火灾时管片可靠度计算及优化研究

Optimization Method on Reliability Calculation and Segment Design under Fire Situation

受火灾高温的影响,隧道衬砌结构可靠性降低。笔者通过自由变形理论,解析计算可靠度优化模型中的结构内力,明确了计算中的随机变量;从结构可靠度指标几何意义出发,基于优化思想确定了可靠度计算公式;考虑火灾下衬砌管片的损伤特点,提出了火灾下管片的功能函数,建立了管片高温下可靠度计算优化模型;最后通过案例分析并利用非线性规划求解优化问题,得到火灾下衬砌可靠度的变化规律,并对管片截面厚度进行了优化设计。研究表明,常规设计管片各处可靠度指标差异较大,隧道拱顶可靠度最低,10 min后失效概率大于0.023,通过优化设计可使火灾持续30 min后满足基本安全。

The reliability of lining structure decreases when influenced by the high temperature of fire accident.Structural forces of the optimization model are obtained based on the free form deformation theory to determine the variables during the calculation. Then,the formula for the reliability index calculation is proposed based on the perspective of the geometrical significance of structure reliability and the optimization method. The performance function of the segment under fire situation is proposed considering the damage characteristics of it. In addition,the optimization model of reliability calculating is established based on the performance function. According to the maximum entropy principle,the method to calculate the statistical parameters of reliability calculating model variable is also proposed. Finally a case study is carried out by solving the optimization problem with nonlinear programming. The regulation of reliability decrease is summarized and the thickness of the lining is also optimized based on the reliability regulation. The result shows there exits great difference of the regularly designed segment reliability among different positions. The minimum reliability occurs at the segment crown where the failure probability is bigger than 0.023 after 10 min. After the optimization design,the new segment could meet the need of basic safety after 30 min of fire.