Browsing by Author "Chen, Suren, advisor"
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Item Open Access Dynamic analysis and fatigue assessment of bridge decks subjected to traffic and corrosion effects(Colorado State University. Libraries, 2013) Salem, Abdalmaged, author; Chen, Suren, advisor; Mahmoud, Hussam, committee member; Ozbek, Mehmet Egemen, committee memberFatigue damage has become one of the most common degradation mechanisms of highway bridge decks, which is primarily caused by passing traffic. The increase of heavy traffic over recent years, especially those overweight trucks, further worsens the situation. In the mean time, highway bridges are subjected to various aggressive environmental conditions leading to serious corrosion problems. Corrosion problem, faced by millions of reinforced concrete structures worldwide, can cause deterioration of the reinforcing steel bars, cracks and spalling on the bridge deck surface. As the bridge deck surface deteriorates over time, the road surface roughness profile will vary accordingly. The varying surface roughness profiles over time will generate increased dynamic loads on the bridge decks through dynamic interaction between surface roughness, vehicles of stochastic traffic and bridge structures. The increased dynamic loads, coupled by the reinforcement deterioration of bridge deck due to corrosion, will further cause accelerated response and fatigue accumulations on the bridge deck. Such a nonlinear time-progressive process continues over time throughout the lifespan of the bridge deck, which has not been systematically characterized or studied. The present study aims to characterize the coupling effects between the time-varying dynamic loads from stochastic traffic, deterioration bridge decks due to corrosion, and bridge performance. To tackle such a problem, firstly, a hybrid FEM-based analytical strategy is developed for the bridge and stochastic traffic system considering the time-dependent corrosion process. Secondly, scenario-based numerical studies are conducted for the typical combinations of traffic, corrosion-induced reinforcement deterioration and associated surface profile variations. Finally, based on the numerical findings, the fatigue damage of the bridge deck over time is analyzed and the remaining life of the prototype bridge decks is assessed under the joint effect of corrosion and stochastic traffic.Item Open Access Dynamic assessment of the long-span cable-stayed bridge and traffic system subjected to multiple hazards(Colorado State University. Libraries, 2016) Zhou, Yufen, author; Chen, Suren, advisor; Ellingwood, Bruce R., committee member; Mahmoud, Hussam N., committee member; Sakurai, Hiroshi, committee memberCritical infrastructure systems, such as long-span bridges, offer the underlying foundation for many aspects of modern society, such as national security, quality of life and economy. Although the total number of long-span bridges is relatively small compared to short-span and medium-span bridges, long-span bridges often serve as backbones for critical interstate transportation corridors and also evacuation routes. Any traffic disruption due to bridge damage, failure, retrofitting or even major traffic accidents following some hazards can become disastrous to local community and emergency response efforts, underscoring the importance of the continued integrity, functionality and resilience following hazardous conditions. Wind and traffic are the major service loads for long-span bridges. The extreme loads may include those caused by various natural or man-made hazards, such as earthquake, hazardous winds (hurricane, tornado), fire, blast, vehicle and barge collision etc. Compared to other hazards, hazardous wind and earthquake are particularly critical for long-span bridges, primarily due to their significant threats to the global structure performance and challenges of appropriately modeling the dynamic coupling effects between the bridge, traffic and hazards. In addition, there is another disastrous event: cable loss, which is very unique and critical for cable-supported bridges and could be caused by various natural and man-made hazards. There exist major challenges in the current state of the art on rationally predicting the long-span bridge performance subjected to multiple service and extreme loads. These challenges include realistic load characterization, methodological limitations and considerations of uncertainties. A suite of holistic analytical frameworks of long-span cable-stayed bridges subjected to various service and hazardous loads are developed, with which insightful numerical analyses of the bridge performance subjected to these loads are carried out in this dissertation. Firstly, two general dynamic assessment frameworks are developed based on the mode superposition and finite element methods respectively for a long-span cable-stayed bridge and traffic system subjected to multiple threats, such as stochastic traffic, wind and some hazardous loads. Although developed based on a long-span cable-stayed bridge, the frameworks can be readily applied to long-span suspension bridges as well as bridges with shorter spans. In both simulation platforms, the bridge model and all individual moving vehicles in the stochastic traffic flow are directly coupled under multiple excitations from bridge deck roughness and other external dynamic loads. Through the established simulation platforms, the global dynamic responses of the bridge and each individual vehicle subjected to various service and extreme loads can be rationally predicted in the time domain. Secondly, built on the proposed general simulation platforms, a novel dynamic safety assessment model and a vehicle ride comfort evaluation model for the bridge-traffic system are further developed. Thirdly, also extended from the proposed simulation platforms, both deterministic and reliability-based assessment frameworks for long-span cable-stayed bridges subjected to breakage of stay cables are established by considering more rational service load conditions as well as cable-breakage characterizations. Lastly, in addition to the in-house programs focusing on research purposes, a hybrid simulation strategy for the bridge under traffic and seismic excitations and a time-progressive simulation methodology for cable breakage events are also developed by taking advantage of the strength offered by commercial finite element software, e.g., SAP2000. These SAP2000-based strategies are expected to facilitate design engineers to more easily understand and conduct the related analyses in future engineering practices.Item Open Access Investigating overturning high sided vehicles through modeling high Reynolds number incompressible flow around a rectangular cylinder near a plane wall boundary(Colorado State University. Libraries, 2023) Sanchez, Daniel K., author; Venayagamoorthy, S. Karan, advisor; Chen, Suren, advisor; Olsen, Daniel, committee memberSafety on public roadways is of paramount importance to road users, road authorities, the local economy, and the general wellbeing of society. High sided vehicles (commonly known as semitrucks in the United States (US) or lorries in the European Union (EU)) are used throughout the world for transporting freight, but they are susceptible to roll-over accidents due to high crosswind. The overturning of high sided vehicles is of concern during extreme wind events. In Boulder, Colorado, it is estimated that eight high wind events (with gusts greater than 75 mph) occur every year. The research field of overturning high sided vehicles is young compared to other areas of knowledge since CJ Baker of the United Kingdom (UK) opened the research field in 1986. The traditional method applied for evaluating the likelihood of a high sided vehicle to overturn is to use the predetermined rolling moment coefficient (Crolling) and translate the wind speed into a rolling moment. The resulting rolling moment can be compared to the restoring moment to determine the force required to overturn the high sided vehicle. This methodology requires that Crolling be accurate with respect to the high sided vehicle being analyzed. A recent study conglomerated many papers that have investigated Crolling, showing wide variation in the expected Crolling for yaw angles between 45° and 90° (a direct crosswind). Through this thesis, it was discovered that some of the variation is due to the fact that Crolling is Reynolds number dependent. In this thesis a comprehensive verification analysis and validation of a computational fluid dynamics (CFD) model was completed. Verification and validation are key components to performing a quality CFD analysis. When referring to verification, this traditionally implies a grid independence study to ensure the CFD results are accurate with respect to the mesh sizing. However, this study explores why a comprehensive verification study is necessary to evaluate the influence of the flow domain size for high Reynolds number incompressible flow around a bluff body. Additionally, it was found for flow around a rectangular cylinder near a plane wall boundary with a gap ratio of 0.407, that the drag coefficient (Cdrag) is dependent on Reynolds number. This fundamental field was connected to the application of overturning high sided vehicles, with the assumption that a 2D rectangular cylinder could represent the trailer section of a high sided vehicle. It was found that traditional studies on overturning high sided vehicles assume the aerodynamic coefficients are Reynolds number independent, whereas the fundamental field shows that there is a Reynolds number dependence. It is apparent that additional work on determining Crolling is needed due to the Reynolds number dependency.Item Open Access Modeling and improving urban human mobility in disaster scenarios(Colorado State University. Libraries, 2020) Zou, Qiling, author; Chen, Suren, advisor; Heyliger, Paul, committee member; van de Lindt, John W., committee member; Chong, Edwin K. P., committee memberNatural and human-made disasters, such as earthquake, tsunami, fire, and terrorist attack, can disrupt the normal daily mobility patterns, posing severe risks to human lives and resulting in tremendous economic losses. Recent disaster events show that insufficient consideration of human mobility behavior may lead to erroneous, ineffective, and costly disaster mitigation and recovery decisions for critical infrastructure, and then the same tragedies may reoccur when facing future disasters. The objective of this dissertation is to develop advanced modeling and decision-making methodologies to investigate the urban human mobility in disaster scenarios. It is expected that the proposed methodologies in this dissertation will help stakeholders and researchers gain a better understanding of emergency human behavior, evaluate the performance of disrupted infrastructure, and devise effective safety management and resilience enhancement strategies. Focusing on the two important mobility modes (i.e., walking and driving) in urban environment, this dissertation (1) develops agent-based crowd simulation models to evaluate the crowd dynamics in complex subway station environment and investigate the interplay among emotion contagion, information diffusion, decision-making process, and egress behavior under a toxic gas incident; (2) develops functionality modeling, interdependency characterization, and decision models to assess and enhance the resilience of transportation networks subject to hazards.Item Open Access Multi-scale traffic performance modeling of transportation systems subjected to multiple hazards(Colorado State University. Libraries, 2019) Hou, Guangyang, author; Chen, Suren, advisor; van de Lindt, John, committee member; Atadero, Rebecca, committee member; Trumbo, Craig, committee memberTransportation systems are very vulnerable to natural or manmade hazards, such as earthquakes, floods, hurricanes, tsunamis, terrorism, etc. In the past years, extreme hazards have caused significant physical and functional damages to transportation systems around the world. Disruption of transportation systems by multiple hazards will impede social and commercial activities, and hamper the post-disaster emergency response and long-term recovery of the damaged community. The main purpose of this dissertation is to develop advanced performance assessment techniques of transportation systems subjected to multiple hazards in the link level and network level. It is expected that the developed techniques in this dissertation will help stakeholders to make risk-informed decisions in terms of effective prevention and preparation measures to enhance and facilitate resilience of transportation systems. A suite of simulation methodologies are developed to evaluate the performance of critical transportation components (e.g. bridges and road segments) and transportation networks subjected to multiple hazards in this dissertation. Firstly, an advanced traffic flow simulation framework is developed to predict the post-hazard performance of a typical highway system under hazardous conditions. Secondly, a simulation methodology is developed to study the traffic performance of degraded road links being partially blocked following extreme events. Thirdly, a new approach is proposed to develop travel time functions of partially blocked roads in urban areas through microscopic traffic simulation. Fourthly, an integrated model is developed to assess single-vehicle traffic safety performance of stochastic traffic flow under hazardous driving conditions. Finally, an integrated probabilistic methodology is developed to model the performance of disrupted infrastructures due to fallen urban trees subjected to extreme winds.Item Open Access Multi-scale urban transportation resilience modeling and adaptive intersection intervention with disruptions(Colorado State University. Libraries, 2023) Yao, Kaisen, author; Chen, Suren, advisor; Heyliger, Paul, committee member; Atadero, Rebecca, committee member; Bradley, Thomas, committee memberGlobal urbanization has triggered increasing demands on modern transportation infrastructure systems by the growing density of population and intensity of human activities in the cities. A great challenge has emerged in recent decades in terms of making urban communities more resilient against physical, social, and economic disruptions. As the backbones of urban communities, road networks are expected to provide essential functionality under various disruptions caused by different extreme events and incidents, such as natural hazards, pandemics, and crashes. In response to the existing challenges, this dissertation research aims to develop multi-scale urban transportation resilience modeling techniques and adaptive intersection intervention strategy against disruptions under hazards. Specifically, this dissertation will (1) identify the appropriate simulation platform for microscopic traffic analysis and intervention under hazardous and disrupted scenarios; (2) develop microscopic flow-based and graph-based urban traffic network modeling techniques under typical disruptions; (3) propose resilience-based performance indexes in both global network and local scales of disrupted traffic systems; (4) develop new traffic speed forecasting techniques considering data disruptions using deep learning technology to offer robust traffic performance forecasting during hazards; and (5) finally establish time-progressive traffic resilience forecasting strategy during hazardous weather to support proactive intervention.Item Open Access Refined-scale crash data analysis using multi-level regression models(Colorado State University. Libraries, 2016) Ma, Xiaoxiang, author; Chen, Suren, advisor; Arabi, Mazdak, committee member; Grigg, Neil S., committee member; Wang, Haonan, committee memberRoad traffic safety has long been a major public health problem for the general public and government agencies. Nevertheless, road traffic crashes continue to bring immeasurable pain and suffering to the society, as well as high financial expenses associated with medical bills and lost productivity. After identifying some key research gaps related to the existing crash modeling such as lack of insightful modeling of crash rates, time-varying explanatory variables, serial correlation, unobserved heterogeneity and multiple dependent variables, the objective of this dissertation is to narrow these gaps by systematically developing advanced multilevel models for traffic safety modeling. It is expected that series of new crash models developed in this dissertation not only contribute to the state-of-the-art crash modeling, but also add to the knowledge toward developing proactive traffic management strategy. The dissertation has eight chapters: Chapter one provides some background information and literature review. Chapter two presents crash rate analysis with data in refined scales to quantify the relation between crash rate and time-varying variables along with other contributing factors. In Chapter three, the unobserved heterogeneity issue on mountainous highways crash rates is examined by developing an advanced random parameter tobit model with panel data in refined temporal scale. Chapter four proposes a correlated random parameter marginalized two-part model as an alternative to study the relationship between crash rate and its contributing factors. Chapter five examines the differences of contributing factors towards injury severity on mountainous (MN) and non-mountainous (NM) highway crashes using mixed logit models. Chapter six studies the effects of weather and traffic characteristics on single-vehicle and multi-vehicle crashes jointly by proposing a multivariate count data model which addresses unobserved heterogeneity across multiple dependent variables. In Chapter seven, a framework of Bayesian multivariate space-time model that can address spatial correlation/heterogeneity, temporal correlation/heterogeneity, and the correlation between different injury severities is introduced. Chapter eight concludes this dissertation by summarizing major findings and sharing some observations in terms of future research.Item Open Access Reliability-based safety evaluation of traffic on rural highway(Colorado State University. Libraries, 2011) Chen, Feng, author; Chen, Suren, advisor; van de Lindt, John W., committee member; Bienkiewicz, Bogusz J., committee member; Sakurai, Hiroshi, committee memberIn the United States as well as other developed countries, road accidents are causing more injuries and casualties than any other natural or man-made hazard. Some vehicles, such as trucks, emergency vehicles and SUVs, often experience increasing risks of single-vehicle accidents under hazardous driving conditions, such as inclement weather and/or complicated topographical conditions. The objective of this research is to establish a reliability-based framework to evaluate the traffic safety through taking account of more realistic adverse driving conditions, such as wind gust, snow-covered or icy road surface, and/or curving. After some background information is introduced in Chapter 1, Chapter 2 covers the development of a mobile mapping technology aiming at collecting site-specific as well as vehicle-specific wind velocity data for traffic safety evaluations. In Chapter 3, an advanced simulation-based single-vehicle accident assessment model considering the coupling effects between vehicles and hazardous driving conditions is developed. In Chapter 4, ten-year accident data involving trucks on rural highway from the Highway Safety Information System (HSIS) is studied to investigate the injury severity of truck drivers by using mixed logit models. Based on the advanced transient dynamic vehicle simulation model, the general framework of a reliability-based assessment model of vehicle safety under adverse driving conditions is finally developed in Chapter 5. In Chapter 6, a case study of I-70 in Colorado to evaluate the traffic safety and operational performance of large trucks is conducted. The integrate study includes individual vehicles for single-vehicle accident risk assessment and the whole traffic on the highway for multi-vehicle accident risk assessment and operational performance evaluation. Finally, conclusions are summarized in Chapter 7.Item Open Access 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 Seismic performance of skewed and curved RC bridges(Colorado State University. Libraries, 2013) Wilson, Thomas, author; Chen, Suren, advisor; Mahmoud, Hussam, advisor; Strong, Kelly, committee member; Johnson, Joshua, committee memberExplicit knowledge of the behavioral response of complex reinforced concrete (RC) highway bridges to seismic events is essential to designing safe transportation systems. In the past, a number of skewed and curved highway bridges have experienced damage or suffered collapse due to earthquakes; and have most recently been observed during the Chile earthquake in 2010. Yet, there is very limited information on the combined effects of skew and curvature on the seismic response of RC bridges, and in particular identifying critical vulnerabilities to localized failures or system collapse. Recent research has also shown that the vertical component of earthquake ground motion, previously not considered, may have significant bearing on the response of highway bridges, particularly in near-fault regions. This study is comprised of two parts, including an examination of skewed and curved RC bridges of various configurations representative of a low seismic region, and an evaluation of the effect of vertical ground motion on complex geometry bridges in a moderate, near-fault, seismic region. Detailed numerical models are developed for various configurations of skew and curvature, and subjected to earthquake ground motion using nonlinear time-history analysis. In part one, detailed finite element models are developed and analyzed for eight bridge configurations of various degrees of skew and curvature, with consistent structural and geometric components. The bridge designs and earthquake hazard level are characteristic of the Mountain West region where the seismic risk is typically classified as low to moderate. Nonlinear time-history analysis is conducted on each bridge configuration for seven sets of earthquake records scaled to a site location in Denver, Colorado. The effects of earthquake input loading direction and abutment support condition, including integral and bearing supports, are also considered. The results show significant impacts on the seismic performance due to the effects of skew and curvature with stacking effects observed in the combined geometries. Insights on the complexities of curvature, skew, loading direction and support condition are made, which may lend themselves to more informed design decisions in the future. Part two of this study presents an assessment of the effect of vertical ground motion on horizontally skewed and curved highway bridges in moderate-to-high seismic regions. A numerical model of a skewed and curved, three-span bridge located in Tacoma, Washington is subjected to a suite of ground motions using non-linear time-history analysis. The ground motions selected represent a range of near-fault records with varying characteristics such as site condition, fault distance, and vertical-to-horizontal acceleration component ratios. The scenario developed characterizes the behavior of a bridge with a short fundamental period of vibration in a moderate seismic zone, where vertical ground motion effects may be applicable yet not considered by structural code. The results of the numerical simulations depict a significant impact from vertical ground motion in the substructure and superstructure, including responses typically not documented in existing studies. The implications of the results for structural designers may be to reconsider the current design approach involving vertical ground motion, particularly with shorter period bridges involving configurations of skew and curvature.