The objective of the research presented in this thesis was to study and optimize the transverse deck reinforcement for a skewed concrete bridge deck supported by Hybrid Composite Beams (HCB's).  An HCB consists of a Glass Fiber Reinforced Polymer outer shell, a concrete arch, and high strength seven wire steel strands running along the bottom to tie the ends of the concrete arch together.  The remaining space within the shell is filled with foam.  The concrete arch does not need to be cast until the beam is in place, making the HCB very light during shipping.  This lowers construction costs and time since more beams can be transported per truck and smaller cranes can be used.  HCB's are quite flexible, so AASHTO LRFD's design model for bridge decks, as a one-way slab continuous over rigid supports, might not apply well to the HCB's deck design. A skewed three HCB girder bridge with a reinforced concrete deck and end diaphragms was built in the laboratory at Virginia Tech.  Concentrated loads were applied at locations chosen to maximize the negative and positive moments in the deck in the transverse direction.  The tests revealed that the transverse reinforcement was more than adequate under service loads. An Abaqus model was created to further study the behavior of the bridge and to help create future design recommendations.  The model revealed that the HCB bridge was behaving more like a stiffened plate at the middle section of the bridge, indicating that the flexibility of the girders needed to be considered. / Master of Science

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17884号 / 工博第3793号 / 新制||工||1580(附属図書館) / 30704 / 京都大学大学院工学研究科建築学専攻 / (主査)教授 中島 正愛, 教授 田中 仁史, 教授 金子 佳生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Self-catalyzed GaAs nanowires (NWs) are grown epitaxially on Si(111) substrates using molecular beam epitaxy (MBE). The dynamics of the droplet are examined to improve NW yield and to control NW morphology. Control and understanding of the NW diameter via droplet dynamics is applied to NW photovoltaics and to novel corrugated NW distributed Bragg reflectors (DBRs). At the beginning of the MBE growth, a Ga pre-deposition step, between 0 s and 500 s in duration, is introduced to improve the yield of the NW arrays. The effect of the pre-deposition time was examined for five different hole diameters and yield was increased to nearly 100% for the appropriate combination of hole diameter and pre-deposition time. Two models were used to model the NW growth progression under different atomic flux ratios. The first model considers the contributions from direct and diffusion fluxes to the droplet and solves coupled equations for the droplet contact angle and the NW radius. The second model treats the contact angle as constant. Both models explained the accompanying experimental observations. Both models could be used to model future NW growths and the choice between the two would depend on the availability of contact angle data and whether the crystal phase must be considered. Absorption in NWs is determined by the diameter and the HE1n modes. The effectiveness of a linearly tapered inverted conical NW is demonstrated using finite element simulations. The photocurrent of an optimized inverted conical NW array is found and shown to be similar to that achieved by optical nanocones and nanowires. Diameter modulations can also be introduced into NW structures periodically to produce corrugated NW distributed Bragg reflectors (DBRs). The tunability of the reflectance peaks is demonstrated and explained by changes to the effective refractive index of the structure. / Thesis / Doctor of Philosophy (PhD) / This thesis seeks to understand the growth processes behind self-catalyzed nanowire growth. Nanowires (NWs) are very thin, vertical columns of semiconducting material. Self-catalyzed growth is a method of producing these structures that uses a droplet at the top of the structure to add material to the structure over time. These structures have numerous applications. This thesis focuses on solar cells and distributed Bragg reflectors (DBRs). Experiments show how control over the droplet can improve NW yield and give significant control of the NW diameter. These experiments are supported by mathematical models. Control over the diameter is important for the applications discussed. Using numerical simulations, it is shown how control over the diameter of the structure can lead to improvements in light absorption in NW solar cells. Additionally, periodic changes to the diameter can be used to create novel NW structures such as DBRs, which is a promising new application.

Chip and scrub seal treatments are common pavement preservation practices that use asphalt emulsions. Their performance has been studied for several years, yet many questions remain. The primary thesis objective was to study near surface behaviors of flexible pavements that are candidates for seal treatments. This study investigated the ability of the bending beam rheometer (BBR) to detect pavement surface changes due to the application of asphalt emulsion. Estimated stiffness and m-value data was recorded for three asphalt concrete mixtures using mixture beams approximately 120 mm long by 12 mm wide by 7.7 mm thick sawn from the surface of asphalt specimens. One mixture was plant mixed and laboratory compacted, while the other two were field-aged mixtures. This study gauges effect of treating specimens with emulsions commonly used in Mississippi in conditioned and unconditioned states.

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An RFI plasma enhanced chemical vapor deposition (PECVD) system and a large-scale RF plasma source immersion ion implantation (PSII) system were designed and built to study two forms of 3-D surface processing, PECVD and PSII. Using the RFI PECVD system, Ti-6Al-4V substrates were coated with diamond-like carbon films with excellent tribological and optical properties. as an innovation, variable angle spectroscopic ellipsometry (VASE) was successfully applied for non-destructive, 3-D, large-area tribological coatings quality investigation.;Based on the experience with the RFI PECVD system, a large-scale RFICP source was designed and built for the PSIL Langmuir probe and optical emission spectroscopy studies indicated that the RFI source produced stable, uniform, and clean plasma. MAGIC code was for the first time used to model PSII process, addressing different target geometries and boundaries, materials, plasma parameters, illustrated sheath formation and evolution, field distribution, ion and electron trajectories, ion incident angles, and dose distributions, which are critical for PSII design and understanding.;The RF PSII system was developed into a versatile large-area, uniform, 3-D surface processing apparatus, capable of PSII, PVD, PECVD, and in situ surface cleaning and interface properties modification, for multilayer, multi-step, and high performance surface engineering. Using the RFI PSII system, for the first time, PSII was studied as a mask-based surface layer conversion technique, for pattern writing by implantation as an alternative to current deposition-based and ink-based direct write technologies. It operates at low substrate temperature, keeps the original surface finish and dimensions, and avoids adhesion problem. A different operating mode of the RF source was discovered to perform biased sputtering of high purity quartz, which turned the RFI PSII system into a novel integrated RF PSII/PVD system for large-area, uniform, nitrogen-doped, and hydrogen-free SiO2 films deposition at low substrate temperatures. Nitrogen-doped SiO2 films with excellent optical properties were deposited on semiconductor, metal, and polymer substrates with excellent adhesion. Ellipsometry was used again for non-destructive SiO2 coatings investigation. FEL test electrodes processed by PSII/PVD showed suppressed field emission. A group of transition metals and an FEL test electrode were also implanted by nitrogen using the PSII mode and analyzed.

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