海洋腐蚀环境下中空夹层钢管混凝土相贯焊接K形节点疲劳性能研究

Fatigue performance of CFDST K-joints under marine corrosive environments

为研究腐蚀环境下中空夹层钢管混凝土相贯焊接K形节点的疲劳性能,开展了3个腐蚀后中空夹层钢管混凝土相贯焊接K形节点疲劳试验,分析了节点疲劳裂纹萌生-扩展-失效机理、刚度退化规律及现有规范中的管节点疲劳寿命预测曲线的适用性。研究表明:腐蚀后节点疲劳裂纹萌生位置与最大热点应力位置和主管侧焊趾附近点蚀严重程度均相关。在高热点应力水平下,应力幅起主导作用,疲劳裂纹萌生寿命N_(2)和失效寿命N_(4)随着应力幅增加而降低;而在较低热点应力水平下,腐蚀程度占主导作用,N_(2)和N_(4)随着腐蚀率增加而降低。试验结果与现有设计规范计算结果对比表明,采用CIDECT建议的S-N曲线预测腐蚀中空夹层钢管混凝土节点的疲劳寿命将偏于不安全,而采用DNV、API等规范相关公式的计算值偏于保守。基于试验结果拟合了95%保证率的腐蚀后中空夹层钢管混凝土相贯焊接K形节点疲劳寿命预测S-N曲线,当疲劳寿命为2×10^(6)时,腐蚀节点的95%保证率的热点应力上下限分别为168.26 MPa和118.67 MPa。

This paper presents an investigation of the fatigue performance of concrete-filled double-skin tubular(CFDST)gap K-joints under corrosive environments.Fatigue tests of three corroded CFDST K-joints were conducted to investigate the fatigue crack initiation,propagation,and failure mechanisms of the corroded joints.Moreover,the degradation law of stiffness of the corroded joints and the applicability of the fatigue life design curves for tubular joints in current design codes were analyzed.Results show that the fatigue crack initiation location of corroded joints is related to both the maximum hot spot positions and the pitting corrosion in the weld toe of the chord.Under the high level of the hot spot stress,the crack-initiation fatigue life N_(2)and end-of-test fatigue life N_(4)decrease with an increase in the stress range,as determined by the hot spot stress range.While under the relatively lower hot spot stress,the determined factor for fatigue life transforms into a corrosion degree,resulting in fatigue life N_(2)and N_(4)decreasing with the corrosion degree increasing.A comparison of experimental results to the calculated results using the current design codes shows that the predicted fatigue life for corroded CFDST joints using the S-N curve recommended by CIDECT might be unsafe,while the fatigue life calculated by using DNV and API is conservative.An S-N curve with a survival probability limit of 95%for predicting the fatigue life of corroded CFDST joints was fitted based on experimental data.The upper and lower limitations of the hot spot with a survival probability limit of 95%were 168.26 MPa and 118.67 MPa,respectively,when the fatigue life was 2×10^(6).