Numerical simulations of negative flexural responses (hogging) in railway prestressed concrete sleepers

By the very nature of ballast, it interacts with concrete sleepers in a special way. Most train-track models do not consider its tensionless characteristic and cannot accurately predict dynamic responses of structural elements assembled for railway tracks. This study has taken into account its natural tensionless property in order to investigate reverse bending moment at the mid span of standard-gauge concrete sleepers, which causes some concerns in many countries. It has been reported that the excessive negative bending moment at the mid span results in associated flexural cracks and centre-bound problems in rail freight and heavy haul networks especially in North America. This paper presents a dynamic finite element model of a railway concrete sleeper in a standardgauge track system, taking into account the tensionless nature of the elastic ballast support. The highlight of this paper is the effect of ballast distributions on the negative flexural responses or hogging moments of railway sleepers in track systems. Using a finite element package STRAND7, the finite element model updating of the concrete sleeper was earlier developed and validated against experimental dynamic characteristics by the authors. The numerical simulation is capable of modelling the tensionless ballast support whereas the supporting boundary condition provides vertical resistance in compression only. The numerical simulations are demonstrated as to investigate the quasi-static and dynamic bending moment resultants of the railway concrete sleeper against the current design methodology. This study points out a key criterion in negative or hogging bending moment calculations at the mid span of sleeper under various support conditions and various length of concrete sleepers.