基于次序定律的既有铁路桥梁新疲劳寿命评估方法

Study of a new assessment approach of fatigue life based sequential law for existing railway bridges

既有铁路桥梁的疲劳寿命评估方法通常基于实测的应力历程、Miner准则和铁路规范。针对Miner准则在进行疲劳寿命评估时,忽略荷载次序效应而导致评估结果不可靠的情况,提出一种新疲劳寿命评估方法。该方法主要基于预测的应力历程、完全已知的Whler曲线和次序定律。首先通过材料试验、现场静动力测试以及有效分析模型,评估桥梁结构状态。编制基于结构评估的相当精确的程序,以此获得桥梁过去和将来的应力历程。将部分已知的Whler曲线转变为完全已知曲线的技术以及基于次序定律的新疲劳模型,也得到讨论。接着通过对比一些材料的理论与实际的损伤行为和疲劳寿命,证实次序定律和完全已知的Whler曲线模化技术能获得更好的与试验相符的结果。最后将新方法应用在实桥疲劳寿命评估实例中,结果表明,相比之前的疲劳理论和Miner准则,新方法可以获得更加准确的剩余疲劳寿命,将次序定律应用在既有铁路桥梁剩余疲劳寿命评估中是非常可行的。

The current fatigue life estimation methods of railway bridges are generally based on combinations of measured stress histories, Miner＇ s rule, and railway codes. In case of existing railway bridges, Miner＇ s rule might provide incorrect results because of its omission of load sequence effect. Therefore, a new assessment approach of fatigue life is presented in this article. The approach mainly consists of predicted stress histories, fully known WiShler curve and sequential law. Firstly, by means of a material test, field static and dynamic load testing and an effective analysis model, structural behavior of a bridge can be estimated. The authors compile a reasonably accurate procedure based structural evaluation to obtain the past and future stress histories. After that, the technique which utilizes transfer of the partially known Wtihler curve to fully known curve and new fatigue model-based sequential law, is also discussed in this article. Further the sequential law and associated fully known S-N curve determination procedure are verified by comparing damage behavior and theoretical fatigue life with real ones of few materials. Finally, the new approach is applied to a real fatigue life evaluation instance of an existing railway bridge. The results show that, the new approach can be applied to obtain relatively accurate remaining fatigue life compared with previous theory and Miner＇ s rule. Hence it is advisable to apply the sequential law for assessment of remaining fatigue lives of existing railway bridges.