Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Giddens, Don P., Committee Co-Chair ; Zhu, Cheng, Committee Chair ; Garcia, Andres J., Committee Member ; Smith, Marc K., Committee Member ; McEver, Rodger P., Committee Member.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 43-45). Also available on the World Wide Web.

Thesis (doctoral)--University of London, 1989.

Thesis (M.S.) University of Missouri-Columbia, 2006. / 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 August 21, 2007) Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Background: The support of intersections in coal mines is an important safety issue in the U.S., as intersections are by far the most common area for unplanned falls of ground. A relatively comprehensive, nation-wide study of falls of ground is coupled with a national survey to mines about their support methods to determine common characteristics of failure and recommend changes to improve stability, and recommendations for future research. Methods: Over 600 fall of ground reports were collected from nine of the 11 Mine Safety and Health Administration (MSHA) District offices, and data was compiled to determine common characteristics of these unplanned falls. Statistical analysis was conducted on the data to examine which variables affected fall dimensions. To obtain data on current support usage, mail and phone surveys were collected with responses from 70 underground coal mines, representing approximately 235 million tons of annual production, or 66% of the U.S. total. These surveys provided a national snapshot of what support mines are using as well as typical extraction height, intersection width, and other details. Rocscience's Phase2 software was used to model a typical coal mine intersection and examine possible stability changes with different support options. Results: Surveys from underground mines revealed that the current industry average for intersection width is 20ft, average bolt length is 6ft, average distance from pillars to the first row of bolts is 3 to 4 ft, and a great majority of mines do not angle bolts over pillars. The fall of ground study confirmed that most falls are thicker than the average bolt length of 6 ft. and tend to be massive, extending past the intersection width of 20ft. The study also showed that falls with longer roof bolts installed typically had thicker falls which broke above the anchorage zone. Statistical analysis found a few questionably significant interactions, with the most prominent being the effect of roof type on fall height. Immediate roof geologies of dark shale and thinly laminated shale resulted in higher roof falls than other types. 2D modeling was unsuccessful at replicating the type of massive shear failures that have been commented on by MSHA personnel and that the study data suggests. It is the author's opinion that Phase2 and 2-D modeling in general may not be powerful or comprehensive enough to capture the true shear behavior of the rock strata in the roof beam because it cannot effectively model failure and dilation. Conclusions: Increasing bolt length may not be the most effective solution to reducing massive intersection failures. Rather, installing angled bolts over pillars may increase the strength of the system at the crucial roof-pillar edge. Weathering of bolts and/or rock are likely contributing to the significant number of cutter failures happening months or years after excavation. Recommendations for future action include 3D modeling of cutter failure and benefits of angled bolts over pillars. More consistent and thorough MSHA 7000 50a forms will enable more accurate statistical analysis and a better understanding of massive failure characteristics.

While inelastic mechanical behaviour of crystalline materials is well-understood in terms of lattice defects, bulk metallic glasses (BMGs) pose significant challenges in this respect due to their disordered structure. They can be produced by rapid cooling from the liquid state (among other technique) and, thus can be frozen as vitreous solids. Due to the absence of a long-range order in atomic structure and a lack of defects such as dislocations, BMGs generally show unique mechanical properties such as high strength and elastic limit, as well as good fracture toughness and corrosion resistance. Typically, inorganic glasses are brittle at room temperature, showing a smooth fracture surface as a results of mode-I brittle fracture. At small scale, it was well documented that inelastic deformation of bulk metallic glasses is localised in thin shear bands. So, in order to understand deformation mechanisms of BMGs comprehensively, it is necessary to investigate formation of shear bands and related deformation process. In this thesis, a history of development of BMGs is presented, followed by a review of fundamental mechanisms of their deformation.

Eccentric braced frames have been a topic of research in seismic design over the past twenty years. The idea of eccentric bracing is a relatively new method used in practice to satisfy seismic design requirements. They have been proven to give reliable results in tests using simulated earthquake events, as well as provide an economical advantage over other framing methods. Two one-story eccentric braced frame models were created using computer generated finite element analysis. The example chosen for this study are discussed further. The maximum shear stress distribution in the link beam of the frame, using finite element analysis, will be investigated herein. The results of the shear stress produced gives insight to shear forces developed in the link beam of eccentric braced frames. The results of shear forces produced are compared with those calculated by structural engineers using commonly used hand calculated equations.

Master of Science / Civil Engineering / Hayder Rasheed / Reverse diagonal shear cracking at the supports of many reinforced concrete girders is a phenomenon affecting a number of KDOT’s low-volume bridges built in the early-to-mid 1900’s. This phenomenon is not addressed in the AASHTO Bridge Design Manual (2002) or ACI specifications. This study investigates the causes of this cracking and creates BRIDGE (Bridge Rating of Inclined Damage at Girder Ends), an Excel-based software to determine the load rating of a user specified bridge exhibiting reverse diagonal shear cracking at the girder supports. A user-interface is created which allows a user to create a grillage model of an existing bridge and to place various rating trucks on the bridge. Equivalent flexibility analysis is used to distribute the truck live loads from within the deck panels to the surrounding girders and diaphragms. Stiffness matrices are utilized to find the nodal displacements then the reactions at the girder supports caused by the truck live loads and bridge dead load. These reactions are checked against RISA software models to test the accuracy of the stiffness matrix application. ABAQUS FE models and Mohr’s circle stress distribution is used to find the driving and clamping forces on the crack. These forces are caused by resolving the dead and live load reactions and the friction force generated between the concrete girder and the rusty steel bearing pad along the shear crack orientation. These clamping and driving forces are used, along with the simplified modified compression field theory to determine the shear capacity of each girder at the reverse cracks. A modified version of Equation 6B.4.1 from the Manual for Bridge Evaluation (2011) is used to find the operating and inventory rating factors for the bridge.

abstract: In sub-Saharan Africa, an invasive form of nontyphoidal Salmonella (iNTS) belonging to sequence type (ST)313 has emerged as a major public health concern causing widespread bacteremia and mortality in children with malaria and adults with HIV. Clinically, ST313 pathovars are characterized by the absence of gastroenteritis, which is commonly found in “classical” nontyphoidal Salmonella (NTS), along with multidrug resistance, pseudogene formation, and chromosome degradation. There is an urgent need to understand the biological and physical factors that regulate the disease causing properties of ST313 strains. Previous studies from our lab using dynamic Rotating Wall Vessel (RWV) bioreactor technology and “classical” NTS strain χ3339 showed that physiological fluid shear regulates gene expression, stress responses and virulence in unexpected ways that are not observed using conventional shake and static flask conditions, and in a very different manner as compared to ST313 strain D23580. Leveraging from these findings, the current study was the first to report the effect of fluid shear on the pathogenesis-related stress responses of S. Typhimurium ST313 strain A130, which evolved earlier than D23580 within the ST313 clade. A130 displayed enhanced resistance to acid, oxidative and bile stresses when cultured in the high fluid shear (HFS) control condition relative to the low fluid shear (LFS) condition in stationary phase using Lennox Broth (LB) as the culture medium. The greatest magnitude of the survival benefit conferred by high fluid shear was observed in response to oxidative and acid stresses. No differences were observed for thermal and osmotic stresses. Based on previous findings from our laboratory, we also assessed how the addition of phosphate or magnesium ions to the culture medium altered the acid or oxidative stress responses of A130 grown in the RWV. Addition of either phosphate or magnesium to the culture medium abrogated the fluid shear-related differences observed for A130 in LB medium for the acid or oxidative stress responses, respectively. Collectively, these findings indicate that like other Salmonella strains assessed thus far by our team, A130 responds to differences in physiological fluid shear, and that ion concentrations can modulate those responses. / Dissertation/Thesis / Masters Thesis Microbiology 2017