Static and Full-Scale Vehicle Crash Tests of a Breakaway Wooden Utility Pole
TRP-03-007-80 (Breakaway Utility Pole)
Edward Post, Terry Wipf, Robert Bolton, Patrick Chastain
Two full-scale static tests and three full-scale vehicle crash tests were conducted to determine the feasibility of a concept for retrofitting in-place wooden utility poles to breakaway under vehicle impacts. The breakaway concept was originally developed and tested in an earlier study by the University of Nebraska-Lincoln (UNL) on "new" 40 ft (12.2 m) Class 4 Southern Yellow Pine utility poles. This study was a continuation of the work conducted by UNL. Basically, the concept consists of two breakaway joints located 2 in (5 cm) and 8 ft (2.4 m) above ground. The breakaway joints were made by drilling a horizontal row of five 1-in. (2.5 cm) diameter holes in the direction of impact and then sawcutting the spaces between the holes. The full-scale static tests showed that the breakaway design is structurally adequate to carry the heavy ice lateral loading conditions specified by the National Electric Safety Code (ANSI) for the midwestern state of Nebraska, but that the breakaway design is not structurally adequate to carry the unbalanced longitudinal loading conditions specified in the ANSI Code. The full-scale vehicle crash tests showed that the breakaway stub design concept was effective in reducing the impact severity of a 2,450 lb (1,110 kg) vehicle collision at 21 mph (34 km/h) and 26 mph (42 km/h). In conclusion, it will be necessary to modify the breakaway design concept to bring the pole back up to its full unmodified strength in the longitudinal direction in order that it can carry the unbalanced longitudinal loading specified in the ANSI Code. It is important to point out that any modification must be done in such a manner as not to significantly change the pole breakaway characteristics.
Breakaway Poles, Roadside Safety, Vehicle Tests