Impact loads from freight wagon wheels with two non-condemnable tread defects: Modelling, field verification, and proposals for regulatory change

Wayside train monitoring systems based on measuring wheel–rail impact forces often register loads exceeding regulatory limits from wheels on which visual inspection finds only defects below the condemning size limits. This paper shows that such readings can be caused by the combined action of two or more non-condemnable tread defects. An impact interaction model built on A. Ya. Kogan’s theory, with the track represented as a beam on a Winkler elastic foundation, is adapted to several consecutively located defects using the time-delay theorem. Calculations are compared with data from the NEVA wayside monitoring system installed at Veimarn station of the Oktyabrskaya Railway (Russia). The medians of measured loads for wheels with double non-condemnable defects and for wheels with single condemnable defects are comparable in the examined groups of four and five wheels, differing by 9% with fully overlapping ranges. For wheelsets with inspection records, a response inversion is found, in which non-condemnable defects with sharp edges produce a larger signal in the 250–350 Hz diagnostic band than a large condemnable defect with a gently sloping entry, while the superposition of impact pulses from closely spaced defects can lead to a condemnable wheel being missed. The results agree with independent European studies favouring a force-based removal criterion over a geometric one. A closed-form classification of the interaction regimes of two defects is given through the flight length of the wheel, and the criterion is generalised to bogies of different design. For the 18-9855 bogie with a 25 t axle load, the inertial decoupling of the side frame reduces the effective impact mass from 926 to 725 kg, so that the track impact at the condemning flat depth is about 7% lower than for the 18–100 bogie despite the higher axle load, and the equivalent condemning depth is about 1.3 mm.