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Articles 1 - 10 of 10
Full-Text Articles in Engineering
A Comprehensive Protocol For Inspection And Assessment Of Aging Steel Bridges: Experiments, Computations And 3d Laser Scanning Of Field Corroded Girders, Georgios Tzortzinis
A Comprehensive Protocol For Inspection And Assessment Of Aging Steel Bridges: Experiments, Computations And 3d Laser Scanning Of Field Corroded Girders, Georgios Tzortzinis
Doctoral Dissertations
According to a recent evaluation, our nation's infrastructure has increasingly presenting signs of deterioration with some elements exhibiting significant deficiencies in conditions and functionality. Regarding the transportation network condition, from the over than 600,000 bridges which are included in the National Bridge Inventory, 46,154 of them are characterized as structurally deficient with the backlog of bridge rehabilitation needs estimated at US$125 billion. Among the many aspects of structural deficiency, corrosion is considered a common cause, both for reinforced concrete and steel bridge deterioration. For steel bridges, corrosion has historically triggered bridge failures resulting to fatalities and injuries. To prevent similar …
Density State And Shear Behavior Of Granular Soils With Influence Of Particle Size Distribution, Yibing Deng
Density State And Shear Behavior Of Granular Soils With Influence Of Particle Size Distribution, Yibing Deng
Doctoral Dissertations
Heterogeneous granular soils are ubiquitous in nature and man-made deposits. Heterogeneity of soil is characterized by its particle size distribution (or fines content for gap-graded soils). The particle size distribution of soil is the main factor that affects its mechanical properties. However, in soil mechanics, the influence of particle size distribution on mechanical properties is only considered in an empirical manner. There are few analytical methods that can explicitly account for the effect of particle size distribution. In this study, there are two purposes: 1) to develop a particle packing theory for modeling the effect of particle size distribution on …
Extracellular Polymeric Substances In Oxygenic Photogranules: Investigation Of Their Role In Photogranulation In A Hydrostatic Environment, Wenye Camilla Kuo-Dahab
Extracellular Polymeric Substances In Oxygenic Photogranules: Investigation Of Their Role In Photogranulation In A Hydrostatic Environment, Wenye Camilla Kuo-Dahab
Doctoral Dissertations
The purpose of this dissertation was to assess the critical role of extracellular polymeric substances (EPS) in the photogranulation of activated sludge, in a hydrostatic environment. The first section evaluates the fate and dynamics of different fractions of EPS in sludge-based photogranulation under hydrostatic conditions. The study shows that during the transformation of activated sludge into a photogranular biomass, sludge’s base-extractable proteins selectively degrade. Strong correlations between base-extracted proteins and the growth of chlorophyll a and chlorophyll a/b ratio suggest that the bioavailability of this organic nitrogen is linked with selection and enrichment of filamentous cyanobacteria under hydrostatic conditions. The …
Multiscale Investigation Of Thixotropy In Soft Clays, Jing Peng
Multiscale Investigation Of Thixotropy In Soft Clays, Jing Peng
Doctoral Dissertations
Fine-grained clay particles of <2 >µm in size are ubiquitous in soils and sedimentary rocks. Due to their platy shape, high aspect ratio, and surface charges, clay particles play a dominant role in controlling the mechanical properties of those fine-grained geomaterials such as soft clays and shales. In physics and engineering, some materials show that the strength and stiffness increases with time even if the boundary conditions remain unchanged (e.g., no change in pressure, temperature, or composition), and such a phenomenon is called thixotropy. It is generally agreed that the principle of thixotropy of wet clays is complex. For a closed, …
Understanding The Safety Impacts Of Left-Turn Infrastructure On The Vulnerable Driving Population, Francis Tainter
Understanding The Safety Impacts Of Left-Turn Infrastructure On The Vulnerable Driving Population, Francis Tainter
Doctoral Dissertations
The severe impact of roadway fatalities has remained a significant concern for researchers in recent years. As of 2015, traffic fatalities were the leading cause of death for individuals between the ages of 15 and 20 years old and a significant safety concern for drivers over the age of 65 years old (otherwise known as the “vulnerable” driving population). Intersection-related crashes have also remained prevalent in these demographic categories. Through four primary crash data evaluations, this dissertation explores the safety implications on the “vulnerable” driving population in the Commonwealth of Massachusetts. Through the utilization of newly developed crash data linkage …
Material Property Heterogeneity In Dimensional Lumber And Its Relationship To Mass Timber Performance, Fiona O'Donnell
Material Property Heterogeneity In Dimensional Lumber And Its Relationship To Mass Timber Performance, Fiona O'Donnell
Doctoral Dissertations
According to the Environmental Protection Agency, buildings account for 38% of the United States' carbon dioxide emissions, providing architects and structural engineers a unique opportunity to mitigate a significant factor driving climate change by implementing innovative and sustainable technology in infrastructure design. Wood and mass timber products are becoming an increasingly popular alternative building material due to their economic and environmental benefits. The natural growth of wood leads to highly heterogeneous material properties. Defects such as checks, knots, and localized slope of grain contribute to some of this variation; however, wood properties vary significantly even in clear wood. Using mass …
Harnessing The Mechanics Of Thin-Walled Metallic Structures: From Plate-Lattice Materials To Cold-Formed Steel Shear Walls, Fani Derveni
Harnessing The Mechanics Of Thin-Walled Metallic Structures: From Plate-Lattice Materials To Cold-Formed Steel Shear Walls, Fani Derveni
Doctoral Dissertations
Thin-walled structures have received a lot of interest during the last years due to their light weight, cost efficiency, and ease in fabrication and transportation, along with their high strength and stiffness. This dissertation focuses on the mechanical performance of thin-walled metallic structures from cold-formed steel shear walls and connections (PART I) to plate-lattice architected materials (PART II) via computational, experimental, and probabilistic methods. Cold-formed steel (CFS) shear walls subjected to seismic loads is the focus of PART I of this dissertation. An innovative three-dimensional shell finite element model of oriented strand board (OSB) sheathed CFS shear walls is introduced …
Buckling Of Thin Cylindrical Shells: Imperfection Sensitivity, Non-Destructive Technique For Capacity Prediction And Application For Wind Turbine Towers, Kshitij Kumar Yadav
Buckling Of Thin Cylindrical Shells: Imperfection Sensitivity, Non-Destructive Technique For Capacity Prediction And Application For Wind Turbine Towers, Kshitij Kumar Yadav
Doctoral Dissertations
The presence of imperfections significantly reduces the load-carrying capacity of thin cylindrical shells and the reduction depends on the shape and the size of the imperfections. As a result, the prediction of the shells' buckling capacity requires a priori knowledge about the imperfections---a difficult, expansive, and time-consuming adventure, if not impossible. Consequently, thin cylindrical shells are designed conservatively using the knockdown factor approach that accommodates the uncertainties associated with the imperfections present in the cylinders; almost all the design codes follow this approach explicitly or implicitly. However, cylindrical shells can be designed more efficiently by making them insensitive to imperfections, …
Optimization And Technology-Based Strategies To Improve Public Transit Performance Accounting For Demand Distribution, Charalampos Sipetas
Optimization And Technology-Based Strategies To Improve Public Transit Performance Accounting For Demand Distribution, Charalampos Sipetas
Doctoral Dissertations
Public transit is important to societies worldwide. The operation of public transit systems is generally associated with great benefits for the users, but there are also cases in which these systems demonstrate inefficient performance. Quantifying transit performance is an important area of research over the last decades. This dissertation presents models to improve transit system performance through optimization techniques and new technologies, recognizing the effects of non-uniform distribution of demand over space and time. The contributions span fixed route transit services and on-demand transit, as well as models for flexible transit operations that lie in between. Regarding fixed route systems, …
Cold-Formed Steel Stud Assemblies Bearing On Concrete Slabs, Abbas Joorabchian
Cold-Formed Steel Stud Assemblies Bearing On Concrete Slabs, Abbas Joorabchian
Doctoral Dissertations
Cold-formed steel (CFS) bearing walls are frequently installed on concrete slabs, which do not provide perfectly rigid and uniform bearing conditions. Existing design guidance assumes bearing conditions have no impact on the axial capacity, though cold-formed steel compressive members are particularly susceptible to end conditions. Studs are typically installed at the edge of concrete slabs, which is prone to spalling and geometric irregularities. Moreover, they are occasionally installed inadvertently overhanging from concrete slabs. In this research project, the impact of non-uniform and partial bearing conditions on the axial strength of cold-formed steel wall assemblies is identified and characterized experimentally and …