腐蚀预应力钢绞线疲劳寿命概率模型

考虑腐蚀程度对钢绞线SN曲线斜率及指定应力幅下特征疲劳寿命的影响，将腐蚀程度作为协变量引入表征疲劳寿命的三参数Weibull模型，将疲劳寿命、应力幅及腐蚀程度统一在概率模型中，构建可以定量评价腐蚀影响的钢绞线疲劳寿命多参数Weibull模型。根据模型的物理含义给出参数取值的限制条件，推导模型参数的极大似然估计算法，进一步采用腐蚀钢绞线疲劳试验数据构建具有概率保证率的疲劳寿命随腐蚀程度与应力幅变化的空间曲面。研究表明：该多参数Weibull模型能够较好地评价腐蚀程度对钢绞线疲劳寿命的定量影响，钢绞线疲劳寿命随着腐蚀程度的增加而迅速减小，相对于应力幅而言腐蚀程度对钢绞线疲劳寿命的影响更显著。低应力幅条件下钢绞线疲劳寿命随腐蚀程度增大而降低更多，低应力幅时疲劳寿命对腐蚀更敏感。随着腐蚀程度的增加，指定疲劳寿命下的许用应力幅迅速降低。该多参数Weibull模型可为在役预应力混凝土结构疲劳性能评定提供理论依据。

Probabilistic model for fatigue life evaluation of corroded prestressing strand

 In this work, the influences of corrosion on fatigue life of prestressing strand were studied. First, a multi-parameter Weibull model for fatigue life evaluation was established based on the current three-parameter Weibull model, which considers the influences of the corrosion degree on the slope of the SN curve and the characteristic fatigue life within a specified stress range for prestressing strands. The corrosion degree and stress range were regarded as the co-variables for the proposed Weibull model. Also, the proposed model can provide the quantitative influences of corrosion on fatigue life of corroded prestressing strands. As a matter of fact, to ensure the physical meaning of the proposed fatigue model, several conditions shall be satisfied for the parameters of the proposed model. The maximum likelihood estimation was employed to estimate the parameters considering all the fatigue data with different corrosion degrees and stress ranges. The spatial surfaces of fatigue life, stress range, and corrosion degree with different survival probabilities were established based on the fatigue data of corroded prestressing strands provided in literature. The results indicate that the proposed Weibull model can be used to evaluate the fatigue life of corroded prestressing strand, which reflects quantitative influences of corrosion degree on fatigue life of prestressing strand. In particular, the results indicate that the fatigue life of prestressing strand is sensitive to corrosion. Fatigue life decreases sharply as corrosion degree increases for corroded prestressing strand. Moreover, the effect is more pronounced for lower stress ranges. The allowable stress range decreases sharply for a specified fatigue life of prestressing strand as the corrosion degree increases. Therefore, to prevent premature fatigue induced failures, avoiding corrosion of prestressing strand during the structural service period is crucial. In brief, the Weibull model proposed in this study can be used to evaluate the fatigue performance of prestressed concrete structures in service.