Calculation Method and Illustration for Bridge Life-cycle Cost Based on Path Probability
In order to solve the problems of fuzzy design concepts,unclear calculation methods and disconnection with relevant specifications in the engineering practice of traditional bridge life-cycle design methods,to improve public safety and traffic comfort,and to reduce the comprehensive cost of construction and operation,a life-cycle cost calculation method for concrete bridges is proposed based on path probability and combined with reliability.Firstly,based on in-depth research on the life-cycle design of bridges and the actual data on bridge maintenance investment obtained from the survey,a formula for calculating the inspection cost of different bridge grades in different service areas is fitted,as well as the value range of maintenance costs for different highway grades and different maintenance costs.Based on this,a benchmark for calculating the life-cycle cost of bridges is established.Secondly,based on the model of rust expansion and cracking of steel bars under the coupling effect of chloride ion erosion and carbonation,a path probability method is used to construct a bridge life-cycle maintenance probability model.Then,by using the Monte Carlo method to solve the problem,linking the maintenance plan and maintenance costs with reliability indicators,and combining the relevant provisions of the code regarding the normal service limit state indicators,a reliability-based life-cycle cost calculation method is proposed.Finally,the proposed method is used to calculate the maintenance probability of different bridge design schemes during the design service life,and the comprehensive construction cost,inspection cost,maintenance cost and total life-cycle cost are estimated based on the corresponding reliability.The result shows that the value of different reliability indicators has a significant impact on the life-cycle cost of design schemes,as the reliability indicator increases,the economic efficiency of the design scheme shows a trend of first rising and then declining.Therefore,the target reliability value in the design process should not be too large.By using a lower reliability indicator,the threshold for durability design can be appropriately relaxed to allow certain durability problems to occur during the use of the bridge,which can be corrected through subsequent maintenance and repair,that is more economical for life-cycle cost.
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