Drop Weight Testing of Brass Breakaway Couplings

This was the first phase of an investigation to determine the suitability of free-cutting brass couplings for use in minimizing vehicular damage and driver or passenger injury when light poles are impacted. Breakaway couplings are required by Federal regulation to fracture when a modest size sedan travelling at 20 miles per hour or greater impacts a supported light pole. The required limit of impact deceleration that would be experienced by persons in this vehicle is limited to 5 m/s [16.4 ft/sec] at 20 and 60 mph. These brass couplings are intended to replace currently used aluminum or steel couplings, which could potentially save significant resources for the State of Illinois, as well as other states. This investigation used drop weight testing on a short strike tube that was attached to the couplings and then to a concrete pedestal which simulated an actual concrete foundation. The focus of the drop weight testing was to determine the size and depth of grooves needed to be cut into the brass couplings to provide the desired breakaway performance. This testing compared a variety of designs produced by the Illinois DOT with the Transpo SPM 4100 high strength steel coupling which had already been approved by the Federal Highway Administration. The test program used a rigid steel cylinder and thick base plate which simulated an actual light pole. Because of the nature of the drop weight test set up, certain variables, including the weight of the light pole and luminaires, its stiffness and radius of gyration, and stiffness of the impact point in an actual crash, could not be simulated. However, these variables were tested later in full scale pendulum impact tests in the second phase of this project.Illinois Department of Transportation ICT R27-26published or submitted for publicationnot peer reviewe