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Title: A BAYESIAN UPDATING APPROACH IN STRUCTURAL HEALTH MONITORING FOR DAMAGE DETECTION AND ASSESSMENT
Creator: Dirbaz, Mojtaba
Date: 2013, 2013-05
Description: The primary goal of Bridge Condition Assessment (BCA) is to determine the condition of a bridge to prevent any catastrophic failure as well as...
Show moreThe primary goal of Bridge Condition Assessment (BCA) is to determine the condition of a bridge to prevent any catastrophic failure as well as to enhance the structure’s safety and serviceability. The structural health and condition of in-service bridges is generally assessed through visual inspections and nondestructive testing and evaluation (NDT/NDE) methods conducted on a pre-set schedule. However, the ratings obtained from current visual inspections on a bridge are subjective, and do not include the uncertainty inherent in the results. Moreover, the condition ratings are often based on independent inspections and do not take into account the dependence of results on previous conditions of a bridge and prior condition ratings compiled for it. Furthermore, there is also a certain level of uncertainty involved in relating subjective ratings to the actual condition of the bridge. This study is aimed at conducting a research on damage detection of existing bridges utilizing available information on their structural conditions. The first part of the research focuses on a new method for assessing the condition of a bridge based on subjective ratings obtained for the bridge. This method will hereafter be referred to as Bayesian Bridge Condition Assessment (BBCA). BBCA consists of three parts: (1) identification of condition states for structural components, (2) determination of a Damage Index (DI), a parameter to describe the extent of damage to a structural component, and (3) determination of an Updated Damage Index (UDI) using Bayesian updating approach. UDI offers an enhanced measure that incorporates not only the relation between subjective rating and the structure’s health condition, but also the significance of new information as it becomes available. The basic assumptions and x general formulations of the Bayesian updating method is presented. Numerical illustrations are provided to demonstrate the applicability of the method to highway bridges. It is shown that the method described in this study is especially applicable to bridges for which visual inspection data are compiled on a periodic basis. One of the methodologies for damage detection and assessment is to use sensor data for identifying the modal characteristics of the structure. The second part of this research focuses on improving upon damage detection methods using sensor and/or modal data. Thus a new method for damage detection and assessment of structures using finite element analysis, and modal data is developed and demonstrated. This method will hereafter be referred to as Bayesian Structural Condition Assessment (BSCA). Using this method, (1) a Finite Element (FE) design model of the structure (undamaged) is constructed; (2) the measured modal data is updated using a Bayesian framework; and (3) the FE model of existing structure (with possibility of damage) is obtained using updated modal data based on an iterative optimization method that is used in estimating the stiffness of the damaged structure. Using these steps, the location and extent of any possible damage is then determined based on the difference between a structural element stiffness for the “as built condition” and “damaged condition.” Several numerical illustrations are presented to demonstrate the capability of the method to detect the location and extent of the damage. This method has been applied to a structural health monitoring benchmark problem; and it has been shown that it can identify the location and extent of damage with more accuracy than most other existing models. Keywords: Bayesian Updating, Condition Assessment of Structures, Modal Data, Visual Inspections, Finite Element Model, Bridges
PH.D in Structural Engineering, May 2013
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Title: NEW DIRECTIONS IN POST-EARTHQUAKE FIRE HAZARD ANALYSIS WITH APPLICATIONS TO MIDWESTERN UNITED STATES
Creator: Farshadmanesh, Pegah
Date: 2017, 2017-05
Description: Post-earthquake fire ignition (PEFI) can lead to severe structural damage following an earthquake. Estimating the risk of such ignitions in...
Show morePost-earthquake fire ignition (PEFI) can lead to severe structural damage following an earthquake. Estimating the risk of such ignitions in buildings and identifying methods to abate it are essential steps in an overall effort to mitigate the impact of post-earthquake fires in urban areas. While several models have been developed for areas with available historical PEFI data, such as the Western United States, no such models have been developed for areas with little or no data specific for post-earthquake fires. Examples of such areas are seismic regions in the Midwestern United States. The lack of PEFI data for these areas is due to the fact that at the time of several significant earthquakes in the early nineteenth century, most earthquake-stricken communities where rural. With the growth of urban areas in the region, a need exists for a methodology that can be effectively used in estimating PEFI risks when no or little historical data is available. In this research, it was found that models for PEFI risk estimation may indeed be developed using available data on ignitions for normal conditions as a basis and then using some type of a modification factor to account for the significance of future earthquakes. This modification factor depends on the characteristics of the region in terms of seismic activities and the type and distribution of buildings and their potential in promoting ignitions. The term “normal condition ignition” (NCI) refers to an ignition that occurs due to everyday activities and routine operations in a building. In a residential building, such activities include, for example, operating heating units and burners, cooking, and mechanical malfunction of appliances. In this research, it was found that four factors specifically affect PEFI risk and can be used to develop models for risk estimation. These are (1) spatial characteristics such as geographic concentration of particular building types; (2) ignitability characteristics, such as the sources of ignitions in a particular building type, (3) earthquake characteristics (such as the peak ground acceleration); and (4) temporal characteristics, such as the time of the earthquake and seasonality. Accordingly, models for estimating the risk of post-earthquake fire ignition occurrence are developed. These models are tested, and the model parameters calibrated, using information in areas for which both the NCI and PEFI data are available (such as in the Western United States). To illustrate the applicability of the models developed and proposed in this study, St. Louis City is considered. This constitutes a major urban area vulnerable to potential future seismic activities because of proximity to the New Madrid Fault Zone. Using the NCI data for this area, PEFI risk values are estimated based on probable future seismic activities in the region. The results are presented in terms of estimated annual risk of post-earthquake fires for the area specifically for residential buildings (such as single or multifamily dwellings). The study further discusses the significance of PEFI models, their limitations and also provides suggestions for the future continuation of the research.
Ph.D. in Civil Engineering, May 2017
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Title: MECHANISMS OF FOAMING, EFFECTS, PREVENTION, AND CONTROL IN ANAEROBIC DIGESTION
Creator: Subramanian, Bhargavi
Date: 2015, 2015-05
Description: Anaerobic digestion (AD) is an essential step to generate energy in the form of biogas from waste. Foaming during AD (AD foaming) is...
Show moreAnaerobic digestion (AD) is an essential step to generate energy in the form of biogas from waste. Foaming during AD (AD foaming) is widespread phenomenon and leads to deterioration of the AD process and operation. In extreme conditions, AD foaming poses a significant safety risk and considerable economic impacts. It is, therefore, necessary to understand the fundamentals of AD foaming to develop effective strategies that can help minimize and prevent the foaming impacts. Several aspects of AD foaming have attracted considerable research attention, however, the focus has been mainly on site specific causes and prevention. The work leading to this thesis was aimed to provide a better understanding of the AD foaming problem, to identify the underlying mechanisms, causes and contributors of foaming and to come up with foam management strategies for full-scale plants. Full-scale cylindrical digester investigations did not identify non-biological factors such as organic loading rate (OLR), mixing, and primary to waste activated sludge (PS:WAS) solids ratio as primary causes of foaming, but foam-causing filaments such as G. amarae and M. parvicella were determined to be primary causes. No foaming was observed over the duration of the study, indicating absence of a primary foaming cause even though the suspected contributors to AD foaming were present. In the case of full-scale egg-shaped digesters (ESD), foaming and foam collapse events were observed over the duration of the study over both during filamentous foaming and non-foaming seasons, indicating that the primary foaming cause requires the contributors to be present. The results of this study demonstrate that ESDs foamed due to high mixing and G. amarae counts above the threshold level (log #6 intersections/mg VSS) in mixed liquor. In both types of digesters, total solids and temperature profiles showed that reducing mixing frequency did not significantly impact digester performance or the homogeneity of the digester contents. Hence, mixing intensity optimization could be an effective strategy in addition to primary cause reduction of foam causing filaments.
Ph.D. in Environmental Engineering, May 2015
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Title: A STRUCTURAL ANALYSIS FRAMEWORK FOR CONCRETE FACED ROCKFILL DAMS
Creator: Quiroz, Juan E.
Date: 2013, 2013-12
Description: Concrete Faced Rockfill Dams (CFRD’s) are commonly built around the world. As energy demands soar and construction methods evolve, the...
Show moreConcrete Faced Rockfill Dams (CFRD’s) are commonly built around the world. As energy demands soar and construction methods evolve, the interest for construction of CFRD’s with larger heights has increased tremendously. However, because of construction of higher CFRD’s, some dams have experienced considerable fractures at the concrete faces. Well known cases include Campos Novos (Brazil), Barra Grande (Brazil), and Mohale (South Africa), where in some instances these cracks have led to dewatering of the reservoir to allow for the concrete slabs repairs. The development of these fractures may be attributed to the highly deformable rockfill body. In general, the state-of-the-art design of CFRD’s is mostly based on common practice rather than rigorous analysis procedures. And as such, cracking problems because of deformability of the rockfill may not be properly predicted unless a detailed analysis is performed. In this work, a new framework for analysis of CFRD’s is developed that is capable of predicting the possible concrete-facing failure. As a part of this framework, a comprehensive non-linear finite element analysis (FEA) scheme is developed to model the construction sequence, the contact interaction between the concrete facing and the rockfill body, and the impounding of the reservoir. As a case study, using the developed framework, the Kárahnjúkar CFRD (Iceland, 198m height) is analyzed, the results are validated by the field measurements, and mitigation measures suggestions are provided. This methodology, based on the results of the investigation, provides guidelines and establishes a framework for analysis of CFRD’s that can be used for design purposes.. Keywords: CFRD, Concrete Faced, Rockfill, Dam, Finite Element Analysis.
PH.D in Structural Engineering, December 2013
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Title: SYSTEMWIDE INTERSECTION SIGNAL TIMING OPTIMIZATION SIMULTANEOUSLY MINIMIZING VEHICLE AND PEDESTRIAN DELAYS
Creator: Roshandeh, Arash Moradkhani
Date: 2013, 2013-07
Description: The ever-growing traffic volume especially in urban areas stretches the transportation system to be operated at near or exceeding capacity and...
Show moreThe ever-growing traffic volume especially in urban areas stretches the transportation system to be operated at near or exceeding capacity and causes congestion. Expanding system capacity and effectively utilizing available capacity could help reduce traffic congestion. In most of cases, adding extra travel lanes in dense urban street networks is not feasible any more due to land scarcity. This study introduces a new method for signal timing optimization that is carried out by adjusting green splits of AM peak, PM peak, and rest of the day timing plans for each signalized intersection in the network without changing the existing cycle lengths and signal coordination to minimize total vehicle and pedestrian delays per cycle. The proposed method contains a basic model that handles vehicle delays only and an enhanced model that simultaneously addresses vehicle and pedestrian delays using two different pedestrian delay estimation methods. Both models are incorporated into an agent-based regional travel demand forecasting tool for detailed traffic assignments using data on Chicago regional travel demand, traffic counts, geometric designs, and signal timing plans for major intersections in the Chicago Central Business District (CBD) street network. The computational experiment reveals that vehicle delays in the CBD area could reduce by 10 percent when only considering vehicle delays and 5 percent when simultaneously considering vehicle and pedestrian delays for signal timing optimization. Considering the intersections safety analysis, it has been found that signals timing optimization in all four areas combined without considering pedestrian delays decreased different crash types under various severities for multiple vehicle collisions as well as vehicle-pedestrian ones. Taking care of both vehicles and pedestrians delay xvi vii simultaneously, using HCM method, just a very few situations represent slight increases in crash frequencies and all other cases indicate crash reductions. Compared with the sensitivity analysis results using the HCM method for calculating pedestrian delays in the enhanced model applications, the Levinson method produces different results even though crash frequency reduction trends are almost the same as HCM method results.
PH.D in Civil Engineering, July 2013
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Title: PROJECT SCHEDULING USING OPTIMIZED FINANCING
Creator: Alavipour, Seyyed Mohammadreza
Date: 2017, 2017-07
Description: Contractors need financing throughout a project, mainly due to retainage, which is the money that the owner withholds to make sure that the...
Show moreContractors need financing throughout a project, mainly due to retainage, which is the money that the owner withholds to make sure that the project is performed properly by the contractor. Even if an owner does not withhold retainage, financing is still necessary because the periodic payments made by the owner are usually delayed. All pertinent studies conducted so far have considered only one source of financing without any consideration of different sources and types of financing, times of cash provisions, interest rates, and repayment options. Actually, if one assumes a predetermined credit limit and one source of financing, as past researchers have done, the optimal financing cost and the schedule that satisfies all constraints may be different than when several sources of financing and undetermined credit limit are considered. The main objective of this research is to focus on the optimization of financing cost by developing a financing optimization model based on different financing alternatives. Far lower financing cost and higher profit are obtained by using the proposed model compared to all models developed in past research. The research is conducted in four stages of development. In Stage 1, a financing optimization model is developed for a schedule that uses normal (not accelerated) activities, and early activity start and finish times. This model can be used before the contract is signed to offer the lower bid or can be used after the contract is signed to obtain higher profit. In Stage 2, the time-cost tradeoff algorithm is added to the model developed in Stage 1, considering accelerated activities between the crash and normal durations. In Stage 3, the model developed in Stage 2 is augmented by considering variable activity start times. Finally, in Stage 4, the model developed in Stage 3 is further improved by expanding time-cost tradeoff to allow for time extensions beyond the contract duration. All models developed in these four stages provide not only minimum financing cost, but also the ideal work schedule that achieves minimum total cost and maximum profit. Moreover, these models provide specific timings for borrowing and repaying funds.
Ph.D. in Civil Engineering, July 2017
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Title: ADVANCING KNOWLEDGE OF INDOOR AEROSOL SOURCES, FATE, TRANSPORT, AND CONTROL
Creator: Azimi, Parham
Date: 2016, 2016-12
Description: Recent evidence suggests that particulate matter (of both indoor and outdoor origin) is one of the most important airborne pollutants driving...
Show moreRecent evidence suggests that particulate matter (of both indoor and outdoor origin) is one of the most important airborne pollutants driving adverse health effects worldwide. Despite our understanding of major indoor aerosol sources that contribute to adverse health effects across the population, gaps in our knowledge of some aspects of the sources, fate, transport, and control of indoor aerosols still remain. This dissertation focuses on filling three major gaps related to indoor aerosols. The first objective of this dissertation is to improve knowledge of the impacts of particle filtration in central heating, ventilation, and air-conditioning (HVAC) systems on fine particles smaller than 2.5 μm in diameter (i.e., PM2.5) and ultrafine particles smaller than 100 nm in diameter (i.e., UFPs) of outdoor origin that penetrate into the indoor environment. Results demonstrate that higher-efficiency HVAC filters can significantly reduce indoor proportions of outdoor PM2.5 and UFPs inside residences, but home vintage, climate zone, and ventilation strategy strongly influence the outcomes due to widely varying air exchange rates, HVAC system runtimes, and sources of ventilation air. The second objective of this dissertation is to improve knowledge of emissions and control of particulate matter from a recently established source of indoor pollutants: desktop three-dimensional (3D) printers. Median estimates of time-varying UFP emission rates ranged from ~108 to ~1011 #/min across all tested combinations, varying primarily by filament material and, to a lesser extent, bed temperature. It was also shown that UFP concentrations within close or moderate proximity to some desktop 3D printer and filament combinations can exceed recommended exposure levels. The most effective control strategies for reducing pollutant concentrations emitted from desktop 3D printers wereinstalling a high-flow spot ventilation system and operating the printer in a sealed enclosure with high efficiency gas and particle filtration. Finally, the third objective of this dissertation is to improve knowledge of the fate, transport, and control of infectious diseases in indoor environments through mathematical modeling of bioaerosol transmission and infection risk. Results demonstrate that Recirculating HVAC filtration can achieve risk reductions at lower costs of operation than equivalent levels of outdoor air ventilation, particularly for MERV 13-16 filters. It was also shown that in addition to the biological characteristics of respiratory pathogens, human activities, interzonal airflows, and physical properties of bioaerosols can substantially impact the infection transmission risk. Further, the dominant pathway for influenza transmission indoors under most conditions was airborne transmission. Finally, estimations of the back-calculated quanta generation rate for influenza viruses were directly in line with the existing data gathered from prior epidemiology studies.
Ph.D. in Environmental Engineering, December 2016
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Title: ASSESSMENT OF STRUCTURAL MATERIALS BY HIGH TEMPERATURE INSTRUMENTED INDENTATION
Creator: Gan, Bin
Date: 2012-12-03, 2012-12
Description: This is an ideal place for me to express my gratefulness to my Ph.D. advisor, Prof. Sammy Tin, who has offered me the financial support and...
Show moreThis is an ideal place for me to express my gratefulness to my Ph.D. advisor, Prof. Sammy Tin, who has offered me the financial support and tremendous freedom in doing research. From working with me through publications and thesis, mentoring me what constitutes a professional and high quality work, nurturing my patience, to giving me advice on how to deliver an insightful presentation, Prof. Tin puts his effort in helping me on every small step that I need to make, as I gradually become more experienced in research and start to make a few achievement along the way. I am deeply indebted to Prof. Tin’s vision, guidance and sustained support. I would like to thank Prof. Philip Nash, Prof. Sheldon Mostovoy and Prof. Sudhakar Nair for being the committee member of my thesis defense, and offering me so many invaluable suggestions. The indispensable help from Russ Janota, the faculty and staff in the MMAE department is acknowledged. The enjoyable interaction with Mengtao, Qizheng, Matt, and other TPTC friends helps me in various aspects. I would like to thank Dr. Hideyuki Murakami and Dr. Takahito Ohmura for hosting me in NIMS. The experience had broadened my horizon and tremendously enhanced my capabilities to conduct independent research. In addition, the research collaboration with Prof. Julia R. Greer and Dr. Robert Maass on freestanding Ni3Al nanoparticles is also fully acknowledged. Furthermore, I am grateful to Prof. Qiang Feng and Prof. Roman Nowak. Their constant support, encouragement, mentoring and nurturing have a profound influence on me. This thesis is dedicated to my beloved parents, Jinlong Gan and Yuxiang Lai, who have built the fortitude into my mind. I also thank my sisters, Liping Gan and Lihong Gan, for their sustained support. Their love and understanding enable me to have a peaceful mind that makes this study possible. I also feel grateful to the deep love and endless patience from Xiaomo Li and the support from her parents.
PH.D in Materials Science and Engineering, December 2012
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Title: SEISMIC COLLAPSE EVALUATION OF NON-DUCTILE CONCENTRICALLY BRACED FRAMES
Creator: Wen, Rou
Date: 2012-11-21, 2012-12
Description: More attentions have been paid on the Non-Ductile Concentrically Braced Frames (ND-CBFs) in low and moderate seismicity regions recently due...
Show moreMore attentions have been paid on the Non-Ductile Concentrically Braced Frames (ND-CBFs) in low and moderate seismicity regions recently due to their low ductility detailing requirements for design and construction. In this work, seismic collapse performances of two ND-CBFs are studied. One 3-story and one 9-story ND-CBF using small response modification coefficients (R=3) are designed firstly. Nonlinear finite element technologies are used to study the behaviors of local components. Practical analytical models for brace/gusset-plate assemblies and steel gravity frames are developed based on finite element simulations and engineering judgment. Three 2D structural models having increased local modeling complexity are developed for each braced frame. Nonlinear static pushover analyses on 3-story frames are conducted to get basic understandings of the damage evolution patterns and the interactions between main brittle braced frames and the steel gravity frames. Nonlinear dynamic analyses references the concepts of Incremental Dynamic Analysis are followed to investigate the seismic collapse responses of studied frames. The seismic assessments referenced the evaluation methods in FEMA P695 for ductile seismic load resisting frames through incremental dynamic analysis are carried out. Studied results show that Non-Ductile Concentrically Braced Frames would have little chance to prevent building collapse under severe ground motions. However, it seems that such buildings at least with low-to-moderate heights would have high probability of collapse prevention for up to moderate ground motions with conventional gravity framing systems used in modern steel buildings.
PH.D in Civil Engineering, December 2012
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