| Among great quantity of highway bridges built in China in recent 20 years,there are increasing damaging or aging bridges because of increasing of traffic and vehicle load as well as natural aging of bridge structure itself. However,the money that can be used to repair these bridges is far lower than the needed money since China is still a developing country and the money is limited. Therefore,how rationally to allocate and use the limited money in order to ensure running smoothly of highway and safety of bridges and how to carry out economic analysis and optimization in bridge maintenance decision are urgent problems with which Chinese bridge field must be faced. For economic analysis and optimization in bridge maintenance decision,there are lots of researches and achievements home and overseas for many years.However,theoretic study on economic analysis and optimization in bridge maintenance decision is still a primary and fundamental stage because of such research involving in multi-field knowledge such as bridge engineering,economics,computer technology and optimization technology,complex of bridge structure itself and lack of deep comprehension for various uncertainties during total lifetime of bridges. Based on such background,the theory and methods of life-cycle economic analysis and optimization in bridge maintenance decision are studied in this paper.The frame of a basic theory on life-cycle economic analysis and optimization in bridge maintenance decision is constructed. The frame is firstly presented in homeland and overseas according to literature indexing. The established models and the presented formulae and analysis methods in the paper are far more simple and efficient than those foreigners have been adopting in maintenance analysis. The theoretic frame built in the paper is a new exploring and attempt and will facilitate development in this aspect of study. It includes main contents and innovative achievements as follows:1. Various linear and non linear deterioration models for concrete bridge structuers are presented and simple and unified computing formulae of these models are given. Combined with Chinese standards,values of parameters of linear deterioration models of bridge reliability and estimated condition state are given. There are many categories of bridge structure and different bridge structures have different deterioration models. The deterioration models built in the paper provide more selection for different deterioration modes'matching rational deterioration models. Accurate prediction of bridge deterioration is a basis of bridge maintenance optimization.2. Multi-categories effect models of bridge maintenance are built and simple and unified index computing formulae of these models are given. Maintenance effect produced from various bridge maintenance actions varies with each other. Therefore,to establish various deterioration effect models is a foundation of maintenance effect analysis and optimization. The maintenance effect models established in the paper are simple and rational for the presented validity functions are used. By help of these models,it is easy to carry out life-cycle economic analysis and optimization in bridge maintenance decision.3. Bridge deterioration models with preventive maintenance are built for concrete bridge structuers. Establishment of indexes computing formulae of various combining cases between different maintenance modes and different deterioration modes without preventive maintenance provides a base for life-cycle economic analysis and multi-objective optimization in bridge maintenance decision.4. A method of economic analysis on bridge maintenance is presented. Some economic indexes used in comparison,assessment and optimization of bridge maintenance strategies are given by means of a presented rational profit method. Computing formulae of dynamic maintenance cost are built according to economics. For investment decision in economics,there are mature methods to assess different investment strategies. There are four main optimization goals in bridge maintenance. They are maintenance cost,bridge life,bridge condition state and bridge reliability. They restrain and influence one another and need to be planed as a whole. Through rational profit method,bridge life,bridge condition state and bridge reliability are converted into profit in the paper. This makes it possible to carry out life-cycle economic analysis and optimization for bridge maintenance strategies in a new and more rational method and to transplant more conceptions and methods from economics to bridge maintenance optimization.5. Basic and combining optimization methods of bridge maintenance are presented. Methods of basic optimization of preventive maintenance are presented through establishment of computing formulae of some parameters such as first essential maintenance time,preventive maintenance times and maintenance effect indexes and computing examples of these formulae. Lumping and overlapping combining optimization methods for bridge maintenance are presented. Indexes computing formulae and optimization steps of the two methods are given and their maintenance effect parameters are calculated through examples. Combining optimization methods between an essential maintenance and one or two preventive maintenance are presented. Indexes computing formulae and optimization examples of these methods are given , respectively. Synchronal consideration of essential and preventive maintenance helps those who neglect preventive maintenance traditionally to drop such a traditional idea. At the same time,this lets the built theoretic frame more complete and practical.6. Based on the above achievements,a program,called as BMOP,of life-cycle economic analysis and optimization in bridge maintenance decision is researched and developed. Combined with actual maintenance actions,examples of application of life-cycle economic analysis and optimization in bridge maintenance decision by using this program are given and this shows applicability and signification of the constructed theoretic frame.
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