考虑长期监测应力时序的钢箱梁桥疲劳评估方法研究

To cover the shortages that the steel box-girder bridge fatigue assessment results may deviate from the actual situation when neglecting long-term monitoring stress sequence, the key scientific problems about the fatigue assessment methodology for steel box-girder bridges considering long-term monitoring stress sequence will be researched systemically. The main contents are as following: (1) The time-dependent law of fatigue load effect will be revealed based on long-term monitoring stress, and the time-dependent function will be proposed. Then, the statistic model of fatigue load effect will be established. After that, the numerical simulation method of time-dependent fatigue load effect considering random and time-varying characteristics of fatigue stress will be suggested. (2) The fully known S-N curves for fatigue assessment of steel box-girder bridge will be provided. Then the non-linear fatigue damage accumulation model considering long-term monitoring stress sequence will be developed. Based on this, the efficiency stress-sequence damage model used for non-linear accumulation fatigue damage calculation will be proposed. (3) The limit state function used for fatigue reliability assessment of steel box-girder bridge will be established based on the efficiency stress-sequence damage model. The statistical models of parameters in the limit state function will be suggested. At last, the fatigue reliability assessment methodology for steel box-girder bridge considering long-term monitoring stress sequence will be developed. (4) The fatigue reliability assessment program for steel box-girder bridge considering long-term monitoring stress sequence will be written and applied in fatigue performance assessment of actual steel box-girder bridges. The results of this project will provide new approach for fatigue assessment of steel box-girder bridges.

针对忽略长期监测应力时序可能造成钢箱梁桥疲劳评估结果偏离实际情况的不足，本项目对"考虑长期监测应力时序的钢箱梁桥疲劳评估方法"的关键科学问题开展系统性研究，主要包括：（1）基于长期监测应力数据揭示疲劳荷载效应的时变规律并建立疲劳荷载效应的时变函数，给出疲劳荷载效应的统计模型，进而提出面向可靠度评估的时变疲劳荷载效应随机模拟方法；（2）形成钢箱梁桥疲劳评估的全空间S-N曲线，建立考虑长期监测应力时序的非线性疲劳损伤累积模式，在此基础上提出非线性疲劳累积损伤计算的高效时序损伤模型；（3）建立基于高效时序损伤模型的钢箱梁桥疲劳可靠度评估极限状态方程，确定极限状态方程参数的概率表述，从而形成考虑长期监测应力时序的钢箱梁桥疲劳可靠度评估方法；（4）集成考虑长期监测应力时序的钢箱梁桥疲劳评估软件，开展考虑长期监测应力时序的疲劳评估方法典型工程应用。研究结果可为钢箱梁桥的疲劳性能评估提供新的途径。

疲劳破坏是影响钢箱梁桥安全的关键因素之一，已有的钢箱梁桥疲劳性能评估方法忽略了长期监测应力次序，造成疲劳评估结果常常偏离实际情况。本项目对“考虑长期监测应力时序的钢箱梁桥疲劳评估方法”的关键科学问题开展了深入研究，主要成果包括：. 针对疲劳荷载效应（包括疲劳应力幅和循环次数）的多峰分布特性，建立了由多种统计模型加权和组成的多峰混合分布模型和模型参数估计方法，突破了单峰分布模型难以准确描述疲劳荷载效应统计特征的缺陷；提出了复杂概率模式下随机样本模拟的数值逆变换抽样方法，解决了大跨桥梁全寿命期疲劳性能评估数据不足的难题。. 基于规范给出的S-N曲线，从理论上推导了覆盖低周疲劳寿命区、有限疲劳寿命区和高周疲劳寿命区的全空间S-N曲线模型，将S-N曲线由有限疲劳寿命区扩展至全空间；进一步引入超高周疲劳损伤累积因子和超低周疲劳强度调整因子，提出了钢箱梁桥疲劳评估的全空间S-N曲线模型，并从几何学角度明确了模型参数的意义。. 建立了考虑长期监测应力时序的钢箱梁桥疲劳损伤累积计算模型和疲劳可靠度评估极限状态方程。采用损伤应力作为疲劳损伤指标，结合钢箱梁桥疲劳评估全空间S-N曲线模型，在上一次损伤应力的基础上计算本次应力循环引起的损伤应力增量。此方法能够有效考虑应力出现次序对疲劳损伤的影响。. 集成了疲劳荷载效应多峰混合分布模型、随机样本数值逆变换抽样方法和考虑长期监测应力时序的钢箱梁桥疲劳损伤计算模型和疲劳可靠度分析方法，对润扬大桥斜拉桥钢箱梁正交异性桥面板在不同工况下的疲劳可靠度进行了计算，探讨了钢箱梁桥疲劳可靠度的退化规律。. 研究结果可为钢箱梁桥的疲劳性能评估提供新的途径，为钢箱梁桥的维护和管理提供技术支持。