Research Papers (2009 – 2013)

Abstract

A Canadian transit authority found extensive moisture and free water trapped behind the side panels on older low floor buses during routine inspection. The corrosion had attacked the longitudinal space frame members leaving areas of significant damage especially where the sill frame, diagonal and vertical members intersected. The corrosion had perforated some frame members completely and the transit authority was concerned that the damage was sufficient to create an area of weakness in the event of a side impact collision. This raised the question of crash worthiness and occupant safety. No US or Canadian federal motor vehicle safety standard exists that examines frame corrosion as part of vehicle compliance testing. Also, there is no out- of-service criterion that is consistent among state or provincial agencies and even the Commercial Vehicle Safety Alliance (CVSA) is ambiguous on an acceptable level of frame corrosion. To ensure a high level of due diligence to public safety, the transit authority wished to determine the extent of the frame weakening and compare it to an undamaged frame through impact testing.

Two similar buses were tested; one with a corroded frame and one with an intact frame. Several portions of the corroded frame were purposely further weakened to replicate the worst case found in the fleet. After preparation, the side panels were re-attached so that the buses were ‘as found’ in normal service. In addition, one side panel was replaced with a 6.35 mm (¼”) thick steel plate as a potential repair procedure for the corroded frames.

A pendulum impactor was chosen to replicate the collision energy of a vehicle striking the side of the bus and impact tests were conducted along both sides. Impact forces were calculated and the deformation measured for each impact. Floor and seat mounted accelerometers were placed in each bus and a body form was positioned on the seat adjacent to the impact. High speed and regular videos were taken of each impact.

Results showed less intrusion and higher lateral accelerations on the non-corroded frame than for the corroded frame. However, expected occupant injury would be minimal for both conditions.

Michael J. Macnabb, Randolph Baerg