Structural Evaluation of the Ontario & Western Railway’s Original Bridge at Fish’s Eddy

A three-span pin-connected through-truss bridge over the East Branch of the Delaware River near Fish's Eddy, NY, was erected in 1882 for the New York, Ontario & Western Railway. Designed by the Central Bridge Works of Buffalo, NY, the structure experienced two collapse events during its rather short fifteen-year life. The first occurred in 1886 when a caboose, derailed by a broken rail, struck the end post of the northernmost span, dropping it into the river and killing the four crewmen riding inside the car. The bridge was rebuilt and continued in service until 1897, when the middle span collapsed while a train of empty coal cars traversed the structure. Since the span was lightly loaded by the empty cars of a train on orders to proceed no faster than five mph, officials were quite surprised by the failure, and were never able to establish a definitive cause. A recent detailed evaluation of the first panel hangers demonstrated that they were especially vulnerable to both routine overstress as well as fatigue under simulated traffic, and that the failure of such a hanger could indeed have been responsible for the 1897 collapse. The authors are currently conducting a comprehensive evaluation of the remaining primary members of the truss to assess whether they also possessed vulnerabilities of a degree similar to the first panel hangers. This study utilizes both the railroad's original 1881 specification for iron bridges as well as the modern-day provisions stipulated by the American Railway and Maintenance-of-Way Association's recommended practices. With regard to loading, this includes the requirements for dead and live load, and where appropriate, impact and rocking effect. Employing the allowable stress criteria given by these design rules, a comparative analysis among the members of the truss will be completed based on the Cooper load capacity of each member. In addition, member stresses resulting from simulated loads based on the actual traffic that the bridge might have been subjected to while in service will be considered. By comparing Cooper capacity to actual equivalent load levels, assessments will be made regarding whether each member would have been overloaded, and if so, to what degree. The paper will examine the history and various details associated with the bridge, including a review of the relevant portions of the railroad's specification for iron bridges governing the design of the primary structure, as well as important observations gleaned from the 1897 collapse. Methods of structural analysis, development of simulated trains and their loads, and the results of the comparative member assessment will be presented. Finally, conclusions will be made regarding the likelihood of an alternative failure mechanism relative to that previously demonstrated for the first panel hangers. This work will contribute to the body of knowledge regarding the history of bridges, and will provide insight for structures of this type and vintage that continue in service today.