Tank Car Load Environment Under Impact Conditions

Abstract

Abstract High coupler vertical loads have been measured in revenue service tests conducted by the Association of American Railroads (AAR) as part of the ‘Freight Equipment Environmental Sampling Tests’ (FEEST) program. These high loads can induce cracks and/or accelerate crack propagation rates, causing premature tank car stub sill separation, leading to compromised safety of operation. This project was initiated to study the vertical load environment experienced by tank cars. A full scale test sequence with static and impact testing of a tank car was conducted, followed by test data analysis. A tank car loaded to 266,200 lb gross rail load (GRL) was instrumented and used as the test car. The static tests consisted of vertical load tests with forces being applied at the coupler head and squeeze tests with loads applied at the rear draft lugs. The impact tests consisted of 2 series of impacts at speeds ranging from 2 mph to 8.5 mph for three coupler mismatch levels. The results showed that significant vertical forces are generated during an impact event, even in the absence of any coupler height mismatch between impacting cars. On average, vertical force peaks of about 45,000 lb were observed at an impact speed of 7.5 mph even when the impacting cars were at the same level. It was also noted that under impact conditions, vertical forces induce 50% of the maximum stress seen at the tank head. Therefore, ignoring the effects of vertical force will lead to an under-estimation of stress levels and fatigue levels in tank cars. In addition, the vertical forces and stresses in critical areas of the stub sill-tank car interface are generally higher when the struck car is lower. Differences (in stress level) over 50% (compared to when the cars are level) were noted when the struck car was 2 in lower than the hammer car. In light of this, it seems prudent to minimize coupler height mismatch whenever and wherever feasible. This research effort was funded by the Office of Research and Development of the Federal Railroad Administration (FRA).