基于路径概率的桥梁全寿命成本计算方法及例证

Calculation Method and Illustration for Bridge Life-cycle Cost Based on Path Probability

为解决传统桥梁全寿命设计方法在工程实践中遇到的设计概念模糊、计算方法不明确及与相关规范脱节的不足,以提高公共安全与交通舒适度,降低建造和运营综合成本,提出了基于路径概率并与可靠度结合的混凝土桥梁全寿命成本计算方法。首先,在深入研究桥梁全寿命设计的基础上,依据调研所得桥梁管养投入实际数据,拟合了不同服役地区不同桥梁等级的检测成本计算公式,以及不同公路等级不同养修成本的养修成本取值区间,以此构建了桥梁全寿命成本计算基准。其次,以钢筋在氯离子侵蚀和碳化耦合作用下的锈胀开裂模型为基础,采用路径概率方法构建了桥梁全寿命养修概率模型。然后,通过蒙特卡洛法进行求解,并将养修方案、养修成本通过可靠度指标联系起来,结合规范中关于正常使用极限状态指标的相关规定,提出基于可靠度的全寿命成本计算方法。最后,采用所提方法计算了不同桥梁设计方案在设计使用寿命期内的养修概率,综合建造成本、检测成本和养修成本估算全寿命成本及其对应的可靠度。结果表明:不同可靠度指标的取值对设计方案的全寿命成本有显著影响,随着可靠度指标的提高不同设计方案的经济性均出现先上升后下降的趋势。因此,设计过程目标可靠度的取值不宜过大,可通过一个较低的可靠度指标,适当放宽耐久性设计准入,以允许桥梁在使用过程出现一定的耐久性问题,并通过后续养修进行矫正,这样对于全寿命成本而言,更具有经济性。

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.