Bridge Impact due to Wheel and Track Irregularities

Abstract

The impact factors in bridge members due to flat wheels and track irregularities were investigated. The maximum wheel flat height was taken as 0.2 in. (5 mm), maximum pier settlement as –0.25 in. (–6.3 mm) and maximum camber error as –0.5 in. (–12.5 mm). The track roughness spectra for class 6 track was used in the analysis, and only selected members of the 175 ft. pinned connections truss bridge were studied. The train of three 70 ton freight cars with spring constants of 11.2 kip/in. (1.96 kn/mm) per wheel were used. The train was moving at various speeds and with initial displacements of 0.25 in. (6.3 mm) and roll of 0.02 rad. Damping of the bridge and vehicle were neglected. The impact factors for the train moving at 50 mph (22.35 m./sec.) seem to agree fairly well with the current American Railway Engineering Association specification. Other conclusions are summarized.