Fatigue Evaluation of the Increased Weight Limit on Transit Railway Bridges

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Fatigue Evaluation of the Increased Weight Limit on Transit Railway Bridges

H. Nassif / K. Ozbay / P. Lou / D. Su

The recent increase of freight railcar weight limits from 263,000 lbs. to 286,000 lbs. raises concerns for the safety of bridges on transit passenger rail systems, since they were not designed for this weight increase. Thus, there is a need to assess the impact of the weight increase on those bridges prior to utilizing passenger lines for freight transportation. This study introduces an accurate approach to ascertaining the remaining fatigue life of steel railway bridges. The analysis results indicate that heavy freight cars have a significant effect on critical locations near bridge supports. The introduction of heavier rail equipment will have a much more significant effect on shorter spans (span lengths of less than 60 ft.) than on long spans. This will allow transit operators or agencies to prioritize and schedule repairs and rehabilitation. An increase of 1,000 freight trains per year will shorten the remaining fatigue life by approximately 2 years. The relationship between annual freight train frequency and remaining fatigue life could help transit operators or agencies to balance the tradeoff between economic benefit and bridge rehabilitation cost.