Studies on the remaining fatigue life and operating safety of three railway bridges with more than 40 years. In the research, the actual strain data under normal operating situation and a test locomotive was collected from more than 10 members of each bridges. The acquired data was used to calibrate the finite element models in computer program. Then the models were employed to analyze the stress of bridges under various types of loads. Moreover, this research also tested tensile strength and fatigue strength of selected bridge members. The analysis and test results were used in evaluating the remaining fatigue life and operating safety according to the AREMA 1999 specification and in comparing the damages from different types of trains. Based on the obtained results, it was found that the fatigue strengths of the tested members were higher than those specified in AREMA 1999. Hence, the fatigue strengths given by AREMA 1999 were adopted. The safety evaluation for normal operating situation showed that all of three bridges, namely Chakri Bridge, KM03 Bridge and KM19 Bridge, had adequate safety and the remaining fatigue life in main structures were higher than 80 years. However, there were some fatigue damages found in a stringer of KM19 Bridge. While the safety evaluation for U20 train load, which is a new load standard, revealed that all these three bridges had inadequate safety. Therefore, it is necessary to strengthen them before adopting U20 in real operation. Furthermore, the bridge test results showed that the damage rate induced from goods-carrying trains is approximately 1.23 to 3.05 times higher than that from passenger trains.
