Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Chemistry and Chemical Biology." Includes bibliographical references.

The panel zone region in columns of seismic resistant steel moment frames are subject to very high shear forces during earthquake loading. Doubler plates are often used to increase the stiffness and strength of the panel zone. The methods and details used to attach doubler plates to columns can affect seismic performance of the panel zone and can also affect cost. The research reported in this thesis was aimed at developing an improved understanding of the advantages and disadvantages of various approaches for detailing and welding doubler plates to columns and how various details perform under cyclic inelastic loading. An extensive series of finite element analyses were conducted to study doubler plate attachment details. Both a shallow W14x398 column and a deep W40x264 column were studied in this research. This thesis provides a detailed description of the finite element modeling techniques used for the research and presents the results of an extensive series of analyses examining a wide variety of issues related to doubler plate design and detailing. / text

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With the increase in complexity of modern electricity grids, the implementation of state-estimators has become a vital aspect of stability and contingency analyses for stable and secure power system operation. Transmission line reactance is an important component in the computation of state-estimators. Two models utilizing real-time synchrophasor data and ERCOT load information are proposed to compute Thevenin equivalent reactance. This thesis presents the results of implementing these methods to estimate the equivalent reactance of a transmission network between The University of Texas at Austin and The University of Texas, PanAm. / text

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The behaviour of sands during loading has been studied in great detail. However, little work has been devoted to understanding the response of sands in unloading. Drained triaxial tests indicate that, contrary to the expected elastic behaviour, sand often exhibit contractive behaviour when unloaded. Undrained cyclic simple shear tests show that the increase in pore water pressure generated during the unloading cycle often exceeds that generated during loading. The tendency to contract upon unloading is important in engineering practice as an increase in pore water pressure during earthquake loading could result in liquefaction. This research contributes to filling the gap in our understanding of soil behaviour in unloading and subsequent reloading. The approach followed includes both theoretical investigation and numerical implementation of experimental observations of stress dilatancy in unload-reload loops. The theoretical investigation is done at the micromechanical level. The numerical approach is developed from observations from drained triaxial compression tests. The numerical implementation of yield in unloading uses NorSand — a hardening plasticity model based on the critical state theory, and extends upon previous understanding. The proposed model is calibrated to Erksak sand and then used to predict the load-unload-reload behaviour of Fraser River sand. The trends predicted from the theoretical and numerical approaches match the experimental observations closely. Shear strength is not highly affected by unload-reload loops. Conversely, volumetric changes as a result of unloading-reloading are dramatic. Volumetric strains in unloading depend on the last value of stress ratio (q/p’) in the previous loading. It appears that major changes in particles arrangement occur once peak stress ratio is exceeded. The developed unload-reload model requires three additional input parameters, which were correlated to the monotonic parameters, to represent hardening in unloading and reloading and the effect of induced fabric changes on stress dilatancy. The calibrated model gave accurate predictions for the results of triaxial tests with load-unload-reload cycles on Fraser River sand.

Determining the fatigue properties (Manson-Coffin and Ramberg-Osgood parameters) for a steel material requires time consuming and expensive testing. In the early stages of a design process, it is not feasible to perform this testing. To help solve this problem numerous researchers have developed estimation methods to estimate the Manson-Coffin parameters from monotonic properties data. Additionally, other researchers have compared the results from these various estimation methods for large material classifications. However, a comprehensive comparison of these estimation methods has not been made for steels in different heat treatment states. More accurate results for the best estimation method can be made with smaller classifications, which have more consistent properties. In this research, best estimation methods are determined for six steel heat treatments. In addition to looking at steel heat treatment classifications, the estimation of the Ramberg-Osgood parameters is also examined through the compatibility conditions. Without them, the approach of estimating the fatigue properties using the estimation methods would not be practically useful. Finally, in the comparison of the estimation methods, an appropriate statistical comparison methodology is utilized; multiple contrasts comparison. This methodology is implemented into the comparison of the different estimation methods, by comparing the estimated lives and the experimental lives as a regression so that the entire life range can be considered. The estimation methods can also be utilized to get estimates of the variability of the fatigue properties given the variability of the monotonic properties data, since there is a functional relationship developed between the two sets of material properties. This variability is necessary for a stochastic design process, in order to obtain a more optimally designed component or structure. Overall the estimation methods have a number of practical applications within a fatigue design process. Their use and implementation needs to be supplemented by the appropriate knowledge of their limitations and for what classifications they give the best results. An expert system is developed to summarize this knowledge to assist an engineer. This research aims to provide this knowledge and expands their use to account for variability in fatigue properties for stochastic analysis.

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