The work described herein examines the fracture behavior of steels used in bridge applications. As part of Transportation Pooled Fund (TPF) Project 5-238, Design and Fabrication Standards to Eliminate Fracture Critical Concerns in Steel Members Traditionally Classified as Fracture Critical, researchers aim to take advantage of advances made in both steel production technology and in the field of fracture mechanics. Testing and analysis of both conventional and High Performance Steel (HPS) grades of bridge steel was conducted as part of this study. This includes both Charpy V-Notch testing, as well as more rigorous elastic-plastic fracture toughness testing. Analysis includes the application of the master curve methodology to statistically characterize fracture behavior in the ductile to brittle transition region. In addition, a database of historic bridge fracture toughness data was compiled and re-analyzed using plasticity corrections to estimate elastic-plastic fracture toughness. Correlations between Charpy V-Notch impact energy and fracture toughness, which forms the basis for the current material specification, were also examined. Application of fracture toughness characterization of both new and historic data results in updated methodologies for addressing fracture in bridge design. / Ph. D.

Reliability analysis of series structural systems with emphasis on problems typical for metal fatigue is addressed. Specific goals include the following: (1) Given the distribution of strength of the components and the distribution of external loads on the system what is the probability of failure of the system? (2) Given the target safety index for the system, what would be the target safety index for the components? Exact solutions in the analysis of series structural systems only exists for some special problems. Some of these special problems are investigated. In particular some special cases of the problem of unequal element reliabilities are considered and some interesting observations are made. Numerical integration is in general required even when an exact solution exists. A correction or adjustment factor is developed for an important class of problems. This factor makes it possible to relate element and system probabilities of failure without numerical integration. However in most cases no exact solution to the structural series system problem exists. Approximations by for instance bounds on the probability of failure or Monte Carlo simulation has been the only way of approximating solutions. These two methods are generally not good approximation schemes since they are either too crude or too expensive. In this dissertation an approximation scheme for analysis of series systems where no exact solution exists is developed. The method only requires a simple numerical integration if the component safety index and the correlation coefficient between failure modes is known. Numerous examples are used to verify the method against known exact results and excellent estimates are obtained. Applications by practical examples is also given. In the appendix the problem of convergence of fatigue life distribution is also summarized.

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Univ., Diss.--Aix-Marseille 3, 2006.

As confirmed by a recent survey conducted among developers of the Apache, Eclipse, and Mozilla projects, two extremely challenging tasks during maintenance are reproducing and debugging field failures--failures that occur on user machines after release. In my PhD study, I have developed several techniques to address and mitigate the problems of reproducing and debugging field failures. In this defense, I will present an overview of my work and describe in detail four different techniques: BugRedux, F3, Clause Weighting (CW), and On-demand Formula Computation (OFC). BugRedux is a general technique for reproducing field failures that collects dynamic data about failing executions in the field and uses this data to synthesize executions that mimic the observed field failures. F3 leverages the executions generated by BugRedux to perform automated debugging using a set of suitably optimized fault-localization techniques. OFC and CW improves the overall effectiveness and efficiency of state-of-the-art formula-based debugging. In addition to the presentation of these techniques, I will also present an empirical evaluation of the techniques on a set of real-world programs and field failures. The results of the evaluation are promising in that, for all the failures considered, my approach was able to (1) synthesize failing executions that mimicked the observed field failures, (2) synthesize passing executions similar to the failing ones, and (3) use the synthesized executions successfully to perform fault localization with accurate results.

A variety of both parametric and nonparametric test statistics have been employed in the finance literature for the purpose of conducting hypothesis tests in event studies. This thesis begins by formally deriving the result that these statistics may not follow their conventionally assumed distribution in finite samples and in some cases even asymptotically. Thus, standard event study test statistics can exhibit a statistically significant bias to size in practice, a result which I document extensively. The bias typically arises due to commonly observed stock return traits, including non-normality, which violate basic assumptions underlying the event study test statistics. In this thesis, I develop an unbiased and powerful alternative: conventional test statistics are normalized in a straightforward manner, then their distribution is estimated using the bootstrap. This bootstrap approach allows researchers to conduct powerful and unbiased event study inference. I adopt the approach in an event study which makes use of a unique data set of failed-bank acquirers in the United States. By employing the bootstrap approach, instead of more conventional and potentially misleading event study techniques, I overturn the past finding of significant gains to failed-bank acquirers. This casts doubt on the common belief that the federal deposit insurance agency's failed-bank auction procedures over-subsidize the acquisition of failed banks.

This thesis proposes an efficient power system simulator to estimate the automatic sequence of events that follow a fault contingency leading to islanding and cascading outages. The simulator is based on a quasi-steady state model that includes island identification, under-frequency load shedding, over-frequency generator tripping, and island load flow. Contingencies can include the outage of generators, loads, or transmission lines. Often times, a fault of one or two of these power system elements can lead to many cascaded outages and system islanding. The simulator utilizes an innovative method that analyzes the null space of the DC load flow susceptance matrix to identify system islands after each disturbance. Once system islands have been determined, each island power imbalance is calculated and the simulator determines based on the power imbalance in each island whether any load shedding, generator tripping, or primary frequency regulation is required. Once these corrective actions are completed each island will either have been found to balance power or will experience blackout. In the islands that have balanced power, a load flow is computed to see if all line flow constraints are satisfied. Any lines with flow constraint violations are faulted, and the iterative process is repeated under all line flow constraints are satisfied. / The results demonstrate the ability of the simulator to quickly and efficiently predict a system's response to contingencies leading to cascading outages and islanding. Simulations were conducted on a 10-bus 13-line network, a 24-bus 38-line network, and a 72-bus 119-line network. / This thesis also examined the highly complex mixed-integer linear problem of identifying the optimum initial outage in the sense that it would cause the maximum amount of load shedding through islanding. The results on a three-line, three-bus test properly identified the line whose initial outage caused overflows leading to system separation and maximum loss of load.

No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 2, 2008) Includes bibliographical references.