Authors: Herbert F. Southgate, William J. Kenis
Addresses: 782 Sherwood Drive, Lexington, KY 40502-2918, USA. ' Federal Highway Administration, Office of Research and Development, Turner Fairbanks Research Centre, 6300 Georgetown Pike, McLean, VA 22101-2296, USA
Abstract: Comparison of weigh-in-motion (WIM) scale data versus static scale data for the same truck indicated uneven loadings between tyres on the same axle and between axles of the same tandem. Fifth-wheel location varied greatly. A study was initiated to determine the effects of gross load, fifth-wheel location, braking and acceleration actions upon the tyre and axle loads. The steering axle displays the heaviest load per tyre on the truck. Braking actions may cause dynamic loads on the steering tyres that exceed the tyre manufacturer|s recommended maximum load. Dual-tyre loads may vary by 11.1 kN (2.5 kips) between the four sets of dual tyres. Under acceleration, the left rear dual of the drive tandem exhibits the greatest force, the right front dual the least, and the other two dual tyres are approximately equal. The uneven loading is a function of torque and the fact that on many tractors, the engine, transmission, and differential are mounted to the left of centre on the tractor frame. Also, all pumps and often the batteries are mounted on the left side. In summary, noted behaviours were different from the expected behaviour. After using two test trucks to determine possible relationships, 150 commercial trucks were sampled from the traffic stream. The same trends were observed for the commercial traffic as seen for the two test trucks. Average rutting measurements on Interstate pavements indicate that rutting in the left wheel track is deeper than the right wheel track. Rutting is more prominent on hills than on flat areas. Thus, rutting is a shear-flow problem within the asphaltic concrete pavement and primarily a function of the torque applied by the tyre under acceleration, or shoving under braking. An approach is offered to estimate the horizontal component causing shearing actions. The original report by Southgate (July 1992) contains greater detail and presents additional concepts not reported here.
Keywords: axle load; fifth-wheel location; static scales; suspension systems; tyre load; tyre torque; shoving forces; uneven load distribution; weigh-in-motion scales; truck dynamics; tyre-pavement interface; tyre-road interface; WIM; rutting measurements; shear flow; asphaltic concrete pavement.
International Journal of Heavy Vehicle Systems, 1996 Vol.3 No.1/2/3/4, pp.399 - 421
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