| The loads on railway steel bridges are repetitive, the fatigue and fracture are the main reasons that engineering constructions lose their capability. Recent years, numbers of railway steel bridges in service of our country are coming into aged period, and these steel bridges appear fatigue cracks of different degree. It's a significant task to evaluate their remaining fatigue life.Fatigue loading chart is a precondition to put up fatigue design and life evaluation. The estimated life of a steel bridge subjected to random load in highly dependent upon damage accumulation caused by fatigue load.Fracture mechanics is adopted to estimate the fatigue life of structural members, and among the rest, crack growth rate formula is studied. Paris crack growth formula is the most widely applied, and it is used to estimate crack growth life of steel bridge.Probabilistic fracture mechanics analyses fatigue reliability of constructions considering probability and statistic. It considers the parameters that influence fatigue crack growth rate are random variables that obey some probabilistic function. This article analyses the fatigue test data of A441 (equal to 16Mn steel of our country) welded steel beams that are tested by NCHRP investigative institution. Statistical properties of each variable are given in crack growth formula.At last, making use of load stress chart of old steel bridge, and looking facture criterion as ultimate state equation to carry through reliability analysis. Adopting Probabilistic fracture mechanics (PFM) to estimate remaining fatigue life of old steel bridge under given reliability.
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