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Citation |
Metcalf D, Ho YJ, Kalevela SA. Transp. Res. Rec. 1993; 1419: 43. |
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Copyright |
(Copyright © 1993, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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DOI |
unavailable |
PMID |
unavailable |
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Abstract |
The Arizona Department of Transportation (ADOT), in an effort to comply with FHWA and NCHRP Report 230 guidelines, and in cooperation with the Texas Transportation Institute (TTI) developed a generic breakaway small sign support system that was implemented in the summer of 1991. The system consists of two 4.5 kg/m (3 lb/ft), 551 MPa (80 ksi) U-channel posts with a 102-mm (4-in.) ground-level splice, (sign post behind the base and separated by two hexagonal spacers) and two Grade 9 bolts 8-mm (5/16-in.) in diameter spaced at 760 mm (3 in.). Shortly after the first installations some single post sign supports reported failed due to winds of approximately 64 km/hr (40 mph). The investigation of the failures involved meetings with ADOT maintenance personnel, U-channel post suppliers, and TTI. Field evaluations of the generic U-channel system were performed. Material property tests were performed on the U-channel posts (purchased as part of the implementation of the generic small sign support). Static and dynamic testing of the U-channel small sign support system were performed as well. Field evaluations indicate that contractor-installed signs have used a variety of spacers. Material property tests indicate that at least some of the U-channels did not meet the 551-MPa (80-ksi) minimum yield point. Static testing indicates that the system should be able to withstand a static load of 160.9 km/hr (100 mph). Dynamic testing, developed specifically for this project by TTI, could not prove that the ADOT generic U-channel single-post sign support can perform satisfactorily under fluttering caused by high winds. Pilot studies, or sign test sites, have been installed in two ADOT maintenance yards and on one ADOT highway. These pilot studies will give field performance data upon which management can make a decision about what ADOT's small sign support of the future will be. In the interim ADOT either will use a minimum of two supports per sign or will specify that square steel tube be used for breakaway small sign supports. Language: en |