Impact of Heavy Freight Railcar on the Remaining Fatigue Life of Centenarian Railway Bridges

Transit agencies own and operate thousands of bridge structures subjected to repetitive train loading. The majority of these bridges were built at the turn of the century and many have exceeded their theoretical fatigue life spans. In New Jersey, the recent increase of the railcar weight limit from 1,170 kN (263,000 lb) to 1,272 kN (286,000 lb) raised concerns for railway bridges that have been in service for more than a century. To prioritize and schedule repairs and rehabilitation events, there is a need to establish refined procedures that would be able to estimate the impact of the increased railcar weight on the remaining life and damage accumulation of bridges. In this paper, three typical railway bridges with various span lengths were selected. Field testing was performed to validate the three-dimensional (3D) finite-element (FE) models of the bridges. A probabilistic approach was developed for fatigue evaluation. For fatigue resistance, a new model was proposed based on previous full-scale fatigue tests. The variance of fatigue resistance increases when the stress range increases based on test results. The new 1,272-kN freight car and its frequency are found to have a significant effect near the supports in terms of remaining fatigue life. Midspan location would not always be the most critical location of the bridge when operating the heavier railcars. An increase of 1,000 freight trains annually will decrease the remaining fatigue life by approximately 2 years. Last, the introduction of heavier railcars will have more significant effects on shorter spans.