Proposed criteria to assess the redundancy of repurposed railroad-flatcars classified as FCMs

Abstract

The use of repurposed railroad flatcars (RRFCs) is an attractive option for low-volume applications due to their modular nature. Further, RRFCs are a sustainable and economical solution for low-volume bridges while providing considerable strength. A limited number of research projects focusing on the development of guidelines to load rate highway bridges constructed out of RRFCs have been conducted in the past. The authors have performed experimental and numerical research on various RRFC bridge configurations to develop guidelines. RRFCs are generally classified as fracture critical members (FCM) since these bridges are comprised of only two cars in the cross section in most cases. Classifying RRFCs as FCMs leads to issues when load rating these bridges, which requires rigorous hands-on inspection every 24-months as per the governing codes that significantly increases the long-term cost. The authors have previously presented the results of laboratory testing of bridges built using RRFCs having fractured primary load carrying component of the one and then both RRFCs. This paper presents a numerical parametric study performed using nonlinear finite element models benchmarked to the previously tested RRFC bridges. The results from both the experimental and numerical studies demonstrated that if certain requirements are met (e.g., utilizing composite concrete decks), RRFCs have adequate reserve strength even in a severely faulted state and need not be classified as FCMs. Additionally, simplified methods have been developed based on the research to assess if a given bridge will meet these criteria which are readily implementable in a typical design office.