Browsing by Subject "Columns"
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Item Analysis and response mechanisms of blast-loaded reinforced concrete columns(2009-05) Williams, George Daniel; Williamson, Eric B., 1968-; Williamson, Eric B., 1968-Terrorism has been an international threat to high occupancy civilian structures, government buildings, and military installations for many years. Statistical data from past terrorist attacks show that transportation infrastructure has been widely targeted, and a bombing of an ordinary highway bridge is a realistic scenario. Recent threats to bridges in the U.S. confirm this concern and have caught the attention of the bridge engineering community. Given that many ordinary highway bridges in the United States support critical emergency evacuation routes, military transportation plans, and vital economic corridors, the loss of a key bridge could result in severe national security, economic, and socioeconomic consequences. Therefore, in this research, a simplified procedure is developed to predict blast loads on bridge columns, and an understanding of the mechanisms that cause damage and ultimately failure of blast-loaded reinforced concrete bridge columns is advanced. To that end, computational fluid dynamics models are constructed and validated using experimental data. These numerical models are used to characterize the structural loads experienced by square and circular bridge columns subjected to blast loads, which is followed by the formulation of a simplified load prediction procedure. Additionally, nonlinear, three-dimensional, dynamic finite element models of blast-loaded reinforced concrete bridge columns are developed and validated using qualitative and quantitative data from recent experimental tests. The results of these analyses illustrate the fact that circular columns cannot be assumed to experience less base shear demand than a square column simply because they experience less net resultant impulse. Furthermore, the column response models developed in this research are used to identify and explain the mechanisms that lead to the spalling of side cover concrete off blast-loaded reinforced concrete members observed in recent experimental tests. Therefore, the results of this research advance the understanding of the structural loads on and the resulting response of reinforced concrete bridge columns subjected to blast loads, and as such these contributions to the structural engineering community enhance the security of the U.S. transportation infrastructure.Item Preliminary analysis of doubler plate attachment details for steel moment resisting frames(2011-05) Shirsat, Priyanka Saiprakash; Engelhardt, Michael D.; Engelhardt, Michael D.; Helwig, Todd A.In steel moment resisting frames, the region of the column located within the beam-column joint is known as the panel zone. When a steel moment resisting frame is subjected to lateral load, due to wind or seismic loads, the panel zone is subject to high shear. In some cases, the shear in the panel zone is sufficiently high that the panel zone must be reinforced to increase its stiffness and/or strength. This is normally accomplished by welding doubler plates to the column in the panel zone region. Doubler plates can be a costly feature in steel moment resisting frames because of the substantial amount of welding involved. There has been a large amount of past research that has investigated the required shear strength and stiffness of the panel zone region to establish a basis for sizing doubler plates. However, very little past research has investigated the details of attaching doubler plates to columns. These attachment details can have a significant influence on the structural performance of panel zone and on cost. The overall goal of this research was to conduct preliminary finite element studies that provide insight into several key issues related to the attachment of doubler plates to columns and to identify issues that require further research. The research involved finite element modeling of a simplified representation of beam-to-column joint subjected to monotonic loading. A total of twenty-one analysis cases with different doubler plate attachment details were studied. Issues that were investigated included the effect of welding different edges of the doubler plate to the column (horizontal edges only, vertical edges only, and all four sides), the effect of extending the doubler plate beyond the panel zone region, and the effect of providing two thinner doubler plates of equivalent total thickness on both sides of the column web instead of one thick doubler plate on one side of the column web. In addition, the forces developed in the doubler plate welds were computed from the finite element analysis and compared with current building code requirements for the design of these welds. Observations and preliminary design recommendations on these issues are provided in this thesis, along with recommendations for further research.Item Somewhere between "us" and "them" : black columnists and their role in shaping racial discourse(2014-12) McElroy, Kathleen Oveta; Poindexter, Paula MaurieCommunication scholarship on black journalists has mostly focused on their lack of empowerment and the constraints that prevent them from engaging as full partners in the journalism industry, which has been shown to be ambivalent about the role of race in professional work. Racial discourse studies assert that blacks have little say in their representation by the media, where African Americans and other minority groups are treated as the negative “them” rather than the positive mainstream “us.” This dissertation examines journalism and racial discourse from a little-explored perspective in both fields: that of elite black columnists, who have the platform and autonomy to discuss news in general and race in particular from an African-American point of view. This dissertation examined the work of 11 African-American columnists who have won the Pulitzer Prize for commentary or write for one of the country’s highest-circulation publications. After textual analyses of more than 3,000 of their columns and in-depth, elite interviews with five columnists, this study found that elite black columnists wrote extensively and strategically about race at a level previously unrecognized in academia. The study found that the columnists heavily relied on biography and history in constructing a black narrative, which is not usually associated with journalistic work but helped them make sense of the black experience and to explain it to their mostly white readership. The research also identified six related frames the columnists used to provide context to news coverage about black America. Three frames explained the “problem people” image of black America: the devaluation of black life, misrepresentation, and destructive racial discourse. Three were correctives to that image: the raising of critical racial consciousness (while unmasking whiteness), black responsibility and black pride, and reverence for the Constitution and American ideals. The findings showed that elite black columnists were actively engaged in what could be called an antiracist racial project: to not only counter inequality and misrepresentation but also to battle the forces within discourse that feed the “us” vs. “them” ideology.