Rail structure interaction (RSI) represents a significant load on longer bridges with continuous welded rail. These forces and effects are even more important on bridges with curved alignment or direct fixation track. Most transit agencies in the United States require that RSI analysis be performed on their bridges. However, the parameters and methodology for this analysis are not clearly defined. Further, most agencies do not indicate how these results are to be used once the analysis is completed and lack any acceptance criteria for the results. This gap in U.S. transit design guidelines was noted over thirty-five years ago but has not yet been addressed.

It is necessary to develop recommendations on the methodology for the analysis based on a rational approach and research. Criteria for judging the results and incorporating them into bridge design are also needed.

A huge expansion in transit systems in the United States is anticipated in the next few years. RSI analysis is currently performed without a uniform or rational basis. It is not known whether the structures are designed using unconservative or overconservative loads since there is no research basis for the various design criteria used by different transit agencies. It is considered a task of high to medium urgency, since it will improve safety and performance of transit structures.

There is high potential for cost savings, both in design/analysis and construction, through more rational methods. Reducing unnecessarily complex analysis and optimizing design with a rational basis can save agencies significant cost, amounting to millions of dollars across the country.

Research will include an RSI analysis that focuses on:

1.    Conditions under which RSI analysis is needed, including need in ballasted track structures

2.    Applicability of simplified TCRP equations and evaluation of limitations

3.    Parameters to be included, including use of gross or cracked concrete section properties, inclusion or exclusion of rail lay temperatures, and need for rail break analysis

4.    Acceptance criteria for rail stresses and/or rail gaps

5.    Use of analysis results in structural design of bridges, including applicable load combinations