Evaluation of Subway Car Shell Condition for Extended Service

This paper presents the result of an evaluation program for the condition of the SEPTA Broad Street subway car shells and their capability to perform during an extended period of revenue service. SEPTA currently is evaluating various system upgrades to address equipment obsolescence and reliability, and wanted to verify that the current car shells are expected to be serviceable during this extended period. The evaluation focused on two aspects of the 1982-built car shells. First, what is the current and predicted condition of the shells and, second, how does the performance of the current car shell design compare to present day designs and requirements? Four sets of activities were done as part of this project. One-third of the fleet was randomly chosen for visual inspections. Service-induced cracks were identified at two locations: in ring welds below the doors, and on the side sill between the corner posts and the anti-climbers. The ring weld cracks have been identified on a small number of cars in the past, and SEPTA continues to monitor and reinforce these areas. The cracks between the corner posts and anticlimbers are also being monitored; to date, none of these cracks has progressed to the point that repair is required. In parallel with the visual inspections, the car shell camber and doorway dimensions were measured on approximately 10% of the fleet. All the measured vehicles had positive camber; doorway dimensions were uniform, except for scattered individual measurements that were car-specific. This part of the evaluation concluded that the car shells are not undergoing significant degradation or cracking. One car was instrumented with strain gauges in potential high-stress areas, and then operated at simulated full passenger-load weight over the Broad Street route. Cyclic strains imposed by simulated revenue service were measured and converted to stresses. This testing confirmed high stresses at the joint between the side sill and the body bolster. The lifetime limiting location on the car shells is in the ring welds below the doors, consistent with the results of the visual inspections. Using conservative assumptions of continuous full passenger loading and minimum material properties, the predicted lifetime to the initiation of visible cracks in this area is 7–14 years of service. This independent evaluation is consistent with the actual experience, and provided confidence in the analysis protocol. SEPTA is monitoring this location and repairing cracks as required. Evaluation of the car shell design with regard to performance in a collision revealed that, unlike most other cars of its era, the Broad Street car shell contains provisions to manage energy absorption during a low-speed collision. Records obtained from a car repair shop showed that, when a Broad Street car had a significant non-revenue end collision, these provisions worked as intended to localize the deformation. In similar collisions, the Broad Street car shell will not perform significantly different from cars built to current industry practices. Results from this study indicate that with continued attention to car shell condition, including regular inspections and limited repairs, the Broad Street car shells will continue to be safe and serviceable for an extended period.