The reflection, refraction, and adsorption of a planar SH wave with stochastic time dependence at a frictionally bonded interface between elastic solids is considered. The incident stress wave is assumed to be a sample function from a zero-mean Gaussian random process with known power spectral density. Exact and approximate solutions are presented for the probability density functions of the transmitted and reflected stress waves and for the rate of slip at the interface. Results are also presented for the stationary and nonstationary mean-square values of these quantities, the mean energy flux partitioning between the various waves, and the mean rate of energy dissipation at the interface. It is shown that for small levels of incident stress, the interface behaves as though perfectly welded, but, for high levels, it behaves as though perfectly lubricated.

The Bayesian method of statistical analysis has been applied to the problem of site assessment of the wind speed distribution. A Rayleigh distribution is used for wind speeds of interest for energy conversion. The mean wind speed is selected as the random parameter and a prior distribution selected to enable computation of the Bayesian distribution of wind speed reflecting both existing regional data and sampling observations. The convergence of the Bayesian distribution to the Rayleigh with increasing data is illustrated in terms of a sufficient statistic of sampling. Utility functions are computed for the power generated by a wind turbine. These are then combined with the Bayesian wind speed distribution to demonstrate two types of decision analysis: (1) Selection of the optimal site for a given wind turbine; and (2) selection of the optimal turbine for a given site.

Deformations and stresses in a fluid saturated porous medium of finite width are analyzed. The porous medium is assumed to be a binary mixture consisting of a linear elastic fluid and a linear elastic solid. The equilibrium equations for the solid constituent and all constitutive equations are expressed in terms of the solid displacements in a two-dimensional space. In addition to these equations the boundary conditions for a surface line load are obtained by separating the problem into symmetric and antisymmetric parts. Governing equilibrium equations are solved using standard and extended finite sine and cosine transformations for symmetric and antisymmetric parts, respectively. The final expressions are obtained by superposing the symmetric and antisymmetric solutions resulting from inverse standard and extended finite sine and cosine transformations. The stresses for the solid and fluid constituents and diffusion forces are obtained in terms of solid displacements by means of constitutive equations. The problem is of practical importance especially in the case of elevated roads which are supported by retaining walls from both sides.

This paper studies methods of parameter estimation for linear multi-degree-of-freedom structural dynamic systems, based on observed records of the external forces and the structural responses. The auto-regressive and moving-average (ARMA) model is used for this purpose. It is found that the ARMA model is a convenient model representing linear multi-degree-of-freedom structural dynamic systems and that the model is highly compatible with the instrumental variable method and the maximum likelihood method of identification. In order to check the accuracy of the estimation methods, analytical simulation studies are performed on the basis of simulated data dealing with the aerodynamic coefficient matrices that appear in the equations of motion of a two-dimensional model of a suspension bridge. Then, these methods are applied to the same equations to identify the coefficient matrices using the field measurement data yielding good estimates of the system parameters even under large output noise conditions.

An engineering approach to the time domain analysis which accounts for the effects of damping is developed for the purpose of evaluating the rigid body response motion of a two-dimensional floating body confined in a fixed basin. The frequency dependent added mass coefficients are first obtained under the assumption of an ideal fluid. Then the equations of motion in the frequency domain are constructed by artificially introducing the damping coefficients. Frequency response functions then follow logically from these equations of motion and are inverse-Fourier transformed to produce the impulse response functions. Essentially, three forms of damping coefficients are considered and experiments are then performed to determine how well these forms reproduce the experimental results. The optimum values of the damping ratios are also estimated from the experiments and their use for the analysis of large scale floating bodies is suggested. Finally, the causality conditions are verified numerically and it is found that they are satisfied at acceptable levels of engineering accuracy.

A phenomenological theory describing the process of gradual damage of brittle rods leading to their ultimate rupture is developed and applied to the problem of spatial and temporal evolution of damage in a free-free rod subjected to a pressure pulse at one of its ends. As a result of nucleation, growth and coalescence of voids, de-cohesions and dislocations, irreversible structural changes occur in a polycrystalline material subjected to certain types of loading. A special internal variable is introduced to characterize the gradual loss of mechanical strength or stiffness. A system of quasi-linear partial differential equations describing the problem is solved numerically using the method of characteristics. Numerical results of damage evolution, energy dissipation, etc. are presented and discussed.

The amplitudes of processing and digitization noise in strong motion earthquake accelerograms are reviewed for hand and automatic digitization. By finding the period bands for which the signal-to-noise ratio in digitized accelerograms is greater than one, dependence of cut-off periods for accelerogram data processing is presented for amplitude scaling in terms of: (1) Earthquake magnitude and epicentral distance; and (2) modified mercalli intensity at the recording site.

The significant improvements in the reliability of ground motion and response spectrum estimates that arise from a new procedure for processing strong-motion earthquake signals using state-of-the-art filter design and implementation techniques are illustrated through a series of case studies. A comparison of results from an existing model, and the proposed model show significant differences in the ground motion and response spectrum characteristics for the same set of filter limits. Drifts in integrated velocity and displacement characteristics and theoretically incorrect asymptotic behavior of response spectrum curves arising out of the existing processing scheme have been eliminated. In addition to the importance of appropriately selecting a low-frequency limit for band-pass filtering the signals, this work demonstrates the sensitivity of the acceleration trace to the particular choice of a high-frequency limit.

An analysis of optimal open-loop critical-mode control for tall buildings excited by earthquakes is presented. It is shown that both the active mass damper and the active tendon system are effective in reducing the building response. Furthermore, the optimal critical-mode control is likely to be as effective as the optimal global control, since the building response under earthquake excitations is usually dominated by a few lowest modes.

The finite element method is used to solve the nonlinear problem of creep bending of a plate. The initial strain approach has been adapted to solve the resulting nonlinear simultaneous equations. The algorithm leads to a time incremental set of equations. An isoparametric thick plate element was used. Good agreement was obtained between the present work and some of the available literature for plates with and without elastic foundations. A load bearing test, on a fresh water ice cover, was carried out and good agreement again was noted between the field data and the numerical model.