Railroad Tie Spacing Related to Wheel-Load Distribution and Ballast Pressure

Currently, there is no formula for tie and direct fixation fastener (DFF) spacing. Because the rail does not bend between the tie/DFF, it is not possible to calculate spacing by the bending stress formula. Usually, rail-stress analysis confirms a trial spacing. Such analysis may support a longer spacing that might not address issues related to load distribution, pressure on formation, torsional rigidity, noise, and vibration. Thus, tie spacing is formulated from the perspective of wheel-load distribution and load dispersion by ballast, considering the fact that ties under the Benkel beam support the vertical load. The DFF/tie spacing is related to the characteristic length of the track, and this study shows that the desired DFF/tie spacing should be less than the characteristic length. Codes and practical examples validate spacing formulated for DFFs, concrete ties, and wood ties. (C) 2014 American Society of Civil Engineers.