Browsing by Subject "Reinforcement"
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Item Anchorage of shear reinforcement in prestressed concrete bridge girders(2014-06) Mathys, Brian ThomasThe Minnesota Department of Transportation has typically used epoxy coated straight legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. With the straight legs of the U-shaped stirrups anchored into the bottom flange of the girders, this configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside of the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside of the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight legged epoxy coated stirrups that included bar pullout tests performed on 13 subassemblage specimens which represented the bottom flanges of prestressed concrete girders in a number of configurations to determine the effectiveness of straight legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.Item Neuroeconomic studies on personality and decision making(2013-07) Hawes, Daniel R.Neural activity causally underlies human cognition and behavior. Investigating the neurobiological principles and computational mechanisms governing brain activity during decision-making provides a way to improve theories of human behavior in the natural as well as social sciences (Glimcher & Rustichini 2004; Rustichini, 2009; Fehr & Rangel, 2009). In this context, the discipline of Neuroeconomics was originally conceived as an endeavor to interrogate neural activity during economic decision-making with the aim of evaluating competing decision theories (Rustichini, 2008; Glimcher, Camerer, Fehr & Poldrack 2009). From this origin, Neuroeconomics has evolved into a full-fledged enterprise of consilience; an attempt to not only test and bridge, but truly unify natural science and social science explanations of human behavior (Wilson, 1998; Glimcher & Rustichini, 2004; Rangel, Camerer & Montague, 2008).This dissertation binds two neuroeconomic studies of decision-making with an introduction and concluding commentary. The introduction presents a brief introduction to Neuroeconomics, meant to locate both research studies in the existing literature and philosophy of this field. The conclusion provides a brief appraisal of the role of Neuroeconomics in further advancing the kind of research into decision-making reported here. Both studies in this dissertation comprise investigations of human behavior during experience-based decision-making, with a special focus on the fundamental value computations that underlie such choice behavior.Study 1 investigates the role of neural reinforcement signals during learning of a strategic decision task from experience.Study 2 investigates the moderating effect of intelligence on neural reinforcement signals during a sequential binary choice task.Study 1 is reproduced from (Hawes, Vostroknutov & Rustichini 2013), and study 2 is reproduced from (Hawes, DeYoung, Gray & Rustichini; under review).