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评估费用与精度的关系是评价在役混凝土桥梁结构耐久性评估是否满足要求的关键所在。以在役混凝土桥梁结构耐久性三层次多指标评估模型为基础,研究了分层随机抽样理论在耐久性评估中的应用问题。探讨了评估费用、评估精度与样本量之间的关系,给出了总样本量及其在各层的最优分配计算公式,以及等级评分值的置信区间。同时分析比较了最优分配与比例分配和指定分配法的优劣。实际工程应用表明:基于最优分配的分层随机抽样法,能够在评估费用与评估精度之间取得较满意的结果。对于精度要求不高的工程,可采用比例分配或指定分配。
The relationship between cost and accuracy is the key to assessing whether the durability assessment of in-service concrete bridge structures meets the requirements. Based on the three-level multi-index assessment model of durability of existing concrete bridges, the application of stratified random sampling theory in durability assessment is studied. The relationship between evaluation cost, evaluation accuracy and sample size was discussed. The total sample size, its optimal distribution formula at each level, and the confidence interval of rating score were given. At the same time, the advantages and disadvantages of optimal distribution and proportional distribution and designated distribution method are analyzed and compared. The practical engineering application shows that the stratified random sampling method based on optimal distribution can achieve more satisfactory results between the evaluation cost and the evaluation accuracy. For less demanding projects, the proportion can be allocated or assigned.