ASSESSMENT OF REMAINING FATIGUE LIFE OF CENTENARIAN RAILWAY BRIDGES

摘要

Transit agencies own and operate thousands of bridge structures subjected to repetitive train loading. The majority of these bridges have been built at the turn of the century and many have exceeded their theoretical fatigue life spans. In New Jersey, the recent increase of railcar weight limits from 1170 kN (263,000 lb) to 1272 kN (286,000 lb) raised additional concerns for railway bridges that have been in service for more than a century. There is a need to establish refined procedures, which are able to estimate the impact of the increased railcar weight on the remaining life and damage accumulation of bridges, in order to prioritize and schedule repairs and rehabilitation events. In this paper, three typical railway bridges with various span lengths were selected in order to investigate the impact of the heavier freight 1272 kN (286,000 lb) railcar on fatigue life of the bridges. Field testing was performed for selected bridges to help understand the behavior of the structure and to validate the 3-D FE models of the bridges. A probabilistic model was developed for fatigue evaluation of railway bridges. In terms of loading, various random variables such as: annual train frequencies, dynamic impact, passenger volume, and freight equipment (locomotives and railcars) weight were considered. The probabilistic fatigue load spectra were derived using Monte Carlo simulation and the Rainflow Counting method. In terms of resistance, the relevant S-N curve is randomized with constant variance in fatigue strength. The heavy freight car and its frequency are found to have a significant effect on the critical locations, near the supports.