Load Factor Method for Dynamic Track Loadings

Abstract

Design of track structural components and foundations is based upon design loads higher than the nominal static values. These design loads generally have been determined using dynamic impact factors as multipliers of the nominal static loads. A review of commonly used impact factors is given, as dependent upon track and vehicle characteristics, and operating conditions. Field measurements of the distribution of static and dynamic wheel loads at five sites are presented. A load factor method, derived from the field measurements, is given that can be used to characterize the distribution of track loads. Although a single wheel or axle load may be appropriate for the design of certain structural components, multiple axle loadings should be used to estimate stresses and deformations that result at depth, or to analyze the loadings on buried structures. The axle spacings on typical freight cars are such that four axles are sufficient to account for multiple axle loadings. An approach is outlined to characterize the complete multiple axle dynamic load distribution for use in a probability‐based design procedure.