Citation

Bronstad ME, Michie JD, White RR. Transp. Res. Rec. 1976; 566: 56-64.

Copyright

(Copyright © 1976, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

The test program discussed in this paper consisted of 19 tests of a breakaway sign support using a 2,000-lb (907-kb) pendulum mass impacting the support at 20 mph (32 km/h). Use of both rigid and crushable bumpers permitted examination of these techniques compared with current momentum change criterion. In addition, the effects of bolt-tightening torque on the slip-base release loads were investigated. Hi-Lok frangible nuts, which control tightening torque, were also evaluated for the design torque condition. Only in the crushable bumper tests were dramatically different results obtained for the various nut-tightening torques when momentum change was used as the criterion. Momentum change with the hard bumper was 65 plus minus 15 lbf-sec (289 plus minus 67 N-s) for all base-nut torque levels. Momentum change with the crushable bumper ranged from 88 lbf-sec (391 N-s) for design torque condition to 398 lbf-sec (1770 N-s) for the overtorqued condition. Repeatibility of slip-base loads was generally good when both a calibrated torque wrench and the Hi-Lok torque control nuts were used. It was concluded that momentum-change criterion is insufficient in evaluating results of pendulum tests using a rigid bumper. Use of a bumper with vehicle crush characteristics appears to provide a superior experimental evaluation.