Loading Spectra for Railway Bridges under Current Operating Conditions

Abstract

Some important results from a research program investigating railway bridges in North America are presented in the paper. A primary goal of the program was to measure the loading spectra to which railway bridges are currently being subjected. Extensive measurements of this type have not been taken for over 20 years. Five bridges were instrumented and the loads from 508 train crossings were recorded. Three main general types of freight were identified. The heaviest and most significant of these were unit commodity trains. The largest dynamic loads recorded due to unit commodity cars were significantly higher than the largest nominal static load for rail cars allowed in free interchange between railroads. Best fit probability distributions were determined from the measured loading spectra for each identified freight type. The loads in the upper five and one percent of each population were calculated from the best fit distributions. Studies demonstrate that today's loading environment is approaching and at times exceeding the current American Railway Engineering Association (AREA) design loadings (Cooper E80 or the Alternate loading) when impact is not considered.