The use of railroad flatcars (RRFCs) as the superstructure in low-volume bridges has been investigated in a research project at Iowa State University. These alternative bridges should enable county engineers to replace old, inadequate county bridges for less money and in a shorter construction time than required for a conventional bridge. Capital saved can be used to improve other areas of secondary road transportation. A feasibility study completed in 1999 by the Bridge Engineering Center at Iowa State University determined that RRFC structures have adequate strength to support Iowa legal traffic loads. In a follow-up research project, two RRFC demonstration bridges with different substructures and RRFC lengths 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 it was determined that the engineered RRFC bridges had live-load stresses significantly below the safe yield strength of the steel and deflections well below the AASHTO bridge design specification limits. Moreover, since analytical procedures were able to predict RRFC bridge behavior, it is possible to analyze each bridge to determine its adequacy for any state's legal traffic loads or for roads with larger hauling loads, such as quarry or coal-hauling roads. From the results of this research, it has been determined that, through proper RRFC selection, connection, and engineering design, RRFC bridges can be a viable, economic alternative for low-volume-road bridges. This paper is also available on CD-ROM (see C 30152 CD-ROM).
Abstract