运营的既有桥梁结构需要定期进行承载力评估，基于概率可靠度的承载力评估是较为理想的方法，但这种方法需要大量的数据作为评估依据。从概率统计学的参数估计出发，推导均值已知和均值未知时的均值和方差置信区间。利用区间分析方法，计算概率可靠度指标的置信区间，进而估算由于抽样误差引起的概率可靠度指标的计算误差。结合桥梁结构的目标可靠度指标及既有桥梁分类的依据，用数值计算的方法分析常规条件下的概率可靠度指标置信区间。结果表明：在数据量较少的情况下，可靠度指标计算的置信区间范围过大，极易导致对桥梁评估的误判或漏判。提出一种既有结构桥梁分类的可能度方法，用可能度度量既有桥梁结构的可靠度具有更加丰富的信息，并且评估结果更客观，便于桥梁养护者进行合理决策。

Periodic assessments of the bearing capacity of operational existing bridge structures are deemed necessary. Probability-based reliability assessment is regarded as an ideal approach for this purpose, although it requires substantial data for thorough evaluation. Commencing from parameter estimation in probability statistics, derived confidence intervals for mean and variance when the mean was either known or unknown. By employing interval analysis methods, confidence intervals of probability reliability indicators were computed, thereby estimating calculation errors in probability reliability indicators due to sampling errors. Through the integration of target reliability indicators of bridge structures and classification criteria for existing bridges, numerical methods were employed to analyze confidence intervals of probability reliability indicators under conventional conditions. The results show that with a limited dataset, the confidence interval range for reliability indicators becomes excessively large, potentially leading to misjudgments or omissions in bridge assessments. A method was proposed for classifying existing structural bridges based on possibility, which assessed the reliability of existing bridge structures with more comprehensive information and produces more objective assessment results, thereby facilitating rational decision-making for bridge maintainers.