The continuous operation of civil and marine structures is essential for maintaining the flow of people and goods. However, structures are exposed to extreme or progressive events during their service time. The uncertainties associated with the occurrence and the magnitude of extreme events (e.g. flooding and scour) may change, leading to unprecedented loading conditions, while the progressive events (e.g. corrosion and fatigue) may jeopardize the structural capacity to resist loads. In order to maintain or improve the structural capacity, repair and maintenance actions need to be applied to structures. However, the determination of these actions may be challenging for decision makers due to (a) limited financial resources to be allocated for a group of structures, (b) uncertainties associated with current structure conditions and future loading conditions, and (c) various decision-making factors (e.g. reliability threshold, decision time, and risk attitude). In order to address these issues, the focus of the research in this dissertation is to enhance the development of management strategies with the application in (a) management of bridge networks under hydraulic events and climate changes, (b) service life extension of ships considering financial feasibility and decision-making factors, and (c) determination of reliability threshold in the decision-making process. The management of bridge networks involves the quantification of regional hazards imposed on the network, performance assessment of structures, and consequence evaluation of potential bridge failure. Regional hazards such as floods may be affected by the changes in the intensity of precipitation due to anticipated climate changes. These hazards may cause extensive damage to bridges, and failure may cause significant costs to bridge managers and result in inconvenience on the daily traffic commute. This research focuses on enhancing the assessment and management of bridges networks vulnerable to regional hydraulic events and climate changes. The integration of transportation network analysis, which reflects the redistribution of traffic flow in the event of bridge failure, is shown to be essential when determining the risk level of bridges. Furthermore, this work includes proposed methodologies for determining optimal management strategies that account for the connection between global climate predictions and regional hydrologic conditions. The crux of determining management strategies, especially for extending ship service lives, is to ensure an adequate safety margin within and beyond the design life. In addition to the loading effect and structural capacity, the safety margin of ships is related to the deterioration acting on the structure. During ship operation, in-service condition surveys are conducted on ship details to assess structural conditions and to inform maintenance actions. This research focuses on the integration of condition surveys of ship details, as well as the timing of conducting surveys, to improve the service life extension for ship structures. While decision makers strive to maintain the safe operation of ships, they should also identify the management strategy that can deliver the best return given the limited budget. This research, from the perspective of cost-effectiveness and profitability, proposes optimization frameworks to clarify the financially feasible life expectancy of different management strategies as well as identify the optimal duration of extended service life for different categories of commercial ships. The last focus of this research emanates from the reliability threshold when determining management strategies. In addition to facilitating decision-making on the management of civil and marine structures, the reliability threshold in terms of target reliability index has been extensively used in design guidelines to ensure adequate safety margin for structures. The level of safety is typically related to the failure mode and severity of failure consequences (e.g. number of potential fatalities). Driven by the emerging application of unmanned ships where there are fewer or no crew members on board, this research specifically focuses on the integration of different acceptance criteria for human safety into the determination of the target reliability index.
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:28156457 |
| Date | 01 January 2021 |
| Creators | Liu, Liang |
| Publisher | Lehigh University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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