海洋環境にあるシールドトンネルのライフサイクル信頼性設計と評価

早大学位記番号:新8235早稲田大

Life-Cycle Management of Civil and Marine Structures under Fatigue and Corrosion Effects

Infrastructure systems are under continuous deteriorating effects due to various environmental and mechanical stressors. These effects can be generated by sudden threats such as earthquakes, tornadoes, blast, and fire, or gradual deterioration due to fatigue and corrosion. Moreover, as indicated in the 2013 American Society of Civil Engineers (ASCE) Report Card of America\u27s Infrastructure, the United States\u27 infrastructure systems are highly deteriorating with a required estimated investment of 3.6 trillion USD to improve their condition within the next seven years. Given the limited financial resources, rational methodologies are required to support the optimum budget allocation while maintaining maximum possible safety levels. Uncertainties associated with the performance prediction, damage initiation and propagation, damage detection capabilities, and the effect of maintenance and retrofit on the structural performance add more challenges to this allocation process. In this context, life-cycle engineering provides rational means to optimize budget allocation and manage an infrastructure system starting from the initial design and construction to dismantling and replacing the system at the end of its service life.This study provides novel management methodologies which support the decision-making process for civil and marine large-scale structural systems under fatigue and corrosion deterioration. Multi-objective optimization models that seek the optimal trade-offs between conflicting life-cycle management (LCM) aspects such as the life-cycle cost and the projected service life are proposed. These models provide the optimum intervention schedules (e.g., inspections and maintenance actions) which fulfil the LCM goals. For the first time in the field of life-cycle management, an approach capable of establishing the optimum inspection, monitoring, and repair actions simultaneously is proposed. Maximizing the expected service life, minimizing the total life-cycle cost, minimizing the maintenance delay, and maximizing the probability of damage detection are examples of the considered optimization goals. It is shown that the implementation of optimum solutions resulting from the proposed management plans can significantly reduce the life-cycle cost. A methodology for planning inspection actions for bridges with multiple critical fatigue details is proposed. This is considered a step forward from the traditional approaches which are only capable of considering one critical fatigue detail. Additionally, this study provides methodologies for the reliability-based performance evaluation of structures under fatigue deterioration. Furthermore, rational approaches which make use of structural health monitoring (SHM) and non-destructive inspection information for the near real-time decision making for deteriorating structures are proposed. Specifically, an approach to obtain the fatigue reliability of aluminium high-speed naval vessels based on SHM information is proposed. By using the proposed approach, the effect of individual operational conditions encountered by the ship on the overall fatigue damage accumulation can be quantified. This quantification is not possible by using the traditional fatigue life estimation methods. Probabilistic reliability methods and Monte Carlo simulation are implemented to account for uncertainties associated with different aspects of the LCM process. Existing large-scale structural systems are analysed to demonstrate the feasibility and effectiveness of the proposed methodologies

Study on bridge inspections, A: identifying barriers to new practices and providing strategies for change

2021 Summer.Includes bibliographical references.Bridge 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

Life-cycle structural reliability of concrete bridges considering spatial variability of corrosion and model updating

This paper presents a computational approach to life-cycle structural reliability assessment of concrete bridges under chloride-induced corrosion considering spatial variability of damage and model updating based on the results of diagnostic activities to gather information on material properties and exposure scenario. The proposed approach implements random fields to account for the effects of spatial variability of corrosion and Bayesian inference for model updating. The main steps of the reliability assessment procedure are presented and discussed with emphasis on the application to an existing prestressed concrete box-girder railway bridge

Probability Model of Corrosion-Induced Cracking Time in Chloride-Contaminated Reinforced Concrete

Corrosion-induced concrete cover cracking caused by chloride ion is an important indication of durability limit state for marine reinforced concrete (RC) structures and can ultimately determine the structural service life. In this paper, considering the random nature of factors affecting the corrosion cracking process, a probabilistic model which expands on the deterministic model of cover cracking time is developed by using Monte Carlo simulation technique. The results showed that the time to corrosion cracking can be modelled by the Weibull distribution. Finally, the probabilistic analysis for the cracking time is applied to an in-site RC bridge girder with four different durability design specifications. It is found that the mean and 90% confidence interval of the cover cracking time will increase with the improvement of durability design level, which means that the difficulty in precise prediction with deterministic model will augment accordingly

Prediction of Corrosion-Induced Crack Width of Corroded Reinforced Concrete Structures

This paper presents an experimental investigation on the crack width induced by the corrosion of reinforcing steel bars in concrete. Reinforcing steel bars with different diameters were corroded using an accelerated test in three types of concrete members, including 24 beams with corroded stirrup and 20 beams with corroded longitudinal reinforcing steel bars. The corrosion patterns and rusts characteristics of the corroded steel bars were examined and compared with those observed in real RC structures. According to the experimental result, the corrosioninduced crack width were analyzed and showed a linear relationship with the corrosion loss of reinforcing steel bar. Finally, an analytical prediction model of crack width was established after considering concrete cover depth and corrosion penetration depth

Health monitoring in proactive reliability management of deteriorating concrete bridges

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Lifetime performance prediction of reinforced concrete structures in multi-threat areas

Reinforced concrete (RC) structures are usually subjected to various natural hazards and environmental stressors during their lifetime. Over the time, structures are continuously aging and rapidly deteriorating in their lifecycle, becoming increasingly vulnerable to catastrophic failures after natural or manmade hazards. Corrosion of steel reinforcement has been identified as one of the major causes of deterioration in reinforced concrete structures. Chloride ingress is the dominant mechanism for initiation of deterioration in coastal regions or areas with high exposure to deicing salts. The chloride-induced crack initiation stage in deterioration process, which defines the end of functional service life for corroded RC structures has been investigated in this study. Crack initiation is governed by the expansion of corrosion products. It was found that crack initiation time is significantly affected by rate of corrosion, thickness of interfacial transmission zone (ITZ), composition of corrosion products, and mechanism of corrosion. Other factors which can also influence crack initiation time are the structure’s geometrical parameters such as concrete cover depth, rebar diameter and spacing, as well as the material parameter concrete tensile strength. Different reinforced concrete structural components have been simulated using nonlinear 3-D finite element (FE) models in order to study their lifetime performance under corrosion. The developed FE models are validated with the available experimental tests. All of the corrosion effects on structural behavior of RC structures, such as reduction of steel cross sectional area, change of steel and concrete properties, as well as deterioration of bond has been implemented into the 3-D FE models. The structural performance of corroded RC beams is obtained through FE analysis. The results show that corrosion influences the strength and ductility of a structure at ultimate condition, and may also cause excessive cracking and deflection, which leads to serviceability failure. Moreover, a large number of RC structures that suffer from corrosion mechanisms are located in high seismic risk areas, which leads to the necessity of investigating the combined effects of corrosion and earthquake in order to provide a more reliable prediction for the lifetime performance of RC structures in both corrosive and high seismic risk areas. Therefore, a comprehensive FE framework has been developed to study the structural response of RC columns under earthquake hazards while they are constantly exposed to chloride attack. This framework is capable of including all of the degrading effects due to chloride-induced corrosion and has been validated by a previous set of experimental test results. The extent of structural degradation has been updated as a function of time. Equivalent static analysis and nonlinear time history analysis have been conducted to evaluate the seismic performance of corroded columns at multiple time periods as well as under various hazard levels. The region, type and extent of damage have been identified and damage states has also been defined. Full details of hysteretic loops, frequency changes, as well as cover crack propagation patterns have been obtained through FE analysis. Furthermore, this study has also considered multiple seismic events occurring during the lifetime of RC structures. Detailed FE models that are able to transfer residual damage from previous earthquake to the next earthquake have been proposed. The extent of damage after each earthquake has been quantified. The result of this study shows that the corrosion can dramatically reduce the strength and stiffness of the column. Under severe earthquake, extensive corrosion may result in a brittle failure of the column without the development of concrete cracks. When a critical section of the column experiences a much higher corrosion risk, the seismic performance can be greatly compromised. Such columns could perform much worse than a column undergoing a consistent corrosion rate at a much older age, thus engineers must be alerted to draw special attention to those columns to prevent catastrophic failure during seismic events. The outcome of this research will provide more reliable predictions for the lifetime performance of RC structures, thus help engineers and inspectors improve their designs, identify necessary test regions and define comprehensive inspection plans, as well as optimize rehabilitation strategies for RC structures under multi-threat areas

Inspection of RC half-joint bridges in England: Analysis of current practice

The strategic road network (SRN) in England carries 33% of traffic in England and Highways England's bridge management systems plays a crucial role in the maintenance of infrastructure assets along the SRN. Reinforced concrete half-joint structures are susceptible to deterioration and hard to inspect, hence they require special attention. Inspection data relating to half-joint structures on the SRN was gathered. Within this portfolio, 252 structures with half-joint-related defects were interrogated to classify the most common defects and identify any potential shortcomings in current inspection practice. Clear correlations were shown to exist between defect classes, emphasising the need for quality control and proper workmanship. A revised inspection methodology for half-joint structures that provides more comprehensive information about crack details, and a greater alignment between defect information and indicators of structural measures, is proposed. Concurrently, knowledge of the zonal crack location, crack orientation and crack severity helps inform decision making about the structural condition. There is scope for use of the methodology in conjunction with automated processing procedures to identify half-joint structures with particular defect characteristics and profiles. In this way, asset managers will be better able to allocate resources to structures with an increased risk of failure.The authors would like to acknowledge the financial support of the Engineering and Physical Sciences Research Council (UK) (EPSRC) through the EPSRC Impact Acceleration Account (IAA) Knowledge Transfer Fellowship ‘Impact Acceleration Account – Strategic Roads Network Infrastructure Alliance’

New Model for Bridge Management System (BMS): Bridge Repair Priority Ranking System (BRPRS), Case Based Reasoning for Bridge Deterioration, Cost Optimization, and Preservation Strategy

Most public transportation agencies (Such as, state department of transportations (DOTs) and department of public works for cities and towns.) in the United States are constantly pursuing ways to improve bridge asset management to optimize their use of limited available funds for rehabilitation, replacement, and preventive maintenance. Given the realities of available funding, there is a significant difference between available funds and funds required for maintaining bridges in good condition. The proper preventative maintenance and treatments should be performed at the right time to be cost effective and extend the life of bridges. Neglecting maintenance can cause higher future costs and further deteriorate the conditions that will increase the risk of bridge closure. This would require complete or partial replacement as well as additional funds needed for detours and traffic control which interrupts services to the motorist and creates more congestion. Development and implementation of a Bridge Management System (BMS) provide states and municipalities with a tool to help identify maintenance repair, prioritize bridge rehabilitation and replacement, develop preservation strategies, and allocate available funds accordingly. The primary objective of this research is to develop a Bridge Management System (BMS) to manage municipal and state bridge assets. Complete, accurate data in well-designed form is vital to a Bridge Management System (BMS). This system will make available work reports, engineering drawings, photographs, and a forecasting model for management staff use. Inventory and condition data are extracted from the U.S. Federal Highway Administration (FHWA) and National Bridge Inventory System (NBIS) coding guidelines. The proposed model provides: (1) A priority ranking system for Rehabilitation and Replacement projects, which enables the decision-makers to understand and compare the overall state of all the bridges in the network. It embraces seven factors condition, criticality, risk, functionally, bridge type, age, and size. (2) A deterioration model that uses optimized case-based reasoning (CBR) method. A similarity measure of classification is developed to identify how close the characteristics of bridge components are to each other based on a scoring system. (3) A cost model that considers different repair strategies and provide bridge repair recommendations with estimated cost repairs. (4)The model feeds data to a forecasting program that prepares 120-year preservation, maintenance, repair and rehabilitation budgets and schedules to sustain a bridge network at the highest performance level under approved budgets. The forecasting option contains default management costs that are upgraded as work report data yields costs based on locality and individual bridge projects. BMS will give accessibility through linkages to all available municipal, and DOT, bridge data in the state. The data will be available through ArcGIS on tablets, laptops, and smartphones with access to cloud storage