Track Modulus: Ballasted and Direct Fixation Track

This paper aims to compute the track modulus. For this purpose, it reviews the computation of the track modulus of a ballasted track, and the formula of the track modulus of a direct fixation (DF) track by Transit Co-operative Research Program. The computation has been found to be wrong, and the formulation has theoretical deficiencies because of incorrect interpretation of the definition of the track modulus although there is an equation based on the beam on an elastic foundation (BOEF) to compute the track modulus of a ballasted track. These are investigated in the paper in detail. A discreetly supported rail structure can be analyzed using numerical means. However, for a static assessment and simple configurations, the BOEF model may be applied on a DF track as an approximation method. The current industry practice applies the BOEF model on a DF track to analyze rail stress, deflection, reaction, etc. Thus, a formulation of the track modulus of a DF track is based on the BOEF model. As a sideline work, this study shows a new expression for the characteristic length, the track modulus, and the relation between track stiffness and mean track stiffness. It also presents limiting values of fastener stiffness and then a formula for fastener spacing.