Life-Cycle Based Bridge Design Process With Its Application In Concrete Continuous Bridges

Traditional bridge design methodology which considers the condition of completing the construction of bridges and the construction management system are the key factors of the durability problems of current bridges and being unable to achieve design life of bridges. With the move towards sustainable development comes the need for this approach to be expanded to encompass the life cycle of bridges. Based on the concept of life cycle from planning, design, construction and management of service phase to demolishment and recycling of materials and components, a comprehensive approach focusing on design methodology and methods of life-cycle based bridge design is developed in the dissertation, in which the general framework, procedure and corresponding design methods etc., for life-cycle based bridge design are included. In details, the following aspects are investigated:1. Life-cycle based bridge design can be composed of six processes: service life design, aesthetics design, performance design, design for environment and ecology, design for inspection, maintenance and repair, life cycle cost analysis. Starting from owners', social and users' needs and requirements, a general framework and a design procedure of life-cycle based bridge design are presented to provide the guides for the design of new bridges and the assessment and management of existing bridges after analyzing the tasks and design methods of six processes.2. Based on the analysis of the factors influencing service life of a bridge, the rules for end of bridge lifetime including unsafe, obsolete and uneconomical are proposed. According to the targets of design life of modern bridge, a life-cycle based general policy for bridge service life design is established. Moreover, three strategies including Strategy A, i.e. total avoiding the deterioration mechanisms, Strategy B, i.e. selecting intelligently an appropriate number and types of co-operating measures and Strategy C, i.e. maintain, repair and replace and their combination to ensure design life of bridges.3. Bridges system is divided into various levels including bridge, technical systems, modules, components, details and materials. According to the number of maintenance, repair and replacement in the life cycle of a bridge, the components are fallen into permanent components, common-maintained components, little-maintained or replaced components and vulnerable components to define their service life on the basis of design life of bridges. Accordingly, the combination of different design strategies and methods are suggested.4. Starting from the environmental exposure in the site, according to the exposure to environmental attack, the relation between the severity of attack on durability and required protection level are developed to provide the basis for the adoption of appropriate strategies for durability design and measures. Moreover, the procedure for durability design based on the assessment of the severity of attack on durability and required protection level from environmental exposure and the assessment and modification of durability design from the analyze of degradation.5. After analyzing the targets and the sequence involved to establish the strategy for inspection, maintenance and repair, the principle for inspection, maintenance and repair are defined. Accordingly, life-cycle cost based the strategy for inspection, maintenance and repair of a bridge is developed. Starting from the analysis of the needs of inspection, maintenance and repair of a bridge, a design procedure of design for inspection, maintenance and repair of a bridge is developed through the analysis of the effect of maintenance and repair on structural performance to attain the application time, interval and corresponding cost of inspection, maintenance and repair action.6. Based on the analysis of the main content of aesthetics design, the evaluation rules and their evaluation index of aesthetics design of a bridge are proposed. Subsequently, constitutes of life cycle cost related to bridge aesthetics design are analyzed. According to above analysis, a design procedure of bridge aesthetics design is developed.7. The concept and main contents of design for environment and ecology is defined on the basis of the comparison between design for environment and ecology and traditional bridge design. The new method which carry out design for energy economy and design for environmental improvement through environmental survey, the analysis of environmental impact and the calculation of the environmental burdens. Based on the analysis of the principle of reusing and recycling for bridges, the methods for design for reusing and recycling are proposed from the points of materials and components. The evaluation indexes are presented based on the concept, assessment rule and main contents of life cycle assessment. The environmental costs and environmental impacts are analyzed and their compute methods are developed. Finally, according to above analysis, a design procedure of design for environment and ecology is developed.8. It is proposed that bridge life cycle cost is composed of life cycle financial cost and life cycle environmental cost after the analysis of the constitutes of life cycle cost related to bridge life cycle design and the methods and formulas to calculate them are also established. Based on the requirement of analysis during various stages, three levels of models for life cycle cost analysis are developed. According to the general framework above, a procedure of bridge life cycle cost analysis are presented. A multi-object optimization method which takes account of five objects including minimizing life cycle financial cost, minimizing life cycle environmental cost, maximizing service life, maximizing target performance (safety) level, optimizing aesthetics performance.9. Aiming at the characteristic of concrete continuous bridge, the analysis programs are developed to carry out life-cycle based design of concrete continuous bridge on the basis of above design processes and corresponding design methods. The application of life-cycle based design process in the concrete continuous bridge and analysis programs are demonstrated through a design example of a 5-span concrete continuous bridge.