Experimental and analytical evaluation of the redundancy of repurposed fracture-critical railroad-flatcars

Abstract

Previous research focused on the development of guidelines to load rate highway bridges constructed out of repurposed railroad flatcars (RRFCs). Those guidelines were based on field testing and finite element analysis conducted on existing RRFC bridges both in the field and in the lab. However, load rating is only one of the issues related to RRFCs as the main components are often classified as fracture critical members (FCMs) since there are only two flatcars in the cross section in most instances. Classifying the individual RRFCs as FCMs requires a rigorous hands-on inspection as per the Code of Federal Regulations, which greatly increases the long-term costs associated with these structures. Hence, while they are attractive to many owners due to their low initial costs and considerable strength, long-term costs due to inspection have deterred some owners from utilizing this viable and renewable alternative for low-volume applications. This paper presents the results of laboratory testing and non-linear finite element analysis of a railroad flatcar bridge specimen constructed with a composite reinforced concrete deck. The results confirm that RRFCs have considerable reserve strength and adequate load redundancy in a severely faulted state and need not be classified as FCMs if certain requirements are met. The paper also presents recommendations for load redistribution factors between primary members of RRFCs obtained through the experimental and verified by numerical studies.