# Analytical and Measured Effects of Short and Heavy Rail Cars on Railway Bridges in the USA
## 5 Conclusions  
The analytical calculations indicated that the effect of short railcars was most prominent on the primary members such as end posts, diagonals, top and bottom chords in truss spans, and bending stresses in girder spans. The test data confirmed that short railcars produced higher stresses on longer bridge spans, as follows: The 12.8-m (42-ft) short railcars produced stresses 29 to 31% higher than 16.2-m (53-ft) common length railcars in top and bottom chords and produced stresses 20 to 21% higher on the end post and diagonal on the 61-m (200-ft) truss span. * Short railcars caused a 30% increase in stress in both the top and bottom chords of the 33.5-m (110-ft) truss span. The end post experienced a 26% stress increase due to short railcars. * The 12.8-m (42-ft) short railcars produced maximum live load stresses of 22 and 26% higher than 16.2-m (53-ft) common length railcars at mid-span locations of the 34.7 m (113-ft, 10-in.) girder and 35-m (115-ft) girder, respectively. * The considered members in trusses and the location on the riveted steel DPG span govern the overall load capacity of the bridge, so shipments of multiple car blocks of short railcars should be carefully planned. * Stringers of the 61-m (200-ft) span did not experience any increase in stresses due to short railcars. However, the stringers experienced full unloading as the train traversed, and therefore, they can be more susceptible to fatigue. The test data confirmed that stringers of the 61-m (200-ft) span did not experience any increase in stresses due to short railcars. The 12.8-m (42-ft) short railcars did not create an increase in fatigue cycle accumulation in the stringers. However, the stringers, which are relatively short when compared to other truss members, experienced full unloading as the train traversed. Since fatigue is governed by the stress range or magnitude of the stress cycles, these short bridge components can be more susceptible to fatigue as compared to longer components that did not experience full unloading due to the train passage. The tested riveted steel DPG span further validated the analytical bridge fatigue model developed at TTCI for girder spans. The analytical calculations indicated that the mid-span might not be the most critical location for fatigue depending on railcar length and span length considerations. Stress ranges at cover plate terminations were the highest for this particular span. The test data confirmed the analytical predictions. Based on the findings from the research presented in the paper, the following implications to be considered by bridge owners and railway bridge engineers are proposed:  
* Bridge load capacity ratings and railway operating restrictions need to consider railcar length in addition to railcar weight. * Shorter rail cars can limit the carload capacity of a bridge due to increased load on a span. * Longer rail cars can shorten the fatigue life of a bridge due to larger stress ranges caused by greater unloading between axles. * The ratio of rail car length to span length is a key parameter. **Author Contributions:** Conceptualization, A.M.R. and D.E.O. ; Data curation, A.M.R. ; Formal analysis, A.M.R. ; Investigation, A.M.R., D.E.O. and S.M.D. ; Methodology, A.M.R. and S.M.D. ; Validation, A.M.R. ; Visualization, A.M.R. ; Writing--original draft, A.M.R. ; Writing--review and editing, D.E.O. and S.M.D. All authors have read and agreed to the published version of the manuscript. This research was conducted as part of the Association of American Railroads' Strategic Research Initiatives Program. Not applicable. The study did not report any data outside of this publication. The authors would like to thank the participating Class 1 Railroads for allowing the TTCI team to take measurements on their bridges and for their valuable support. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.