness matrix is symmetric for the associated flow rule (g = f) but it is non-symmetric for the non-associated flow rule (g $\not=$ f). All the components of the elastoplastic matrix for the Lade's model$\sp{\lbrack 11\rbrack}$ are also given. A parametric study was carried out to determine the validity of the associated and the non-associated flow rules for various stress paths in the deviatoric plane. The results demonstrate the inability of the associated flow rule to capture the soil behavior, except at stress levels very close to the hydrostatic axis.

A comprehensive study is made of an approximate model for the computation of the dynamic pressures and associated forces induced by ground shaking on rigid embedded vaults (2, 10). For rigidly supported vaults, it is shown that, due to the lack of shearing resistance of the medium surrounding the vault, the model is unable to predict the forces induced under static conditions of loading, and that it generally leads to much higher results than those obtained by available exact solutions (20). The soil surrounding the vault is hence modelled by a new set of impedances (20). It is shown then that the effect of base flexibility is to reduce the forces induced on massless vaults. Evaluation is also made of the effect of the vault mass. It is finally shown that the difference in the responses computed by the original and modified models decreases in importance with increasing flexibility.