ABSTRACT
By the late 1990s, economic and population growth resulted in significant freight movement. It is expected that the rail freight traffic will grow sharply for the next 20 years. Therefore, substantial demand will be put on the already heavily-used railroad system. The freight railroad system enables cost-effective movement of large volume of freight, and is important because the alternative transportation methods, vehicles and trucks, cause concerns about congestion, air quality, and safety. However, the cost to build and maintain the rail infrastructure and equipment is very high, and it is very difficult to make long-term investment in railroad infrastructure. Additionally, many railroad bridges were built before World War II and are approaching their design life span, which creates additional concerns. In New Jersey freight railcars utilize portions of passenger rail network to reach their destinations, sharing lines with NJ Transit commuter rail service. An increase in the maximum railcar weight from 263,000 lbs to 286,000 lbs as mandated by the Federal Rail Association (FRA) raises concerns for the passenger rail system, since its bridges were not originally designed for 286,000 lbs cars.
In this study, a typical railway bridge on various New Jersey passenger rail lines that is used for freight was selected to investigate the impact of the heavy freight railcar on fatigue life of the bridges. Field testing was performed for the selected bridge to understand the behavior (strain, deflection and velocity) of the structure under various train loads. The collected field testing data were used to validate the 3-D FE model of the bridge. A probabilistic model is proposed for fatigue evaluation of a railway bridge located in NJ Transit line. On the loading side, the dynamic impact and the annual train frequencies fti were considered as random variables to derive the probabilistic train load spectra with Monte Carlo simulation. The calibrated 3-D finite element model of the selected bridge was used to calculate the stress histories from train loading. Fatigue load spectra for this bridge was then develop by converting the stress histories into stress ranges through rainflow counting method. On the resistance side, the relevant S-N curve is randomized with constant variance in fatigue strength. The performance function for fatigue evaluation is given by a modified form of the Palmgren-Miner damage law. The reduction in the remaining fatigue life of the selected bridges under increased loading is estimated as 24 years and 27 years, if the target reliability indices are assigned as 3.5 and 2.5, respectively. Probability of fatigue failure. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig160_1.tif"/>
