Browsing by Author "Jia, Gaofeng, committee member"
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Item Open Access A modeling toolkit for comparing AC vs. DC electrical distribution efficiency in buildings(Colorado State University. Libraries, 2021) Othee, Avpreet, author; Cale, James, advisor; Young, Peter, committee member; Herber, Daniel, committee member; Jia, Gaofeng, committee memberAn increasing proportion of electrical devices in residential and commercial buildings operate from direct current (DC) power sources. In addition, distributed power generation systems such as solar photovoltaic (PV) and energy storage natively produce DC power. However, traditional power distribution is based on an alternating current (AC) model. Performing the necessary conversions between AC and DC power to make DC devices compatible with AC distribution results in energy losses. For these reasons, DC distribution may offer energy efficiency advantages in comparison to AC distribution. However, reasonably fast computation and comparison of electrical efficiencies of AC-only, DC-only, and hybrid AC/DC distributions systems is challenging because DC devices are typically (nonlinear) power-electronic converters that produce harmonic content. While detailed time-domain modeling can be used to simulate these harmonics, it is not computationally efficient or practical for many building designers. To address this need, this research describes a toolkit for computation of harmonic spectra and energy efficiency in mixed AC and DC electrical distribution systems, using a Harmonic Power Flow (HPF) methodology. The toolkit includes a library of two-port linear and nonlinear device models which can be used to construct and simulate an electrical distribution system. This dissertation includes a description of the mathematical theory and framework underlying the toolkit, development and fitting of linear and nonlinear device models, software implementation in Modelica, verification of the toolkit with laboratory measurements, and discussion of ongoing and future work to employ the toolkit to a variety of building designs.Item Open Access A study on bridge inspections: identifying barriers to new practices and providing strategies for change(Colorado State University. Libraries, 2021) Abdallah, Abdelrahman M., author; Atadero, Rebecca A., advisor; Ozbek, Mehmet E., advisor; Jia, Gaofeng, committee member; Chai, Dae Seok, committee memberBridge inspections are one of the key elements required for a successful bridge management process to ensure adequate bridge performance. Inspections significantly inform maintenance decisions and can help in managing maintenance activities to achieve a reliable bridge network. In the United States (U.S.) routine visual inspections are required for most bridges at a maximum interval of 24-months regardless of the bridge condition. However, limitations of current bridge inspection practices impact the quality of information provided about bridge condition and the subsequent decisions made based on that information. Accordingly, the overarching goal of this research project is to support bridge inspection practices by providing a systematic and rational framework for bridge inspection planning and identifying the factors that can facilitate innovation and research transfer in the bridge inspection field. To do so, this dissertation includes three separate yet related studies; each focusing on essential aspects of bridge inspection planning. Much research in bridge inspection has been conducted to improve the inspection planning process. The first study provides an overview of current bridge inspection practices in the U.S. and conducts a systematic literature review on innovations in the field of bridge inspection planning to identify research gaps and future needs. This study provides a background on the history of bridge inspection in the U.S., including current bridge inspection practices and their limitations, and analyzes the connections between nondestructive evaluation techniques, deterioration models and bridge inspection management. The primary emphasis of the first study is a thorough analysis of research proposing and investigating different methodologies for inspection planning. Studies were analyzed and categorized into three main types of inspection planning approaches; methods that are based on: reliability, risk analysis, and optimization approaches. This study found that one of the main barriers that may be preventing the implementation of new inspection planning frameworks in practice is that the approaches presented focus on a single bridge element or deterioration mechanism in the decision-making process. Additionally, it was concluded that approaches in the literature are either complex to apply or depend solely on expert judgement. Limitations of the uniform calendar-based approach used to schedule routine inspections have been reported in the literature. Accordingly, the objective of the second study is to provide a new systematic approach for inspection planning that integrates information from bridge condition prediction models, inspection data, and expert opinion using Bayesian analysis to enhance inspection efficiency and maintenance activities. The proposed uncertainty-based inspection framework can help bridge owners avoid unnecessary or delayed inspections and repair actions, determine the inspection method, and consider more than one deterioration process or bridge component during the inspection planning process. The inspection time and method are determined based on the uncertainty and risks associated with the bridge condition. As uncertainty in the bridge condition reaches a defined threshold, an inspection is scheduled utilizing nondestructive techniques to reduce the uncertainty level. The framework was demonstrated on a new and on an existing reinforced concrete bridge deck impacted by corrosion deterioration. The results showed that the framework can reduce the number of inspections compared to conventional scheduling methods, while also reducing the uncertainty regarding the transition in the bridge deck condition and repair time. As identified through the first study, over the last two decades many researchers have focused on providing new ideas to improve conventional bridge inspection practices, however, little guidance is provided for implementing these new research products in practice. This, along with resistance to change and complexity of the proposed ideas, resulted in a lack of consistency and success in applying new technologies in bridge inspection programs across state departments of transportation (DOTs). Accordingly, the third paper presents a qualitative study set out to identify the factors that can help improve research products and accelerate change and research transfer in bridge inspection departments. This study used semi-structured interviews, written interviews, and questionnaires for data collection and engaged with twenty-six bridge staff members from different DOTs. The findings of this study are expected to be both specific to changes in bridge inspection practice and have some generalizability to other significant changes to engineering practice at DOTs. To improve research products, this study suggested that researchers need to collaborate more with DOT staff members and provide relevant research products that are not specific to certain bridge cases and can be applied on different bridges. Also, to facilitate change in transportation organizations, change leaders should focus on showing the need for change, gaining support from the FHWA, allocating the required resources, and enhancing the capacity of DOT staff members through training and effective communication. The investigation also presented participants' opinions on some of the aspects related to conventional inspection practices such as their support of a uniform inspection interval over a variable interval, and the main barriers limiting the use of NDE methods. This study contributes to the body of knowledge in the bridge inspection field by providing a new inspection planning approach that depends on the uncertainty and the risks associated with the bridge condition and uses both computational methods and expert judgment allowing bridge owners select inspection time and method while considering more than one deterioration process or bridge element. In addition, this study presents some of the factors that can help reduce the gap between research and practice and facilitate innovation and change in transportation organizations.Item Open Access Investigation of mechanistic deterioration modeling for bridge design and management(Colorado State University. Libraries, 2017) Nickless, Kyle, author; Atadero, Rebecca, advisor; Jia, Gaofeng, committee member; Shuler, Scott, committee memberThe ongoing deterioration of highway bridges in Colorado dictates that an effective method for allocating limited management resources be developed. In order to predict bridge deterioration in advance, mechanistic models which analyze the physical processes causing deterioration are capable of supplementing purely statistical models and addressing limitations associated with bridge inspection data and statistical methods. A review of existing analytical models in the literature was conducted. Due to its prevalence throughout the state of Colorado and frequent need for repair, corrosion-induced cracking of reinforced concrete (RC) decks was selected as the mode of deterioration for further study. A mechanistic model was developed to predict corrosion and concrete cracking as a function of material and environmental inputs. The model was modified to include the effects of epoxy-coated rebar, waterproofing membranes, asphalt overlays, joint deterioration, and deck maintenance. Probabilistic inputs were applied to simulate inherent randomness associated with deterioration. Model results showed that mechanistic models may be able to address limitations of statistical models and provide a more accurate and precise prediction of bridge degradation in advance. Preventative maintenance may provide longer bridge deck service life with fewer total maintenance actions than current methods. However, experimental study of specific deterioration processes and additional data collection are needed to validate model predictions. Maintenance histories of existing bridges are necessary to predicting bridge deterioration and improving bridge design and management in the future.Item Open Access Optimizing resilience decision-support for natural gas networks under uncertainty(Colorado State University. Libraries, 2019) Ameri, Mohammad Reza, author; van de Lindt, John W., advisor; Chen, Suren, committee member; Jia, Gaofeng, committee member; Shields, Martin, committee memberCommunity resilience in the aftermath of a hazard requires the functionality of complex, interdependent infrastructure systems become operational in a timely manner to support social and economic institutions. In the context of risk management and community resilience, critical decisions should be made not only in the aftermath of a disaster in order to immediately respond to the destructive event and properly repair the damage, but preventive decisions should to be made in order to mitigate the adverse impacts of hazards prior to their occurrence. This involves significant uncertainty about the basic notion of the hazard itself, and usually involves mitigation strategies such as strengthening components or preparing required resources for post-event repairs. In essence, instances of risk management problems that encourage a framework for coupled decisions before and after events include modeling how to allocate resources before the disruptive event so as to maximize the efficiency for their distribution to repair in the aftermath of the event, and how to determine which network components require preventive investments in order to enhance their performance in case of an event. In this dissertation, a methodology is presented for optimal decision making for resilience assessment, seismic risk mitigation, and recovery of natural gas networks, taking into account their interdependency with some of the other systems within the community. In this regard, the natural gas and electric power networks of a virtual community were modeled with enough detail such that it enables assessment of natural gas network supply at the community level. The effect of the industrial makeup of a community on its natural gas recovery following an earthquake, as well as the effect of replacing conventional steel pipes with ductile HDPE pipelines as an effective mitigation strategy against seismic hazard are investigated. In addition, a multi objective optimization framework that integrates probabilistic seismic risk assessment of coupled infrastructure systems and evolutionary algorithms is proposed in order to determine cost-optimal decisions before and after a seismic event, with the objective of making the natural gas network recover more rapidly, and thus the community more resilient. Including bi-directional interdependencies between the natural gas and electric power network, strategic decisions are pursued regarding which distribution pipelines in the gas network should be retrofitted under budget constraints, with the objectives to minimizing the number of people without natural gas in the residential sector and business losses due to the lack of natural gas in non-residential sectors. Monte Carlo Simulation (MCS) is used in order to propagate uncertainties and Probabilistic Seismic Hazard Assessment (PSHA) is adopted in order to capture uncertainties in the seismic hazard with an approach to preserve spatial correlation. A non-dominated sorting genetic algorithm (NSGA-II) approach is utilized to solve the multi-objective optimization problem under study. The results prove the potential of the developed methodology to provide risk-informed decision support, while being able to deal with large-scale, interdependent complex infrastructure considering probabilistic seismic hazard scenarios.Item Embargo Resilience of transportation network during post-earthquake emergency response and recovery stages(Colorado State University. Libraries, 2023) Wu, Yangyang, author; Chen, Suren, advisor; Bradley, Thomas, committee member; Mahmoud, Hussam, committee member; Jia, Gaofeng, committee memberEarthquakes can cause casualty, injuries, and extensive infrastructure damages and significantly disrupt transportation networks. Disrupted transportation networks resulting from damaged bridges or debris may cause delays on emergency response activities and impact traffic efficiency and safety during the post-earthquake recovery stage. A functioning post-hazard transportation network is the backbone to support the effective emergency response and maintain efficient post-hazard recovery plans of the whole community. The main purpose of this dissertation is to model and improve the resilience performance of transportation networks during both post-earthquake emergency response and recovery stages. It is expected that the proposed methodologies in this dissertation will help making risk-informed decisions in terms of pre-hazard mitigation planning, emergency medical service management, and post-earthquake restoration planning to enhance the resilience of transportation networks. A suite of novel methodologies is proposed to evaluate and enhance the resilience performance of transportation networks subjected to major earthquakes in this dissertation. Firstly, a resilience modeling framework of traffic networks is developed to simulate the transportation performance during post-earthquake emergency medical response considering interactions between infrastructures, people, and hazard. Secondly, a new approach is proposed to quantify the comprehensive redundancy of transportation networks during post-earthquake emergency medical response considering search-and-rescue efforts and life vitality decay. Thirdly, a methodology is proposed to evaluate the resilience performance of traffic networks in private-vehicle-based post-earthquake emergency medical response considering bridge failure, building debris, and emergency traffic flow. Fourthly, a novel methodology is proposed to assess the post-earthquake resilience of transportation networks considering link functionality, travel time and traffic safety. Finally, a model to simulate time-dependent resilience of degraded transportation networks during post-hazard recovery period is developed to incorporate the time-evolving travel demand of the community.Item Open Access Shake table testing of hybrid wood shear wall system(Colorado State University. Libraries, 2019) Anandan, Yeshwant Kumar, author; van de Lindt, John, advisor; Jia, Gaofeng, committee member; Chong, Edwin K. P., committee memberCross-Laminated Timber (CLT) is an engineered, prefabricated mass timber product that has shown excellent structural and mechanical properties. With the growing application of CLT in industry, there have been a number of research projects carried out to introduce CLT in tall buildings located in high seismic regions. The concept of post-tensioning mass timber has been adopted from concrete systems and this led to development of seismically resilient structural systems that can undergo multiple earthquake and continue to re-center. This thesis presents the results of a shake table test program that focused on testing of a one-story full-scale hybrid wood shear wall system comprised of a post-tensioned CLT wall panel with Light-frame wood shear (LiFS) wall panels on each side. The testing was conducted at CSU's Engineering Research Center shake table. The objective of this study was to combine the advantages of the post-tensioned CLT systems with those of LiFS walls. The hybrid shear wall system in the testing had two LiFS walls on either side of a post-tensioned rocking CLT wall panel. Mild steel rods were used as post-tensioning rods in this experiment and the test structure also included gravity frames constructed with wood studs (but no sheathing) and a CLT floor diaphragm to support a seismic weight of 12,000 lbs. The structure was subjected to the 1989 Loma Prieta ground motion record scaled to different intensities. The final test used the original 1994 Northridge ground motion record from the Rinaldi record station, with a slight reduction to be able to be accommodated by the 20 inch shake table actuator stroke. This test was conducted to understand the collapse mechanism of the structure and demonstrated the ability of the post-tensioned CLT to re-center the structure after 5% inter-story drifts and also the ability of the LiFS walls to act as energy dissipation and lateral force resisting systems.Item Open Access The effects of design decisions on service life and life cycle cost for a concrete slab in a parking garage(Colorado State University. Libraries, 2017) Badr, Ali, author; Atadero, Rebecca, advisor; Jia, Gaofeng, committee member; Valdes-Vasquez, Rodolfo, committee memberParking garages are unique structures that are useful and common as part of the transportation infrastructure system in the US. Large percentage of these structures is open which expose them to ambient environment and in some cases deleterious chloride exposures. Corrosion of embedded steel is the main cause for concrete deterioration and chloride exposure is one of the major causes for corrosion. Therefore, designing these structures for durability is essential to extend their service life and reduce their degradation status and future repair costs. Improving the durability of these structures can be a costly process at the construction phase that might leave owners of parking garages reluctant about increasing the upfront costs. Therefore, Life-365 software has been used in this study to investigate the service life and life cycle cost impacts of different design decisions throughout the lifetime on a reinforced concrete slab element in a parking garage. Life Cycle Cost Analysis "LCCA" is a process that weights the trade-offs of different phases cost including initial construction and subsequent maintenance and repair throughout the design life period and can help understand the long-term value of additional upfront costs. In Life-365, service life is the sum of two periods: the initiation period and the propagation period while LCC is the sum of three cost phases :the construction phase, the barrier phase and the repair phase which starts at the end of the service life period and extends the remainder of design life. The design decisions or design variables that are investigated in this study include varying the concrete cover distance to the embedded steel, varying the w/cm ratio, using different supplementary cementitious materials, using different barriers and reinforcement types. The geographic location of the parking garage was chosen as Denver, Colorado. Corrosion is likely to occur in this city where harsh environmental conditions are present, including snow falling into parking garages' decks or using deicing salts to melt accumulated snow on roads which can be carried by tires or underneath automobiles. Results of this study showed that using supplementary cementitious materials are the best design variables to consider in terms of saving money for the concrete slab during its design life, besides increasing the concrete cover distance. In addition, a combination of SCMs with a low w/cm ratio has proven to be very effective in terms of reducing costs especially when it is used with higher concrete cover. This study can help designers and owners of these structures in managing and allocating the resources they have more effectively.