考虑非平稳因素的混凝土桥梁概率极限状态评估

PROBABILISTIC LIMIT STATE ASSESSMENT OF CONCRETE BRIDGES CONSIDERING NON-STATIONARY FACTORS

为建立混凝土桥梁构件的概率极限状态评估方法,借助等超概率原则分析我国在役桥梁构件评估周期及评估基准期,引入个体风险准则、社会风险准则、生命质量指标及成本优化方法确定构件运营阶段目标可靠指标,分别考虑非平稳及平稳概率模型进行荷载效应及抗力评估值确定,基于可靠度理论开展运营阶段评估分项系数校准,并以一座在役桥梁为例进行算例分析。结果发现:考虑我国在役桥梁运维实际情况,构件评估周期、评估基准期可分别取为6年、10年;对于一级、二级、三级延性破坏构件,评估目标可靠指标分别建议为3.37、3.13及2.85;采用一般运行状态或密集运行状态下平稳车辆荷载效应模型进行评估时,评估标准值可分别取为设计汽车荷载效应的0.705倍及0.805倍,考虑非平稳车载过程进行评估时,可在连续非平稳过程离散化的基础上,引入动态广义极值模型确定评估基准期内荷载效应最大值分布,并以0.95分位值作为评估标准值;对于重要性等级为一级的延性构件,恒载效应及抗力评估分项系数分别建议为1.056与1.194,一般运行状态与密集运行状态汽车荷载效应评估分项系数建议值分别为1.081与1.054,研究成果可为现行桥梁构件安全评估方法修订提供参考。

To develop a probabilistic limit state assessment method for concrete bridge components,a probabilistic transformation principle was introduced to analyze the rating period and rating reference period.The individual risk criterion,social risk criterion,life quality index and cost optimization principle were employed to determine the target reliability index in an operation stage.Both non-stationary and stationary probabilistic models were considered to derive the rating values of load effect and resistance.In addition,the reliability theory was adopted to conduct the calibration of partial factors and an existing bridge was used to complete a case study.The results show that the rating period and rating reference period can be taken as 6 years and 10 years,respectively,considering the actual bridge maintenance conditions.For the ductile components with safety level I,II,and III,the target reliability index of safety assessment is suggested as 3.37,3.13 and 2.85,respectively.When the stationary-probabilistic-vehicle load effect models of a general operating state and an intensive operating state are employed,the characteristic value of safety assessment can be taken as 0.705 and 0.805 times of design vehicle load effect,respectively.When the non-stationarity of vehicle load process is considered in the safety assessment,the extreme value distribution within a rating reference period can be modeled by a generalized extreme value distribution based on the discretization of continuous stochastic process,and the corresponding 0.95 fractile can be adopted.For the ductile component of safety level I,the partial factors of dead load effect and resistance are proposed as 1.056 and 1.194,respectively,and the partial factors of vehicle load effect corresponding with general operating state and intensive operating state are proposed as 1.081 and 1.054,respectively.The achievements mentioned above can be referenced for the adjustments of the current safety assessment method of existing bridge component specified in the standard.