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2012

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Articles 1081 - 1093 of 1093

Full-Text Articles in Civil and Environmental Engineering

Bond, Transfer Length, And Development Length Of Prestressing Strand In Self-Consolidating Concrete, Krista Beth Porterfield Jan 2012

Bond, Transfer Length, And Development Length Of Prestressing Strand In Self-Consolidating Concrete, Krista Beth Porterfield

Masters Theses

"Due to its economic advantages, the use of self-consolidating concrete (SCC) has increased rapidly in recent years. However, because SCC mixes typically have decreased amounts of coarse aggregate and high amounts of admixtures, industry members have expressed concerns that the bond of prestressing strand in SCC may be compromised. While the bond performance of prestressing strand in a new material such as SCC is an important topic requiring investigation, the results are only applicable if the research is completed on strands with similar bond quality as the strands used in the field. Therefore, the objectives of this research program were …

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Effects Of High Volume Fly Ash And Powder Activators On Plastic And Hardened Concrete Properties, Drew Alexander Davis Jan 2012

Effects Of High Volume Fly Ash And Powder Activators On Plastic And Hardened Concrete Properties, Drew Alexander Davis

Masters Theses

This study was performed to examine the effects of high volumes of Class C fly ash modified by powder activators upon the plastic and hardened properties of concrete. In a companion study, five Missouri area cements and five Class C fly ashes were examined for incompatibilities, with the most and least reactive combinations being scaled up to full scale concrete testing. Two baseline concrete mixtures were examined, the only difference in mixtures being the sources of portland cement and fly ash. Fly ash replacement was examined at 50% and 70% replacement (by total cementitious mass). Three powder activators were used …

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Shear And Fracture Behavior Of High-Volume Fly Ash Reinforced Concrete For Sustainable Construction, Carlos Andres Ortega Ordonez Jan 2012

Shear And Fracture Behavior Of High-Volume Fly Ash Reinforced Concrete For Sustainable Construction, Carlos Andres Ortega Ordonez

Doctoral Dissertations

"Concrete is the most widely used man-made material on the planet. Unfortunately, producing Portland cement generates carbon dioxide (a greenhouse gas) at roughly a pound for pound ratio. High-volume fly ash (HVFA) concrete- concrete with at least 50% of the cement replaced with fly ash - offers a potential "green" solution. However, because it is still relatively new and has some disadvantages, there are still many questions that need to be answered. Most research to date has consisted only of the evaluation of the strength and durability of HVFA concrete mixtures, while only a limited number of studies have implemented …

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Thermal Field Investigations And Applications To Integral Abutment Bridges With Frp Panels, Bo Kong Jan 2012

Thermal Field Investigations And Applications To Integral Abutment Bridges With Frp Panels, Bo Kong

LSU Doctoral Dissertations

Expansion joints are often considered as one of the most vulnerable elements affecting the sustainability of traditional jointed bridges. Over the past several decades, a new type of integral abutment bridge (IAB) has been proposed, where the joints are eliminated at the abutments and/or along the length of the bridges. Although with wide acceptances, the IABs have not been largely applied in practice. Many arguments are unsettled and there are no national design guidelines currently. Among all, the thermal behavior is one of the most concerned issues, and that, to a large extent, limits the maximum length of IABs that …

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Thermal Stress Analysis Of Jointed Plain Concrete Pavements Containing Fly Ash And Slag, Yoonseok Chung Jan 2012

Thermal Stress Analysis Of Jointed Plain Concrete Pavements Containing Fly Ash And Slag, Yoonseok Chung

LSU Doctoral Dissertations

With the current demand for Portland cement concrete (PCC) sustainability, supplementary cementitious materials (SCMs) are used in concrete mixtures. The SCMs positively impact the environmental and economic aspects of concrete mixtures and improve the mixture properties in both fresh and hardened concrete. In this research, one control and twenty-four ternary mixtures, with various combinations of fly ashes (Class C and F), slags (Grade 100 and 120), and Portland cement were fabricated. The thermal properties (coefficient of thermal expansion (CTE), thermal conductivity, and heat capacity) and mechanical properties of the selected ternary mixtures were measured at various ages. Temperature gradients were …

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Global And Local Performance Of Prestressed Girder Bridges With Positive Moment Continuity Detail, Tanvir Hossain Jan 2012

Global And Local Performance Of Prestressed Girder Bridges With Positive Moment Continuity Detail, Tanvir Hossain

LSU Doctoral Dissertations

Global as well as local behavior of prestressed girder bridges made continuous by adding continuity diaphragms with a recently proposed positive moment continuity detail were investigated in this study. The focus of the investigation is on the positive moment caused by temperature gradients, time dependent effects such as creep and shrinkage, and some live load positions, and on the force transfer mechanisms through the diaphragm. The study utilized different approaches including analytical models for temperature evaluations and finite element models for structural assessments. Field data from a bridge using the new detail were used to validate the developed models. The …

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Synthesis And Characterization Of Geopolymers For Infrastructural Applications, Jian He Jan 2012

Synthesis And Characterization Of Geopolymers For Infrastructural Applications, Jian He

LSU Doctoral Dissertations

In this study, the synthesis process, composition, and microstructure as well as mechanical properties of geopolymers generated by 3 different kinds of raw materials (i.e., metakaolin, mixture of red mud and fly ash, mixture of red mud and rice husk ash) was explored. For geopolymers from identical raw materials, variable parameters involved in the synthesis were examined to investigate the extent and degree of geopolymerization. Uniaxial compression testing was used to examine the mechanical properties (i.e. compressive strength, stiffness, and failure strain). Then the composition and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well …

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Continuum And Crystal Strain Gradient Plasticity With Energetic And Dissipative Length Scales, Danial Faghihi Shahrestani Jan 2012

Continuum And Crystal Strain Gradient Plasticity With Energetic And Dissipative Length Scales, Danial Faghihi Shahrestani

LSU Doctoral Dissertations

This work, standing as an attempt to understand and mathematically model the small scale materials thermal and mechanical responses by the aid of Materials Science fundamentals, Continuum Solid Mechanics, Misro-scale experimental observations, and Numerical methods. Since conventional continuum plasticity and heat transfer theories, based on the local thermodynamic equilibrium, do not account for the microstructural characteristics of materials, they cannot be used to adequately address the observed mechanical and thermal response of the micro-scale metallic structures. Some of these cases, which are considered in this dissertation, include the dependency of thin films strength on the width of the sample and …

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Dynamic Route Choice In Hurricane Evacuation, Meisam Akbarzadeh Jan 2012

Dynamic Route Choice In Hurricane Evacuation, Meisam Akbarzadeh

LSU Doctoral Dissertations

In this research a framework is developed for modeling route choice in hurricane evacuation. Two behavioral hypotheses are evaluated which together with the route choice model, constitute the contributions of the research. The first hypothesis states that beside congestion, other variables such as familiarity with the route, availability of fuel and shelter, facility class, and length of route have an effect on an evacuees' route choice. The second hypothesis states that as time passes and storm conditions change, the impact each variable has on route choice changes. The logit structure was used for modeling the choice process and stated choice …

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Blast And Impact Resistance Of "Long" Carbon Fiber Reinforced Concrete, Darwin Ishmael Keener Jan 2012

Blast And Impact Resistance Of "Long" Carbon Fiber Reinforced Concrete, Darwin Ishmael Keener

Masters Theses

"Traditional reinforced concrete is one of the most commonly used materials for protective structures. However, conventional reinforced concrete (RC) is susceptible to significant spalling (small to medium sized chunks of concrete detaching from the original member) during blast events. The force of the blast turns spalled concrete into projectiles, resulting in secondary fragmentation. Furthermore, the concrete debris makes for difficult and uncertain footing. Both phenomena endanger personnel and complicate post-blast recovery efforts. Changes need to be made to conventional reinforced concrete structures to improve their blast and impact survivability and fragmentation resistance in order to protect personnel and facilitate post-blast …

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Development Of Hydrograph-Based Approach To Modeling Fate And Transport Of Sediment-Borne Bacteria In Lowland Rivers, Bhuban Ghimire Jan 2012

Development Of Hydrograph-Based Approach To Modeling Fate And Transport Of Sediment-Borne Bacteria In Lowland Rivers, Bhuban Ghimire

LSU Doctoral Dissertations

Fecal pollution is one of the major factors responsible for water quality impairments of rivers and streams, particularly organic-rich fine-grained lowland streams. While predicting fecal pollution is generally required in the development of water quality restoration plans like Total Maximum Daily Loads, no single model has been widely recognized as an efficient and effective tool for estimating fecal pollution. This dissertation develops a simple yet effective modeling approach, called Hydrograph-based Approach, to bacterial fate and transport modeling in lowland rivers. The new hydrograph-based approach is simple and efficient in terms of its less data requirements as compared with other models. …

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Fatigue Performance Of Existing Bridges Under Dynamic Loads From Winds And Vehicles, Wei Zhang Jan 2012

Fatigue Performance Of Existing Bridges Under Dynamic Loads From Winds And Vehicles, Wei Zhang

LSU Doctoral Dissertations

During the life cycle of bridges, varied amplitude of stress ranges on structural details are induced by the random traffic and wind loads. The progressive deteriorated road surface conditions might accelerate the fatigue damage accumulations. Micro-cracks in structural details might be initiated. An effective structural modeling scheme and a reasonable fatigue damage accumulation rule are essential for stress range acquisitions and fatigue life estimation. The present research targets at the development of a fatigue life and reliability prediction methodology for existing steel bridges under real wind and traffic environment with the capability of including multiple random parameters and variables in …

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Field Investigation Of Wave And Surge Attenuation In Salt Marsh Vegetation And Wave Climate In A Shallow Estuary, Ranjit S. Jadhav Jan 2012

Field Investigation Of Wave And Surge Attenuation In Salt Marsh Vegetation And Wave Climate In A Shallow Estuary, Ranjit S. Jadhav

LSU Doctoral Dissertations

This research investigates and quantifies the effectiveness of salt marsh vegetation in reducing storm-induced waves and surge, and the potential for wetland erosion due to wave action, using field measurements on the Louisiana coast. To quantify wave attenuation and wave energy dissipation by vegetation (Spartina alterniflora), wave data were measured along a transect using pressure transducers during two tropical storms. Measurements showed that incident waves attenuated exponentially over the vegetation. The linear spatial wave height reduction rate increased from 1.5% to 4% /m as incident wave height decreased. The bulk drag coefficient estimated from the field measurements decreased with increasing …

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