公路钢大桥疲劳可靠性分析------外文翻译.doc

Fatigue Reliability of Steel Highway Bridge Details 钢结构公路大桥疲劳可靠性分析 1. Purpose and Scope 目的和范围 The objective of this study was to develop a simplified method of predicting the fatigue reliability of steel bridge details with pre-existing cracks. The expected life of a steel highway bridge subjected to random, variable-amplitude traffic cycles is highly dependent upon damage accumulation caused by various fatigue mechanisms. The proposed probabilistic model mainly addresses randomness associated with the stress spectra imposed upon the cracked detail by vehicular passages. 本研究的目的是一种简化方法预测钢桥疲劳裂缝 Specifically, a method of incorporating inspection data (e.g., the presence and size of cracks) into a fracture mechanics-based fatigue model to predict detail reliability is proposed. Traditionally, fracture mechanics fatigue models are based upon Paris’ Law which represents the damage rate in terms of crack growth per stress cycle. This analysis is especially well-suited for structures which are subjected to time-continuous stress fluctuations. However, the loading on bridge structures caused by vehicular passages is more episodic in nature. Through the field testing of numerous bridges, it has been observed that the stress block induced by the passage of a single vehicle has common attributes for a particular bridge which are dependent upon its construction and road surface. Random vehicle factors (such as weight, speed, and suspension properties) determine its precise shape. Typically, each stress block is characterized by a dominant pseudo-static portion superimposed with higher frequency dynamic fluctuations and followed by a transient die-out. Accordingly, the proposed model treats a vehicle passage as a randomly arriving discrete block of stress cycles and calculates crack growth per loading block, as opposed to crack growth per stress cycle. Furthermore, the model accounts for crack closure effects by predicting the occurrence of damage only when the crack is ope