Damage Mechanism And Maintenance Strategy On Out-of-plane Fatigue For Existing Steel Bridges

Recently, strength, rigidity and stability play a key role in steel structure design, but bridge structures constructed following those guiding principles are commonly facing fatigue problems. Out-of-plane distortional fatigue mainly consist web breathing fatigue and web-gap distortional fatigue, which are quite universal in steel bridge structures. The former is caused by using the post-buckling strength of girder webs which may cause the girder behaving evident character of "breathing" and inducing fatigue cracks initiate at the boundaries of the webs. The latter is caused by interaction between conjunction members which were not considered during design state. The interaction made the structure details lay on a complex stress station and is prone to out of plane displacement and lead to structure failure.Reviewd the documents about out-of-plane distortional fatigue in steel bridges at home and abroad, this paper analysed the common fatigue details of out-of-plane distortional fatigue in steel bridges, at the same time, a parametric analysis is developed to study their fatigue mechanisms. Uses the measured data of a railway steel bridge, fatigue life of out-of-plane distortion is evaluated, In this thesis, the following aspects are investigated:1. Research result and method of out-of-plane distortional fatigue at home and abroad. was summarized. Since out-of-plane distortional fatigue was affected by uncertain factors, usually stresses during the loading process was get through tests, and then combined with traditional fatigue analysis method or fracture mechanics approach gave an assessment of crack propagation and remaining life.2. Analysis with 3-D finite element models was developed to investigate the mechanics behaviors of typical out-of-plane fatigue details of bridge structure as well as the factors affecting out-of-plane fatigue, at last, an advice to avoid out-of-plane fatigue for future steel bridges was proposed.3. Verification analysis for several typical out-of-plane fatigue retrofit methods was carried out through numerical method, so their applicable condition was determined.4. Combine the numerical result and in-situ measurements, analysis on formation mechanism of out-of-plane fatigue cracks in the existing railway bridges was developed, assessment of the remaining life use fracture mechanics method was carried out as well. Finally an advice for further maintenance strategy was proposed.