About the research
Timber has been a common railroad bridge material since the railroads first emerged in the United States. Up to the mid-19th century, timber was the primary railroad bridge material and thousands of miles of timber bridges were constructed as the railroads developed and spread across the country. There are still over 500 miles of timber bridges that are still in-service on the nations? railroads and, given the proven performance history, many new timber bridges are constructed annually. Most of these bridges are used in trestles as ballast deck or open deck configurations. Ballast decks typically consist of a timber deck which supports a layer of ballast where the track ties and rail are placed. Open decks consist of two longitudinal timber chords which directly support the bridge ties and rail. Many timber bridges exist today that have been in service approximately 50 years or more and are at, or near, the end of their useful service life. With the recent increase in vehicle loads, these old bridges are put in even greater jeopardy of meeting service needs. This study focused on the static and dynamic load distribution characteristics of three recently rehabilitated timber railroad bridges. The bridges were rehabilitated with the addition of glued laminated helper stringers and both deflection and acceleration data were recorded during load tests. The load tests included a train consisting of cars of known weight. Load test data was also recorded for revenue train traffic.