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Flyovers, or grade separated bridges or roads, are a type of urban infrastructure that has been used to facilitate high-speed vehicular movement. This once-popular strategy of the west, despite being considered as a failure for sustainable urban growth, has been adopted in Bangladesh to combat traffic congestion in Dhaka that has a crippling effect on daily life of the citizens. As was anticipated by many urban planners and architects, these expensive structures did little to reduce traffic congestion, but created additional problems of noise and air pollution as well as reduced pedestrian mobility. More importantly, these flyovers created wasted void spaces underneath that are uncomfortable, devoid of human scale and act as physical and visual barriers that cause tears on the urban fabric. The objective of this thesis is to explore how architecture can unlock the potential of the unused spaces under the flyovers in Dhaka, by turning these linear leftover spaces into dignified public places that improves the daily lived experiences of the urban dwellers, by minimizing the disruptions caused by the flyover and by realizing the potential inherent in the robust structure of the flyover. This thesis examines a democratized way of building, where the role of architecture is to facilitate organic and heterogeneous growth, addition and modification to the flyover in order to bring the human scale back to the massive flyover structure through a reconciliation of top-down and bottom-up approaches. The architectural interventions respond to the site conditions, potentials and demands. The architectural outcome is based on the concepts of creating a threshold, architecture as armature and parasitic structures. / Master of Architecture / Flyovers, or grade separated bridges or roads, are a type of urban infrastructure that has been used to facilitate high-speed vehicular movement. This once-popular strategy of the west, despite being considered as a failure for sustainable urban growth, has been adopted in Bangladesh to combat traffic congestion in Dhaka that has a crippling effect on daily life of the citizens. As was anticipated by many urban planners and architects, these expensive structures did little to reduce traffic congestion, but created additional problems of noise and air pollution as well as reduced pedestrian mobility. More importantly, these flyovers created wasted empty spaces underneath that are uncomfortable and act as physical and visual barriers that cause tears on the urban fabric. The objective of this thesis is to explore how architecture can unlock the potential of the unused spaces under the flyovers in Dhaka, by turning these linear leftover spaces into dignified public places that improves the daily lived experiences of the urban dwellers, by minimizing the disruptions caused by the flyover and by realizing the potential inherent in the robust structure of the flyover. This thesis examines a democratized way of building, where the role of architecture is to facilitate organic and de-centralized growth, addition and modification to the flyover in order to bring the human scale back to the massive flyover structure through a reconciliation of top-down and bottom-up approaches. The architectural interventions respond to the site conditions, potentials and demands. The architectural outcome is based on the concepts of creating a threshold, architecture as armature and parasitic structures.

Many experiments demonstrate that the effects of hydrogen solutes decrease macroscopic fracture stresses and strains in ductile materials. Hydrogen-related failures have occurred in nearly all industries involving hydrogen-producing environments. The financial losses incurred from those failures reaches millions if not billions of dollars annually. With the ever-urgent needs for alternative energy sources, there is a strong push for a hydrogen economy from government and private sectors. Safe storage and transportation of hydrogen increases the momentum for studying hydrogen-related failures, especially in ductile materials. To quantify ductile material damage with the effects of hydrogen embrittlement, it is necessary to add hydrogen effects into the void nucleation, void growth, and void coalescence equations. In this research, hydrogen-enhanced void nucleation is our focus, with hydrogen-enhanced void growth and void coalescence t be studied in the future. Molecular Dynamic (MD) and Monte Carlo (MC) simulations with Embedded Atom Method (EAM) potentials were performed to study how hydrogen affects dislocation nucleation, dislocation structure formation and nanovoid nucleation at nickel grain boundaries. The results were inserted into the continuum void nucleation model by Horstemeyer and Gokhale, and the relationships between stress triaxiality-driven void nucleation, grain boundary hydrogen concentrations and local grain geometries were extracted. MD and MC simulations with EAM potentials were also performed to study how hydrogen interstitials affect the dislocation nucleation, dislocation structure formation and subsequent anovoid nucleation of single crystal nickel in different hydrogen-charging conditions. Evolutions of dislocation structures of nickel single crystal with different hydrogen concentrations were compared. The effects of nanovoid nucleation stress and strain at different hydrogen concentrations were quantified. The results were also inserted into the Horstemeyer and Gokhale model and the relationship between stress triaxiality-driven void nucleation and hydrogen concentration caused by stress gradient, which showed similar trends as the grain boundary studies. From nanoscale studies and existing experimental observations, a continuum void nucleation model with hydrogen effects was proposed and used in a continuum damage model based upon Bammann and coworkers. The damage model was implemented into user material code in FEA code ABAQUS. Finite element analyses were performed and the results were compared to the experimental data by Kwon and Asaro.

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