Research On Multi-objective Bridge Preservation Decision-making Method Based On Improved Technical Condition Evaluation

The highway bridges with the characteristics of long service period in hostile environment inevitably have become declined as long as they begin on service.As the material aging and bridge technical condition getting worse with time,the whole bridge would be a potential and huge risk.Therefore,it is an urgent problem to be solved by using positive risk prevention technique and reasonable utilization of limit preservation fund for ensuring the safety and durability of bridge.The main contents and achievements of this research are shown as the follows in detail.(1)Improving the scheme of classification of bridge types or elements and the corresponding indexes.According to the ambiguous classification problem for specific bridge or elements,the 21 types of bridges are explicitly spread out as well as the distinct and clear classification methods for their elements.This scheme includes almost 99% types of bridges all over the country,which avoid the misjudgment of bridge and elements with self-defined type.According to the problem of current standard with incomplete defects types,the quantitative indexes including the defect indexes of durability and structure for element technical condition has been proposed in this dissertation.The indexes include much part of the missed defect types,in which avoid the data mess caused by self-defined defect type.The qualitative indexes including functional status,capability status,working status and also risk status.It helps to inspect and evaluate the relation between elements or structures,and safety of bridges.(2)Improving the evaluation method of bridge technical condition.Based on the above scheme mentioned in part1,the AHP and Delphi methods are used to classify the evaluation of element level(EL)into 5 levels,it provides a basis for element-based bridge preservation.The proposed method divide evaluated results into bridge condition level(BCL)based on structural safety and bridge condition index(BCI)based on asset management.With the validations of 322 bridge main beams,the results show that the proposed element condition grade is more specific to fine preservation.With the validations of 112 bridges,the results show that the BCL and BCI can represent the structural safety and asset value of bridges.(3)Exploring the prediction method for the main elements technical condition.Considering the deficient of inspection and evaluation data currently,a prediction curve of technical condition for the main elements of bridge had been proposed by using nonlinear regression and statistical methods.The prediction curve of component score for main beam,pier and abutment of concrete bridge is proposed based on the "Standards for Technical Condition Evaluation of Highway Bridges".Based on the improved element condition level proposed in this paper,the level prediction curves are constructed.The prediction curves with upper and lower also are amended,which is affected by heavy load traffic volume(including the traffic volume of large truck,oversize truck and container truck)for the main beam elements which are significantly affected by heavy load traffic in the deterioration process.(4)Establishing the decision-making economic analysis system of network level bridge preservation.By analyzing the economic roots for building strongly and maintaining lightly.The concept of asset characteristics of bridge maintenance is put forward,and the formula of economic benefits generated by bridge maintenance is established.By considering the deficiencies of using life cycle cost analysis on bridge preservation and decision-making.The Life Expectancy Cost analysis method is proposed.It is based on the surplus value and maintenance benefit analysis method of the bridge.On this basis,a bridge maintenance benefit-cost ratio(BCR)model is formed,which provides a theoretical basis for network level bridge preservation decision-making.(5)A multi-objective network level bridge preservation decision-making method is proposed.In view of the problem that most of the existing algorithms used in bridge preservation decision-making are single bridge analysis methods,which cannot effectively support network level bridge.A method based on NSGA-II genetic algorithm is proposed.Firstly,the large scale elements of the network level bridges that need to be maintained are encoded in binary mode by genetic coding method to realize the maintenance group decision model in two-dimensional space.Then,based on the realistic problem that the maintenance cost increases greatly for the optimal bridge performance,the benefit objective function is established to balance the relationship between bridge performance and maintenance cost.Finally,a series of non-inferior optimal solution sets of maintenance countermeasures are obtained according to non-dominated ranking and elite strategy.Therefore,the preservation decisions of network level bridges are realized.The cases analysis show that the algorithm can solve the optimal strategy under different capital conditions,and achieve the effective balance between bridge performance and capital.