Recent studies on railway-track substructure at TTCI

Railway-track substructure is the foundation of the railway-track infrastructure and consists of four major components:ballast,sub-ballast,subgrade and drainage.Safety and performance of the track infrastructure,to a large degree,depends on the performance of the track substructure.Adequate support from the track substructure is the most critical element needed for good track performance.When properly constructed and maintained,the ballasted track is the most cost-effective track structure for railway operations,especially for heavy-haul freight operations.Good track-substructure support is characterized by good drainage and strong resistance of the ballast,sub-ballast and subgrade layers to excessive deformation and failures under repeated dynamic wheel loads.As the track substructure plays such important roles,research concerning track substructure has been broad and extensive around the world,with many universities and research institutes conducting various studies and investigations.This paper provides an overview of the recent research conducted at Transportation Technology Center,Inc.(TTCI),a subsidiary of the Association of American Railroads(AAR),in the following areas:ballast mud pumping and its effects on track performance,remediation of subgrade mud pumping,remediation of ballast pockets,ground-penetrating radar(GPR)for inspecting track substructure,and development of software tools with focus on track-substructure functions and management.

A vertical coupling dynamic analysis method and engineering application of vehicle–track–substructure based on forced vibration

Purpose–This study aims to propose a vertical coupling dynamic analysis method of vehicle–track–substructure based on forced vibration and use this method to analyze the influence on the dynamic response of track and vehicle caused by local fastener failure.Design/methodology/approach–The track and substructure are decomposed into the rail subsystem and substructure subsystem,in which the rail subsystem is composed of two layers of nodes corresponding to the upper rail and the lower fastener.The rail is treated as a continuous beam with elastic discrete point supports,and spring-damping elements are used to simulate the constraints between rail and fastener.Forced displacement and forced velocity are used to deal with the effect of the substructure on the rail system,while the external load is used to deal with the reverse effect.The fastener failure is simulated with the methods that cancel the forced vibration transmission,namely take no account of the substructure–rail interaction at that position.Findings–The dynamic characteristics of the infrastructure with local diseases can be accurately calculated by using the proposed method.Local fastener failure will slightly affect the vibration of substructure and carbody,but it will significantly intensify the vibration response between wheel and rail.The maximum vertical displacement and the maximum vertical vibration acceleration of rail is 2.94 times and 2.97 times the normal value,respectively,under the train speed of 350 km$h
1.At the same time,the maximum wheel–rail force and wheel load reduction rate increase by 22.0 and 50.2%,respectively,from the normal value.Originality/value–This method can better reveal the local vibration conditions of the rail and easily simulate the influence of various defects on the dynamic response of the coupling system.