BACKGROUND     

Rail structure interaction (RSI) is the detailed study of the complex nonlinear interactions and forces exchanged between railway tracks and bridge structures. RSI induces a nonnegligible combination of loads, displacements, and dynamic effects on longer span bridges utilizing continuous welded rail. An RSI analysis is required to understand the force transfer mechanism and stresses induced in the rail. Rail displacement relative to the bridge superstructure and transmission of forces to bridge components also is part of the analysis. The interaction effects include thermal effects between the rail and superstructure, longitudinal deformation of the substructure under temperature loads, train braking/traction loads, seismic loading, and vertical live load effects. These forces and effects become even more significant on curved bridges utilizing direct fixation tracks.

Most transit agencies require an RSI analysis be performed on their bridges or systems, and their RSI provisions vary greatly on parameters, methodology, and acceptance criteria. There are no industry-wide RSI analysis guidelines or acceptance criteria within the US transit sector, and most agencies do not address the utilization of RSI results in their design.  It is necessary to develop recommendations for the methodology of analysis based on a rational approach and research. Additionally, criteria for evaluating and integrating the RSI results into bridge design are needed.

OBJECTIVE

The objective of this research is to provide guidance on developing and implementing RSI analysis to transit agencies and designers, as well as incorporating the RSI analysis results into the design of applicable transit structures and components.

RESEARCH PLAN

The results of this research project should be easily implementable by public transportation professionals, including transit bridge designers. The contractor shall identify appropriate research methods (such as calculations, numerical studies, field measurements, partnerships with transit agencies, etc.) and present the information (case studies, frameworks, guidance, fact sheets, etc.), and consider that the target audience is transit systems of all sizes.

 The research should include, at a minimum: 

• Identification of the conditions necessitating RSI analysis, considering:
  • Track types (direct-fixation track, ballasted track, embedded track) and features (sleeper spacings, alignment)
  • Specific operational conditions
  • Structure types
  • Track structure connections and rail specifications
  • Environmental conditions (thermal, seismic, etc.)
• Utilization of analysis results in structural design of bridges, including applicable limit states, load combinations, train loading models and environmental loads
• Assessment of the applicability of the simplified equations outlined in TCRP Report 71: Direct-Fixation Track Design Specifications, Research, and Related Materials and an evaluation of their limitations
• Specification of RSI analysis parameters to be included, such as:
  • Incorporating gross or cracked concrete section properties
  • Considering the inclusion or exclusion of rail lay temperatures
  • Assessing the necessity for rail break analysis
• Establishment of acceptance criteria for rail stresses and/or rail gaps
• Validation of data (numerical and experimental) and real-world applications
• Guidance on mitigation strategies to reduce excessive rail stresses and deformations

The research plan shall be divided into tasks that present, in detail, the work proposed in each task. The research plan shall describe appropriate deliverables (which also represent key project milestones) including, at a minimum:  

• Interim report and in-person panel meeting. The interim report should include the analyses and results of completed tasks, an update of the remaining tasks, and a detailed outline of the final research product(s). The panel meeting will occur after the panel review of the interim report. The interim report and in-person panel meeting should occur after the expenditure of no more than 40 percent of the project budget. 
• Draft report.
• Final report.
• Technical memorandum, titled “Implementation of Research Findings and Products”.
  

STATUS: A response has been received for this RFP. The project panel will meet to determine next steps.