特大跨缆索桥钢箱梁疲劳应力特性对比性研究

疲劳应力监测是特大跨缆索桥结构健康监测和安全评估的关键环节。研究发现，对于结构健康监测系统采集的海量应变数据，局部时段不能反映出应变的整体特性，且交通载荷和环境载荷在不同类型的大跨缆索桥如斜拉桥和悬索桥结构中产生的响应是不同的。为了对桥梁的实际运营状态和应力水平有总体而全面的认识，需要对采集数据进行统计分析。本文以润扬悬索桥和斜拉桥钢箱梁应变时程数据为基础，分析了半年内两桥疲劳应力谱的特征；拟合了各自的疲劳损伤增量的概率密度函数。研究表明：对半年样本容量的参数估计显示，润扬悬索桥和斜拉桥的相对累积损伤均不拒绝对数正态分布，且前者均值均高于后者。在相同的环境和车辆载荷下，由车辆和变温载荷所引起的总疲劳损伤增量，悬索桥高于斜拉桥，且前者为后者的两倍以上。考虑了噪声影响的应变时程比去除噪声后的应变时程所造成的损伤增量高出一倍。而耦合了引起材料热胀冷缩的温度变形的影响，其应变时程造成的累积损伤增量比不考虑其影响所造成的损伤增量高出30%。因此，需要严格控制随机干扰和温度变形的影响，将真实的动态应变信息加以提取后才能进行大跨缆索桥的疲劳状态评估。

Comparison study on characteristic of fatigue stresses in steel box-girders of long span cable bridges

The monitoring of fatigue stress is a key issue of structural health monitoring and safety assessment of long-span bridges. For a mass of data recorded by health monitoring system, daily data differ in thousands ways. Data in local period of time cannot reflect whole strain character and in different types of bridges such as a cable-stayed bridge and a suspension bridge, responses due to vehicle load and environment load are diverse. In order to acquire roundly actual running state and stress level, statistical analysis of vast data recorded is needed. This paper is aimed at investigating the feature of fatigue stress spectrum on the steel box-girders under service loading on the basis of strain history data recorded by structural health monitoring system installed on Runyang Suspension Bridge and Cable-stayed Bridge. The probability density function of fatigue damage increments of each bridge is simulated. The result of parameter estimation of half-year-samples shows that, relative accumulative damage increments are submitted to lognormal distribution in both bridges. In the same environment and vehicle loads, fatigue damage due to vehicle and temperature varying in suspension bridge is twice higher than that in cable-stayed bridge. Damage increments induced by strain history containing noise is twice higher than those after getting rid of noise, and damage increments coupling with temperature deformation goes beyond 30% of those without regard to temperature deformation. Therefore, controlling sternly impacts of noise and temperature deformation, and picking-up actual dynamic strain messages to evaluate fatigue state of long span cable bridges are needed.