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Performance Evaluation of Brass Breakaway Couplings




Joseph Putjenter, Scott Rosenbaugh, Karla Lechtenberg, Ronald Faller, John Reid, Dean Sicking




Existing breakaway couplings have several disadvantages, including proprietary in nature, prohibitively expensive, inconsistent energy absorption due to temperature effects, and variable fatigue strength due to corrosion. Thus, the Illinois Department of Transportation (ILDOT) developed a free-cutting, brass breakaway coupling for use on luminaire or support poles. The free-cutting, brass breakaway couplings in combination with luminaire poles were evaluated according to the Test Level-3 (TL-3) safety performance criteria found in NCHRP Report No. 350. A total of 7 tests were conducted at the Valmont/UNL-MwRSF pendulum testing facility in compliance with the impact criteria corresponding to test designation no. 3-60. The results of these tests were then used to predict the high-speed test results, test designation no. 3-61, using the FHWA-approved extrapolation equation. Luminaire poles used were selected to provide one of two worst-case impact scenarios: (1) a tall massive pole that requires the most energy to rotate the pole, or (2) the lightest and weakest pole that may bend, fracture, or crush before the couplings break away. Successful tests of these two scenarios then provided a range of pole sizes that could be used in combination with the brass couplings. Upon completion of the physical testing and extrapolation analysis, aluminum luminaire poles with nominal heights between 30 ft (9.1 m) and 55 ft (16.8 m) and weights less than 755 lb (343 kg) were found to satisfy the TL-3 safety performance criteria when evaluated with the brass couplings. However, the selected and tested heavy steel poles failed to satisfy the change in velocity limit for the high-speed test. Therefore, an analytical analysis was conducted to identify the largest steel poles that are compatible with the brass couplings.


Highway Safety, Pendulum Test, Roadside Appurtenances, Compliance Test, NCHRP Report No. 350, Breakaway Brass Couplings, Non-Proprietary Couplings, Breakaway Pole

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