RAILROAD FLATCAR BRIDGES FOR ECONOMICAL BRIDGE REPLACEMENT SYSTEMS

This study considers the use of railroad flatcars (RRFCs) as the superstructure in low-volume bridges for replacing older, inadequate bridges. A 1999 feasibility study determined that RRFC structures have adequate strength to support Iowa legal traffic loads. In a followup project, two RRFC demonstration bridges with different substructures and types and lengths of RRFCs were designed, constructed and tested to validate the conclusions of the feasibility study. Bridge behavior predicted by grillage models was supported by data from field load tests, and design recommendations were developed for determining live load distribution in the RRFC bridges. It was also determined that the engineered RRFC bridges had live load stresses significantly below the steel yield strength and deflections significantly lower than the AASHTO bridge design specification limits. Finally, it was proved that RRFC bridges can be constructed for lower cost and in a shorter construction time frame than required for a conventional bridge. These results show that RRFC bridges are a viable economic alternative for low-volume road bridges. The success of these demonstration bridges is linked to careful RRFC selection, design of longitudinal connections between flatcars, and engineering design and construction practices.